The serological characteristics of γA-anti-A and anti-B were studied using, as a source, either colostrum, or fractions relatively rich in γA obtained from selected potent antisera. γA-anti-A and anti-B were never hemolytic nor did they sensitize red cells to agglutination by anticomplement globulin sera.

γA-anti-A, like γG-anti-A and unlike γM-anti-A was unaffected by heating at 56°C for 3 hr. On the other hand in the following three characteristics the behavior of γA fell between that of γG- or γM-anti-A: sensitivity to inactivation by 2-mercaptoethanol, ease of neutralization by A substance and degree of enhancement of agglutination in a medium of serum rather than saline. The agglutination produced by γA-anti-A was regularly enhanced by addition of anti-γA-globulin serum.

In searching for γA-blood group antibodies of other specificities the following sera were tested: anti-D (32 examples); anti-c (2 examples); anti-Lea or -Leb (3 examples); anti-K (3 examples); anti-Fya (3 examples), and anti-Jka (3 examples). Only 3 sera, all containing anti-D, sensitized red cells to agglutination by anti-γA. There were no discrepancies between results obtained with four different anti-γA-globulin sera. Approximately half the sera were fractionated on DEAE-cellulose, and the fractions rich in γA tested for their ability to sensitize red cells to agglutination by anti-γA; no additional examples of γA-antibodies were detected.

One of the three examples of γA-anti-D appeared in the serum of a woman during the course of deliberate reimmunization. γA-anti-D appeared only after three intravenous injections of red cells although the γG-anti-D titer rose considerably after a single injection. 3 yr after a fourth injection of Rh-positive cells γA-anti-D, as well as γG-anti-D, was still present in the serum.

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