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A blood-borne molecule that increases in abundance as we age blocks regeneration of brain cells and promotes cognitive decline. The molecule in question, known as beta-2 microglobulin, or B2M, is a component of a larger molecule called MHC I (major histocompatibility complex class I), which plays a major role in the adaptive immune system.
A growing body of research indicates that the B2M-MHC I complex, which is present in all cells in the body except red blood cells and plasma cells, can act in the brain in ways not obviously related to immunity—guiding brain development, shaping nerve cell communication, and even affecting behavior.Image credit: Holly Gellerman, Island Conservation
