The NOD-like receptors (NLRs) are cytosolic pattern-recognition receptors, which are critically involved in mucosal immune defense. The association of the NLR, NOD2, with inflammatory bowel disease first pointed to the NLRs potential function as guardians of the intestinal barrier. Since then, several studies have emphasized the importance of NLRs in maintaining gut homeostasis and intestinal infections, and in shaping the microbiota. In this review, we will highlight the function of NLRs in intestinal inflammation.

Countries with a high incidence of helminth infections are characterized by high morbidity and mortality to infections with intracellular pathogens such as Salmonella. Some patients with Salmonella-Schistosoma co-infections develop a so-called “chronic septicemic salmonellosis,” with prolonged fever and enlargement of the liver and spleen. These effects are most likely due to the overall immunoregulatory activities of schistosomes such as induction of Tregs, Bregs, alternatively activated macrophages, and degradation of antibodies. However, detailed underlying mechanisms are not very well investigated. Here, we show that intraperitoneal application of live Schistosoma mansoni eggs prior to infection with Salmonella Typhimurium in mice leads to an impairment of IFN-γ and IL-17 responses together with a higher bacterial load compared to Salmonella infection alone. S. mansoni eggs were found in granulomas in the visceral peritoneum attached to the colon. Immunohistological staining revealed IPSE/alpha-1, a glycoprotein secreted from live schistosome eggs, and recruited basophils around the eggs. Noteworthy, IPSE/alpha-1 is known to trigger IL-4 and IL-13 release from basophils which in turn is known to suppress Th1/Th17 responses. Therefore, our data support a mechanism of how schistosomes impair a protective immune response against Salmonella infection and increase our understanding of helminth-bacterial co-infections.

The intracellular pathogen Salmonella enterica serovar Typhimurium causes intestinal inflammation characterized by edema, neutrophil influx and increased pro-inflammatory cytokine expression. A major bacterial factor inducing pro-inflammatory host responses is lipopolysaccharide (LPS). S. Typhimurium ΔmsbB possesses a modified lipid A, has reduced virulence in mice, and is being considered as a potential anti-cancer vaccine strain. The lack of a late myristoyl transferase, encoded by MsbB leads to attenuated TLR4 stimulation. However, whether other host receptor pathways are also altered remains unclear. Nod1 and Nod2 are cytosolic pattern recognition receptors recognizing bacterial peptidoglycan. They play important roles in the host's immune response to enteric pathogens and in immune homeostasis. Here, we investigated how deletion of msbB affects Salmonella's interaction with Nod1 and Nod2. S. Typhimurium Δ msbB-induced inflammation was significantly exacerbated in Nod2 −/− mice compared to C57Bl/6 mice. In addition, S. Typhimurium ΔmsbB maintained robust intestinal colonization in Nod2 −/− mice from day 2 to day 7 p.i., whereas colonization levels significantly decreased in C57Bl/6 mice during this time. Similarly, infection of Nod1 −/− and Nod1/Nod2 double-knockout mice revealed that both Nod1 and Nod2 play a protective role in S. Typhimurium ΔmsbB-induced colitis. To elucidate why S. Typhimurium ΔmsbB, but not wild-type S. Typhimurium, induced an exacerbated inflammatory response in Nod2 −/− mice, we used HEK293 cells which were transiently transfected with pathogen recognition receptors. Stimulation of TLR2-transfected cells with S. Typhimurium ΔmsbB resulted in increased IL-8 production compared to wild-type S. Typhimurium. Our results indicate that S. Typhimurium ΔmsbB triggers exacerbated colitis in the absence of Nod1 and/or Nod2, which is likely due to increased TLR2 stimulation. How bacteria with “genetically detoxified” LPS stimulate various innate responses has important implications for the development of safe and effective bacterial vaccines and adjuvants.

BackgroundAbout one third of patients infected with human immunodeficiency virus (HIV) also have chronic hepatitis due to hepatitis C virus (HCV). HCV therapy with simeprevir, pegylated interferon alfa (PegIFNα) and ribavirin (RBV) have been shown to be superior to PegIFNα + RBV alone in non-HIV patients, but no randomized trials in patients with HCV genotype 1 (HCV-1) / HIV coinfection are available.MethodsThis was a historical comparison of study C212 (simeprevir + PegIFNα-2a + RBV in patients with HCV-1/HIV coinfection) with studies in which HCV-1/HIV coinfected patients were treated with PegIFNα-2a + RBV alone. A systematic literature search was performed to identify eligible studies. Efficacy and safety results of PegIFNα-2a + RBV studies were combined in random- and fixed-effects inverse-variance weighted meta-analyses of proportions using the Freeman-Tukey double arcsin transformation method, and compared with the results of study C212.ResultsThe literature search revealed a total of 2392 records, with 206 articles selected for full-text review. Finally, 11 relevant articles reporting on 12 relevant study groups were included. Results on sustained virologic response 24 weeks after end of treatment (SVR24) were available from all 12 study groups. Pooled SVR24 for PegIFNα-2a + RBV from the random-effects meta-analysis was 28.2 % (95 % CI 23.8 % to 32.9 %). The comparison between study C212 (SVR24 = 72.6 %; 95 % CI 63.1 % to 80.9 %) revealed substantial superiority of simeprevir + PegIFNα-2a + RBV compared to PegIFNα-2a + RBV alone, with an absolute risk difference of 45 % (95 % CI 34 to 55). This finding was robust in a sensitivity analysis that only included historical studies with a planned treatment duration of at least 48 weeks and the same RBV dose as in study C212. No increases in the frequency of important adverse event categories including anemia were identified, but these analyses were limited by the low number of studies.ConclusionThis historical comparison provides first systematic evidence for the superiority of simeprevir + PegIFNα-2a + RBV compared to PegIFNα-2a + RBV in patients with HCV-1 / HIV coinfection. Given the limitations of the historical comparison for safety endpoints, additional data on the comparative safety of simeprevir in patients with HCV-1 / HIV coinfection would be desirable.Trial registrationIdentifier for study TMC435-TiDP16-C212 (ClinicalTrials.gov): NCT01479868.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-015-1311-3) contains supplementary material, which is available to authorized users.