Schistosoma japonicum: Semiquantitative assessment of circulating immune complexes, serum Clq and C3, and their relationship to renal pathology and hepatic fibrosis in rabbits

Abstract

Ten New Zealand white rabbits were infected either once or four times with variable numbers of Schistosoma japonicum cercariae. Four animals served as the uninfected controls. All rabbits were bled at semimonthly intervals. Serum samples were examined for circulating immune complexes using an [ 125I]Clq assay, or for Clq and C3 levels by single radial immunodiffusion. Control and experimental animals were necropsied at 32–39 weeks postinfection, and the kidneys and livers were removed. Some kidney specimens were quick-frozen in isopentane-liquid nitrogen, cut with a cryostat, and examined by direct or indirect immunofluorescent techniques for immunoglobulin, complement (C3), or parasite antigen glomerular localization. Other kidney specimens were fixed in formalin, sectioned, stained with H&E or PAS, and examined for evidence of histopathology. Liver specimens were treated in a similar manner. Diffuse renal lesions appeared in only 2 of 10 rabbits in the present study. However, each of these two animals had prominent and persistent levels of circulating [ 125I]Clq material (immune complex), and the animal with the highest concentration of immune complex had the most severe nephropathologic changes. C3 levels were consistently depressed in the animal with severe renal pathology but were elevated in all other animals at some point in the infection. Circulating immune complex and serum C3 and Clq values moved in concert for most of the infected rabbits with the principal exception being the animals with diffuse renal lesions. It is of considerable interest and potential etiological significance that the four rabbits with the highest levels of circulating immune complex had the most extensive hepatic fibrosis.