[Fibronectin: an important component of bronchoalveolar defense?].

Fibronectin, an important nonimmune opsonin, was found in the bronchoalveolar lavage fluid (BAL) of 29 healthy volunteers using a sensitive radioimmunoassay. The mean FN content was 9.5 micrograms FN/mg albumin. The BAL FN was immunologically and functionally similar to plasma FN and showed opsonic activity which increased uptake of gelatin coated beads by human alveolar macrophages. Therefore, BAL contains a functionally intact FN which may serve as an opsonin for the clearance of particles and microorganisms in the terminal airways.