M cell maturation and cDC activation determine the onset of adaptive immune priming in the neonatal Peyer's patch.

Early-life immune development is critical to long-term host health. However, the mechanisms that determine the pace of postnatal immune maturation are not fully resolved. Here, we analyzed mononuclear phagocytes (MNPs) in small intestinal Peyer's patches (PPs), the primary inductive site of intestinal immunity. Conventional type 1 and 2 dendritic cells (cDC1 and cDC2) and RORgt+ antigen-presenting cells (RORgt+ APC) exhibited significant age-dependent changes in subset composition, tissue distribution, and reduced cell maturation, subsequently resulting in a lack in CD4+ T cell priming during the postnatal period. Microbial cues contributed but could not fully explain the discrepancies in MNP maturation. Type I interferon (IFN) accelerated MNP maturation but IFN signaling did not represent the physiological stimulus. Instead, follicle-associated epithelium (FAE) M cell differentiation was required and sufficient to drive postweaning PP MNP maturation. Together, our results highlight the role of FAE M cell differentiation and MNP maturation in postnatal immune development.

Staphylococcus aureus Activates the Aryl Hydrocarbon Receptor in Human Keratinocytes.

Staphylococcus aureus is an important pathogen causing various infections, including - as most frequently isolated bacterium - cutaneous infections. Keratinocytes as the first barrier cells of the skin respond to S. aureus by the release of defense molecules such as cytokines and antimicrobial peptides. Although several pattern recognition receptors expressed in keratinocytes such as Toll-like and NOD-like receptors have been reported to detect the presence of S. aureus, the mechanisms underlying the interplay between S. aureus and keratinocytes are still emerging. Here, we report that S. aureus induced gene expression of CYP1A1 and CYP1B1, responsive genes of the aryl hydrocarbon receptor (AhR). AhR activation by S. aureus was further confirmed by AhR gene reporter assays. AhR activation was mediated by factor(s) <2 kDa secreted by S. aureus. Whole transcriptome analyses and real-time PCR analyses identified IL-24, IL-6, and IL-1beta as cytokines induced in an AhR-dependent manner in S. aureus-treated keratinocytes. AhR inhibition in a 3D organotypic skin equivalent confirmed the crucial role of the AhR in mediating the induction of IL-24, IL-6, and IL-1beta upon stimulation with living S. aureus. Taken together, we further highlight the important role of the AhR in cutaneous innate defense and identified the AhR as a novel receptor mediating the sensing of the important skin pathogen S. aureus in keratinocytes.

Evaluation of Integrated HPV DNA as Individualized Biomarkers for the Detection of Recurrent CIN2/3 during Post-Treatment Surveillance.

PURPOSE: Post-treatment follow-up in women with cervical pre-cancers (CIN3) is mandatory due to relapse in up to 10% of patients. Standard follow-up based on hrHPV-DNA/cytology co-testing has high sensitivity but limited specificity. The aim of our prospective, multicenter, observational study was to test the hypothesis that an individualized viral-cellular-junction test (vcj-PCR) combined with cytology has a lower false positive rate for the prediction of recurrence compared to standard co-testing. METHODS: Pre-surgical cervical swabs served for the identification of HPV16/18 DNA integration sites by next-generation-sequencing (NGS). Samples taken at 6, 12 and 24 months post-surgery were evaluated by cytology, hrHPV-DNA and the patients' individual HPV-integration sites (vcj-PCR on the basis of NGS). RESULTS: Integration sites were detected in 48 of 445 patients (10.8%), 39 of them had valid follow-up data. The false positive rate was 18.2% (95% CI 8.6-34.4%) for standard hrHPV/cytology at six months compared to 12.1% (95% CI 4.8-27.3%) for vcj-PCR/cytology, respectively (McNemar p = 0.50). Six patients developed recurrences (1 CIN2, 5 CIN3) during follow-up. Standard co-testing detected all, whereas vcj-PCR/cytology detected only five patients with recurrences. Data of 269 patients without evidence of HPV16/18 integration were subject to post-hoc analyses. Standard co-testing revealed a false positive rate of 15.7% (95% CI 11.7-20.7%) and predicted ten of fourteen recurrences at six months. CONCLUSIONS: Although highly specific on its own vcj-PCR could not detect all recurrent CIN2/3. Possible reasons for this unexpected result may be multifocal lesions, intratumoral heterogeneity with respect to HPV integration and/or incident CIN.

Natural C. elegans Microbiota Protects against Infection via Production of a Cyclic Lipopeptide of the Viscosin Group.

Caenorhabditis elegans is associated in nature with a species-rich, distinct microbiota, which was characterized only recently [1]. Thus, our understanding of the relevance of the microbiota for nematode fitness is still at its infancy. One major benefit that the intestinal microbiota can provide to its host is protection against pathogen infection [2]. However, the specific strains conferring the protection and the underlying mechanisms of microbiota-mediated protection are often unclear [3]. Here, we identify natural C. elegans microbiota isolates that increase C. elegans resistance to pathogen infection. We show that isolates of the Pseudomonas fluorescens subgroup provide paramount protection from infection with the natural pathogen Bacillus thuringiensis through distinct mechanisms. We found that the P. lurida isolates MYb11 and MYb12 (members of the P. fluorescens subgroup) protect C. elegans against B. thuringiensis infection by directly inhibiting growth of the pathogen both in vitro and in vivo. Using genomic and biochemical analyses, we further demonstrate that MYb11 and MYb12 produce massetolide E, a cyclic lipopeptide biosurfactant of the viscosin group [4, 5], which is active against pathogenic B. thuringiensis. In contrast to MYb11 and MYb12, P. fluorescens MYb115-mediated protection involves increased resistance without inhibition of pathogen growth and most likely depends on indirect, host-mediated mechanisms. This work provides new insight into the functional significance of the C. elegans natural microbiota and expands our knowledge of bacteria-derived compounds that can influence pathogen colonization in the intestine of an animal.