Comprehensive characterisation of age-related changes in cell subpopulations and tissue structural properties in secondary lymphoid organs.

Population aging is an escalating global phenomenon, wherein age-related alterations in the human immune system exacerbate the susceptibility to diseases including infections and autoimmune disorders. Secondary lymphoid organs (SLOs) are key locations for the execution of immunological responses by mature immune cells; however, age-related changes in SLOs remain relatively understudied. To address this gap, this study employed comprehensive approaches including single-cell RNA sequencing (scRNA-seq) data analysis, immunofluorescence staining, flow cytometry, and morphological analysis, to clarify the age-related alterations in SLOs in mice. The results demonstrated that aging caused senescent immune cells to accumulate and subpopulations to reorganize, with a decrease in the proportion of naïve T cells, whilst an increase in regulatory T (Treg) cells, cytotoxic T lymphocytes (CTLs), and exhausted T (Tex) cells. Notably, CD4+ and CD8+ T cells exhibited distinct senescence patterns in Peyer's patches, suggesting tissue-specific responses to aging, which may arise from differential exposure to gut microbiota. In addition to the alterations in immune cell populations, we also identified increased stromal cell senescence and altered distributions of marginal reticular cells and follicular dendritic cells, which may further contribute to age-related immune dysfunction. Finally, examining SLO structural features, including size, fibrosis, stiffness, and pigmentation, revealed degenerative changes that impair immune function. Collectively, this study will assist with the development of strategies aimed at delaying aging and treating age-related diseases.