Evaluation of phagocytic activity in human monocyte-derived dendritic cells

Dendritic cells play a central role in initiation of primary T lymphocyte r esponses to foreign antigens. Their potency in antigen presentation vis-A-v is reported low or lack of ability to phagocytize particulate matter has li mited our understanding of the role that they play in inducing immunity to particulate antigens. One hypothesis is that dendritic cells may possess a high phagocytic capacity when immature and located in peripheral tissues, w hich they lose on maturation. Our goal was to characterize the phagocytic c apacity in human immature dendritic cells. The phagocytic capacity of human monocyte-derived immature dendritic cells was studied by morphological and morphometric means, and compared to that of professional phagocytes, human alveolar macrophages, their progenitors, the peripheral blood monocytes, a nd mature dendritic cells. Phagocytic index (proportion of phagocytic cells ) was decreased by 42.8% (immature dendritic cells) and 74.2% (mature dendr itic cells) with respect to monocytes. Similarly, the phagocytic index was decreased by 46.5% (immature dendritic cells) and 75.9% (mature dendritic c ells) with respect to macrophages. Volume density of phagocytized particles was decreased by 76.1% (immature dendritic cells) and 96.7% (mature dendri tic cells) with respect to the monocytes. However, volume density was decre ased by 34.3% (immature dendritic cells) and 91% (mature dendritic cells) w ith respect to alveolar macrophages. These results show that human monocyte -derived immature dendritic cells possess a phagocytic capacity that is low er than that of peripheral blood monocytes and alveolar macrophages but hig her than that of mature dendritic cells.