The manner of immune complex deposition on the glomeruli in acute serum sickness induced by cationized ferritin

In order to investigate the effect of charge-modified antigen on the glomerular localization of immune complexes (IC), we studiedd the manner of IC deposition in the system of acute serum sickness (accelerated) induced by "electron microscope visible" native (NF) and cationized ferritin (CF) using immunoenzymatic electron microscopy. NF or CF ferritin was administered to each four rabbits at a dose of 50mg/rabbit int-ravenously, and on 14 th day after the first injection of antigens, renal biopsies were performed before and after second injection of antigens. Circulating antigens disappeared on 4-6th day in NF group and on 6 day in CF group after the first antigen administration. Free circulating antibodies (IgG class) to NF or CF became detectable from 8 th day after the first antigen injection by enzyme immunoassay. Deposition of IgG and complement were observed only after the second antigen injection by immunofluorescence study; in a mesangial pattern in NF group, while in a peripheral granular linear pattern in CF group. By electron microscopy, ferritin particles were observed in mesangial area in NF group, while in subendothelial sites of glomerular base-ment membrane in CF group. By immunoenzymatic electron microscopy, a lot of CF particles were observed on subendothelial sites accompanied by peroxidase positive materials (rabbit IgG). These results suggest that both NF and CF are not acting as "planted antigens", because neither antigen nor antibody could be detected in the glomerulas on 14 days, even when free antibodies against ferritin were found in the circulation. We speculated that glomerular deposits may cause by circulating IC because they could take place only when both antigen and antibody were present in the circulation. The difference of intraglomerular localization of IC between NF and CF groups might be due to some characteristic changes of antigen caused by chemical cationization; possibly changes in size and charge of IC.