Summary The transcriptional control of CD1d-restricted NKT cell development has remained elusive. We report that PLZF (promyelocytic leukemia zinc finger; Zbtb16), a member of the BTB/POZ-ZF family of transcription factors which includes the CD4 lineage-specific c-Krox (Th-POK, Zbtb7b), is exquisitely specific to CD1d-restricted NKT cells and human MR1-specific MAIT cells. PLZF was induced immediately after positive selection of NKT cell precursors and PLZF-deficient NKT cells failed to undergo the intrathymic expansion and effector differentiation that characterize their lineage. Instead, they preserved a naïve phenotype and were directed to lymph nodes. Conversely, transgenic expression of PLZF induced CD4 thymocytes to acquire effector differentiation and migrate to non-lymphoid tissues. We suggest that PLZF is a transcriptional signature of NKT cells that directs their innate-like effector differentiation during thymic development.

HPK1 is a Ste20-related serine-threonine kinase that inducibly associates with the adaptors SLP-76 and Gads after T cell receptor (TCR) signaling. Here, HPK1 deficiency resulted in enhanced TCR-induced phosphorylation of SLP-76, phospholipase C-gamma1 and the kinase Erk, more-persistent calcium flux, and increased production of cytokines and antigen-specific antibodies. Furthermore, HPK1-deficient mice were more susceptible to experimental autoimmune encephalomyelitis. Although the interaction between SLP-76 and Gads was unaffected, the inducible association of SLP-76 with 14-3-3tau (a phosphorylated serine-binding protein and negative regulator of TCR signaling) was reduced in HPK1-deficient T cells after TCR stimulation. HPK1 phosphorylated SLP-76 and induced the interaction of SLP-76 with 14-3-3tau. Our results indicate that HPK1 negatively regulates TCR signaling and T cell-mediated immune responses.

The NADPH oxidase activity of phagocytes and its generation of reactive oxygen species (ROS) is critical for host-defense, but ROS overproduction can also lead to inflammation and tissue injury. Here we report that TRPM2, a non-selective and redox-sensitive cation channel, inhibits ROS production in phagocytic cells and prevents endotoxin-induced lung inflammation in mice. TRPM2-deficient mice challenged with endotoxin (lipopolysaccharide) showed an increased inflammatory signature and decreased survival compared to controls. TRPM2 functions by dampening NADPH oxidase-mediated ROS production through depolarization of the plasma membrane in phagocytes. Since ROS also activates TRPM2, our findings establish a negative feedback mechanism inactivating ROS production through inhibition of the membrane potential-sensitive NADPH oxidase.

Activation-induced cytidine deaminase (AID) is required for immunoglobulin (Ig) gene class switch recombination (CSR), somatic hypermutation (SHM), and somatic hyperconversion. In general, high AID expression is found in mature B cells that are responding to antigens. However, AID expression and SHM have also been detected in developing B cells from transgenic mice that have a limited Ig repertoire. Here we demonstrate that AID expression, ongoing CSR, and active SHM occur in developing B cells from wild-type mice. Further, our results suggest that somatic variants arising from developing B cells in the bone marrow further diversify in the spleen of unimmunized mice. AID expression in developing B cells is T cell independent but involves engagement of B cell receptors and Toll-like receptors. Early AID expression can increase the preimmune repertoire of developing B cells, may provide an innate population of IgG- and IgA-expressing cells, and could be involved in receptor editing of self-reactive immature B cells.