Inhibition of IL 2-driven proliferation of murine T lymphocyte clones by supraoptimal levels of immobilized anti-T cell receptor monoclonal antibody

Both cloned murine helper T lymphocytes (HTL) and cytolytic T lymphocytes (CTL) proliferated and secreted lymphokines when stimulated with immobilized anti-T cell receptor monoclonal antibody (anti-TCR mAb). However, although proliferation of CTL increased and reached plateau levels as concentrations of anti-TCR mAb were increased, the proliferation of HTL decreased with high concentrations of anti-TCR mAb. A reduction of IL 2-dependent proliferation by CTL was observed when IL 2 was added to cultures of CTL in the presence of high concentrations of anti-TCR mAb, whereas IL 2-independent proliferation appeared to be unaffected by these concentrations of anti-TCR mAb. Inhibition of IL 2-driven proliferation caused by high concentrations of immobilized anti-TCR mAb did not seem to be mediated by soluble factors. Cells continued to express cell surface receptors for IL 2 and transferrin after treatment with immobilized anti-TCR mAb. Inhibition of IL 2-driven proliferation by high concentrations of immobilized anti-TCR mAb may represent a mechanism for regulating the proliferation of T lymphocytes. This inhibitory mechanism is initiated by stimulation of the T cell receptor, in this case by immobilized anti-TCR mAb, and is independent of other cells and factors.     

Activation of autoreactive cytolytic T lymphocyte clone against human melanoma by anti-T3 monoclonal antibody and autologous accessory cells

A cytotoxic T-lymphocyte (CTL) clone Tc1.8 was derived in a limiting dilution culture from a single cell that was derived from melanoma-involved lymph node lymphocytes activated in in vitro coculture against the autologous melanoma cells (VIP). The clone Tc1.8 (T3+, T8+, T4-, and Leu7-) expressed restricted cytolytic activity against only the autologous target VIP. As it aged in continuous culture containing interleukin 2, Tc1.8 lost cytolytic activity. The cytolytic function could be restored, however, with monoclonal antibody (MoAb) against T3 (OKT3) or with F(ab')2 fractions of OKT3, and upon restimulation with irradiated accessory cells. OKT3-mediated reinduction of cytotoxicity by the aged Tc1.8 could not be achieved if the T3 molecules were modulated from the effector cell surface following overnight incubation of Tc1.8 with saturating concentrations of OKT3 MoAb. Following reactivation with OKT3 Tc1.8 gained cytolytic function against NK targets in addition to VIP. Reactivation with F(ab')2 fractions of OKT3 and with autologous accessory cells, however, maintained its restricted antigen fidelity. The NK-like activity of Tc1.8 upon reactivation with OKT3 resulted from conjugate formation between the activated Tc1.8 and NK targets via the activating ligand itself. Thus, upon stimulation with anti-T3 MoAb and with autologous accessory cells, independently, the autoreactivity could be restored in an aged and inactive CTL clone.     

Inhibition of lymphocyte proliferation by monoclonal antibody directed against the T3 antigen on human T cells

Peripheral blood mononuclear cells from 40% of normal donors are mitogenically unresponsive to UCHT1, a monoclonal antibody reactive to the T3 surface molecule on human T lymphocytes. Cell preparations from non-UCHT1 responders were used to examine whether and how interaction of UCHT1 with the T3 molecule affects T-cell functionality. It was found that UCHT1 profoundly (greater than 85%) suppressed lymphocyte proliferation induced by plant mitogens (phytohemagglutinin (PHA) and concanavalin A (Con A], recall antigen (candidin), and allogeneic non-T cells. The antibody abrogated both the production of interleukin 2 (IL-2) by and the expression of IL-2-specific receptors on T lymphocytes stimulated by PHA or allogeneic non-T cells. UCHT1 was maximally suppressive when added to cells within 2 hr (PHA stimulation) or 1 day (allogeneic non-T cell activation) after the initiation of the culture period. The inhibiting activity of UCHT1 could be related to its ability to modulate T3 molecules from the T-cell surface: both actions displayed the same antibody concentration dependence and had a comparable time dependence. Moreover, after modulation, unresponsive lymphocytes regained responsiveness to PHA in parallel with reexpression of surface T3 molecules. These findings are consistent with the idea that the human T3 molecule functions as an essential signal transducer during the early phases of T-cell activation.     

Regulation by anti-CD2 monoclonal antibody of the activation of a human T cell clone induced by anti-CD3 or anti-T cell receptor antibodies

In this study the effect of anti-cluster designation (CD) 2 monoclonal antibodies (mAb) on the activation of a cloned human T cell line, HY837, after triggering the CD3/T cell receptor (TcR) complex by anti-CD3 or anti-TcR mAb is described. HY837, which reacts with a series of mAb directed at different epitopes on the TcR, could be induced to proliferation and interleukin 2 (IL-2) production by soluble mAb directed at the CD3/TcR complex in the absence of accessory cells. mAb directed at the CD2 epitope T11-1 were shown to block the IL-2 production by HY837, as well as the expression of the IL-2 receptor, induced by anti-CD3 mAb, resulting in the inhibition of the proliferative response. The effect of anti-CD2 mAb on the proliferative response of HY837, induced by anti-CD3 mAb, was not due to a competition for Fc binding sites. In contrast, the proliferative responses and IL-2 production of HY837, induced by mAb directed at the TcR, were shown to be enhanced by the action of the anti-CD2 mAb. These results indicate that effects mediated by anti-CD3/TcR mAb cannot always be extrapolated to antigen-mediated effects and show that anti-CD2 mAb may regulate the T cell response, induced by mAb directed at the CD3/TcR complex, depending on which part of this complex is triggered during activation.     

Stimulation of the antigen and interleukin-2 receptors on T lymphocytes activates distinct tyrosine protein kinases

The T cell antigen receptor complex (TCR) and the interleukin 2 (IL-2) receptor are responsible for signal transduction that results in T lymphocyte activation and proliferation. Stimulation of either the TCR or the IL-2 receptor induces an increase in tyrosine phosphorylation of several cellular proteins indicating that signal transduction by both of these receptors involves the activation of a tyrosine protein kinase. Although the tyrosine protein kinases activated by these receptors have not yet been characterized the receptors themselves are known not to contain a tyrosine protein kinase domain. To determine if these receptors are coupled to the activation of similar or distinct tyrosine protein kinases we examined the patterns and kinetics of tyrosine phosphorylation induced by stimulation of these receptors on a cloned cell line. Hut 78.3 cells co-express the TCR and the p75 IL-2 receptor. These cells were stimulated with either OKT3 antibodies, specific for the TCR, or with IL-2. Signal transduction by these receptors was found to increase the tyrosine phosphorylation of a set of proteins unique to each stimulus. The kinetics of the tyrosine phosphorylation induced by OKT3 antibodies also differed from that induced by IL-2. The OKT3-dependent tyrosine phosphorylation reached maximal levels within 2.5 min and began to decline by 5 min after stimulation. In contrast, the IL-2-induced tyrosine phosphorylation did not achieve maximal levels until 15 min after the addition of IL-2 and the proteins remained phosphorylated even after 60 min of incubation. In addition the tyrosine phosphorylations induced by OKT3 and IL-2 were not affected by prior stimulation with the other agent. These results demonstrate that the TCR and IL-2 receptor are coupled to different signal transduction pathways responsible for the independent activation of distinct tyrosine protein kinases.     

Role of accessory molecules in signal transduction of cytolytic T lymphocyte by anti-T cell receptor and anti-Ly-6.2C monoclonal antibodies

Accessory molecules present on the cell surface of cytolytic T lymphocytes (CTL) play an important role in their activation. Antigen-specific recognition by CTL is inhibited by antibodies against Lyt-2, L3T4, or LFA-1 molecules. Presently it is not known whether these molecules function by binding a ligand such as class I or class II on the target cell or by delivering a signal that down-regulates T cell activation. In the present study we utilized anti-T cell antibodies including anti-T3 and anti-T cell receptor (alpha/beta) as well as an anti-Ly-6.2C monoclonal antibody to activate CTL clones to kill irrelevant targets or secrete BLT esterase. The redirected lysis assay system utilizes the fact that heteroconjugates between anti-T3, and anti-T cell receptor, or anti-Ly-6.2C and anti-trinitrophenyl can trigger CTL lysis of trinitrophenyl-coupled targets that did not express antigen. In this system anti-Lyt-2 antibodies as well as anti-LFA-1 antibodies inhibited triggering via T cell receptor-related molecules but not via the anti-Ly-6.2C heteroconjugate. In addition, the anti-Lyt-2 was shown to inhibit conjugate formation in the heteroaggregate assay system suggesting that the anti-Lyt-2 antibodies acted early in inhibiting CTL activity. Similar results were observed in a system in which the CTL clones were triggered to secrete a BLT-esterase-like activity in the absence of target cells. Anti-T3 coated on plastic was shown to activate BLT-esterase secretion. This secretion was inhibited by anti-Lyt-2 and anti-LFA-1. Thus, it would appear that both the Lyt-2 molecule and the LFA-1 molecule act as signal-transducing elements involved in CTL activation. In particular, the Lyt-2 molecule appears to preferentially function in receptor-mediated T cell activation.     

Hepatitis B virus-reactive human T lymphocyte clones: antigen specificity and helper function for antibody synthesis

To study immunity to hepatitis B surface antigen (HBsAg) at the cellular level, lymphocytes were obtained from the peripheral blood of hepatitis B vaccine recipients and were examined for various immune responses to HBsAg in vitro. The peripheral blood mononuclear cells (PBM) from most of the vaccinees did not proliferate to a great extent to HBsAg in vitro. However, HBsAg-reactive lymphocyte lines and clones were obtained from some of these individuals if the PBM were stimulated in vitro with HBsAg and were maintained in the presence of T cell growth supplement. Most of the HBsAg-reactive T cell clones obtained were found to be antigen-specific and some of them provided help in the production of anti-HBsAg antibodies by a cell population enriched for HBsAg-binding cells. These results indicate that HBsAg-specific T and B cells exist in the circulation of hepatitis B vaccine recipients, although they are at limiting concentrations for the in vitro cell proliferation and antibody production assays.     

The events of primary T cell activation can be staged by use of Sepharose-bound anti-T3 (64.1) monoclonal antibody and purified interleukin 1

A mitogenic anti-CD3 ("T3") monoclonal antibody (64.1), that stimulates polyclonal T cell activation by a mechanism believed to be similar to antigen via binding to the T cell receptor complex, was utilized in soluble (SOL) and Sepharose-bound (SEPH) forms to dissect the role of accessory cells (AC) and interleukin 1 (IL 1) in supporting T cell activation. The T cell activation pathway was dissected into "early" events including expression of interleukin 2 receptors (IL 2R), increased RNA content, IL 2 release, and "late" (DNA synthesis) events. Unseparated peripheral blood mononuclear cells progressed through all stages of activation when stimulated by either form of 64.1. Stringent AC depletion by plastic adherence, nylon wool adherence, and L-leucine methyl ester (selectively lyses AC) prevented early and late T cell responses to either form of 64.1. The addition of highly purified IL 1 replenished both early and late T cell responses to SEPH-64.1 but not to SOL-64.1. Although SOL-64.1 stimulation of purified T cells induced modulation of the CD3 complex, only SEPH-64.1 induced IL 1 responsiveness, and exogenous IL 1 was then able to support synthesis of RNA, secretion of IL 2, expression of IL 2R, and ultimately, DNA synthesis. Therefore, the stages of early T cell activation owing to stimulation of the CD3-T cell receptor complex and IL 1 responsiveness have been dissected.     

Interleukin 2-driven T lymphocyte proliferation is dependent upon a surface antigen distinct from the interleukin 2 receptor: requirements for inhibition of T-cell proliferation by monoclonal antibody 5C3

A monoclonal antibody (5C3) to an antigen expressed on activated guinea pig T lymphocytes that did not react with the interleukin 2 (IL-2) receptor, but inhibited IL-2-driven proliferative responses has been previously characterized. The present study provides further analysis of the inhibitory capacity of 5C3 for T-cell proliferation and of the relationship between the expression of the antigen defined by 5C3 and the capacity of cells to respond to IL-2. 5C3 inhibited proliferation of T-cell blasts to IL-2-containing fluids when added as late as 8 hr prior to termination of a 26-hr culture. 5C3 pretreatment of the IL-2-responsive blast cells was also sufficient to detect significant inhibition of proliferation. FACS analysis of these blasts indicated that maximal 5C3 binding was required for pretreatment to result in inhibition of IL-2-driven proliferation. Delayed addition of 5C3 to culture or pretreatment with 5C3 of responding cells also resulted in inhibition of proliferation of immune T lymphocytes to antigen-pulsed-presenting cells. Lastly, although modulated 5C3- blasts failed to proliferate to IL-2, induction of the 5C3-bearing molecule on these 5C3- blasts correlated with restoration of the ability of these cells to proliferate to IL-2. Collectively, these results further support the hypothesis that monoclonal antibody 5C3 interferes with a critical signal in the IL-2 growth pathway.     

Stimulation of a T helper cell class 2 clone with immobilized anti-T cell receptor antibody activates a Ca2+ and protein kinase C-independent lethal signaling pathway.

Stimulation of an IL-2-dependent variant of the Th2 clone D10.G4.1 with antibodies (Ab) specific for CD3 epsilon or the TCR-alpha beta caused either activation of the clone to secrete the autocrine lymphokine IL-4, or lethal activation in which the cells secreted high quantities of IL-4 but then died within 2 days. High densities of immobilized Ab delivered a lethal signal, whereas soluble forms of Ab and low densities of immobilized Ab caused productive activation in which cell viability was maintained. Lethal activation was not prevented by accessory cells, IL-1, or IL-2, or by co-cross-linkage of CD4 and TCR. The lethal signal was not mediated via a soluble effector from the activated cells. Lethal signaling was insensitive to cyclosporin A or dexamethasone. Studies with activators of protein kinase C (PKC), and PKC inhibitors, indicated that direct activation of PKC was not sufficient for lethal signaling. Nor could direct activation of PKC prevent the lethal signal. The lethal signal was not caused by Ca2+ mobilization mediated by Ca2+ ionophore and there was no evidence of apoptosis. The combination of a PKC activator and Ca2+ ionophore was not lethal, thereby showing that together these events are not sufficient. That these signal pathways were not necessary for lethal activation was evidenced by their inability to lower the density of immobilized anti-CD3 required to cause cell death. In this model, ligation of the TCR specifically activates a Ca2+/PKC-independent lethal signal transduction pathway.     

Ta1, a novel 105 KD human T cell activation antigen defined by a monoclonal antibody

By using a murine monoclonal antibody produced against an IL 2-dependent human T cell line, we defined a T lineage-specific molecule, termed Ta1, that is expressed strongly on activated T lymphocytes of both the T4 and T8 subsets, as well as on T cell lines and clones, but only weakly on a fraction of resting T cells. SDS-PAGE analysis of immunoprecipitates from 125I-labeled, activated T cells demonstrates a single major band of apparent m.w. 105 KD under both reducing and nonreducing conditions. Unlike anti-IL 2 receptor antibodies, anti-Ta1 does not inhibit T cell proliferative responses to mitogen, antigen, or IL 2-containing medium. Moreover, anti-Ta1 has no effect on T cell-mediated cytotoxicity. Ta1 appears to be a novel human T cell-specific activation antigen that may serve as a useful marker of T cell activation in human disease.     

Regulation of influenza virus-specific cytotoxic T cell responses by monoclonal antibody to a human T cell differentiation antigen

The results in this report indicate that the OKT3 monoclonal antibody, which is specific for a human T cell differentiation antigen present on 90 to 95% of peripheral T cells, can exert several effects that regulate the generation and expression of human influenza virus-immune cytotoxic T lymphocytes (CTL). The OKT3 antibody, but not OKT1 or OKT11 (which bind to all peripheral T cells), is able to inhibit anti-influenza CTL effector cell activity. An F(ab')2 preparation of OKT3 IgG were as effective as whole IgG for the inhibition of CTL effectors, indicating that the inhibitory activity of the antibody was not a function of the Fc portion of the molecule. OKT3 IgG and OKT3 F(ab')2 fragments (but not OKT4, OKT8, or OKI were able to inhibit the generation of anti-influenza CTL. The culture of human lymphoid cells with OKT3 in the presence or absence of influenza virus induced radioresistant cells that could suppress the CTL response of fresh autologous lymphocytes to influenza. These results suggest that T cell functions can be regulated by signals that are initiated by the binding of antibody to cell surface molecules that may not be related to the T cell antigen-specific receptor(s).     

Activation of human T lymphocytes via the CD2 antigen results in tyrosine phosphorylation of T cell antigen receptor zeta-chains.

The phosphorylation of the invariant chains associated with the human TCR has been investigated after the stimulation of T lymphocytes with CD2 mAb T11(2) and T11(3), PHA, or phorbol 12,13-dibutyrate. As described previously, stimulation of T cells with either CD2 mAb or phorbol 12,13-dibutyrate resulted in the phosphorylation of the CD3 gamma-chain. The combination of T11(2) and T11(3) mAb also induced phosphorylation of the TCR zeta-chain. The phosphorylated zeta-polypeptide of CD2-activated cells was immunoprecipitated with antiphosphotyrosine antibodies and migrated to a 21- to 23-kDa position during SDS/PAGE. These results indicate that stimulation of human T cells via the CD2 Ag with the T11(2) and T11(3) mAb activates not only protein kinase C but also tyrosine kinase(s), resulting in the phosphorylation of the CD3 gamma-chain and the tyrosine phosphorylation of the zeta-chain, respectively.     

Characterization of a murine monoclonal antibody specific for an allotypic determinant on T cell antigen receptor

Repeated immunization of normal C57L/J (H-2b) mice with peripheral T cells from BALB.B (H-2b) mice results in the production of antibodies which react with the T cell receptor. A monoclonal antibody-producing hybridoma, F23.1, was isolated from immunized C57L/J mice showing this property. This monoclonal antibody recognizes approximately 25% of peripheral T cells in BALB mice. It stains approximately the same fraction of T cells and precipitates the same heterodimer as the rat monoclonal antibody described previously that was made against isolated receptor material. The allotypic determinant recognized by this monoclonal antibody is present in most common laboratory strains (BALB, C57BL, CBA, A, DBA, C3H) and is absent in C57L, C57BR, and SJL mice. Sorting peripheral T cells from BALB.B or (SJL X BALB/c)F1 mice for the F23.1+ and F23.1- subsets revealed that both populations contain approximately the same CTL precursor frequency for alloantigen. Thus, the T cell receptor allotype defined by F23.1 is present on CTL. Furthermore, cytotoxicity mediated by an F23.1+ CTL line could be blocked specifically by the F23.1 monoclonal antibody. Under appropriate conditions, the monoclonal antibody F23.1 bound to Sepharose 4B beads can induce resting peripheral T lymphocytes of allotype-positive strains to proliferate.     

Monocyte-independent interleukin-2 production and proliferation of human T cells in response to murine hybridomas expressing the OKT3 monoclonal antibody: interleukin-1 is not required for T-cell proliferation

We report a new, monocyte-independent system for the induction of activation and proliferation of human T cells in response to murine hybridomas expressing the OKT3 monoclonal antibody (OKT3 hybridomas). Incubation of nylon-wool-nonadherent (NA) lymphocytes or purified T cells with OKT3 hybridomas resulted in interleukin-2 (IL-2) production, expression of IL-2 receptor, modulation of the CD3 antigen, and proliferation. In contrast, murine hybridomas (OKT4, OKT8, anti-HLA-DR, and others) expressing monoclonal antibodies (mAb) other than OKT3 did not induce T-cell activation and proliferation. T cells did not respond to OKT3 mAb alone. OKT3 hybridomas alone did not produce interleukin-1 (IL-1) or other soluble factors that might be involved in the induction of IL-2 production by T cells, and they did not contain membrane-bound IL-1. In addition, IL-1 activity was not detected in cultures of NA-lymphocytes and OKT3 hybridomas, clearly demonstrating that IL-1 was not required, at least in this system, for T-cell activation and proliferation. Direct cell-cell contact between T cells and OKT3 hybridomas was required for IL-2 production. Thirty to fifty percent of T cells formed conjugates with the OKT3 hybridomas but not with the OKT4 or OKT8 hybridomas. Both conjugate formation and IL-2 production were significantly inhibited by the OKT3 mAb and by the anti-LFA-1 mAb. The cells responsible for IL-2 production were found to be of the T3+ T4+ T8- Leu 7- Leu 11- phenotype. IL-2 activity produced by NA-lymphocytes in response to OKT3 hybridomas became detectable as early as 1 hr and reached a maximum by 8 hr, preceding IL-2 receptor expression, modulation of the CD3 antigen, and [3H]thymidine incorporation of T cells. T cells produced higher concentrations of IL-2 in response to OKT3 hybridomas than in response to equal numbers of monocytes and OKT3 mAb. Addition of monocytes to cultures of T cells and OKT3 hybridomas resulted in suppression of IL-2 production in a concentration-dependent manner, suggesting that monocytes regulate the levels of IL-2 production. This monocyte-independent system may be useful for further dissection of T-cell activation and proliferation and its regulation by monocytes.     

Depletion of mouse alpha beta T cell antigen receptor bearing lymphocytes by neonatal monoclonal antibody treatment.

Neonatal treatment with a monoclonal antibody specific for the alpha beta TCR results in mice with a long term, severe depletion in the number of alpha beta T cells in the periphery. Significant numbers of T cells reappear in the periphery about age 65 days, but these cells tend to lack expression of CD4 or CD8. Splenocytes of antibody-treated mice are less sensitive to mitogen stimulation or stimulation with MHC allogeneic cells. The level of serum IgG but not IgM was decreased by the treatment. Anti-alpha beta TCR antibody treatment decreased single-positive T lymphocytes that express high levels of the CD3/alpha beta TCR complex from the thymus, suggesting that the treatment could act in part by affecting negative selection of alpha beta TCR+ thymocytes. This treatment does not, however, detectably affect either the homing or the numbers of gamma delta T cells which are abundant in the intestinal epithelium, but which remain a minor population in the spleen and lymph nodes. This supports the hypothesis that gamma delta T cells are developmentally autonomous from alpha beta T cells. These mice provide an excellent model system for assessing the developmental and functional role of gamma delta T lymphocytes in vivo.     

Tyrosine phosphorylation of the human T cell antigen receptor zeta-chain: activation via CD3 but not CD2

TCR stimulation by Ag or anti-receptor antibodies in murine T cells results in the activation of two independent protein kinases, protein kinase C (PKC) and a protein tyrosine kinase. Similarly, stimulation of murine Thy-1 or Ly-6 with mAb also results in activation of both of these kinase pathways. Tyrosine phosphorylation in all cases occurs on the TCR zeta-chain. It is known that Ag and anti-receptor antibodies activate PKC in human T cells. In this study we demonstrate that mitogen or anti-CD3 antibodies activate tyrosine phosphorylation of the human TCR-zeta-chain. PMA, which activates PKC, does not result in zeta-chain tyrosine phosphorylation. Stimulation of human T cells by antibodies that bind the CD2 molecule is an alternate mode of inducing T cell proliferation. These antibodies surprisingly do not induce tyrosine phosphorylation of the zeta-chain. Thus, different methods of cellular activation can result in distinguishable patterns of receptor-mediated biochemical signaling events.     

Effects of in vivo administration of anti-T3 monoclonal antibody on T cell function in mice. I. Immunosuppression of transplantation responses

Anti-T3 mAb are being increasingly used clinically in the treatment of organ graft rejection. However, there has not previously been a murine model in which the effects of these mAb on the immune system could be studied in vivo. We have established such a model using the anti-murine-T3 mAb, 145-2C11. Administration of 145-2C11 led to rapid depletion of T cells from peripheral blood and suppression of skin graft rejection. However, depletion of T cells from spleen and lymph node was both delayed and incomplete. Full recovery of T cell number was dependent on the presence of a thymus, but treatment of thymectomized animals revealed that depletion was not the mechanism by which the mAb induced immunosuppression. Rather, alterations in TCR expression may play a more important role. TCR had modulated from T cells in spleen and lymph node early after treatment, and TCR expression remained subnormal for at least 51 days posttreatment. However, subnormal TCR expression alone could not fully explain the observed T cell dysfunction, inasmuch as a period of time existed after TCR re-expression during which T cells appeared to be anergic to CTL and MLR reactivity. These findings implicate T cell dysfunction as an important element in the induction of immunosuppression after anti-T3 administration.     

Effects of anti-Lyt-2 and anti-L3T4 monoclonal antibodies on the function of cytotoxic T lymphocyte/helper T lymphocyte hybrid T cell clones

CTL/HTL hybrid clones provide a unique system that allows detailed analysis of the role of Lyt-2, L3T4, and other structures involved in T cell functions. We have demonstrated previously that the fusion of cloned murine CTL and helper T lymphocytes with defined specificity generated hybrid cells that expressed both Lyt-2 and L3T4 as well as two TCR. Data obtained with these hybrid clones demonstrated that cytolysis is closely linked to the CTL TCR. We have analyzed the effects of anti-Lyt-2 and anti-L3T4 as well as anti-TCR mAb on cytolysis, proliferation, and lymphokine release by a number of hybrid clones. We found that anti-Lyt-2 and anti-L3T4 mAb were able to inhibit both proliferation and lymphokine release by the hybrid clones in response to stimulation of either the CTL or helper T lymphocyte parent TCR. In contrast, only anti-Lyt-2 and anti-CTL TCR mAb were able to block cytolysis of target cells bearing the Ag recognized by the CTL TCR. These results provide further evidence that cytolysis is closely linked to the CTL TCR and that Lyt-2 and L3T4 have more than a passive role as accessory molecules on the surface of T lymphocytes.     

The role of three distinct Ia-like antigen molecules in human T cell proliferative responses: effect of monoclonal anti-Ia-like antibodies

Murine monoclonal antibodies (MoAb) to three distinct Ia-like molecules were studied for their inhibitory effects on antigen- and alloantigen-induced T cell proliferations. The MoAb were classified into three groups according to the molecules they recognized. Both the group I MoAb reacting with DR molecules and the group III MoAb were capable of inhibiting T cell proliferative responses to PPD- and HSV-Ag-pulsed APC, autologous B-LCL, and alloantigens. On th other hand, the group II MoAb, which reacted with a determinant on the molecule carrying MB1 determinants, was only capable of inhibiting T cell responses to alloantigens. These results suggest that the structure of the molecules correlates with the functional repertoire of the human Ia-like antigens.