ABSTRACT: Objective: Chronic periodontitis typically affects individuals aged 40–50. Aging impairs immunity, sustains chronic inflammation, and enhances autoimmunity, a process called "immunosenescence", which contributes to the development of type 2 diabetes and rheumatoid arthritis (RA). Thymic involution after puberty reduces naive T cells, promoting senescent CD4+ T cells. The reason is that senescent T cells attempt to complement this reduction by proliferating to their limits, maintaining their absolute numbers through “homeostatic proliferation”. These cells, characterized by PD-1/CD153 expression, show reduced proliferation and increased senescence-associated secretory phenotype (SASP) cytokines. This study investigates how ligature-induced periodontitis (LIP) in mice affects CD4+ T cell senescence. Materials and Methods: Balb/c mice aged 5, 10, 18, 26, 34, and 42 weeks received LIP by silk ligation around maxillary second molars. Splenic CD4+ T cells were extracted and cultured with IL-2, anti-TCRβ, and anti-CD28 for 1 to 3 days to mimic homeostatic proliferation. Senescence markers were compared between LIP and control groups before and after in vitro stimulation. RNA sequencing (RNA-seq) analysis was performed to identify differentially expressed genes. Results: No significant difference was observed in PD-1/CD153 double-positive cells between the LIP group and the control group at any age of mice. However, after in vitro stimulation, the LIP group showed a higher proportion of PD-1/CD153 double-positive cells, peaking at 18 weeks. SASP cytokines (osteopontin, IL-6) in the LIP group were higher than that in the control graoup. Senescence-associated β-galactosidase (SAβ-gal)-positive CD4+ T cells were more prevalent, indicating accelerated senescence in LIP group. Additionally, fewer cells in LIP group were in the S phase, suggesting cell cycle arrest. RNA-seq suggested "inflammatory response," "T cell differentiation," “STAT protein phosphorylation," and “JAK-STAT signalling pathway" in the LIP group. Among the upregulated genes in the LIP group, Cx3cr1, a marker selectively expressed by senescent CD4⁺ T cells; Il1rn, which reflects the inflammation-regulating capacity of senescent CD4⁺ T cells by antagonizing IL-1β signalling; Il4, indicative of Th2 differentiation and B cell activation via the JAK/STAT6 pathway; and Endog, a mitochondrial nuclease implicated in age-related cellular stress and telomere dysfunction, were ranked high. Conclusions: These results suggest that LIP accelerates CD4+ T cell senescence, potentially exacerbating systemic inflammation. Future experiments will involve transferring splenic CD4+ T cells from LIP and control groups into T cell-deficient mice to evaluate in vivo homeostatic proliferation and its role in experimental RA.
