Innate Immune Responses after Airway Epithelial Stimulation with <i>Mycobacterium bovis</i> Bacille-Calmette Guérin

Mycobacterium bovis bacilli Calmette-Guerin (BCG) is used as a benchmark to compare the immunogenicity of new vaccines against tuberculosis. This live vaccine is administered intradermal, but several new studies show that changing the route to mucosal immunisation represents an improved strategy. We analysed the immunomodulatory functions of BCG on human neutrophils and primary airway epithelial cells (AECs), as the early events of mucosal immune activation are unclear. Neutrophils and the primary epithelial cells were found to express the IL-17A receptor subunit IL-17RA, while the expression of IL-17RE was only observed on epithelial cells. BCG stimulation specifically reduced neutrophil IL-17RA and epithelial IL-17RE expression. BCG induced neutrophil extracellular traps (NETs), but did not have an effect on apoptosis as measured by transcription factor forkhead box O3 (FOXO3). BCG stimulation of AECs induced CXCL8 secretion and neutrophil endothelial passage towards infected epithelia. Infected epithelial cells and neutrophils were not found to be a source of IL-17 cytokines or the interstitial collagenase MMP-1. However, the addition of IFNγ or IL-17A to BCG stimulated primary epithelial cells increased epithelial IL-6 secretion, while the presence of IFNγ reduced neutrophil recruitment. Using our model of mucosal infection we revealed that BCG induces selective mucosal innate immune responses that could lead to induction of vaccine-mediated protection of the lung.牛分枝杆菌卡介苗（Mycobacterium bovis bacilli Calmette-Guerin, BCG）常被用作基准疫苗，用于对比评估新型抗结核病疫苗的免疫原性。该活疫苗传统采用皮内接种途径，但多项最新研究显示，将接种途径改为黏膜免疫可带来更优的免疫策略。由于黏膜免疫激活的早期事件尚不明确，本研究分析了卡介苗对人中性粒细胞与原代气道上皮细胞（AECs）的免疫调节功能。实验发现，中性粒细胞与原代上皮细胞均表达IL-17A受体亚基IL-17RA，而IL-17RE的表达仅见于上皮细胞。卡介苗刺激可特异性下调中性粒细胞IL-17RA与上皮细胞IL-17RE的表达水平。卡介苗可诱导中性粒细胞胞外陷阱（neutrophil extracellular traps, NETs）形成，但对通过转录因子叉头框O3（FOXO3）检测的细胞凋亡无显著影响。对原代气道上皮细胞的卡介苗刺激可诱导CXCL8分泌，并促进中性粒细胞向感染上皮的跨内皮迁移。研究未发现感染上皮细胞与中性粒细胞可作为IL-17细胞因子或间质胶原酶MMP-1的来源。然而，在卡介苗刺激的原代上皮细胞中加入干扰素γ（IFNγ）或IL-17A可上调上皮细胞IL-6的分泌，而干扰素γ的存在则会抑制中性粒细胞募集。通过本研究构建的黏膜感染模型，我们证实卡介苗可诱导选择性黏膜固有免疫应答，这可能介导疫苗对肺部的保护作用。