Blood group antibody levels were measured in 526 irradiated survivors of the 1945 atomic bombing of Hiroshima and in 516 nonirradiated subjects. The study was undertaken in order to determine the age changes in antibody levels in irradiated and nonirradiated subjects, as well as to investigate the pattern of blood agglutinin levels in the Japanese population for comparison with that of Caucasians. The following observations were made:

1. In 475 people of group A, 228 of group B, and 339 of group O, the mean serum levels of anti-A and anti-B antibodies were virtually identical irrespective of the blood group of the subjects.

2. In individual group O subjects, the titers of anti-A and anti-B antibodies were very highly correlated (correlation coefficient of +.92).

3. Females exhibited higher antibody levels, although the magnitude of the difference was small.

4. Peak antibody titers were reached at age 20-30, with progressive linear regression in levels with advancing age. Peak titers in early adulthood were 5-10 times higher than those of the very elderly.

5. No correlation between blood group antibody levels and atomic irradiation was detected, whether irradiation was represented by (a) presence or absence of acute radiation symptoms in 1945, (b) distance from the hypocenter, or (c) numerical dosage estimate.

6. As one of a battery of tests of physiologic aging designed for detection of irradiation induced nonspecific aging acceleration, blood group antibody levels seem of modest value. After age 30, the linear correlation with chronologic age is -.72.

7. Differences in blood group antibody levels in Japanese and Caucasians indicate that (a) Caucasians have higher anti-A antibody levels as compared to anti-B levels than do Japanese, and (b) the peak antibody level occurs at an earlier age in Caucasians than in Japanese. It is not clear whether these differences are related to race and heredity or to external antigenic stimulation with A and B antigenic materials, but studies of blood group antibody levels in different racial groups should help elucidate the nature of these differences.

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