T-cell-specific expression of kinase-defective Eph-family receptor protein, EphB6 in normal as well as transformed hematopoietic cells

Although most kinase-defective growth factor receptor proteins are associated with pathogenic conditions, a kinase-defective Eph-family receptor protein, EphB6, is expressed in normal human tissues. We generated monoclonal antibodies specific for human EphB6 to characterize its expression on human hematopoietic cells. A very small population of normal human peripheral white blood cells (0.57 ± 0.07%, n = 12) expressed EphB6. The EphB6-positive cells were CD2⁺, CD7⁺, CD3⁺ and CD4⁺ or CD8⁺ lymphocytes, but they did not express CD19 or CD11b. In human bone marrow, only 1.5 ± 0.19% of lymphocytes expressed EphB6. Compared with the expression in peripheral lymphocytes, prominent expression of EphB6 protein was demonstrated in CD4⁺CD8⁺ double-positive mouse thymocytes. The T-cell lineage-specific expression was strictly conserved in human leukemia/lymphoma cells. Among T-cell-derived leukemia cells, the expression level of EphB6 seemed to decrease with maturation of the cells. These results suggest that EphB6 expression is regulated in T-cell development.