Inhibitor of interleukin 1 in normal human urine. Different effects on mouse thymocytes and on a murine T-cell line.

We investigated whether urine from normal individuals contains inhibitors of interleukin 1 (IL-1). Diafiltered urine from normal afebrile donors suppressed IL-1-induced interleukin 2 (IL-2) activity of mouse thymocyte supernatants. These supernatants, however, strongly suppressed IL-2-induced [3H]thymidine incorporation into the IL-2-sensitive cell line CTLL-2, whereas the urine preparations did not. This phenomenon was caused by an increased amount of thymidine secreted by the urine-treated thymocytes. Therefore, in order to prevent interference, experiments were carried out with excess [3H]thymidine. Under these circumstances, suppression of IL-1- and to a lesser extent IL-2-induced DNA synthesis was still observed, whereas the synergistic effect of IL-1 on IL-2-induced DNA synthesis was only marginally reduced. We conclude that suppression of IL-1-induced IL-2 production by mouse thymocytes is a major effect of the IL-1-inhibitory factor(s) in normal urine. When the murine EL4 cell line was used, the diafiltered urine failed to inhibit IL-1-induced IL-2 production. The detection of an IL-1 inhibitor in urine is therefore dependent on the target cells as well as the effects of IL-1 on these cells.