Stimulatory and inhibitory soluble mediators produced by stimulated lymphocytes and tested in human and murine in vitro systems.

The cellular origin and target specificity of two types of soluble mediators viz., the inhibitor of DNA synthesis (IDS) and the stimulator of DNA synthesis (SDS) have been studied. These mediators were produced by human and murine lymphocytes derived from different organs and stimulated by different mitogens, viz. phytohaemagglutinin (PHA-P), concanavalin A (Con A) and lipopolysaccharide (LPS). Their target effect was quantitated by assessing the 3H-thymidine incorporation of murine and human lymphocytes stimulated by different T and B cell mitogens (Con A, PHA and LPS). IDS activity was detected in supernatants of PHA stimulated lymphocytes originated from immunologically hyporeactive patients (tumor-bearing patients, pregnant women) in contrast to majority of control patients. Marked "SDS" activity was produced by normal lymphocytes as tested in human and murine lymphocytes stimulated by Con A or PHA, while IDS activity was detected if the target cells were stimulated by LPS. The effects of "SDS" failed to show species specificity using human and murine test-systems.