pH Optima in Immune Hemolysis: A Comparison between Guinea Pig and Human Complement *

Abstract

The pH optima of the immune lysis of sensitized sheep red cells by human and guinea pig complement have been investigated. Both human and guinea pig complement function best at pH 6.5, but human complement is more sensitive to pH alteration. Study of the effects of pH alteration upon the formation of lysis of sensitized red cell-complement component intermediates has demonstrated that the enhanced potency of human complement action at pH 6.5 results from a stimulation of the third complement component. The significance of these observations relative to certain "pH-dependent" human hemolytic systems is discussed.