Zinc functions as a damage-associated signal after thymic damage. Zinc ions (Zn²⁺) are normally highly concentrated intracellularly, and zinc plays a critical role in thymopoiesis (baseline). After damage, dying thymocytes release Zn²⁺ into the extracellular space, activating endothelial cells via the G protein-coupled receptor GPR39. GPR39 signaling triggers the release of BMP4, which sustains regeneration of cortical and medullary thymic epithelial cells (cTEC, mTEC) to promote de novo T-cell production. Professional illustration by Patrick Lane, ScEYEnce Studios.