Neutralization of sendai virus by the IgG subclass antibodies of the guinea pig.

A comparative study was made of the neutralizing activities of IgG subclasses IgG1 and IgG2, fractionated from guinea pig antisera against Sendai virus. The yields of IgG2 from the antisera were about 16 times as much as those of IgG1. The neutralizing activity of IgG2 per unit weight was four times as high as that of IgG1. This neutralizing activity of both IgG subclasses was enhanced about 10 times by addition of antibodies to the L-chain of guinea pig immunoglobulin. It is suggested that, in the complement-dependent neutralization of the virus, IgG1 and IgG2 activate the complement through the alternative and the classical pathway, respectively.