Cloned helper T lymphocytes exposed to interleukin 2 become unresponsive to antigen and concanavalin A but not to calcium ionophore and phorbol ester

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Abstract
Two cloned murine helper T lymphocyte (HTL) lines were used to investigate the immunoregulatory properties of highly purified interleukin 2 (IL2). The clone, designated J6.19, secretes lymphokines, including IL2, and proliferates when stimulated with ovalbumin in the presence of I-Ak-bearing spleen cells, while the alloreactive clone, L2, secretes lymphokines, including IL2, and proliferates when stimulated with Mlsa,d-bearing spleen cells. When either clone was exposed to a high concentration of pure IL2 for 1 to 2 days in the absence of either antigen or spleen cells, the HTL became unresponsive to rechallenge with antigen. Unresponsiveness to antigen was indicated by an inability of HTL to proliferate or secrete usual amounts of IL 2 or colony-stimulating factor. Within 5–7 days after exposure to IL2, the cloned HTL again responded to antigen. Thus, in addition to being a growth factor for HTL, IL2 can limit the magnitude of the HTL response to antigen. L2 or J6.19 cells could also be induced to secrete lymphokines by the lectin, concanavalin A (Con A) or by a combination of the calcium ionophore, A23187, and phorbol myristate acetate (PMA). After exposure of L2 or J6.19 cells to sufficient IL2 to induce unresponsiveness to antigen, cells were also unresponsive to Con A, as indicated by a reduction in the level of lymphokines secreted. In contrast, lymphokine levels stimulated by A23187/PMA were comparable to those produced by cells not exposed to IL2. The failure of antigen to stimulate lymphokine release and proliferation by HTL previously exposed to IL2 therefore may result from an inability of HTL to recognize antigen or to transduce effectively the antigen recognition signal. Several T cell surface molecules are known to be involved in antigen activation of HTL; these include the antigen receptor and the “associative recognition” structures L3T4 and LFA-1. We observed that L2 cells, rendered unresponsive to antigen by exposure to IL2, expressed normal levels of antigen receptor, as identified by the monoclonal antibody, KJ16–133.18. Furthermore, expression of L3T4 and LFA-1 was not decreased. Unresponsiveness to antigen induced by IL2 thus could not be correlated with decreases in the expression of antigen receptors, L3T4, or LFA-1. Unresponsive HTL may therefore be capable of recognizing antigen but the signal generated by antigen binding may be attenuated during its transduction, resulting in the failure of cloned HTL to proliferate or secrete lymphokines at the usual levels.