Calcium signals regulate the functional differentiation of thymic iNKT cells

How natural or innate‐like lymphocytes generate the capacity to produce IL‐4 and other cytokines characteristic of type 2 immunity remains unknown. Invariant natural killer T (iNKT) cells differentiate in the thymus into NKT1, NKT2, and NKT17 subsets, similar to mature, peripheral CD4 + T helper cells. The mechanism for this differentiation was not fully understood. Here, we show that NKT2 cells required higher and prolonged calcium (Ca 2+ ) signals and continuing activity of the calcium release‐activated calcium (CRAC) channel, than their NKT1 counterparts. The sustained Ca 2+ entry via CRAC pathway in NKT2 cells was apparently mediated by ORAI and controlled in part by the large mitochondrial Ca 2+ uptake. Unique properties of mitochondria in NKT2 cells, including high activity of oxidative phosphorylation, may regulate mitochondrial Ca 2+ buffering in NKT2 cells. In addition, the low Ca 2+ extrusion rate may also contribute to the higher Ca 2+ level in NKT2 cells. Altogether, we identified ORAI‐dependent Ca 2+ signaling connected with mitochondria and cellular metabolism, as a central regulatory pathway for the differentiation of NKT2 cells.