This study suggests that activation of the NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome contributes to thymic involution and decreases thymic export of naive T cells in aged individuals. The authors found that myeloid cells in the mouse thymus showed an age-dependent progressive increase in the activation of caspase 1. Aged mice had higher levels of free cholesterol and ceramides, and these age-related 'danger' signals could promote caspase 1 activation in macrophages. Notably, age-related caspase 1 activation and thymic involution was reduced in mice deficient in the inflammasome components NLRP3 and ASC. Furthermore, aged NLRP3- or ASC-deficient mice had increased numbers of cortical epithelial cells and T cell progenitors and a more diverse peripheral T cell repertoire compared with wild-type controls. Aged NLRP3-deficient mice also showed increased T cell reconstitution in a model of haematopoietic stem cell transplantation. The authors suggest that pharmacological inhibition of the inflammasome could boost immune function in elderly patients.