Type I Interferon Contributes to Noncanonical Inflammasome Activation,Mediates Immunopathology,and Impairs Protective Immunity during Fatal Infection with Lipopolysaccharide-Negative Ehrlichiae

Ehrlichia species are intracellular bacteria that cause fatal ehrlichiosis, mimicking toxic shock syndrome in humans and mice. Virulent ehrlichiae induce inflammasome activation leading to caspase-1 cleavage and IL-18 secretion, which contribute to development of fatal ehrlichiosis. We show that fatal infection triggers expression of inflammasome components, activates caspase-1 and caspase-11, and induces host-cell death and secretion of IL-1β, IL-1α, and type I interferon (IFN-I). Wild-type and Casp1^−/− mice were highly susceptible to fatal ehrlichiosis, had overwhelming infection, and developed extensive tissue injury. Nlrp3^−/− mice effectively cleared ehrlichiae, but displayed acute mortality and developed liver injury similar to wild-type mice. By contrast, Ifnar1^−/− mice were highly resistant to fatal disease and had lower bacterial burden, attenuated pathology, and prolonged survival. Ifnar1^−/− mice also had improved protective immune responses mediated by IFN-γ and CD4⁺ Th1 and natural killer T cells, with lower IL-10 secretion by T cells. Importantly, heightened resistance of Ifnar1^−/− mice correlated with improved autophagosome processing, and attenuated noncanonical inflammasome activation indicated by decreased activation of caspase-11 and decreased IL-1β, compared with other groups. Our findings demonstrate that IFN-I signaling promotes host susceptibility to fatal ehrlichiosis, because it mediates ehrlichia-induced immunopathology and supports bacterial replication, perhaps via activation of noncanonical inflammasomes, reduced autophagy, and suppression of protective CD4⁺ T cells and natural killer T-cell responses against ehrlichiae.Ehrlichia chaffeensis is the causative agent of human monocytotropic ehrlichiosis, a highly prevalent life-threatening tickborne disease in North America.^{1, 2, 3} Central to the pathogenesis of human monocytotropic ehrlichiosis is the ability of ehrlichiae to survive and replicate inside the phagosomal compartment of host macrophages and to secrete proteins via type I and type IV secretion systems into the host-cell cytosol.⁴ Using murine models of ehrlichiosis, we and others have demonstrated that fatal ehrlichial infection is associated with severe tissue damage caused by TNF-α–producing cytotoxic CD8⁺ T cells (ie, immunopathology) and the suppression of protective CD4⁺ Th1 immune responses.^{5, 6, 7, 8, 9, 10, 11, 12, 13, 14} However, neither how the Ehrlichia bacteria trigger innate immune responses nor how these responses influence the acquired immunity against ehrlichiae is entirely known.Extracellular and intracellular pattern recognition receptors recognize microbial infections.^{15, 16, 17, 18} Recently, members of the cytosolic nucleotide-binding domain and leucine-rich repeat family (NLRs; alias NOD-like receptors), such as NLRP3, have emerged as critical pattern recognition receptors in the host defense against intracellular pathogens. NLRs recognize intracellular bacteria and trigger innate, protective immune responses.^{19, 20, 21, 22, 23} NLRs respond to both microbial products and endogenous host danger signals to form multimeric protein platforms known as inflammasomes. The NLRP3 inflammasome consists of multimers of NLRP3 that bind to the adaptor molecules and apoptosis-associated speck-like protein (ASC) to recruit pro–caspase-1 and facilitate cleavage and activation of caspase-1.^{15, 16, 24} The canonical inflammasome pathway involves the cleavage of immature forms of IL-1β and IL-18 (pro–IL-1β and pro–IL-18) into biologically active mature IL-1β and IL-18 by active caspase-1.^{25, 26, 27, 28} The noncanonical inflammasome pathway marked by the activation of caspase-11 has been described recently. Active caspase-11 promotes the caspase-1–dependent secretion of IL-1β/IL-18 and mediates inflammatory lytic host-cell death via pyroptosis, a process associated with the secretion of IL-1α and HMGB1.^{17, 29, 30, 31} Several key regulatory checkpoints ensure the proper regulation of inflammasome activation.^{16, 32} For example, blocking autophagy by the genetic deletion of the autophagy regulatory protein ATG16L1 increases the sensitivity of macrophages to the inflammasome activation induced by TLRs.³³ Furthermore, TIR domain-containing adaptor molecule 1 (TICAM-1; alias TRIF) has been linked to inflammasome activation via the secretion of type I interferons α and β (IFN-α and IFN-β) and the activation of caspase-11 during infections with Gram-negative bacteria.^{2, 34, 35, 36, 37, 38, 39}We have recently demonstrated that fatal ehrlichial infection induces excess IL-1β and IL-18 production, compared with mild infection,^{8, 12, 13, 14} and that lack of IL-18 signaling enhances resistance of mice to fatal ehrlichiosis.¹² These findings suggest that inflammasomes play a detrimental role in the host defense against ehrlichial infection. Elevated production of IL-1β and IL-18 in fatal ehrlichiosis was associated with an increase in hepatic expression of IFN-α.¹⁴ IFN-I plays a critical role in the host defense against viral and specific bacterial infections.^{28, 36, 37, 40, 41, 42, 43} However, the mechanism by which type I IFN contributes to fatal ehrlichial infection remains unknown. Our present results reveal, for the first time, that IFNAR1 promotes detrimental inflammasome activation, mediates immunopathology, and impairs protective immunity against ehrlichiae via mechanisms that involve caspase-11 activation, blocking of autophagy, and production of IL-10. Our novel finding that lipopolysaccharide (LPS)-negative ehrlichiae trigger IFNAR1-dependent caspase-11 activation challenges the current paradigm that implicates LPS as the major microbial ligand triggering the noncanonical inflammasome pathway during Gram-negative bacterial infection.     

Dendritic Cell and NK Cell Reciprocal Cross Talk Promotes Gamma Interferon-Dependent Immunity to Blood-Stage Plasmodium chabaudi AS Infection in Mice

Dendritic cells (DCs) are important accessory cells for promoting NK cell gamma interferon (IFN-γ) production in vitro in response to Plasmodium falciparum-infected red blood cells (iRBC). We investigated the requirements for reciprocal activation of DCs and NK cells leading to Th1-type innate and adaptive immunity to P. chabaudi AS infection. During the first week of infection, the uptake of iRBC by splenic CD11c⁺ DCs in resistant wild-type (WT) C57BL/6 mice was similar to that in interleukin 15^−/− (IL-15^−/−) and IL-12p40^−/− mice, which differ in the severity of P. chabaudi AS infection. DCs from infected IL-15^−/− mice expressed costimulatory molecules, produced IL-12, and promoted IFN-γ secretion by WT NK cells in vitro as efficiently as WT DCs. In contrast, DCs from infected IL-12p40^−/− mice exhibited alterations in maturation and cytokine production and were unable to induce NK cell IFN-γ production. Coculture of DCs and NK cells demonstrated that DC-mediated NK cell activation required IL-12 and, to a lesser extent, IL-2, as well as cell-cell contact. In turn, NK cells from infected WT mice enhanced DC maturation, IL-12 production, and priming of CD4⁺ T-cell proliferation and IFN-γ secretion. Infected WT mice depleted of NK cells, which exhibit increased parasitemia, had impaired DC maturation and DC-induced CD4⁺ Th1 cell priming. These findings indicate that DC-NK cell reciprocal cross talk is critical for control and rapid resolution of P. chabaudi AS infection and provide in vivo evidence for the importance of this interaction in IFN-γ-dependent immunity to malaria.     

Type I Interferon Modulates Monocyte Recruitment and Maturation in Chronic Inflammation

Chronic inflammation is characterized by continuous recruitment and activation of immune cells such as monocytes in response to a persistent stimulus. Production of proinflammatory mediators by monocytes leads to tissue damage and perpetuates the inflammatory response. However, the mechanism(s) responsible for the sustained influx of monocytes in chronic inflammation are not well defined. In chronic peritonitis induced by pristane, the persistent recruitment of Ly6C^hi inflammatory monocytes into the peritoneum was abolished in type I interferon (IFN-I) receptor-deficient mice but was unaffected by the absence of IFN-γ, tumor necrosis factor-α, interleukin-6, or interleukin-1. IFN-I signaling stimulated the production of chemokines (CCL2, CCL7, and CCL12) that recruited Ly6C^hi monocytes via interactions with the chemokine receptor CCR2. Interestingly, after 2,6,10,14-tetramethylpentadecane treatment, the rapid turnover of inflammatory monocytes in the inflamed peritoneum was associated with a lack of differentiation into Ly6C^lo monocytes/macrophages, a more mature subset with enhanced phagocytic capacity. In contrast, Ly6C^hi monocytes differentiated normally into Ly6C^lo cells in IFN-I receptor-deficient mice. The effects of IFN-I were specific for monocytes as granulocyte migration was unaffected in the absence of IFN-I signaling. Taken together, our findings reveal a novel role of IFN-I in promoting the recruitment of inflammatory monocytes via the chemokine receptor CCR2. Continuous monocyte recruitment and the lack of terminal differentiation induced by IFN-I may help sustain the chronic inflammatory response.Chronic inflammation is a pathological condition characterized by unremitting production of cytokines and other mediators in response to persistent microbial infection or chemical agents.¹ In autoimmune disorders such as systemic lupus erythematosus (SLE), endogenous antigens also may play an important role in perpetuating a chronic inflammatory state.² Regardless of the cause, a common feature of chronic inflammation is the persistent homing of circulating monocytes to the site of injury.¹Two major subsets of blood monocytes have been identified in mice. Inflammatory monocytes (also called Ly6C^hi monocytes), characterized by surface expression of Ly6C and the chemokine receptor CCR2, are released from the bone marrow and actively recruited to inflamed tissue.³ Under steady-state conditions, Ly6C^hi monocytes mature in the circulation into residential (Ly6C^lo) monocytes, which express CX3CR1 and infiltrate noninflamed tissues where they differentiate into residential tissue macrophages.^3,4 On their recruitment to sites of injury, inflammatory monocytes also can differentiate into macrophages with enhanced phagocytic activity or into dendritic cells, which capture antigens for presentation to lymphocytes.^5,6,7,8 Tissue monocytes/macrophages also can amplify the immune response by secreting inflammatory cytokines and chemokines to recruit additional immune cells. In chronic inflammation, however, persistent production of these inflammatory mediators can lead to tissue damage, resulting in cycles of tissue destruction and repair. The mechanism(s) responsible for the continuous recruitment of monocytes in chronic inflammation are not well defined.Intraperitoneal administration of 2,6,10,14 tetramethylpentadecane (TMPD; also known as pristane) potently induces chronic inflammation in mice. The influx of mononuclear and polymorphonuclear leukocytes to the peritoneal cavity persists for months after injection of this hydrocarbon oil.⁹ The chronic inflammatory state also promotes tumorigenesis, as TMPD was found to induce plasmacytomas more than three decades ago.¹⁰ TMPD is used to stimulate monoclonal antibody production by hybridoma cells injected i.p., an effect of chronic interleukin (IL)-6 production in response to the oil.¹¹ TMPD treatment stimulates the development of ectopic lymphoid tissue, a feature often associated with chronic inflammatory states.⁹ Ectopic lymphoid tissue may play a key role in the induction of lupus-like autoimmune disease (autoantibodies, glomerulonephritis, arthritis, and pulmonary vasculitis) in TMPD-treated mice.^12,13How TMPD causes chronic inflammation is not well understood, but a pathological role of several cytokines has been suggested. IL-6 is essential for generating plasmacytomas,¹⁴ whereas IL-12 is required for the development of TMPD-induced glomerulonephritis.¹⁵ Recently, it was found that type I interferons (IFN-I, including IFN-α and IFN-β) and type II interferon (IFN-γ) both contribute to autoantibody production in TMPD-treated mice.^12,16 Using TMPD-induced chronic peritonitis as a model, we examined the mechanism(s) underlying the chronic recruitment of monocytes and granulocytes to the inflamed peritoneum.     

B Cells Modulate Systemic Responses to Pneumocystis murina Lung Infection and Protect On-Demand Hematopoiesis via T Cell-Independent Innate Mechanisms when Type I Interferon Signaling Is Absent

HIV infection results in a complex immunodeficiency due to loss of CD4⁺ T cells, impaired type I interferon (IFN) responses, and B cell dysfunctions causing susceptibility to opportunistic infections such as Pneumocystis murina pneumonia and unexplained comorbidities, including bone marrow dysfunctions. Type I IFNs and B cells critically contribute to immunity to Pneumocystis lung infection. We recently also identified B cells as supporters of on-demand hematopoiesis following Pneumocystis infection that would otherwise be hampered due to systemic immune effects initiated in the context of a defective type I IFN system. While studying the role of type I IFNs in immunity to Pneumocystis infection, we discovered that mice lacking both lymphocytes and type I IFN receptor (IFrag^−/−) developed progressive bone marrow failure following infection, while lymphocyte-competent type I IFN receptor-deficient mice (IFNAR^−/−) showed transient bone marrow depression and extramedullary hematopoiesis. Lymphocyte reconstitution of lymphocyte-deficient IFrag^−/− mice pointed to B cells as a key player in bone marrow protection. Here we define how B cells protect on-demand hematopoiesis following Pneumocystis lung infection in our model. We demonstrate that adoptive transfer of B cells into IFrag^−/− mice protects early hematopoietic progenitor activity during systemic responses to Pneumocystis infection, thus promoting replenishment of depleted bone marrow cells. This activity is independent of CD4⁺ T cell help and B cell receptor specificity and does not require B cell migration to bone marrow. Furthermore, we show that B cells protect on-demand hematopoiesis in part by induction of interleukin-10 (IL-10)- and IL-27-mediated mechanisms. Thus, our data demonstrate an important immune modulatory role of B cells during Pneumocystis lung infection that complement the modulatory role of type I IFNs to prevent systemic complications.     

Type I Interferon Signaling Regulates Activation of the Absent in Melanoma 2 Inflammasome during Streptococcus pneumoniae Infection

Streptococcus pneumoniae, a Gram-positive bacterial pathogen, causes pneumonia, meningitis, and septicemia. Innate immune responses are critical for the control and pathology of pneumococcal infections. It has been demonstrated that S. pneumoniae induces the production of type I interferons (IFNs) by host cells and that type I IFNs regulate resistance and chemokine responses to S. pneumoniae infection in an autocrine/paracrine manner. In this study, we examined the effects of type I IFNs on macrophage proinflammatory cytokine production in response to S. pneumoniae. The production of interleukin-18 (IL-18), but not other cytokines tested, was significantly decreased by the absence or blockade of the IFN-α/β receptor, suggesting that type I IFN signaling is necessary for IL-18 production. Type I IFN signaling was also required for S. pneumoniae-induced activation of caspase-1, a cysteine protease that plays a central role in maturation and secretion of IL-18. Earlier studies proposed that the AIM2 and NLRP3 inflammasomes mediate caspase-1 activation in response to S. pneumoniae. From our results, the AIM2 inflammasome rather than the NLRP3 inflammasome seemed to require type I IFN signaling for its optimal activation. Consistently, AIM2, but not NLRP3, was upregulated in S. pneumoniae-infected macrophages in a manner dependent on the IFN-α/β receptor. Furthermore, type I IFN signaling was found to contribute to IL-18 production in pneumococcal pneumonia in vivo. Taken together, these results suggest that type I IFNs regulate S. pneumoniae-induced activation of the AIM2 inflammasome by upregulating AIM2 expression. This study revealed a novel role for type I IFNs in innate responses to S. pneumoniae.     

Coinfection with an Intestinal Helminth Impairs Host Innate Immunity against Salmonella enterica Serovar Typhimurium and Exacerbates Intestinal Inflammation in Mice

Salmonella enterica serovar Typhimurium is a Gram-negative food-borne pathogen that is a major cause of acute gastroenteritis in humans. The ability of the host to control such bacterial pathogens may be influenced by host immune status and by concurrent infections. Helminth parasites are of particular interest in this context because of their ability to modulate host immune responses and because their geographic distribution coincides with those parts of the world where infectious gastroenteritis is most problematic. To test the hypothesis that helminth infection may negatively regulate host mucosal innate immunity against bacterial enteropathogens, a murine coinfection model was established by using the intestinal nematode Heligmosomoides polygyrus and S. Typhimurium. We found that mice coinfected with S. Typhimurium and H. polygyrus developed more severe intestinal inflammation than animals infected with S. Typhimurium alone. The enhanced susceptibility to Salmonella-induced intestinal injury in coinfected mice was found to be associated with diminished neutrophil recruitment to the site of bacterial infection that correlated with decreased expression of the chemoattractants CXCL2/macrophage inflammatory protein 2 (MIP-2) and CXCL1/keratinocyte-derived chemokine (KC), poor control of bacterial replication, and exacerbated intestinal inflammation. The mechanism of helminth-induced inhibition of MIP-2 and KC expression involved interleukin-10 (IL-10) and, to a lesser extent, IL-4 and IL-13. Ly6G antibody-mediated depletion of neutrophils reproduced the adverse effects of H. polygyrus on Salmonella infection. Our results suggest that impaired neutrophil recruitment is an important contributor to the enhanced severity of Salmonella enterocolitis associated with helminth coinfection.     

Increased Systemic Cytokine/Chemokine Expression in Asthmatic and Non‐asthmatic Patients with Bacterial,Viral or Mixed Lung Infection

This study was aimed to determine the profiles of serum cytokines (IL‐1β, TNF‐α, IL‐4, IL‐5) and chemokines (MCP‐1: monocyte chemoattract protein‐1 and RANTES: regulated on activation normal T cell expressed and secreted) in individuals with an asthmatic versus a non‐asthmatic background with bacterial, viral or mixed acute respiratory infection. Asthmatic (n = 14) and non‐asthmatic (n = 29) patients with acute viral, bacterial or mixed (bacterial and viruses) respiratory infection were studied. Patients were also analysed as individuals with pneumonia or bronchitis. Healthy individuals with similar age and sex (n = 10) were used as controls. Cytokine/chemokine content in serum was determined by ELISA. Increased cytokine/chemokine concentration in asthmatic and non‐asthmatic patients was observed. However, higher concentrations of chemokines (MCP‐1 and RANTES) in asthmatic patients infected by viruses, bacteria or bacteria and viruses (mixed) than in non‐asthmatic patients were observed. In general, viral and mixed infections were better cytokine/chemokine inducers than bacterial infection. Cytokine/chemokine expression was similarly increased in both asthmatic and non‐asthmatic patients with pneumonia or bronchitis, except that RANTES remained at normal levels in bronchitis. Circulating cytokine profiles induced by acute viral, bacterial or mixed lung infection were not related to asthmatic background, except for chemokines that were increased in asthmatic status.     

Protection of Rabbits Against Local Vaccinia Virus Infection by Brucella abortus and Polyacrylic Acid in the Absence of Systemic Interferon Production

Brucella abortus and polyacrylic acid, two agents whose interferon-inducing capacity in the mouse has been well established, failed to stimulate circulating interferon production in rabbits, yet protected rabbits against local vaccinia virus infection.     

Helicobacter pylori Infection Impairs the Mucin Production Rate and Turnover in the Murine Gastric Mucosa

To protect the surface of the stomach, the epithelial cells secrete a mucus layer, which is mainly comprised of the MUC5AC mucin. Further protection is provided by a thick glycocalyx on the apical surface of the epithelial cell, with the cell surface mucin MUC1 as a major component. Here, we investigate the production rate and turnover of newly synthesized mucin in mice and analyze the effects of early colonization and chronic infection with H. pylori. Metabolic incorporation of an azido GalNAc analog (GalNAz) was used as a nonradioactive method to perform pulse experiments in the whole animal. First, the subcellular movement of newly synthesized mucin and mucin turnover was determined in uninfected mice. Based on the time line for mucin transport and dissemination, 2, 6, and 12 h after GalNAz injection was selected to collect the stomachs from mice infected with H. pylori strain SS1 during early colonization (7 days) and chronic infection (90 days). The results demonstrated that the speed from the start of glycosylation to the final destination is faster for the membrane-bound mucin to reach the glycocalyx (2 h) than for the secretory mucins to become secreted into the mucus layer (5 h). Furthermore, infection with H. pylori reduces the rate of mucin turnover and decreases the levels of Muc1. Since H. pylori colonizes this mucus niche, the decreased turnover rate indicates that H. pylori creates a more stable and favorable environment for itself by impairing the defense mechanism for clearing the mucosal surface of pathogens by mucus flow.     

Cytokine Secretion in Long-standing Diabetes Mellitus Type 1 and 2: Associations with Low-grade Systemic Inflammation

Low-grade systemic chronic inflammation is a very well-known feature of diabetes mellitus (DM). The purpose of this study was the assessment of the proinflammatory cytokine secretion profile in long-standing diabetes along with the presence of features of systemic inflammation. Metabolic parameters and serum high-sensitivity C-reactive protein, interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha levels were determined in 20 patients with type 1 DM and 21 patients with type 2 DM and compared to 34 healthy subjects. The number of cytokine-secreting peripheral blood mononuclear cells (PBMCs), before and after mitogenic stimulation, was also determined in the same groups. Adverse lipid profile, higher levels of inflammatory markers, and higher count of cytokine-secreting cells were observed more prevalently in type 2 diabetics than in controls. After stimulation, the increase in number of cytokine-secreting cells was higher in controls. In conclusion, patients with DM have evidence of low-grade inflammation and abnormal PBMC function that could be related to long-term sequelae, the accelerated atherosclerotic process, and the susceptibility to infections.     

Close Association between Pulmonary Disease Manifestation in Mycoplasma pneumoniae Infection and Enhanced Local Production of Interleukin-18 in the Lung, Independent of Gamma Interferon

To investigate pathophysiologies of Mycoplasma pneumoniae infection from an immunological point of view, we measured the levels of interleukin-18 (IL-18) (originally designated gamma interferon [IFN-γ]-inducing factor) in 19 serum samples from 10 patients with pneumonia without pleural effusion (ages 1 to 16 years), 3 serum and 13 pleural fluid samples from 11 patients with pleural effusions (ages 11 months to 15 years), and 18 serum and 27 cerebrospinal fluid samples from 24 patients with central nervous system complications (ages 1 to 15 years). IL-18 was measured by a commercially available enzyme-linked immunosorbent assay kit (MBL, Nagoya, Japan). In addition, the levels of tumor necrosis factor alpha, IFN-γ, IL-6, IL-12, and KL-6 (a mucin-like glycoprotein expressed on type 2 pneumocytes) were measured in selected samples. The results concerning pleural effusions showed that elevated levels of IL-18 in pleural fluid, but not in serum, were solely associated with a sustained fibrotic change of the lung on chest roentgenography which might represent a pathological feature of intraluminal organization. All the pleural fluid samples with elevated levels of IL-18 were positive by PCR for M. pneumoniae DNA. There was no association between IL-18 and IFN-γ levels in serum or in the pleural fluid. On the other hand, elevated levels of IL-18 in serum, but not in cerebrospinal fluid samples, were observed in the cases complicated by central nervous system involvement, including profound brain dysfunction with seizures. Our study demonstrated that M. pneumoniae can induce IL-18 and that the enhanced local production of IL-18 in the lung is closely associated with pulmonary disease manifestation.     

Dectin-2 Deficiency Promotes Th2 Response and Mucin Production in the Lungs after Pulmonary Infection with Cryptococcus neoformans

Dectin-2 is a C-type lectin receptor that recognizes high mannose polysaccharides. Cryptococcus neoformans, a yeast-form fungal pathogen, is rich in polysaccharides in its cell wall and capsule. In the present study, we analyzed the role of Dectin-2 in the host defense against C. neoformans infection. In Dectin-2 gene-disrupted (knockout) (Dectin-2KO) mice, the clearance of this fungus and the inflammatory response, as shown by histological analysis and accumulation of leukocytes in infected lungs, were comparable to those in wild-type (WT) mice. The production of type 2 helper T (Th2) cytokines in lungs was higher in Dectin-2KO mice than in WT mice after infection, whereas there was no difference in the levels of production of Th1, Th17, and proinflammatory cytokines between these mice. Mucin production was significantly increased in Dectin-2KO mice, and this increase was reversed by administration of anti-interleukin 4 (IL-4) monoclonal antibody (MAb). The levels of expression of β1-defensin, cathelicidin, surfactant protein A (Sp-A), and Sp-D in infected lungs were comparable between these mice. In in vitro experiments, IL-12p40 and tumor necrosis factor alpha (TNF-α) production and expression of CD86 and major histocompatibility complex (MHC) class II by bone marrow-derived dendritic cells and alveolar macrophages were completely abrogated in Dectin-2KO mice. Finally, the disrupted lysates of C. neoformans, but not of whole yeast cells, activated Dectin-2-triggered signaling in an assay with nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cells expressing this receptor. These results suggest that Dectin-2 may oppose the Th2 response and IL-4-dependent mucin production in the lungs after infection with C. neoformans, and it may not be required for the production of Th1, Th17, and proinflammatory cytokines or for clearance of this fungal pathogen.     

Type I Interferon controls the onset and severity of autoimmune manifestations in lpr mice

Type I Interferons (IFN-I) are immunoregulatory cytokines that enhance activation and survival of many cellular components of the immune system. In the present work, we evaluated the effect of IFN-I on the development of the lymphoproliferative disorder in Fas-defective lpr mice. We report that sustained injection of polyinosinic:polycytidylic acid, a potent inducer of IFN-I, in B6 lpr mice resulted in a dramatic aggravation of the renal disease, higher titers of autoantibodies, a 10-fold increase in serum Ig and accumulation of activated lymphocytes. Moreover, introducing a null mutation for the IFN-I-Receptor gene into the lpr background resulted in dramatic decrease of immune complexes deposition in the kidney and reduced lymphadenopathy. While several recent reports correlated serum levels of IFN-alpha with disease activity in systemic Lupus erythematosus patients, our findings establish a causal link from IFN-I production to the onset and severity of another related autoimmune syndrome.     

Role of Leptin and SOCS3 in Inhibiting the Type I Interferon Response During Obesity

Obesity provokes an imbalance in the immune system, including an aberrant type I interferon response during some viral infections and after TLR stimulation. SOCS3 overexpression and altered systemic leptin levels could be responsible for the reduced type I interferon production in people with obesity and, eventually, significantly increase the risk of viral infection. The aim of this study was to determine whether SOCS3- and leptin-induced tolerance are responsible for the reduced type I interferon production in people with obesity. SOCS3 overexpression in PBMCs from people with obesity was inhibited with the small interfering RNA (siRNA) assay, and leptin-induced tolerance was evaluated in PBMCs from non-obese volunte\ers and U937 cells treated with TLR ligands. SOCS3, but not SOCS1, gene silencing via siRNA increased the type I interferon response in PBMCs obtained from people with obesity. On the other hand, leptin induced SOCS3 expression and inhibited type I interferons in PBMCs from healthy donors and in U937 monocytes stimulated with TLR ligands. Taken together, these results demonstrate that reduced type I interferon production in obesity is caused by SOCS3 overexpression as well as tolerance induced by leptin. Here, we demonstrate a key role of leptin and SOCS3 in inhibiting the type I interferon response during obesity.     

Inefficiency of C3H/HeN Mice to Control Chlamydial Lung Infection Correlates with Downregulation of Neutrophil Activation during the Late Stage of Infection

We previously reported that massive infiltration of neutrophils in C3H/HeN （C3H） mice could not efficiently control Chlamydia muridarum （Cm） infection and might contribute to the high susceptibility of these mice to lung infection. To further define the nature of neutrophil responses in C3H mice during chlamydial infection, we examine the expression of adhesion molecules and CDllb related to neutrophils infiltration and activation, respectively, following intranasal Cm infection. The results showed that the expression of selectins （E-selectin, P-selectin and L-selectin）, and intercellular cell adhesion molecule-1 （ICAM-1） in the lung of C3H mice increased more significantly than in C57BL/6 （B6） mice, the more resistant strain. These results correlated well with the massive neutrophils infiltration in C3H mice. In contrast, CDllb expression on peripheral blood and lung neutrophils in C3H mice exhibited a significant reduction compared with B6 mice during the late phage of infection （day 14）. These findings suggest that the high-level expression of adhesion molecules in C3H mice may enhance neutrophils recruitment to the lung, but the decline of CDllb expression on neutrophils may attenuate neutrophil function. Therefore, CDllb down-regulation on neutrophils may contribute to the failure of C3H mice to control chlamydial lung infection.     

Quinolinic Alkaloids from Galipea longiflora Krause Suppress Production of Proinflammatory Cytokines in vitro and Control Inflammation in vivo upon Leishmania Infection in Mice

An antileishmanial activity of quinolinic alkaloids from Galipea longiflora Krause, known as Evanta, has been demonstrated. We have previously shown that, apart from its leishmanicidal effect, in vitro pretreatment of spleen cells with an alkaloid extract of Evanta (AEE) interfered with the proliferation and interferon‐γ production in lymphocytes polyclonally activated either with concanavalin A or anti‐CD3. In the present study, we investigated if AEE could interfere with antigen‐specific lymphocyte activation. We found that in vitro and in vivo treatment reduced recall lymphocyte responses, as measured by IFN‐γ production (55% and 63% reduction compared to untreated cells, respectively). Apart from IFN‐γ, the production of IL‐12 and TNF was also suppressed. No effects were observed for meglumine antimoniate (SbV), the conventional drug used to treat leishmaniasis. When mice infected with Leishmania braziliensis promastigotes in the hind footpad were treated with AEE, the dynamics of the infection changed and the footpath thickness was efficiently controlled. The parasite load was also reduced but to a lesser extent than upon treatment with SbV. Combined treatment efficiently controlled both the thickness and parasite load as smaller lesions during the entire course of the infection were seen in the mice treated with AEE plus SbV compared with AEE or SbV alone. We discuss the benefits of combined administration of AEE plus SbV.