Differentially TLR‐activated DCs direct disparate human CD4+ Th17 & Th1 differentiation

The role of differential TLR activation of human DCs on CD4+ Th17 & Th1 differentiation was examined. First, the production of cytokines, thought to be important in Th17/Th1 differentiation, by various TLR‐activated DCs was examined. Pam3Cys, a TLR2 ligand, & LPS, a TLR4 ligand, induced monocyte‐derived (mo) DCs to produce increased levels of IL23 & IL6 but decreased levels of IL12p70. Conversely, poly I:C, a TLR3 ligand, & ssRNA, a TLR7/8 ligand, induced moDCs to produce lower levels of IL23 & IL6 but increased levels of IL12p70. Second, differentially TLR‐activated moDCs were co‐cultured with naïve allogeneic human CD4+ T cells (CD45RO‐) for 5–7 days, & the T cells were examined for their Th17/Th1 differentiation by IL17 & IFNγ ELISOT analysis. LPS‐activated moDCs directed increased Th17 differentiation, whereas poly I:C‐activated moDCs directed increased Th1 differentiation. Using an APC‐free system, Th17 differentiation was maximally enhanced in the presence of IL1, IL6, & TGFβ in contrast to recent publications. Depletion of CD25+ T cells from naïve CD4+ T cell populations decreased Th17 differentiation in the DC‐T cell co‐culture system, implicating CD25+, CD45RO‐ CD4+ T cells as the major source of TGFβ in the co‐cultures. Overall, these results suggest that less toxic derivatives of TLR4 ligands could be used as adjuvants to promote both Th17 & Th1 differentiation in vaccines and other immunotherapies.