Biochemical and genetic analysis of the OKa blood group antigen

The monoclonal antibody TRA-1-85 recognizes a cell surface antigen which is expressed by all human cell types tested, including red blood cells (RBCs), but not by mouse cells. All the human RBCs tested were TRA-1-85 positive except those with the rare phenotype Ok(a-). Oka is a blood group antigen of very high frequency and only three unrelated Ok(a-) people are known. The red cells of all three propositi were negative with the TRA-1-85 antibody. To confirm the relationship between the TRA-1-85 antibody and anti-Oka, the immune antibody found in the serum of Ok(a-) individuals, Western blot analysis was used: the TRA-1-85 antibody and anti-Oka gave identical but complex patterns of reactivity in Western blot analysis of human cell lysates or membranes. This suggests that the anti-Oka and TRA-1-85 antibodies recognize the same cell-surface determinant and implies that Oka is not restricted in its expression to the surface of RBCs but is expressed on white blood cells (WBCs) of Ok(a+) individuals and all human cell lines tested to date. WBCs from one of the Ok(a-) propositi were tested and found to be negative with the TRA-1-85 antibody. Finally, the species specificity of the TRA-1-85 antibody has been exploited by the use of somatic cell hybrids and DNA transfection techniques to examine the genetic control of the Oka antigen defined by the TRA-1-85 antibody. We report that the determinant is controlled by a single gene OK present on human chromosome 19.