Rabbit alveolar macrophages stimulated with endotoxin and lung fragments from endotoxemic rabbits produce a leukocyte infiltration-inducing factor that lacks IL-1, TNFα or chemotactic activity

We reported previously that rabbit pleural and peritoneal macrophages (Møs) and human Mø stimulated with endotoxin (LPS) release a protein factor of 45 to 60 kd that induces local polymorphonuclear leukocyte (PMNL) infiltration upon intradermal injection in rabbits. In the case of the human Mø product, it was shown to be distinct from interleukin-1 (IL-1), tumor necrosis factors (TNFα granulocyte macrophage colony stimulating factor (GMCSF), IL-6, and lower molecular weight PMNL chemotactic factors. Here, we examined resident rabbit alveolar Mø to determine if they produce a similar factor following in vitro or in vivo exposure to LPS. Following LPS exposure (0.3 to 30 ng/ml), alveolar Møs obtained from normal rabbits by bronchoalveolar lavage released PMNL recruiting activity within 3 h, as measured by the accumulation of ⁵¹Cr labeled blood PMNL at injected skin sites. Production of this activity was blocked by cycloheximide; it was heat labile and not affected by polymyxin B, which neutralized the LPS. On gel filtration chromatography, a major peak of activity was eluted at 45 to 60 kd and was free of IL-1 but partially overlapped with rabbit TNFα Although active in vivo in PMNL recruitment into the tissues, these fractions did not induce PMNL migration in vitro in a filter chemotaxis assay. After sodium dodecyl sulfate (SDS), polyacrylamide gel electrophoresis (PAGE) the predominant PMNL recruiting factor (PRF) eluted from gel slices corresponded to 22 to 32 kd, suggesting that this protein is a dimer under gel filtration conditions. These gel eluates did not contain TNFα activity. Following iv administration of sublethal doses of LPS (3 μg/kg) or of antibiotic killed Escherichi coli (10⁹/kg), peripheral lung fragments from perfused lungs spontaneously produced this PRF during ex vivo culture without further LPS stimulation. Lung tissue from normal rabbits did not release PRF spontaneously. We conclude that resident alveolar Møs produce a PRF protein in response to LPS that is distinct from IL-1, TNFα and chemotactic factors and that the production of a similar protein by lung cells (probably Møs) is probably induced in vivo during endotoxemia or bacteremia. This factor may contribute to PMNL accumulation in the lung during pathologic processes.