The mast cell mediator PGD2 suppresses IL-12 release by dendritic cells leading to Th2 polarized immune responses in vivo.

Dendritic cells (DC) and mast cells (MC) are colocalized in superficial organs such as the skin. Both cell types recognize and respond to pathogens. DC capture and transport antigens to the draining lymph node for CD4+ T cell priming and T helper 1 (Th1) or Th2 polarization. As MC are mainly associated with Th2 responses, DC-MC interactions may favor Th2 priming by DC. Here, we show the role of different MC mediators on IL-12 and IL-10 production by DC. While histamine, leukotriene C4, heparin and chondroitin sulfate A had little and unspecific effects on the cytokine production, prostaglandin D2 (PGD2) downregulated IL-10, IL-12p70 and p40. After subcutaneous (s.c.) injection of ovalbumin (OVA)-loaded, lipopolysaccharide (LPS)-matured DC into Th1-prone C57BL/6 mice, the levels of IFN-gamma produced by Th1 cells were decreased while IL-4 production remained low. When TNF-matured DC were pretreated with PGD2, loaded with the endotoxin-free antigen KLH and injected s.c. into Th2-prone BALB/c mice, we found a dose- and time-dependent upregulation of IL-4 and downregulation of IFN-gamma by T cells. Together, MC-derived PGD2 instructs DC to polarize CD4+ T cells towards Th2 responses. As a consequence, such a DC-MC cooperation may contribute to the maintenance of Th2 responses in allergic patients.