CCL19 and CCL21 Chemokines Induce Endocytosis and Augment Antigen Presentation in Human Mature Dendritic Cells.

Dendritic cells (DCs) are potent antigen presenting cells capable of regulating immune responses. DCs lose the ability to capture and process antigens during maturation. In the present study, we examined the effects of CCR7 ligands, CCL19 and CCL21, on endocytosis and antigen presentation in human mature dendritic cells. Immature DCs were generated from peripheral blood monocytes by culturing with GM-CSF and IL4 for 2–3 days. For maturation, immature DCs were cultured with the addition of TNF_α, IL1_β, IL6 and prostaglandin E² for another 24 hours. Immature or mature DCs were incubated with FITC-dextran with or without CCL19. Immature DCs internalized FITC-dextran efficiently independent of the presence of CCL19 after 1 hour incubation. On the other hand, mature DCs scarcely internalized FITC-dextran without CCL19. In the presence of CCL19, however, mature DCs internalized FITC-dextran significantly (approximately 60% positive). The effect of CCL19 on the uptake of FITC-dextran in mature DCs was dose and time dependent. CCL21 exerted a similar effect on mature DCs. Next, we examined whether CCL19 facilitates antigen presentation in mature dendritic cells. CD4⁺ T cells were cultured with irradiated autologous mature DCs which had been incubated with leukemia cell lysate with or without CCL19. Marked proliferation of CD4⁺ T cells occurred only when these cells were cultured with mature DCs loaded with leukemia cell lysate in the presence of CCL19. This is the first demonstration that chemokines have a pivotal role in endocytosis and antigen presentation by human monocyte-derived dendritic cells to the best of our knowledge. These results demonstrated that generation of potent antigen-loaded mature DCs in relatively short term culture using various cytokines and chemokines may have an important clinical implication to facilitate DC-based immunotherapy.