A human quantitative polymorphism related to Xg blood groups.

A monoclonal antibody, 12E7, raised against lymphocytes from a patient with a T-cell acute lymphocytic leukaemia reacts strongly with cortical thymocytes and, to a lesser extent, with other human cells. The antigen defined by 12E7 is not expressed on mouse or hamster cells; this species specificity allowed us to investigate the genetics of the expression of the 12E7 antigen using human--rodent somatic-cell hybrids. Hybrid cells which contain the human X chromosome as the only human genetic contribution react with 12E7. The X-linkage of the gene, or genes, controlling 12E7 antigen expression and the fact that 12E7 antigen is also expressed on red blood cells led us to investigate the possibility of a relationship with the X-linked Xg blood group system. Although the 12E7 and Xga antigens seem to be different antigenic determinants specified by different loci, we report here a sex-limited effect involving the Xg phenotype on the expression of 12E7 antigen.