BONE MARROW-DERIVED DENDRITIC EPIDERMAL T-CELLS EXPRESS T-CELL RECEPTOR-ALPHA-BETA-CD3 AND CD8 - EVIDENCE FOR THEIR EXTRATHYMIC MATURATION

The majority of murine Thy-1+ dendritic epidermal T cells (DETC) express virtually identical TCR encoded by Vgamma5 and Vdelta1 genes and are derived from early fetal thymic precursors. However, not consistent with this notion is an early finding that DETC arise continuously from bone marrow (BM) precursors by a thymus-independent mechanism. To address this issue, donor-type DETC were characterized in lethally irradiated mice that were reconstituted by Thy-1-disparate BM cells with or without a thymus. The BM-derived DETC, unlike their normal TCR-gammadelta counterparts, were found to express the TCR-alphabeta/CD3 complex and CD8, and their migration to the epidermis occurred independently of the thymus. The numbers of the BM-derived DETC increased with time and reached a plateau 6 mo after BM transfer, at which time the TCR-alphabeta/CD3 complex was expressed on a small fraction of the DETC in athymic BM chimeras. Although no further increase in the number was observed at later times, at 1 yr after transfer most of the BM-derived DETC came to express the TCR-alphabeta/CD3 complex in the absence of thymic influence. By contrast, most of BM-derived T cells in other lymphoid organs from athymic BM chimeras still failed to express the TCR-alphabeta/CD3 complex even at 1 yr after transfer. These results suggest that extrathymic differentiation of BM-derived DETC could occur with the epidermal microenvironment.