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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of T cells often requires both activation signals delivered by ligation of the TCR and those resulting from costimulatory interactions between certain T cell surface accessory molecules and their respective counter-receptors on APC. CD11a/CD18 complex on T cells modulate the activation of T cells by interacting with its counter-receptors intracellular adhesion molecule (ICAM-1) (CD54) and/or ICAM-2 on the surface of APC. The costimulatory ability of ICAM-1 has been demonstrated. Using a soluble ICAM-2 Ig fusion protein (receptor globulin, Rg) we demonstrate the costimulatory effect of ICAM-2 during the activation of CD4+ T cells. When coimmobilized with anti-TCR-1 mAb ICAM-2 Rg induced vigorous proliferative response of CD4+ T cells. This costimulatory effect of ICAM-2 was dependent on its coimmobilization with mAb directed at the CD3/TCR complex but not those directed at CD2 or CD28. Both resting as well as Ag-primed CD4+ T cells responded to the costimulatory effects of ICAM-2. The addition of mAb directed at the CD11a or CD18 molecules almost completely inhibited the responses to ICAM-2 Rg. These results are consistent with the role of CD11a/CD18 complex as a receptor for ICAM-2 mediating its costimulatory effects. Stimulation of T cells with coimmobilized anti-TCR-1 and ICAM-2 resulted in the induction of IL-2R (CD25), and anti-Tac (CD25) mAb inhibited this response suggesting the contribution of endogenously synthesized IL-2 during this stimulation. These results demonstrate that like its homologue ICAM-1, ICAM-2 also exerts a strong costimulatory effect during the TCR-initiated activation of T cells. The costimulatory effects generated by the CD11a/CD18:ICAM-2 interaction may be critical during the initiation of T cell activation by ICAM-1low APC.
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PMID:Intercellular adhesion molecule-2, a second counter-receptor for CD11a/CD18 (leukocyte function-associated antigen-1), provides a costimulatory signal for T-cell receptor-initiated activation of human T cells. 134 50

Human myoblasts, cultured from muscle and purified to greater than 95%, were investigated for their capacity to act as facultative APC. The myoblasts reacted with antidesmin mAb and had the capacity to fuse into multinucleated myotubes in appropriate medium. The expression of HLA class I, HLA-DR, HLA-DP, HLA-DQ, intercellular adhesion molecule-1 (ICAM-1/CD54), lymphocyte function-associated (LFA) molecules LFA-1 (CD11a/CD18), LFA-2 (CD2), and LFA-3 (CD58) was investigated by FACS analysis before and after induction for various times with human rIFN-gamma, TNF-alpha, or both. Without cytokine induction, myoblasts expressed only HLA-class I and LFA-3. IFN-gamma alone or in combination with TNF-alpha induced the expression of HLA-DR and ICAM-1 reaching a plateau after 48 h, followed by HLA-DP and even later HLA-DQ. TNF-alpha alone induced only ICAM-1. The functional capacity of myoblasts to present Ag to CD4+ T cells was investigated using autologous T cell lines specific for tuberculin, tetanus toxoid, and human myelin basic protein. Noninduced myoblasts or myoblasts treated with TNF-alpha alone could not present any of these Ag to the T cells. However, myoblasts treated with IFN-gamma induced Ag-specific proliferation. In the presence of relevant Ag, myoblasts were killed by the T cells as observed by microscopy and measured by 51Cr release. Ag-specific T cell proliferation and myoblast killing was inhibited in the presence of anti-DR mAb. These results suggest that human myoblasts may act as facultative APC during local immune reactions in muscle.
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PMID:Human myoblasts as antigen-presenting cells. 135 32

Although ligation of the CD3/TCR complex initiates an activation signal in T cells, additional costimulatory signals generated during cell-to-cell interactions with APC transduced via ligation of CD11a/CD18 and CD28 by their specific counter-receptor intercellular adhesion molecule (ICAM)-1 and B7, respectively, are required for optimal T cell proliferation and cytokine synthesis. Using soluble IgC gamma 1 fusion proteins of these costimulatory counter-receptors, we have recently shown that unactivated resting CD4+ T cells and Ag-primed CD4+ T cells differ in their response to the costimulation by ICAM-1 and B7. Preferential proliferative responses of resting T and Ag-primed T cells to ICAM-1 and B7, respectively, prompted us to speculate that ICAM-1-induced signals may regulate coupling of the CD28 signaling pathway. Furthermore, both B7 and ICAM-1 are co-expressed on APC and thus, may co-regulate activation-driven maturation of T cells. In this study, we have examined regulatory effects of IgC gamma 1 fusion proteins of B7, ICAM-1, and ICAM-2 (a homologue of ICAM-1) on each other's costimulation. We first demonstrate that TCR-directed costimulation of resting CD4+ T cells with ICAM-1 (ICAM-1 priming) but not ICAM-2 induces increased responsiveness to B7. Priming of CD4+ T cells with ICAM-1 induced higher expression of both CD18 and CD28 than that with either B7 or ICAM-2. Cross-linking of CD28 induced faster and significantly higher cytoplasmic free calcium mobilization response in ICAM-1-primed CD4+ T cells than in resting, B7-primed, or ICAM-2-primed CD4+ T cells. B7 synergized with ICAM-1 but not ICAM-2 to augment proliferative responses of not only resting CD4+ T cells but also those that had been primed with either ICAM. Unlike resting or ICAM-2-primed CD4+ T cells, ICAM-1-primed CD4+ T cells efficiently proliferated in response to the synergistic costimulation of B7 and ICAM-2. In contrast, both ICAM-1 and ICAM-2 inhibit B7-driven proliferation of Ag-primed CD4+ T cells. Thus, B7 and ICAM-1 exert contrasting regulatory effects on the proliferation of CD4+ T cells depending on their state of activation-induced maturation.
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PMID:Differential regulatory effects of intercellular adhesion molecule-1 on costimulation by the CD28 counter-receptor B7. 138 17

Recent attention has focused on the role keratinocytes (KC) may play in the induction of T cell-mediated inflammatory responses in skin, particularly because KC, when activated by immunologic stimuli, express MHC class II Ag and secrete immunomodulatory cytokines. We tested the capacity of normal human KC that were stimulated with PMA to induce PBMC proliferation. PMA-treated, but not untreated, KC induced proliferation of allogeneic as well as autologous PBMC; in addition, when purified CD4+ or CD8+ T cells were used as responders, each subset proliferated. PBMC proliferation was not due to direct action of PMA on PBMC, nor to contamination of KC cultures with Langerhans cells (LC) or dermal APC. Pretreatment with different protein kinase C inhibitors abrogated the capacity of PMA-stimulated KC to induce proliferation. Paraformaldehyde-fixed PMA-KC stimulated PBMC proliferation, whereas supernatants from PMA-treated KC failed to do so, indicating that a membrane-associated activity on PMA-KC contributes to the induction of PBMC proliferation. PMA induced intercellular adhesion molecule-1 (ICAM-1) expression on KC; furthermore, mAb against ICAM-1 or against its ligand lymphocyte function-associated Ag (LFA-1) (CD11a/CD18) significantly, but incompletely, reduced the stimulatory capacity of PMA-treated KC, indicating that ICAM-1/LFA-1 interaction contributed to PBMC proliferation. IFN-gamma or TNF-alpha also induced ICAM-1 on KC, but these KC failed to stimulate proliferation, suggesting that PMA induces additional signals from KC, which act in concert with ICAM-1 to promote proliferation. Finally, mAb against HLA-ABC or HLA-DR did not inhibit proliferation. We conclude that PMA can activate KC to stimulate T cell proliferation in a MHC-independent fashion. This activation is mediated by protein kinase C and in part by the induction of ICAM-1 expression on KC.
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PMID:Phorbol myristate acetate-activated keratinocytes stimulate proliferation of resting peripheral blood mononuclear lymphocytes via a MHC-independent, but protein kinase C- and intercellular adhesion molecule-1-dependent, mechanism. 167 Sep 43

The role of leukocyte function-associated Ag-1 (LFA-1) in intercellular adhesion is well documented. Previously, we demonstrated that the LFA-1 molecule (CD11a/CD18) can also regulate the induction of proliferation of peripheral blood T cells. In these studies, we observed opposite effects of antibodies against CD11a (LFA-1-alpha-chain) or CD18 (LFA-1-beta-chain). Here, we determined the effects of anti-CD11a and anti-CD18 mAb on proliferation of cloned influenza virus-specific T cells. Anti-CD18 mAb had similar inhibiting effects on the proliferative response of T cell clones induced by immobilized anti-CD3 mAb as it had on the response of peripheral blood T cells. In contrast to its costimulatory effect on resting peripheral blood T cells, anti-CD11a mAb did not increase the proliferation of cloned T cells. Similar differences in effects of anti-CD11a and anti-CD18 mAb were observed when proliferation of the T cell clones was induced by immobilized anti-TCR mAb. When proliferation was induced by influenza virus presented by monocytes as APC, both anti-CD11a and anti-CD18 mAb inhibited T cell proliferation. However, when EBV-transformed B cells were used as APC, neither anti-CD11a nor anti-CD18 mAb inhibited proliferation. These results demonstrate that the effects of antibodies against CD11a (LFA-1-alpha) or CD18 (LFA-1-beta) on T cell proliferation depend on 1) the stage of activation of the T cells, 2) the activation stimulus and its requirement for intercellular adhesion involving LFA-1, and 3) the type of cell used to present Ag.
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PMID:Analysis of the role of leukocyte function-associated antigen-1 in activation of human influenza virus-specific T cell clones. 197 Mar 49

Hybridoma fusions with hamster hosts were undertaken to generate mAbs to mouse spleen dendritic cells. Two mAb were obtained and used to uncover the distinct integrins of these APC. One, 2E6, bound a determinant common to all members of the CD11/CD18 family, most likely the shared 90 kD CD18 beta chain. 2E6 immunoprecipitated the characteristic beta 2 integrin heterodimers from lymphocytes (p180, 90; CD11a) and macrophages (p170,90; CD11b), but from dendritic cells, a p150,90 (presumably CD11c) integrin was the predominant species. 2E6 inhibited the binding function of the CD11a and CD11b integrins on B cells and macrophages in appropriate assays, but 2E6 exerted little or no inhibition on the clustering of dendritic cells to T cells early in primary MLR, suggesting a CD11/CD18-independent mechanism for this binding. The second mAb, N418, precipitated a 150, 90 kD heterodimer that shared the 2E6 CD18 epitope. This N418 epitope may be the murine homologue of the previously characterized human CD11c molecule, but the epitope was only detected on dendritic cells. N418 did not react with peritoneal macrophages, anti-Ig-induced spleen B blasts, or bulk lymph node cells. When used to stain sections of spleen, N418 stained dendritic cells in the T-dependent areas, much like anti-class II mAbs that were also generated in these fusions. In addition, N418 revealed nests of dendritic cells that punctuated the rim of marginal zone macrophages between red and white pulp. This localization positioned most dendritic cells at regions where arterial vessels and T cells enter the white pulp. We conclude that the p150, 90 heterodimer is the major beta 2 integrin of spleen dendritic cells, and we speculate that it may function to localize these APC at sites that permit access to the recirculating pool of resting T cells.
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PMID:The distinct leukocyte integrins of mouse spleen dendritic cells as identified with new hamster monoclonal antibodies. 218 32

Staphylococcal enterotoxins, also known as superantigens (SAg), bind class II MHC molecules on APC and upon direct cell-to-cell contact stimulate proliferation of T cells expressing appropriate V beta gene products. The T cell surface molecule CD28 binds its costimulatory counter-receptor, B7 expressed on APC, and augments IL-2 production and T cell growth. Although the role of B7 costimulation during Ag-specific responses of T cells is established, its involvement during the activation of T cells with SAg has not been examined. Using a soluble Ig C gamma 1 chimera of CTLA-4, a second receptor for B7 and a homologue of CD28, this study examines the role of B7 expressed on APC during the induction of proliferation of CD4+ T cells upon stimulation with SAg (SAg/staphylococcal enterotoxins). CTLA-4lg, which has a higher avidity for B7 than CD28, had no effect on the synthesis of IL-2 as well as proliferative responses of CD4+ T cells induced by SAg presented on allogeneic EBV-transformed B cells, and IFN-gamma-activated endothelial cells. In contrast, T cell proliferation induced by alloAg presentation by the same APC was significantly inhibited by CTLA-4lg. mAb directed at the CD11a/CD18 molecule inhibited both SAg-induced and alloAg-induced proliferation of T cells. AlloAg-primed CD4+ T cells, which expressed both class II MHC and intercellular adhesion molecule-1 but not B7, presented SAg to and induced proliferation of both resting and SAg-primed T cells. These responses were inhibited by mAb directed at CD11a/CD18 but not by CTLA-4 Rg. These results suggest that SAg-induced responses differ from those induced by alloAg in that they are not obligatorily dependent on the costimulation by B7. In contrast, adhesive interaction between CD11a/CD18 on T cells and its counter-receptor on SAg-presenting cells is necessary and probably sufficient to support SAg-induced proliferation of T cells.
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PMID:Proliferation of human T lymphocytes induced with superantigens is not dependent on costimulation by the CD28 counter-receptor B7. 767 19

Optimal stimulation of CD4+ T cells in an immune response requires not only signals transduced via the CD3/TCR complex but also costimulatory signals delivered as a consequence of interactions between T-cell surface-associated costimulatory R and their counter-R on APC. CD28 plays a crucial role as a dominant costimulatory R during the induction of CD4+ T-cell proliferation by interacting with counter-R B7 on APC to sustain IL-2 production. The absence of CD28-mediated costimulation has been postulated to result in T-cell anergy or unresponsiveness. The costimulatory effects of CD28 can be generated with its natural counter-R B7 or mAb directed at CD28. Using soluble C gamma 1 chimeras of B7, ICAM-1, and VCAM-1, we have recently shown that B7 costimulates TCR-dependent proliferation of Ag-primed CD4+ T cells more efficiently than that of resting nonactivated CD4+ T cells. In contrast, proliferation of resting CD4+ T cells can be efficiently costimulated by either ICAM-1 or VCAM-1 via interactions with their R CD11a/CD18 (LFA-1/beta 2 integrin) and CD29/CD49d (VLA-4/beta 1 integrin), respectively. TCR-directed preactivation of resting CD4+ T cells with ICAM-1 can induce increased responsiveness to B7 costimulation. In this study, we show that prior TCR-directed activation of resting CD4+ T cells with VCAM-1 induced increased responsiveness to B7 costimulation. VCAM-1 also synergized with B7 to bring about supraoptimal proliferation of CD4+ T cells. In addition, costimulation of resting T cells with VCAM-1 significantly increased not only surface expression of CD28 but also CD28-mediated mobilization of intracellular free [Ca2+]i. Similar activation of T cells with fibronectin also resulted in increased B7 responsiveness, suggesting the involvement of VLA-4 molecule. VCAM-1 costimulation induced hyperresponsiveness to B7 costimulation in both CD18+ (normal) and CD18- (leukocyte adhesion deficient) T cells. Thus, VCAM-1 may play an important costimulatory role during the activation of resting T cells and, by augmenting responsiveness to B7, facilitate optimal development of immunological memory in addition to various regulatory and effector functions.
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PMID:Costimulation via vascular cell adhesion molecule-1 induces in T cells increased responsiveness to the CD28 counter-receptor B7. 768 25

Integrin ligands intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) can efficiently costimulate proliferation of resting T cells but not that of Ag-specific T cells. In contrast, CD28 ligand B7 and CD2 ligand leukocyte function-associated Ag (LFA-3) can support IL-2 synthesis and proliferation of Ag-specific T cells more efficiently than that of resting T cells. The molecular basis for this differential costimulation of T cells is poorly understood. In this study, using mAb and soluble IgC gamma 1 chimeras of these adhesion molecules, we demonstrate that coligation of the TCR and CD11a/CD18 (LFA-1/beta 2 integrin) or CD29/CD49d (very late activation Ag-4/beta 1 integrin) using anti-TCR mAb and either ICAM-1 or VCAM-1 induces activation-dependent death of DRw6-specific CD4+ T cells. Similar coligation of the TCR with CD2 or CD28 using either mAb or ligands LFA-3 or B7 not only lacked the ability to induce death but also failed to reverse or inhibit integrin-facilitated death of DRw6-specific T cells. Each of these ligands augmented anti-TCR mAb-induced transcription of IL-2 and IL-4 genes. Exogenous addition of IL-2 and IL-4 did not reverse the integrin-supported T cell death. The death-promoting costimulatory effects of ICAM-1 and VCAM-1 were observed with Ag-specific chronically stimulated T cells but not with either resting T cells or those activated in short-term cultures. Treatment of T cells with cyclosporin A or a protein tyrosine kinase inhibitor herbimycin A inhibited ICAM-1 or VCAM-1-promoted activation-induced T cell death. The Ag-specific T cells that survived death-promoting effects of ICAM-1 or VCAM-1 proliferated efficiently upon restimulation with these ligands. Exposure of DRw6-specific T cells to DRw6+ B7+ ICAM-1+ LFA-3+ VCAM-1+ APC but not DR3+ B7+ ICAM-1+ LFA-3+ VCAM-1+ APC induced death of these T cells. This effect was blocked by pretreatment of T cells with mAb directed at CD18 or CD29 but not with those against CD2 or CD28. Taken together, these results suggest that TCR-directed engagement of integrins by their ligands ICAM-1 or VCAM-1 induces activation-dependent death of some perhaps more differentiated Ag-specific T cells and this may be an important homeostatic mechanism by which functional expression of Ag-specific T cells is regulated during an ongoing immune response.
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PMID:Costimulation with integrin ligands intercellular adhesion molecule-1 or vascular cell adhesion molecule-1 augments activation-induced death of antigen-specific CD4+ T lymphocytes. 768 6

Adhesion molecules of leucocytes Leu-CAMs, also called beta-2 integrins, are heterodimeric glycoproteins which play a crucial role in interactions of leucocytes between themselves or with fundamental intercellular substances. They comprise 3 elements: LFA-1 (CD11a/CD18) expressed at the surface of leucocytes, and in particular lymphocytes, M01 or MAC-1 (CD11b/CD18), and p 150.95 (CD11c/CD18) expressed only on granulocytes, monocytes and macrophages. Their structure, function and regulation are studied. These 3 elements differ in the ligand(s) to which they adhere. LFA-1 intervenes in the adhesion of lymphocytes T and B and of cells presenting with the APC antigen; it therefore plays an important role in lymphoblast proliferation, T-cell cytotoxicity and immunoglobulin synthesis. M01 and p 150.95 intervene in the adhesion of particles and germs opsonized by serum complement, thereby playing a fundamental role in the body's defence against bacterial and fungal infections. They also intervene in the adhesion of leucocytes onto the vascular endothelium and in their migration through this vascular wall towards the inflammatory focus. The pathologies related to a congenital deficiency of these adhesion molecules or to the alterations they acquired are dealt with. The use of monoclonal antibodies directed against leucocyte adhesion in animal experiments opens new therapeutic vistas.
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PMID:[Adhesion molecules of Leu-CAMs leukocytes]. 824 68


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