Acquired Immunity in Rabbits to Infection with Group A Type 30 Hemolytic Streptococcus: Its Relation to Antibodies to the M Protein

Abstract

One one-thousandth of a milliliter of a blood broth culture of hemolytic streptococcus Type 30, Gay strain, when injected intrapleurally in rabbits is uniformly fatal to normal animals (18/18). This same strain of streptococcus injected subcutaneously at the angle of the jaw produces a severe local infection, but the majority of animals survive and develop antibodies to one or more of the antigens of this strain. When anti M precipitins and skin sensitivity develop, animals are usually protected against subsequent intrapleural infection with the same organism (11/14). When anti M precipitins and skin sensitivity do not develop, animals die of subsequent intrapleural infection (7/7). When anti M precipitins and skin sensitivity are partially neutralized by previous intravenous injection of M antigen, animals usually survive reinfection (3/5). When anti M precipitins and skin sensitivity are completely neutralized by previous intravenous injection of M antigen, animals usually die following subsequent infection (10/11). On the other hand, when anti C precipitins and skin sensitivity are neutralized by intravenous injection of Group A “C” antigen, previous to challenge, the immunity of the animals is usually unaffected and they resist intrapleural infection with the streptococcus (7/8). In all eight of these animals M antibodies still remained. Antibodies and skin sensitivity to the nucleoprotein Cl8K appear irregularly and without relation to immunity.