Analysis of the recovery of CD247 expression in a PID patient: insights into the spontaneous repair of defective genes.

Mutations in T-cell antigen receptor (TCR) subunit genes cause rare immunodeficiency diseases characterized by impaired expression of the TCR at the cell surface and selective T lymphopenia. Here, detailed analyses of spontaneously arising somatic mutations that recover CD247, and thus TCR expression, in a newly identified CD247-deficient patient are described. The recovery of CD247 expression in some patient T cells was associated with both reversion of the inactivating mutation and a variant with a compensating mutation that could reconstitute TCR expression, but not as efficiently as wild-type CD247. Multiple mutations were found in CD247 complementary DNAs (cDNAs) cloned from the patient as well as in cDNA and genomic DNA from other individuals, suggesting that genetic variation in this gene is frequent. Analyses of other genes mutated in primary immunodeficiency diseases (PIDs) where reversions have been described also revealed a higher rate of mutation than that observed for genes mutated in PIDs where revertants have not been identified or control genes. These data support the hypothesis that the occurrence of somatic mutations that may reconstitute genetic defects in PID is related to an increased propensity of those genes to mutate.

B Lymphocyte commitment program is driven by the proto-oncogene c-Myc.

c-Myc, a member of the Myc family of transcription factors, is involved in numerous biological functions including the regulation of cell proliferation, differentiation, and apoptosis in various cell types. Of all of its functions, the role of c-Myc in cell differentiation is one of the least understood. We addressed the role of c-Myc in B lymphocyte differentiation. We found that c-Myc is essential from early stages of B lymphocyte differentiation in vivo and regulates this process by providing B cell identity via direct transcriptional regulation of the ebf-1 gene. Our data show that c-Myc influences early B lymphocyte differentiation by promoting activation of B cell identity genes, thus linking this transcription factor to the EBF-1/Pax-5 pathway.

NKG2H-Expressing T Cells Negatively Regulate Immune Responses.

The biology and function of NKG2H receptor, unlike the better characterized members of the NKG2 family NKG2A, NKG2C, and NKG2D, remains largely unclear. Here, we show that NKG2H is able to associate with the signaling adapter molecules DAP12 and DAP10 suggesting that this receptor can signal for cell activation. Using a recently described NKG2H-specific monoclonal antibody (mAb), we have characterized the expression and function of lymphocytes that express this receptor. NKG2H is expressed at the cell surface of a small percentage of peripheral blood mononuclear cell (PBMC) and is found more frequently on T cells, rather than NK cells. Moreover, although NKG2H is likely to trigger activation, co-cross-linking of this receptor with an NKG2H-specific mAb led to decreased T cell activation and proliferation in polyclonal PBMC cultures stimulated by anti-CD3 mAbs. This negative regulatory activity was seen only after cross-linking with NKG2H, but not NKG2A- or NKG2C-specific monoclonal antibodies. The mechanism underlying this negative effect is as yet unclear, but did not depend on the release of soluble factors or recognition of MHC class I molecules. These observations raise the intriguing possibility that NKG2H may be a novel marker for T cells able to negatively regulate T cell responses.