Appearance of slow-reacting, complement-requiring hemagglutination-inhibiting antibody in swine infected with pseudorabies virus.

Slow-reacting, complement-requiring hemagglutination-inhibiting (HI) antibody was detected in sera from pigs infected with pseudorabies virus; approximately 16 hemolytic units of complement were necessary for the detection of such antibody. Higher HI antibody titers were obtained when antigen and serum were allowed to incubate before addition of complement than when all three components were incubated at the same time. A HI test was developed in which antigen-serum mixtures were incubated at 4 degrees C for 48 h and then with complement at 37 degrees C for 1 h; this gave an improved sensitivity over the previous incubation without complement.