ISG15 is an interferon (IFN)-α/β-inducible, ubiquitin-like intracellular protein. Its conjugation to various proteins (ISGylation) contributes to antiviral immunity in mice. We describe human patients with inherited ISG15 deficiency and mycobacterial, but not viral diseases. The lack of intracellular ISG15 production and protein ISGylation was not associated with cellular susceptibility to any viruses tested, consistent with the lack of viral diseases in these patients. By contrast, the lack of mycobacterium-induced ISG15 secretion by leukocytes — granulocytes in particular — reduced the production of IFN-γ by lymphocytes, including natural killer cells, probably accounting for the enhanced susceptibility to mycobacterial disease. This experiment of Nature shows that human ISGylation is largely redundant for antiviral immunity, but that ISG15 plays an essential role as an IFN-γ-inducing secreted molecule for optimal antimycobacterial immunity.

Whole-exome sequencing reveals a homozygous splice-site mutation in the gene encoding STIM1 in a child with classic Kaposi sarcoma.

The family of peptidoglycan recognition proteins (PGRPs) are associated with the recognition of the peptidoglycan of microbes and subsequent activation of signaling pathways for immune response. Here the crystal structure of Drosophila PGRP-LB is determined at a resolution of 2.0 A and shows an active-site cleft with a zinc cage. Poor conservation of surface residues at the cleft predicts a widely varying individual specificity of PGRPs for molecular patterns on microbial cell walls. At the back of this cleft is a putatively conserved distinctive groove. The location and mainly hydrophobic nature of the groove indicate that the back face serves for subsequent signaling after clustering of PGRP molecules by binding to polymeric cell wall components.

Isolated congenital asplenia (ICA) is characterized by the absence of a spleen at birth in individuals with no other developmental defects. The patients are prone to life-threatening bacterial infections. The unbiased analysis of exomes revealed heterozygous mutations in RPSA in 18 patients from eight kindreds, corresponding to more than half the patients and over one third of the kindreds studied. The clinical penetrance in these kindreds is complete. Expression studies indicated that the mutations carried by the patients - a nonsense, a frameshift duplication and five different missense - cause autosomal dominant ICA by haploinsufficiency. Population genetic studies showed that RPSA was subject to purifying selection. RPSA encodes ribosomal protein SA, a component of the small subunit of the ribosome. This discovery establishes an essential role for RPSA in human spleen development.

Objective: To determine the proportion of children with herpes simplex encephalitis (HSE) displaying TLR3 deficiency, the extent of TLR3 allelic heterogeneity, and the specific clinical features of TLR3 deficiency. Methods:We determined the sequence of all exons of TLR3 in 110 of the 120 patients with HSE enrolled in our study who do not carry any of the previously described HSE-predisposing mutations of TLR3 pathway genes (TLR3, UNC93B1, TRIF, TRAF3, and TBK1). All the new mutant TLR3 alleles detected were characterized experimentally in-depth to establish the causal relationship between the genotype and phenotype.Results: In addition to the 3 previously reported TLR3-deficient patients from the same cohort, 6 other children or young adults with HSE carry 1 of 5 unique or extremely rare (minor allele frequency ,0.001) missense TLR3 alleles. Two alleles (M374T, D592N) heterozygous in 3 patients are not deleterious in vitro. The other 3 are deleterious via different mechanisms: G743D1R811I and L360P heterozygous in 2 patients are loss-of-function due to low levels of expression and lack of cleavage, respectively, and R867Q homozygous in 1 patient is hypomorphic. The 3 patients' fibroblasts display impaired TLR3 responses and enhanced herpes simplex virus 1 susceptibility. Overall, TLR3 deficiency is therefore found in 6 (5%) of the 120 patients studied. There is high allelic heterogeneity, with 3 forms of autosomal dominant partial defect by negative dominance or haploinsufficiency, and 2 forms of autosomal recessive defect with complete or partial deficiency. Finally, 4 (66%) of the 6 TLR3-deficient patients had at least 1 late relapse of HSE, whereas relapse occurred in only 12 (10%) of the total cohort of 120 patients.Conclusions: Childhood-onset HSE is due to TLR3 deficiency in a traceable fraction of patients, in particular the ones with HSE recurrence. Mutations in TLR3 and TLR3 pathway genes should be searched and experimentally studied in children with HSE, and patients with proven TLR3 deficiency should be followed carefully. TLR3 is one of the most highly conserved TLRs in humans that have evolved under the strongest purifying selection.1 TLR3 recognizes double-stranded RNA (dsRNA), a by-product produced during the viral replication of most viruses, including herpes simplex virus 1 (HSV-1).2 The most common known clinical consequence of human TLR3 deficiency is childhood herpes simplex encephalitis (HSE). Childhood HSE is a rare life-threatening complication of primary infection with HSV-1, a common neurotropic dsDNA virus that is innocuous in most children.3 HSE is the most common form of sporadic viral encephalitis in Western countries. 4,5 The pathogenesis of HSE had long remained unclear. Our recent studies have demonstrated that HSE may result from singlegene inborn errors of TLR3-mediated immunity in some children, 6 with homozygous or

Human OX40 is necessary for robust CD4+ T cell memory and confers selective protective immunity against HHV-8 infection in endothelial cells.

Germline mutations in FASL and FAS impair Fas-dependent apoptosis and cause recessively or dominantly inherited autoimmune lymphoproliferative syndrome (ALPS). Patients with ALPS typically present with no other clinical phenotype. We investigated a large, consanguineous, multiplex kindred in which biological features of ALPS were found in the context of severe bacterial and viral disease, recurrent hepatopathy and encephalopathy, and cardiac malformations. By a combination of genome-wide linkage and whole-exome sequencing, we identified a homozygous missense mutation in FADD, encoding the Fas-associated death domain protein (FADD), in the patients. This FADD mutation decreases steady-state protein levels and impairs Fas-dependent apoptosis in vitro, accounting for biological ALPS phenotypes in vivo. It also impairs Fas-independent signaling pathways. The observed bacterial infections result partly from functional hyposplenism, and viral infections result from impaired interferon immunity. We describe here a complex clinical disorder, its genetic basis, and some of the key mechanisms underlying its pathogenesis. Our findings highlight the key role of FADD in Fas-dependent and Fas-independent signaling pathways in humans.

Summary Downregulation of MHC class I on the cell surface is an immune evasion mechanism shared by many DNA viruses including cowpox virus. Previously, a cowpox virus protein, CPXV203, was shown to downregulate MHC class I. Here, we report that CPXV12 is the only other MHC class I regulating protein of cowpox virus and it uses a mechanism distinct from that of CPXV203. Whereas CPXV203 retains fully assembled MHC class I by exploiting the KDEL-mediated endoplasmic reticulum retention pathway, CPXV12 binds to the peptide-loading complex and inhibits peptide loading on MHC class I molecules. Viruses deleted of both CPXV12 and CPXV203 demonstrated attenuated virulence in a CD8 T cell-dependent manner. These data demonstrate that CPXV12 and CPXV203 proteins combine to ablate MHC class I expression and abrogate antiviral CD8 T cell responses.