Human metapneumovirus respiratory infection affects both innate and adaptive intestinal immunity

Introduction

Respiratory infections are one of the leading causes of morbidity and mortality worldwide, mainly in children, immunocompromised people, and the elderly. Several respiratory viruses can induce intestinal inflammation and alterations in intestinal microbiota composition. Human metapneumovirus (HMPV) is one of the major respiratory viruses contributing to infant mortality in children under 5 years of age worldwide, and the effect of this infection at the gut level has not been studied.

Methods

Here, we evaluated the distal effects of HMPV infection on intestinal microbiota and inflammation in a murine model, analyzing several post-infection times (days 1, 3, and 5). Six to eight-week-old C57BL/6 mice were infected intranasally with HMPV, and mice inoculated with a non-infectious supernatant (Mock) were used as a control group.

Results

We did not detect HMPV viral load in the intestine, but we observed significant changes in the transcription of IFN-γ in the colon, analyzed by qPCR, at day 1 post-infection as compared to the control group. Furthermore, we analyzed the frequencies of different innate and adaptive immune cells in the colonic lamina propria, using flow cytometry. The frequency of monocyte populations was altered in the colon of HMPV -infected mice at days 1 and 3, with no significant difference from control mice at day 5 post-infection. Moreover, colonic CD8+ T cells and memory precursor effector CD8+ T cells were significantly increased in HMPV-infected mice at day 5, suggesting that HMPV may also alter intestinal adaptive immunity. Additionally, we did not find alterations in antimicrobial peptide expression, the frequency of colonic IgA+ plasma cells, and levels of fecal IgA. Some minor alterations in the fecal microbiota composition of HMPV -infected mice were detected using 16s rRNA sequencing. However, no significant differences were found in β-diversity and relative abundance at the genus level.

Discussion

To our knowledge, this is the first report describing the alterations in intestinal immunity following respiratory infection with HMPV infection. These effects do not seem to be mediated by direct viral infection in the intestinal tract. Our results indicate that HMPV can affect colonic innate and adaptive immunity but does not significantly alter the microbiota composition, and further research is required to understand the mechanisms inducing these distal effects in the intestine.

SEN1990 is a predicted winged helix-turn-helix protein involved in the pathogenicity of Salmonella enterica serovar Enteritidis and the expression of the gene oafB in the SPI-17

Excisable genomic islands (EGIs) are horizontally acquired genetic elements that harbor an array of genes with diverse functions. ROD21 is an EGI found integrated in the chromosome of Salmonella enterica serovar Enteritidis (Salmonella ser. Enteritidis). While this island is known to be involved in the capacity of Salmonella ser. Enteritidis to cross the epithelial barrier and colonize sterile organs, the role of most ROD21 genes remains unknown, and thus, the identification of their function is fundamental to understanding the impact of this EGI on bacterium pathogenicity. Therefore, in this study, we used a bioinformatical approach to evaluate the function of ROD21-encoded genes and delve into the characterization of SEN1990, a gene encoding a putative DNA-binding protein. We characterized the predicted structure of SEN1990, finding that this protein contains a three-stranded winged helix-turn-helix (wHTH) DNA-binding domain. Additionally, we identified homologs of SEN1990 among other members of the EARL EGIs. Furthermore, we deleted SEN1990 in Salmonella ser. Enteritidis, finding no differences in the replication or maintenance of the excised ROD21, contrary to what the previous Refseq annotation of the protein suggests. High-throughput RNA sequencing was carried out to evaluate the effect of the absence of SEN1990 on the bacterium's global transcription. We found a downregulated expression of oafB, an SPI-17-encoded acetyltransferase involved in O-antigen modification, which was restored when the deletion mutant was complemented ectopically. Additionally, we found that strains lacking SEN1990 had a reduced capacity to colonize sterile organs in mice. Our findings suggest that SEN1990 encodes a wHTH domain-containing protein that modulates the transcription of oafB from the SPI-17, implying a crosstalk between these pathogenicity islands and a possible new role of ROD21 in the pathogenesis of Salmonella ser. Enteritidis.

Novel evidence on sepsis-inducing pathogens: from laboratory to bedside

Sepsis is a life-threatening condition and a significant cause of preventable morbidity and mortality globally. Among the leading causative agents of sepsis are bacterial pathogens Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes, along with fungal pathogens of the Candida species. Here, we focus on evidence from human studies but also include in vitro and in vivo cellular and molecular evidence, exploring how bacterial and fungal pathogens are associated with bloodstream infection and sepsis. This review presents a narrative update on pathogen epidemiology, virulence factors, host factors of susceptibility, mechanisms of immunomodulation, current therapies, antibiotic resistance, and opportunities for diagnosis, prognosis, and therapeutics, through the perspective of bloodstream infection and sepsis. A list of curated novel host and pathogen factors, diagnostic and prognostic markers, and potential therapeutical targets to tackle sepsis from the research laboratory is presented. Further, we discuss the complex nature of sepsis depending on the sepsis-inducing pathogen and host susceptibility, the more common strains associated with severe pathology and how these aspects may impact in the management of the clinical presentation of sepsis.