CD7 expression in reactive and malignant human skin T-lymphocytes

CD7, a molecule normally expressed on 90% of CD4+ T cells, is often deficient on the malignant T cells of cutaneous T cell lymphoma. Therefore deletion of CD7 is considered a specific marker for the diagnosis of cutaneous T cell lymphomas. Because an expansion of CD4+CD7- cells may also be observed in benign lymphocyte-mediated dermatoses, we present our experience concerning CD7 expression in both cutaneous T cell lymphomas and a broad variety of T cell-mediated inflammatory dermatoses using an immunohistochemical approach on frozen sections from 45 patients. No, or at most scarce, expression of CD7 was detectable in the inflammatory skin conditions investigated as compared to CD3-positive cells. In cutaneous T cell lymphomas, a striking reduction of CD7 reactive cells was found in either reactive or malignant T cell components. Our findings indicate that CD7-negative T cells are more common within both benign and neoplastic T cell infiltrates than was previously demonstrated and suggest that, using a conventional immunoenzymatic technical approach on fresh-frozen sections, CD7 deletion is an unreliable criterion for the immunohistological diagnosis of T cell-mediated skin infiltrates.