Dectin-1 in the control of Th2-type T cell responses.

Dendritic cells (DCs) are major antigen-presenting cells (APCs) that can induce and control host immune responses. DCs express pattern recognition receptors (PRRs), which can translate external and internal triggers into different types of T cell responses. The types of CD4⁺ T cell responses elicited by DCs (e.g., Th1, Th2, Th17, Th21, Th22 and regulatory T cells (Tregs)) are associated with either host immunity or inflammatory diseases, including allergic diseases and autoimmune diseases. In particular, the pathogenic functions of Th2-type T cells in allergic immune disorders have been well documented, although Th2-type T cell responses are crucial for immunity against certain parasite infections. Recent evidence also indicates that the inflammatory Th2 signatures in cancers, including breast and pancreatic cancers, are highly associated with poor clinical outcomes in patients. It is thus important to find cellular/molecular targets expressed in DCs that control such inflammatory Th2-type T cell responses. In a recent paper published in The Journal of Immunology, we demonstrated that Dectin-1 expressed on the two major human DC subsets, myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), has opposing roles in the control of Th2-type CD4⁺ T cell responses. Dectin-1 expressed on mDCs decreases Th2-type CD4⁺ T cell responses, while Dectin-1 expressed on pDCs favors Th2-type CD4⁺ T cell responses. This finding expands our understanding of the roles of DCs and Dectin-1 expressed on DCs in the pathogenesis of Th2-associated diseases and in host immunity to microbial infections and cancers.