Showing papers in "Immunology in 2003"
TL;DR: A variety of viruses have been characterized that exploit bottlenecks in the MHC class I pathway, such as peptide translocation by the transporter associated with antigen processing as mentioned in this paper.
Abstract: Presumably because of the selective pressure exerted by the immune system, many viruses have evolved proteins that interfere with antigen presentation by major histocompatibility complex (MHC) class I molecules. These viruses utilize a whole variety of ingenious strategies to inhibit the MHC class I pathway. Viral proteins have been characterized that exploit bottlenecks in the MHC class I pathway, such as peptide translocation by the transporter associated with antigen processing. Alternatively, viral proteins can cause the degradation or mislocalization of MHC class I molecules. This is often achieved by the subversion of the host cell's own protein degradation and trafficking pathways. As a consequence elucidation of how these viral proteins act to subvert host cell function will continue to give important insights not only into virus-host interactions but also the function and mechanism of cellular pathways.
389 citations
TL;DR: A population of DC in the mucosae that exhibit the plasmacytoid phenotype, secrete interferon‐α (IFN‐α) following stimulation with oligodeoxynucleotides containing certain cytosine‐phosphate‐guanosine (CpG) motifs and can differentiate naïve T cells into cells that exhibit regulatory properties is identified.
Abstract: Repetitive stimulation of naive T cells by immature splenic dendritic cells (DC) can result in the differentiation of T-cell lines with regulatory properties. In the present study we identified a population of DC in the mucosae that exhibit the plasmacytoid phenotype, secrete interferon-alpha (IFN-alpha) following stimulation with oligodeoxynucleotides containing certain cytosine-phosphate-guanosine (CpG) motifs and can differentiate naive T cells into cells that exhibit regulatory properties. Although these DC appear to be present in both spleen and mesenteric lymph nodes (MLN), only CpG-matured DC from the MLN (but not the spleen) were able to differentiate naive T cells into T regulatory 1-like cells with regulatory properties. The activity of these DC failed to sustain robust T-cell proliferation and thereby enhanced the suppressive efficacy of CD4+ CD25+ T regulatory cells. These DC are the major CD8alpha+ DC population in the Peyer's patches (PP). Given their significant presence in mucosal tissue, we propose that these DC may provide a mechanistic basis for the homeostatic regulation in the gut by eliciting regulatory cell suppressor function and poorly supporting T helper cell proliferation at a site of high antigenic stimulation like the intestine.
248 citations
TL;DR: Human sIgA was found to facilitate biofilm formation by normal human gut flora and by Escherichia coli on cultured human epithelial cell surfaces under conditions in which non‐adherent bacteria were repeatedly washed away.
Abstract: It is critical, both for the host and for the long-term benefit of the bacteria that colonize the gut, that bacterial overgrowth with subsequent bacterial translocation, which may lead to sepsis and death of the host, be avoided Secretory IgA (sIgA) is known to be a key factor in this process, agglutinating bacteria and preventing their translocation in a process termed 'immune exclusion' To determine whether human sIgA might facilitate the growth of normal enteric bacteria under some conditions, the growth of human enteric bacteria on cultured, fixed human epithelial cells was evaluated in the presence of sIgA or various other proteins Human sIgA was found to facilitate biofilm formation by normal human gut flora and by Escherichia coli on cultured human epithelial cell surfaces under conditions in which non-adherent bacteria were repeatedly washed away In addition, the presence of sIgA resulted in a 64% increase in adherence of E coli to live cultured epithelial cells over a 45-min period Mucin, another defence factor thought to play a key role in immune exclusion, was found to facilitate biofilm formation by E coli Our findings suggest that sIgA may contribute to biofilm formation in the gut
179 citations
TL;DR: It is reported that, in a nicotinic environment, monocyte‐derived DCs manifest lower endocytic and phagocytic activities, and it is suggested that nicotine can exert its immunosuppressive effects on immune surveillance through functional impairment of the DC system.
Abstract: Nicotine alters a wide range of immunological functions, including innate and adaptive immune responses. To date, no studies have been reported showing the immunoregulatory effects of nicotine on dendritic cells (DCs), which are critical cells for initiation of cell-mediated immunity against infection and neoplastic diseases. In this work, we report that, in a nicotinic environment, monocyte-derived DCs manifest lower endocytic and phagocytic activities. Interestingly, although immature DCs undergo maturation in response to bacterial antigen lipopolysaccharide, they produce decreased levels of pro-inflammatory cytokines, notably interleukin-12, and reveal a reduced ability to stimulate antigen-presenting cell-dependent T-cell responses. Importantly, the reduction in T-cell responses is associated with a diminished ability of DCs to induce differentiation and expansion of type 1 T cells, as evidenced by a decreased frequency of interferon-gamma-producing effector cells. These results strongly suggest that nicotine can exert its immunosuppressive effects on immune surveillance through functional impairment of the DC system.
172 citations
TL;DR: It is concluded that Hp plays a modulating role on the Th1/Th2 balance by promoting a dominant Th1 cellular response, which points to a role of acute‐phase proteins in balancing immune responses.
Abstract: Summary
T helper cell type 1 (Th1) and type 2 (Th2) immune responses are characterized by a different pattern of cytokine expression following T-cell activation. Alterations of the ratio of Th1 to Th2 cells are important determinants of susceptibility to viral and parasitic infections, allergies, anti-tumour responses, and autoimmunity. In this work we bring new evidence for an effect of haptoglobin (Hp), a positive acute-phase protein, on T-lymphocyte functions. We show that Hp specifically interacts with both resting and activated CD4+ and CD8+ T cells. This specific binding results in a strong suppression of induced T-cell proliferation. In addition, Hp exhibits a strong in vitro inhibitory effect on Th2 cytokine release, while the production of interferon-γ (IFN-γ) and interleukin-2 (IL-2) is only slightly inhibited at high Hp doses. As a result, the presence of Hp promotes Th1 activation over Th2 activation in vivo as evidenced in Hp-deficient mice. Anti-CD3 monoclonal antibody injection indeed resulted in predominant IL-4 production in Hp−/− mice, in contrast to predominant IFN-γ production in Hp+/+ mice. We conclude that Hp plays a modulating role on the Th1/Th2 balance by promoting a dominant Th1 cellular response. This points to a role of acute-phase proteins in balancing immune responses.
168 citations
TL;DR: The present report has delineated porcine blood DC and NIPC, permitting a more detailed understanding of innate immune defences, particularly in response to infections.
Abstract: Peripheral blood contains two major particular infrequent dendritic cells (DC) subsets linking the innate and specific immune system, the myeloid DC and plasmacytoid DC equivalent to the natural interferon-producing cells (NIPC). The functional characterization of these cells demands large volumes of blood, making a large animal model more appropriate and beneficial for certain studies. Here, two subsets of porcine blood mononuclear cells expressing swine workshop cluster 3 (SWC3, a SIRP family member), are described and compared to monocytes. The blood DC specialized in T-cell stimulation were major histocompatibility complex (MHC) class II + , CD80/86 + , CD1 + / - , CD4, and in contrast to monocytes CD14 - . A CD16 and a CD16 + subset could be discriminated. Granulocyte-macrophage colony-stimulating factor and interleukin-3 were survival factors for this DC subset, and culture induced an up-regulation of MHC class II and CD80/86. The second subset described, are porcine NIPC, typically CD4 + + , MHC class II l o w , CD80/86 l o w , CD1, CD8 / l o w , CD16 - / l o w and CD45RA - / l o w . Porcine NIPC had high interleukin-3 binding capacity, and survived in response to this cytokine. Their unique function was strong interferon type I secretion after virus stimulation. Both subsets were endocytically active when freshly isolated, and down-regulated this activity after in vitro maturation. Taken together, the present report has delineated porcine blood DC and NIPC, permitting a more detailed understanding of innate immune defences, particularly in response to infections.
149 citations
TL;DR: It is raised the possibility, not as yet established, that NF‐κB activation may be responsible for the synergistic effect of IL‐1β on IL‐6‐induced CRP expression.
Abstract: C-reactive protein (CRP), the prototypical human acute phase protein, is produced primarily by hepatocytes. Its expression is modestly induced by interleukin (IL)-6 in Hep3B cells while IL-1, which alone has no effect, synergistically enhances the effects of IL-6. In previous studies of the proximal CRP promoter, we found that signal transducer and activator of transcription-3 (STAT3) and C/EBPβ -mediated IL-6-induced transcription and that Rel p50 acted synergistically with C/EBPβ, in the absence of p65, to enhance CRP transcription. Neither a requirement nor a binding site for the classic nuclear factor (NF)-κB heterodimer p50/p65 were found. The current studies were undertaken to determine whether similar novel transcription factor interactions might regulate the endogenous CRP gene. Transiently overexpressed p50 or p65 induced CRP mRNA accumulation in Hep3B cells. The heterodimer p50/p65 was markedly more effective than p50 or p65 homodimers. Co-overexpression of p50 or p65 with C/EBPβ or STAT3 synergistically enhanced CRP expression. Maximal expression was observed with overexpression of all four transcription factors; comparable effects were observed with IL-1β treatment of cells overexpressing STAT3 + C/EBPβ. Data from the Human Genome Project revealed 13 potential κB sites in the first 4000 bases of the CRP promoter, only one of which, centred at −2652, bound nuclear p50/p65 heterodimer activated by IL-1β. Our findings indicate that classical NF-κB activation can participate in endogenous CRP induction, and that activated NF-κB may synergistically enhance the effects of C/EBPβ and STAT3. They raise the possibility, not as yet established, that NF-κB activation may be responsible for the synergistic effect of IL-1β on IL-6-induced CRP expression.
147 citations
TL;DR: It is reported that systemic inflammation markedly induces inosine‐containing mRNA to approximately 5% of adenosine in total mRNA, and up‐regulation of ADAR1‐mediated RNA editing is confirmed in vitro in T lymphocytes and macrophages stimulated with a variety of inflammatory mediators.
Abstract: Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional modification of pre-mRNA catalysed by an RNA-specific adenosine deaminase (ADAR). A-to-I RNA editing has been previously reported in the pre-mRNAs of brain glutamate and serotonin receptors and in lung tissue during inflammation. Here we report that systemic inflammation markedly induces inosine-containing mRNA to approximately 5% of adenosine in total mRNA. Induction was the result of up-regulation of A-to-I RNA editing as both dsRNA editing activity and ADAR1 expression were increased in the spleen, thymus and peripheral lymphocytes from endotoxin-treated mice. Up-regulation of ADAR1 was confirmed in vitro in T lymphocytes and macrophages stimulated with a variety of inflammatory mediators including tumour necrosis factor-alpha and interferon-gamma. A late induction of RNA editing was detected in concanavalin A-activated splenocytes stimulated with interleukin-2 in vitro. Taken together, these data suggest that a large number of inosine-containing mRNAs are produced during acute inflammation via up-regulation of ADAR1-mediated RNA editing. These events may affect the inflammatory and immune response through modulation of protein production.
130 citations
TL;DR: In this paper, the authors define distinct signalling mechanisms that regulate lipopolysaccharide (LPS)-mediated induction of IL-12 p40 and p35 in macrophages and which may therefore provide therapeutic targets for precise and specific fine-tuning of cytokine responses.
Abstract: Bioactive interleukin (IL)-12 is a 70 000-molecular weight (MW) heterodimeric cytokine comprising p40 and p35 chains. However, p40 can also form homodimers that antagonize bioactive IL-12 or heterodimerize with p19 to form IL-23, which exhibits overlapping yet distinct functions to that of IL-12. We now define distinct signalling mechanisms that regulate lipopolysaccharide (LPS)-mediated induction of IL-12 p40 and p35 in macrophages and which may therefore provide therapeutic targets for precise and specific fine-tuning of cytokine responses. Thus, whilst LPS-induced p38 mitogen-activated protein kinase (MAPkinase) activation is required for the induction of both p40 and p35 subunits, Erk MAPkinase signalling mediates negative feedback regulation of p40, but not p35, production. Such Erk MAPkinase activation is downstream of calcium influx and targets LPS-induced IL-12 p40 transcription by suppressing the synthesis of the transcription factor, interferon regulatory factor-1 (IRF-1). In contrast, negative regulation of the p35 subunit of IL-12 occurs via a calcium-dependent, but Erk-independent, mechanism, which is likely to involve nuclear factor (NF)-kappa B signalling. Finally, the importance of both Erk and p38 MAPkinases in differentially regulating IL-12 p40 and p35 production is underscored by each being targeted by ES-62, a product secreted by parasitic filarial nematodes to polarize the immune system towards an anti-inflammatory phenotype conducive to their survival.
123 citations
TL;DR: The immunoregulatory capacity of hsp70 and its potential therapeutic value are reviewed, as hSp70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen‐presenting cells to elicit peptide‐specific immunity and, in contrast to its reported pro‐inflammatory effects, the administration of recombinant h Sp70 can attenuate experimental autoimmune disease.
Abstract: Amongst the families of intracellular molecules that chaperone and assist with the trafficking of other proteins, notably during conditions of cellular stress, heat shock protein (hsp) 70 is one of the most studied. Although its name suggests that expression is exclusively induced during cellular hyperthermia, members of the hsp70 family of proteins can be constitutively expressed and/or induced by a range of other cellular insults. The ubiquitous presence of hsp70 in eukaryotic and prokaryotic cells, combined with its high degree of sequence homology and intrinsic immunogenicity, have prompted the suggestion that inappropriate immune reactivity to hsp70 might lead to pro-inflammatory responses and the development of autoimmune disease. Indeed, hsp70 has been shown to be a potent activator of innate immunity and aberrant expression of hsp70 in certain organs promotes immunopathology. However, studies also suggest that hsp70 might have immunotherapeutic potential, as hsp70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen-presenting cells to elicit peptide-specific immunity and, in contrast to its reported pro-inflammatory effects, the administration of recombinant hsp70 can attenuate experimental autoimmune disease. This review focuses on the immunoregulatory capacity of hsp70 and its potential therapeutic value.
123 citations
TL;DR: The use of specific signalling inhibitors permitted us to establish that JAK2/STAT1α‐ and Erk1/Erk2‐dependent pathways are the main players in IFN‐γ‐inducible Mφ NO generation, and suggest that ErK1/ Erk2 are responsible for STAT1α Ser727 residue phosphorylation inIFN‐β‐stimulated M φ, thus contributing to the full activation of STAT1 α.
Abstract: Nitric oxide (NO) produced by macrophages (Mphi) in response to interferon-gamma (IFN-gamma) plays a pivotal role in the control of intracellular pathogens. Current knowledge of the specific biochemical cascades involved in this IFN-gamma-inducible Mphi function is still limited. In the present study, we evaluated the participation of various second messengers--Janus kinase 2 (JAK2), signal transducer and activator of transcription (STAT) 1alpha, MAP kinase kinase (MEK1/2), extracellular signal-regulated kinases 1 and 2 (Erk1/Erk2) and nuclear factor kappa B (NF-kappaB)--in the regulation of NO production by IFN-gamma-stimulated J774 murine Mphi. The use of specific signalling inhibitors permitted us to establish that JAK2/STAT1alpha- and Erk1/Erk2-dependent pathways are the main players in IFN-gamma-inducible Mphi NO generation. To determine whether the inhibitory effect was taking place at the pre- and/or post-transcriptional level, we evaluated the effect of each antagonist on inducible nitric oxide synthase (iNOS) gene and protein expression, and on the capacity of IFN-gamma to induce JAK2, Erk1/Erk2 and STAT1alpha phosphorylation. All downregulatory effects occurred at the pretranscriptional level, except for NF-kappaB, which seems to exert its role in NO production through an iNOS-independent event. In addition, electrophoretic mobility shift assay (EMSA) analysis revealed that STAT1alpha is essential for IFN-gamma-inducible iNOS expression and NO production, whereas the contribution of NF-kappaB to this cellular regulation seems to be minimal. Moreover, our data suggest that Erk1/Erk2 are responsible for STAT1alpha Ser727 residue phosphorylation in IFN-gamma-stimulated Mphi, thus contributing to the full activation of STAT1alpha. Taken together, our results indicate that JAK2, MEK1/2, Erk1/Erk2 and STAT1alpha are key players in the IFN-gamma-inducible generation of NO by Mphi.
TL;DR: The results underscore the role of MT extracts in the induction of macrophage‐derived chemokines responsible for the orchestrated recruitment of PMNs, monocytes, and Th1 and γδ T cells, as well as in the regulation of γ δ function.
Abstract: Granuloma is a typical feature of tuberculosis. We evaluated the chemotaxis of selected human leucocyte subsets induced by macrophages incubated with Mycobacterium tuberculosis (MT)-derived products in vitro. The release of monocyte chemotactic protein 1 (MCP-1) and interleukin-8 (IL-8) correlated with the specific induction of strong chemotaxis towards monocytes and polymorphonuclear leucocytes (PMNs). gammadelta and T helper type 1 (Th1) alphabeta lymphocytes were chemoattracted, while T-resting, IL-2-activated and Th2 lymphocytes were unaffected. Activation with mycobacterium-derived, phosphate-containing components, modulated the chemokine receptor profile of gammadelta T lymphocytes as well as their pattern of cyto-chemokine production, disclosing a potential for their active participation in granuloma formation. In particular, CXCR3 and IP-10, which we found to be released by MT-pulsed alveolar macrophages, seem to represent the receptor-counter-receptor pair implicated in the chemotaxis of gammadelta lymphocytes. Immunohistochemical analysis and in situ hybridization revealed the in vivo presence of IL-8, MCP-1 and IL-10 in lymph node and lung tuberculous granulomas. Our results underscore the role of MT extracts in the induction of macrophage-derived chemokines responsible for the orchestrated recruitment of PMNs, monocytes, and Th1 and gammadelta T cells, as well as in the regulation of gammadelta function.
TL;DR: Results show that HBV infection compromises the antigen‐presenting function of MoDC with concomitant impairment of T helper cell type 1 responses, and 3TC treatment can overcome HBV‐MoDC‐related T‐cell hyporeactivity and this underscores its important role in enhanced immune responses to HBV.
Abstract: Dendritic cells (DC) are the most potent antigen-presenting cells and play a central role in the induction of antiviral immune responses. Recently, we have shown that monocyte-derived DC (MoDC) from patients with chronic hepatitis B virus (HBV) infection are functionally impaired. In our present study MoDC from healthy subjects were propagated in vitro and inoculated with HBV particles to investigate the precise mechanisms that underly MoDC dysfunction. T-cell proliferation assays revealed an impaired allostimulatory capacity of HBV-inoculated MoDC (HBV-MoDC) as well as a lower potential of stimulating autologous T cells against a recall antigen in comparison to control-MoDC. Interleukin-2, tumour necrosis factor-alpha and interferon-gamma production by T cells in proliferation assays with HBV-MoDC was significantly lower than with control-MoDC and correlated with lower IL-12 production in HBV-MoDC cultures. The presence of the nucleoside analogue lamivudine (3TC), an inhibitor of HBV replication, restored impaired allostimulatory function of HBV-MoDC and up-regulated major histocompatibility complex class II expression. These results show that HBV infection compromises the antigen-presenting function of MoDC with concomitant impairment of T helper cell type 1 responses. This may play an important role for viral immune escape leading to chronic HBV infection. However, 3TC treatment can overcome HBV-MoDC-related T-cell hyporeactivity and this underscores its important role in enhanced immune responses to HBV.
TL;DR: The results suggest that the signalling capacity of TLR4 as affected by loss‐of‐function mutations does not influence human or experimental sepsis caused by polymicrobial infection, and other innate immune receptors may compensate forTLR4 defects.
Abstract: Genetically determined responsiveness to microbial stimuli such as lipopolysaccharide (LPS) may affect the pathophysiology of human sepsis. The D299G mutation in human Toll-like receptor-4 (TLR4) impairs LPS signalling in homozygous and heterozygous individuals. To investigate whether the presence of the TLR4(D299G) mutation may correlate with the development or outcome of sepsis following major visceral surgery the presence of TLR4(D299G) mutation was analysed in 307 Caucasian patients (154 without and 153 with sepsis). Sepsis was caused in 84% of patients by polymicrobial infection. The presence of the mutant TLR4 did not significantly correlate with development or outcome of sepsis. Serum levels of tumour necrosis factor, interleukin (IL)-10, and IL-6 at sepsis onset did not significantly differ between patients carrying wild-type and mutant TLR4. Moreover, studies in a murine model of polymicrobial septic peritonitis demonstrated that TLR4-deficiency did neither influence the systemic cytokine response nor the development of organ injury. The results suggest that the signalling capacity of TLR4 as affected by loss-of-function mutations does not influence human or experimental sepsis caused by polymicrobial infection. Thus, in polymicrobial infection, other innate immune receptors may compensate for TLR4 defects.
TL;DR: The results suggest that AM and particularly DC by secreting IL‐12 shortly after BCG delivery induce the long‐term persistence of IFN‐γ‐secreting T cells percolating in BCG‐loaded lung tissue.
Abstract: We showed in a previous study that the intranasal (i.n) delivery of bacille Calmette-Guerin (BCG) to BP2 mice (H-2q) inhibits eosinophilia and bronchial hyperreactivity in a mouse model of asthma. The present work has been performed to characterize the leucocyte lineages recruited to the lungs of mice after i.n. delivery of BCG and potentially involved in the polarization of T lymphocytes. The different antigen-presenting cells (APC) recruited to bronchoalveolar lavage (BAL) and to lung tissue of mice shortly after the delivery of BCG were analysed in parallel as well as their capacity to drive the immune response towards a T helper type 1 cytokine production. Alveolar macrophages (AM) from the BAL were CD11c+, F4/80+ and CD11b-, and in the lung tissue two major populations of potential APC were detected: one CD11c-, F4/80+, CD11b+ and I-Aq- was identified as interstitial macrophages (IM) and a second expressing CD11c+ and I-Aq+ antigens, negative for CD11b and F4/80 markers as leucocytic dendritic cells (DC). Freshly isolated DC up-regulated CD11b and CD40 antigens after overnight culture, but remained negative for CD8alpha antigen, suggesting a myeloid origin. Lung DC which produced high amount of interleukin (IL)-12 were potent inducers of naive CD4+ T lymphocyte priming, as assessed by interferon-gamma (IFN-gamma) production by these naive CD4+ T cells. Lung explants recovered long term after BCG delivery produced sustained levels of IFN-gamma. Our results suggest that AM and particularly DC by secreting IL-12 shortly after BCG delivery induce the long-term persistence of IFN-gamma-secreting T cells percolating in BCG-loaded lung tissue.
TL;DR: Two sublines of HMC‐1 are described with different phenotypes and designated by the locations of specific mutations in the c‐kit proto‐oncogene, providing both information on the biological consequences of mutations in Kit and recognition of the availability of what in reality are two distinct cultured human mast cell lines.
Abstract: The human mast cell line (HMC)-1 cell line is growth-factor independent because of a constitutive activity of the receptor tyrosine kinase Kit. Such deregulated Kit activity has also been suggested causative in gastrointestinal stromal tumours (GISTs) and mastocytosis. HMC-1 is the only established continuously growing human mast cell line and has therefore been widely employed for in vitro studies of human mast cell biology. In this paper we describe two sublines of HMC-1, named HMC-1(560 ) and HMC-1(560,816 ), with different phenotypes and designated by the locations of specific mutations in the c-kit proto-oncogene. Activating mutations in the Kit receptor were characterized using the pyrosequencing trade mark method. Both sublines have a heterozygous T to G mutation at codon 560 in the juxtamembrane region of the c-kit gene causing an amino acid substitution of Gly-560 for Val. In contrast, only HMC-1(560,816) cells have the c-kitV816 mutation found in mast cell neoplasms causing an Asp-->Val substitution in the intracellular kinase domain. Kit was constitutively phosphorylated on tyrosine residues and associated with phosphatidylinositol 3'-kinase (PI 3-kinase) in both variants of HMC-1, but this did not lead to a constitutive phosphorylation of Akt or extracellular regulated protein kinase (ERK), which are signalling molecules normally activated by the interaction of stem cell factor (SCF) with Kit. The documentation and characterization of two sublines of HMC-1 cells provides both information on the biological consequences of mutations in Kit and recognition of the availability of what in reality are two distinct cultured human mast cell lines.
TL;DR: The evidence from knockout mice, spontaneous mouse models of autoimmunity and human disease that defective regulation by B cell inhibitory receptors can lead to autoIMmunity is reviewed, and probable physiological roles in immune regulation are described.
Abstract: The immune system of any organism must maintain a fine balance between activation and inhibition. It must possess adequate reactivity to raise an effective immune response to target non-self molecules while not harming the organism itself. Essential to this process is the ability to control the timing and place of activation and to limit the extent of, and eventually terminate, activation. Failure to maintain this balance will result in either immunodeficiency or autoimmunity. Inhibitory receptors are involved in this regulation, a number having been shown to be critical in controlling the B cell immune response.
There are two broad classes of inhibitory receptor − most are of the immunoglobulin (Ig) superfamily while the remainder are lectin-like molecules. They share a number of structural and functional similarities. Each inhibitory receptor contains one or more immunoreceptor tyrosine-based inhibitory motifs (ITIMs) within its cytoplasmic domain essential for generation and transduction of inhibitory signals. The ITIM consists of a six amino acid consensus sequence (Ile/Val/Leu/Ser)-X-Tyr-X-X-(Leu/Val).1 Ligation of the inhibitory receptor to an immunoreceptor tyrosine-based activatory motif (ITAM)-containing activatory molecule results in tyrosine kinase phosphorylation of the tyrosine residue within the ITIM2 by lyn.3 Tyrosine phosphorylation of the ITIM allows it to bind and activate phosphatases containing an src homology 2 (SH2) domain. Two classes of SH2-containing inhibitory phosphatases have been identified: the protein tyrosine phosphatases SHP-1 and SHP-2, and the phosphoinositol phosphatases SHIP and SHIP2. These classes have separate downstream signalling pathways through which they modulate cellular inhibition. In general, each class of phosphatase interacts with the ITIMs of different inhibitory receptors but each inhibitory receptor appears to act predominantly through only one class of phosphatase.4
A number of inhibitory receptors have been described on B cells, the details of which are summarized in Fig. 1 and Table 1. We will concentrate on three of these, FcγRII, CD22 and PD−1, and in addition will discuss lyn, SHP-1 and SHIP, which are crucial elements in the signalling pathways of the inhibitory receptors. We will describe their probable physiological roles in immune regulation, and then review the evidence from knockout mice, spontaneous mouse models of autoimmunity and human disease that defective regulation by B cell inhibitory receptors can lead to autoimmunity.
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Figure 1
B cell inhibitory receptors.
TL;DR: The recent studies that have defined the molecules required for B‐cell development and maturation as well as the theories on how signals may be regulated at each stage are summarized.
Abstract: Signalling through the B-cell antigen receptor (BCR) is required throughout B-cell development and peripheral maturation. Targeted disruption of BCR components or downstream effectors indicates that specific signalling mechanisms are preferentially required for central B-cell development, peripheral maturation and repertoire selection. Additionally, the avidity and the context in which antigen is encountered determine both cell fate and differentiation in the periphery. Although the signalling and receptor components required at each stage have been largely elucidated, the molecular mechanisms through which specific signalling are evoked at each stage are still obscure. In particular, it is not known how the pre-BCR initiates the signals required for normal development or how immature B cells regulate the signalling pathways that determine cell fate. In this review, we will summarize the recent studies that have defined the molecules required for B-cell development and maturation as well as the theories on how signals may be regulated at each stage.
TL;DR: It is proposed that fluctuations in CCR3 expression on human BM CD34+ cells may facilitate chemokine‐mediated progenitor cell mobilization to the peripheral circulation and the resultant development of pulmonary eosinophilia, a cardinal feature of asthma.
Abstract: There is increasing evidence that primitive progenitors migrate from the bone marrow (BM) via the peripheral circulation to tissue sites where they undergo in situ differentiation to provide a continued source of effector cells, such as eosinophils, during an allergic inflammatory response. To study mechanisms of progenitor cell mobilization in allergic reactions, we investigated fluctuations in the expression of the eotaxin receptor, CC chemokine receptor 3 (CCR3), on CD34+ cells from stable asthmatics following allergen (i.e. antigen) challenge. BM aspirates were taken from seven early responder (ER) and 10 dual responder (DR) asthmatics who, following antigen challenge developed only an early bronchoconstrictor response and an early and late- bronchoconstrictor response, respectively. Expression of CCR3 was detected on primitive (CD34+ cells) and eosinophil-lineage committed progenitors (CD34+ interleukin-5 receptor alpha-subunit+ cells) by flow cytometry and confirmed by co-localization of CCR3 messenger RNA to CD34 immunopositive cells using in situ hybridization. When preantigen levels were compared to 24-hr postantigen levels, significant increases in BM CD34+ CCR3+ cells were detected in DR, who also developed a significant sputum and blood eosinophilia and increased methacholine airway responsiveness. In contrast, a significant attenuation of BM CD34+ CCR3+ cells was observed in ER. In a dose-dependent manner eotaxin, but not interleukin (IL)-5, stimulated CD34+ progenitor cell migration in vitro. This migrational response to eotaxin was abrogated by anti-CCR3 monoclonal antibody and primed by preincubation with IL-5. We propose that fluctuations in CCR3 expression on human BM CD34+ cells may facilitate chemokine-mediated progenitor cell mobilization to the peripheral circulation and the resultant development of pulmonary eosinophilia, a cardinal feature of asthma.
TL;DR: Evidence is provided that the uterus, and potentially the entire upper reproductive tract, are important sites for the initial events involved in HIV infection, and the hormonal regulation of HIV receptor expression may affect a woman's susceptibility to HIV infection during her menstrual cycle.
Abstract: Human immunodeficiency virus-1 (HIV-1) is primarily a sexually transmitted disease. Identification of cell populations within the female reproductive tract that are initially infected, and the events involved in transmission of infection to other cells, remain to be established. In this report, we evaluated expression of HIV receptors and coreceptors on epithelial cells in the uterus and found they express several receptors critical for HIV infection including CD4, CXCR4, CCR5 and galactosylceramide (GalC). Moreover, expression of these receptors varied during the menstrual cycle. Expression of CD4 and CCR5 on uterine epithelial cells is high throughout the proliferative phase of the menstrual cycle when blood levels of oestradiol are high. In contrast, CXCR4 expression increased gradually throughout the proliferative phase. During the secretory phase of the cycle when both oestradiol and progesterone are elevated, CD4 and CCR5 expression decreased whereas CXCR4 expression remained elevated. Expression of GalC on endometrial glands is higher during the secretory phase than during the proliferative phase of the menstrual cycle. Because epithelial cells line the female reproductive tract and express HIV receptors and coreceptors, it is likely that they are one of the first cell types to become infected. The hormonal regulation of HIV receptor expression may affect a woman's susceptibility to HIV infection during her menstrual cycle. Moreover, selective coreceptor expression could account for the preferential transmission of R5-HIV-1 strains to women. In addition, these studies provide evidence that the uterus, and potentially the entire upper reproductive tract, are important sites for the initial events involved in HIV infection.
TL;DR: One of the crucial unanswered questions in the development of T-cellregulation is the origin of CD4, as well as the role of ‘cell reprograming’ in immune regulation.
Abstract: One of the crucial unanswered questions in the field of T-cell regulation is the origin of CD4+ CD25+ regulatory T cells. Does the thymus produce regulatory T cells as a functionally mature separate lineage, or can some T cells acquire regulatory function in the periphery? While mice live for 2·5 years, humans can live for eight decades and beyond. The constraints on the persistence of human CD4+ CD25+ regulatory T cells will therefore be more extreme as a result of thymic involution early in the human lifespan. A central question is whether the full complement of CD4+ CD25+ regulatory T cells are generated early in life and if so, how do they manage to persist? A consistent observation in both mice and humans is that CD4+ CD25+ T cells in adults have the phenotypic characteristics of a highly differentiated T-cell population. This review seeks to reconcile the observations that CD4+ CD25+ T cells are anergic but highly differentiated. We suggest that it is possible that a subpopulation of CD4+ CD25+ regulatory T cells may arise in the periphery as a consequence of anergy induction in antigen-specific CD4+ T cells that are approaching end-stage differentiation.
TL;DR: Results show a strong link between CAV antibody status, CAV replication, and the ability to generate REV‐specific CTL, and it is likely that the immunosuppressive effects of subclinical infection have previously been underestimated.
Abstract: Infection with chicken anaemia virus (CAV), a circovirus, can result in immunosuppression and subsequent increased susceptibility to secondary infections. This is the first report of impairment of pathogen-specific cytotoxic T lymphocytes (CTL) after natural and experimental infection of chickens with CAV and Marek's disease virus (MDV) or reticuloendotheliosis virus (REV). MDV- and REV-specific CTL were generated at 7 days post infection by 9-30-day-old-chickens that were positive for maternal antibodies to CAV at 9-17 days of age. Replication of CAV could not be demonstrated in these chickens using quantitative real-time polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR assays. In contrast, REV-specific CTL failed to develop when chickens negative for maternal antibodies at 9-17 days of age were infected. Infection with CAV at 45 days of age after CAV maternal antibodies had waned also caused a decreased REV-specific CTL response. In these chickens increased levels of CAV DNA of up to 107 copy numbers per micro g DNA and increased relative transcript levels of CAV by up to a factor of 106 were detected by quantitative real-time PCR and RT-PCR. Interleukin (IL)-1beta and IL-2 mRNA levels were not significantly affected by CAV infection at 7 or 14 days p.i. Similar assays for interferon-gamma (IFN-gamma) transcripts demonstrated a 10-fold increase in IFN-gamma mRNA levels at 7 days post infection following REV or REV + CAV infection, while CAV alone caused a two- to fourfold increase. These results show a strong link between CAV antibody status, CAV replication, and the ability to generate REV-specific CTL. It is likely that the immunosuppressive effects of subclinical infection have previously been underestimated.
TL;DR: While alum‐induced IL‐18 can facilitate Th2 induction, the addition of exogenous IL‐16 cannot further enhance the alum‐ induced Th2 response, OVA‐specific immunoglobulin G1 and IgE production remain unaffected.
Abstract: Previous studies have shown that the antigen-specific T helper 2 (Th2) response induced by alum
adjuvants is interleukin (IL)-4 independent. As a role for IL-18 in Th2 induction has recently been
described, in addition to its role in enhancing Th1 responses, we have studied the Th2 response
induced by ovalbumin (OVA) adsorbed to alum in wild-type and IL-18-deficient mice. Our results
indicate that while endogenous IL-18 facilitates alum-induced IL-4 production, OVA-specific
immunoglobulin G1 (IgG1) and IgE production remain unaffected. Furthermore, antigen-specific
Th1 responses induced with alum/IL-12-adsorbed OVA were demonstrated to be highly IL-18
dependent. Despite these observations, injection of BALB/c mice with exogenous IL-18 adsorbed
to alum/OVA did not alter IL-4 or interferon-g production by T cells and had little effect on the
relative production of IgG1/IgG2a antibody subclasses compared with alum/OVA inoculated mice.
However, the previously described synergism between IL-12 and IL-18 in Th1 induction was
evident as the Th1-promoting activity of alum/IL-12 against adsorbed OVAwas greatly augmented
by the coadministration of IL-18. These results indicate that while alum-induced IL-18 can
facilitate Th2 induction, the addition of exogenous IL-18 cannot further enhance the alum-induced
Th2 response.
TL;DR: Results clearly show that both ERα and ERβ are required for complete down‐regulation of B lymphopoiesis while only ERα is needed to up‐regulate immunoglobulin production in both bone marrow and spleen.
Abstract: Oestrogen treatment down-regulates B lymphopoiesis in the bone marrow of mice Meanwhile it up-regulates immunoglobulin production To understand better the oestrogen action on bone marrow male mice lacking oestrogen receptor alpha (ERalpha; ERKO mice), lacking ERbeta (BERKO mice), lacking both receptors (DERKO mice) or wild-type (wt) littermates were castrated and treated for 25 weeks with 30 microg/kg 17beta-oestradiol (E2) or vehicle oil as controls The B lymphopoiesis in the bone marrow was examined by flow cytometry and mature B-cell function was studied using an ELISPOT assay enumerating the B cells in bone marrow and spleen that were actively producing immunoglobulins In wt mice the frequency of B-lymphopoietic (B220+) cells in the bone marrow decreased from 15% to 5% upon E2 treatment In ERKO and BERKO mice significant reduction was seen but not of the same magnitude In DERKO mice no reduction of B lymphopoiesis was seen In addition, our results show that E2 mediated reduction of different steps in B lymphopoiesis require only ERalpha or both receptors In wt and BERKO mice E2 treatment resulted in significantly increased levels of B cells actively producing immunoglobulin, while in ERKO and DERKO mice no such change was seen Similar results were found in both bone marrow and spleen In conclusion our results clearly show that both ERalpha and ERbeta are required for complete down-regulation of B lymphopoiesis while only ERalpha is needed to up-regulate immunoglobulin production in both bone marrow and spleen
TL;DR: Results represent the first report describing possible enhancement of allergic response by EDs through increasing IL‐4 production in CD4+ T cells and antigen‐specific IgE levels in the sera via the stimulation of Ca2+/calcineurin‐dependent NF‐AT activation.
Abstract: Bisphenol A (BPA) and p-nonylphenol (NP) are representative endocrine disruptors (EDs) that may have adverse effects on human health. The influence of these compounds on allergic immune responses remains unclear. In this study, we have examined the effects of BPA and NP on production of interleukin-4 (IL-4), a pro-inflammatory cytokine closely associated with allergic immune responses. Both BPA and NP significantly enhanced IL-4 production in keyhole limpet haemocyanin (KLH)-primed CD4+ T cells in a concentration-dependent manner. Treatment with BPA or NP in vivo resulted in significant increase of IL-4 production in CD4+ T cells and of antigen-specific immunoglobulin E (IgE) levels in the sera of KLH-primed mice. Furthermore, BPA and NP enhanced the activation of IL-4 gene promoter in EL4 T cells transiently transfected with IL-4 promoter/reporter constructs, and the enhancing effect mapped to a region in the IL-4 promoter containing binding sites for nuclear factor (NF)-AT. Activation of T lymphocytes by phorbol 12-myristate 13-acetate/ionomycin resulted in markedly enhanced binding activities to the NF-AT site, which significantly increased upon addition of BPA or NP, as demonstrated by the electrophoretic mobility shift assay, indicating that the transcription factor NF-AT was involved in the enhancing effect of BPA and NP on IL-4 production. The enhancement of IL-4 production by BPA or NP was significantly reduced by nitrendipine, a blocker of Ca2+ influx, and by FK506, a calcineurin inhibitor. FK506 inhibited the NF-AT–DNA binding activity and IL-4 gene promoter activity enhanced by BPA or NP. These results represent the first report describing possible enhancement of allergic response by EDs through increasing IL-4 production in CD4+ T cells and antigen-specific IgE levels in the sera via the stimulation of Ca2+/calcineurin-dependent NF-AT activation.
TL;DR: It is found that arginase I was the most significantly up‐regulated gene in the murine spinal cord during experimental autoimmune encephalomyelitis (EAE), indicating that arkinase plays important roles in autoimmune inflammation in the central nervous system.
Abstract: Using a high throughput gene microarray technology that detects approximately 22 000 genes, we found that arginase I was the most significantly up-regulated gene in the murine spinal cord during experimental autoimmune encephalomyelitis (EAE). By Northern blot and arginase enzyme assay, we detected high levels of arginase I mRNA and protein, respectively, in the spinal cord of EAE mice, but not in the spinal cord of normal mice or mice that had recovered from EAE. In vitro, both microglia and astrocytes produced arginase and nitric oxide synthase, two enzymes that are involved in arginine metabolism. To explore the roles of arginase in EAE, we injected the arginase inhibitor amino-6-boronohexanoic acid (ABH) into mice during the inductive and effector phases of the disease. Compared with mice that received vehicle control, mice treated with ABH developed milder EAE with delayed onset, reduced disease score and expedited recovery. Spleen mononuclear cells from ABH-treated mice produced more nitric oxide and secreted less interferon-gamma and tumour necrosis factor-alpha as compared to control mice. These results indicate that arginase plays important roles in autoimmune inflammation in the central nervous system.
TL;DR: Findings suggest a DC‐mediated mechanism of immunosupression by CsA on human peripheral blood DC subsets, which has capacities to affect not only T cells but also antigen‐presenting cells such as B cells and dendritic cells
Abstract: Cyclosporin A (CsA) is a potent immuno-suppressant and is approved for the treatment of various disease conditions. The molecular biological mechanism of CsA has been investigated intensively in T cells and has been shown to involve the intracellular calcineurin pathway. Recently, it was reported that CsA has capacities to affect not only T cells but also antigen-presenting cells such as B cells and dendritic cells (DCs). DCs are a master regulator of immune responses that have an integral capacity to prime naive T cells. In the present study, we investigated the biological effects of CsA on human peripheral blood DC subsets: CD11c+ myeloid and CD11c- lymphoid subsets. CsA inhibited the up-regulation of co-stimulatory molecules induced with or without microbial stimuli and CD40L on both CD11c+ and CD11c- subsets. In addition, CsA negatively regulated the endocytic activity of CD11c+ DC during the immature state. CsA inhibited the interleukin-12 (IL-12) production, but augmented the IL-10 production from the LPS-stimulated CD11c+ subset, whereas CsA reduced the interferon-alpha (IFN-alpha) production from the CD11c- subset infected with Sendai virus (SV). Both the LPS-stimulated CD11c+ subset and SV-infected CD11c- subset preferentially induced the development of IFN-gamma-producing T helper-type 1 (Th1) cells. Pretreatment of these DC subsets with CsA inhibited the Th1 skewing. These findings suggested a DC-mediated mechanism of immunosuppression by CsA.
TL;DR: The data suggest that ApoE inhibits T‐cell activation by reducing the density of immune stimulatory proteins on antigen‐presenting cells by inhibiting the expression of such molecules after in vivo stimulation with interferon‐γ.
Abstract: Apolipoprotein E (ApoE) is synthesized by a variety of cells including macrophages. These cells activate T lymphocytes by antigen presentation, while the T-cell cytokine, interferon-γ, inhibits macrophage ApoE expression.ApoE inhibits T-cell proliferation in culture but its role in immune responses has been unclear. The ApoE-deficient (E 0 ) mouse permits an evaluation of the immunological role of ApoE. We have analysed T-cell responses to an exogenous antigen (ovalbumin) and polyclonal mitogen (concanavalin A) in E 0 and ApoE + / + mice. Macrophages of E 0 mice stimulated T-cell activation more effectively as antigen-presenting cells than macrophages from ApoE + / + mice. Both proliferation and interferon-y secretion were enhanced in T cells activated in the context of antigen-presenting cells from E 0 mice. Since the macrophage-T-cell interaction depends on interactions between cell surface molecules, we assessed the expression of such molecules after in vivo stimulation with interferon-y. This treatment caused an increased expression of the co-stimulatory surface proteins CD40 and CD80, and also of the major histocompatibility complex class II molecules I-A b on macrophages of E 0 mice compared with ApoE + / + . Our data suggest that ApoE inhibits T-cell activation by reducing the density of immune stimulatory proteins on antigen-presenting cells.
TL;DR: It is demonstrated that IL‐1α, through activating the TRAF6‐NF‐κB pathway, serves as the most potent inducer for TLR2 up‐regulation, and plays an important role in the regulation of hepatocyte functions by augmenting the hepatocyte response to bacteria or bacterial products.
Abstract: We have previously reported that the expressions of TLR2 and TLR4 mRNA are differentially regulated in mouse liver and in the parenchymal cells. In the present study, we investigated the mechanism of the up-regulatory effects of interleukin-1alpha (IL-1alpha), tumour necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS), or bacterial lipoprotein (BLP) on TLR2 mRNA expression in primary cultured murine hepatocytes. Although TLR2 mRNA stability was not affected, these treatments enhanced NF-kappaB activity and TLR2 gene transcription simultaneously. The up-regulation of TLR2 transcription in response to these reagents was completely inhibited by blocking the NF-kappaB activation pathway, demonstrating a pivotal role of NF-kappaB activation in the regulation of hepatocyte TLR2 transcription. The expression of TLR2 protein by hepatocytes was also remarkably up-regulated by IL-1alpha and, to a lesser extent, by TNF-alpha as well, but not by LPS or BLP. In addition, pretreatment of mice with IL-1alpha markedly increased the BLP (a ligand for TLR2)-induced serum level of serum amyloid A (SAA), an acute-phase protein predominantly produced by hepatocytes, indicating that IL-1alpha may also up-regulate functional TLR2 in vivo. These results demonstrate that IL-1alpha, through activating the TRAF6-NF-kappaB pathway, serves as the most potent inducer for TLR2 up-regulation, and plays an important role in the regulation of hepatocyte functions by augmenting the hepatocyte response to bacteria or bacterial products.
TL;DR: RSV replication seemed to be essential for modulation of IFN‐γ production because a virus preparation inactivated by UV irradiation had no effect and one reason for multiple reinfections by RSV might be the subversion of antiviral immune responses by interference of RSV with DC function.
Abstract: Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants under 6 months of age. Since an RSV infection does not necessarily prevent a reinfection, we asked whether RSV might subvert an effective immune response by interfering with the function of dendritic cells (DCs). Immature DCs cultured from cord blood stem cells and infected with RSV reduced the rate of interferon-gamma (IFN-gamma) production in co-cultured autologous naive T cells stimulated with the superantigen TSST-1. Maturation of DCs in response to poly(IC) but not to CD40 ligand did overcome the inhibitory effect of RSV. Further experiments demonstrated that induction of apoptosis, a selective increase in CD86 expression and lack of release of pro-inflammatory cytokines were associated with inhibition of IFN-gamma generation. In addition, RSV replication seemed to be essential for modulation of IFN-gamma production because a virus preparation inactivated by UV irradiation had no effect. Hence, one reason for multiple reinfections by RSV might be the subversion of antiviral immune responses by interference of RSV with DC function.