Inhibition of DNA synthesis in human peripheral and lamina propria lymphocytes by 5-aminosalicylic acid and hydrocortisone.

5-Aminosalicylic acid (5-ASA) and hydrocortisone (HC) have potent antiinflammatory activity, and are commonly used in the treatment of patients with inflammatory bowel disease. Both agents have been reported to modulate immune function in human and animal models. We investigated the effect of 5-ASA and HC on cell proliferation of normal human peripheral blood lymphocytes (PBL) and normal colonic lamina propria lymphocytes (LPL). Both 5-ASA (0.01-4 mM) and HC (0.01-10 microM) significantly inhibited 3H-thymidine incorporation (Thd) into PBL and LPL in a dose dependent manner. Maximal inhibition occurred with the highest concentration tested of both 5-ASA and HC. We found a significantly greater inhibition of DNA synthesis for 5-ASA (4 mM) upon LPL vs. PBL (94 vs. 32%, p less than 0.001). However, DNA synthesis inhibition by HC was similar in PBL and LPL. The profoundly greater inhibitory effect of 5-ASA upon LPL suggests a specific modulation of the mucosal immune system.