Quantitative Sub-Groups of the B Antigen in Man and their Occurrence in Three Racial Groups

Abstract

NUMEROUS authors^1–5 have described rare variants of the B blood group antigen which may differ qualitatively from other B antigens. Formaggio⁶ concluded from his examination of 250 samples of B agglutinogens that differences within the B group were quantitative rather than qualitative. During the performance of 50 per cent end-point hæmagglutination assays of the B-anti-B system⁷, it was noted that B cells from a Negroid individual were more strongly agglutinated than were those of Caucasoid origin. The probability–log assay curves in Fig. 1 show the difference observed with four doubling dilutions of anti-B serum in an equilibrium system with equal numbers of the two types of B cells of equal freshness. The percentages of cells agglutinated were obtained by the free-cell counting technique described in an earlier paper⁸ and are plotted against the logarithms of the antiserum concentrations. Since the parallel assay curves indicated that these agglutinogens differed quantitatively rather than qualitatively, the relative ‘strength’ of the B cells could be ascertained from the 50 per cent hæmagglutination end-points or HD₅₀'s interpolated from the assay curves. A ratio of the HD₅₀'s showed that the Gaucasoid cell possessed only 60 per cent of the agglutinating strength of the Negroid cell. This difference was observed with numerous samples from these same individuals over a period of two years, and thus appears to be an intrinsic property of the agglutinogen from a given individual. The stronger cell was tentatively assigned a value of unity and provisionally designated B^1.0 while the weaker Caucasoid cell was termed B^0.6 to avoid confusion with the terminology B₁₀₀, B₈₀, B₆₀ etc., proposed by Hirszfeld^9,10 for the B_c (complete) antigen and its transition forms.