Complement Dependent Killing of Mycoplasma Pneumoniae by Antibody: Kinetics of the Reaction

Abstract

The neutralization or killing of Mycoplasma pneumoniae by either rabbit or human antiserum required a heat-labile factor from non-immune serum. Killing was rapid, but could be stopped by dilution, thus permitting study of the reaction. The absolute number of organisms killed in a constant time interval was independent of the initial number of organisms present, making this reaction analogous to complement-mediated lysis of sensitized red blood cells. Although the rate of killing was influenced by antibody content, the level of normal serum factor appeared to have a much larger influence on the rate of the reaction. This heat-labile factor is apparently complement or some components of complement: it can be blocked by a chelating agent, is sensitive to salt concentration, and can be removed by prior absorption with a non-related complement-fixing antigen-antibody complex. Killing did not take place at 4°C, suggesting that the reaction is enzymatically controlled. The relative rates of killing appear to parallel lipid CF titers, but the measurement of antibody is 10 times as sensitive.