INVESTIGATIONS OF MENINGOCOCCAL INFECTION. III. THE BACTERICIDAL ACTION OF NORMAL AND IMMUNE SERA FOR THE MENINGOCOCCUS 1

Abstract

Differences in the general susceptibility of strains of Group I meningococci were associated with differences in the behavior of these organisms in the bactericidal test with immune sera. Susceptible strains were killed, while resistant strains survived, in the presence of human complement; Resistant strains were killed in the presence of rabbit complement or human defibrinated blood. Fresh immune sera were lacking in bactericidal action for both resistant and susceptible strains. When these sera were diluted in the presence of an appropriate neutral complement, strong bactericidal antibody was demonstrable. The bactericidal action of fresh normal serum was inhibited by the addition of specific antiserum. This inhibition was not associated with detectable fixation of hemolytic complement. It is considered to be a manifestation of the prozone phenomenon. The injn. of small quantities of specific antiserum in rabbits produced an increase in bactericidal property. Larger doses caused inhibition of killing. In some instances this may have been due to the anticomplementary action of conc. antiserum; in others, complement was not affected. Injn. of conc. antiserum in 2 human subjects resulted in the enhancement of bactericidal action in defibrinated blood, for the resistant strain, and a diminution in the bactericidal action of serum and defibrinated blood, for the susceptible strain. No detectable alteration of complement was observed. The intraven. injn. in rabbits of a conc. rabbit antimeningococcal serum resulted in the disappearance of detectable hemolytic complement for as long as 24 hrs. After the intraven. injn. of meningococci, bacteremia persisted for a considerably longer period in rabbits receiving antiserum than in control rabbits. Similar results were obtained using an antimeningococcal horse serum, free from any demonstrable anticomplementary effect. Two factors, operating singly or together, appear to be responsible for these results: the prozone phenomenon due to antibody excess and anti-complementary action.