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Identification of a transient lymphoid population in the murine epidermis
Publication . Almeida, Francisca Monjardino Ferreira de, 1987-; Ginhoux, Florent; Graça, Luís, 1971-
T cell progenitors are known to migrate from the fetal liver in embryos and the bone marrow in adults to the thymus where they differentiate into naïve T cells and then egress to peripheral tissues. However, different studies have shown that a pool of T cell progenitors may also exist in the periphery. Here, we identify a lymphoid population resembling these progenitors which transiently seed the epidermis during late embryogenesis in both WT and T cell-deficient mice, which we named ELCs (Epidermal Lymphoid Cells). These Thy1+CD2+ cells lack expression of CD3 and TCRαβ/γδ at their surface, reminiscent of the phenotype of extra or intra-thymic T cell progenitors, as well as Natural Killer cells. Similarly to dendritic epidermal T cells (DETC), ELCs are radio-resistant and capable of self-renewal, suggesting that the pool of ELCs that seed the skin during embryogenesis maintains itself throughout life. Additionally, ELCs have partial expression of T cell lineage markers, such as CD3 in their cytoplasm and expression of pTα. However, when introduced to in vitro, ex vivo and in vivo differentiation assays, ELCs did not differentiate into conventional T cells or DETCs, conclusively showing that they are not T cell progenitors. Nonetheless, upon phenotype analysis ELCs revealed to be IL15-dependent, express NK-lineage markers such as NK1.1, CD49b and CD244 and produce IFN-γ and IL-2 under stimulatory conditions. On top of that, ELCs have also shown to be dependent on the transcription factors Runx3 and Nfil3. Altogether, we report the discovery of a unique population of lymphoid cells within the murine epidermis with characteristics that point towards ELCs being a pool of NK-like cells. Whether ELCs interact with other immune or non-immune cell populations leading to unique immune functions in the epidermis remains to be investigated. Moreover, further studies would have to be addressed in order to further characterize the true origin, nature and function of such a population.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/72641/2010