Anti-viral innate immune response in young and old macrophages and microglia

The innate immune system constitutes a powerful antiviral defense system; however, dysregulation of innate immunity causes and contributes to diseases (inflammation). Aging has been associated with a waning of innate immune control; however, the underlying molecular mechanisms are not understood. Macrophages are considered one of the major cell types mediating innate immune responses. They exist in various forms throughout the body as part of the mononuclear phagocyte system. These include blood-resident systemic macrophages and microglia, which mediate defence of the central nervous system. The aim of my study was to comparatively analyse the anti-viral responses of primary Monocyte-derived macrophages (MDMs) and Monocyte-derived microglia (MMGs) and to assess age-related differences in their antiviral responses. To this end, a robust and reproducible differentiation protocol was established to generate both MDMs and MMGs from PBMC-derived monocytes of the same young (< 27 years) and aged donors (> 52 years). Subsequently, these cells were infected with a macrophage-tropic model virus, the Flavivirus Zika Virus (ZIKV). Gene expression (qRT-PCR) and protein levels of key innate immune mediators (LEGENDplex) were analysed under homeostatic conditions and following ZIKV infection. On average, MMGs displayed higher baseline expression of innate immune genes (CCL5, IL1B, MX1, OAS1) and elevated secretion of proinflammatory cytokines, including IL-6, TNFα, and IL-28A, compared to MDMs, while age-stratified analysis showed low-grade inflammation in the aged group. However, upon ZIKV infection, both MMGs and MDMs derived from young donor cells further induced innate defences, including anti-viral gene expression (qPCR: OAS1, MX1) and cytokine production (Multiplex ELISA: IL1-β, IL-8, IFN-β). Of note, in both MDMs and MMGs, the anti-viral gene expression upon ZIKV was higher in younger donors. The secreted cytokine concentrations at 24 hours post-infection reflected this trend, with higher activation in young compared to aged donors. Finally, my data shows that replication of ZIKV in young MDMs and MMGs is attenuated. Taken together, this in vitro model provides a reproducible platform to study the impact of ageing on innate immune defences. Our findings suggest that MMGs are intrinsically more primed than MDMs, and that aging skews both cell types toward heightened basal inflammation but impaired antiviral responses—potentially contributing to slower viral clearance and increased disease severity in older individuals.