Abstract: AIMTo investigate the role of 1α,25-dihydroxyvitamin D₃ (calcitriol) and its analogues tacalcitol and 24,25(OH)₂D₃ on the phagocytosis of human monocyte-derived dendritic cells (MoDC). METHODSMoDC were generated in vitro by differentiating monocytes in the presence of GM-CSF and IL-4 for 5 days. Expression of mannose receptor (MR) and Fcγ receptors (FcγRs) by MoDC was analysed by flow cytometry. Zymosan ingestion was measured to assess the phagocytosis of MoDC. RESULTSMoDC expressed high level of MR and FcγRs and showed the capacity of zymosan ingestion. Calcitriol and tacalcitol but no 24,25(OH)₂D₃ not only upregulated the expression of MR and FcγRs on MoDC but also correspondingly enhanced their phagocytosis by increasing zymoasan ingestion. Furthermore, the upregulatory role occurred in the early stage of MoDC differentiation and was irreversible. The upregulatory role of calcitriol was dose dependent. CONCLUSIONCalcitriol and its analogue tacalcitol may play an important role in dendritic cell binding and capturing foreign antigens at the initiation of immune response.