5-AMINOSALICYLIC ACID ABROGATES T-CELL PROLIFERATION BY BLOCKING INTERLEUKIN-2 PRODUCTION IN PERIPHERAL-BLOOD MONONUCLEAR-CELLS

The antiinflammatory agent sulfasalazine (SS) is prescribed to treat C rohn's disease, ulcerative colitis and rheumatoid arthritis. Activated T cells are present within diseased mucosal and synovial sites. We te sted whether SS or its metabolites 5-aminosalicylic acid (5-ASA) and s ulfapyridine (SP) inhibited the T-cell activation products interleukin 2 (IL-2) and interleukin 2 receptor alpha-chain (IL-2R alpha). Experi ments were performed in phytohemaglutinin- and phorbol ester-stimulate d peripheral blood mononuclear cells. Radioactive thymidine and leucin e incorporation assayed DNA and protein synthesis, respectively. Enzym e-linked immunosorbent assay and Northern blot analysis measured IL-2 and IL-2R alpha. Lactate dehydrogenase release determined cell viabili ty, and intracellular free calcium was measured by an indole fluoresce nt indicator. SS and 5-ASA, but not SP, inhibited T-cell proliferation and protein synthesis in phytohemaglutinin- and phorbol ester-stimula ted peripheral blood monomuclear cells. 5-ASA (625 mu M) markedly redu ced culture supernatant IL-2 protein levels by 92% and steady-state IL -2 messenger RNA levels 4.4-fold at 24 and 18 hr, respectively. The su pplementation of IL-2 restored T-cell proliferation only in 5-ASA-trea ted cultures. SS, 5-ASA and SP did not alter intracellular calcium acc umulation after mitogenic stimulation. SS and 5-ASA (625 mu M) caused 71% and 37% cytotoxicity, respectively, in 72-hr cultures. 5-ASA inhib its T-cell proliferation in part by blocking IL-2 messenger RNA accumu lation and protein production downstream of the rise in cytosolic calc ium. Inhibition of IL-2 production is an additional mechanism of actio n for 5-ASA.