Thymus-independent generation of Thy-1+ epidermal cells from a pool of Thy-1− bone marrow precursors

Abstract Thy-1 + dendritic epidermal cells (Thy-1 + DEC) and immature thymocytes share several phenotypic features: CD45 + , Thy-1 + , asialo-GM1 + , CD3 + , CD4 − , and CD8 − . In view of this similarity, it has been suggested that the epidermis may be a site of either post-thymic or extra-thymic T-cell development. In order to address this issue, we used C3H/He/Han (Thy-1.2) → AKR/Ola (Thy-1.1) radiation bone marrow chimeras. Animals were first either thymectomized or shamthymectomized, then lethally irradiated (750R) and, finally, reconstituted with allogeneic bone marrow cells previously depleted of Thy-l-bearing cells. Six weeks after bone marrow transplantation, spleens and lymph nodes of shamtreated animals, but not of thymectomized animals, contained large numbers of CD3 + donor-type Thy-1 + cells. The epidermis of both thymectomized and sham-treated animals contained not only many recipient-type CD3 + , Thy-1 + DEC, but also small numbers of CD3 − , donor-type Thy-1 + cells. After 4 months, the frequency of donor cells had greatly increased, but they still lacked CD3 antigens. Most of the donor cells had a rounded shape, but some exhibited a dendritic configuration. These results demonstrate that Thy-1-bone marrow-derived precursors of Thy-1 + DEC can migrate to the epidermis without thymic influence and yet acquire Thy-1 antigens during their journey. Although donor-type Thy-1 + epidermal cells failed to mature into CD3 + dendritic epidermal cells, the experimental model used in this study may be a versatile tool for studying the influence of thymic and extrathymic epithelia on T-cell maturation.