Tissue debris at the injury site is coated by plasma fibronectin and subsequently removed by tissue macrophages.

Fibronectin (Fn) is a normal plasma and extracellular matrix glycoprotein that is thought to be important in reticuloendothelial system function as well as in promoting adhesion of various cell types to basement membranes and to each other. Plasma Fn levels are depressed following almost any type of trauma. It opsonizes circulating tissue debris for removal by the fixed cells of the reticuloendothelial system. It has been assumed but not proven that Fn also opsonizes tissue debris at the site of the injury for subsequent phagocytosis by tissue macrophages. In this study, rats were given intracardiac injections of Fn coupled with fluorescence isothiocyanate (Fn-FITC) and human serum albumin-rhodamine isothiocyanate (HSA-RITC). Abdominal Rebuck skin windows were then prepared. Within 24 hours, debris at the sites of injury were observed to be coated with Fn-FITC but not HSA-RITC. This Fn-labeled debris was subsequently ingested by macrophages at the site. No macrophages were found that had taken up HSA-RITC. Thus, Fn is seen to coat tissue debris and effete cells within the wound, and the coated material is subsequently removed by tissue macrophages.