Forward genetic analysis of Toll-like receptor responses in wild-derived mice reveals a novel antiinflammatory role for IRAK1BP1

Although inflammatory cytokines produced by activation of Toll-like receptors (TLRs) are essential for early host defense against infection, they also mediate a vast array of pathologies, including autoimmune disease, hypersensitivity reactions, and sepsis. Thus, numerous regulatory mechanisms exist in parallel with proinflammatory pathways to prevent excessive release of these potent effector molecules. We report elucidation of a novel regulatory function for interleukin receptor–associated kinase (IRAK)-1 binding protein 1 (IRAK1BP1, also known as SIMPL) through quantitative trait locus mapping of the TLR response in wild-derived mouse strains. This gene emerged as a negative regulator of TLR2-mediated interleukin (IL)-6 production in MOLF/Ei mice, which expressed IRAK1BP1 mRNA in an allele-specific manner when crossed with the C57BL/6J strain. Human peripheral blood mononuclear cells and primary macrophages from two other wild-derived mouse strains also induced IRAK1BP1 mRNA by 4 hours after stimulation with agonists of various TLRs. Examination of its effects on IL-6 and other cytokines demonstrated that IRAK1BP1 regulates transcription of a specific subset of TLR-responsive genes, producing an overall antiinflammatory profile. Our results reveal that IRAK1BP1 is a critical factor in preventing dangerous overproduction of proinflammatory cytokines by the innate immune system and in influencing the specificity of TLR responses. Furthermore, these results show that the genetic diversity of wild-derived mouse strains makes them a valuable model of important human gene functions that have been lost in some laboratory-inbred strains

Constitutive interferon signaling maintains critical threshold of MLKL expression to license necroptosis

Interferons (IFNs) are critical determinants in immune-competence and autoimmunity, and are endogenously regulated by a low-level constitutive feedback loop. However, little is known about the functions and origins of constitutive IFN. Recently, lipopolysaccharide (LPS)-induced IFN was implicated as a driver of necroptosis, a necrotic form of cell death downstream of receptor-interacting protein (RIP) kinase activation and executed by mixed lineage kinase like-domain (MLKL) protein. We found that the pre-established IFN status of the cell, instead of LPS-induced IFN, is critical for the early initiation of necroptosis in macrophages. This pre-established IFN signature stems from cytosolic DNA sensing via cGAS/STING, and maintains the expression of MLKL and one or more unknown effectors above a critical threshold to allow for MLKL oligomerization and cell death. Finally, we found that elevated IFN-signaling in systemic lupus erythematosus (SLE) augments necroptosis, providing a link between pathological IFN and tissue damage during autoimmunity

The Toll-like Receptor Protein Rp105 Regulates Lipopolysaccharide Signaling in B Cells

The susceptibility to infections induced by Gram-negative bacteria is largely determined by innate immune responses to bacteria cell wall lipopolysaccharide (LPS). The stimulation of B cells by LPS enhances their antigen-presenting capacity and is accompanied by B cell proliferation and secretion of large quantities of LPS-neutralizing antibodies. Similar to macrophages and neutrophils, the LPS-induced activation of B cells is dependent on Toll-like receptor (TLR)4. Here, we demonstrate that the responses of B cells to LPS are also regulated by another TLR protein, RP105, which is predominantly expressed on mature B cells in mice and humans. The analysis of mice homozygous for the null mutation in the RP105 gene revealed impaired proliferative and humoral immune responses of RP105-deficient B cells to LPS. Using originally LPS-unresponsive Ba/F3 cells expressing exogenous TLR4 and RP105, we demonstrate the functional cooperation between TLR4 and RP105 in LPS-induced nuclear factor κB activation. These data suggest the existence of the TLR4–RP105 signaling module in the LPS-induced B cell activation

Mast cells regulate CD4+ T-cell differentiation in the absence of antigen presentation

Producción CientíficaBackground: Given their unique capacity for antigen uptake, processing, and presentation, antigen-presenting cells (APCs) are critical for initiating and regulating innate and adaptive immune responses. We have previously shown the role of nicotinamide adenine dinucleotide (NAD+) in T-cell differentiation independently of the cytokine milieu, whereas the precise mechanisms remained unknown. Objective: The objective of this study is to further dissect the mechanism of actions of NAD+ and determine the effect of APCs on NAD+-mediated T-cell activation. Methods: Isolated dendritic cells and bone marrow–derived mast cells (MCs) were used to characterize the mechanisms of action of NAD+ on CD4+ T-cell fate in vitro. Furthermore, NAD+-mediated CD4+ T-cell differentiation was investigated in vivo by using wild-type C57BL/6, MC−/−, MHC class II−/−, Wiskott-Aldrich syndrome protein (WASP)−/−, 5C.C7 recombination-activating gene 2 (Rag2)−/−, and CD11b-DTR transgenic mice. Finally, we tested the physiologic effect of NAD+ on the systemic immune response in the context of Listeria monocytogenes infection. Results: Our in vivo and in vitro findings indicate that after NAD+ administration, MCs exclusively promote CD4+ T-cell differentiation, both in the absence of antigen and independently of major APCs. Moreover, we found that MCs mediated CD4+ T-cell differentiation independently of MHC II and T-cell receptor signaling machinery. More importantly, although treatment with NAD+ resulted in decreased MHC II expression on CD11c+ cells, MC-mediated CD4+ T-cell differentiation rendered mice resistant to administration of lethal doses of L monocytogenes. Conclusions: Collectively, our study unravels a novel cellular and molecular pathway that regulates innate and adaptive immunity through MCs exclusively and underscores the therapeutic potential of NAD+ in the context of primary immunodeficiencies and antimicrobial resistance.National Institutes of Health (grants R01NS073635 , R01MH110438 , R01HL096795 , U01HL126497 and R01AG039449)Instituto de Salud Carlos III (grant PI10/02 511)Fundación Ramón Areces (grant CIVP16A1843