Studies of an interleukin 1 inhibitor: characterization and clinical significance

Supernatants from 24 h cultures of human peripheral blood mononuclear cells (PBMNC) were fractionated and tested for interleukin (IL-1) activity in the mouse thymocyte assay with phytohaemagglutinin (PHA). By the addition of individual supernatant fractions together with partially purified IL-1 to the thymocyte assay, we demonstrate the presence of strong inhibitory activity with a mol. wt of 5,000-9,000 and an isoelectric point of 4.5-5.6. The activity is both heat (56 degrees C) and acid (pH 1.5) resistant. This inhibitor has no detectable suppressive effect on optimal and suboptimal concanavalin A (Con A), pokeweed mitogen (PWM), and PHA responses of PBMNC. The action of the inhibitor appears to be specifically directed against IL-1 action on thymocytes and has no inhibitory effect on interleukin 2 (IL-2) activity. The findings show that adherent PBMNC produce both IL-1 and a factor which opposes IL-1 action on thymocytes but not on peripheral (mature) T cells. This factor may regulate T cell maturation, activation, and proliferation.