Novel CD11b+Gr-1+Sca-1+ myeloid cells drive mortality in bacterial infection

Cell type-specific modulation of metabolic, immune-regulatory, and anti-microbial pathways by CD101

T lymphocytes and myeloid cells express the immunoglobulin-like glycoprotein cluster of differentiation (CD)101, notably in the gut. Here, we investigated the cell-specific functions of CD101 during dextran sulfate sodium (DSS)-induced colitis and Salmonella enterica Typhimurium infection. Similar to conventional CD101-/- mice, animals with a regulatory T cell-specific Cd101 deletion developed more severe intestinal pathology than littermate controls in both models. While the accumulation of T helper 1 cytokines in a CD101-deficient environment entertained DSS-induced colitis, it impeded the replication of Salmonella as revealed by studying CD101-/- x interferon-g-/- mice. Moreover, CD101-expressing neutrophils were capable to restrain Salmonella infection in vitro and in vivo. Both cell-intrinsic and -extrinsic mechanisms of CD101 contributed to the control of bacterial growth and spreading. The CD101-dependent containment of Salmonella infection required the expression of Irg-1 and Nox2 and the production of itaconate and reactive oxygen species. The level of intestinal microbial antigens in the sera of inflammatory bowel disease patients correlated inversely with the expression of CD101 on myeloid cells, which is in line with the suppression of CD101 seen in mice following DSS application or Salmonella infection. Thus, depending on the experimental or clinical setting, CD101 helps to limit inflammatory insults or bacterial infections due to cell type-specific modulation of metabolic, immune-regulatory, and anti-microbial pathways.

CD200Rhigh neutrophils with dysfunctional autophagy establish systemic immunosuppression by increasing regulatory T cells

Distinct neutrophil populations arise during certain pathological conditions. The generation of dysfunctional neutrophils during sepsis and their contribution to septicemia-related systemic immune suppression remain unclear. In this study, using an experimental sepsis model that features immunosuppression, we identified a novel population of pathogenic CD200Rhigh neutrophils that are generated during the initial stages of sepsis and contribute to systemic immune suppression by enhancing regulatory T (Treg) cells. Compared to their CD200Rlow counterparts, sepsis-generated CD200Rhigh neutrophils exhibit impaired autophagy and dysfunction, with reduced chemotactic migration, superoxide anion production, and TNF-α production. Increased soluble CD200 blocks autophagy and neutrophil maturation in the bone marrow during experimental sepsis, and recombinant CD200 treatment in vitro can induce neutrophil dysfunction similar to that observed in CD200Rhigh neutrophils. The administration of an α-CD200R antibody effectively reversed neutrophil dysfunction by enhancing autophagy and protecting against a secondary infection challenge, leading to increased survival. Transcriptome analysis revealed that CD200Rhigh neutrophils expressed high levels of Igf1, which elicits the generation of Treg cells, while the administration of an α-CD200R antibody inhibited Treg cell generation in a secondary infection model. Taken together, our findings revealed a novel CD200Rhigh neutrophil population that mediates the pathogenesis of sepsis-induced systemic immunosuppression by generating Treg cells.

A double-edged sword: interactions of CX3CL1/CX3CR1 and gut microbiota in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic chronic disease initiated by an abnormal immune response to self and can affect multiple organs. SLE is characterized by the production of autoantibodies and the deposition of immune complexes. In regard to the clinical observations assessed by rheumatologists, several chemokines and cytokines also contribute to disease progression. One such chemokine and adhesion molecule is CX3CL1 (otherwise known as fractalkine). CX3CL1 is involved in cell trafficking and inflammation through recognition by its receptor, CX3CR1. The CX3CL1 protein consists of a chemokine domain and a mucin-like stalk that allows it to function both as a chemoattractant and as an adhesion molecule. In inflammation and specifically lupus, the literature displays contradictory evidence for the functions of CX3CL1/CX3CR1 interactions. In addition, the gut microbiota has been shown to play an important role in the pathogenesis of SLE. This review highlights current studies that illustrate the interactions of the gut microbiota and CX3CR1 in SLE.

Neutrophil phenotypes implicated in the pathophysiology of post-traumatic sepsis

Background

The disruption of immune homeostasis after trauma is a major cause of post-traumatic organ dysfunction and/or sepsis. Recently, a variety of neutrophil phenotypes with distinct functions have been identified and suggested as involved in various clinical conditions. The association between neutrophil phenotypes and post-traumatic immunodeficiency has also been reported, yet the specific neutrophil phenotypes and their functional significance in post-traumatic sepsis have not been fully clarified. Therefore, we sought to investigate neutrophil phenotypic changes in a murine model, as these may hold prognostic value in post-traumatic sepsis.

Materials and methods

Third-degree burns affecting 25% of the body surface area were used to establish trauma model, and sepsis was induced 24 h later through cecal ligation and puncture (CLP). The Burn/CLP post-traumatic sepsis model and the Sham/CLP control model were established to assess the immunological status after trauma. Histopathological evaluation was performed on the spleen, liver, kidneys, and lung tissues. Immunological evaluation included the assessment of neutrophil markers using mass cytometry as well as cytokine measurements in serum and ascitic fluid through multiplex analysis using LUMINEX®.

Results

The Burn/CLP group had a lower survival rate than the Sham/CLP group. Histopathological examination revealed an impaired immune response and more advanced organ damage in the Burn/CLP group. Furthermore, the Burn/CLP group exhibited higher levels of transforming growth factor-beta 1 in the blood and generally lower levels of cytokines than the Sham/CLP group. CD11b, which is involved in neutrophil adhesion and migration, was highly expressed on neutrophils in the Burn/CLP group. The expression of CD172a, which is related to the inhibition of phagocytosis, was also upregulated on neutrophils in the Burn/CLP group. The expression of sialic acid-binding lg-like lectin F and CD68 also differed between the two groups.

Conclusion

Different neutrophil phenotypes were observed between Burn/CLP and Sham/CLP groups, suggesting that neutrophils are implicated in the immune imbalance following trauma. However, further studies are needed to prove the causal relationships between neutrophil phenotypes and outcomes, including survival rate and organ dysfunction.

Single-cell transcriptomics reveals distinct cell response between acute and chronic pulmonary infection of Pseudomonas aeruginosa

Knowledge of the changes in the immune microenvironment during pulmonary bacterial acute and chronic infections is limited. The dissection of immune system may provide a basis for effective therapeutic strategies against bacterial infection. Here, we describe a single immune cell atlas of mouse lungs after acute and chronic Pseudomonas aeruginosa infection using single-cell transcriptomics, multiplex immunohistochemistry, and flow cytometry. Our single-cell transcriptomic analysis revealed large-scale comprehensive changes in immune cell composition and high variation in cell-cell interactions after acute and chronic P. aeruginosa infection. Bacterial infection reprograms the genetic architecture of immune cell populations. We identified specific immune cell types, including Cxcl2⁺ B cells and interstitial macrophages, in response to acute and chronic infection, such as their proportions, distribution, and functional status. Importantly, the patterns of immune cell response are drastically different between acute and chronic infection models. The distinct molecular signatures highlight the importance of the highly dynamic cell-cell interaction process in different pathological conditions, which has not been completely revealed previously. These findings provide a comprehensive and unbiased immune cellular landscape for respiratory pathogenesis in mice, enabling further understanding of immunologic mechanisms in infection and inflammatory diseases.

Effectiveness of Bone Marrow-Derived Platelet-Rich Fibrin on Rotator Cuff Healing in a Rabbit Degenerative Model

BACKGROUND

Platelet-rich fibrin (PRF) is a second-generation platelet concentrate. Although peripheral blood-derived PRF (P-PRF) is commonly applied in biological augmentation, there is no report about the therapeutic effect of bone marrow-derived PRF (BM-PRF) for degenerative rotator cuff tears (RCTs).

PURPOSE/HYPOTHESIS

To examine the effects of platelet-rich plasma (PRP), P-PRF, and BM-PRF during rotator cuff repair (RCR) in degenerative RCTs in rabbits. We hypothesized that BM-PRF would accelerate the bone-tendon healing after RCR.

STUDY DESIGN

Controlled laboratory study.

METHODS

Degenerative RCT models were created 2 weeks before beginning the study, and 68 juvenile rabbits were divided into 4 groups: the control, PRP, P-PRF, and BM-PRF groups. RCR without augmentation was done in the control group. PRP was prepared by centrifuging peripheral blood twice using a plastic tube. P-PRF and BM-PRF were prepared by centrifuging peripheral blood and bone marrow, respectively, using a glass tube. Rabbits from PRP, P-PRF, and BM-PRF groups were administered the augmentation in a similar fashion for RCR, between the rotator cuff and the footprint of the humerus. At 4, 8, and 12 weeks, rabbits were euthanized and histologically assessed using hematoxylin and eosin staining, Alcian blue staining, and immunohistochemical staining for type I and III collagen. The sections were also evaluated with immunofluorescence staining of vascular endothelial growth factor (VEGF) at 4 weeks.

RESULTS

The continuity was significantly better in the BM-PRF group at 4 weeks (P < .05). Immunofluorescence staining demonstrated that VEGF-positive stained cells were significantly greater in the BM-PRF group than in the control group (P < .01). The modified tendon maturing score was significantly greater in the BM-PRF group than in the control and PRP groups at 12 weeks (P < .05). There was no significant difference in the modified tendon maturing score of the P-PRF group compared with the control group.

CONCLUSION

The rabbit model of degenerative RCTs demonstrated that RCR combined with BM-PRF enhanced tendon-bone continuity and increased the VEGF-positive cells at 4 weeks and obtained preferable tendon-bone maturation at 12 weeks.

CLINICAL RELEVANCE

RCR augmented with BM-PRF has the potential to improve clinical outcomes for RCTs.

Gr1+ myeloid-derived suppressor cells participate in the regulation of lung-gut axis during mouse emphysema model

Background: Chronic obstructive pulmonary disease (COPD) is often accompanied by intestinal symptoms. Myeloid-derived suppressor cells (MDSCs) possess immunosuppressive ability in cancer, chronic inflammation, and infection. The aim of this study was to verify the distribution of MDSCs in emphysema mouse model and participation in lung–gut cross-talk.

Methods: Adult male C57BL/6 mice were exposed to cigarette smoke (CS) for 6 months or injected with porcine pancreas elastase to establish emphysema models. Flow cytometry and immunohistochemistry analysis revealed the distribution of MDSCs in tissues. The expression of inflammation and MDSCs-associated genes in the small intestine and colon were analyzed by real-time PCR.

Results: The small intestine and colon of CS-induced emphysematous mice displayed pathological changes, CD4⁺/CD8⁺ T cells imbalance, and increased neutrophils, monocytes, and macrophages infiltration. A significant expansion of MDSCs could be seen in CS-affected respiratory and gastrointestinal tract. Importantly, higher expression of MDSCs-related effector molecules inducible nitric oxide synthase (INOS), NADPH oxidase 2 (NOX2), and arginase 1 (ARG-1) suggested the immunosuppressive effect of migrated MDSCs (P<0.05).

Conclusion: These data provide evidence for lung–gut axis in emphysema model and the participants of MDSCs.

IM156, a new AMPK activator, protects against polymicrobial sepsis

IM156, a novel biguanide with higher potency of AMP‐activated protein kinase activation than metformin, has inhibitory activity against angiogenesis and cancer. In this study, we investigated effects of IM156 against polymicrobial sepsis. Administration of IM156 significantly increased survival rate against caecal ligation and puncture (CLP)‐induced sepsis. Mechanistically, IM156 markedly reduced viable bacterial burden in the peritoneal fluid and peripheral blood and attenuated organ damage in a CLP‐induced sepsis model. IM156 also inhibited the apoptosis of splenocytes and the production of inflammatory cytokines including IL‐1β, IL‐6 and IL‐10 in CLP mice. Moreover, IM156 strongly inhibited the generation of reactive oxygen species and subsequent formation of neutrophil extracellular traps in response to lipopolysaccharide in neutrophils. Taken together, these results show that IM156 can inhibit inflammatory response and protect against polymicrobial sepsis, suggesting that IM156 might be a new treatment for sepsis.

Persistent Cutaneous Leishmania major Infection Promotes Infection-Adapted Myelopoiesis

Hematopoietic stem/progenitor cells (HSPC) are responsible for the generation of most immune cells throughout the lifespan of the organism. Inflammation can activate bone marrow HSPCs, leading to enhanced myelopoiesis to replace cells, such as neutrophils, which are attracted to inflamed tissues. We have previously shown that HSPC activation promotes parasite persistence and expansion in experimental visceral leishmaniasis through the increased production of permissive monocytes. However, it is not clear if the presence of the parasite in the bone marrow was required for infection-adapted myelopoiesis. We therefore hypothesized that persistent forms of Leishmania major (cutaneous leishmaniasis) could also activate HSPCs and myeloid precursors in the C57Bl/6 mouse model of intradermal infection in the ear. The accrued influx of myeloid cells to the lesion site corresponded to an increase in myeloid-biased HSPCs in the bone marrow and spleen in mice infected with a persistent strain of L. major, together with an increase in monocytes and monocyte-derived myeloid cells in the spleen. Analysis of the bone marrow cytokine and chemokine environment revealed an attenuated type I and type II interferon response in the mice infected with the persistent strain compared to the self-healing strain, while both strains induced a rapid upregulation of myelopoietic cytokines, such as IL-1β and GM-CSF. These results demonstrate that an active infection in the bone marrow is not necessary for the induction of infection-adapted myelopoiesis, and underline the importance of considering alterations to the bone marrow output when analyzing in vivo host-pathogen interactions.

Single cell analysis of M. tuberculosis phenotype and macrophage lineages in the infected lung

In this study, we detail a novel approach that combines bacterial fitness fluorescent reporter strains with scRNA-seq to simultaneously acquire the host transcriptome, surface marker expression, and bacterial phenotype for each infected cell. This approach facilitates the dissection of the functional heterogeneity of M. tuberculosis-infected alveolar (AMs) and interstitial macrophages (IMs) in vivo. We identify clusters of pro-inflammatory AMs associated with stressed bacteria, in addition to three different populations of IMs with heterogeneous bacterial phenotypes. Finally, we show that the main macrophage populations in the lung are epigenetically constrained in their response to infection, while inter-species comparison reveals that most AMs subsets are conserved between mice and humans. This conceptual approach is readily transferable to other infectious disease agents with the potential for an increased understanding of the roles that different host cell populations play during the course of an infection.

The immune modulatory effects of mitochondrial transplantation on cecal slurry model in rat

Background

Sepsis has a high mortality rate, but no specific drug has been proven effective, prompting the development of new drugs. Immunologically, sepsis can involve hyperinflammation, immune paralysis, or both, which might pose challenges during drug development. Recently, mitochondrial transplantation has emerged as a treatment modality for various diseases involving mitochondrial dysfunction, but it has never been tested for sepsis.

Methods

We isolated mitochondria from L6 muscle cells and umbilical cord mesenchymal stem cells and tested the quality of the isolated mitochondria. We conducted both in vivo and in vitro sepsis studies. We investigated the effects of intravenous mitochondrial transplantation on cecal slurry model in rats in terms of survival rate, bacterial clearance rate, and the immune response. Furthermore, we observed the effects of mitochondrial transplantation on the immune reaction regarding both hyperinflammation and immune paralysis. To do this, we studied early- and late-phase cytokine production in spleens from cecal slurry model in rats. We also used a lipopolysaccharide (LPS)-stimulated human PBMC monocyte model to confirm the immunological effects of mitochondrial transplantation. Apoptosis and the intrinsic apoptotic pathway were investigated in septic spleens.

Results

Mitochondrial transplantation improved survival and bacterial clearance. It also mitigated mitochondrial dysfunction and apoptosis in septic spleens and attenuated both hyperinflammation and immune paralysis in the spleens of cecal slurry model in rats. This effect was confirmed with an LPS-stimulated human PBMC study.

Conclusions

In rat polymicrobial cecal slurry model, the outcome is improved by mitochondrial transplantation, which might have an immunomodulatory effect.

Novel Sca-1+ macrophages modulate the pathogenic progress of endotoxemia

Macrophages are important innate immune cells that play crucial roles in inflammatory responses. Accumulating evidence has demonstrated macrophage heterogeneity based on biomarkers, functions, and localization. Here, we report a novel stem cell antigen-1 (Sca-1)-positive macrophage population induced in the pathological conditions caused by lipopolysaccharide (LPS). Sca-1 is only upregulated in macrophages but not in monocytes and neutrophils upon LPS injection. Sca-1⁺ macrophages develop from resident peritoneal macrophages. LPS-induced Sca-1⁺ macrophage generation was partly blocked by anti-IFN-γ antibody, suggesting a role of IFN-γ in the process. LPS-stimulated production of IL-6, TNF-α, and CCL2 is significantly lower in Sca-1⁺ macrophages compared to their counterpart Sca-1^- macrophages. Depletion of Sca-1⁺ macrophages using anti-Sca-1 antibody significantly increased survival rate and reduced lung and kidney damage in an LPS-induced sepsis model. Taken together, we discovered a novel population of Sca-1⁺ macrophages in LPS-induced septic conditions.