Endotoxin-stimulated human macrophages produce a factor that induces polymorphonuclear leucocyte infiltration and is distinct from interleukin-1, tumour necrosis factor alpha and chemotactic factors.

Previously we reported that rabbit macrophages (M phi) in the presence of nanogram quantities of endotoxin (LPS) release factors that induce polymorphonuclear leucocyte (PMNL) infiltration into the skin of rabbits following i.d. injection. The predominant factor was a de novo synthesized protein of 45,000 MW on gel filtration that was distinguishable from IL-1 but not from TNF alpha. Here we examined human monocytes, in vitro monocyte-derived M phi and peritoneal M phi for the production of an analogous protein. Upon stimulation with LPS, they all rapidly (6 hr) produced a factor(s) that caused PMNL accumulation in the skin of rabbits when injected i.d. This activity, referred to as PMNL-recruiting activity (PRA), was heat labile and its production was blocked by cycloheximide. By Sephadex-G100 chromatography the major PRA of cultured M phi or peritoneal M phi had a molecular weight (MW) of 45,000-60,000. The active fractions were free of IL-1 (less than 0.2 U/ml) and Superose-12 FPLC chromatography separated the peak of PRA, which eluted at 45,000 MW, from TNF alpha, eluting at 20,000 MW. The peak PRA was not neutralized by antisera to IL-1 alpha, IL-1 beta, TNF alpha, IL-6 or GM-CSF, indicating that it was distinct from these cytokines. The major PRA did not induce the migration of PMNL in vitro in a filter chemotaxis assay. In contrast to the M phi, the major PRA produced by LPS-stimulated monocytes eluted at 15,000-20,000 MW, contained IL-1 activity and was neutralized by antisera to IL-1 alpha and IL-1 beta. Monocytes from a few donors also produced the 45,000-60,000 MW PRA simultaneously. We conclude that human peritoneal M phi and in vitro monocyte-derived M phi exposed to LPS secrete a protein of 45,000-60,000 MW, which is a potent inducer of PMNL infiltration but is distinct from IL-1, TNF alpha, IL-6, GM-CSF and PMNL chemotactic factors.