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PubMed1992

Differential effect of interleukin 1 on naive and memory CD4+ T cells.

Freshly derived murine CD4+ T cells are divided into naive and memory cells based on the expression of CD45 isoforms. Cross-linking the T cell receptor CD3 complex either by plastic-bound anti-CD3 antibodies or the antibody presented on non-lymphoid Fc gamma receptor type II-positive Chinese hamster ovary cells in absence of competent antigen-presenting cells fails to activate naive cells to either secrete cytokines or to proliferate. In contrast, memory cells secrete their characteristic cytokines [interleukin (IL) 2, IL4, and interferon-gamma] and show significant proliferation to this stimulus. IL 1 however, is required for their optimal clonal expansion. Differential expression of IL 1 receptor mRNA in memory cells also correlate with their responsiveness to IL 1. Thus, these data reveal a basic difference in the requirements for activation of naive and memory CD4+ T cells.

Animals↗

PubMed1988

Expression of the T cell gamma gene by a functionally defined human T cell clone. Characterization at DNA, RNA, and cell membrane level.

In the present study we describe one CD2+CD3+ clone termed DS6 which expressed neither CD4 nor CD8 differentiation antigens and failed to react with WT31, a monoclonal antibody directed against the T cell antigen receptor alpha/beta heterodimer. This clone was isolated from peripheral blood T lymphocytes of a patient with a prolonged immunodeficiency after allogeneic bone marrow transplantation. Normal-sized T cell gamma gene transcripts were detected in DS6 by northern analysis, whereas no mature beta or alpha chain mRNA were found. The rearrangement of TCR beta chain genes and T cell gamma genes was analysed. While in DS6, TCR beta chain genes remain in germinal configuration, and a unique pattern of monoallelic T cell gamma gene rearrangement was observed. The rearrangement involves the recently described V gamma 5 segment and the J gamma 1 joining segment, which is located upstream of the C gamma 1 constant region. To determine the molecular structure present on DS6, an immunoprecipitation was performed with monoclonal anti-CD3 antibody and a rabbit antiserum raised against gamma protein. We have observed, in association with the CD3 complex, a 90 kDa structure which under reducing conditions resolves into three subunits of 45, 40 and 37 kDa. We demonstrated that the rabbit anti-gamma serum only immunoprecipitates the two lower bands. The upper band corresponds to a presently undefined T cell receptor chain. Next, we showed the non major histocompatibility complex (MHC)-restricted cytolytic activity exhibited by these CD3+CD4-CD8- cloned T cells and inhibition of the natural killer (NK)-like activity by the anti-CD3 monoclonal antibody. The triggering of CD2 or CD3 molecules increased IL-2 receptor expression on DS6 but failed to induce cell proliferation. This contrasts with recent results obtained with gamma-expressing T cell clones and illustrates the functional heterogeneity of the cells bearing the second T cell receptor.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1994

Signal transduction by the B cell antigen receptor and its coreceptors.

B lymphocyte antigen receptors, membrane immunoglobulins (mIg), function in focusing and internalization of antigen for subsequent presentation to T cells and in transmembrane transduction of signals leading to cell activation, anergy, or deletion. Until quite recently, the ability of this receptor to transduce signals in spite of a virtual lack of cytoplasmic structure, left a significant gap in our understanding of how it is coupled to cytoplasmic signal propagators. Studies conducted during the past five years have defined a mIg-associated protein complex homologous to the CD3 complex associated with the T cell antigen receptor. Components of this disulfide linked heterodimeric complex, Ig-alpha and Ig-beta, contain an approximately 26 residue sequence motif termed ARH1, also known as TAM, which binds to cytoplasmic effectors, including src-family tyrosine kinases, and contains all structural information needed for signal transduction. Receptor associated src-family kinases which are activated following receptor cross-linking, also associate with downstream effectors, including phospholipase C gamma (PLC gamma), p21ras. GTPase activating protein (GAP), phosphatidylinositol 3-kinase (PI3-k) and microtubule associate protein kinase (MAPk2). In some cases, these associations are induced by receptor cross-linking and lead directly to effector activation. The current literature indicates that these interactions may occur in sequence and culminate in the activation of three major pathways of signal propagation including those mediated by PLC gamma, p21ras and PI3-k. This chapter reviews various molecular aspects of the B cell antigen receptor complex, including extended structure of the complex, and receptor-effector interactions and their biologic consequences. Finally, an integrated model of antigen receptor signaling is presented.

Amino Acid Sequence↗

PubMed1991

Different subpopulations of developing thymocytes are associated with adherent (macrophage) or nonadherent (dendritic) thymic rosettes.

Thymic rosettes (ROS), structures consisting of thymic lymphoid cells attached to a central stromal cell, were isolated from mouse thymus by collagenase digestion and unit-gravity elutriation. The ROS were then separated into those where the stromal cells were either macrophage-like (M-ROS) or dendritic cell-like (D-ROS), on the basis of the differences in adherence properties or in the level of MAC-1 surface antigen. The ROS were then dissociated and the thymocyte content analyzed by immunofluorescent staining and flow cytometry. M-ROS and D-ROS differed in thymocyte composition, although the major component of both was the CD4+CD8+ cortical thymocyte. D-ROS were enriched in thymocytes expressing high levels of surface T-cell antigen receptor (TcR) and the associated CD3 complex, and these included both CD4+CD8-CD3++ and CD4-CD8+CD3++ mature thymocytes. M-ROS were enriched in CD4-CD8- thymocytes and had a reduced content of thymocytes expressing high TcR-CD3 levels; they nevertheless contained some mature thymocytes, but only of the CD4+CD8-CD3++ category. Several lines of evidence indicated that the mature thymocytes in ROS were cells recently formed in the cortex, and were not from the medullary pool. ROS-associated mature thymocytes expressed lower levels of H-2K than free, mature thymocytes. The CD4+CD8+CD3++ subpopulation, believed to be a developmental intermediate between cortical thymocytes and mature T cells, was present in both ROS populations. Further, late intermediates leading to both mature T-cell categories were evident in D-ROS, but only those leading to CD4+CD8-CD3++ T cells were evident in M-ROS. The results are compatible with a role for ROS in TcR-specificity selection and in the final maturation steps in the thymic cortex.

Animals↗

PubMed1986

Distinct epitopes on the T cell antigen receptor of HPB-ALL tumor cells identified by monoclonal antibodies.

The T cell antigen receptor is a approximately 90,000 dalton disulfide linked heterodimer that is non-covalently associated with the CD3 complex. Prior studies have demonstrated that anti-CD3 or -Ti antibodies can mimic antigen and induce cellular proliferation and the secretion of lymphokines. An early event in activation via CD3/Ti is a rapid increase in concentration of intracellular Ca2+ levels. In the present studies, we have produced a panel of monoclonal antibodies (MAb) against the Ti expressed on HPB-ALL tumor cells. All MAb immunoprecipitate a approximately 90,000 dalton disulfide linked heterodimer and induced co-modulation of Ti and CD3. On the basis of competitive binding studies, four distinct epitopes on the Ti of HPB-ALL were identified with MAb L38, L39, L41, and L42. These epitopes were additionally discriminated on the basis of reactivity with normal polyclonal T cell populations and functional effects on HPB-ALL. L39 reacted with a monomorphic epitope present on approximately 2 to 5% of peripheral blood T lymphocytes from all donors examined and was specifically mitogenic for peripheral blood T cells expressing this epitope. L39+ T cells in blood included both CD4+ and CD8+ lymphocytes. In contrast, L38, L41, and L42 failed to react with peripheral blood T cells and were not mitogenic for peripheral blood lymphocytes. Anti-Leu-4, L38, L39, and L41 MAb all induced a rapid increase in (Ca2+)i in HPB-ALL tumor cells, similar to previous findings with anti-CD3 and anti-Ti MAb against various tumor cells and peripheral blood T cells. In contrast, L42 MAb did not induce a substantial increase in (Ca2+)i. Failure of L42 to induce a substantial increased (Ca2+)i could not be attributed to the apparent titer, avidity, or isotype of the antibody. These findings suggest that induction of increased (Ca2+)i upon binding of Ti is epitope dependent. Furthermore, these data demonstrate that several distinct public and private epitopes can be identified on the T cell antigen receptor.

Antibodies, Monoclonal↗

PubMed1995

T cells infiltrating non-Hodgkin's B cell lymphomas show altered tyrosine phosphorylation pattern even though T cell receptor/CD3-associated kinases are present.

Although tumor infiltrating lymphocytes (T-TIL) from B cell non-Hodgkins lymphoma patients contain tumor-reactive T cells, they display poor proliferation and IFN-gamma production when stimulated through the TCR-CD3. To determine if there was altered signaling linked to TCR-CD3 ligation, tyrosine phosphorylation was examined in T-TIL because it represents an early and critical event in T cell activation. After stimulation with anti-CD3 Ab, Western blotting with anti-phosphotyrosine showed reduced phosphorylation in T-TIL when compared with peripheral blood-derived T cells from normal individuals. The altered phosphorylation was not due to the reduced expression of signaling elements linked to the TCR-CD3 complex. T-TIL expressed normal levels of CD3 epsilon, TCR zeta chain, and the three tyrosine kinases, p56lck (Lck), p59fyn, and ZAP-70. However, in T-TIL, anti-Lck Ab reacted with a 60-kDa protein, which appears to be the phosphorylated form of Lck. Binding of anti-Lck Ab to the 60-kDa protein was blocked by Lck peptide. In addition, anti-Lck Ab immunoprecipitated a phosphorylated 60-kDa protein from gamma-32P-labeled T-TIL that was not seen in normal resting T cells. In vitro kinase assay studies also demonstrated that TCR-CD3 engagement increased the kinase activity of Lck in normal T cells but not in T-TIL. These results suggest that although T-TIL from B cell non-Hodgkins lymphoma patients contain the signal transduction molecules associated with TCR-CD3 activation pathway, they are impaired in tyrosine phosphorylation and Lck activity, which may contribute to the functional defects of these cells.

Humans↗

PubMed1990

Tissue-specific nuclear factors mediate expression of the CD3 delta gene during T cell development.

An obligatory step towards T cell maturation is expression of the CD3 gene products which occurs very early during thymic differentiation and may even precede migration to the thymus. Delineation of the transcriptional mechanisms that determine expression of the CD3 complex in immature and mature T cells will help us understand the molecular events that govern T cell development. We have previously reported that a 400 bp region 3' of the CD3 delta gene functions as a transcriptional enhancer with strong specificity for T cells. Here we identify two elements in the CD3 delta enhancer which mediate its T cell restricted function. Element delta A can function as an independent enhancer while element delta B has no independent function but augments the activity of element delta A. Together, delta A and delta B are sufficient to reconstitute the activity of the CD3 delta enhancer. Nucleoprotein complexes found in mature T cells have been identified whose presence correlates with activity of these two elements. Since these protein binding sites are conserved in other genes of the TCR-CD3 complex, elements delta A and delta B and their cognate nuclear factors may play an important role in T cell development.

Antigens, CD↗

PubMed1994

The T cell antigen receptor CD3:CD4 molecular complex is diminished on the surface of pulmonary lymphocytes.

CD4, a 55-kd cell surface glycoprotein, binds to class II major histocompatibility complex (MHC) (Ia) antigens and functions as a coreceptor for the T cell antigen receptor (Ti alpha beta)-CD3 complex. We have observed that critical elements of the T cell antigen multireceptor complex, including Ti alpha beta, CD3, CD4, but not CD8, were diminished on CD45RO+ pulmonary T lymphocytes but not CD45RO+ peripheral blood T lymphocytes (PBL). Epitopes mapping from the first (D1) to the fourth (D4) extracytoplasmic Ig-like domains of CD4 were expressed to a lesser degree on pulmonary T cells than on PBL (P = 0.002). CD4 expression on pulmonary T cells did not increase after 72 hours of ex vivo culture in complete medium but was restored toward control levels by stimulation with phytohemagglutinin, anti-CD3, or interleukin-2. CD4 mRNA isolated from lung T cells and PBL co-migrated on Northern blots and the total levels of CD4 mRNA were comparable, suggesting that diminished CD4 expression by pulmonary T cells might reflect a posttranscriptional change. To determine whether CD4bright T cells convert with mitogen stimulation to CD4dim cells, PBLs were stimulated with immobilized anti-CD3, anti-CD4, or a molecularly engineered anti-CD3:CD4 bispecific monoclonal antibody and the ratio of the CD4:CD3 mean fluorescence staining intensities was calculated at days 3 and 13. The CD4:CD3 ratio decreased primarily for cells stimulated with anti-CD3:CD4, suggesting that co-ligation of CD3 and CD4 is required for the generation of CD4dim T cells. We conclude that diminished Ti alpha beta-CD3:CD4 expression is a characteristic of T cells in lung that is not shared by peripheral blood T cells in vivo, and speculate that this change reflects T cell activation in a millieu of limited interleukin-2 availability.

Antibodies, Bispecific↗

PubMed1997

The interchain disulfide bond between TCR alpha beta heterodimers on human T cells is not required for TCR-CD3 membrane expression and signal transduction.

In the present paper, it was attempted to define the amino acids or regions on TCR beta molecules that determine the TCR alpha-TCR beta interaction. Sequence studies on HBP-ALL variant cells with an intrinsic deficiency in TCR alpha beta dimer formation elucidated a conserved amino acid motif in the TCR-C beta beta-strand E, = Y(C)(L)(S)SRLR(V)(S)(A); this motif seems to represent one interaction area for the TCR alpha-TCR beta interaction. In addition, amino acids in the connecting peptide may be shaped in a precise structure (by the interactions with CD3 molecules?) involved in TCR alpha-TCR beta dimerization. This result was supported by the finding that the interchain disulfide bond between TCR alpha and beta chains is not required for membrane expression or transmembrane signal transduction of TCR alpha beta-CD3 complexes. Finally, comparative results from two membrane TCR-CD3-negative Jurkat variants R4.9 and E6.E12 suggest that TCR-C beta exon 1- and 2-encoded amino acids are important for the TCR beta-CD3 gamma epsilon association.

Amino Acid Sequence↗

PubMed1996

Immature T cells in peripheral lymphoid organs of recombinase-activating gene-1/-2-deficient mice. Thymus dependence and responsiveness to anti-CD3 epsilon antibody.

Thymocytes of mice deficient in the recombinase-activating gene (RAG)-1 or RAG-2 cannot express and receive signals through the pre-TCR. As a result, thymocyte development in these mice terminates at the CD4/8 double negative (DN), IL-2R-alpha-positive stage. Nevertheless, RAG-deficient DN thymocytes express functional CD3 complexes and can therefore be induced by anti-CD3 epsilon mAb to mature to the CD4+8+ double positive stage. In the present paper we demonstrate that the peripheral lymphoid organs (lymph nodes, spleen) and peripheral blood of RAG-deficient mice harbor an immature T cell population which, similar to RAG-deficient DN thymocytes, contains high levels of cytoplasmic CD3 epsilon and responds to anti-CD3 epsilon mAb in vivo. With respect to surface phenotype (Thy1.2+, PgP-1+, HSA+, Fc gamma RII/III-, IL-2R-alpha-, c-kit-), these cells are similar to intermediate stage RAG-deficient DN thymocytes. Moreover, they express mRNA for pre-TCR-alpha and for the nondeleted RAG. Following injection of anti-CD3 epsilon mAb, these cells proliferate, down-regulate heat stable Ag and PgP-1, and partially differentiate to CD4+ and CD8+ double positive and single positive cells. The induced population displays a mixed phenotype, between that of immature thymocytes and lymph node T cells in normal mice. Induction is successful in thymectomized RAG-deficient mice, suggesting that it occurs in the periphery. However, after thymectomy, inducible cells disappear with an approximate half-life of 10 to 14 days. We suggest that DN thymocytes can emigrate and repopulate peripheral lymphoid organs of RAG-deficient mice. These cells respond to CD3 signaling by aberrant maturation, possibly due to the inappropriate microenvironment of peripheral lymphoid organs.

Animals↗

PubMed1995

Developmental regulation of TCR-CD3-dependent [Ca2+]i responses of individual normal and pp59fyn-deficient T lymphocytes.

The aim of this study was to ascertain whether different types of T-cell receptor (TCR)-mediated [Ca2+]i signals could begin to explain the different cellular responses of mature and immature T cells to ligation of the TCR-CD3 complex. Using a digital fluorescence imaging system, we measured and compared [Ca2+]i of individual cells from immature and mature murine T-cell populations following application of CD3-epsilon monoclonal antibody (mAb). Our approach revealed distinctions among developmental subsets which were not seen by previous measurements of [Ca2+]i in bulk cell populations. The CD3-mediated [Ca2+]i responses of individual thymocytes were very complex. Latencies to peak [Ca2+]i varied greatly among thymocytes, but the responses of splenic T cells were synchronized, novel evidence that the timing of [Ca2+]i responses may be an important informative parameter for TCR-CD3 signalling. In addition, among cells responding to CD3 mAb, higher peak [Ca2+]i responses correlated with maturity (CD4+ CD8+ thymocytes < single-positive thymocytes < splenic T cells). Examination of cells from pp59fyn-deficient mice showed that pp59fyn deficiency affects the amplitude and probability, but not the latency or synchrony, of CD3-mediated [Ca2+]i responses of CD4+ CD8+ and CD4+ CD8- thymocytes. All subsets showed equivalent receptor-independent mobilization of [Ca2+]i. These developmentally distinct [Ca2+]i features most probably reflect meaningful developmental changes in how the TCR-CD3 complex couples to intracellular signalling machinery including pp59fyn. By clearly showing how [Ca2+]i responses change during development, these results support the hypothesis that distinctive types of [Ca2+]i responses drive thymocyte differentiation.

Animals↗

PubMed1991

Molecular analysis of the interaction of p56lck with the CD4 and CD8 antigens.

The CD4 and CD8 antigens on the surface of T cells appear to bind to major histocompatibility complex (MHC) class II and I antigens, respectively. These antigens also synergize with the Ti(TcR)/CD3 complex in the potentiation of T-cell proliferation. Our earlier work demonstrated that the CD4 and CD8 receptors are coupled to a protein-tyrosine kinase termed p56lck from normal and transformed T lymphocytes. The p56lck protein is a member of the src family and its homology with receptor-kinases such as the epidermal growth factor receptor (EGFR) make it an important candidate in signal transduction. In this paper, we show in transfectants that p56lck interacts with the cytoplasmic tail of the CD4 antigen. Murine p56lck can interact across species with the human CD4 receptor. Furthermore, peptide competition studies showed that a specific sequence within the cytoplasmic tail of CD4 interacts with the kinase. Cysteine residues also appear to play key roles in this interaction. Lastly, we show biochemically that the CD4:p56lck complex can physically associate with the epsilon chain of the CD3 complex on HPB-ALL transformed T cells. This interaction may provide a bridge by which events related to ligand binding to Ti(TcR)/CD3 may trigger T cells via the CD4/CD8:p56lck complex.

Amino Acid Sequence↗

PubMed1996

[CD4-CD8- to CD4-CD8+ transition induced by anti-CD3 mAb in vitro cell culture system].

In our experiments, we have observed the effect of anti-CD3 mAb in inducing the differentiation of CD4-CD8- (double negative, DN) thymocytes into CD4+ CD8+ (double positive, DP) cells in an in vitro cell culture system including IL-7 for maintaining the growth of TN thymocytes. When TN thymocytes were stimulated by immobilized anti-CD3 mAb for 3 days, CD4-CD8+ cells generated, which were mostly immediate precursors of CD4+CD8+ thymocytes according to their surface TCR beta expression. The transition from DN to DP thymocytes accompanied with downregulation of interleukin 2 receptor (IL-2 R) alpha chain, and the TCR alpha beta-CD3 expression induced by IL-7 was also inhibited. Anti-CD3 mAb was effective only before the appearance of functional TCR-alpha beta-CD3 complex. Taking together, the results strongly suggest that anti-CD3 mAb induced DN thymocyte defferentiation is through the pre-TCR complex.

Animals↗

PubMed1996

Surface T cell Fas receptor/CD95 regulation, in vivo activation, and apoptosis. Activation-induced death can occur without Fas receptor.

Fas-mediated apoptosis is a form of cell death that operates through a receptor-ligand interaction. The FasR has been implicated directly in peripheral T cell tolerance and activation-induced apoptosis of T cells in vitro, although to date its expression on murine peripheral T cells has been characterized incompletely. In this study, we document substantial expression of FasR on the vast majority of recent thymic emigrants and resting peripheral T lymphocytes. FasR ligation can induce death in a minor (approximately 5%) subset of these cells. By contrast to rather slow activation-mediated FasR up-regulation in vitro, we demonstrate that in vivo T cell activation by alpha CD3 mAb or superantigen results in rapid up-regulation of the FasR. This up-regulation is paralleled by the kinetics of activation-induced apoptosis in lymph node T cells. However, we demonstrate that the FasR is not necessary for activation-induced cell death. Lymph node T cells from young, healthy, FasR expression-deficient MRL-Ipr/Ipr and animals could be activated in vivo through the TCR-CD3 complex. Most importantly, MRL-Ipr/Ipr T cells underwent massive activation-induced apoptosis in response to high and intermediate doses of alpha CD3. At a low alpha CD3 dose, however, both MRL-Ipr/Ipr and MRL +/+ T cells were activated similarly, but only the latter underwent adequate apoptosis. Taken together, these findings suggest that in vivo, the Fas pathway may not be the only regulator of activation-induced T cell death, but that this pathway may be critical in regulating responses to weak stimuli.

Animals↗

PubMed1995

Regulation of thymocyte development through CD3: functional dissociation between p56lck and CD3 sigma in early thymic selection.

We studied the extent of functional linkage between CD3 sigma and p56lck in pre-TCR-dependent thymocyte development. Differentiation of DN to DP cells was examined by treatment of RAG2/CD3 sigma and RAG1/p56lck double-deficient mice with anti-CD3 epsilon antibodies. The results suggest that CD3 sigma has no specific role in this maturation step, but may be important for amplification of signaling through the pre-TCR. In contrast, p56lck is the main protein tyrosine kinase associated with signaling through the pre-TCR-CD3 complex. In DP thymocytes, the Ca2+ response to anti-CD3 epsilon was totally abolished in CD3 sigma-I-but only reduced in p56lck-I-mice, and in vivo responses to anti-CD3 epsilon differed from one another. Thus, CD3 sigma and p56lck are functionally not tightly associated and their deficiencies cause distinct developmental defects.

Animals↗

PubMed1997

HIV glycoprotein gp120 inhibits TCR-CD3-mediated activation of fyn and lck.

HIV major glycoprotein gp120 interacts with CD4 molecules and perturbs signaling through the TCR-CD3 complex. We examined the effects of gp120 on TCR-CD3-induced phosphorylation and activation of the src-type protein tyrosine kinases (PTK), fyn and lck. gp120 caused minimal changes in lck phosphorylation or lck enzymatic activity, but preincubation of Jurkat cells with gp120 for 20 min strongly inhibited TCR-CD3-mediated phosphorylation and activation of lck and fyn, as well as phosphorylation of CD3 zeta. Inhibition of TCR-CD3 signaling in T cells preincubated with gp120 was paralleled by inhibition of T cell proliferation to the antigen tetanus toxoid. Neither surface CD4 expression nor CD4-lck association was affected by gp120. Furthermore, gp120 inhibited lck phosphorylation induced by cross-linking of TCR-CD3 and CD4 suggesting that the inhibition of lck phosphorylation could not be simply accounted for by sequestration of CD4 molecules. gp120 selectively enhanced the phosphorylation of the lck peptide containing the autoinhibitory tyrosine residue Tyr505 relative to the lck peptide containing the positive regulatory residue Tyr394, suggesting that a qualitative alteration in lck may underlie the inhibition of TCR-CD3 signaling by gp120.

CD4 Antigens↗

PubMed1996

Cytotoxic activity against tumour cells mediated by intermediate TCR cells in the liver and spleen.

Morphological and phenotypic characterization in previous studies has indicated that intermediate (int) T-cell receptor (TCR) cells or T natural killer (TNK) cells may stand at an intermediate position between NK cells and high TCR cells of thymic origin in phylogenetic development. In this study, a functional study on cytotoxic activity against various tumour targets was performed in each purified subset. When a negative selection method entailing in vivo injection of anti-asialo GM, antibody or anti-interleukin (IL)-2R beta monoclonal antibody (mAb) was applied, IL-2R beta 1 CD3 NK cells were found to have the highest NK activity while IL-2R beta 1 int CD3 (or TCR) cells had a lower level of the NK activity. High CD3 cells (freshly isolated) did not have any such activity. Sorting experiments further revealed that the NK function mediated by int CD3 cells was augmented when they were exposed to anti-CD3 mAb. anti-TCR alpha beta, or anti-TCR-delta mAb. This phenomenon was not observed in NK cells and high CD3 cells. More importantly, when anti-CD3 mAb (or anti-TCR mAb) was added to the assay culture, int CD3 cells became cytotoxic against even NK-resistant tumour (Fc gamma R-. Fas+) targets. Liver mononuclear cells or int CD3 cells exposed to anti-CD3 mAb for 6 hr showed an elevated level of perforin in their cytoplasms. The present results suggest that int CD3 cells are usually non-cytotoxic against various tumours but become functional after being stimulated via the TCR CD3 complex.

Animals↗

PubMed1994

Retention of unassembled components of integral membrane proteins by calnexin.

Quality control mechanisms prevent the cell surface expression of incompletely assembled multisubunit receptors such as the T cell receptor (TCR). The molecular chaperone function of calnexin (IP90, p88), a 90-kilodalton protein that resides in the endoplasmic reticulum (ER), in the retention of representative chains of the TCR-CD3 complex in the ER was tested. Truncation mutants of calnexin, when transiently expressed in COS cells, were exported from the ER and either accumulated in the Golgi or progressed to the cell surface. CD3 epsilon chains cotransfected with the forms of calnexin that were not retained in the ER exited the ER and colocalized with calnexin. Since engineered calnexin determined the intracellular localization of the proteins associated with it, it is concluded that calnexin interacts with incompletely assembled TCR components and retains them in the ER.

Amino Acid Sequence↗