NLRP6 negatively regulates innate immunity and host defence against bacterial pathogens

Members of the intracellular nucleotide-binding and oligomerization domain (NOD)-like receptor (NLR) family contribute to immune responses through activation of nuclear factor-kappa B (NF-kappa B), type I interferon and inflammasome signalling(1). Mice lacking the NLR family member NLRP6 were recently shown to be susceptible to colitis and colorectal tumorigenesis(2-4), but the role of NLRP6 in microbial infections and the nature of the inflammatory signalling pathways regulated by NLRP6 remain unclear. Here we show that Nlrp6-deficient mice are highly resistant to infection with the bacterial pathogens Listeria monocytogenes, Salmonella typhimurium and Escherichia coli. Infected Nlrp6-deficient mice had increased numbers of monocytes and neutrophils in circulation, and NLRP6 signalling in both haematopoietic and radioresistant cells contributed to increased susceptibility. Nlrp6 deficiency enhanced activation of mitogen-activated protein kinase (MAPK) and the canonical NF-kappa B pathway after Toll-like receptor ligation, but not cytosolic NOD1/2 ligation, in vitro. Consequently, infected Nlrp6-deficient cells produced increased levels of NF-kappa B-and MAPK-dependent cytokines and chemokines. Thus, our results reveal NLRP6 as a negative regulator of inflammatory signalling, and demonstrate a role for this NLR in impeding clearance of both Gram-positive and -negative bacterial pathogens

Rac1 Regulates the NLRP3 Inflammasome Which Mediates IL-1beta Production in Chlamydophila pneumoniae Infected Human Mononuclear Cells

Chlamydophila pneumoniae causes acute respiratory tract infections and has been associated with development of asthma and atherosclerosis. The production of IL-1β, a key mediator of acute and chronic inflammation, is regulated on a transcriptional level and additionally on a posttranslational level by inflammasomes. In the present study we show that C. pneumoniae-infected human mononuclear cells produce IL-1β protein depending on an inflammasome consisting of NLRP3, the adapter protein ASC and caspase-1. We further found that the small GTPase Rac1 is activated in C. pneumoniae-infected cells. Importantly, studies with specific inhibitors as well as siRNA show that Rac1 regulates inflammasome activation in C. pneumoniae-infected cells. In conclusion, C. pneumoniae infection of mononuclear cells stimulates IL-1β production dependent on a NLRP3 inflammasome-mediated processing of proIL-1β which is controlled by Rac1

Assessment of ambiguous base calls in HIV-1 pol population sequences as a biomarker to identify recent infections in HIV-1 incidence studies

An increase in the proportion of ambiguous base calls in HIV-1 pol population sequences during the course of infection has been demonstrated in different study populations, and sequence ambiguity thresholds to classify infections as recent or nonrecent have been suggested. The aim of our study was to evaluate sequence ambiguities as a candidate biomarker for use in an HIV-1 incidence assay using samples from antiretroviral treatment-naive seroconverters with known durations of infection (German HIV-1 Seroconverter Study). We used 2,203 HIV-1 pol population sequences derived from 1,334 seroconverters to assess the sequence ambiguity method (SAM). We then compared the serological incidence BED capture enzyme immunoassay (BED-CEIA) with the SAM for a subset of 723 samples from 495 seroconverters and evaluated a multianalyte algorithm that includes BED-CEIA results, SAM results, viral loads, and CD4 cell counts for 453 samples from 325 seroconverters. We observed a significant increase in the proportion of sequence ambiguities with the duration of infection. A sequence ambiguity threshold of 0.5% best identified recent infections with 76.7% accuracy. The mean duration of recency was determined to be 208 (95% confidence interval, 196 to 221) days. In the subset analysis, BED-CEIA achieved a significantly higher accuracy than the SAM (84.6 versus 75.5%, P < 0.001) and results were concordant for 64.2% (464/723) of the samples. Also, the multianalyte algorithm did not show better accuracy than the BED-CEIA (83.4 versus 84.3%, P = 0.786). In conclusion, the SAM and the multianalyte algorithm including SAM were inferior to the BED-CEIA, and the proportion of sequence ambiguities is therefore not a preferable biomarker for HIV-1 incidence testing

A recent human immunodeficiency virus outbreak among people who inject drugs in Munich, Germany, is associated with consumption of synthetic cathinones

Background: Needle and syringe sharing among people who inject drugs (PWID) can result in a rapid regional spread of a human immunodeficiency virus (HIV) variant. Such outbreaks have been identified recently in several countries and have raised public health attention because of an association with new psychoactive substances (NPS). Methods: Dried serum spots from approximately 60% of newly diagnosed HIV cases in Germany in 2013-2018 were received together with statutory notification data. Samples were sequenced in the pol-region, genotyped, and viral phylogenies were analyzed. For selected samples, the hepatitis C virus (HCV) status and the presence of NPS were determined. Results: An outbreak of closely related 27 subtype C infections with a core of 11 cases with almost identical sequences was identified using phylogenetic analyses. The first case of the outbreak was diagnosed in 2015, and the last one was in 2018. With exception of 3 infections, all were reported from Munich, the capital of the federal state of Bavaria. Of 26 analyzed outbreak members, 24 (92.3%) had a resolved or viremic HCV coinfection. In 8 of 18 (44%) cases, α-pyrrolidinopentiothiophenone and/or the related substance α-pyrrolidinoheptiophenone was identified. Conclusions: Despite harm reduction services in place, HIV outbreaks of considerable size can occur in PWID. The establishment of a real-time molecular surveillance is advised to rapidly identify outbreaks and target prevention measures

Single cell RNA-sequencing-based analysis of CD4(+) T-cell subset-specific susceptibility to transcriptional modulation by HIV-1 latency-reversing agents

Shock-and-kill is one of the conceptually most advanced strategy towards establishment of an HIV-1 cure. Treatment with latency-reversing agents (LRAs), including histone deacetylase inhibitors with chromatin-remodeling capabilities, combined with anti-retroviral therapy, reactivates HIV-1 transcription in vivo. However, LRA treatment fails to significantly reduce the HIV-1 reservoir in HIV-1-positive individuals, indicating that it is probably insufficient to eliminate latently infected cells. The global and T-cell subset-specific impact of individual LRAs on the transcriptome of CD4(+) T-cells, the main HIV-1 reservoir containing cell type in vivo, remains understudied. Here, using single cell RNA-sequencing, we characterize LRA treatment-induced alterations of CD4 (+) T-cell subset composition and of subpopulation-specific transcriptomes, using Vorinostat and Panobinostat as two prototypic HDAC inhibitors. Ex vivo exposure of CD4(+) T-cells from an aviremic HIV-1-positive individual to Panobinostat markedly reduced the percentage of T(REG)cells. Furthermore, it altered expression of a multitude of interferon-regulated genes, resulting in suppression of several well-characterized antiviral genes, and in enhancement of selected interferon-regulated genes with proviral activities. These changes were most pronounced in T(N), T(CM), T(TM) and T(EM), and less pronounced in T(REG). Exposure to Vorinostat resulted in a comparably mild change of cellular transcriptomic profile, regarding both the number of deregulated genes and their fold change of expression. Nevertheless, selected interferon-regulated genes exhibited a subset-specific expression profile upon Vorinostat treatment. Finally, some genes were deregulated by both treatments in a subset-specific manner. We conclude that treatment by both individual HDAC inhibitors induces an overall proviral milieu in CD4(+) T-cells subsets. While this proviral state might be favorable for efficient HIV-1 reactivation, we hypothesize that it may impede the instruction of activation of cellular and adaptive immunity required for effective killing of reactivated cells