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

Murine L cells expressing the products of transfected HLA-DR1 genes functioned as APC for two influenza-specific, human Th cell clones with comparable efficiency to a DR1-expressing human lymphoblastoid cell line. In order to investigate the restriction specificity of the two Th clones, a transfectant expressing the species-mismatched MHC class II dimer DR1:I-E was tested as an APC. Both T cells showed no loss of Ag sensitivity due to substitution of the murine chain. One of the Th clones, TLC 72, showed even greater degeneracy by responding to Ag in the context of I-Ek. Taking into account the lower level of MHC class II expression on the I-Ek transfectant, there is remarkably little loss of efficiency of Ag-induced T cell activation due to the substitution of I-E for DR as restriction element. The Ag-specific responses of both clones were inhibited by anti-CD4 antibody when DR-transfected L cells or human lymphoblastoid cells were used as APC. This inhibition was also seen when Ag was presented to TLC72 by the I-Ek-expressing transfectant. Whether this inhibition is the result of negative signaling or of blocking an interaction between human CD4 and I-Ek is discussed. Similarly the inhibitory effects of mAb against the T cell accessory molecule LFA/1 were the same for both clones when either the transfectants or the lymphoblastoid cell line were used as APC, suggesting that L cells may express a molecule that is capable of acting as a ligand for human LFA/1. The results presented here further illustrate the value of transfectants in analyzing T cell recognition and accessory cell requirements. The patterns of degeneracy of MHC restriction exhibited by these clones provides a platform for a more detailed analysis of key residues involved in MHC class II-restricted T cell Ag recognition.
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PMID:Structural and functional studies of HLA-DR restricted antigen recognition by human helper T lymphocyte clones by using transfected murine cell lines. 245 38

The effect of human T cell leukemia/lymphoma virus type I (HTLV-I) infection on the function and the phenotype of a human proliferating/cytotoxic T cell clone, specific for tetanus toxin, was investigated. During the period after infection, two distinct phases were observed, based on growth properties, phenotype, and functional activity of the infected cells. Phase I HTLV-I infected cells (0 to about 150 days after infection) proliferated in an IL-2-dependent way, but without the requirement for repetitive antigenic stimulation. No differences in expression of the CD2, CD3, CD4, Tp103, and CD28 Ag between these cells and the parental cells could be demonstrated, with the exception of the expression of IL-R p55 and HLA-DR Ag, which were constitutively expressed on the phase I cells. The phase I HTLV-I-infected cells, as well as the parental 827 cells reacted with a mAb specific for an epitope on the variable part of the TCR beta-chain, indicating that the TCR was not altered after HTLV-I infection. Like the parental clone, the phase I cells proliferated in response to tetanus toxin, but the tetanus toxin-specific response of the phase I cells did not require the presence of APC. Results of experiments, in which the levels of intracellular Ca2+ were measured, indicated that HTLV-I cells can acquire the capability to process Ag and present that to themselves. Phase I HTLV-I-infected T cells had lost their cytotoxic activity which was likely to be due to an effect on the lytic machinery rather than on Ag recognition by the TCR, inasmuch as it was found that phase I HTLV-I-infected T cells did no longer contain N-alpha-benzyloxy-L-lysine thiobenzylester-serine esterase activity. Furthermore, it was found that phase I HTLV-I-infected T cells had a diminished capacity to form conjugates with target cells. From a period of about 200 days after HTLV-I infection, phase II cells emerged that proliferated strongly in the absence of IL-2 and that had lost all functional activity. These cells did not express the CD3/T cell receptor complex on their surface. Phase I as well as phase II HTLV-I-infected cells were targets for CTL raised in the autologous donor.
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PMID:Human T cell leukemia/lymphoma virus type I infection of a CD4+ proliferative/cytotoxic T cell clone progresses in at least two distinct phases based on changes in function and phenotype of the infected cells. 246 94

PBMC from healthy adult individuals seropositive for measles virus (MV) were tested for their capacity to proliferate to UV-inactivated MV (UV-MV) or to autologous MV-infected EBV-transformed B cell lines (EBV-BC). MV-specific T cell responses were observed in 11 of 15 donors tested (stimulation index greater than 2), when optimal doses of UV-MV were used in proliferative assays. T cell clones were generated from PBMC of three donors responding to MV, by using either UV-MV or MV-infected autologous EBV-BC as APC. Stimulation with UV-MV generated exclusively CD3+ CD4+ CD8- MV-specific T cells, whereas after stimulation of PBMC with MV-infected EBV-BC, both CD3+ CD4+ CD8- and CD3+ CD4- CD8+ MV-specific T cell clones were obtained. Of 19 CD4+ T cell clones tested so far, 7 clones reacted specifically with purified fusion protein and 1 with purified hemagglutinin protein. Seven clones proliferated in response to the internal proteins of MV. Three clones reacted to whole virus but not to one of the purified proteins, whereas one clone seemed to recognize more than one polypeptide. Some of the T cell clones, generated from in vitro stimulation of PBMC with UV-MV, failed to recognize MV Ag when MV-infected EBV-BC were used as APC instead of UV-MV and PBMC. CD3+ CD4+ CD8- T cell clones recognized MV in association with HLA class II Ag (HLA-DQ or -DR), and most of them displayed CTL activity to autologous MV-infected EBV-BC. All CD4+ HLA class II-restricted CTL clones thus far tested were capable of assisting B lymphocytes for the production of MV-specific antibody. The CD4- CD8+ T cell clone MARO 1 recognized MV in association with HLA class I molecules and displayed cytotoxic activity toward MV-infected EBV-BC.
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PMID:Measles virus-specific human T cell clones. Characterization of specificity and function of CD4+ helper/cytotoxic and CD8+ cytotoxic T cell clones. 246 43

To elucidate the acquisition of self tolerance in the thymus, full-allogeneic thymic chimeras were constructed. Athymic C3H and BALB/c nude mice were reconstituted with the thymic lobes of BALB/c and B10.BR fetuses, respectively, that were organ cultured for 5 days in the presence of 2'-deoxyguanosine. T cells in these chimeras were tolerized to the host MHC in both MLR and CTL assays. In contrast, T cells in the chimeras exhibited split tolerance for the thymic MHC haplotype. CTL specific for class I MHC of the thymic haplotype were generated not only from the peripheral T cells of the chimeras but also from thymocytes re-populated in the engrafted thymic lobes. However, T cells in these chimeras responded poorly to the class II MHC of the thymic haplotype in a standard MLR assay. In a syngeneic MLR culture upon stimulation with enriched APC of the thymic haplotype, only 22 to 48% of the responses were mediated by CD4+ cells, and proliferations of CD4- cells were prominent. There were no haplotype-specific suppressor cells detected which would cause the unresponsiveness to the thymic class II MHC. These results indicated that the thymic lobes treated with 2'-deoxyguanosine were defective in the ability to induce the transplantation tolerance for the class I MHC expressed on the thymus, although the same thymic lobes were able to induce the transplantation tolerance for the thymic class II MHC.
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PMID:Split tolerance in nude mice transplanted with 2'-deoxyguanosine-treated allogeneic thymus lobes. 252 79

Interactions between CTL and target cells occur in the absence of specific antigen recognition and precede subsequent interaction of the TCR with its specific antigen. This antigen-independent adhesion progresses through two different pathways, one involving the interaction of CD2 with LFA-3 on the target cell, the second the interaction of LFA-1 with ICAM-1. Such antigen-independent adhesions are critical for the activation of T cells via the TCR. Also, CD4 and CD8 can serve as adhesion molecules by binding to monomorphic determinants expressed on class II and class I MHC antigens, respectively, on the target cells, but compared to LFA-1 and CD2 antigens their contribution to conjugate formation is minor. CD4 and CD8 are required for effective T-cell activation in situations where the intrinsic affinity of the TCR or antigen expression is low, suggesting that CD4 and CD8 enhance the avidity of T cells for target cells by binding to class II and class I antigen, respectively. However, CD4 and CD8 are also involved in post-binding events that lead to CTL activation and subsequent lysis of the target cells. On the other hand, blocking of anti-TCR/CD3 mAb-induced CTL reactivity by anti-CD4/CD8 mAbs does not necessarily involve an interference with the binding of CD4 and CD8 to their respective ligands and it has been proposed that the TCR and CD4 or CD8 form functional complexes that are required for optimal T-cell activation. It is still unclear whether blocking by anti-CD4/CD8 mAbs is based on the prevention of complex formation of the TCR with CD4 or CD8, since formation of such complexes has yet to be demonstrated. The alternative hypothesis, that anti-CD4/anti-CD8 mAbs can directly confer negative regulatory signals to the CTL is not supported by our studies with antibody-directed lysis mediated by a CD4+, CD8+ CTL clone. Anti-CD4/CD8 mAbs can also inhibit T-cell cytotoxicity induced by other T-cell surface activation antigens such as CD2 or Tp103. In these situations, the triggering may involve signals transferred via CD3 requiring functional CD3/CD8 or CD3/CD4 complexes. Although most studies investigating the sequence of events leading to T-cell activation are carried out with CTL, preliminary data indicate that the same mechanisms described here for CTL activation are probably also valid for the interactions of T-helper cells with APC or B cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Interplay between the TCR/CD3 complex and CD4 or CD8 in the activation of cytotoxic T lymphocytes. 252 3

We have used double-immunofluorescence labeling to determine the surface distributions of LFA-1 and CD4, and the intracellular distributions of the cytoskeletal protein talin and of the microtubule organizing center (MTOC) of cloned Th cells in 1:1 cell couples with antigen (Ag)-specific APC of the B cell type (B-APC). The Th cell was directed to a peptide fragment of the Ag OVA in the context of IAd. The B-APC was the transfected A20 B hybridoma cell A20-HL, bearing on its surface a surface Ig specific for the hapten TNP, and pulsed with different concentrations of DNP-OVA. At sufficiently high doses of DNP-OVA (greater than 100 ng/ml), in essentially all couples, LFA-1, CD4, and talin were each concentrated at the Th cell membrane where it was in contact with the B-APC, and the MTOC inside the Th cell was reoriented to face the contact region. At lower doses of DNP-OVA (between 50 and 10 ng/ml), in all couples, LFA-1 and talin were concentrated at the Th/B-APC contact region, but the extent of CD4 clustering, MTOC reorientation, and Th cell proliferation all decreased with decreasing Ag dose. With no Ag, none of these effects was observed. These and other data indicate that two distinct signals are received by the Th cell that is specifically bound to its B-APC. The first signal, at low Ag doses, stimulates a linkage of LFA-1 and talin in the Th cell, and a specific LFA-1-mediated intercellular adhesion; the second signal, at higher Ag doses, is required to induce Th cell proliferation, with which the Th-MTOC reorientation and CD4 clustering are correlated.
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PMID:The specific interaction of helper T cells and antigen-presenting B cells. IV. Membrane and cytoskeletal reorganizations in the bound T cell as a function of antigen dose. 253 Mar

CD4 (T4) is a 60 kD glycoprotein expressed on a subset of T lymphocytes. CD4 augments T cell responses to suboptimal Ag stimulation. In addition, the CD4 molecule is the receptor for HIV-1. CD4 is phosphorylated on serine residues within the cytoplasmic domain and its cell surface expression is decreased in response to PMA, APC bearing the appropriate Ag or HIV infection. The kinetics of CD4 phosphorylation and modulation are similar, suggesting that the two events may be related. L3T4, the murine CD4 equivalent, is not modulated from the surface of mature, peripheral T cells in response to PMA. The difference in the ability to modulate L3T4 and CD4 in response to PMA may be due to differences between the two molecules or to differences between the cells in which they are expressed. To further define the requirements for CD4 modulation, we used retroviral vectors to transfer the cDNA for CD4 and various mutants of CD4 into two murine T cell hybridomas that express L3T4. One of these hybridomas, By155.16, does not modulate L3T4 in response to PMA and the other, 5D5.63, does modulate L3T4 in response to PMA. When expressed by these hybridomas CD4 is not modulated from the surface of By155.16 and is modulated from the surface of 5D5.63 in response to PMA. In both of these hybridomas, CD4 is phosphorylated on serine residues in response to PMA. A mutant form of CD4, CD4 delta, was constructed in which the majority of the cytoplasmic domain was deleted. When expressed in 5D5.63, CD4 delta was not modulated in response to PMA. Replacing the cytoplasmic domain of CD4 with that of the human IL-2 receptor did not reconstitute the ability of CD4 to be modulated. These results suggest that the inability to modulate L3T4 from the surface of murine peripheral T cells is due to features of the cell and not the molecule. Furthermore, the cytoplasmic domain of CD4 is required for its modulation from the cell surface in response to PMA.
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PMID:Requirements for modulation of the CD4 molecule in response to phorbol myristate acetate. Role of the cytoplasmic domain. 278 43

The present study investigated the possibility that protein Ag fragments in the form of peptides could serve as the priming Ag in the generation of a MHC class I-restricted immune response. Trypsin-digested chicken ovalbumin (OVA-TD) fragments were used as the model Ag. The results demonstrate the peptides within OVA-TD, when injected into C57BL/6 mice, could prime T cells which lysed H-2b Ia-EL4 target cells in an OVA-TD-specific manner. In contrast to priming with OVA-TD, immunization of mice with intact OVA did not lead to generation of CTL against OVA-TD or OVA. Furthermore, target cells sensitized with intact OVA failed to be recognized by OVA-peptide-specific CTL indicating that the target cells serving as APC were unable to generate the relevant peptide determinants recognized by the T cells. These results support the idea that the processing pathway within APC for class I-restricted T cells may differ from that used for class II-restricted T cells. Using OVA-TD-specific CTL clones (phenotypically Thy 1+, CD8+, CD4-, Pgp-1+) isolated from primed animals to screen OVA-TD fractions separated by HPLC, two T cell peptide determinants were identified corresponding to OVA sequences 111-122 and 370-381. Both determinants were recognized by CTL clones in the context of the H-2Db molecule.
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PMID:Induction of class I MHC-restricted, peptide-specific cytolytic T lymphocytes by peptide priming in vivo. 278 56

Immunologically important among the known biologic activities of IL-1 is its ability to function as a co-factor for responses mediated by lymphokine secreting CD4+ Th cells. In contrast to its known effects in CD4+ T cell responses, IL-1 is not known to play a role in CD8+ T cell responses. In the present study, we have assessed the ability of murine recombinant IL-1 to function as a co-factor for stimulating CD8+ T cells to secrete lymphokines such as IL-2. We found that, in conjunction with either Ag or mitogen, IL-1 is able to stimulate lymphokine-secreting CD8+ T cells. Furthermore, we found that, as a consequence of its stimulation of lymphokine-secreting CD8+ T cells, IL-1 is able to reconstitute MHC class I allospecific cytolytic T lymphocyte responses by cell populations depleted of both accessory cells and CD4+ T cells. These results demonstrate that the biologic activity of IL-1 is not restricted to CD4+ cell responses, and suggests that IL-1 can function as a co-factor for the stimulation of lymphokine-secreting Th cells regardless of their CD4/CD8 phenotype. If IL1 acts directly on lymphokine-secreting T cells or on the APC with which they interact is not yet certain.
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PMID:IL-1 as a co-factor for lymphokine-secreting CD8+ murine T cells. 297 May 6

Purified peripheral blood T lymphocytes and the CD8-CD4+ and CD4-CD8+ T cell subsets, exhaustively depleted of APC have been studied for their capacity to respond to mAb directed against the CD3-Ti Ag-specific TCR complex and against the CD2 SRBCR. It is demonstrated that high affinity IL-2R can be readily induced by either anti-CD3 and/or anti-CD2 stimulation. However, IL-2 production can be observed only in the CD4+CD8- T cell subset. These results clearly contrast data obtained with purified CD4-CD8+ T cells, which are able to proliferate when the CD3-Ti complex is activated in the presence of APC. The data presented in the present study demonstrate that a simplified model for T cell activation and clonal expansion of the two major T cell subsets involve only the CD3-Ti complex and the CD2 Ag. Under conditions where the activation signals for the T cells are restricted only to the activation of CD3-Ti and CD2, the CD4+CD8- T cells respond with IL-2 production and expression of high affinity IL-2R, whereas the CD4-CD8+ T cell subset depends on exogenous IL-2 provided by the CD4+CD8- cells. These data do not, however, exclude an involvement of other cell-surface signals for regulation and control of T cell activation and T cell effector functions.
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PMID:Differential in vitro activation of CD8-CD4+ and CD4-CD8+ T lymphocytes by combinations of anti-CD2 and anti-CD3 antibodies. 325 28


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