Enhancement of hemagglutination inhibition by complement.

Experiments were conducted to determine the effect of specific antibody and complement on hemagglutination inhibition of influenza virus. It was found that early immunoglobulin M antibody to influenza virus inhibited the hemagglutinating capacity of the virus. When fresh guinea pig serum was added, the inhibiting capacity of the serum was elevated from four- to eightfold When guinea pig serum was treated with known complement inhibitors, it lost its capacity to enhance hemagglutination. The use of functionally purified complement components indicated that the first, second, and fourth components were necessary and sufficient for enhancement of hemagglutination inhibition by specific antibody to influenza virus.