Observations on the Gy-a and Hy antigens and the antibodies that define them.

Two high frequency antigens, Hy (Holley) and Gy-a (Gregory), show an apparent association. All individuals lacking Gy-a are whites and these individuals are Hy-negative. A second group of Hy-negative individuals are blacks. All of these react weakly with anti-Gy-a. Neither Gy-a nor Hy are well developed on cord cells, although antibodies to both factors have been stimulated by pregnancy. Anti-Gy-a and anti-Hy antibodies react best in the antihuman globulin test. These antibodies have low avidity, high titers, and have been implicated as causing transfusion reactions.