Fluorescent opsonization assay: binding of plasma fibronectin to fibrin-derivatized fluorescent particles does not enhance their uptake by macrophages.

A simple method for assessing the opsonic properties of plasma fibronectin is described. The method is based on the uptake of protein-derivatized fluorescent particles by mouse peritoneal macrophages. With this system, fibronectin stimulated the uptake of gelatin conjugated to carboxylated fluorescent particles. In contrast to the gelatinized particles, neither the covalent nor noncovalent interaction of fibronectin with fibrin particles stimulated their uptake by macrophages. These results provide additional evidence that fibronectin is not a conventional opsonin and that enhanced phagocytosis is not an obligatory response by macrophages to fibronectin-coated particles.