ALMOST A CENTURY AGO, the first red cell blood groups, as determined by human sera, were described. During the subsequent years, great progress was made in the recognition and grouping of relationships of various specificities. There currently are 276 discrete red cell antigens. While 61 remain to be classified, 215 of these antigens can be grouped into 23 distinct systems. In 12 of the systems there exists a null cell, which is totally devoid of any representative antigens for that system. The recognition of a link between these biologic factors and a person's susceptibility to a particular disease has encouraged in-depth analyses of the individuals with these unusual phenotypes.The discoveries of extracellular hair-like appendages of microorganisms called pili, fimbriae, or (later) adhesins, that are directly related to infectivity, and of the hemagglutinating properties of bacteria that express these extracellular appendages were the first findings related to the bacterial cell-eukaryotic cell interaction. The contribution of these early findings to the understanding of the pathogenesis of infection, however, was not recognized for a long time. Nevertheless, Escherichiu coli induced different hemagglutination patterns of both human and animal red cells, which indicated that microorganisms could detect a variety of cell types and, thus, a variety of tissue ligands.2 Further studies explored the interaction between bacterial cells and other types of cells, including yeast, plant cells, and cells of animal and human origin^.^-^ For example, E. coli carrying the type 1 fimbriae were found to attach to mannans and aggregate yeast cells.An advancement in the understanding of the pathogenic properties of organisms that cause urinary tract infections came with the use of human uroepithelial cells as targets for the binding of E. coli, Proteus mirubilis, Abbreviations: CR = complement receptor; DAF = decay-accelerating factor; Gal = galactose; GalNAc = N-acetyl-galactosamine; GPI = glycophosphatidylinositol; NeuAc = N-acetyl-neuraminic acid; RCA = regulators of complement activation; SCR(s) = short consensus repeat(s); S R region = serine-and threonine-rich domain.

A low frequency of the Doa antigen in Japanese was confirmed by a further testing of 502 donors and 79 families. In the family studies, Doa was shown to be independent of the Diego or Jr systems.

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