Demonstration of a subpopulation of Ia+ T-helper cells in mycosis fungoides and the Sézary syndrome.

This is a report of the finding of a T-cell subpopulation bearing T-helper cells and Ia antigens in specimens of skin from patients with mycosis fungoides and the Sézary syndrome. Frozen sections of skin tissue from eight patients examined with monoclonal antibodies against mature T-cells, helper T-cells, suppressor T-cells, and Ia antigens exhibited similar staining patterns by a modified immunoperoxidase method. Antibodies against mature T-cells and helper T-cells stained 70-80% of the lymphocytes in the dermis. The antibody defining the phenotype of suppressor T-cells labelled 5-10% of the lymphocytes scattered throughout the lesions. Eighty to 90% of the lymphocytes took the stain for Ia antigen. Anti-thymocyte antibody (OKT6) stained cells in both the epidermis and dermis of the specimens. Of nonmalignant conditions examined, lesions from five cases of lichen planus exhibited a quantitatively different staining pattern than that of mycosis fungoides in that the number of T-helper cells was about equal to the number of T-suppressor cells. The findings reported are evidence for a homogeneous population of T-helper, Ia-positive lymphocytes in the cutaneous lesions of mycosis fungoides and the Sézary syndrome.