Antibody responses to bacteria. The effect of the immunoglobulin type of anti-bacterial antibody on immunoconglutinin stimulation in rabbits and guinea-pigs.

Three manifestations of the antibody response of rabbits and guinea-pigs to injections of killed bacteria have been examined, namely, complement-fixing and agglutinating anti-bacterial antibodies and immunoconglutinins (I-Ks) directed against fixed complement. Animals given intramuscular injections of the bacteria in Freund's complete adjuvant before a course of intravenous injections were compared with those receiving the latter course only. The prior immunization with organisms in adjuvant increased the I-K responses in rabbits. This was correlated with an increase in that part of the complement-fixing, anti-bacterial antibody contained in the IgG fraction. The animals receiving the course of intravenous injections only, produced more agglutinating anti-bacterial antibody (which was shown to be predominantly IgM in type) and less I-K. In guinea-pigs there was little difference in the I-K response between animals receiving the two injection schedules. The prior immunization with organisms in adjuvant did produce higher levels of anti-bacterial antibody, but in this species the increase was mainly in the IgM fraction. It is suggested that in both species the presence of complement-fixing anti-bacterial antibody of IgG immunoglobulin type is necessary for the stimulation of I-K production and that high levels of IgM antibody may have an inhibitory effect. High titres of I-K can be produced regularly by injecting bacteria intravenously into rabbits with predominantly IgG anti-bacterial antibodies. Where these do not occur naturally they can be produced in response to two intramuscular injections of bacteria in adjuvant. In guinea-pigs it was difficult to produce predominantly IgG anti-bacterial antibody and high titres of I-K were difficult to achieve.