Immune complex size determines the clearance rate of a circulating antigen in schistosome-infected mice

Previous studies showed that the clearance rate of gut-associated proteoglycan (GASP), a specific excretory-secretory antigen, was enhanced in mice infected with low schistosome burdens compared to heavily infected and control mice. Because the size of immune complexes alters the clearance rate of antigens, in the present experiments the size of GASP-containing immune complexes was determined after injection of radiolabeled GASP into lightly and heavily infected and control mice. The size and amount of immune complexes were determined by sucrose density centrifugation, agarose electrophoresis, and (NH4)2SO4 precipitation. All three methods showed that lightly infected mice had larger and quantitatively more GASP-containing immune complexes than did heavily infected mice. The differences in clearance between lightly and heavily infected mice, therefore, appear to be due to the presence of smaller, and quantitatively less, immune complexes in the heavily infected mice.