Long-Term Retention of Mature NK1.1+ NKT Cells in the Thymus

Abstract

The NKT cell pool in the thymus contains immature (NK1.1−) and mature (NK1.1+) subsets that represent distinct linear stages of a linear developmental pathway. An unexplained paradox is why immature NK1.1− NKT cells are mainly exported to the periphery instead of the more mature and more abundant NK1.1+ NKT cells. In this study we have determined that mature NK1.1+ NKT cells are retained by the thymus to form an extremely long-lived resident population capable of rapid and prolonged production of IFN-γ and IL-4. The retention of mature NKT cells provides an explanation for why the periphery is mainly seeded by immature NK1.1− cells despite mature NK1.1+ NKT cells being more abundant in the thymus. This is the first study to identify a mature T cell subset retained within the thymus and is additional evidence of the distinct developmental pathways of mainstream T cells and NKT cells.