Antigen-Specifically Activated CD8+ and Double-Negative T Cells Accumulate in the Brain of Alzheimer's Disease Mice.

Emerging evidence suggests adaptive immunity plays a key role in cognitive function and neurodegenerative diseases. However, the specific contribution of T cells in Alzheimer's disease (AD) remains poorly understood. Despite successful T cell modulation in other neurological conditions, similar strategies in AD remain underexplored due to gaps in our understanding of antigen-specific T cell activity and antigen-unspecific bystander activation in the diseased brain. In this study, we used flow cytometry to characterize T cell populations and their activation mode in an AD mouse model. By assessing GFP expression in C57BL/6J-Tg(Nr4a1-EGFP/cre)820Khog; Tg(APPswe,PSEN1dE9)85Dbo/Mmjax mice, we distinguished antigen-dependent from antigen-independent activation in CD4⁺, CD8⁺, and double-negative T cells (DNTs). This approach allows analysis of the full repertoire of antigen-specifically activated T cells in a physiological immune system without prior knowledge of target antigens. AD-like amyloid pathology progression was monitored by monthly scoring until mice reached 2, 6, 10-12 or 15-18 months of age and Aβ-quantification via thioflavine S staining. Antigen-specific activation during AD development was assessed by comparing AD mice with wild-type littermates. At 15-18 months, AD mice exhibited elevated numbers of activated, highly differentiated DNTs, along with increased antigen-specific CD8⁺ and DNT cells relative to controls. These results indicate a significant role for antigen-dependent immune activity in AD, highlighting CD8⁺ T cells and DNTs as potential therapeutic targets.