Abstract
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline associated with the deposition of amyloid-β (Aβ) plaques, hyperphosphorylation of tau protein, and neuronal loss. Vascular inflammation and leukocyte trafficking may contribute to AD pathogenesis, and a better understanding of these inflammation mechanisms could therefore facilitate the development of new AD therapies. Here we show that T cells extravasate in the proximity of cerebral VCAM-1+ vessels in 3xTg-AD transgenic mice, which develop both Aβ and tau pathologies. The counter-ligand of VCAM-1 - α4β1 integrin, also known as very late antigen-4 (VLA-4) - was more abundant on circulating CD4+ T cells and was also expressed by a significant proportion of blood CD8+ T cells and neutrophils in AD mice. Intravital microscopy of the brain microcirculation revealed that α4 integrins control leukocyte-endothelial interactions in AD mice. Therapeutic targeting of VLA-4 using antibodies that specifically block α4 integrins improved the memory of 3xTg-AD mice compared to an isotype control. These antibodies also reduced neuropathological hallmarks of AD, including microgliosis, Aβ load and tau hyperphosphorylation. Our results demonstrate that α4 integrin-dependent leukocyte trafficking promotes cognitive impairment and AD neuropathology, suggesting that the blockade of α4 integrins may offer a new therapeutic strategy in AD.