Contribution of Dendritic Cell Subsets to T Cell-Dependent Responses in Mice.

BATF3-deficient mice that lack CD8(+) dendritic cells (DCs) showed an exacerbation of chronic graft-versus-host disease (cGVHD), including T follicular helper (Tfh) cell and autoantibody responses, whereas mice carrying the Sle2c2 lupus-suppressive locus with a mutation in the G-CSFR showed an expansion of CD8(+) DCs and a poor mobilization of plasmacytoid DCs (pDCs) and responded poorly to cGVHD induction. Here, we investigated the contribution of CD8(+) DCs and pDCs to the humoral response to protein immunization, where CD8(neg) DCs are thought to represent the major inducers. Both BATF3(-/-) and Sle2c2 mice had reduced humoral and germinal center (GC) responses compared with C57BL/6 (B6) controls. We showed that B6-derived CD4(+) DCs are the major early producers of IL-6, followed by CD4(-)CD8(-) DCs. Surprisingly, IL-6 production and CD80 expression also increased in CD8(+) DCs after immunization, and B6-derived CD8(+) DCs rescued Ag-specific adaptive responses in BATF3(-/-) mice. In addition, inflammatory pDCs (ipDCs) produced more IL-6 than all conventional DCs combined. Interestingly, G-CSFR is highly expressed on pDCs. G-CSF expanded pDC and CD8(+) DC numbers and IL-6 production by ipDCs and CD4(+) DCs, and it improved the quality of Ab response, increasing the localization of Ag-specific T cells to the GC. Finally, G-CSF activated STAT3 in early G-CSFR(+) common lymphoid progenitors of cDCs/pDCs but not in mature cells. In conclusion, we showed a multilayered role of DC subsets in priming Tfh cells in protein immunization, and we unveiled the importance of G-CSFR signaling in the development and function pDCs.