Tissue specific regulation of innate immune effector response during invasive bacterial infection

Natural barriers, like skin or airways, serve as a first-line of defense mechanism for humans to prevent infections. These barrier tissues are commonly colonized by different bacterial entities. Prior damage of the natural barriers due to severe burn injury or viral infection can lead to translocation of colonizing bacteria to deeper tissue, resulting in invasive infection, morbidity, and mortality. Colonizing bacteria, upon passing the barrier can exhibit their pathogenic potential to cause invasive infections such as necrotizing tissue infections. The triggered cellular response of humans after bacterial invasion results in profound tissue damage, and imbalanced inflammation. The extent of this response and the following sequence depends on a complex interplay between the epithelium, stromal matrix and the resident immune system, and is tightly regulated by the activity of specific cytokine signaling pathways. The important human pathogen Staphylococcus aureus is frequently found on the skin and airway tissues, exhibiting unique invasive disease potential and sophisticated ability to efficiently counteract the human innate immune defense. S. aureus utilizes their wide-repertoire of virulence factors and exotoxins to cause epithelial disruption, to escape from innate immune mediated killing and to cause tissue damage and severe infection. Additionally, these virulence factors, especially exotoxins exhibit significant cell/species specificity, tissue-tropism with human cells being the most sensitive towards these toxins. The central question regarding how the loss of barrier function by prior damage due to burn injury or viral infections mediated hyperinflammation causes innate immune dysfunction is not well understood. Finally, the exact molecular mechanisms contributing to this dysregulated immune response and concomitant inflammation imbalance at the tissue site of infection are currently not well studied. Progress in the field has been hampered by the lack of experimental systems to that allows to study these processes in detail in a human tissue-like settings. In this project, we aim to gain an in-depth understanding of the tissue specific innate immune signatures that regulate antibacterial immune response in airway tissue. We will employ novel immunocompetent, multicellular organotypic airway tissue models, engineered to resemble the host physiological environment, ex vivo immune functional assays and in vivo mice model of pneumonia to study the immune response mechanisms during infection. Specifically, in aim 1 we will (i) characterize the inherent bacterial virulence properties that can lead to dysregulation in epithelial barrier functions and innate immune effector response during S. aureus infection. We will apply an unbiased multiparameter single-cell analysis combined with quantification of pathways involved in antibacterial defense mechanisms against S. aureus infection. In aim 2 we will (i) determine how burn injury or viral infection mediated hyperinflammation induces immune dysregulation of myeloid cells thereby abrogating innate immune effector response against secondary bacterial infection in airway tissue. Here we will make use of both plasma as well as cellular samples collected from patient suffering from severe burn injury or viral infections (SARS-CoV-2 and influenza) during their acute and recovery phase of hypercytokinemia. (ii) we will focus on how synergism in cytokine signaling pathways especially, TNFa-IFN?-IL4 cytokine axis causes dysregulation in innate immune effector mechanisms against S. aureus. Successful completion of this project has the potential to generate important new knowledge on the fundamentals of host defense strategies in human barrier tissues during invasive bacterial infections. Similarly, the pathways and the factors identified in this project can have a direct translational and clinical implications for development of new treatment strategies and therapeutic targets.