Increased type I interferon (IFN-I) production and IFN-stimulated gene (ISG) expression are linked to the pathogenesis of systemic lupus erythematosus (SLE). Although the mechanisms responsible for dysregulated IFN-I production in SLE remain unclear, autoantibodymediated uptake of endogenous nucleic acids is thought to play a role. 2,6,10,14-tetramethylpentadecane (TMPD; also known as pristane) induces a lupus-like disease in mice characterized by immune complex nephritis with autoantibodies to DNA and ribonucleoproteins. We recently reported that TMPD also causes increased ISG expression and that the development of the lupus is completely dependent on IFN-I signaling (Nacionales, D.C., K.M. Kelly-Scumpia, P.Y. Lee, J.S. Weinstein, R. Lyons, E. Sobel, M. Satoh, and W.H. Reeves. 2007. Arthritis Rheum. 56:3770 -3783). We show that TMPD elicits IFN-I production, monocyte recruitment, and autoantibody production exclusively through a Tolllike receptor (TLR) 7 -and myeloid differentiation factor 88 (MyD88) -dependent pathway. In vitro studies revealed that TMPD augments the effect of TLR7 ligands but does not directly activate TLR7 itself. The effects of TMPD were amplifi ed by the Y-linked autoimmune acceleration cluster, which carries a duplication of the TLR7 gene. In contrast, deficiency of Fc ␥ receptors (Fc ␥ Rs) did not affect the production of IFN-I. Collectively, the data demonstrate that TMPD-stimulated IFN-I production requires TLR7/MyD88 signaling and is independent of autoantibody-mediated uptake of ribonucleoproteins by Fc ␥ Rs.

Neonates exhibit an increased risk of sepsis mortality compared with adults. We show that in contrast to adults, survival from polymicrobial sepsis in murine neonates does not depend on an intact adaptive immune system and is not improved by T cell-directed adaptive immunotherapy. Furthermore, neonates manifest an attenuated inflammatory and innate response to sepsis, and have functional defects in their peritoneal CD11b ؉ cells. Activation of innate immunity with either a Toll-like receptor 4 (TLR4) or TLR7/8 agonist, but not a TLR3 agonist, increased the magnitude, but abbreviated the early systemic inflammatory response, reduced bacteremia, and improved survival to polymicrobial sepsis. TLR4 agonist pretreatment enhanced peritoneal neutrophil recruitment with increased oxidative burst production, whereas the TLR7/8 agonist also enhanced peritoneal neutrophil recruitment with increased phagocytic ability. These benefits were independent of the adaptive immune system and type I interferon signaling. Improving innate immune function with select TLR agonists may be a useful strategy to prevent neonatal sepsis mortality. IntroductionSepsis causes profound defects in innate and acquired immunity. In septic adults, circulating leukocytes fail to mount an attenuated inflammatory response, monocytes have defective antigen presentation in part due to reduced MHC class II expression, and dendritic cells and lymphocytes exhibit increased apoptosis. [1][2][3][4] These deficiencies contribute to a failure to clear primary pathogens, an increased propensity to develop superinfections, and an inability to mount adaptive immune responses. Considerable progress has been made in understanding the pathogenesis of and identifying potential immunomodulatory therapies for treating sepsis in adult animals. For example, MyD88 and type I interferon signaling pathways 5,6 are important requisites for innate and inflammatory host defense responses to pathogens. 7,8 Stimulating the innate immune system with Toll-like receptor (TLR) agonists improves survival in adult animal models of sepsis. 9,10 Similarly, absence of the adaptive immune system 11 or an inability of B cells to produce antibodies 12 predisposes adult mice to a poor outcome in sepsis. Correction of adaptive immune dysfunction by prevention of lymphocyte apoptosis or treatment with agonistic glucocorticoid-induced tumor necrosis factor (TNF) receptor antibody (anti-GITR) to stimulate effector T-cell function, improves survival in animal models of adult sepsis. 11,13 These studies highlight the importance of both the innate and adaptive immune systems in eliminating invading pathogens in adult mammals. However, the mechanisms of protective immunity in neonates that do not possess a fully intact immune system, and who develop sepsis at increased rates, 14 are less clear.More than 1 million babies die each year worldwide within the first 4 weeks of life from sepsis. 15 Neonatal sepsis mortality is higher than in children and adults, 16,17 peaking in premature infants, where r...

Regulatory T cells (Tregs), including natural CD4+CD25+ Tregs and inducible IL-10 producing T regulatory type 1 (TR1) cells, maintain tolerance and inhibit autoimmunity. Recently, increased percentages of Tregs have been observed in the blood of septic patients, and ex vivo-activated Tregs were shown to prevent polymicrobial sepsis mortality. Whether endogenous Tregs contribute to sepsis outcome remains unclear. Polymicrobial sepsis, induced by cecal ligation and puncture, caused an increased number of splenic Tregs compared with sham-treated mice. Splenic CD4+CD25+ T cells from septic mice expressed higher levels of Foxp3 mRNA and were more efficient suppressors of CD4+CD25− T effector cell proliferation. Isolated CD4+ T cells from septic mice displayed increased intracellular IL-10 staining following stimulation, indicating that TR1 cells may also be elevated in sepsis. Surprisingly, Ab depletion of total CD4+ or CD4+CD25+ populations did not affect mortality. Furthermore, no difference in survival outcome was found between CD25 or IL-10 null mice and wild-type littermates, indicating that Treg or TR1-generated IL-10 are not required for survival. These results demonstrate that, although sepsis causes a relative increase in Treg number and increases their suppressive function, their presence does not contribute significantly to overall survival in this model.

Diffuse alveolar hemorrhage is an uncommon yet often fatal complication of systemic lupus erythematosus (SLE). Advances in the treatment of alveolar hemorrhage have been hampered due to the heterogeneity of clinical findings and the lack of suitable animal models. A single intraperitoneal injection of pristane induces a lupus-like syndrome characterized by lupus-related autoantibodies and glomerulonephritis in non-autoimmune prone strains of mice. In addition, C57BL/6 (B6) mice frequently develop alveolar hemorrhage within a few weeks of pristane injection. Immunopathogenesis of pristane-induced alveolar hemorrhage was investigated in the present study. Early (2-4 weeks after injection) mortality due to hemorrhage was unique to C57BL/6 and C57BL/10 strains of mice. Recruitment of the macrophages and neutrophils preceded the hemorrhage by several days and hemorrhage started 3-7 days after pristane injection in some mice, peaked at 2 weeks (84% in B6) and then resolved by 4 weeks in a majority of mice. Alveolar hemorrhage was independent of MyD88-, or TLR7 pathways, in contrast to autoantibody production and glomerulonephritis, and also was independent of FcγR or Fas. Rag1-/- mice had a reduced prevalence of alveolar hemorrhage compared to B6 (P = 0.01) congenics. However, T-cell receptor deficient mice developed alveolar hemorrhage at a rate comparable to wild type controls, while B6 Igμ-/- mice surprisingly had a strikingly reduced prevalence (7% vs 84% in B6, P < 0.0001). Reconstitution of B6 Igμ-/- mice with wild type B cells increased the prevalence to 50% (P = 0.028). Pristane-induced alveolar hemorrhage is a useful model to study the pathogenesis and develop new therapy for this underappreciated and often life-threatening complication of SLE.