Aicardi-Goutières syndrome (AGS) is a rare, genetically determined early-onset progressive encephalopathy. To date, mutations in six genes have been identified as etiologic for AGS. Our Japanese nationwide AGS survey identified six AGS-affected individuals without a molecular diagnosis; we performed whole-exome sequencing on three of these individuals. After removal of the common polymorphisms found in SNP databases, we were able to identify IFIH1 heterozygous missense mutations in all three. In vitro functional analysis revealed that IFIH1 mutations increased type I interferon production, and the transcription of interferon-stimulated genes were elevated. IFIH1 encodes MDA5, and mutant MDA5 lacked ligand-specific responsiveness, similarly to the dominant Ifih1 mutation responsible for the SLE mouse model that results in type I interferon overproduction. This study suggests that the IFIH1 mutations are responsible for the AGS phenotype due to an excessive production of type I interferon.

RNA viruses use various strategies to condense their genetic information into small genomes. Potyviruses not only use the polyprotein strategy, but also embed an open reading frame, pipo, in the P3 cistron in the –1 reading frame. PIPO is expressed as a fusion protein with the N-terminal half of P3 (P3N-PIPO) via transcriptional slippage of viral RNA-dependent RNA polymerase (RdRp). We herein show that clover yellow vein virus (ClYVV) produces a previously unidentified factor, P3N-ALT, in the +1 reading frame via transcriptional slippage at a conserved G1–2A6–7 motif, as is the case for P3N-PIPO. The translation of P3N-ALT terminates soon, and it is considered to be a C-terminal truncated form of P3. In planta experiments indicate that P3N-ALT functions in cell-to-cell movement along with P3N-PIPO. Hence, all three reading frames are used to produce functional proteins. Deep sequencing of ClYVV RNA from infected plants endorses the slippage by viral RdRp. Our findings unveil a virus strategy that optimizes the coding capacity.

The presence of Langhans giant cells (LGCs) is one of the signatures of systemic granulomatous disorders such as tuberculosis and sarcoidosis. However, the pathophysiological mechanism leading to LGC formation, especially the contribution of the T cells abundantly found in granulomas, has not been fully elucidated. To examine the role of T cells in LGC formation, a new in vitro method for the induction of LGCs was developed by co-culturing human monocytes with autologous T cells in the presence of concanavalin A (ConA). This system required close contact between monocytes and T cells, and CD4+ T cells were more potent than CD8+ T cells in inducing LGC formation. Antibody inhibition revealed that a CD40-CD40 ligand (CD40L) interaction and IFN-γ were essential for LGC formation, and the combination of exogenous soluble CD40L (sCD40L) and IFN-γ efficiently replaced the role of T cells. Dendritic cell-specific transmembrane protein (DC-STAMP), a known fusion-related molecule in monocytes, was up-regulated during LGC formation. Moreover, knock-down of DC-STAMP by siRNA inhibited LGC formation, revealing that DC-STAMP was directly involved in LGC formation. Taken together, these results demonstrate that T cells played a pivotal role in a new in vitro LGC formation system, in which DC-STAMP was involved, and occurred via a molecular mechanism that involved CD40-CD40L interaction and IFN-γ secretion.

Familial hemophagocytic lymphohistiocytosis (FHL) is a potentially lethal genetic disorder of immune dysregulation that requires prompt and accurate diagnosis to initiate life-saving immunosuppressive therapy and to prepare for hematopoietic stem cell transplantation. In the present study, 85 patients with hemophagocytic lymphohistiocytosis were screened for FHL3 by Western blotting using platelets and by natural killer cell lysosomal exocytosis assay. Six of these patients were diagnosed with FHL3. In the acute disease phase requiring platelet transfusion, it was difficult to diagnose FHL3 by Western blot analysis or by lysosomal exocytosis assay. In contrast, the newly established flow cytometric analysis of IntroductionThe granule-dependent cytotoxic pathway is a major immune effector mechanism used by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. 1 The pathway involves a series of steps, including cell activation, polarization of the lysosomal granules to the immunologic synapse, exocytosis of lytic proteins such as perforin and granzymes, and induction of apoptosis in the target cells. 2 In addition to its central role in the defense against intracellular infections and in tumor immunity, this pathway also plays an important role in the regulation of immune homeostasis. Defects in the granule-dependent cytotoxic pathway result in a catastrophic hyperinflammatory condition known as hemophagocytic lymphohistiocytosis (HLH). 1,3 HLH is a life-threatening syndrome of immune dysregulation resulting from the uncontrolled activation and proliferation of CTLs, which leads to macrophage activation and the excessive release of inflammatory cytokines. 4,5 Clinical diagnosis of HLH is made on the basis of cardinal signs and symptoms including prolonged fever and hepatosplenomegaly, and by characteristic laboratory findings such as pancytopenia, hyperferritinemia, hypofibrinogenemia, increased levels of soluble IL-2 receptor, and low or absent NK cell activity. 5,6 HLH can be classified into primary (genetic) or secondary (acquired) forms according to the underlying etiology, although this distinction is difficult to make in clinical practice. 4,5 Familial hemophagocytic lymphohistiocytosis (FHL) encompasses major forms of primary HLH for which mutations in the genes encoding perforin (PRF1; FHL2), 7 Munc13-4 (UNC13D; FHL3), 8 syntaxin-11 (STX11; FHL4), 9 and syntaxinbinding protein 2 (also known as Munc18-2) (STXBP2; FHL5) 10,11 have been identified to date. Perforin is a cytolytic effector that forms a pore-like structure in the target cell membrane. Munc13-4, syntaxin-11, and Munc18-2 are involved in intracellular trafficking or the fusion of cytolytic granules to the plasma membrane and the subsequent delivery of their contents into target cells. 1,12 Consequently, defective cytotoxic activity of CTLs and NK cells is one of the hallmark findings of FHL, 7,8,[13][14][15][16] although NK cell activity is also decreased in some cases of secondary HLH. 15,[17][18][19][20] Prompt and accurate diagnosis o...