INHIBITION OF INTERLEUKIN-2 PRODUCTION AND ALTERATION OF INTERLEUKIN-2 MESSENGER-RNA PROCESSING BY HUMAN T-T CELL HYBRIDOMA-DERIVED SUPPRESSOR FACTORS

We investigated the mechanisms by which two human T-T cell hybridoma-d erived suppressor factors (SFs) (designated 160 and 169) (Platsoucas e t al., Hybridoma 1987;6:589; Kunicka et al., Hybridoma 1989;8:127) inh ibit the proliferative response to mitogens by human peripheral blood mononuclear cells (PBMCs). Interleukin 2 (IL-2) production by human PB MCs cultured with concanavalin A or OKT3 monoclonal antibody for 12 or 36 hr in the presence of 160 or 169 SF was found to be inhibited >80% when compared to control PBMC cultures stimulated with mitogen in the absence of SFs. This suppression of IL-2 production was not due to th e SFs interfering with IL-2-induced proliferation of the IL-2-dependen t murine cell clone used to determine the levels of IL-2. The prolifer ative responses of SF-treated PBMCs could not be restored by addition of exogenous recombinant human IL-2 (rIL-2) (1-100 U/ml). Furthermore, inhibition of the proliferative responses by the SFs could not be rev ersed by addition of exogenous rIL-1, rIL-2, or rIL-4 alone or in pair ed combinations. The expression of IL-2 receptors (TAC Ag) on concanav alin A-activated cultures at 12- or 36-hr time points was not affected by treatment with the SFs. Both the 160 and 169 hybridoma-derived SFs were found to cause the accumulation of an mRNA of 2.8 kb that hybrid ized with an IL-2-specific oligonucleotide probe. This 2.8-kb transcri pt was in addition to the expected 1.0-kb, transiently expressed IL-2 message, and it could be superinduced in the presence of cycloheximide . These results suggest that these SFs may be influencing RNA splicing pathways. These SFs appear to be useful molecules for probing the reg ulatory controls of lymphocyte proliferation and may constitute import ant physiological regulators of the immune response. In addition, they may have clinical activity for the treatment of patients that receive d transplants, patients with autoimmune diseases, and others.