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 inflammatory cells at die site of tissue injury. Mononuclear phagocytes (MO) represent key cellular mediators of inflammation via the production of regulatory and chemokinetic cytokines. One such cytokine, macrophage inflammatory protein-1alpha (MIP-1alpha), has been shown to be one of the major inducible chemotaxins expressed from murine macrophage cell lines (RAW 264.7). We postulated that MIP-1alpha is a major monocyte chemoattractant produced by resident MO, and the magnitude of production of this chemotaxin may depend upon die specific population of MO studied. To test this hypothesis, we isolated alveolar macrophages (AMO) and peritoneal macrophages (PMO) from CD-1 mice by bronchoalveolar and peritoneal lavage, respectively. Recombinant murine MIP-1alpha accounted for significant neutrophil chemokinetic rather than chemotactic activity, as assessed by checkerboard analysis. LPS-stimulated AMO-derived monocyte chemotactic activity (MCA) was significantly neutralized by specific rabbit anti-murine MIP-1alpha serum. In contrast, PMO-derived conditioned media failed to produce MCA attributable to MIP-1alpha. The production of MIP-1alpha was then characterized from both AMO and PMO. While unstimulated AMO and PMO failed to express MIP-1alpha mRNA, both AMO and PMO challenged with lipopolysaccharide (LPS) expressed MIP-1alpha mRNA in a time-dependent fashion. However, significant disparity in the secretion of MIP-1alpha protein was noted between the 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 LPS-stimulated PMO, as compared with AMO, reflect both impairment in MIP-1alpha protein translation and secretion. The expression of MIP-1alpha from AMO and PMO appears to be regulated by both prostaglandin E2 (PGE2) and dexamethasone (Dex), as these immunomodulators reduced MIP-1alpha mRNA and protein expression in a dose-dependent fashion. PGE2(10(-6) M) and Dex (10(-6) M) maximally inhibited the production of LPS-challenged AMO-derived MIP-1alpha protein by 43.6 +/- 12.5% and 52.5 +/- 9.2%, respectively. In summary, our findings support the premise that MO isolated from different tissue compartments have disparity in the production of MIP-1alpha, and that this chemotactic factor exerts significant 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 as MIP-1alpha.