The expression of receptors for IgA on human monocytes and calcitriol-treated HL-60 cells.

In this study, we investigated the expression of IgA Fc receptors (FcR alpha) by human myeloid cells. By using a sensitive cytofluorometric IgA binding assay, we found that approximately 85% of peripheral blood monocytes bound IgA in an isotype-specific fashion. The HL-60 human promyelocytic leukemia cell line failed to express FcR alpha; however, treatment of HL-60 cells with the differentiating agent calcitriol induced the expression of FcR alpha on greater than 90% of these cells. Monocytes and calcitriol-treated HL-60 cells were capable of ingesting IgA-coated erythrocyte targets, suggesting that phagocytosis could be mediated through FcR alpha. The induced HL-60 cell system represents a useful model for further studies on FcR alpha expression and function.