PJA-BP expression and TCR δ deletion during human T cell differentiation

Recombination of δRec to ψJα will delete the TCR δ gene, which is thought to play an important role in the bifurcation of the TCR αβ versus TCR γδ differentiation lineages. We recently detected a DNA-binding protein in human thymocytes, the so-called PJA-BP, which recognizes the ψJα gene segment and might be one of the factors involved in the regulation of preferential δRec–ψJα rearrangements. We now investigate PJA-BP expression and its correlation with TCR δ gene deletion in thymocytes. Our electrophoretic mobility shift assay experiments showed that the PJA-BP is evolutionary conserved in human, murine and simian thymocytes. Using a large series of human hematopoietic malignancies (n J 30), we conclude that PJA-BP expression is thymocyte specific and seems to be restricted to thymocytes committed to the TCR αβ lineage. Analysis of seven well-defined human thymocyte subpopulations showed that preferential δRec–ψJα rearrangements as well as PJA-BP expression can be detected from the immature CD34–/CD1F/ CD3–/CD4F/CD8αFβ– thymocyte differentiation stage onwards. These experiments indicate that expression of PJA-BP in human thymocytes starts simultaneously with preferential δRec–ψJα rearrangements, which supports our hypothesis that PJA-BP is one of the factors involved in the preferential recombination of δRec to ψJα.