Showing papers on "Cytotoxic T cell published in 1992"

Restoration of viral immunity in immunodeficient humans by the adoptive transfer of T cell clones.

Abstract: The adoptive transfer of antigen-specific T cells to establish immunity is an effective therapy for viral infections and tumors in animal models. The application of this approach to human disease would require the isolation and in vitro expansion of human antigen-specific T cells and evidence that such T cells persist and function in vivo after transfer. Cytomegalovirus-specific CD8+ cytotoxic T cell (CTL) clones could be isolated from bone marrow donors, propagated in vitro, and adoptively transferred to immunodeficient bone marrow transplant recipients. No toxicity developed and the clones provided persistent reconstitution of CD8+ cytomegalovirus-specific CTL responses.

Apoptosis and Programmed Cell Death in Immunity

Abstract: Death of some cells in the mammalian body is clearly programmed. In the immune system there are many examples of programmed cell death, during development of lymphocytes as well as at later stages, after interaction with antigen. Many of these examples display the morphology of apoptosis: They undergo shrinkage and zeiosis, the nucleus collapses, and chromatin is cleaved into nucleosomal fragments. The cell is rapidly recognized by phagocytes and disposed of without releasing its contents. In some but not all cases of apoptosis, new macromolecular synthesis is required. Cytotoxic T cells induce changes in their targets that are morphologically apoptotic. The mechanism of apoptosis is currently under active investigation.

The presence of interleukin 4 during in vitro priming determines the lymphokine-producing potential of CD4+ T cells from T cell receptor transgenic mice.

Abstract: To study the factors that determine whether CD4+ T cells produce interleukin 4 (IL-4) or interferon gamma (IFN-gamma) upon stimulation we used a system allowing naive T cells to be primed in vitro by specific antigen. Dense CD4+ T cells were purified from mice that expressed transgenes encoding a T cell receptor specific for pigeon cytochrome C peptide 88-104 in association with I-Ek. These T cells produced very limited amounts of IL-4 and IFN-gamma upon immediate challenge with 88-104 and antigen-presenting cells (APC). However, after an initial "priming" culture in which they were incubated for 4 d in the presence of 88-104, APC, and 1,000 U/ml IL-4, the T cells acquired the capacity to produce substantial amounts of IL-4 upon rechallenge but made very little IFN-gamma. Cells primed in the absence of IL-4 produced IFN-gamma upon rechallenge but virtually no IL-4. The inhibitory effect of IL-4 on IFN-gamma production did not appear to be mediated by the induction of IL-10 production since IL-10 addition to initial cultures did not suppress priming for IFN-gamma production, nor did anti-IL-10 block the inhibitory effect of IL-4. IFN-gamma itself did not increase priming for IFN-gamma production, nor did anti-IFN-gamma reduce such priming. IFN-gamma did, however, diminish priming for IL-4 production when limiting amounts of IL-4 (100 U/ml) were used in the initial culture. The dominant effect of IL-4 in determining the lymphokine-producing phenotype of primed cells was observed with dendritic cells (DC), activated B cells, and I-Ek-transfected fibroblasts as APC. However, the different APC did vary in their potency, with DC being superior to activated B cells, which were superior to transfected fibroblasts.

Shigella flexneri induces apoptosis in infected macrophages

Abstract: The Gram-negative bacterial pathogen Shigella flexneri causes dysentery by invading the human colonic mucosa. Bacteria are phagocytosed by enterocytes, escape from the phagosome into the cytoplasm and spread to adjacent cells. After crossing the epithelium, Shigella reaches the lamina propria of intestinal villi, the first line of defence. This tissue is densely populated with phagocytes that are killed in great numbers, resulting in abscesses. The genes required for cell invasion and macrophage killing are located on a 220-kilobase plasmid. We report here on the mechanism of cytotoxicity used by S. flexneri to kill macrophages. Each of four different strains was tested for its capacity to induce cell death. An invasive strain induced programmed cell death (apoptosis), whereas its non-invasive, plasmidcured isogenic strain was not toxic; neither was a mutant in ipa B (ref. 10) (invasion protein antigen), a gene necessary for entry. A non-invasive strain expressing the haemolysin operon of Escherichia coli induced accidental cell death (necrosis), demonstrating that other bacterial cytotoxic mechanisms do not lead to apoptosis. This is the first evidence that an invasive bacterial pathogen can induce suicide in its host cells.

Programmed death of T cells in HIV-1 infection

Abstract: In human immunodeficiency virus (HIV) infection, functional defects and deletion of antigen-reactive T cells are more frequent than can be explained by direct viral infection. On culturing, both CD4+ and CD8+ T cells from asymptomatic HIV-infected individuals died as a result of programmed cell death (apoptosis). Apoptosis was enhanced by activation with CD3 antibodies. Programmed cell death, associated with impaired T cell reactivity, may thus be responsible for the deletion of reactive T cells that contributes to HIV-induced immunodeficiency.

Activation-induced death by apoptosis in CD4+ T cells from human immunodeficiency virus-infected asymptomatic individuals.

Abstract: In immature thymocytes, T cell receptor for antigen (TCR) mobilization leads to an active T cell suicide process, apoptosis, which is involved in the selection of the T cell repertoire. We have proposed that inappropriate induction of such a cell death program in the mature CD4+ T cell population could account for both early qualitative and late quantitative CD4+ T lymphocyte defects of human immunodeficiency virus (HIV)-infected individuals (Ameisen, J.C., and A. Capron. 1991. Immunol. Today. 4:102). Here, we report that the selective failure of CD4+ T cells from 59 clinically asymptomatic HIV-infected individuals to proliferate in vitro to TCR mobilization by major histocompatibility complex class II-dependent superantigens and to pokeweed mitogen (PWM) is due to an active CD4+ T cell death process, with the biochemical and ultrastructural features of apoptosis. Activation-induced cell death occurred only in the CD4+ T cell population from HIV-infected asymptomatic individuals and was not observed in T cells from any of 58 HIV-seronegative controls, including nine patients with other acute or chronic infectious diseases. Activation-induced CD4+ T cell death was prevented by cycloheximide, cyclosporin A, and a CD28 monoclonal antibody (mAb). The CD28 mAb not only prevented apoptosis but also restored T cell proliferation to stimuli, including PWM, superantigens, and the tetanus and influenza recall antigens. These findings may have implications for the understanding of the pathogenesis of acquired immune deficiency syndrome and for the design of specific therapeutic strategies.

Compositions that mediate killing of hiv-infected cells

Abstract: A method for directing a cytotoxic T cell to an HIV-I-infected cell, which comprises contacting the infected cell with a bispecific proteinaceous molecule comprising two binding domains, wherein the first binding domain comprises a CD4 domain or domains and the second binding domain comprises an anti-CD3 binding region.

Regulation of Immunity to Parasites by T Cells and T Cell-Derived Cytokines

Abstract: Parasitic protozoa and helminths are a diverse group of organisms which together form a major cause of infectious disease in humans and livestock. Studies in animal models have revealed that T lymphocytes and the cytokines they produce play a crucial role in determining the outcome of parasitic infection in terms of both protective immunity and immunopathology. Of particular interest is recent evidence that different parasitic infections in the context of different host genetic background can trigger polarized CD4+ T cell subset responses. The set of cytokines produced by these different T helper responses, in turn, can have opposing effects on the parasite, resulting in either control of infection or promotion of disease. Moreover, cytokines produced by one CD4+ subset can block either the production and/or activity of the cytokines produced by the other subset. The establishment of this state of cross-regulation may be important for parasite survival. CD8+ T cells also appear to play a dual effector/regulatory role in parasite immunity and immunopathology, although the mechanisms underlying their induction and function are less well understood. CD(8+)-mediated cytolytic killing functions have now been demonstrated against a number of different intracellular protozoa, although IFN-gamma produced by the same effector cells may also be critical in host community. In addition to providing highly relevant models for studying the selection and immunobiologic function of T-cell subsets, research on T lymphocyte-parasite interactions is crucial for the design of effective vaccines and immunotherapies and thus has broad practical as well as theoretical ramifications.

Major histocompatibility complex class I-restricted T cells are required for resistance to Mycobacterium tuberculosis infection.

Abstract: Mice with a targeted disruption in the beta 2-microglobulin (beta 2m) gene, which lack major histocompatibility complex class I molecules and consequently fail to develop functional CD8 T cells, provided a useful model for assessing the role of class I-restricted T cells in resistance to infection with virulent Mycobacterium tuberculosis. Of mutant beta 2m-/-mice infected with virulent 10(6) M. tuberculosis, 70% were dead or moribund after 6 weeks, while all control mice expressing the beta 2m gene remained alive for > 20 weeks. Granuloma formation occurred in mutant and control mice, but far greater numbers of tubercle bacilli were present in the lungs of mutant mice than in controls, and caseating necrosis was seen only in beta 2m-/-lungs. In contrast, no differences were seen in the course of infection of mutant and control mice with an avirulent vaccine strain, bacille Calmette-Guerin (BCG). Immunization with BCG vaccine prolonged survival of beta 2m-/-mice after challenge with M. tuberculosis for 4 weeks but did not protect them from death. These data indicate that functional CD8 T cells, and possibly T cells bearing gamma delta antigen receptor, are a necessary component of a protective immune response to M. tuberculosis in mice.

Role for c-myc in activation-induced apoptotic cell death in T cell hybridomas

Abstract: Immature T cells and some T cell hybridomas undergo apoptotic cell death when activated through the T cell receptor complex, a phenomenon that is probably related to antigen induced negative selection of developing T cells. This activation-induced apoptosis depends on active protein and RNA synthesis in the dying cells, although none of the genes required for this process have previously been identified. Antisense oligonucleotides corresponding to c-myc block the constitutive expression of c-Myc protein in T cell hybridomas and interfere with all aspects of activation-induced apoptosis without affecting lymphokine production in these cells. These data indicate that c-myc expression is a necessary component of activation-induced apoptosis.

The adenovirus E1A proteins induce apoptosis, which is inhibited by the E1B 19-kDa and Bcl-2 proteins.

Abstract: Cooperation between the adenovirus E1A and E1B oncogenes is required for transformation of primary quiescent rodent cells. Although expression of E1A alone will stimulate cell proliferation sufficient to initiate transformed focus formation, proliferation fails to be sustained and foci degenerate. Coexpression of either the 19-kDa or 55-kDa E1B oncoproteins with E1A permits high-frequency transformation by overcoming this cytotoxic response. Without E1B 19-kDa protein expression, however, transformants remain susceptible to induction of cell death. Rapid loss of viability is coincident with nucleolytic cleavage of DNA in intranucleosomal regions and chromatin condensation, hallmarks of programmed cell death (apoptosis). Furthermore, overexpression of a known suppressor of apoptosis, the Bcl-2 protooncogene, can rescue E1A-induced focus degeneration. Thus E1A-dependent stimulation of cell proliferation is accompanied by apoptosis and thereby insufficient to singly induce transformation. High-frequency transformation requires a second function encoded by the E1B 19-kDa protein to block apoptosis.

Crosslinking CD4 by human immunodeficiency virus gp120 primes T cells for activation-induced apoptosis

Abstract: During human immunodeficiency virus (HIV) infection there is a profound and selective decrease in the CD4+ population of T lymphocytes. The mechanism of this depletion is not understood, as only a small fraction of all CD4+ cells appear to be productively infected with HIV-1 in seropositive individuals. In the present study, crosslinking of bound gp120 on human CD4+ T cells followed by signaling through the T cell receptor for antigen was found to result in activation-dependent cell death by a form of cell suicide termed apoptosis, or programmed cell death. The data indicate that even picomolar concentrations of gp120 prime T cells for activation-induced cell death, suggesting a mechanism for CD4+ T cell depletion in acquired immune deficiency syndrome (AIDS), particularly in the face of concurrent infection and antigenic challenge with other organisms. These results also provide an explanation for the enhancement of infection by certain antibodies against HIV, and for the paradox that HIV appears to cause AIDS after the onset of antiviral immunity.

Alterations in signal transduction molecules in T lymphocytes from tumor-bearing mice.

Abstract: Impaired immune responses occur frequently in cancer patients or in tumor-bearing mice, but the mechanisms of the tumor-induced immune defects remain poorly understood. In an in vivo murine colon carcinoma model (MCA-38), animals bearing a tumor longer than 26 days develop CD8+ T cells with impaired cytotoxic function, decreased expression of the tumor necrosis factor-alpha and granzyme B genes, and decreased ability to mediate an antitumor response in vivo. T lymphocytes from tumor-bearing mice expressed T cell antigen receptors that contained low amounts of CD3 gamma and completely lacked CD3 zeta, which was replaced by the Fc epsilon gamma-chain. Expression of the tyrosine kinases p56lck and p59fyn was also reduced. These changes could be the basis of immune defects in tumor-bearing hosts.

Coexpression and functional cooperation of CTLA-4 and CD28 on activated T lymphocytes.

Abstract: T cell costimulation by molecules on the antigen presenting cell (APC) is required for optimal T cell proliferation. The B7 molecule on APC binds the T lymphocyte receptor CD28, triggering increased interleukin 2 (IL-2) production and subsequent T cell proliferation. CTLA-4 is a predicted T cell membrane receptor homologous to CD28, which also binds the B7 counter receptor, but whose distribution and function are unknown. Here we have developed monoclonal antibodies (mAbs) specific for CTLA-4 and have investigated these questions. mAbs were produced that bound CTLA-4 but not CD28, and that blocked binding of CTLA-4 to B7. CTLA-4 expression as measured by these mAbs was virtually undetectable on resting T cells, but was increased several hundred-fold during T cell activation. On activated lymphocytes, CTLA-4 was expressed equally on CD4+ and CD8+ T cell subsets and was coexpressed with CD25, CD28, and CD45RO. CTLA-4 expression was lower than that of CD28, reaching a maximum of approximately 1/30-50 the level of CD28. Despite its lower expression, CTLA-4 was responsible for much of the B7 binding by large activated T cells. Anti-CTLA-4 mAb 11D4 and anti-CD28 mAb 9.3 acted cooperatively to inhibit T cell adhesion to B7, and to block T cell proliferation in primary mixed lymphocyte culture. When coimmobilized with anti T cell receptor (TCR) mAb, anti-CTLA-4 mAbs were less effective than anti-CD28 mAb 9.3 at costimulating proliferation of resting or activated T cells. However, coimmobilized combinations of anti-CD28 and anti-CTLA-4 were synergistic in their ability to augment anti-TCR-induced proliferation of preactivated CD4+ T cells. These results indicate that CTLA-4 is coexpressed with CD28 on activated T lymphocytes and cooperatively regulates T cell adhesion and activation by B7.

Dendritic cells exposed to human immunodeficiency virus type-1 transmit a vigorous cytopathic infection to CD4+ T cells.

Abstract: The paucity of virus-laden CD4+ cells in individuals infected with human immunodeficiency virus type-1 (HIV-1) contrasts with the greatly reduced numbers and function of these lymphocytes. A pathway is described whereby dendritic cells carry HIV-1 to uninfected T cells, amplifying the cytopathic effects of small amounts of virus. After exposure to HIV-1, dendritic cells continue to present superantigens and antigens, forming clusters with T cells that are driven to replicate. Infection of the dendritic cells cannot be detected, but the clustered T cells form syncytia, release virions, and die. Carriage of HIV-1 by dendritic cells may facilitate the lysis and loss of antigen specific CD4+ T cells in acquired immunodeficiency syndrome.

CD1b restricts the response of human CD4-8- T lymphocytes to a microbial antigen

Abstract: MOLECULES encoded by the human GDI locus on chromosome 1 (ref. 33) are recognized by selected CD4−8− T-cell clones expressing either αβ or γδ T-cell antigen receptors1,2. The known structural resemblance of GDI molecules to antigen-presenting molecules encoded by major histocompatibility complex (MHG) genes on human chromosome 6 (refs 3, 4, 34, 35), suggested that GDI may represent a family of antigen-presenting molecules separate from those encoded in the MHC1,5,6. Here we report that the proliferative and cytotoxic responses of human CD4−8− αβTCR+ T cells specific for Mycobacterium tuberculosis can be restricted by GDlb, one of the four identified protein products of the GDI locus. The responses of these T cells to M. tuberculosis seemed not to involve MHG encoded molecules, but were absolutely dependent on the expression of GDlb by the antigen-presenting cell and involved an antigen processing requirement similar to that seen in MHC class Il-restricted antigen presentation. These results provide, to our knowledge, the first direct evidence for the proposed antigen-presenting function of GDI molecules and suggest that the GDI family plays a role in cell-mediated immunity to microbial pathogens.

B Cells Turn Off Virgin But Not Memory T Cells

Abstract: There are three possible outcomes when a T cell recognizes a cell bearing a self or foreign antigen. (i) The T cell is not sufficiently signaled and is unaffected. (ii) The T cell is activated. (iii) The T cell is turned off. The differentiation state of the T cell is critical to the outcome. Although both virgin and memory T cells can be activated by antigens presented by "professional" antigen-presenting cells such as dendritic cells, they differ in their responses to B cells. Experienced T cells respond to antigen presented by B cells, whereas virgin T cells are rendered tolerant. These findings may relate to the phenomena of low- and high-zone tolerance, neonatal tolerance, and the beneficial effect of blood transfusions on allograft survival.

Differential expression of apoptosis-related Fas antigen on lymphocyte subpopulations in human peripheral blood.

Abstract: The Fas Ag is a newly defined cell-surface molecule that may mediate apoptosis. The antibody against Fas Ag can induce the apoptotic cell death in cell lines expressing this Ag. PBL subpopulations at various ages were here examined for Fas expression by two-or three-color flow-cytometric analyses using anti-Fas mAb. It was found that Fas Ag was appreciably detected on a proportion of T and B cells, whereas its expression was absent for NK cells. For CD4+ and CD8+ T cells, Fas Ag was expressed preferentially on CD45RO+ (memory or previously activated) populations, but not on CD45RO- naive ones. TCR-gamma/delta+ T cells, especially their CD45RO+ subsets, also expressed Fas Ag. Expectably, neonatal T cell subpopulations, most of which had the naive (CD45RO-) phenotype, expressed little Fas Ag. Fas-expressing B cells dominated in surface(s) IgD- populations, but neonatal B cells as well as adult sIgD+ B cells had little Fas Ag. The Fas Ag was inducible after in vitro mitogenic stimulation of naive T and B cells from neonatal blood. These observations suggested that expression of Fas Ag on T and B cells in the peripheral blood might reflect their in vivo Ag-activated status. In contrast to Fas-expressing cultured cell lines, however, viability of in vitro stimulated T and B cells as well as freshly isolated CD45RO+ T cells was not significantly changed after the treatment with anti-Fas mAb, indicating that additional cellular conditions to Fas expression might be required for anti-Fas-induced cell death.

Intrahepatic cytotoxic T lymphocytes specific for hepatitis C virus in persons with chronic hepatitis.

Abstract: Hepatitis C virus (HCV) is a major cause of post-transfusion and sporadic hepatitis worldwide, leading to chronic liver disease in at least 50% of infected individuals. The pathogenic mechanisms that result in chronic hepatitis are unknown. Lymphocytes are typically observed within the hepatic parenchyma, but the functional characteristics of these cells have not been defined. In this study, liver-infiltrating lymphocytes from two subjects with chronic HCV hepatitis were cloned at limiting dilution and tested for HCV-specific cytolytic activity using autologous target cells infected with vaccinia viruses expressing recombinant HCV Ag or sensitized with synthetic HCV peptides. In both subjects, HCV-specific, HLA class I-restricted CTL were identified that recognized epitopes in variable regions of either the envelope or nonstructural proteins. These results demonstrate the presence of HCV-specific CTL at the site of tissue damage in persons with chronic HCV hepatitis, and provide a means to evaluate the possible pathogenic role of these cells in HCV infection.

Development of humanized bispecific antibodies reactive with cytotoxic lymphocytes and tumor cells overexpressing the HER2 protooncogene.

Abstract: The HER2 protooncogene encodes a 185-kD transmembrane phosphoglycoproteins, human epidermal growth factor receptor 2 (p185HER2), whose amplified expression on the cell surface can lead to malignant transformation. Overexpression of HER2/p185HER2 is strongly correlated with progression of human ovarian and breast carcinomas. Recent studies have shown that human T cells can be targeted with bispecific antibody to react against human tumor cells in vitro. We have developed a bispecific F(ab')2 antibody molecule consisting of a humanized arm with a specificity to p185HER2 linked to another arm derived from a murine anti-CD3 monoclonal antibody that we have cloned from UCHT1 hybridoma. The antigen-binding loops for the anti-CD3 were installed in the context of human variable region framework residues, thus forming a fully humanized BsF(ab')2 fragment. Additional variants were produced by replacement of amino acid residues located in light chain complementarity determining region 2 and heavy chain framework region 3 of the humanized anti-CD3 arm. Flow cytometry analysis showed that the bispecific F(ab')2 molecules can bind specifically to cells overexpressing p185HER2 and to normal human peripheral blood mononuclear cells bearing the CD3 surface marker. In additional experiments, the presence of bispecific F(ab')2 caused up to fourfold enhancement in the cytotoxic activities of human T cells against tumor cells overexpressing p185HER2 as determined by a 51Cr release assay. These bispecific molecules have a potential use as therapeutic agents for the treatment of cancer.

Differential costimulatory effects of adhesion molecules B7, ICAM-1, LFA-3, and VCAM-1 on resting and antigen-primed CD4+ T lymphocytes.

Abstract: Optimal proliferation of T cells although initiated via ligation of the CD3/TCR complex requires additional stimulation resulting from adhesive interactions between costimulatory receptors (R) on T cells and their counter-R on APC. At least four distinct adhesion molecules (counter-R) present on APC, B7, ICAM-1 (CD54), LFA-3 (CD58), and VCAM-1 have been individually shown to costimulate T cell activation. Because some of these molecules may be expressed simultaneously on APC, it has been difficult to examine relative contributions of individual counter-R during the induction of T cell proliferation. We have produced soluble IgC gamma 1 fusion chimeras (receptor globulins or Rg) of B7, ICAM-1, LFA-3, and VCAM-1 and compared their relative abilities to costimulate proliferation of resting or Ag-primed CD4+ T cells. When co-immobilized with mAb directed at TCR alpha beta or CD3 but not CD2 or CD28, each Rg induced proliferation of both resting and Ag-primed CD4+ cells. In contrast, similarly co-immobilized CD7 Rg or ELAM-1 Rg were ineffective. Resting CD4+ T cells produced more IL-2, expressed significantly higher levels of IL-2R alpha, and proliferated more efficiently when costimulated with either ICAM-1 Rg or VCAM-1 Rg than with B7 Rg or LFA-3 Rg. CD4+ CD45RO+ memory T cells proliferated more vigorously in response to the costimulation by each of the four Rg than CD4+ CD45RA+ naive T cells. In contrast with the behavior of resting CD4+ T cells, proliferation of Ag-preactivated CD4+ T cells was most efficient when costimulated by B7 Rg. The costimulatory effect of LFA-3 Rg on Ag-primed CD4+ T cells was weaker than that of B7 Rg but was significantly greater than that of either ICAM-1 Rg or VCAM-1 Rg. These results suggest that resting and Ag-primed CD4+ T cells preferentially respond by proliferation to different costimulatory counter-R. ICAM-1 and VCAM-1 may be involved in the initiation of proliferation of Ag-responsive T cells, and B7 and LFA-3 may facilitate sustained proliferation of Ag-primed T cells. The cumulative costimulation by the above counter-R may facilitate optimal expression of various regulatory and effector functions of T cells.

IL-10 is produced by subsets of human CD4+ T cell clones and peripheral blood T cells.

Abstract: Murine IL-10 has been reported originally to be produced by the Th2 subset of CD4+ T cell clones. In this study, we demonstrate that human IL-10 is produced by Th0, Th1-, and Th2-like CD4+ T cell clones after both Ag-specific and polyclonal activation. In purified peripheral blood T cells, low, but significant, levels of IL-10 were found to be produced by the CD4+CD45RA+ population, whereas CD4+CD45RA- "memory" cells secreted 5- to 20-fold higher levels of IL-10. In addition, IL-10 was produced by activated CD8+ peripheral blood T cells. Optimal induction of IL-10 was observed after activation by specific Ag and by the combination of anti-CD3 mAb and the phorbol ester tetradecanoyl phorbol acetate, whereas the combination of calcium ionophore A23187 and 12-O-tetradecanoylphorbol-13-acetate acetate was a poor inducer of IL-10 production. Kinetic studies indicated that IL-10 was produced relatively late as compared with other cytokines. Maximal IL-10 mRNA expression in CD4+ T cell clones and purified peripheral blood T cells was obtained after 24 h, whereas maximal IL-10 protein synthesis occurred between 24 h and 48 h after activation. No differences were observed in the kinetics of IL-10 production among Th0, Th1-, and Th2-like subsets of CD4+ T cell clones. The results indicate a regulatory role for IL-10 in later phases of the immune response.

Identification of a novel surface protein on activated CD4+ T cells that induces contact-dependent B cell differentiation (help).

Abstract: CD4+ T lymphocytes provide contact-dependent stimuli to B cells that are critical for the generation of specific antibody responses in a process termed T helper function. The surface structures on activated CD4+ T cells that mediate this function are not fully known. We previously reported the isolation of a functionally unique subclone of the Jurkat leukemic T cell line (D1.1) that constitutively expressed contact-dependent helper effector function. To identify T cell surface molecules that mediate contact-dependent T helper function, a monoclonal antibody (mAb), designated 5c8, was generated that inhibits D1.1-mediated B cell activation and immunoprecipitates a novel 30-kD protein structure from surface-iodinated D1.1 cells. Normal CD4+ T cells express 5c8 antigen (Ag) transiently 5-6 h after activation by phorbol myristate acetate and phytohemagglutinin with maximal expression 5-6 h after activation and absence of expression by 24 h. In contrast, neither resting nor activated CD8+ T cells express 5c8 Ag. In functional studies, mAb 5c8 inhibits the ability of fixed, activated CD4+ T cells to induce B cell surface CD23 expression. In addition, mAb 5c8 inhibits the ability of CD4+ T cells to direct terminal B cell differentiation driven by pokeweed mitogen. Taken together, these data suggest that 5c8 Ag is a novel, activation-induced surface T cell protein that is involved in mediating a contact-dependent element of the helper effector function of CD4+ T lymphocytes.

IL-10 inhibits mitogen-induced T cell proliferation by selectively inhibiting macrophage costimulatory function.

Abstract: IL-10, a newly designated cytokine primarily produced by the Th2 subset of CD4+ T lymphocytes and Ly-1+ B lymphocytes, has recently been hypothesized to inhibit cytokine production by Th1 T cell clones by blocking accessory cell- (AC) dependent costimulatory function. To evaluate the effect of IL-10 on Con A-induced proliferative responses of resting murine T cells, purified T cells were cultured with different types of AC. The addition of IL-10 produced a 70 to 90% inhibition of resting T lymphocyte proliferation when purified populations of macrophages were used as AC, but had no effect on the AC function of T-depleted spleen cells, activated B cells, dendritic cells, or L cells. The inhibitory effects of IL-10 were inversely related to the concentration of mitogen and could be reversed by the addition of the neutralizing anti-IL-10 mAb, SXC1. The inhibition of macrophage AC function was not related to the induction of a suppressor cytokine as stimulation by mixtures of macrophages and limiting numbers of dendritic cells was not inhibited. The decrease in proliferative responses was primarily secondary to inhibition of IL-2 production although the failure of exogenous IL-2 to completely reconstitute the response suggested that IL-10 may also exert inhibitory effects on the induction of expression of a functional IL-2R. These results are most consistent with a model in which IL-10 inhibits the induction of expression on macrophages of a critical costimulatory molecule that may be constitutively expressed on other types of AC.

Molecular cloning of ICAM-3, a third ligand for LFA-1, constitutively expressed on resting leukocytes

Abstract: The co-ordinated function of effector and accessory cells in the immune system is assisted by adhesion molecules on the cell surface that stabilize interactions between different cell types. Leukocyte function-associated antigen 1 (LFA-1) is expressed on the surface of all white blood cells and is a receptor for intercellular adhesion molecules (ICAM) 1 and 2 (ref. 3) which are members of the immunoglobulin superfamily. The interaction of LFA-1 with ICAMs 1 and 2 provides essential accessory adhesion signals in many immune interactions, including those between T and B lymphocytes and cytotoxic T cells and their targets. In addition, both ICAMs are expressed at low levels on resting vascular endothelium; ICAM-1 is strongly upregulated by cytokine stimulation and plays a key role in the arrest of leukocytes in blood vessels at sites of inflammation and injury. Recent work has indicated that resting leukocytes express a third ligand, ICAM-3, for LFA-1 (refs 11, 12). ICAM-3 is potentially the most important ligand for LFA-1 in the initiation of the immune response because the expression of ICAM-1 on resting leukocytes is low. We report the expression cloning of a complementary DNA, pICAM-3, encoding a protein constitutively expressed on all leukocytes, which binds LFA-1. ICAM-3 is closely related to ICAM-1, consists of five immunoglobulin domains, and binds LFA-1 through its two N-terminal domains.