Monoclonal antibody directed against interleukin 2. I. Inhibition of T lymphocyte mitogenesis and the in vitro differentiation of alloreactive cytolytic T cells.

Our recent studies have detailed the generation of B cell hybridomas whose IgG product significantly inhibits interleukin 2 (IL-2)-dependent T cell replication. Given the capacity of such hybridoma antibody to interfere with the activity of mouse, rat, and human IL-2, we asked whether anti-IL-2 IgG would mediate similar inhibitory effects on other in vitro immune responses. In this communication, we report that addition of purified anti-IL-2 monoclonal antibody to either mitogen- or alloantigen-stimulated spleen cells exerted markedly deleterious effects on both resultant T cell proliferation and the generation of cytolytic effector cells. These results provide serological evidence in support of the integral role that IL-2 plays in controlling antigen/mitogen-induced T cell proliferation and serves further to define the ability of monoclonal antibody against IL-2 to function as an immunosuppressive agent.

On the relation of products of activated lymphocytes to cell-mediated cytolysis.

Experiments have been designed to test the hypothesis that soluble mediator production and T-cell-mediated cytotoxicity are necessarily related phenomena, and that soluble mediators may be involved in the mechanism of cytolysis. To this end, agents known to inhibit T-cell-mediated lysis in vitro have been studied for their effects on the production of two lymphocyte-derived mediators, lymphotoxin (LT) and migration inhibitory factor (MIF). A clear dissociation between mediator production and cell-mediated cytolysis was found using inhibitors of protein synthesis. Pactamycin and emetine, in doses of 10(-7) M to 10(-6) M, suppressed production of MIF and LT with only slight effect on killing of mastocytoma cells by immune T cells. On the other hand colchicine and vinblastine inhibited T-cell-mediated cytolysis in a dose-related manner but had no significant effect on either MIF or LT production, A striking dichotomy was also observed after augmentation of intracellular cyclic 3'5' adenosine monophosphate (cAMP) levels with cholera enterotoxin. Increased cAMP levels were associated with abrogation of direct lytic activity, but were without significant effect on MIF or LT production in guinea pigs or mice. These findings indicate that mediator production and direct lymphocyte-mediated cytolysis can be experimentally dissociated and represent independent cell-mediated immune functions.

Cell-mediated immunity and antibody responses in the respiratory tract after local and systemic immunization.

The cell-mediated immune response on the secretory surface of the lower respiratory tract was investigated and compared to the systemic cell-mediated immune response and to the secretory and systemic antibody responses. Guinea pigs were immunized either parenterally or locally with dinitrophenylated human IgG. The effect of rendering animals tolerant on the local cell-mediated response and on the local antibody response was also studied. The antibody response in the bronchial washing fluids was predominantly of the IgA class. In the animals rendered tolerant by administering large doses of the antigen intravenously, the secretory antibody response was significantly reduced to about 40% of the levels in the animals which were not tolerant. Cellular immunity was assayed using the inhibition of macrophage migration. In animals which were immunized subcutaneously, splenic lymphocytes strongly inhibited the migration of normal guinea pig macrophages; however cells obtained from bronchial washings from the same animals exhibited little or no inhibition of macrophage migration in the presence of antigen. In the animals which were immunized by nose drops, splenic lymphocytes showed virtually no inhibition of macrophage migration; however, bronchial washing lymphocytes strongly inhibited the migration of normal macrophages. Thus, nose drop immunization gave rise to a significantly greater local cellular immune response than did parenteral immunization. In those animals which were immunized by nose drops after a tolerizing dose of antigen, there was virtually no inhibition of macrophage migration by either the cells from the spleens or bronchial washings. Studies were done which demonstrated that a substance similar to macrophage-inhibition factor was liberated by the bronchial washing cells on incubation with the antigen. Studies were also done which indicated that secretory antibody played no role in the inhibition of macrophage migration when bronchial washing lymphocytes were used. Lymphocytes were purified from bronchial washings and were found to inhibit normal macrophage migration in the presence of antigen to the same extent that the mixed population of lymphocytes and pulmonary macrophages did. Thus this study supports the concept that local cellular immunity can be initiated independently of systemic cellular immunity.

Evidence for direct linkage between antigen recognition and lytic expression in effector T cells.

The relationship between antigen recognition and lytic expression by effector T cells was examined by coculturing two cytolytically active lymphoid cell populations. When antigen recognition between the populations could occur only in one direction, then cytotoxicity was expressed only in that direction and the population whose antigens were recognized lost its lytic activity. In contrast, the cocultured effector cell population fully maintained its lytic potential. This lack of reciprocal inactivation was taken as evidence that T-cell receptor accomodation by surface antigen is linked to the expression of cytolytic activity by effector T lymphocytes.

The generation and specificity of cytotoxic T cells raised against syngeneic tumor cells bearing AKR/Gross murine leukemia virus antigens.

Efforts were made to generate C57BL/6 cytotoxic effector cells to a syngeneic leukemia (E{male}G2) bearing AKR/Gross virus antigens. As we were unable to induce significant cytotoxic activity by immunization with up to 10(8) irradiated E{male}G2 cells, even when cells from such primed animals were subsequently restimulated with E{male}G2 cells in vitro, C57BL/6 mice were immunized with an aliogeneic, virus-producing AKR leukemic cell line (AKR SL3). Peritoneal exudate cells and, to a lesser degree, spleen cells from these mice showed significant lytic activity toward the immunizing allogeneic tumor but not toward E{male}G2. When spleen cells were harvested from animals {approximately equal to}10 d after injection of AKR SL3 and rechallenged in vitro with either E{male}G2 or AKR.H-2(b) SL1, another tumor that displays AKR/Gross virus antigens, then a vigorous cytotoxic response against E{male}G2 and AKR. H-2(b) SL1 was obtained. Effector cells generated by AKR SL3 priming followed by in vitro stimulation with E{male}G2 or AKR.H-2(b) SL1 lysed only cells of H-2(b) haplotype which were strongly positive for the display of serologically detectable AKR/Gross virus antigens. Thus, AKR SL3 cells were not lysed nor were EL4 cells (H-2(b); but only weakly positive for gp70). Cells not bearing the MuLV antigens tested for, such as P815 mastocytoma cells and spleen cell "blasts" from C57BL/6 and CBA (H-2(k)) mice, were also insusceptible to attack. The cytotoxic effector cells induced bore Thy 1.2 alloantigen and were of the Lyt 1+2+ phenotype. Collectively, these findings are consistent with the conclusion that the cytotoxic T cells raised against E{male}G2 are directed against AKR/Gross virus-associated antigens and are H-2 restricted. It will be of interest to determine the relevance of such effector cells to the known resistance of the C57BL/6 mouse to AKR/Gross virus-induced leukemia.

Cell-mediated immunity shown by lymphocytes from the respiratory tract.

Cell-mediated immunity, as evidenced by inhibition of macrophage migration in the presence of antigen, was associated with lymphocytes obtained from the respiratory tract of guinea pigs immunized by dinitrophenylated human immunoglobulin G in nose drops, but not from those immunized parenterally. However, splenic lymphocytes from parenterally immunized animals inhibited macrophage migration while those from locally immunized animals did not.

Properties of a subpopulation of T cells bearing histamine receptors.

C57BL/6 mice immunized i.p. with alloantigen (P815 mastocytoma cells) develop cytolytically active thymus-derived (T) splenic lymphocytes. The definition of specific histamine receptor sites on effector T cells has been studied by measuring the in vitro effects of the hormone on cytolytic activity. Histamine was found to inhibit cytolysis reversibly and to increase lymphoid cell cyclic AMP levels. Both of these histamine activities were reversed by burimamide and metiamide; neither activity was affected by diphenhydramine or pyrilamine. These findings indicate that modulation of effector T cell activity by histamine is mediated only by one of the subtypes of tissue histamine receptors, designated a histamine-type 2 receptor. This receptor appears to be present on cytolytically active cells; there is no evidence for activation by histamine of auxiliary or "suppressor" cells. The estimated dissociation constant (KB) for the burimamide-receptor complex (9 times 10-minus 6 tm) and for the metiamide-receptor complex (8 times 10-minus 7 M) indicated that the histamine receptor on T cells is quite similar to histamine-type 2 receptors in other tissues. Cells bearing such receptors could not be isolated by passage through a column of histamine-coated tsepharose beads. The cytolytic activity of spleen cells taken from mice early (days 7-9) after immunization is virtually unaffected by histamine in vitro. In contrast, the activity of spleen cells taken from mice later in the immune response is progressively more susceptible to inhibition by histamine. After reaching a maximum at day 11, the spleen cell cytolytic activity falls in a pattern that parallels the increase in susceptibility to histamine. The susceptibility of effector T cells to histamine appears also to reflect their site of origin, for peritoneal exudate effector cells were found to be significantly less sensitive than spleen cells to inhibition by histamine. The progressive increase in inhibition by histamine apparently reflects the appearance of greater numbers of specific histamine-type 2 receptors, and is probably a general phenomenon, for spleen cells from A/J or C3H mice immunized with either P815 mastocytoma (H-2d) or EL-4 (H-2b) cells showed the same effect. However, the appearance of histamine receptors could be altered by prior immunization with an unrelated alloantigen: thus, when A/J mice are preimmunized with EL-4, a subsequent immunization with mastocytoma cells results in peak spleen anti-H-2d activity at day 9 instead of days 11-13, and the appearance of significant (greater than 40 percent) inhibition by histamine as early as day 8 instead of day 16. The physiological role of the histamine receptors is as yet undefined, though their unexpected rate of appearance on effector T cells, coincident with a decline in the number of lytically active cells in vivo, may be a significant hint that hormone receptors play a role in the control of T-cell proliferation.

In vivo suppression of the immune response to alloantigen by cholera enterotoxin.

The immune response of C57BL/6 mice to allogeneic (DBA/2) mastocytoma cell suspensions was profoundly suppressed by intraperitoneal administration of 1 mug cholera enterotoxin 4 days after antigenic stimulation. The immune response assayed 11 days after antigen showed decreased cytolytically active thymusderived (T) lymphocytes and markedly depressed serumagglutinating titers. A comparable suppression of the immune response to skin allografts (DBA/2-->C57BL/6) was also effected by cholera toxin administration, although there was no prolongation of allograft survival. The mechanism of the immune suppression is apparently related to the known adenylate cyclase stimulatory activities of choleragen.

Effects of cholera toxin on in vitro models of immediate and delayed hypersensitivity. Further evidence for the role of cyclic adenosine 3',5'-monophosphate.

Cholera enterotoxin inhibits the antigen-induced. IgE-mediated release of histamine from human leukocytes and the lysis of allogeneic mastocytoma cells by splenic lymphocytes from specifically immunized mice. This effect requires a prolonged preincubation time of the toxin with the lymphocyte/leukocyte preparations: a demonstrable inhibition requires about 30 min of pre-incubation and the toxin activity is still increasing at 90-180 min. Cholera enterotoxin also stimulates adenyl cyclase and leads to increased levels of cyclic AMP in the lymphocyte/leukocyte preparations. The concentration of toxin required for both cyclic AMP accumulation and inhibition of the biologic responses is about the same (ca. 1 ng/ml), and the time course of cyclic AMP accumulation parallels the development of inhibitory activity. Both activities, inhibition of the in vitro hypersensitivity reactions and cyclic AMP accumulation, are blocked by cholera antitoxin and by a toxoid prepared from the toxin (choleragenoid). These are specific antagonists in that they do not block the inhibiting activity or rise in cyclic AMP levels caused by other adenyl cyclase stimulators. Because cholera enterotoxin has no known activity other than the stimulation of adenyl cyclase and because of its unusual time course and the availability of specific antagonists, this data considerably strengthens the hypothesis that the cyclic AMP system influences the expression of these two forms of hypersensitivity phenomena.

Display of the neutral glycolipid ganglio-n-tetraosylceramide (asialo GM1) on cells of the natural killer and T lineages.

Analysis was made of the display of the neutral glycolipid asialo GM1 on cells involved in the differentiation and expression of natural killer (NK) and T cell-mediated cytotoxicity in vitro. Removal of asialo GM1-bearing cells from CBA spleens, by treatment with a specific rabbit antibody in the presence of complement, led not only to the abrogation of NK cell activity but also to the lack of responsiveness of such populations to polyinosinic: polycytidylic acid (poly I:C) and to interferon, indicating that both NK cells and interferon-responsive cells of the NK cell lineage bear asialo GM1. Cytotoxic T lymphocytes (CTLs) induced by mixed lymphocyte culture in vitro were unaffected by treatment with antiasialo GM1 serum in the presence of complement, but normal spleen cells subjected to this treatment failed to mount CTL responses to alloantigen, even in the presence of an exogenous source of Interleukin-2 (IL-2). Furthermore, spleen cell populations depleted of asialo GM1-bearing cells showed a decreased ability to produce IL-2 in response to mitogenic stimulation.

The treatment of induced immune deficiency with interleukin-2.

In vivo generation of alloreactive cytotoxic T lymphocytes (CTL) was found to be inhibited by treatment of mice with either cyclophosphamide or the glucocorticoid, hydrocortisone acetate. The effects of these immunosuppressive agents could be overcome, however, by the in vivo administration of IL-2 from both murine and human sources. Both human IL-2 derived by recombinant DNA techniques as well as the natural protein from mouse and man all reverse the unresponsive state. A single injection of IL-2 was sufficient to reverse the effect of cyclophosphamide treatment, while additional injections with as little as 8 micrograms of protein ablated the steroid-induced suppression. Furthermore, the responder cells generated in vivo following IL-2 therapy were shown to be antigen specific in terms of their lytic capacity. Thus, IL-2 therapy appears to restore the in vivo responsiveness of immunosuppressed recipients to allogeneic tumor cell challenge. These data demonstrate the importance of IL-2 as an immunoregulatory molecule in vivo and suggest its future use as a potent therapeutic.