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The authors identify programmed cell death ligand-1 (PD-L1), an immunity suppressor produced by cancer cells, as a new pain inhibitor and a neuromodulator. They report that PD-L1 is produced by melanoma and normal neural tissues and that it inhibits acute and chronic pain. Via activation of PD-1, its receptor, PD-L1 decreases the excitability of nociceptive neurons in mouse and human dorsal root ganglia.
In a rodent model of viral infection, immune activation causes impairments in motor-learning-dependent cortical synaptic remodeling that are mediated by peripheral monocytes rather than by CNS-resident microglia.
Recent evidence suggests that T cells and their derived cytokines affect the brain in disease and health. In this Opinion article, Kipnis and colleagues describe their effects and possible underlying mechanisms, and propose an evolutionary model to explain why the T cell-derived cytokine interferon-γ has both pro-social and immune effects.