Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown previously that specific Ag presentation is prevented by the inhibition of protein synthesis but nonspecific presentation is not. In the present paper, Ag presentation by Ag-specific B cells was examined for sensitivity to brefeldin A (BFA), which blocks protein export from the endoplasmic reticulum. A20-HL B lymphoma expressing surface receptors specific for TNP was used as a B cell, and TNP-OVA was used as a specific Ag. The presence of BFA during pulsing of A20-HL cells with TNP-OVA inhibited the ability of the pulsed cells to stimulate 42-6A T cell clone, specific for OVA323-339 and Iad. The inhibition was not due to nonspecific toxicity of BFA, because the presence of BFA during pulsing of A20-HL cells with OVA323-339 did not affect their APC function. Ag binding to the receptor on A20-HL cells and internalization by the cells were observed in the presence of BFA. Thus, BFA might inhibit intracellular processing of specific Ag or intracellular complex formation of antigenic peptide from specific Ag with MHC class II molecules. Nonspecific Ag presentation by A20-HL cells, however, was resistant to BFA. A20-HL cells pulsed with OVA in the presence of BFA, even after fixation, could stimulate 42-6A cells to produce IL-2, although the IL-2 production was lower than that induced by A20-HL cells pulsed in the absence of BFA. These results suggest that the processing pathways for specific Ag and nonspecific Ag are different from each other, at least partly, in A20-HL cells.
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PMID:Inhibition by brefeldin A of the specific B cell antigen presentation to MHC class II-restricted T cells. 194 Mar 37

We report a methodology for selecting APC with mutations that have impaired their ability to present Ag to T cells. A20 B lymphoblastoid cells were mutagenized and then repeatedly cocultured with murine T-T hybridomas in the presence of specific Ag. During these cocultures, the T-T hybridomas kill the competent APC, allowing the outgrowth of inactive variants. Two variants, A20.M1 and A20.M2, were isolated and studied in detail. These variants are impaired in their ability to present multiple Ag to T cells. This defect is also observed for the presentation of processing independent peptides by fixed APC indicating that a lesion exists in a post-Ag processing step. The level of expression of MHC molecules is unaffected and the functional defect in the APC is not localized to a particular MHC molecule. In contrast, these mutants were found to have a selective decrease in the expression of the murine homolog of ICAM-1, and the residual ability of these cells to present Ag was not blocked by anti-ICAM-1 mAb. Conversely, Ag presentation by the wild-type A20 is inhibited by anti-ICAM-1 mAb. Similarly, anti-LFA-1 mAb inhibited the response of T cells to Ag presented by the wild-type A20 to a much greater degree than by the mutant cells, indicating that LFA-1 is involved in interaction of T cells with the former, but not latter, APC. In the apparent absence of a contribution of LFA-1 to the T cell-APC interaction, either as a result of mAb blocking or the disruption of the APC membrane, the mutant and wild-type APC have a similar level of Ag-presenting activity. Reconstitution of ICAM-1 expression in these mutants by transfection with murine ICAM-1 cDNA fully restores their ability to present Ag. Together these results demonstrate that a murine ICAM-1 homolog is expressed on A20 B cells, where it functions as a major cell interaction molecule. The degree of functional impairment in these mutant APC gives insight into the contribution of cell interaction molecules to efficient Ag presentation and T cell-B cell interaction. Finally, these results also demonstrate the feasibility of selecting APC with mutations affecting Ag presentation.
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PMID:Role of ICAM-1 in antigen presentation demonstrated by ICAM-1 defective mutants. 197 Dec 92

In the process of generating culture supernatant from T cell clones, with anti-CD3 antibodies and the B lymphoma A20 as APC, a striking difference in the stimulation of TH1 and TH2 clones was observed, i.e., TH2 clones produced higher levels of lymphokines than TH1 clones. This prompted us to test the hypothesis that differential killing of APC (thus the removal of stimuli) by T cells led to differential T cell activation. By studying a panel of five TH1 and seven TH2 clones, it was demonstrated that TH1 clones mediated significantly higher levels of cytotoxicity toward A20 cells in the presence of soluble anti-CD3 antibody (as opposed to immobilized anti-CD3). Although T cell clones could, when activated with immobilized anti-CD3, produce lymphokines cytotoxic to A20 cells, experiments in which lymphokine production was blocked indicated that T cell clones, in the presence of soluble anti-CD3, mediated killing of A20 through direct cytotoxicity. A higher level of cytotoxicity, by TH1 compared with TH2 clones, was not restricted to anti-CD3 or a particular target cell type, because it also occurred with Con A- or Ag-dependent killing (a monocyte-macrophage cell line), and LPS blasts. Furthermore, the higher cytotoxic activity of TH1 clones compared with TH2 clones was independent of the stage of T cell activation and was unlikely a result of the length of in vitro culture. High levels of killing of APC led to low levels of T cell activation, the significance of which may be as a negative feedback mechanism in the immune response. Other biologic relevancies of higher cytotoxic activity in TH1 vs TH2 cells were also discussed.
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PMID:Heterogeneity in direct cytotoxic function of L3T4 T cells. TH1 clones express higher cytotoxic activity to antigen-presenting cells than TH2 clones. 197 81

Specific and nonspecific Ag-presentation by B cells was examined for the sensitivity to the treatment with emetin, an irreversible protein synthesis inhibitor. For this aim, A20-HL B lymphoma cells expressing surface IgM receptors specific for TNP were used as APC. OVA and TNP-OVA were used as nonspecific and specific Ag, respectively. The treatment with emetin greatly impaired the ability of A20-HL cells to present specific Ag, but not nonspecific Ag, to 42-6A cloned T cells specific for OVA. The ability of the emetin-treated A20-HL cells to present nonspecific Ag indicates that the treated cells are able to process nonspecific Ag and to present processed Ag. Ag binding and the internalization by A20-HL cells through surface receptors were not affected by the emetin treatment. A20-HL cells took up specific Ag for stimulation of 42-6A cells in the presence of cycloheximide, a reversible protein synthesis inhibitor. These results suggest that the action of emetin is localized to the intracellular processing of specific Ag, not of nonspecific Ag. Thus, the processing pathway for specific Ag seems to be different from that for nonspecific Ag.
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PMID:Differential sensitivity of specific and nonspecific antigen-presentation by B cells to a protein synthesis inhibitor. 239 15

The kinetics of presentation of class II-restricted T cell determinants of influenza virus hemagglutinin (HA) was investigated over a 48-h time course after pulsing of A20 B lymphoma APC with non-replicative virus or isolated HA. At intervals after Ag pulse, APC were fixed with paraformaldehyde to arrest Ag processing and to preserve the expression levels of the presented determinants. Expression of T cell sites at each time point was probed by a panel of BALC/c T hybridomas specific for the HA of influenza A/Puerto Rico/8/34 virus, recognizing either site 1 (residues 111 to 119), site 2 (126 to 138), or site 3 (302 to 313). Characteristic patterns of presentation were observed for each site: sites 2 and 3 achieved maximal expression by 8 h post pulse, but declined thereafter, whereas site 1 presentation continued to increase over time. The quantitative expression of each T cell site was affected by the proteolysis inhibitor leupeptin, resulting in partial inhibition of site 1, complete blocking of site 2, but enhancement of site 3. However, the expression kinetics of sites 1 and 3, which could be observed in the presence of the inhibitor, remained qualitatively unchanged. These observations indicate that some T cell determinants (e.g., HA site 1) may exhibit a greater longevity of expression on APC than other antigenic sites of the same protein. Differences in the persistence of surface expression of distinct T cell sites may be a factor in their relative immunodominance.
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PMID:Individual class II-restricted antigenic determinants of the same protein exhibit distinct kinetics of appearance and persistence on antigen-presenting cells. 245 19

Inoculation of P815 tumor cells (DBA/2 origin) into the anterior chamber of eyes of BALB/c mice normally produces anterior chamber-associated immune deviation (ACAID) whereby delayed hypersensitivity (DH) responses to the minor H alloantigens of the tumor cells are suppressed. Based on our previous work showing an association of Langerhans cell infiltration into central cornea with the abrogation of ACAID, we have hypothesized that the induction of ACAID may depend upon the avoidance of local antigen processing within the anterior chamber. In this study, we have examined whether various putative antigen-presenting cells coinjected with allogeneic P815 cells into the anterior chamber could alter the course of the subsequent systemic alloimmune response. BALB/c recipients of intracameral P815 cells admixed with BALB/c spleen cells, B cells, or A20 B lymphoma cells developed ACAID. However, recipients of tumor cells admixed with cutaneous epidermal cells containing LC, and those receiving intracameral P815 cells admixed with purified LC developed vigorous DBA/2-specific delayed hypersensitivity responses. We conclude that avoidance of antigen processing and presentation by specialized APC such as dendritic LC within the anterior chamber is a condition for the induction of ACAID. Since under normal circumstances the anterior chamber is lined by tissues that are devoid of LC and contain very few class II MHC-expressing cells, this immunologically privileged site appears to be designed physiologically to avoid the unique form of local antigen presentation offered by dendritic LC--a condition that favors induction of selective immunologic incompetence.
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PMID:Induction of delayed hypersensitivity to alloantigens coinjected with Langerhans cells into the anterior chamber of the eye. Abrogation of anterior chamber-associated immune deviation. 249

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

Activation of the Fas cell surface molecule, either by specific antibody or by its as yet unidentified ligand, has been shown to induce apoptosis. Because apoptosis is also evoked in target cells by cytolytic T cells, we investigated whether the Fas pathway is involved in CD4+ T cell-mediated cytotoxicity. Analysis of Fas expression in APC, such as the B lymphoma A20.2J and MHC class II-transfected fibroblasts RT2.3, revealed a correlation between the degree of expression and sensitivity to cytotoxic attack, high level of Fas expression in A20.2J being associated with efficient lysis. To examine whether increased Fas expression in RT2.3 would render these cells more susceptible to CD4+ CTL lysis, they were transfected with a Fas gene expression vector. Indeed, Fas- but not mock-transfected RT2.3 proved to be more sensitive to lysis by either Ag specifically or nonspecifically activated CD4+ CTL. Similarly, MHC class II-negative, Fas-transfected L1210 leukemia cells were lysed with nonspecifically activated CD4+ CTL. The importance of the Fas engagement in CD4+ CTL-mediated cytotoxicity is further substantiated by the failure of both cloned and normal CD4+ CTL to lyse B cell blasts from Ipr mice. These mice are known to have a defect in functional Fas expression. Although the bulk of CD4+ T cell-mediated lysis appears to be Fas induced, the fact that the effector phase of A20.2J lysis is only partially Ca2+ independent indicates that other pathways also contribute to target cell death.
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PMID:Fas antigen is the major target molecule for CD4+ T cell-mediated cytotoxicity. 750 60

Mixed isotype MHC class II molecules (E alpha dA beta d) occur at extremely low levels on the surface of normal mouse B cells and macrophages, as determined by surface staining with an E alpha dA beta d-specific hamster mAb, H71-258.41. The surface levels of mixed isotype on the B cell lymphoma line A20 are approximately 1 to 2% that of surface I-A, whereas the levels of these molecules on normal mouse B cells were estimated to be at least two to four times less than those on A20. Nevertheless, other investigators have recently reported that immunization of normal H-2d mice with the sperm whale myoglobin peptide 110-121 (SWM(110-121)) elicits T cells, predominantly, V beta 8.2+, that recognize the peptide only in context of E alpha A beta. We have characterized a large number of SWM(110-121)-specific T cell hybridomas from several strains of H-2d haplotype mice. All of the V beta 8.2+ 110-121-specific hybridomas were found to be restricted by E alpha dA beta d, whereas, of the V beta 8.2- 110-121-specific group, approximately half recognized the peptide through E alpha dA beta d whereas the remainder were restricted by either I-Ad or I-Ed. mAb inhibition experiments revealed that 14-4-4S (E alpha-specific) could block presentation by mixed isotype completely, while MK-D6 (A beta d-specific) and H71-258.41 (E alpha dA beta d-specific) only inhibited presentation when the concentration of peptide was limiting. Although A20 expresses very low levels of mixed isotype, 10 to 100 nmol of the peptide produced a detectable response, illustrating the remarkable efficiency in presenting this peptide through E alpha dA beta d. The ability of normal mouse APC to use this restriction element despite its extremely low expression has important implications for the activation of T cells by low levels of peptide-MHC complexes.
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PMID:Expression and function of mixed isotype MHC class II molecules in normal mice. 825 92

Glycosphingolipid- and cholesterol-rich membrane microdomains (rafts) in T-cells are important in triggering and regulation of T(H)-cell activation in immunological synapses (IS), which in turn may control the T-cell repertoire in lymph nodes and at the periphery. It is less known, however, how the "presynaptic side" controls formation and function of IS. We investigated here activation signals and synapse formation frequency of murine IP12-7 T(H) hybridoma cell specific to influenza virus HA-peptide upon stimulation with two B-lymphoma cells, A20 and 2PK3, pulsed with peptide antigen. Confocal microscopic colocalization and FRET data consonantly revealed clustered distribution and constitutive raft-association of a major fraction of MHC-II molecules in both APCs. Costimulatory molecules (CD80 and CD86), not associated constitutively with rafts, were expressed at much lower level in A20 cells. T-cells responded to 2PK3 APC with much higher signal strength than to A20 cells, in good correlation with the frequency of IS formation, as assessed by microscopic conjugation assay. Disruption of rafts by cholesterol depletion in 2PK3 cells largely decreased the magnitude of T(H) cell activation signals, especially at low peptide antigen doses, similarly to masking CD4 with mAb on T-cells. The frequency of IS formation was reduced by blocking LFA-1 on T-cells and CD80 on APCs, by lowering the temperature below the phase transition of the membrane or by disrupting actin cytoskeleton. These data together suggest that the surface density and affinity/stability of peptide-MHC-II complexes and the costimulatory level are primary determinants for an efficient TCR recognition and the strength of the subsequent T-cell signals, as well as of the IS formation, which additionally requires a cytoskeleton-dependent remodeling of APC surface after the initial TCR signal. The threshold of T-cell activation can be further set by rafting MHC-II domains via concentrating high affinity ligands and promoting thereby T-cells for sensing low density antigen. Our data also demonstrate that B-cells, similarly to dendritic cells, could also provide T-cells with antigen-independent weak survival signals, likely associated with integrin engagement.
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PMID:Rafting MHC-II domains in the APC (presynaptic) plasma membrane and the thresholds for T-cell activation and immunological synapse formation. 1508 35


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