Complement Fixation and pH

Abstract

IBE and Wardlaw have re-investigated the effect of pH on the activity of complement¹. They confirmed previous reports² that the haemolytic activity of complement decreases with increasing pH and, in addition, presented evidence that complement fixation increases with increasing pH. They were able to increase the complement fixation titre of an antigen four-fold by raising the pH. of the reaction mixture from 7.15 to 8.56. Stein and Van Ngu³, however, showed that complement fixation titres can be increased by reducing the amount of complement used in the test. Thus, increased complement fixation sensitivity at relatively high pH may be due to loss of complement activity rather than to increased complement fixation. Experiments were devised to test this hypothesis.