Migratory CD11b+ conventional dendritic cells induce T follicular helper cell dependent antibody responses

T follicular helper (Tfh) cells are a subset of CD4+ T cells that promote antibody production during vaccination. Conventional dendritic cells (cDCs) efficiently prime Tfh cells; however, conclusions regarding the nature of the cDC responsible for instructing Tfh cell differentiation have differed between recent studies. We found that these discrepancies might exist, in part, due to the unusual sites used for immunization in murine models, which differentially bias which DC subsets access antigen. We used intranasal immunization as a physiologically relevant route of exposure that we show delivers antigen to all tissue DC subsets. Using a combination of mice in which the function of individual DC subsets is impaired and different formulations of antigen delivery, we determined that CD11b+ migratory type 2 conventional DCs (cDC2s) are necessary and sufficient for Tfh induction. DC-specific deletion of the guanine nucleotide exchange factor DOCK8 resulted in an isolated loss of CD11b+ cDC2 but not CD103+ cDC1 migration to lung-draining lymph nodes. Impaired cDC2 migration or development in DC-specific Dock8 or Irf4 knockout mice, respectively, led to reduced Tfh cell and antibody development, whereas loss of CD103+ cDC1s in Batf3-/- mice did not. Loss of cDC2-mediated Tfh responses was associated with impaired antibody-mediated protection from live influenza virus challenge. We show that migratory cDC2s uniquely carry antigen into the sub-anatomic regions of the lymph node where Tfh cell priming occurs, the T-B border. This work identifies the DC responsible for Tfh cell-dependent antibody responses, in particular when antigen dose is limiting or is encountered at a mucosal site, which could ultimately inform the formulation and delivery of vaccines. Overall design: RNA-seq of CD11b+ and CD103+ dendritic cells from the mediastinal lymph nodes滤泡辅助性T细胞（T follicular helper, Tfh）是CD4阳性T细胞的一个亚群，可在疫苗接种过程中促进抗体产生。常规树突状细胞（conventional dendritic cells, cDCs）可高效启动Tfh细胞的活化，但近期不同研究中关于指导Tfh细胞分化的cDC亚群特性的结论存在分歧。我们发现，这些结论差异部分源于小鼠模型中所采用的非常规免疫接种位点——这类位点会差异化地影响不同DC亚群接触抗原的情况。本研究采用鼻腔免疫这一符合生理暴露特征的免疫途径，经证实该途径可将抗原递送至所有组织DC亚群。通过联合使用个体DC亚群功能受损的小鼠模型与不同配方的抗原递送策略，我们明确了CD11b阳性迁移型2型常规树突状细胞（cDC2s）是诱导Tfh细胞活化的必要且充分条件。DC特异性敲除鸟苷酸交换因子DOCK8，会选择性导致CD11b阳性cDC2向肺引流淋巴结的迁移受损，却不会影响CD103阳性cDC1的迁移。在DC特异性Dock8敲除小鼠与DC特异性Irf4敲除小鼠中，分别出现的cDC2迁移或发育受损，会导致Tfh细胞与抗体生成能力下降；而Batf3基因敲除（Batf3-/-）小鼠中CD103阳性cDC1的缺失则无此影响。cDC2介导的Tfh细胞应答受损，会伴随抗体介导的活流感病毒攻击防护能力下降。我们证实，迁移型cDC2可特异性将抗原递送至Tfh细胞活化启动的淋巴结亚解剖区域——T细胞-B细胞边界。本研究明确了介导Tfh细胞依赖性抗体应答的DC亚群，尤其适用于抗原剂量受限或于黏膜部位接触抗原的场景，该发现可为疫苗的配方与递送策略提供参考。总体实验设计：对取自纵隔淋巴结的CD11b阳性与CD103阳性树突状细胞进行RNA测序。