Antigen-reactive cloned helper T cells. II. Exposure of murine cloned helper T cells to IL 2-containing supernatant induces unresponsiveness to antigenic restimulation and inhibits lymphokine production after antigenic stimulation

Cloned murine helper T lymphocytes (HTL) reactive to alloantigen or to ovalbumin (OVA) become unresponsive to antigenic restimulation after exposure to antigen or to culture supernatant fluids (SF) containing multiple lymphokine activities. Unresponsiveness is manifest by a failure of antigen-stimulated cells to incorporate thymidine or to produce lymphokines after antigenic challenge. Antigen-unresponsive HTL, however, will incorporate thymidine when exposed to an exogenous source of interleukin 2 (IL 2). The duration of unresponsiveness to antigen is correlated with the concentration of IL 2 in SF to which the cloned HTL had been exposed. Chromatographic fractionation of IL 2-containing supernatant from EL-4 thymoma cells (EL-4 SF) yielded a pool of SF that was enriched for IL 2 activity. Exposure of HTL to lymphokines contained in this pool induced unresponsiveness to antigen that was comparable to that observed when HTL were exposed to unfractionated EL-4 SF. Unresponsiveness to antigen also developed after cloned HTL were stimulated with concanavalin A (Con A) or with OVA and syngeneic splenic filler cells. We have used monoclonal antibody (mAb) GK1.5 (anti-L3T4) to investigate the role of lymphokine production in the induction of unresponsiveness. This antibody did not inhibit IL 2-induced thymidine incorporation by cloned HTL, and did not inhibit the induction of unresponsiveness after exposure of cloned HTL to EL-4 SF. In the presence of mAb GK1.5, however, HTL that were stimulated with Con A or OVA did not become unresponsive to antigenic restimulation, an effect that was overcome by the addition of EL-4 SF. These results suggest that HTL become unresponsive to antigen after exposure to IL 2-containing SF, and that stimulation by antigen or Con A can induce the unresponsive state by virtue of stimulating lymphokine production.