TCR repertoire analysis quantifies effect of irradiation to homeostasis of iNKT cell development in the thymus of mice

Thymic T cell development shows homeostasis in which T cell production recovers after temporal impairment by various stressors. Invariant natural killer T (iNKT) cells in the thymus contribute to recovery of thymic development after irradiation owing to their greater tolerance to irradiation compared to conventional thymocytes. However, whether and how iNKT cell development recovers from irradiation remains unknown. Here we show that iNKT cells in the thymus exhibits much slower post-irradiation recovery than conventional thymocytes. We compared T cell receptor (TCR) alpha chain repertoire of the thymus in 42 days after irradiation and quantified the sustained decline in the number of iNKT cells against other thymocytes. We found that fluctuation of V and J genes usage does not correlate with the number iNKT cells suggesting that differentiation process of iNKT cells after TCR gene rearrangement is impaired by irradiation. Mathematical modelling of recovery dynamics of iNKT cells implied that lack of rapid proliferation immediately after irradiation unlike conventional thymocytes contributes to the prolonged reduction of iNKT cell population. These findings may suggest possibility on association between the prolonged reduction of iNKT cells after irradiation and autoimmune diseases caused by irradiation in bone marrow transplantation.