Induction of local immunity to group A streptococci type M50 in mice by non-type-specific mechanisms.

The possibility of inducing immunity in the upper respiratory tract against type M50 group A streptococci was studied in mice. The M50 type exhibited an LD100 a of 10(5) colony-forming units (CFU) when administered intranasally (i.n.), and of 10(7) CFU when introduced intraperitoneally (i.p.). I.n. administered vaccines prepared from M types 12, 18, 30, 49, 50 and 55 were equally efficient in preventing lethal infection after i.n. challenge with type M50. Subcutaneous (s.c.) immunization with type 18 had no effect, whereas s.c. immunization with type 50 was effective against i.n. challenge with type 50. Neither with i.n. nor s.c., did vaccination with type 18 - in contrast to with type 50 - protect against i.p. challenge with type 50. The results strongly suggest that local immunity against M50 group A streptococci can be achieved using a non-type-specific mechanism. Once the local barrier had been overcome, protection against systemic infection was type-specific in accordance with classic concepts.