Obesity’s role in severe flu outcomes unveiled by new study

Researchers in a pivotal study recently featured in Nature Communications have uncovered vital insights into why individuals with obesity are at an elevated risk for severe influenza. This comprehensive investigation combines both human clinical data and animal model analysis to unravel the complexities of immune response in obesity that heighten the vulnerability to influenza.

The global health landscape is facing a critical challenge with the rising prevalence of obesity, affecting over 13% of adults worldwide. The risks associated with obesity have been underscored during viral pandemics, such as the H1N1 outbreak and the recent COVID-19 pandemic, where obesity has been consistently linked with worse outcomes and heightened severity of respiratory infections.

This latest study seeks to bridge the knowledge gap in understanding how obesity mechanistically contributes to increased susceptibility to viral infections, beyond the recognised impacts of altered lung function, cardiovascular issues, and metabolic disturbances.

Researchers embarked on a meticulous study design, sampling blood and airway cells from individuals with obesity —those with a BMI over 35 kg/m^2—undergoing bariatric surgery. The study meticulously matched these participants with control subjects of normal weight, ensuring parity in age, gender, and ethnicity.

The investigative team conducted thorough clinical sampling using state-of-the-art techniques, including blood analysis, nasal synthetic absorptive matrix (SAM) sampling, and bronchoscopy.

A suite of laboratory experiments followed. These involved exposing various cell types, including bronchoalveolar lavage (BAL) cells and bronchial epithelial cells (BECs), to different strains of influenza viruses. The response of these cells was measured through advanced techniques like RNA extraction, protein quantification, and a range of assays including flow cytometry and metabolomics.

In vivo studies also played a role, with mice models used to examine the effects of administering recombinant mouse leptin followed by influenza virus infection. This holistic approach aimed to dissect the immune response in both the peripheral and airway-specific compartments.

The study’s findings are eye-opening. Contrary to initial assumptions, the researchers found no significant difference in the response of bronchial epithelial cells between individuals with obesity and individuals of a  normal-weight, suggesting that epithelial inflammation is not inherently altered in those with obesity during influenza infection.

However, the study did identify a significant compromise in the antiviral responses of BAL macrophages from patients with obesity. These cells displayed a reduced induction of critical interferons, such as IFN-α, IFN-β, and IFN-λ, which are vital components of the body’s antiviral defence system. Moreover, the production of key pro-inflammatory cytokines like IL-6, IL-8, and TNF was found to be less effective in individuals with obesity.

Metabolomic analysis of the BAL fluid identified significant changes in metabolite levels in patients with obesity, providing a clue to altered biochemical pathways in the lungs due to obesity.

The data from the MOSAIC cohort added a further layer of understanding, highlighting that immune dysregulation in patients with obesity was confined to the airway mucosa, with no significant systemic immune disturbances.

The study’s revelations pave the way for potential therapeutic strategies, including the manipulation of leptin pathways, which may be pivotal in mitigating the risk of severe influenza infections in populations with obesity.

By casting light on the molecular and immunological shifts that occur in the context of obesity, this research could form the foundation for developing tailored interventions that bolster the immune response in this high-risk group, enhancing their resilience to influenza and other viral respiratory infections.