Memory B cells, unlike naive B cells, require a reduced level of STAT3 activation to differentiate into antibody-secreting plasmablasts in response to IL-10 and IL-21; however, this process requires IL-21R expression in both naive and memory cells.

Germline heterozygous IKZF1 mutations cause dysgammaglobulinemia; hematologic abnormalities, including B-cell defect; and autoimmune diseases.

Viruses that are typically benign sometimes invade the brainstem in otherwise healthy children. We report bi-allelic DBR1 mutations in unrelated patients from different ethnicities, each of whom had brainstem infection due to herpes simplex virus 1 (HSV1), influenza virus, or norovirus. DBR1 encodes the only known RNA lariat debranching enzyme. We show that DBR1 expression is ubiquitous, but strongest in the spinal cord and brainstem. We also show that all DBR1 mutant alleles are severely hypomorphic, in terms of expression and function. The fibroblasts of DBR1-mutated patients contain higher RNA lariat levels than control cells, this difference becoming even more marked during HSV1 infection. Finally, we show that the patients' fibroblasts are highly susceptible to HSV1. RNA lariat accumulation and viral susceptibility are rescued by wild-type DBR1. Autosomal recessive, partial DBR1 deficiency underlies viral infection of the brainstem in humans through the disruption of tissue-specific and cell-intrinsic immunity to viruses.

Significance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population.

Polycomb-group (PcG) genes encode multimeric nuclear protein complexes, PcG complex 1 and 2. PcG complex 2 was proved to induce transcription repression and to further methylate histone H3 at lysine-27 (H3K27). Subsequently PcG complex 1 is recruited through recognition of methylated H3K27 and maintains the transcription silencing by mediating monoubiquitination of histone H2A at lysine-119. Genetic evidence demonstrated a crucial role for PcG complex 1 in stem cells, and Bmi1, a member of PcG complex 1, was shown to sustain adult stem cells through direct repression of the INK4a locus encoding cyclin-dependent kinase inhibitor, p16CKI, and p19ARF. The molecular functions of PcG complex 1, however, remain insufficiently understood. In our study, deficiency of Rae28, a member of PcG complex 1, was found to impair ubiquitin-proteasome-mediated degradation of Geminin, an inhibitor of DNA replication licensing factor Cdt1, and to increase protein stability. The resultant accumulation of Geminin, based on evidence from retroviral transduction experiments, presumably eliminated hematopoietic stem cell activity in Rae28-deficient mice. Rae28 mediates recruiting Scmh1, which provides PcG complex 1 an interaction domain for Geminin. Moreover, PcG complex 1 acts as the E3 ubiquitin ligase for Geminin, as we demonstrated in vivo as well as in vitro by using purified recombinant PcG complex 1 reconstituted in insect cells. Our findings suggest that PcG complex 1 supports the activity of hematopoietic stem cells, in which high-level Geminin expression induces quiescence securing genome stability, by enhancing cycling capability and hematopoietic activity through direct regulation of Geminin.Rae28 ͉ Scmh1 ͉ HSCs ͉ ubiquitination ͉ DNA replication licensing

Background Germline heterozygous mutations in human STAT1 can cause loss of function (LOF), as in patients with Mendelian susceptibility to mycobacterial diseases (MSMD), or gain of function (GOF), as in patients with chronic mucocutaneous candidiasis (CMC). LOF and GOF mutations are equally rare and can affect the same domains of STAT1, especially the coiled-coil and DNA-binding domains (CCD/DBD). Moreover, 6% of CMC patients with a GOF STAT1 mutation develop mycobacterial disease, obscuring the functional significance of the identified STAT1 mutations. Current computational approaches, such as combined annotation-dependent depletion, do not distinguish LOF and GOF variants Objective Estimate variations in CCD/DBD of STAT1 Method Mutagenized 342 individual wild-type amino acids in CCD/DBD (45.6% of full-length STAT1) to alanine and tested the mutants for STAT1 transcriptional activity. Results Of these 342 mutants, 201 were neutral, 30 LOF, and 111 GOF in a luciferase assay. This assay system correctly estimated all previously reported LOF mutations (100%) and slightly fewer GOF mutations (78.1%) in CCD/DBD of STAT1. We found that GOF alanine mutants occurred at the interface of the antiparallel STAT1 dimer, suggesting that they destabilize this dimer. This assay also precisely predicted the impact of two hypomorphic and dominant-negative mutations, E157K and G250E, in CCD of STAT1 that we found in two unrelated MSMD patients. Conclusion Systematic alanine-scanning assay is a useful tool to estimate the GOF or LOF status and impact of heterozygous missense mutations in STAT1 identified in patients with severe infectious diseases, including mycobacterial and fungal diseases.

Patients carrying two loss-of-function (or hypomorphic) alleles of STAT1 are vulnerable to intracellular bacterial and viral diseases. Heterozygosity for loss-of-function dominant-negative mutations in STAT1 is responsible for autosomal dominant (AD) Mendelian susceptibility to mycobacterial disease (MSMD), whereas heterozygosity for gain-of-function loss-of-dephosphorylation mutations causes AD chronic mucocutaneous candidiasis (CMC). The two previously reported types of AD MSMD-causing STAT1 mutations are located in the tail domain (p.L706S) or in the DNA-binding domain (p.E320Q and p.Q463H), whereas the AD CMC-causing mutations are located in the coiled-coil domain. We identified two cases with AD-STAT1 deficiency in two unrelated patients from Japan and Saudi Arabia carrying heterozygous missense mutations affecting the SH2 domain (p.K637E and p.K673R). p.K673R is a hypomorphic mutation that impairs STAT1 tyrosine phosphorylation, whereas the p.K637E mutation is null and affects both STAT1 phosphorylation and DNA-binding activity. Both alleles are dominant-negative and result in impaired STAT1-mediated cellular responses to IFN-γ and IL-27. By contrast, STAT1-mediated cellular responses against IFN-α and IFN-λ1 were preserved at normal levels in patients’ cells. We describe here the first dominant mutations in the SH2 domain of STAT1, revealing the importance of this domain for tyrosine phosphorylation and DNA-binding, as well as for anti-mycobacterial immunity.

Background The capacity of CD8+ T cells to control infections and mediate anti-tumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8+ T cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8+ T cell immunity in humans is unknown. Objective To determine which signaling pathways mediate the effects of IL-21 on human CD8+ T cells and whether defects in these pathways contribute to disease pathogenesis in primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade. Methods Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in STAT1, STAT3 or IL21R were used to assess the respective roles of these genes in human CD8+ T cell differentiation in vivo and in vitro. Results Mutations in STAT3 and IL21R, but not STAT1, lead to a decrease in multiple memory CD8+ T cell subsets in vivo, indicating that STAT3 signaling – possibly downstream of IL-21R - regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naïve CD8+ T cells. However, this defect was overcome by TCR engagement. Conclusion The IL-21R/STAT3 pathway is required for many aspects of human CD8+ T cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3 and IL-21R-deficient individuals.