Thy-1⁺ epidermal cells in nude mice are distinct from their counterparts in thymus-bearing mice: A study of morphology, function, and T cell receptor expression

We have evaluated the morphology, function, and TCR mRNA and DNA profiles of Thy-1⁺ epidermal cells (EC) derived from athymic (nude) mice. Based on these criteria we demonstrate that Thy-1⁺ EC in nude mice are predominantly round and angular and located in follicular epithelium, as compared to predominantly dendritic, interfollicular Thy-1⁺ EC found in normal CBA or BALB/c mice. Functionally, Thy-1⁺ EC from normal mice proliferate and elaborate IL-2 in response to stimulation by Con A; by contrast, nude Thy-1⁺ EC fail to proliferate or secrete IL-2 in response to Con A. Nude Thy-1⁺ EC proliferate markedly in response to low-dose IL-2 alone; Thy-1⁺ EC from normal mice give only modest proliferative responses to IL-2. Both populations of cells proliferate and elaborate IL-2 in response to PMA and calcium ionophore. Short-term cultured Thy-1⁺ EC from nude mice resemble Thy-1⁺ EC from normal animals in that they express no detectable functional TCR-α and β-RNA. Normal Thy-1⁺ EC express abundant levels of functional RNA for TCR-γ and δ-chains and for the CD3 δ-chain, whereas nude Thy-1⁺ EC produce no detectable TCR-δ and no CD3 δ-RNA and only truncated, presumably germ-line TCR-γ transcripts, as suggested by lack of hybridization with γ-V region probes and by lack of detectable rearrangements in the γ-genes. These phenotypic, functional, and genotypic characteristics of Thy-1⁺ EC from nude mice suggest that these cells are at a very early stage of T cell differentiation.