MCP-1 secretion in lung from nonsmoking patients with coal worker's pneumoconiosis

Exposure to coal dust leads to the development of coal worker's pneumoconiosis (CWP), a disease associated with an accumulation of macrophages in the lower respiratory tract. Mechanisms controlling monocyte recruitment are still poorly understood. Since monocyte chemoattractant protein-1 (MCP-1) is recognized as a potent chemotactic factor for blood monocytes, we analysed the presence of MCP-1 in the pulmonary compartment of patients with CWP. Bronchoalveolar lavage fluid (BALF) from 16 nonsmoking control subjects and 27 nonsmoking CWP patients (16 with simple pneumoconiosis (SP) and 11 with progressive massive fibrosis (PMF)) was analysed. Alveolar macrophages (AMs) were purified by adherence and BALF was concentrated tenfold by lyophilization. MCP-1 was measured in BALF and in 3 h AM supernatants using a sandwich enzyme-linked immunosorbent assay (ELISA). The localization of MCP-1 in lung tissue was determined by immunohistochemistry on tissue sections from three patients with CWP and two control subjects. MCP-1 levels were significantly higher in concentrated BALF from patients with SP or PMF (median 370 and 555 pg x mL-1, respectively) than in those from control subjects (median 11 pg x mL-1) (p<0.001). Released MCP-1 in AM supernatants was enhanced in patients with CWP (median 83 pg x mL-1) but compared to controls (median 41 pg x mL-1) this level did not reach significance. Although significantly increased, AM counts in BALF from patients with CWP did not correlate with MCP-1 levels. MCP-1 levels in BALF correlated with MCP-1 levels in AM supernatants (p=0.47; p<0.02). In control lung specimens, MCP-1 was expressed by a few AMs, type II pneumocytes and perivascular smooth muscle cells. CWP sections were characterized by an increased number of AMs and mainly by the presence of fibroblasts (in the myogenic area of fibrotic lesions) and hyperplastic type II pneumocytes, which were strongly immunostained for MCP-1. Our data demonstrate that: 1) patients with coal worker's pneumoconiosis have a marked pulmonary overproduction of monocyte chemoattractant protein-1; and 2) in addition to alveolar macrophages, fibroblasts (probably myofibroblasts) and hyperplastic type II pneumocytes may also be responsible for this increased level of monocyte chemoattractant protein-1 in coal worker's pneumoconiosis.