Adaptive Immunity and Alzheimer’s Disease: Dual Roles in Neurodegeneration and Neuroprotection with Therapeutic Implications

Alzheimer's disease (AD) is a progressive neurodegenerative disorder defined by amyloid-β (Aβ) plaques, tau hyperphosphorylation, and neuroinflammation. Although earlier work emphasized brain-resident glia (microglia and astrocytes), recent studies highlight adaptive immune cells, particularly T and B lymphocytes, as modulators of AD pathology. This review synthesizes animal and human findings from 2022-2025 to provide updated insights into the multifaceted roles and therapeutic potential of adaptive immunity in AD. Infiltration of peripheral T and B cells into the brain parenchyma links peripheral immunity to central nervous system (CNS) pathology. Both infiltrating lymphocytes and resident glia show context-dependent dual effects, either exacerbating neurodegeneration or promoting neuroprotection. Therapeutic strategies under active investigation include modulation of CD4⁺ T cell differentiation, adoptive transfer of regulatory T cells, and next-generation active vaccines for AD. Overall, selective modulation of discrete immune subsets may enable adaptive-immunity-based treatments, a complex yet promising avenue for AD therapy.