The objective of this study was 1) to investigate the in vivo production of IL-8 in patients undergoing IL-2 immunotherapy and 2) to study the influence of IL-1Ra, soluble TNF receptor p75 (TNFsRp75), and a TNFsRp75-Fc fusion protein on IL-2-induced IL-8 production in vitro. Circulating IL-8 was assessed both in plasma and erythrocyte lysates prepared from patients undergoing IL-2 immunotherapy. IL-8 was detectable in the plasma within 2-4 h after the first IL-2 infusion, reached a peak level after 4 h, and declined rapidly to undetectable within 8 h. Erythrocyte-bound IL-8 was also detected within 4 h of the first IL-2 dose, but levels were higher than those measured in plasma and remained elevated long after the plasma levels had become undetectable. On day 4 of therapy, the increases in both plasma and the erythrocyte-lysate IL-8 levels induced by an IL-2 injection were less pronounced than on day 1. Although IL-1Ra and TNFsRp75-Fc individually had only a modest suppressive effect on IL-2-induced IL-8 production by PBMC in vitro, the combination of IL-1Ra and TNFsRp75-Fc markedly down-regulated IL-2-induced IL-8 synthesis and steady-state mRNA levels. TNFsRp75 had no effect on IL-2-induced IL-8 synthesis. Our studies suggest that the transient detection of IL-8 in plasma early in the course of IL-2 treatment is due to erythrocyte sequestration and that suppressed synthesis, due in part to high levels of circulating IL-1 and TNF antagonists, may play a role later in the course of treatment.