Impaired Cytokine Secretion Contributes to Age-Dependent Immune Dysfunction in SARS Coronavirus Response and Is Restored by Young CD11b-Positive Cell Transfer

COVID-19 mortality disproportionately affects the elderly, yet the cellular and molecular factors contributing to age-related immune system remodeling remain unclear. Using SARS-CoV-derived ssRNA sequences, we modeled age-dependent immune responses in mice. Aged mice exhibited higher mortality and severe lung inflammation upon viral ssRNA challenge, mirroring clinical observations. We uncovered a pre-existing inflammatory state in aged mice, characterized by elevated baseline levels of specific immune cells and cytokines correlating with poor outcomes. Age-related immune dysfunction stemmed from impaired IRF7 signaling and defective SNARE-mediated cytokine secretion in CD11b⁺ cells. Notably, the adoptive transfer of young CD11b⁺ cells to aged mice exposed to SARS-CoV2 ssRNA reduced mortality, alleviated lung inflammation, and normalized cytokine profiles. These findings provide insights into age-related immune dysregulation during viral challenges and suggest potential therapeutic strategies for severe COVID-19 in the elderly.