EXPRESSION OF CLASS-II MAJOR HISTOCOMPATIBILITY ANTIGENS BY KERATINOCYTES IN CUTANEOUS T-CELL LYMPHOMA

Background. Expression of various class II MHC antigens by lesional ke ratinocytes may play an important role in the pathophysiology of a wid e variety of human dermatoses including cutaneous T cell lymphoma (CTC L). Nevertheless, there is relatively little information available con cerning the concurrent expression Of HLA-DR, -DP, and -DQ class II MHC antigens in CTCL. Therefore, our aim in this study was to determine t he prevalence, localization, extent, temporal sequence, and consistenc y of class II MHC antigen expression by lesional keratinocytes in CTCL . Methods. We used a semiquantitative immunohistologic analysis to ana lyze HLA-DR, -DP, and -DQ expression by lesional keratinocytes in 66 s kin biopsies obtained from 39 patients with CTCL. Results. Class II MH C antigen expression by keratinocytes was observed in 77% of cases. Ex pression was detected on the cytoplasmic membrane and within the cytop lasm. It varied among cases from focal to confluent. There was a hiera rchy of antigen expression in terms of both extent and time course. HL A-DR was expressed first and most extensively, followed by HLA-DP and then HLA-DQ. Comparative studies of multiple serial or concurrent acti ve lesions from 13 cases indicated that the overall pattern and extent of antigen expression was relatively constant within individual patie nts. Conclusions. There was no apparent correlation between class II M HC antigen expression and the clinical stage of disease, the type of C TCL skin lesion, or the overall density of the lesional T cell infiltr ate. The hierarchy of keratinocyte class II MHC antigen expression obs erved in this study paralleled that noted in earlier studies of cultur ed keratinocytes exposed to recombinant interferon-gamma in vitro. Thi s suggests that lesional cytokine levels may be the critical factor go verning class II MHC antigen expression by lesional keratinocytes in C TCL.