Lupus Risk Variant Increases pSTAT1 Binding and Decreases ETS1 Expression.

Genetic variants at chromosomal region 11q23.3, near the gene ETS1, have been associated with systemic lupus erythematosus (SLE), or lupus, in independent cohorts of Asian ancestry. Several recent studies have implicated ETS1 as a critical driver of immune cell function and differentiation, and mice deficient in ETS1 develop an SLE-like autoimmunity. We performed a fine-mapping study of 14,551 subjects from multi-ancestral cohorts by starting with genotyped variants and imputing to all common variants spanning ETS1. By constructing genetic models via frequentist and Bayesian association methods, we identified 16 variants that are statistically likely to be causal. We functionally assessed each of these variants on the basis of their likelihood of affecting transcription factor binding, miRNA binding, or chromatin state. Of the four variants that we experimentally examined, only rs6590330 differentially binds lysate from B cells. Using mass spectrometry, we found more binding of the transcription factor signal transducer and activator of transcription 1 (STAT1) to DNA near the risk allele of rs6590330 than near the non-risk allele. Immunoblot analysis and chromatin immunoprecipitation of pSTAT1 in B cells heterozygous for rs6590330 confirmed that the risk allele increased binding to the active form of STAT1. Analysis with expression quantitative trait loci indicated that the risk allele of rs6590330 is associated with decreased ETS1 expression in Han Chinese, but not other ancestral cohorts. We propose a model in which the risk allele of rs6590330 is associated with decreased ETS1 expression and increases SLE risk by enhancing the binding of pSTAT1.

Hemophagocytosis causes a consumptive anemia of inflammation.

Cytopenias of uncertain etiology are commonly observed in patients during severe inflammation. Hemophagocytosis, the histological appearance of blood-eating macrophages, is seen in the disorder hemophagocytic lymphohistiocytosis and other inflammatory contexts. Although it is hypothesized that these phenomena are linked, the mechanisms facilitating acute inflammation-associated cytopenias are unknown. We report that interferon γ (IFN-γ) is a critical driver of the acute anemia observed during diverse microbial infections in mice. Furthermore, systemic exposure to physiologically relevant levels of IFN-γ is sufficient to cause acute cytopenias and hemophagocytosis. Demonstrating the significance of hemophagocytosis, we found that IFN-γ acts directly on macrophages in vivo to alter endocytosis and provoke blood cell uptake, leading to severe anemia. These findings define a unique pathological process of broad clinical and immunological significance, which we term the consumptive anemia of inflammation.

Perforin is a critical physiologic regulator of T-cell activation.

Individuals with impaired perforin-dependent cytotoxic function (Ctx(-)) develop a fatal inflammatory disorder called hemophagocytic lymphohistiocytosis (HLH). It has been hypothesized that immune hyperactivation during HLH is caused by heightened infection, defective apoptosis/responsiveness of Ctx(-) lymphocytes, or enhanced antigen presentation. Whereas clinical and experimental data suggest that increased T-cell activation drives HLH, potential abnormalities of T-cell activation have not been well characterized in Ctx(-) hosts. To define such abnormalities and to test these hypotheses, we assessed in vivo T-cell activation kinetics and viral loads after lymphocytic choriomeningitis virus (LCMV) infection of Ctx(-) mice. We found that increased T-cell activation occurred early during infection of Ctx(-) mice, while they had viral burdens that were identical to those of WT animals, demonstrating that T-cell hyperactivation was independent of viral load. Furthermore, cell transfer and signaling studies indicated that increased antigenic stimulation, not a cell-intrinsic defect of responsiveness, underlay heightened T-cell activation in vivo. Finally, direct measurement of viral antigen presentation demonstrated an increase in Ctx(-) mice that was proportional to abnormal T-cell activation. We conclude that perforin-dependent cytotoxicity has an immunoregulatory role that is distinguishable from its pathogen clearance function and limits T-cell activation in the physiologic context by suppressing antigen presentation.

Mice with a selective impairment of IFN-gamma signaling in macrophage lineage cells demonstrate the critical role of IFN-gamma-activated macrophages for the control of protozoan parasitic infections in vivo.

IFN-gamma has long been recognized as a cytokine with potent and varied effects in the immune response. Although its effects on specific cell types have been well studied in vitro, its in vivo effects are less clearly understood because of its diverse actions on many different cell types. Although control of multiple protozoan parasites is thought to depend critically on the direct action of IFN-gamma on macrophages, this premise has never been directly proven in vivo. To more directly examine the effects of IFN-gamma on cells of the macrophage lineage in vivo, we generated mice called the "macrophages insensitive to IFN-gamma" (MIIG) mice, which express a dominant negative mutant IFN-gamma receptor in CD68+ cells: monocytes, macrophages, dendritic cells, and mast cells. Macrophage lineage cells and mast cells from these mice are unable to respond to IFN-gamma, whereas other cells are able to produce and respond to this cytokine normally. When challenged in vitro, macrophages from MIIG mice were unable produce NO or kill Trypanosoma cruzi or Leishmania major after priming with IFN-gamma. Furthermore, MIIG mice demonstrated impaired parasite control and heightened mortality after T. cruzi, L. major, and Toxoplasma gondii infection, despite an appropriate IFN-gamma response. In contrast, MIIG mice displayed normal control of lymphocytic choriomeningitis virus, despite persistent insensitivity of macrophages to IFN-gamma. Thus, the MIIG mouse formally demonstrates for the first time in vivo, the specific importance of direct, IFN-gamma mediated activation of macrophages for controlling infection with multiple protozoan parasites.