Use of protein A-treated sera in unmasking herpes simplex virus type 1 (HSV-1) immunoglobulin A and identifying HSV-1 immunoglobulin G as the predominant neutralizing antibody.

Treatment of human sera with protein A reduced the amounts of immunoglobulin G (IgG), IgA, and IgM detected by radial immunodiffusion. This treatment also decreased the amount of herpes-specific IgG and IgM detected by radioimmunoassay, whereas it increased and even unmasked the amount of herpes-specific IgA detected. Comparison of protein A-treated sera with untreated sera indicated that herpes simplex virus type 1 IgG was responsible for more than 92 to 99% of the serum neutralizing activity.