AbstractThe migration of polymorphonuclear leukocytes (PMN) in response to recombinant interleukin‐1 (IL‐1), tumor necrosis factor‐alpha (TNF), C5a, and f‐met‐leu‐phe‐lys (FMLPL) in vivo was studied using a mouse subcutaneous sponge implantation model. In this model sponges were implanted in C3H/OUJ mice, and 2 days later they were injected with the test sample. After varying times, sponges were removed and digested with collagenase, and total cell counts and differentials were enumerated. IL‐1 was found to stimulate a significant influx of PMN, which peaked at 6 hr and declined to near baseline levels by 24 hr. This response was dose‐dependent, with the greatest response observed when 5 units of IL‐1 were injected. When the IL‐1 concentration was increased to 10 U, the total number of PMN migrating into the sponge was decreased, compared with that observed with 5 U of IL‐1. The overall number of PMN migrating into the sponge 6 hr after injecting 5 U of IL‐1 averaged 269% of the number of PMN migrating randomly into the sponge. No difference in the total number of macrophages or lymphocytes in control or IL‐1‐injected sponges was observed in this time frame. Heat treatment of the IL‐1 at 90°C for 30 min ablated the response. Similar studies with TNF and C5a showed that both of these agents also stimulated an influx of PMN that peaked 6 hr postinjection. In contrast, FMLPL did not stimulate a PMN response. When IL‐1 and TNF were injected simultaneously, an additive response was observed. These data indicate that IL‐1, TNF, and C5a can all stimulate a PMN response in vivo and support the hypothesis that these substances are actively involved in the mobilization of PMN to inflammatory sites in vivo.