Neutralization kinetics of bovine viral diarrhea virus by hyperimmune serum: one or multi-hit mechanism

The kinetics of bovine viral diarrhea (BVD) virus neutralization (VN) by hyperimmune serum followed first order kinetics at low dilutions (1:8 and 1:16) of hyperimmune bovine serum. A lag phase in the VN curve occurred when the serum was further diluted. Addition of rabbit anti-bovine IgG, but not anti-IgM, significantly increased the degree of VN after BVD virus was reacted with further diluted (1:256 dilution) anti-BVD bovine hyperimmune serum. Incubation of virus-hyperimmune serum (1:64 dilution) at 4 degrees C for 0 to 60 min, followed by incubation at 37 degrees C indicated VN occurred as a two-stage process: a binding (temperature-independent) phase that was followed by a triggering (temperature-dependent) phase. The data favor the thesis that neutralization of BVD virus occurs by a multi-hit mechanism and requires combination of at least two molecules of antibody with each virus.