Immunoregulatory events in the skin of patients with cutaneous T-cell lymphoma

BACKGROUND: Involved skin of patients with cutaneous T-cell lymphoma, mycosis fungoides type, contains an increased number of bone marrow-derived epidermal cells that express class II major histocompatibility complex molecules and an infiltrate of both activated non-malignant and malignant T cells. However, the mechanism by which the T cells achieve and maintain their activated state is uncertain. The aim of this article is, therefore, to review recent studies from the literature dealing with immunoregulatory events in patients with mycosis fungoides and Sézary syndrome. OBSERVATIONS: The nonmalignant T cells seem to be activated through the T-cell receptor by lesional epidermal CD1a+CD36+ macrophagelike cells that, on a cell per cell basis, are more potent antigen-presenting cells than normal CD1a+ Langerhans' cells present in uninvolved epidermis. In contrast, the malignant T cells have different activation requirements, because they can only be stimulated through antigen independent pathways, such as CDw60, CD28, and CD2. The malignant T cells produce T-helper (Th)-2 cytokines, and because interferon gamma (IFN-gamma)-producing Th1 cells are present in the early lesions of mycosis fungoides, nonmalignant tumor-infiltrating T cells may represent Th1 cells. Because Th1 cytokines counteract Th2 cytokines, tumor-infiltrating T cells may potentially have the capacity to downregulate the growth of the malignant cells. CONCLUSION: The balance between progression vs remission in mycosis fungoides is related to complex interactions between the malignant T cells, nonmalignant T cells, and hyperstimulative antigen-presenting cells present within the skin.