IL-17 triggers the onset of cognitive and synaptic deficits in early stages of Alzheimer’s disease

Neuroinflammation in patients with Alzheimer’s disease (AD) and related mouse models has been recognized for decades, but the contribution of the recently described meningeal immune population to AD pathogenesis remains to be addressed. Here, using the 3xTg-AD model, we report an accumulation of interleukin-17 (IL-17)-producing cells, mostly γδ T cells, in the brain and the meninges of female, but not male, mice, concomitant with the onset of cognitive decline. Critically, IL-17 neutralization into the ventricles is sufficient to prevent short-term memory and synaptic plasticity deficits at early stages of disease. These effects precede blood-brain barrier disruption and amyloid-beta or tau pathology, implying an early involvement of IL-17 in AD pathology. When IL-17 is neutralized at later stages of disease, the onset of short-memory deficits and amyloidosis-related splenomegaly is delayed. Altogether, our data support the idea that cognition relies on a finely regulated balance of “inflammatory” cytokines derived from the meningeal immune system. [Display omitted] •IL-17-producing cells accumulate in the brain and the meninges of 3xTg-AD mice•The increase of IL-17 producers associates with short-term memory deficits•Neutralization of IL-17 prevents cognitive impairments and synaptic dysfunction•IL-17 triggers Alzheimer’s disease onset independently of Aβ and tau pathology Using a mouse model of Alzheimer’s disease, Brigas et al. demonstrate that the onset of cognitive decline associates with an accumulation of IL-17-producing cells in the brain and the meninges. Targeting IL-17 into the ventricle prevents short-term memory and neuronal synaptic plasticity deficits at early stages of disease.