IN CUTANEOUS T-CELL LYMPHOMA, CLASS-II MHC MOLECULES ON CD1(-PRESENTING CELLS ARE UP-REGULATED IN INVOLVED COMPARED WITH UNINVOLVED EPIDERMIS() ANTIGEN)

CD1(+) antigen-presenting cells in involved epidermis of patients with cutaneous T-cell lymphoma exhibit an enhanced functional capacity to activate autologous CD4(+) T cells compared with CD1(+) antigen-presen ting cells from uninvolved and normal epidermis. Class II major histoc ompatibility complex molecules are involved in antigen presentation, a nd their expression on CD1(+) Langerhans cells is known to vary. The e xpression of all three class II: (HLA-DR, -DQ, -DP) molecules was ther efore determined on CD1(+) epidermal cells from both involved and unin volved epidermis, using flow cytometry. The involved CD1(+) epidermal cells exhibited a 1.5-1.6-fold, statistically significant increase in fluorescence intensity after staining of the class TT molecules (HLA-D R, -DQ, -DP) compared with CD1(+) epidermal cells from uninvolved epid ermis. The autologous CD4(+) T-cell activation was almost completely b locked by anti-HLA-DR, and partly by anti-HLA-DQ and anti-HLA-DP. In c ontrast, an antibody against class I, and an irrelevant control antibo dy, had no blocking effect. In a pokeweed mitogen assay it was demonst rated that autologous CD4(+) T cells, activated by involved epidermal cells, demonstrated suppressor activity rather than helper activity. T he suppressor activity was dependent on the presence of HLA-DR-positiv e epidermal cells. Thus, in cutaneous T-cell lymphoma, class LT molecu les on the individual CD1(+) antigen-presenting cell are upregulated i n clinically involved compared with uninvolved epidermis, and these mo lecules are crucially involved in activation of CD4(+) T cells.