Showing papers in "Immunology and Cell Biology in 1997"

The role of CD45 and CD45-associated molecules in T cell activation.

Abstract: CD45 (lymphocyte common antigen) is a receptor-linked protein tyrosine phosphatase that is expressed on all leucocytes, and which plays a crucial role in the function of these cells. On T cells the extracellular domain of CD45 is expressed in several different isoforms, and the particular isoform(s) expressed depends on the particular subpopulation of cell, their state of maturation, and whether or not they have previously been exposed to antigen. It has been established that the expression of CD45 is essential for the activation of T cells via the TCR, and that different CD45 isoforms display a different ability to support T cell activation. Although the tyrosine phosphatase activity of the intracellular region of CD45 has been shown to be crucial for supporting signal transduction from the TCR, the nature of the ligands for the different isoforms of CD45 have been elusive. Moreover, the precise mechanism by which potential ligands may regulate CD45 function is unclear. Interestingly, in T cells CD45 has been shown to associate with numerous molecules, both membrane associated and intracellular; these include components of the TCR-CD3 complex and CD4/CD8. In addition, CD45 is reported to associate with several intracellular protein tyrosine kinases including p56lck and p59fyn of the src family, and ZAP-70 of the Syk family, and with numerous proteins of 29-34 kDa. These CD45-associated molecules may play an important role in regulating CD45 tyrosine phosphatase activity and function. However, although the role of some of the CD45-associated molecules (e.g. CD45-AP and LPAP) has become better understood in recent years, the role of others still remains obscure. This review aims to summarize recent findings on the role of CD45 and CD45-associated molecules in T cell activation, and to highlight issues that seem relevant to ongoing research in this area.

Molecular mimicry: can epitope mimicry induce autoimmune disease?

Abstract: Mimicry of host antigens by infectious agents may induce cross-reactive autoimmune responses to epitopes within host proteins which, in susceptible individuals, may tip the balance of immunological response versus tolerance toward response and subsequently lead to autoimmune disease. Epitope mimicry may indeed be involved in the pathogenesis of several diseases such as post-viral myocarditis or Chagas disease, but for many other diseases in which it has been implicated, such as insulin-dependent diabetes mellitis or rheumatoid arthritis, convincing evidence is still lacking. Even if an epitope mimic can support a cross-reactive T or B cell response in vitro, its ability to induce an autoimmune disease in vivo will depend upon the appropriate presentation of the mimicked host antigen in the target tissue and, in the case of T cell mimics, the ability of the mimicking epitope to induce a proliferative rather than anergizing response upon engagement of the MHC-peptide complex with the T cell receptor. B cell presentation of mimicking foreign antigen to T cells is a possible mechanism for instigating an autoimmune response to self antigens that in turn can lead to autoimmune disease under particular conditions of antigen presentation, secondary signalling and effector cell repertoire. In this review evidence in support of epitope mimicry is examined in the light of the necessary immunological considerations of the theory.

The role of dendritic cells in T cell activation

Abstract: Dendritic cells (DC) are distinguishable from other antigen-presenting cells by their potent antigen-presenting capacity. They are not only efficient at presenting peptide antigen but can also process and present soluble protein antigen sto antigen-specific T cells and cloned T cell lines. They are very strong stimulators of both allogeneic and syngeneic mixed lymphocyte reactions and have a unique capacity to stimulate naive T cells. The potent functional capacity of DC is related to a high-level expression of major histocompatibility complex class I/II molecules and constitutive expression of costimulatory molecules, such as CD80/CD86, as well as heat stable antigen, CD40 and the leucocyte function antigen (LFA) family of adhesion molecules. Recent studies have shown that DC are also involved in regulation of the immune response via induction of both central and peripheral tolerance.

Multi-epitope DNA vaccines

Abstract: The evolution of vaccine strategies has seen a move from whole organisms to recombinant proteins, and further towards the ultimate in minimalist vaccinology, the epitope. The epitope-based approach is clearly compelling as only a relatively tiny, but immunologically relevant, sequence is often capable of inducing protective immunity against a large and complex pathogen. The post-reductionist era in epitope-based vaccinology has seen a quest to re-construct complexity and design vaccines containing many epitopes. The hope is that such multi-epitope vaccines might induce immunity against multiple antigenic targets, multiple strain variants, and/or even multiple pathogens. The ability of DNA vaccination to co-deliver a series of antibody and/or CD4 T cell epitopes remains largely unexplored. Successful viral vector and DNA-based experimental vaccines coding for multiple contiguous CD8 CTL epitopes have, however, recently been described. This simple CTL poly-epitope (or polytope) strategy may find application in the design of vaccines against several diseases including EBV, HIV and cancer.

Cytokines and costimulatory molecules as genetic adjuvants.

Abstract: DNA vectors expressing an antigen derived from a pathogen or a cancerous cell have been shown, after inoculation into experimental animals, to trigger de novo synthesis of foreign proteins, which induce an immune response. This immune response can be modulated by coinoculation of vectors encoding either cytokines or costimulatory molecules. A variety of cytokines such as granulocyte/macrophage colony-stimulating factor (GM-CSF), IL-2, IL-4, IL-12 and IFN-gamma, as well as the costimulatory molecule B7.1, have been tested to date for their ability to amplify the immune response to genetic vaccines. Although the results obtained thus far clearly show that coadministration of vectors expressing immunomodulatory molecules, such as cytokines, may increase the efficacy of genetic vaccines, this approach is currently considered unsuitable for use in human patients due to the potential side effects of persistent cytokine expression.

SLAM and its role in T cell activation and Th cell responses

Abstract: Following the initial events of T cell activation, triggered by binding of specific peptide-MHC complex to the TCR for antigen and engagement of costimulatory molecules, a number of activation molecules are expressed on the cell surface. Many of these molecules regulate T cell function, T-T cell interactions and the interaction of T cells with other cells. One such molecule is SLAM, a multifunctional 70 kDa glycoprotein member of the Ig superfamily with multiple isoforms. SLAM is rapidly induced on naive T cells and B cells following activation. Engagement of SLAM by a specific antibody (mAb A12) results in IL-2-independent T cell expansion and induction/up-regulation of IFN-gamma by activated T cells, including Th2 cells. SLAM was found to be a high-affinity self-ligand mediating molecular and cellular homophilic interactions. In this review we discuss SLAM as a receptor involved in T cell expansion and in directing immune responses to a Th0-Th1 pathway.

Interleukin-5 and eosinophils induce airway damage and bronchial hyperreactivity during allergic airway inflammation in BALB/c mice

Abstract: The cytokines IL-4 and IL-5 secreted from antigen-activated CD4+ T cells are thought to play central roles in the clinical expression and pathogenesis of asthma. However, there is conflicting evidence in animal models of allergic airway inflammation as to the relative importance of IL-5 and eosinophils to the mechanisms underlying the induction of bronchial hyperreactivity and morphological changes to the airways in response to aeroallergen. In a recent investigation, the development of aeroallergen-induced bronchial hyperreactivity in BALB/c mice was thought to be exclusively regulated by IL-4, with no role for IL-5 or eosinophils being demonstrated. In contrast, allergic airway disease could not be induced in IL-5-deficient mice of the C57BL/6 strain. A model of allergic airway inflammation, which displays certain phenotypic characteristics of late-phase asthmatic responses, was used in the present investigation to establish a role for IL-5 and eosinophils in the initiation of bronchial hyperreactivity and in the pathogenesis of allergic airway disease in BALB/c mice. Sensitization and repetitive aerosolization of mice with ovalbumin resulted in a severe airway inflammatory response which directly correlated with the induction of extensive airway damage and bronchial hyperreactivity to beta-methacholine. Treatment of mice with anti-IL-5 mAb before aeroallergen challenge, abolished blood and airway eosinophilia, lung damage and significantly reduced bronchial hyperreactivity. These results show that IL-5 and eosinophilic inflammation play a substantial role in the pathophysiology of allergic airway disease and, moreover, that aeroallergen-induced bronchial hyperreactivity is not exclusively regulated by IL-4. These results also suggest that eosinophils are predominantly responsible for regulating aeroallergen-induced structural changes to the airways which contribute, in part, to the mechanism underlying the induction of bronchial hyperreactivity. Thus, there are at least two distinct pathophysiological mechanisms for the induction of aeroallergen-induced airway occlusion.

Antarctic isolation: immune and viral studies

Abstract: Stressful environmental conditions are a major determinant of immune reactivity. This effect is pronounced in Australian National Antarctic Research Expedition populations exposed to prolonged periods of isolation in the Antarctic. Alterations of T cell function, including depression of cutaneous delayed-type hypersensitivity responses and a peak 48.9% reduction of T cell proliferation to the mitogen phytohaemagglutinin, were documented during a 9-month period of isolation. T cell dysfunction was mediated by changes within the peripheral blood mononuclear cell compartment, including a paradoxical atypical monocytosis associated with altered production of inflammatory cytokines. There was a striking reduction in the production by peripheral blood mononuclear cells of the predominant pro-inflammatory monokine TNF-alpha and changes were also detected in the production of IL-1, IL-2, IL-6, IL-1ra and IL-10. Prolonged Antarctic isolation is also associated with altered latent herpesvirus homeostasis, including increased herpesvirus shedding and expansion of the polyclonal latent Epstein-Barr virus-infected B cell population. These findings have important long-term health implications.

B cell life span : a review

Abstract: Debate has surrounded the subject of B cell life span since it was first measured in mice in the early 1970s. In the 25 years which have passed since then, it has become increasingly apparent that the methods employed to measure rates of B cell turnover, such as [3H]-thymidine labelling, cell transfer or cell ablation, brought about significant disruptions to normal physiology which in themselves might have affected B cell turnover. More recently the use of bromodeoxyuridine has overcome many of these methodological difficulties and has allowed rates of B cell renewal to be measured within B cell subpopulations defined by multiparameter flow cytometry. Such studies have largely resolved the issue, concluding that about 85% of peripheral B cells are phenotypically mature and display first-order exponential kinetics defined by a half-life of 5-6 weeks, whilst the remainder are short-lived with a life span of several days. This review examines both traditional and recent methods and discusses the influence of age, self-tolerance and randomness in the overall shaping of a kinetically stable mature B cell population.

Postnatal changes in mucosal immune response: a physiological perspective of breast feeding and weaning.

Abstract: There are profound changes of immune activity during infancy from suppression during breast feeding, activation with weaning, and later intrinsic down-regulation after weaning. Breast feeding, as well as protecting against infections, seems to have a fundamental role in modifying the immune system against certain disease states. Transforming growth factor (TGF)beta in breast milk may mediate this immunosuppressive effect. Although the infant immune system is not in an adult state, the notion that the infant immune system is immature is difficult to reconcile with evidence that most infants respond appropriately to immunization and to infections. The systemic immune system of neonates may be subject to Th2 immune deviation, while the mucosal immune system, particularly of the gastrointestinal tract and probably the respiratory tract, is up-regulated with physiological inflammation during infancy. Weaning is associated with a peak of intestinal immune activation which includes mucosal mast cells and T cells. The physiological effects of this activation are promotion of epithelial growth of the small intestine and initial activation of mechanisms leading to subsequent down-regulation of the physiological heightened immune activity. This coincides with the development of mucosal (oral) tolerance to food and bacterial antigens.

Dna vaccination against virus infection and enhancement of antiviral immunity following consecutive immunization with dna and viral vectors

Abstract: DNA vaccination against virus infection and enhancement of antiviral immunity following consecutive immunization with DNA and viral vectors

Gene gun-based nucleic acid immunization alone or in combination with recombinant vaccinia vectors suppresses virus burden in rhesus macaques challenged with a heterologous SIV.

Abstract: Gene gun-based DNA immunization alone or in combination with recombinant vaccinia vectors was evaluated for the ability to elicit protective immune responses in rhesus macaques challenged with a pathogenic, heterologous simian immunodeficiency virus (SIV). Six monkeys primed with seven consecutive doses of DNA encoding SIVmac239 gp120 and gp160 (DNA + DNA) were divided into two groups. Three of these animals received another DNA booster immunization and the remaining three received a booster immunization containing a homologous, live recombinant vaccinia virus expressing SIVmac251 gp160 (DNA + VAC). In addition, a group of 15 animals primed with recombinant vaccinia vectors were divided into two groups. One group of six monkeys received another immunization of vaccinia (VAC + VAC) and the other nine animals received a DNA (mac239) booster immunization (VAC + DNA). Geometric mean end-point IgG titres in the DNA + VAC and VAC + DNA groups were substantially higher than the responses seen in the VAC + VAC and DNA + DNA groups, demonstrating a synergistic relationship between DNA-based vaccines and recombinant vaccinia virus-based vaccines. All vaccinates and five naive controls were challenged 19 weeks after the final booster immunization with 10 animal infectious doses of SIVDelta/B670. The vaccines did not prevent infection. However, all vaccine groups showed significant virus load reductions from seven to 56 days post challenge when compared to controls. Although the DNA + DNA group developed the lowest prechallenge antibody responses, the most significant reduction (200-fold) in virus load was associated with this group. In addition, a significant delay in CD4+ T cell loss relative to controls was observed in the DNA + DNA group. These results demonstrate that a gene gun-based DNA vaccine provided some attenuation of infection and CD4+ T cell loss after a heterologous challenge.

Human cytokines suppress apoptosis of leukaemic cd5+ b cells and preserve expression of bcl-2

Abstract: Leukaemic CD5+ B cells obtained from B cell chronic lymphocytic leukaemia (B-CLL) patients rapidly undergo apoptosis during in vitro culture. This is associated with down-regulation in expression of bcl-2. Spontaneous apoptosis of these cells contrasts their enhanced longevity in vivo and suggests that apoptosis-inhibitory factors may be responsible for the accumulation of leukaemic cells in B-CLL. The effect of different cytokines on apoptosis and bcl-2 expression was examined in six populations of leukaemic CD5+ B cells. Consistent with previous data, IL-4 and IFN-gamma suppressed apoptosis in 6/6 and 5/6 cell populations, respectively. Interestingly, the ability to suppress apoptosis in leukaemic CD5+ B cells was also found to be a property of IL-2, IL-6, IL-13 and TNF-alpha. In the presence of these cytokines, 10-40% more viable cells were detected, compared with unstimulated cultures. Enhancement of cell viability and suppression of apoptosis were associated with a delay in down-regulation of bcl-2. These results suggest a role for autocrine and paracrine growth factors in the pathogenesis of B-CLL, and indicate that cytokines which prevent apoptosis in vitro may be targets for treating this malignancy.

DNA vaccines for the treatment of autoimmune disease.

Abstract: DNA vaccines represent one of the most significant developments in vaccine technology in recent years. Although, in general, studies have primarily focused on the induction of protective immune responses against infectious pathogens, the technology may prove useful for other immune-related diseases, including autoimmunity. Autoimmune disease results from a breakdown in tolerance to self antigens; however, the same fundamental immunological reactions that control immune responses to foreign antigens are also likely to operate during the course of autoimmune disease. These include the reciprocal regulation of Th cell subsets. Th1 cells appear to be involved in many organ-specific autoimmune diseases while suppression of disease is associated with cells of the Th2 phenotype. It has been possible, therefore, to suppress many of the pathological consequences of autoimmunity by manipulating the Th1/Th2 cell balance. The induction of Th2 responses by DNA immunization might therefore be expected to have a profound effect on the course of autoimmune disease. Indeed, we have demonstrated that DNA immunization can protect animals against the autoimmune central nervous system inflammatory disease, experimental autoimmune encephalomyelitis (EAE). As many other autoantigens have now been identified, the application of this technology to other autoimmune diseases warrants investigation.

DNA vaccines for bacterial infections.

Abstract: DNA vaccines are an exciting development in vaccine technology which may have a special role in preventing viral infections and as 'theracines' for cancer. Their use in preventing bacterial infections has, by comparison, been less well documented. While it is unlikely that traditional, highly successful and cheap vaccines for diseases such as diphtheria will be replaced by DNA vaccines, naked DNA may be particularly appropriate for preventing bacterial infections where cytotoxic T cells confer protection, or where a Th1 type T cell response mediates resistance. For example, DNA vaccines containing different mycobacterial antigens have been shown to inhibit overt infections by Mycobacterium tuberculosis in rodent models. The use of DNA vaccines in bacterial infections may be complicated by fundamental differences between prokaryotic and eukaryotic genes and gene products, including mRNA stability, codon bias, secondary structures surrounding native start sequences and glycosylation. These problems can be solved by re-synthesis of bacterial genes to produce 'new' sequences which are more highly expressed by eukaryotic cells.

Dna cancer vaccines : a gene gun approach

Abstract: A wide variety of approaches, all using gene transfer, have been tested experimentally as alternative means to vaccinate against cancer, either prophylactically or therapeutically. These include both ex vivo and in vivo gene transfer to tumour and/or non-tumour cells, using both viral and non-viral vectors. The transferred DNA has varied widely as well, including genomic or cDNA encoding tumour-associated or oncofoetal antigens, cytokines, histocompatibility molecules, and costimulatory molecules. Several of these approaches have been applied in human clinical trials. This review summarizes those approaches, then compares and evaluates various methods using cytokine DNA in conjunction with autologous tumour cells, with particular emphasis on particle-mediated gene transfer via a gene gun. Finally, prospects and needs for further development are discussed.

Antigen presentation by MHC class II molecules

Abstract: The treamendous explosion in the field of MHC research in the last 5 years has significantly advanced our understanding of antigen processing pathways, particularly with regard to details of MHC class II-mediated antigen presentation MHC class II molecules at the surface of antigen presenting cells present antigenic peptides to CD4+ T helper cells However for effective cell surface antigen presentation, a number of highly synchronized events must first take place intracellulary The monomorphic protein, invariant chain (Ii), is a crucial participant in MHC class II antigen presentation Acting as a molecular chaperone, this molecule escorts the newly synthesized class II heterodimers from the endoplasmic reticulum into the endosomal system During this manoeuvre, the interaction of li with class II serves to prevent premature association of antigenic peptide Once the complex reaches the acidic environment of the endosomes, li is proteolytically degraded and dissociates, leaving the class II binding site available for binding antigenic peptide derived from exogenous proteins The final Ii fragment to be displaced CLIP (class II-associated invariant chain peptides), must be physically removed from the class II binding groove with assistance from another MHC-encoded molecule, DM The interaction of DM with class II also aids in the subsequent rapid loading of high-affinity antigen-derived peptides into the MHC class II groove The stable peptide-loaded complexes are now ready to exit the endocytic compartments to present their peptide antigen to specific T helper cells at the cell surface

Activation and signal transduction via mitogen-activated protein (MAP) kinases in T lymphocytes.

Abstract: The various mitogen-activated protein (MAP) kinases have central roles in the signalling pathways of T lymphocytes. Their activation is uniquely dependent on dual phosphorylation of a serine/threonine and a tyrosine residue and is regulated by several levels of kinases in parallel cascades. In addition, both the MAP kinases and their upstream, activating kinases are regulated by several phosphatases. Although each of the MAP kinases have many cytoplasmic substrates, their ability to translocate to the nucleus means that they can transmit signals from the cytoplasm directly to transcription factors, which are sometimes nuclear bound. The MAP kinase cascades are activated in T lymphocytes by a variety of different external stimuli. They play an important role in transducing both the signal from T cell receptor and costimulatory molecules, on the T cell surface, and are able to regulate several of the transcription factors controlling the expression of critical genes, including that for IL-2. This review examines how the activation of several MAP kinases is regulated, their role in signal transduction initiated by a variety of stimuli, and how this may lead to different cellular responses.

DNA vaccines for parasitic infections.

Abstract: There has been a tremendous explosion in the area of DNA vaccine research over the last 4 years, particularly in relation to antiviral vaccines. This report discusses the development and application of this new technology with regard to parasitic infections. Progress has been made towards the development of a vaccine against malaria, cryptosporidiosis, leishmaniasis, toxoplasmosis and schistosomiasis. In the future, nucleic acid vaccines will be a useful tool to help control these and other parasitic infections.

Nucleic acid vaccination of sheep: Use in combination with a conventional adjuvanted vaccine against Taenia ovis

Abstract: This report describes the use of a nucleic acid vaccine in a large outbred animal species both alone and in combination with a conventionally adjuvanted vaccine. The gene encoding a host-protective antigen (45W) from the sheep parasite Taenia ovis was cloned into the expression vector pcDNA3 and the resultant plasmid termed pcDNA3-45W. Eleven of 15 sheep injected either intramuscularly or intradermally with pcDNA3-45W mounted a serum antibody response to 45W which for both routes of injection was predominantly IgG1. However, the level of antibody elicited by the nucleic acid vaccine was low and repeated vaccinations did not boost the response. Injection of pcDNA3-45W into animals in which an immune response had previously been generated by vaccination with recombinant 45W using Quil A as adjuvant (rec45W vaccine), did not result in enhanced antibody levels. Initial vaccination with pcDNA3-45W and subsequently with the rec45W vaccine resulted in antibody levels significantly higher (P < 0.05) than those obtained in sheep which had only received the rec45W vaccine. This enhanced antibody response was predominantly of the IgG1 subclass (IgG1 : IgG2, 5 : 1) in animals injected with the nucleic acid vaccine by the i.m. route. Surprisingly, a second rec45W vaccination of these animals led to little or no increase in IgG1 levels and a 10-fold increase in IgG2 resulting in a predominance of 45W-specific IgG2 (IgG1 : IgG2, 0.25 1). These studies revealed that nucleic acid vaccination has efficacy, albeit limited, in the sheep and supports previous investigations which showed that antibody responses elicited by immunization are determined by both the route and mode of antigen delivery.

Dependence of the adaptive immune response on innate immunity: some questions answered but new paradoxes emerge.

Abstract: Dependence of the adaptive immune response on innate immunity: Some questions answered but new paradoxes emerge

Vaccines for control of fertility and hormone-dependent cancers *

Abstract: This article traces and reviews the development of vaccines against two reproductive hormones, luteinizing hormone release hormone (LHRH) and human chorionic gonadotrophin (hCG). The heterospecies dimer (HSD)-dehydrogenase hCG vaccine is the first to have completed phase II clinical trials providing evidence for the prevention of pregnancy in humans by immunization with this vaccine. The vaccine acts without blocking ovulation or disturbance of menstrual bleeding. Its effect is fully reversible and fertility is regained with decline of the antibodies. The antibody response in humans is directed against immunodominant epitopes located in the core part of beta hCG, distinct from the C-terminal region. However, problems arising from carrier-conjugated vaccines against 'self' hormones such as carrier-induced immuno-suppression on repeated immunization are evoked and solutions discussed. The LHRH vaccine, a model semi-synthetic vaccine, can be used in both sexes and has applications in regulation of fertility of animals. It has therapeutic applications as a cost-effective approach in clinical conditions where LHRH agonists and antagonists have therapeutic action. The vaccine has undergone phase I and II clinical trials in advanced-stage carcinoma of prostate patients with encouraging results.

Plant immunomodulators for termination of unwanted pregnancy and for contraception and reproductive health.

Abstract: Neem (Azadirachta indica) seed and leaf extracts have spermicidal, anti-microbial, anti-fungal and anti-viral properties. They are also immunomodulators that induce primarily a TH1 type response. These properties are being exploited to develop two different useful methods of fertility control. Neem extracts given orally at early post-implantation stage terminate pregnancy in rodents and primates. Treatment has no residual permanent effect and fertility is regained in subsequent cycles. The mechanism by which the action occurs is not fully clear. A transient increase in CD4 and more significantly in CD8 cells is noticed in mesenteric lymph nodes and spleen. A rise in immunoreactive and bioactive TNF-alpha and IFN-gamma in draining lymph nodes, serum and foetal-placental tissue is observed. A polyherbal cream and pessary have been developed containing three active ingredients of plant origin. These have synergistic spermicidal properties on human sperm as determined by the Sander Cramer test. Their use before mating has high contraceptive efficacy in rabbits and baboons. Another interesting property is their inhibitory action on a wide spectrum of micro-organisms, including Candida albicans, C. tropicalis, Neisseria gonorrhoeae, the multidrug-resistant Staphylococcus aureus and urinary tract Escherichia coli, Herpes simplex-2 and HIV-1. Phase I clinical trials have been completed in India, Egypt and the Dominican Republic, and indicate the safety of the formulation, its acceptability and beneficial action invaginosis due to infections.

Inhibition of IL‐2 production by nitric oxide: A novel self‐regulatory mechanism for Th1 cell proliferation

Abstract: Cloned Th1 cells, but not Th2 cells, specific for malaria antigen, produce nitric oxide (NO) when activated with specific antigen or Con A. Furthermore, NO inhibits proliferation of, and production of IL-2 and IFN-gamma by, Th1 but not Th2 cells. Here, it is demonstrated that the inhibition of Th1 cell proliferation by the NO donor S-nitroso-N-acetyl penicillamine (SNAP) can be reversed by the addition of rIL-2 but not of rIFN-gamma, suggesting that the inhibition of Th1 cells by NO may be preventing the production of IL-2. Dose-response studies showed that Th1 cells produce optimal levels of IL-2 and a proliferative response, and no detectable NO, when stimulated with relatively low concentrations of antigen or mitogen in vitro. As the antigen/mitogen increased, however, high levels of NO were produced, accompanied by a concomitant reduction in IL-2 secretion and T cell proliferation. The proliferation of, and IL-2-IFN-gamma production by, naive CD4+ T cells from normal spleens activated with Con A in vitro can be similarly inhibited by SNAP. These results suggest that NO may serve as a self-regulatory molecule preventing the over-expansion of Th1 cells. Unrestricted Th1 cell activity has been implicated in a range of immunopathologies and autoimmune diseases. The proposed mechanism for down-regulation of Th1 cell function may also account for the suppression of lymphocyte proliferation observed in malaria infections.

Blood group antibodies are made by CD5 + and by CD5 − B cells

Abstract: The B1 subset of B lymphocytes is associated with the production of low-affinity, polyspecific antibodies. B1 cells are generally recognized by their expression of CD5, and comprise the majority of neonatal B cells. The neonate responds to a restricted range of antigens, and generally makes low-affinity IgM antibody. Published data suggest that antibodies against the blood group antigens A and B are found occasionally in cord blood, and develop rapidly in infants as a result of cross-reactivity with bacterial carbohydrate antigens. This suggests that CD5+ B1 cells may be specialized to make antibodies against such carbohydrate antigens. In this study we evaluated the appearance of antibodies against the blood group (ABO) antigens in human infants, using reagents which specifically distinguish between IgM (made by the infant) and IgG (mainly of maternal origin) and immunofluorescence to detect low levels of antibody. Having established that antibody is always detectable by 8 months of age, and frequently much earlier, we developed a plaque assay to examine the phenotype of cells making antibody against blood group antigens. At 8 months of age, CD5+ and CD5- cells were both capable of making anti-blood group antibody.

Inhibition of Toxoplasma gondii replication in IFN-gamma-activated human intestinal epithelial cells.

Abstract: Toxoplasma gondii is an obligate intracellular parasite which is responsible for severe disease after congenital infection and in immunocompromised patients, for which there is no effective therapy. In acquired toxoplasmosis, T. gondii first invade enterocytes and are disseminated throughout the body. Treatment of the adherent human intestinal cell line CaCO2 with recombinant human IFN-gamma inhibited the replication of T. gondii. Growth of the parasite was measured in vitro by [3H]-uracil incorporation assays 18 h after infection. This assay showed that when cells were pretreated with IFN-gamma concentrations ranging from 2.5 to 5000 U/ml, a high degree of inhibition of T. gondii replication could be observed, with the effect being dose dependent. This could be of relevance as a first line of defence against human Toxoplasma infection. Inhibition is due to a different mechanism from that existing in mouse macrophages and human fibroblasts: L-arginine-dependent production of reactive nitrogen intermediates, reactive oxygen intermediates synthesis or production of indoleamine 2.3 dioxygenase were not responsible for inhibition of T. gondii proliferation.

Toward clinical trials of dna vaccines against malaria

Abstract: In mid 1997 the first malaria DNA vaccine will enter clinical trials. This single gene DNA vaccine encoding the Plasmodium falciparum circumsporozoite protein (PfCSP) will be studied for safety and immunogenicity. If these criteria are met, a multi-gene DNA vaccine designed to induce protective CD8+ T cell responses against P. falciparum infected hepatocytes will be subsequently assessed for safety, immunogenicity and capacity to protect immunized volunteers against experimental challenge with P. falciparum sporozoites. Our perspectives on malaria vaccine development in general, and on a multi-gene DNA vaccine in particular, have been recently reviewed. Herein, we review the rationale and experimental foundation for the anticipated P. falciparum DNA vaccine trials.

Dendritic cells as antigen-presenting cells in vivo

Abstract: Antigen-presenting cells are of central importance for the generation and regulation of T cell-mediated immune responses. The specialized features of dendritic cells as antigen-presenting cells in selecting rare clones of antigen-specific T cells and activating them in vivo are described.

Protection from autoimmune diabetes by adjuvant therapy in the non-obese diabetic mouse: the role of interleukin-4 and interleukin-10.

Abstract: Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease that is characterized by the destruction of insulin-producing beta-cells in the pancreatic islets. A single administration of CFA prevents clinical hyperglycaemia in non-obese diabetic (NOD) mice. We have previously shown that CFA administration does not eliminate insulitis in the pancreas of the treated animals, but diverts the disease process from a destructive to a non-destructive pathway. We provide evidence that this phenomenon may be under cytokine control. Neutralizing monoclonal antibodies against IL-4 and IL-10 were injected, singularly or in combination, into CFA-treated NOD mice. Antibody treatment did not lead to the development of overt diabetes; however, a marked impairment of glucose tolerance was shown in about one half of the mice treated with a combination of the two antibodies at the end of the study. This functional abnormality correlated with the histological loss of pancreatic islet tissue. These studies suggest a role for IL-4 and IL-10 in CFA-induced protection from diabetes in the NOD mouse. They also suggest that, in this animal model, the nature of the autoimmune response to islet tissue (either destructive or non-destructive) may reflect the relative proportion of Th1- and Th2-type cytokines produced in the lesions.

Cellular responses and Mycobacterium bovis BCG growth inhibition by bovine lymphocytes.

Abstract: Cellular responses of a group of cattle immunized subcutaneously with a low dose of Mycobacterium bovis bacille Calmette-Guerin vaccine (BCG) were measured in vitro and compared with nonimmunized control animals. PBMC taken from immunized animals proliferated and produced IFN-gamma in the presence of M. bovis BCG culture filtrate proteins. The addition of PBMC from immunized animals to M. bovis BCG-infected autologous macrophages also resulted in secretion of IFN-gamma. In contrast, the responses of PBMC from control animals were comparatively low over the period of study. In experiments to study the interaction of non-adherent lymphocytes with infected macrophages, M. bovis BCG growth was inhibited in cultures containing autologous PBMC from immunized and non-immunized control animals. The degree of inhibition was related to lymphocyte concentration but did not correlate with IFN-gamma production. Treatment of macrophages with recombinant IFN-gamma prior to, or postinfection did not alter the intracellular growth kinetics of mycobacteria. It appears, therefore, that although M. bovis BCG immunization of cattle stimulates the generation of a T cell-mediated immune response to M. bovis BCG, the cattle may already possess a high level of innate resistance to M. bovis BCG that requires the presence of lymphocytes.