Functional and molecular aspects of transient T cell unresponsiveness: role of selective interleukin-2 deficiency.

Defects of T cell (Tc) proliferation have been demonstrated in several autoimmune diseases. Detailed mechanisms governing activation and proliferation of Tc are still not completely known. Here we show that under certain conditions human peripheral blood lymphocytes, once activated by anti-CD3, fail to respond to a subsequent restimulation via the Tc-receptor. Peripheral blood mononuclear cells (PBMC) were preactivated by anti-CD3 for 96 h following restimulation by anti-CD3, interleukin (IL)-2 and other mitogens. In control experiments unstimulated PBMC were incubated in medium alone. Immunophenotypes were analysed by flow cytometry. Cytokine production was determined by reverse transcription-polymerase chain reaction and intracellular signalling protein contents of Tc were compared by Western blotting. Furthermore, apoptosis was detected by terminal deoxyribose transferase-mediated deoxyuridine triphosphate nick end labelling assay. Unstimulated PBMC proliferate well after subsequent stimulation with anti-CD3, whereas IL-2 induces only limited proliferation. In contrast, preactivated cells respond only minimally to restimulation with anti-CD3, but IL-2 induces a marked proliferation. Both preactivated and unstimulated Tc respond well to restimulation by phytohaemagglutinin (PHA). In contrast, preactivated Tc show only a weak response to concanavalin A. Interestingly, when cells have been allowed to rest for 168 h, the responsiveness of preactivated Tc is restored. Immunoblots reveal that preactivated cells have a higher intracellular content of zeta-chain and p56lck. No differences are found concerning apoptosis after restimulation with anti-CD3 or the expression of ERK 1/2. The unresponsiveness to restimulation is due to an impairment of the transcription of the IL-2 gene and this defect is temporary. Despite the lack of proliferation, preactivated Tc phenotypically maintain an intermediate stage of activation. These data show how the same cell population can change its functional phenotype into a non-responder state.