The thymus contributes naïve, self MHC reactive, self tolerant T cells to the peripheral
immune system throughout life, albeit with a log-linear decline with age. Quantification of
thymic function is clinically relevant in the setting of lymphoablation, but a phenotypic marker
distinguishing recent thymic emigrants from long lived naïve T cells remains elusive. T cell
receptor excision circles (TREC) are present in thymocytes exiting the thymus and
quantification of the most frequent of these, the δrec-ψJα rearrangement has been widely …