Role of alveolar macrophages in the pathogenesis of idiopathic interstitial pneumonia

Abstract

To clarify role of alveolar macrophages in the pathogenesis of idiopathic interstitial pneumonia (IIP), we studied (1) the localization and expression of monocyte chemoattractant protein-1 (MCP-1) in IIP by immunohistochemistry and in situ hybridization. (2) the role of MCP-1 in macrophage recruitment to be lung, and (3) the clinical usefulness of measuring MCP-1. (1) In IIP, MCP-1 was observed in cuboidal and flattened metaplastic epithelial cells, alveolar macrophages, and vascular endothelial cells. In contrast, no epithelial cells from patients without IIP stained positive for MCP-1, although alveolar macrophages and vascular endothelial cells were labeled. MCP-1 production by epithelial cells in IIP may be caused by the metaplastic nature of the epithelial cells and may be a main cause of the irreversible progression of IIP. (2) MCP-1 levels in bronchoalveolar lavage fluid (BALF) were significantly higher in the IIP, the interstitial pneumonia due to collagen vascular disease (IP-CVD) and sarcoidosis groups than in normal controls. In the IIP group, the MCP-1 level was significantly higher than in any other patient groups. In all three groups of patients, the monocyte chemotactic activity in BALF correlated positively with the MCP-1 levels in BALF, and were neutralized by anti-MCP-1. (3) BALF MCP-1 levels were significantly higher than serum MCP-1 levels in the IIP group, and they were lower in the IP-CVD and non-specific interstitial pneumonia groups. Serum MCP-1 levels reflected the activity of interstitial lung diseases, especially during treatment with corticosteroids. These results indicate (1) that MCP-1 plays a significant role in the recruitment of monocytes into the lung in IIP, (2) that measuring MCP-1 levels both in BALF and in serum may help discriminate IIP from other types of interstitial lung diseases, and (3) that monitoring the serum MCP-1 level may be useful in estimating the activity of interstitial lung diseases.