Immune complex processing in C1q-deficient mice

Complement and Fc gamma receptors are known to mediate the processing of im mune complexes (IC), and abnormalities in these mechanisms may predispose t o the development of lupus. We explored the processing of IC in mice defici ent in complement component C1q. I-125-labelled IC comprising Hepatitis B s urface antigen (HBsAg)/human anti-HBsAg (HBsAg/Ab) were injected intravenou sly and the sites of IC clearance determined by direct counting of organ up take at various time points. The liver and spleen were the main sites of IC uptake in all mice. The splenic uptake of IC was significantly reduced in the C1q-deficient mice compared with the control mice. C1q-deficient mice a lso exhibited an initial accelerated hepatic uptake of IC similar to that s een in human subjects with hypocomplementaemia. The hepatic localization of IC at later time points was similar in both groups of mice. These data in mice are consistent with previous observations in humans that confirm that the classical pathway of complement plays an important role in the appropri ate processing of IC in vivo.