Impaired phagocytic function and increased immune complexes in diabetics with severe microangiopathy

An increase in circulating immune complexes (AgAb) of medium size has been observed in diabetics with late complications. This increase may be related either to an increased formation or reduced clearance. Alternatively, both mechanisms may be involved. As medium-sized AgAb determined by the C1q solid phase method are mainly removed from circulation by the fixed phagocytes of the reticulo-endothelial system, we investigated the function of these cells using a colloid clearance test in diabetics with various degrees of microangiopathy. Microaggregated iodinated human serum albumin was injected into 30 diabetic volunteers with severe (group 1), moderate (group 2), and absent (group 3) microangiopathy, and into 40 normal volunteers. The colloid clearance was significantly reduced in diabetics with severe microangiopathy in comparison with patients who had no sign of microangiopathy, or with normal subjects. A significant correlation was found between reduced colloid clearance and increased levels of circulating AgAb determined by C1q solid phase method. Results of this study suggest that the increase in circulating AgAb observed in patients with severe microangiopathy may result from an impaired function of mixed phagocytes.