The Frequency and Properties of pH‐Dependent Anti‐M

Abstract

The accidental finding of an agglutinin in ACD plasma, not demonstrable in unmodified serum from the same donor, led to the discovery of a pH‐dependent antibody with anti‐M specificity. Two additional examples were found shortly thereafter. Screening of 1,000 random group N donors disclosed 21 similar examples of pH‐dependent natural anti‐M. Titers of the 24 antibodies studied in detail ranged from 1:1 to 1:128, with most falling in the lower range. The more potent sera reacted well at room temperature, provided the pH was kept in the proper range, the low‐titered sera were active only at 4 C. With increasing pH the agglutination could be abolished in every case. Under certain conditions, a prozone‐like effect was observed in titrations in which the initial acidification of the serum was kept marginal. This was shown to be the result of the buffemg effect of the serum at low dilutions, preventing acidification by the usually slightly acid (pH 5.6–6.0) saline. The optimum pH for demonstration of this type of anti‐M was found to be 6.5.