Plasma fibronectin therapy and lung protein clearance with bacteremia after surgery

Plasma fibronectin modulates macrophage phagocytic function and can also incorporate into the insoluble tissue pool of fibronectin where it influences endothelial cell adhesion and tissue integrity. We studied the effect of postoperative bacteremia on lung protein clearance in relation to plasma fibronectin levels using the unanesthetized sheep lung lymph fistula model and the effect of infusion of purified human plasma fibronectin on lung protein clearance. Sheep received live Pseudomonas aeruginosa (5 X 10(8) iv) at a time of normal plasma fibronectin (590 +/- 37 micrograms/ml) or 5 days later at a time corresponding to elevation of plasma fibronectin (921 +/- 114 micrograms/ml). After the first bacterial challenge, there was a 22% decrease (P less than 0.05) in plasma fibronectin. Lung lymph flow (QL) initially increased 308% (P less than 0.05) by 2 h (0 h = 4.7 +/- 1.1 ml/h; 2 h = 14.4 +/- 3.5 ml/h), and the total protein lymph-to-plasma concentration ratio (L/P) declined. This was followed by a sustained second phase response over 3-12 h which was characterized by a 202-393% elevation in QL (P less than 0.05), an increase in the L/P ratio, and a 240-480% (P less than 0.05) increase in lung transvascular protein clearance (TVPC = QL X L/P). Sheep with elevated fibronectin levels also manifested the early (2 h) elevation in QL (P less than 0.05) coupled with a decline in L/P ratio after the second bacterial challenge, but the second-phase increase in TVPC was markedly attenuated. Intravenous infusion of 500 mg of human plasma fibronectin into normal sheep to elevate the fibronectin level comparable to that in the hyperfibronectinemic sheep also attenuated (P less than 0.05) the second-phase (3-12 h) increase in lung protein clearance with sepsis. Thus elevation of plasma fibronectin during postoperative Gram-negative bacteremia may protect the lung vascular barrier. This response may be mediated by either fibronectin's opsonic support of phagocytic function or its influence on lung endothelial cell adhesion.