Analysis of influenza-mediated alterations in alveolar type II epithelial cell (AECII) responsiveness as a mechanism underlying enhanced susceptibility to secondary pneumococcal infection

II型肺泡上皮细胞（AECII）是下呼吸道的常住细胞，具有越来越多的免疫潜力。它们是甲型流感病毒（IAV）复制的目标，并通过产生细胞因子和趋化因子对病毒感染迅速作出反应。然而，不仅病毒感染会引发AECII反应，而且它们也会对细菌配体产生反应，并被证明在本质上有助于抗菌防御。来自历史和最近流感大流行的流行病学数据清楚地表明，流感后继发性细菌感染的易感性大大增强，特别是肺炎链球菌。虽然这种协同作用最初是通过病毒感染破坏上皮来解释的，但我们今天知道，IAV对宿主呼吸免疫具有长期调节作用。该项目旨在揭示iav介导的AECII对细菌触发的反应性变化作为潜在机制。迄今为止，尽管AECII在抗菌防御中起作用，但它们在病毒/细菌协同作用中可能扮演的角色一直被忽视——然而，迄今为止，它们的特征还不够充分。因此，我们将首先详细描述AECII抗肺炎球菌反应，随后评估病毒感染恢复后iav介导的变化。这一方面将在全球基因转录水平上进行，通过微阵列分析从感染小鼠分离的原发AECII。另一方面，我们的目标是通过分析细菌对AECII的渗透和诱导细胞凋亡的原位和体外作用，增加我们对AECII与细菌的直接相互作用的理解，这些细胞来自naïve以及以前感染过IAV的宿主。重要的是，在这里，我们还将考虑影响AECII/肺炎球菌相互作用的细菌因素，包括选定的肺炎链球菌血清型的不同菌株。综上所述，这些分析将阐明解决的IAV感染如何印记呼吸道上皮，影响其对肺炎球菌接触的反应，从而增加对继发性细菌感染的易感性。通过考虑AECII作为流感后呼吸免疫调节的新参与者，我们的目标是全面了解IAV和肺炎链球菌之间协同作用的过程-这将是未来治疗和预防策略发展的关键基础。

Type II alveolar epithelial cells (AECII) are resident cells of the lower respiratory tract with an increasingly recognized immunological potential. They are targeted by the influenza A virus (IAV) for replication and rapidly react to viral infection with the production of cytokines and chemokines. However, not only viral infections trigger AECII responses, but they also respond to bacterial ligands and have been shown to essentially contribute to anti-bacterial defense. Epidemiological data from historic as well as recent influenza pandemics clearly documents strongly enhanced susceptibility to secondary bacterial infection following influenza, especially with S. pneumoniae. While this synergism was originally explained by epithelial destruction through the viral infection, we know today that IAV has a long-term modulating effect on host respiratory immunity. The proposed project aims at uncovering IAV-mediated changes in the responsiveness of AECII towards bacterial triggers as an underlying mechanism. AECII have so far been neglected as possible players in the viral/bacterial synergism, despite their role in anti-bacterial defense - which is however insufficiently characterized to date. Therefore we will first characterize the AECII anti-pneumococcal response in detail to subsequently assess IAV-mediated alterations present after recovery from the viral infection. This will take place on the one hand on a global gene transcriptional level through microarray analyses of primary AECII isolated from infected mice. On the other hand we aim at increasing our understanding of the direct interaction of AECII with the bacterium by analyzing bacterial penetration of AECII and induction of apoptosis both in situ and ex vivo with primary cells from naïve as well as previously IAV infected hosts. Importantly, here we will also take into account bacterial factors influencing the AECII/pneumococcal interaction by including different strains of selected S. pneumoniae serotypes. Taken together, these analyses will shed light on how a resolved IAV infection imprints the respiratory epithelium, affecting its responsiveness to pneumococcal encounters and thereby enhancing susceptibility to secondary bacterial infections. By taking AECII into account as new players in respiratory immune modulation following influenza, we are aiming towards a complete understanding of the processes underlying the synergism between IAV and S. pneumoniae - an understanding which will be the crucial basis for the development of strategies for treatment and prophylaxis in the future.