Effect of fibronectin on C3b and Fc receptor-mediated phagocytosis by peripheral blood monocytes in uraemic patients.

The influence of human fibronectin was evaluated on the phagocytosis in vitro of C. albicans (C3b receptor-mediated) and IgG antibody-coated sheep erythrocytes (Fc receptor-mediated) by the peripheral blood monocytes of 40 uraemic patients undergoing periodic haemodialysis. Some nutritional parameters (albumin, transferrin, C4, C3, haematocrit, lymphocyte count, height and bodyweight) were also evaluated. Results showed significantly decreased plasma fibronectin (P less than 0.001) and reduced C3b receptor (R)- and FcR-mediated phagocytosis in uraemic patients (P less than 0.001). A strict correlation was found between fibronectin and C3bR-mediated phagocytosis (P less than 0.001) and between fibronectin and FcR-mediated phagocytosis (P less than 0.05). In 20 patients with decreased fibronectin concentrations and reduced phagocytic function, the in vitro incubation of peripheral blood monocytes with 50 micrograms/ml of purified fibronectin significantly enhanced C3bR-(P less than 0.001) but not FcR-mediated phagocytosis. Study of nutritional parameters in the uraemic patients revealed that values of fibronectin, C3, IgG and albumin were significantly reduced. Fibronectin correlated significantly (P less than 0.001) with C3. A good relationship (P less than 0.05) was also found between the plasma fibronectin and bodyweight loss. A greater incidence of infectious disease was observed in patients with decreased plasma fibronectin than in uraemic patients with normal values (P less than 0.05). The results suggest that a decrease in plasma fibronectin in uraemic patients could impair the peripheral blood monocyte phagocytic capacity and be potentially dangerous, predisposing the patient to infections. The determination of fibronectin concentration in these patients may, therefore, have a potential value as an indicator of peripheral blood monocyte phagocytic function.