The proliferative response of human T-lymphocyte clones, (TLC) specific for self-major histocompatibility complex (MHC) products either alone or associated with PPD epitopes are inhibited in vitro by dexamethasone (DEX) and by a non-specific inhibitory factor(s) (nsINH) produced by PPD-activated T-cells. The inhibiting effect has been investigated by preincubating autoreactive and PPD-specific TLC with nsINH or DEX. Results obtained indicate that T-lymphocytes are the target of these two immunoregulatory molecules. Moreover, the addition of exogenous recombinant interleukin 2 (rIL-2) substantially reverses the inhibition observed in both nsINH- or DEX-treated cultures.