Core Viewpoint - The research published by Yale University confirms the presence of T cells in the healthy brains of mice and humans, specifically in the subfornical organ (SFO), indicating that T cells can reside in the brain under normal conditions, contrary to previous beliefs about the blood-brain barrier and immune cell isolation [3][11]. Group 1: Research Findings - The study reveals that T cells in the SFO are enriched and play a crucial role in monitoring gut and fat tissue information, which is essential for regulating feeding and behavior [3][11]. - T cells in the SFO are distinct from those in the meninges, as they express proteins like CXCR6 that allow them to remain in brain tissue and secrete immune signaling proteins such as IFNγ [8][11]. - The research indicates a relationship between dietary habits and the quantity of T cells in the brain, with high-fat diets leading to an increase in T cells in both fat tissue and the brain [8][9]. Group 2: Mechanisms of Interaction - The study demonstrates that fasting increases T cell numbers in the brain while decreasing them in fat tissue, suggesting that dietary intake can dynamically regulate T cell migration to the central nervous system [9][11]. - Antibiotic intervention to deplete gut microbiota resulted in a significant reduction of T cells in the brain, indicating that gut microbiota may influence immune cell homeostasis in the central nervous system [9][11]. - The presence of T cells in the brain is linked to feeding behavior, as T cell-deficient mice took longer to find food when hungry compared to normal mice, highlighting their role in foraging and eating behaviors [9][11].