Lactic acid bacteria (LAB) are gut symbionts that can be used as a model to understand the host-microbiota cross talk under unpredictable environmental conditions, such as wildlife ecosystems. The aim of this study was to determine whether viable LAB can be informative of the health status of wild boar populations. We monitored the genotype and phenotype of LAB based on markers that included safety and phylogenetic origin, antibacterial activity, and immunomodulatory properties. A LAB profile dominated by lactobacilli appears to stimulate protective immune responses and relates to strains widely used as probiotics, resulting in a potentially healthy wildlife population, whereas microbiota overpopulated by enterococci was observed in a hostile environment. These enterococci were closely related to pathogenic strains that have developed mechanisms to evade innate immune systems, posing a potential risk for host health. Furthermore, our LAB isolates displayed antibacterial properties in a species-dependent manner. Nearly all of them were able to inhibit bacterial pathogens, raising the possibility of using them as an a la carte antibiotic alternative in the unexplored field of wildlife disease mitigation. Our study highlights that microbiological characterization of LAB is a useful indicator of wildlife health status and the ecological origin from which they derive. IMPORTANCE The wildlife symbiotic microbiota is an important component for the greater diversity and functionality of their bacterial populations, influencing host health and adaptability to its ecosystem. Although many microbes are partly responsible for the development of multiple physiological processes, only certain bacterial groups, such as lactic acid bacteria (LAB), have the capacity to overpopulate the gut, promoting health (or disease) when specific genetic and environmental conditions are present. LAB have been exploited in many ways due to their probiotic properties, particularly lactobacilli; however, their relationship with wildlife gut-associated microbiota hosts remains to be elucidated. On the other hand, it is unclear whether LAB such as enterococci, which have been associated with detrimental health effects, could lead to disease. These important questions have not been properly considered in the field of wildlife and, therefore, should be clearly addressed.

Summary Mononuclear phagocytes defend tissues, present antigens, and mediate recovery and healing. To date, we lack a marker to unify mononuclear phagocytes in humans or that informs us about their origin. Here, we reassess mononuclear phagocyte ontogeny in human blood through the lineage receptor CSF1R, in the steady state and in COVID-19. We define CSF1R as the first sensitive and reproducible pan-phagocyte lineage marker, to identify and enumerate all conventional monocytes, and the myeloid dendritic cells. In the steady state, CSF1R is sufficient for sorting and immuno-magnetic isolation. In pathology, changes in CSF1R are more sensitive than CD14 and CD16. In COVID-19, a significant drop in membrane CSF1R is useful for stratifying patients, beyond the power of cell categories published thus far, which fail to capture COVID-19 specific events. Importantly, CSF1R defines cells which are neither conventional monocytes nor DCs, which are missed in published analysis. CSF1R decrease can be linked ex vivo to high CSF1 levels. Blood assessment of CSF1R+ cells opens a developmental window to the Mononuclear Phagocyte System in transit from bone marrow to tissues, supports isolation and phenotypic characterisation, identifies novel cell types, and singles out CSF1R inhibition as therapeutic target in COVID-19 and other diseases.

Mononuclear phagocytes are a widely distributed family of cells contributing to innate and adaptive immunity. Circulating monocytes and tissue macrophages participate in all stages of SARS COVID-19. They contribute to comorbidities predisposing to clinical infection, virus resistance and dissemination, and to host factors that determine disease severity, recovery and sequelae. Assays are available to detect viral infection and antibody responses, but no adequate tests have been developed to measure the activation level of monocytes and tissue macrophages, and the risk of progression to a fatal hyperinflammatory syndrome. Blood monocytes provide a window on the systemic immune response, from production to tissue recruitment, reflecting the impact of infection on the host. Ready availability of blood makes it possible to monitor severity and the risk of potentially lethal complications, by developing tests to assess the status of monocyte activation and its potential for further inflammatory dysregulation after recruitment to tissues and during recovery.

[This corrects the article DOI: 10.3389/fmicb.2020.01394.].

Type-I interferon (IFN-I) cytokines are produced by innate immune cells in response to microbial infections, cancer and autoimmune diseases. These cytokines trigger protective responses in neighbouring cells through the activation of IFN-I stimulated genes. One of the most predominant pathways associated with IFN-I production is mediated by the cytosolic sensors STING and MAVS, intracellular adaptors that become activated in the presence of microbial nucleic acids in the cytoplasm, leading to IFN-I production via TANK-binding kinase (TBK)-1 and IFN regulatory factors. However, the role of these sensors in responses induced by beneficial microbes has been relatively unexplored. Here we have screened 12 representative strains of lactic acid bacteria (LAB), a group of beneficial microbes found in fermented food and probiotic formulations worldwide, for their ability to trigger IFN-I responses. Two isolates ( Lactobacillus plantarum and Pediococcus pentosaceus ) induced an IFN-I production that was significantly higher that the rest, both in macrophage cell lines and human primary macrophages. This response correlated with stronger interaction with macrophages and was susceptible to phagocytosis inhibitors, suggesting bacterial internalisation. Accordingly, macrophages deficient for STING and, to a lesser extent, MAVS failed to respond to the two LAB, showing reduced TBK-1 phosphorylation and IFN-I activation. Furthermore, LAB-induced IFN-I was biologically active and resulted in expression of interferon stimulated genes, which was also STING- and MAVS-dependent. Our findings demonstrate a major role for STING in the production of IFN-I by beneficial bacteria and the existence of bacteria-specific immune signatures, which can be exploited to modulate protective responses in the host.

Mycobacterium tuberculosis (Mtb) infects macrophages and macrophage-derived foam cells, a hallmark of granulomata in tuberculous lesions. We analyzed the effects of lipid accumulation in human primary macrophages and quantified strong triglyceride and phospholipid remodeling which depended on the dietary fatty acid used for the assay. The enrichment of >70% in triglyceride and phospholipids can alter cell membrane properties, signaling and phagocytosis in macrophages. In conventional macrophage cultures, cells are heterogeneous, small or large macrophages. In foam cells, a third population of 30% of cells with increased granularity can be detected. We found that foam cell formation is heterogenous and that lipid accumulation and foam cell formation reduces the phagocytosis of Mtb. Under the conditions tested, cell death was highly prevalent in macrophages, whereas foam cells were largely protected from this effect. Foam cells also supported slower Mtb replication, yet this had no discernible impact on the intracellular efficacy of four different antitubercular drugs. Foam cell formation had a significant impact in the inflammatory potential of the cells. TNF-α, IL-1β, and prototypical chemokines were increased. The ratio of inflammatory IL-1β, TNF-α, and IL-6 vs. anti-inflammatory IL-10 was significantly higher in response to Mtb vs. LPS, and was increased in foam cells compared to macrophages, suggestive of increased pro-inflammatory properties. Cytokine production correlated with NF-κB activation in our models. We conclude that foam cell formation reduces the host cell avidity for, and phagocytosis of, Mtb while protecting the cells from death. This protective effect is associated with enhanced inflammatory potential of foam cells and restricted intracellular growth of Mtb.

Background: Wildlife poses a significant burden for the complete eradication of bovine tuberculosis (bTB). In particular, wild boar (Sus scrofa) is one of the most important reservoirs of Mycobacterium bovis, the causal agent of bTB. Wild boar can display from mild TB lesions, usually found in head lymph nodes, to generalized TB lesions distributed in different anatomical regions; but rarely clinical signs, which complicates the diagnosis of Mycobacterium bovis infection and bTB control. Among the possibilities for this variability in lesion distribution is the influence of the host-beneficial commensal-primed immune barrier. In this respect, beneficial microbes may delay bTB dissemination as a consequence of an antagonistic competition for nutrients and phagocytes. In order to explore this possibility, we have tested whether typical commensals such as lactobacilli have the capacity to reduce the survival rate of the surrogate M. bovis strain Bacillus Calmette-Guerin (BCG); and to modulate its phagocyte intake. Results: Three Lactobacillus species, L. casei, L. plantarum, and L. salivarius, isolated from wild boar feces displayed a pH-dependent inhibitory activity against BCG and influenced its intake by porcine blood phagocytes in a species-dependent manner. All lactobacilli showed a very significant bactericidal effect against BCG at low pH, but only isolates of L. plantarum and L. casei displayed such antimycobacterial activity at neutral pH. The genomes of these isolates revealed the presence of two-peptide bacteriocins whose precursor genes up-regulate in the presence of BCG cells. Furthermore, L. plantarum reduced significantly the BCG phagocytic intake, whereas L. casei had the opposite effect. L. salivarius had no significant influence on the phagocytic response to BCG. Conclusions: Our in vitro results show that lactobacilli isolated from wild boar antagonize BCG as a consequence of their antimycobacterial activity and a competitive phagocytic response. These findings suggest that commensal bacteria could play a beneficial role in influencing the outcome of bTB dissemination. Further work with lactobacilli as a potential competitive pressure to control bTB will need to take into account the complex nature of the commensal microbiome, the specific immunity of the wild boar and the in vivo infection context with pathogenic strains of M. bovis.