Dynamics in development of experimental streptococcal immunity in mice.

The interrelation between the humoral and cellular factors in the development of immunity to experimental streptococcal infection was investigated. Early resistance to infection was caused by stimulating the phagocytic cells to function efficiently in the absence of opsonins. Subsequently, the appearance of cytophilic antibodies provided further means for elimination of streptococci. Thus, in the early stages of specific antistreptococcal immunity, resistance was observed in the absence of circulating anti-M antibodies. The type-specific antibodies that appeared in the later stage did not seem to improve clearance of streptococci in the splanchnic tissues. After an intravenous lethal challenge of mice with virulent streptococci, these antibodies did not provide increased protection. The circulating anti-M antibodies were shown to play a beneficial, indeed, a crucial, role when the infection occurred in a region in which the phagocytic cells were present in a rather limited number.