Decreased C3 Levels in a Chronic Virus Infection: Equine Infectious Anemia

There is increasing evidence that complement-dependent immune reactions are pathogenetically important in virus diseases. One indication of in vivo complementfixing immune reactions is the lowering of plasma C3 levels. A study was made of the circulating plasma C3 levels in 12 horses infected with equine infectious anemia (EIA) virus. Purified equine C3 was prepared from euglobulin precipitates of horse serum using triethylaminoethyl (TEAE) column chromatography with subsequent Pevikon block electrophoresis. Monospecific antisera prepared in rabbits was used in single radial immunodiffusion to quantitate C3 levels. A significant reduction of C3 was detected in 6 of 12 horses with active clinical disease. All horses with reduced C3 levels had C3-coated erythrocytes and deposits of immunoglobulin and C3 in the glomeruli. These findings further indicate that immune processes are active in the pathogenesis of EIA.