The role of toll-like receptor-9 in type II epithelial cells and fibroblasts during influenza and s. Aureus coinfection

The National Heart, Lung, and Blood Institute awarded the Regents of the University of Michigan $100,228 on December 1, 2026, under the Cardiovascular Diseases Research program (CFDA 93.837) to conduct research on the role of Toll-like Receptor-9 (TLR9) in type II epithelial cells and fibroblasts during influenza and Staphylococcus aureus coinfection.

The research addresses the mechanism by which TLR9 expression in lung structural cells contributes to poor outcomes during influenza-bacterial coinfections. The investigator's central hypothesis is that TLR9 upregulation in epithelial cells and fibroblasts following influenza virus infection alters cytokine production to impair alveolar macrophage phagocytosis and killing of methicillin-resistant Staphylococcus aureus (MRSA). Preliminary data indicate that mice lacking TLR9 only in epithelial cells have decreased bacterial burden following coinfection, suggesting that TLR9 expression in structural cells is detrimental during coinfection. The project will identify the specific role of TLR9 in these lung structural cells using mouse models of influenza-MRSA coinfection.

Work will be performed at the University of Michigan in Ann Arbor, Michigan. The period of performance runs from December 1, 2026, through April 30, 2029.

Abstract

Evidence from pandemics and seasonal epidemics indicates that influenza is associated with bacterial coinfections which increases morbidity and mortality. One of the most common bacteria found in coinfection is staphylococcus aureus, and methicillin resistant staphylococcus aureus (mrsa) is a newer strain that is resistant to methicillin antibiotics which has made infections more difficult to treat. Viruses and bacteria are recognized by extra-cellular or intracellular pattern recognition receptors (prrs). Toll like receptor 9 (TLR9) is a class of prrs that senses bacterial and viral DNA containing unmethylated cytosine-guanidine motifs. Tlrs have been associated with exacerbation of disease and increase inflammation during infections. Most research to date has investigated the function of TLR9 in immune cells, but the function of TLR9 in non-immune cells is much less understood. Studies from our laboratory have shown that TRL9 knockout mice fare better during coinfection suggesting that TLR9 is associated with more inflammation and poor survival outcomes. Additionally, we have preliminary data indicating that TLR9 expression in structural cells is detrimental during coinfection. In this proposal we seek to identify the role of TLR9 in lung structural cells, mainly epithelial cells and fibroblasts, during coinfection with influenza virus and mrsa. We have preliminary data showing that TLR9 is upregulated in epithelial cells and fibroblasts following influenza virus infection, and mice that lack TLR9 only in epithelial cells have a decreased bacterial burden following coinfection indicating improvement in disease burden. In this proposal my central hypothesis is that upregulation of TLR9 in epithelial cells and/or fibroblasts post-IAV alters cytokine production to impair alveolar macrophage phagocytosis and killing of mrsa and results in increased bacterial burden and lung injury during coinfection. This hypothesis will be tested through two specific aims: 1) assess the upregulation of TLR9 in lung alveolar epithelial type II cells post-IAV and its effects on innate host responses during coinfection with IAV and mrsa and 2) investigate the upregulation of TLR9 in lung fibroblasts post-IAV and its effects on macrophage antibacterial function during coinfection with IAV and mrsa. Experiments for these aims will be completed with the use of genetically engineered mouse models, cells derived from such mice, and in vitro assays to study the effect of TLR9 on macrophage phagocytosis and killing of mrsa. The results from these innovative studies may inform treatments that help improve coinfection outcomes. Completion of this proposal will also allow me to receive rigorous training in experimental design, implementation, and interpretation that will help me become a successful, independent scientist.