Opsonins are critical for phagocytosis of particulate material and microorganisms by pulmonary alveolar macrophages (PAM) in the terminal airways. The opsonic protein fibronectin (FN) is a 440,000 mol wt glycoprotein mediating clearance of gelatin-coated particles from blood by reticuloendothelial cells. Increasing evidence suggests that specific cell-membrane receptors for FN mediate these interactions. Because of its potential importance as a nonimmune opsonin for PAM in the bronchoalveolar space, we studied the following: 1) the FN content in bronchoalveolar lavage (BAL) fluid; 2) whether PAM are a possible source of BAL-FN, and 3) if endogenous PAM-FN serves as an opsonin for particles with known FN-binding properties. (1) FN is present in BAL fluid of healthy humans; (2) mean FN levels in BAL fluid are significantly higher in smokers than in nonsmokers; (3) PAM are a likely source of FN in BAL fluid; (4) FN is not a membrane-bound receptor in PAM, but appears at the cell-membrane binding sites for gelatin-coated particles. Taken together, these findings suggest that PAM-FN may serve as a specific endogenous opsonin for uptake of denatured collagen, fibrin, or staphylococci in the lower respiratory tract of humans.
|Number of pages||3|
|Issue number||5 Suppl.|
|State||Published - Jan 1 1982|