Biological Sex Differences after High and Low Doses of Influenza A Virus Infection in a Diet-induced Obesity Mouse Model

Abstract Obesity is an independent risk factor for influenza A virus (IAV) pathogenesis. In non-obese hosts, following IAV infection, adult females develop more severe disease than males. Limited research on biological sex differences following IAV infection in individuals with obesity forms the basis for this study. Male and female C57BL/6J mice were treated with high-fat or low-fat diets to obtain mice with or without obesity. They were inoculated intranasally with a high (103) or low dose (101.5 TCID50) of mouse-adapted A/California/04/2009 H1N1 IAV and followed for 21 days post-infection (dpi) for morbidity. Subsets of mice were euthanized at different dpi to measure lung virus titers, histopathological changes, cellular infiltration, and cytokine induction. After a high-dose infection, females with obesity demonstrated shorter median survival time, greater parenchymal inflammation, and heightened induction of inflammatory markers than males with obesity. After a low-dose infection, females than males, and mice with obesity than the non-obese mice, exhibited severe morbidity. Female mice with obesity exhibited the greatest disease severity, where 25% (2/8) reached humane endpoint. Delayed but persistent inflammatory changes were observed in females with obesity, characterized by relatively lower pathological changes, lesser induction of cytokines and chemokines, and reduced myeloid and lymphoid infiltration in the lungs at 3 dpi followed by sustained pathological changes and cytokine and chemokine induction at 21 dpi. Our study suggests that the biological sex difference following IAV infection persists during obesity. Females with obesity experience greater influenza disease severity than males, possibly driven by more severe dysregulation of inflammatory responses. Importance The prevalence of obesity is increasing worldwide. The risk of developing severe disease following influenza virus infection is higher in individuals with obesity. Males and females with obesity differ in terms of fat deposition and inflammatory and metabolic biomarkers. These differences can alter the outcomes of influenza-induced disease pathogenesis. The observation of sex differences in IAV pathogenesis among non-obese hosts underscores the importance of determining whether similar differences occur in the context of obesity. Indeed, our study suggested that females with obesity experience greater disease severity than males with obesity after IAV infection. Understanding the immunological mechanisms of such differences will advance precision medicine approaches to develop safer and more effective preventive and therapeutic strategies against influenza for the high-risk populations with obesity.