Materials
Purified horse IgG1 and a mixture of horse IgG1 and IgG4 were kindly provided by Dr. Bettina Wagner at Cornell University. S. equi-specific mouse sera were obtained from adult female outbred CD-1 Swiss mice (Charles River Laboratories, Wilmington, Mass.) 21 days after they were inoculated subcutaneously with 1 x 107 cfu S. equi strain SEM1. Convalescent sera from 3 horses suffering from strangles were obtained 30 days after diagnosis. GAS M1 Mac was prepared as previously described [5].