Foxp3 expression in cutaneous T‐cell lymphocytic infiltrates

BACKGROUND: The primary function of regulatory T cells (Treg cells) is to regulate the function and proliferation of immunologically responsive T cells; the transcription factor Foxp3 is expressed by this cell populace and is held to be the standard marker for Treg cells. DESIGN: A variety of cutaneous T-cell lymphocytic infiltrates were evaluated for Foxp3 expression. RESULTS: Of the 95 cases, 33 (35%) were reactive, 40 (42%) were prelymphomatous cutaneous T-cell dyscrasia and 22 were (23%) T-cell lymphoma. The reactive category included dermatomyositis, lupus erythematosus, hypersensitivity reactions and graft-vs.-host disease. The prelymphomatous dyscrasia category was represented chiefly by pityriasis lichenoides chronica (PLC) and pigmented purpuric dermatosis (PPD). The Foxp3 reactivity was less than 10% for cases of dermatomyositis and lupus erythematosus, 23% for hypersensitivity cases, 0% for graft-vs.-host disease, 16% for the dyscrasias and 11% for the lymphomas. Intermediate grade and aggressive lymphomas had very few Foxp3+ cells (< 5%). There were fewer numbers of Foxp3+ T cells in the monoclonal variants of PLC and PPD. CONCLUSIONS: T-reg cells may play a role in controlling the extent of T-cell proliferations in the skin with a lack of T-regulatory function permissive to the development of various T-cell disorders.