ABSTRACT
Fibronectin is a high-molecular-weight opsonic protein known to influence macrophage uptake of nonbacterial particulate matter. The concentration of fibronectin in serum and the quantity of fibronectin in the inflamed peritoneal space were examined in rats after intraperitoneal casein injection. Fibronectin levels were studied in relation to the opsonic activity of the serum, as assayed by the uptake of gelatin-coated. 51Cr-labeled, fixed sheep erythrocytes by adherent peritoneal macrophage monolayers. Intraperitoneal inflammation resulted in a marked increase in peritoneal fluid fibronectin that lasted throughout a 4-day observation period. The opsonic activity of serum also increased after casein challenge at 24, 48, and 72 h. The elevation in the level of fibronectin in the peritoneal space appeared to coincide with or closely precede the maximal increase in concentration of inflammatory peritoneal macrophages. After casein injection, when serum immunoreactive fibronectin increased, an enhancement in phagocytic clearance of blood-borne gelatin-coated test particles was also observed. It is suggested that the elevation of fibronectin in blood during intraperitoneal inflammation may mediate enhanced liver phagocytic function. The increased amount of fibronectin in the inflamed peritoneal space may also influence the phagocytic activity of peritoneal macrophages.
