Analysis of immune cell remodeling and functional alterations induced by aging and obesity in mice.

As human life expectancy increases, aging and obesity have become major contributors to immune dysfunction. Aging impairs homeostatic regulation and increases disease susceptibility, while a Western-style diet and sedentary lifestyle accelerate obesity, particularly in older individuals. Together, they promote chronic inflammation and immunosenescence. To investigate immune alterations associated with aging and obesity, we used young (2-month-old) and aged (14-month-old) C57BL/6 mice feed either a normal diet (10 % fat) or high-fat diet (HFD; 60 % fat) for 13 weeks. HFD increased body mass index (BMI), total cholesterol, and liver enzymes (ALT, AST). Hematological analysis revealed age- and obesity-associated changes in white blood cell composition. High-dimensional immune profiling of splenic cells using flow cytometry and CyTOF showed that aging and HFD led to reduced T cells, NK cells, and monocytes, while B cells, neutrophils, and eosinophils increased. Notably, aging was associated with expansion of aging-associated B cells (ABCs) and PD-1+ T cells, while obesity promoted MHCIIlow macrophages. Inflammatory cytokine production (IL-6, TNF-α) was elevated in splenocytes following LPS stimulation. Feature importance analysis identified ALT, total cholesterol, BMI, IL-6, neutrophils, eosinophils, and MHCIIlow macrophages as key markers distinguishing aging and obesity. In conclusion, aging and obesity jointly remodel the immune landscape, promoting chronic inflammation and T cell exhaustion. Our findings offer insight into age- and obesity-related immune decline and suggest potential biomarkers for monitoring immune health in metabolic aging.