The formation of immune complexes with subsequent clearance is a physiological process during the acute phase of an immune reaction. When antibody-antigen aggregates develop in rising quantities they become detectable in the peripheral blood as so-called circulating immune complexes ( CIC). The formation of CIC is a common event during chronic parasitic infection like schistosomiasis, filariasis, leishmaniasis, trypanosomiasis, toxoplasmosis, and quartan malaria. Only the deposition of immune complexes may cause severe pathological changes in the host.
During parasitic infection various circulating antigens appear at different developmental stages. Due to a selective immune response only few of them are complexed by antibodies. The antibody–antigen interaction may lead to structural changes in the antigen. The clearance of immune complexes depends on the structure of the antigen and the quality (affinity) and quantity of the antibody.
Immune complexes are able to bind complement compounds and to activate the cellular immune response via Fc-receptors. Resulting pathological changes are either membrane proliferative glomerulonephritis or, when the antigen is tissue bound, an Arthur’s Phenomenon.
CICs are a common phenomenon in the sera of Wuchereria bancrofti -infected patients. Renal abnormalities like chronic progressive glomerulonephritis are reported for patients with malaria (Plasmodium malariae) and Bancroftian filariasis. Also, a chronic Leishmania infantum-infection in dogs may cause glomerulonephritis.