Discordant expression of antigens between intraepidermal and intradermal T cells in mycosis fungoides.

Using immunohistochemical methods, the authors studied the expression of pan-T- and majority-T-cell antigens (CD5, CD2, CD3, TCR-beta, CD7) and T-cell subset antigens (CD4, CD8) in cutaneous T cells in mycosis fungoides (MF) (177 biopsies from 124 patients) and a variety of inflammatory lesions (45 biopsies from 45 patients). The authors detected the absence of pan-T- or majority-T-cell antigens, or of both T-cell subset antigens, from T cells in the epidermis but not the dermis in 15 MF biopsies (8%) from 11 MF patients (9%), but in none of the inflammatory skin lesions. The opposite picture, characterized by lack of antigen expression by the dermal T cells only, was not seen in any of the MF or inflammatory lesions. The absence of antigen expression by epidermal but not dermal T cells, which the authors have termed antigen discordance, was most prevalent for CD5, CD7, and TCR-beta, each being discordant in 6% to 7% of MF cases or patients tested. Among the MF biopsies showing antigen discordance, 14 of 15 biospies (93%) from 10 of 11 patients (91%) were discordant for two or more antigens. Antigen discordance was not an artifact of treatment, because none of the patients showing discordance was receiving treatment at the time of their initial discordant biopsy. The discordance was the only immunophenotypic abnormality detected in 8 of 15 (53%) of the discordant MF biopsies. Thus, this antigen discordance was an important diagnostic feature that allowed the immunophenotypic distinction of MF from a variety of inflammatory skin lesions.