Conventional type 2 lung dendritic cells are potent inducers of follicular helper T cells in the asthmatic lung

Follicular helper T (Tfh) cells represent a unique subset of helper CD4+ T cells in lymphoid follicles. Recently, Tfh cells were shown to play an important role in asthma through B cell differentiation. Conventional lung DCs are classified into two major subsets: conventional type 1 (cDC1) and type 2 (cDC2). Although the two subsets are different in driving particular T cell responses, the subset that induces Tfh cells in the asthmatic lung primarily has yet to be fully elucidated.We evaluated Tfh cells, defined by the expression of CD4 and CXCR5, in HDM-challenged mice. Next, we characterized cDC1 and cDC2 purified from antigen-primed lung and examined their Tfh cell-inducing capacity. Additionally, the ability of lung DC-induced Tfh cells to cause germinal center B (GCB) cells to produce antigen-specific IgE was assessed.In HDM-challenged mice, Bcl-6-expressing Tfh cells were significantly increased in the mediastinal lymph nodes. Lung cDC2, but not lung cDC1, increased after HDM priming, and cDC2 secreted larger amounts of IL-6 with higher ICOS-L expression than cDC1. In the co-cultures with OVA-specific naïve CD4+ T cells, cDC2 from OVA-primed lung induced Bcl-6-expressing Tfh cells more efficiently, together with larger amounts of IL-6 and IL-21, than cDC1. Blockage of IL-6 or ICOS-L significantly reduced Tfh cell induction. Finally, cDC2-induced Tfh cells enabled GCB cells to produce OVA-specific IgE.In asthmatic lung, cDC2 is the primary DC subset responsible for Tfh cell differentiation and plays an important role in humoral immunity in asthma by inducing Tfh cells.