ANTIGEN SITE DISTRIBUTION AMONG WEAK A RED-CELL POPULATIONS - STUDY OF A3, AX AND AEND VARIANTS

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 32  (2) , 233-244
Abstract
The distribution of the A receptors was studied among agglutinated and free populations of A variant RBC [red blood cells] (A3, Ax, Aend) known to be partially or weakly agglutinated by human anti-A reagents. Following separation of the red cell populations and disaggregation of the clumps by mild treatment with soluble blood group substances, it was shown that among A3 RBC, the agglutinated RBC have at least 5 times as many A receptors per cell as the corresponding free RBC, these latter however being strongly A positive. The differences between the A antigenic content of the Ax RBC was less pronounced. The most striking result was obtained with the Aend RBC, where 2 populations are demonstrated; the 1st, including 5-10% of the RBC, strongly agglutinates with anti-A and contains erythrocytes of high antigenic content (140,000 A receptors per cell). The 2nd, including the majority of RBC, could not be differentiated from the control O RBC. A wide heterogeneity of antibody binding capacity of the various populations of A3, Ax and Aend red cells, was demonstrated following ultrastructural examination by immunological electron microscopy with peroxidase-conjugated antibodies. An heterogeneity of labeling from one cell to another was revealed in the same population of red blood cells. Comparison of weak A RBC and O RBC enzymatically converted into A RBC, demonstrates a similar pattern of reactivity between these cells, and supports the relationship between antigen site density and red cell agglutination. The typical pattern of agglutinability of A3 and A-x RBC apparently rises from their heterogeneous antigenic content and from the occurrence of an antigenic threshold below which red cells become non-agglutinable. The typical mixed-field agglutination pattern of Aend RBC probably reflects the occurrence of a true dual population of RBC.