Summary: Regulatory T cells (Tregs), known for controlling immune responses, may also help stabilize mood and protect cognition. New research links the Treg-regulating transcription factor Foxp3 to anxiety-, depression-like behaviors and to cognitive decline in an Alzheimer’s disease mouse model.
Foxp3 (forkhead box P3) is a transcription factor that directs the development and function of regulatory T cells. While Tregs are central to maintaining immune balance, growing evidence suggests they also influence brain function and behavior. Reduced Foxp3 expression has been observed in people with major depressive disorders, and experimental reduction of Tregs in mice produces measurable changes in mood-related behaviors and memory performance.
Key facts
- Regulatory T cells (Tregs), governed by Foxp3, have links to mood regulation and cognitive health.
- Experimental depletion of Tregs causes anxiety- and depression-like behavior in mice, reversible when Foxp3-expressing cells are restored.
- In an Alzheimer’s disease mouse model, removing Tregs accelerated markers of brain inflammation and worsened memory-related outcomes, implying an immune contribution to cognitive decline.
Researchers led by Giulio Maria Pasinetti used a mouse line engineered for temporary depletion of Foxp3-expressing Tregs to test the behavioral and neurobiological consequences of Treg loss. The mice underwent standard behavioral assays that assess anxiety- and depression-like responses, such as light/dark preference, general locomotion, and measures of passive coping.
Compared with control animals, Treg-depleted mice spent more time hiding in the dark, showed reduced movement, and displayed behaviors interpreted as decreased motivation and heightened despair—patterns consistent with anxiety and depression in rodent models. Importantly, these behavioral changes were reversed after the animals’ Foxp3-expressing cell population was restored, indicating a causal relationship between Treg presence and mood-related behavior.
To explore mechanisms, the team examined immune activity in the blood and brain. Depletion of Foxp3-expressing cells produced a transient rise in peripheral innate immune cells, including granulocytes, monocytes, and macrophages, and increased expression of matrix metalloprotease-9. The authors propose that some activated peripheral immune cells cross the blood–brain barrier and trigger inflammasome activation within the hippocampal formation.
Within the brain, markers of innate immune activation—most notably caspase-1 activity and the release of interleukin-1β (IL-1β)—increased in the hippocampus following Treg depletion. This inflammatory response in a brain region crucial for mood regulation and memory provides a plausible link between peripheral immune changes and neurobehavioral outcomes.
The study also examined 5xFAD mice, a well-established model of Alzheimer’s disease. Depleting Foxp3-expressing cells in these mice amplified caspase-1 activation and IL-1β secretion in the hippocampus, coinciding with higher levels of amyloid-beta (Aβ1–42) and greater plaque burden. These immune and proteinopathy changes were associated with an acceleration of cognitive decline at a presymptomatic stage in the model, suggesting that Treg loss can exacerbate Alzheimer’s-like pathology via inflammatory pathways.
Taken together, the results support a model in which Foxp3 and Treg-mediated regulation of the peripheral immune system influence brain innate immunity. When Tregs are depleted, peripheral immune activation can promote hippocampal inflammasome signaling, increasing IL-1β and caspase-1 activity and producing transient anxiety- and depression-like behaviors or accelerating cognitive deterioration in a vulnerable brain.
About this neuroscience and psychology research news
Author: Giulio Maria Pasinetti
Source: PNAS Nexus
Contact: Giulio Maria Pasinetti – PNAS Nexus
Image: Image credited to Neuroscience News
Original research (open access): “Transient anxiety and depression-like behaviors are linked to the depletion of Foxp3-expressing cells via inflammasome in the brain” by Giulio Maria Pasinetti et al., PNAS Nexus.
Abstract (concise)
Foxp3 controls regulatory T cells that modulate peripheral immunity. This study shows that temporary depletion of Foxp3-expressing cells in mice causally induces transient anxiety- and depression-like behaviors linked to inflammasome activation in the hippocampal formation. Restoration of Foxp3-expressing cells reverses neurobehavioral changes and reduces hippocampal caspase-1 activity and IL-1β release. Peripheral immune alterations—including increased granulocytes, monocytes, macrophages, and matrix metalloprotease-9—accompanied these changes. In an Alzheimer’s disease mouse model (5xFAD), Treg depletion increased caspase-1 activation, IL-1β secretion, amyloid-beta accumulation, and accelerated cognitive decline, supporting a role for Foxp3 and Tregs in modulating immune-to-brain signaling relevant to mood disorders and neurodegeneration.