Idiopathic pulmonary fibrosis is an immunologically mediated pulmonary disorder in which activated alveolar macrophages (AM) and neutrophils play cardinal roles in the pathogenesis of the inflammatory lung lesion. The factors responsible for the induction and perpetuation of the neutrophilic alveolitis are not known. Recently, a novel cytokine (Interleukin-8) was described that is released by activated mononuclear phagocytes and a variety of other cell types, and it exhibits potent chemotactic activity for polymorphonuclear leukocytes (PMN). Increased expression of IL-8 has been described in other inflammatory disorders characterized by neutrophilic infiltration, including psoriasis, rheumatoid arthritis, and the sepsis syndrome, but no studies have assessed this cytokine in the context of interstitial pulmonary disorders. We have previously shown that normal human AM release IL-8 upon appropriate stimulation, but data assessing the expression of IL-8 by human AM in specific pulmonary disease states are lacking. In this study, we examined the expression of steady-state mRNA for IL-8 by human alveolar macrophages obtained by bronchoalveolar lavage (BAL) from patients with idiopathic pulmonary fibrosis (IPF) or sarcoidosis and from healthy volunteers. Because it is known that adherence to plastic culture plates may up-regulate gene expression for IL-8 in the absence of additional stimulation, we extracted mRNA immediately from the cell pellet obtained by BAL rather than using cultured alveolar macrophage monolayers. Northern blot analysis was performed to determine IL-8 mRNA expression. We found that BAL cells from patients with IPF constitutively expressed mRNA for IL-8, and the amount of IL-8 mRNA (as assessed by laser densitometry) correlated with the percent of neutrophils on BAL.(ABSTRACT TRUNCATED AT 250 WORDS)