Circulating antigens, immune complexes and C3d levels in human schistosomiasis: relationship with Schistosoma mansoni egg output.

Circulating schistosome antigens (CSA), circulating immune complexes (CIC) and C3 breakdown product - C3d - were investigated in human schistosomiasis in comparison to the S. mansoni egg count. A close relationship was observed between the mean number of eggs/g of stool and the detection of CSA (evaluated by the radioimmunoprecipitation-PEG assay - Ripega), CIC (Clq-binding test) and C3d levels (quantitated by radial immunodiffusion). All the patients with more than 500 S. mansoni eggs/g of stool also presented antigen '4', specific of the genus Schistosoma, in the serum. A significant correlation was noticed between levels of CSA and CIC. This suggests the involvement of several schistosome antigens in the detected CIC. No relationship was noted between CIC and C3d levels. In contrast, there was a highly significant correlation between levels of CSA and C3d. The interaction between certain schistosome antigens and the complement system is discussed.