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

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Abstract
Background. Expression of various class II MHC antigens by lesional keratinocytes may play an important role in the pathophysiology of a wide variety of human dermatoses including cutaneous T cell lymphoma (CTCL). Nevertheless, there is relatively little information available concerning the concurrent expression of HLA‐DR, ‐DP, and ‐DO class II MHC antigens in CTCL. Therefore, our aim in this study was to determine the prevalence, localization, extent, temporal sequence, and consistency of class II MHC antigen expression by lesional keratinocytes in CTCL. Methods. We used a semiquantitative immunohistologic analysis to analyze HLA‐DR, ‐DP, and ‐DO. expression by lesional keratinocytes in 66 skin biopsies obtained from 39 patients with CTCL. Results. Class II MHC antigen expression by keratinocytes was observed in 77% of cases. Expression was detected on the cytoplasmic membrane and within the cytoplasm. It varied among cases from focal to confluent. There was a hierarchy of antigen expression in terms of both extent and time course. HLA‐DR was expressed first and most extensively, followed by HLA‐DP and then HLA‐DQ. Comparative studies of multiple serial or concurrent active lesions from 13 cases indicated that the overall pattern and extent of antigen expression was relatively constant within individual patients. Conclusions. There was no apparent correlation between class II MHC antigen expression and the clinical stage of disease, the type of CTCL skin lesion, or the overall density of the lesional T cell infiltrate. The hierarchy of keratinocyte class II MHC antigen expression observed in this study paralleled that noted in earlier studies of cultured keratinocytes exposed to recombinant interferon‐γin vitro. This suggests that lesional cytokine levels may be the critical factor governing class II MHC antigen expression by lesional keratinocytes in CTCL.