Modulation of the expression of CD4 on HL-60 cells by exposure to 1,25-dihydroxyvitamin D₃

The CD4 molecule functions as a receptor for the binding and infectivity of the human immunodeficiency virus (HIV). It is of interest, therefore, to develop procedures for its down-regulation. In the present study, the effect of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on the expression of cell surface antigens of the HL-60 promyelocytic leukemia cell line was analyzed. Exposure of HL-60 cells to 1,25(OH)₂D₃ resulted in down-regulation of CD4 as assessed by their staining with the Leu-3a monoclonal antibody (MoAb). This treatment increased the staining of HL-60 cells with the monocyte-specific 63D3 MoAb. In contrast to the rapid elimination of cell surface CD4 by exposure of HL-60 to phorbol myristate acetate (PMA), the maximal reduction of CD4 by 1,25(OH)₂D₃ was attained within 48 h after the beginning of the exposure.