EXPRESSION AND REGULATION OF MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA BY MURINE ALVEOLAR AND PERITONEAL-MACROPHAGES

A number of disease states are characterized by the accumulation of in flammatory cells at die site of tissue injury. Mononuclear phagocytes (MO) represent key cellular mediators of inflammation via the producti on of regulatory and chemokinetic cytokines. One such cytokine, macrop hage inflammatory protein-1alpha (MIP-1alpha), has been shown to be on e of the major inducible chemotaxins expressed from murine macrophage cell lines (RAW 264.7). We postulated that MIP-1alpha is a major monoc yte chemoattractant produced by resident MO, and the magnitude of prod uction of this chemotaxin may depend upon die specific population of M O studied. To test this hypothesis, we isolated alveolar macrophages ( AMO) and peritoneal macrophages (PMO) from CD-1 mice by bronchoalveola r and peritoneal lavage, respectively. Recombinant murine MIP-1alpha a ccounted for significant neutrophil chemokinetic rather than chemotact ic activity, as assessed by checkerboard analysis. LPS-stimulated AMO- derived monocyte chemotactic activity (MCA) was significantly neutrali zed by specific rabbit anti-murine MIP-1alpha serum. In contrast, PMO- derived conditioned media failed to produce MCA attributable to MIP-1a lpha. The production of MIP-1alpha was then characterized from both AM O and PMO. While unstimulated AMO and PMO failed to express MIP-1alpha mRNA, both AMO and PMO challenged with lipopolysaccharide (LPS) expre ssed MIP-1alpha mRNA in a time-dependent fashion. However, significant disparity in the secretion of MIP-1alpha protein was noted between th e two MO populations, as AMO secreted 47-fold more MIP-1alpha than did an equivalent number of PMO as determined by specific ELISA. Analysis of cell lysates suggests that the reduced levels of MIP-1alpha from L PS-stimulated PMO, as compared with AMO, reflect both impairment in MI P-1alpha protein translation and secretion. The expression of MIP-1alp ha from AMO and PMO appears to be regulated by both prostaglandin E2 ( PGE2) and dexamethasone (Dex), as these immunomodulators reduced MIP-1 alpha mRNA and protein expression in a dose-dependent fashion. PGE2(10 (-6) M) and Dex (10(-6) M) maximally inhibited the production of LPS-c hallenged AMO-derived MIP-1alpha protein by 43.6 +/- 12.5% and 52.5 +/ - 9.2%, respectively. In summary, our findings support the premise tha t MO isolated from different tissue compartments have disparity in the production of MIP-1alpha, and that this chemotactic factor exerts sig nificant neutrophil chemokinetic and monocyte chemotactic bioactivity. Furthermore, the in vivo anti-inflammatory properties of PGE2 and Dex may be due, in part, to the regulation of MO-derived cytokines such a s MIP-1alpha.