Persistent CD3-crosslinking down-regulates interleukin-2 responsiveness in interleukin-2-competent cloned T cells: the possible involvement of protein kinase C.

To investigate the regulation of interleukin-2 (IL-2) responsiveness of T cells, a human CD4+ T-cell clone with constitutive expression of IL-2 receptors was stimulated with recombinant IL-2 (rIL-2) in the presence or absence of immobilized anti-CD3 monoclonal antibodies (alpha CD3imm MoAb). Incubation of T cells with alpha CD3imm MoAb decreased IL-2-induced proliferation which could not be ascribed to the modulation of IL-2 receptor expression nor to cell death. Phorbol-myristate-acetate (PMA), an activator of protein kinase C (PKC), also induced down-regulation of IL-2 responsiveness. The alpha CD3sol MoAb, inducing Ca(2+)-mobilization without activating PKC, did not inhibit IL-2 responsiveness whereas cyclosporine A (CsA), a drug that inhibits the Ca(2+)-dependent activation pathway, did not prevent the induction of IL-2 hyporesponsiveness induced by alpha CD3imm MoAb. It is concluded that modulation of IL-2 responsiveness of T cells via the T-cell receptor/CD3 complex (TCR/CD3) may be mediated by a PKC-activating signal.