Migration Of Phagocytes Research Articles

Differential requirement of formyl peptide receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. Here, we investigate the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed in a murine TB model utilizing hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion had no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1−/− mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased Mtb persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1−/− neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

The Level of Vitamin D in Patients with Susceptible Pulmonary Tuberculosis and Evaluation of its Influence on the Clinical Course of the Disease

Vitamin D insufficiency or deficiency is defined as a very common condition in the general population. On the one hand, vitamin D deficiency is associated with several adverse health conditions, on the other hand, vitamin D supplements are inexpensive and safe to use, which makes it an attractive therapeutic option for both doctors and patients, especially for groups risk among the population. Several researchers claim that vitamin D metabolites play an important role in the coordinated work of the body’s immune system by inducing the migration of phagocytes, modulating the Th1—Th2 cell balance, and differentiating T-regulatory cells. Objective — to determine the level of vitamin D in patients with susceptible pulmonary tuberculosis and to evaluate its influence on the clinical course of the disease. Materials and methods. The randomized case-control study included 45 patients with newly diagnosed pulmonary tuberculosis of the lungs with preserved sensitivity and 30 practically healthy individuals (PHI) of the control group. The level of vitamin D in blood serum was examined using the VD (Vitamin D) ELISA Kit (Optics Valley Biomedical Industrial Park, Wuhan, China (430075)), for the quantitative detection of vitamin D in blood serum, number: EU2541, parameter: 1.563—100 ng/ml. Results and discussion. According to the results of our study, it was established that the average level of 25(OH)D concentration in the blood serum of patients with pulmonary tuberculosis was (18.46 ± 4.23) ng/ml, in the control group it was (28.834 ± 5.79) ng/ml and was statistically significant (p = 0.001). Our multivariate studies with binary logistic regression showed a strong direct relationship between the presence of a specific tubercular process and vitamin D deficiency (< 20 ng/ml) (OR 2.817, 95 % CI 1.287—4.894, p < 0.005. Conclusions. Vitamin D deficiency was noted in 94 % of patients with pulmonary tuberculosis with severe intoxication syndrome (7—10 points). In tuberculosis with moderate intoxication syndrome (4—6 points), 69.7 % of patients had a vitamin D deficiency, which practically did not differ from indicators in patients with mild intoxication syndrome (1—3 points) — 67.2 % of people.

LECT2 mediates antibacterial immune response induced by Nocardia seriolae infection in the northern snakehead

Leukocyte-derived chemotaxin-2 (LECT2) is a multifunctional immunoregulator that plays several pivotal roles in the host's defense against pathogens. This study aimed to elucidate the specific functions and mechanisms of LECT2 (CaLECT2) in the northern snakehead (Channa argus) during infections with pathogens such as Nocardia seriolae (N. seriolae). We identified CaLECT2 in the northern snakehead, demonstrating its participation in the immune response to N. seriolae infection. CaLECT2 contains an open reading frame (ORF) of 459 bp, encoding a peptide of 152 amino acids featuring a conserved peptidase M23 domain. The CaLECT2 protein shares 62%–84 % identities with proteins from various other fish species. Transcriptional expression analysis revealed that CaLECT2 was constitutively expressed in all examined tissues, with the highest expression observed in the liver. Following intraperitoneal infection with N. seriolae, CaLECT2 transcription increased in the spleen, trunk kidney, and liver. In vivo challenge experiments showed that injecting recombinant CaLECT2 (rCaLECT2) could protect the snakehead against N. seriolae infection by reducing bacterial load, enhancing serum antibacterial activity and antioxidant capacity, and minimizing tissue damage. Moreover, in vitro analysis indicated that rCaLECT2 significantly enhanced the migration, respiratory burst, and microbicidal activity of the head kidney-derived phagocytes. These findings provide new insights into the role of LECT2 in the antibacterial immunity of fish.

Differential requirement of Formyl Peptide Receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection.

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. This study investigates the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed using a TB model of hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion showed no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1 -/- mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased bacterial persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1 -/- neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

Deletion of Tmem268 in mice suppresses anti-infectious immune responses by downregulating CD11b signaling

Transmembrane protein 268 (TMEM268) is a novel, tumor growth-related protein first reported by our laboratory. It interacts with the integrin subunit β4 (ITGB4) and plays a positive role in the regulation of the ITGB4/PLEC signaling pathway. Here, we investigated the effects and mechanism of TMEM268 in anti-infectious immune response in mice. Tmem268 knockout in mice aggravated cecal ligation and puncture-induced sepsis, as evidenced by higher bacterial burden in various tissues and organs, congestion, and apoptosis. Moreover, Tmem268 deficiency in mice inhibited phagocyte adhesion and migration, thus decreasing phagocyte infiltration at the site of infection and complement-dependent phagocytosis. Further findings indicated that TMEM268 interacts with CD11b and inhibits its degradation via the endosome–lysosome pathway. Our results reveal a positive regulatory role of TMEM268 in β2 integrin-associated anti-infectious immune responses and signify the potential value of targeting the TMEM268–CD11b signaling axis for the maintenance of immune homeostasis and immunotherapy for sepsis and related immune disorders.

Formyl Peptide Receptor 1 regulates early control of Mycobacterium tuberculosis infection.

Abstract Formyl peptide receptors (FPR) are playing a pivotal role in phagocyte migration in response to bacterial and host-derived chemoattractants. Despite their established roles, their involvement in immunity to tuberculosis remains unexplored. In this study, we investigated the contributions of Fpr1 and Fpr2 to host defense against Mycobacterium tuberculosis (Mtb) infection. Fpr1 and Fpr2 expression increased in the lungs of rabbits as early as 3 hours and remained elevated during the chronic phase of infection. Additionally, these receptors were increasingly expressed in neutrophils of mice highly susceptible to infection, implying a potential role in the host response to Mtb. We assessed bacterial burden, lung damage, and cellular inflammation following infection of Fpr1-/- and Fpr2-/- mice with a hypervirulent W-Beijing lineage strain of Mtb. While Fpr2 deletion exhibited no discernible impact on host resistance, Fpr1 deficiency compromised bacterial control in the lungs. This effect was particularly pronounced in genetically susceptible mice treated with Fpr1-specific inhibitors. In vitro experiments demonstrated that bone marrow–derived neutrophils and macrophages lacking Fpr1 were incapable of controlling intracellular Mtb growth. Collectively, our findings underscore the differential roles of Fpr1 and Fpr2 in the host defense against Mtb infection, highlighting Fpr1 as a potential therapeutic target for enhancing immune responses against tuberculosis.

Th17 Cell and Inflammatory Infiltrate Interactions in Cutaneous Leishmaniasis: Unraveling Immunopathogenic Mechanisms.

The inflammatory response during cutaneous leishmaniasis (CL) involves immune and non-immune cell cooperation to contain and eliminate Leishmania parasites. The orchestration of these responses is coordinated primarily by CD4+ T cells; however, the disease outcome depends on the Th cell predominant phenotype. Although Th1 and Th2 phenotypes are the most addressed as steers for the resolution or perpetuation of the disease, Th17 cell activities, especially IL-17 release, are recognized to be vital during CL development. Th17 cells perform vital functions during both acute and chronic phases of CL. Overall, Th17 cells induce the migration of phagocytes (neutrophils, macrophages) to the infection site and CD8+ T cells and NK cell activation. They also provoke granzyme and perforin secretion from CD8+ T cells, macrophage differentiation towards an M2 phenotype, and expansion of B and Treg cells. Likewise, immune cells from the inflammatory infiltrate have modulatory activities over Th17 cells involving their differentiation from naive CD4+ T cells and further expansion by generating a microenvironment rich in optimal cytokines such as IL-1β, TGF-β, IL-6, and IL-21. Th17 cell activities and synergies are crucial for the resistance of the infection during the early and acute stages; however, if unchecked, Th17 cells might lead to a chronic stage. This review discusses the synergies between Th17 cells and the inflammatory infiltrate and how these interactions might destine the course of CL.

Tree Frog-Derived Cathelicidin Protects Mice against Bacterial Infection through Its Antimicrobial and Anti-Inflammatory Activities and Regulatory Effect on Phagocytes.

Due to excessive use or abuse in the food industry, agriculture, and medicine, many pathogens are developing resistance against conventional antibiotics. Antimicrobial peptides (AMPs) hold promise as effective therapeutic options for the treatment of bacterial infections. Herein, a novel cathelicidin antimicrobial peptide (Zs-CATH) was identified from the tree frog Zhangixalus smaragdinus. Zs-CATH mainly adopted an amphipathic β-sheet structure in a membrane-mimetic environment. It showed broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria in vitro and significantly protected mice from lethal infections induced by Gram-negative bacteria Escherichia coli ATCC 25922 or Gram-positive bacteria Staphylococcus aureus ATCC 25923 in vivo. In addition, Zs-CATH exerted a strong anti-inflammatory effect by neutralizing lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and promoting macrophage M2 polarization, thus inhibiting the secretion of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) and enhancing the production of M2 macrophage markers IL-10, IL-4, and CD206. The MAPK and NF-κB inflammatory signaling pathways and transcriptional activator 6 (STAT6) were involved in this effect. In mice, Zs-CATH rapidly recruited neutrophils and monocytes/macrophages to the abdominal cavity but not T and B lymphocytes. Zs-CATH did not exhibit a direct chemoattractant effect on phagocytes but significantly promoted phagocyte migration in the presence of macrophages. Zs-CATH stimulated macrophages to secrete chemokines CXCL1, CXCL2, and CCL2, which mediated the recruitment of phagocytes. Furthermore, Zs-CATH promoted the production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs), which are oxygen-dependent and oxygen-independent mechanisms of the microbicidal activity of neutrophils, respectively. Zs-CATH exhibited no toxic side effects on mammalian cells and mice. These findings show that in addition to direct antibacterial activity, Zs-CATH also possesses the ability to modulate immune and inflammatory processes during bacterial infection, showing potential for development as anti-infective and/or anti-inflammatory agents.

Sphingosine 1 phosphate production is an important mediator of skin inflammation and host defense in hyperglycemic mice.

Abstract Staphylococcus aureus (MRSA) skin infections are characterized by the initial recruitment of neutrophils followed by the establishment of a localized abscess. An abscess comprises a fibrous capsule, viable and apoptotic neutrophils, and bacteria in the abscess core. Along with eliminating bacteria, the clearance of dead neutrophils (efferocytosis) is crucial to restoring tissue homeostasis. Efferocytosis is a tightly regulated process initiated when dying cells secrete “find-me” signals such as Sphingosine 1 phosphate (S1P) that trigger phagocyte migration resulting in apoptotic neutrophil clearance. S1P binds to five different G protein-coupled receptors (S1PR1–5). Our data show that obese and hyperglycemic mice are more susceptible to MRSA skin infection, characterized by increased lesion size, bacterial loads, and poor abscess formation. In hyperglycemic mice, we also observed increased dead cells on days 1 and 9 post-infection with MRSA. When we assessed in vivo efferocytosis, we observed a lower ratio of ingestion of dead cells in the skin of hyperglycemic mice compared to euglycemic mice. Imaging mass spectrometry and lipidomic analysis revealed that while S1P levels are decreased, phosphoethanolamine (a product of the S1P degradation) is increased before and on day 1 post-infection in obese mice. We found that S1pr3 is significantly increased, whereas S1pr4 and S1pr5 are decreased in the infected skin obese. Topical S1P treatment reduced lesion size and bacterial load in the skin of hyperglycemic mice. Our data suggest that S1P deficiency during skin infections culminates in less efferocytosis, accumulation of dead cells, uncontrolled infection, and delay in the resolution of the infection.

From bench to bedside: Calprotectin (S100A8/S100A9) as a biomarker in rheumatoid arthritis.

S100A9/S100A8 (calprotectin), a member of the S100 protein family, has been shown to play a pivotal role in innate immunity activation. Calprotectin plays a critical role in the pathogenesis of rheumatoid arthritis (RA), as it triggers chemotaxis, phagocyte migration and modulation of neutrophils and macrophages. Higher calprotectin levels have been found in synovial fluid, plasma, and serum from RA patients. Recent studies have demonstrated better correlations between serum or plasma calprotectin and composite inflammatory disease activity indexes than c-reactive protein (CRP) or the erythrocyte sedimentation rate (ESR). Calprotectin serum levels decreased after treatment, independently of the DMARD type or strategy. Calprotectin has shown the strongest correlations with other sensitive techniques to detect inflammation, such as ultrasound. Calprotectin independently predicts radiographic progression. However, its value as a biomarker of treatment response and flare after tapering is unclear. This update reviews the current understanding of calprotectin in RA and discusses possible applications as a biomarker in clinical practice.

The nature of the fungal cargo induces significantly different temporal programmes of macrophage phagocytosis

Phagocytosis is an essential component of our immune defence against fungal pathogens. Differences in the dynamics of phagocyte migration, recognition, uptake and phagolysosome maturation are dependent on the characteristics of the fungal cargo, and in particular to differences in cell wall composition and cellular morphology. However, studies that have focused on phagocyte interactions with individual fungal species have not enabled comparisons in the kinetics of these interactions to be made between these different species. We therefore used live cell video microscopy to examine the temporal dynamics of phagocytosis for a range of fungal cargoes by thioglycollate–elicited peritoneal macrophages from C57BL/6 mice. Uniform populations of macrophages were challenged at the same time with yeast cells of Candida albicans, Candida glabrata, Saccharomyces cerevisiae and Cryptococcus neoformans (wild–type and an acapsular mutant, cap59Δ), and spores of Aspergillus fumigatus and Mucor circinelloides to enable standardized comparative interactions to be quantified from different stages of phagocytosis. Differences in the rate of uptake of fungal cells varied by up to 26–fold, whilst differences in time to induce phagosome acidification varied by as much as 29–fold. Heat-killing or opsonizing the fungal targets markedly affected the kinetics of the interaction in a species–specific manner. Fungal and macrophage killing assays further revealed cargo–specific differences in phagocytosis and diversity in fungal evasion mechanisms. Therefore, simultaneous assessment of the interaction of macrophages with different fungal pathogens highlighted major differences in the kinetics and growth responses during fungus–phagocyte interactions that are likely to impact on pathogenesis and virulence.

Structural basis for recognition of N-formyl peptides as pathogen-associated molecular patterns

The formyl peptide receptor 1 (FPR1) is primarily responsible for detection of short peptides bearing N-formylated methionine (fMet) that are characteristic of protein synthesis in bacteria and mitochondria. As a result, FPR1 is critical to phagocyte migration and activation in bacterial infection, tissue injury and inflammation. How FPR1 distinguishes between formyl peptides and non-formyl peptides remains elusive. Here we report cryo-EM structures of human FPR1-Gi protein complex bound to S. aureus-derived peptide fMet-Ile-Phe-Leu (fMIFL) and E. coli-derived peptide fMet-Leu-Phe (fMLF). Both structures of FPR1 adopt an active conformation and exhibit a binding pocket containing the R2015.38XXXR2055.42 (RGIIR) motif for formyl group interaction and receptor activation. This motif works together with D1063.33 for hydrogen bond formation with the N-formyl group and with fMet, a model supported by MD simulation and functional assays of mutant receptors with key residues for recognition substituted by alanine. The cryo-EM model of agonist-bound FPR1 provides a structural basis for recognition of bacteria-derived chemotactic peptides with potential applications in developing FPR1-targeting agents.

Tetraspanin CD82 restrains phagocyte migration but supports macrophage activation

SummaryPhagocytes migrate into tissues to combat infection and maintain tissue homeostasis. As dysregulated phagocyte migration and function can lead to inflammation or susceptibility to infection, identifying molecules that control these processes is critical. Here, we show that the tetraspanin CD82 restrains the migration of neutrophils and macrophages into tissues. Cd82−/− phagocytes exhibited excessive migration during in vivo models of peritoneal inflammation, superfusion of CXCL1, retinopathy of prematurity, and infection with the protozoan parasite L. mexicana. However, with the latter, while Cd82−/− macrophages infiltrated infection sites at higher proportions, cutaneous L. mexicana lesions were larger and persisted, indicating a failure to control infection. Analyses of in vitro bone-marrow-derived macrophages showed CD82 deficiency altered cellular morphology, and impaired gene expression and metabolism in response to anti-inflammatory activation. Altogether, this work reveals an important role for CD82 in restraining phagocyte infiltration and mediating their differentiation in response to stimulatory cues.

Pulmonary toxicity and gene expression changes in response to whole-body inhalation exposure to multi-walled carbon nanotubes in rats

Purpose: To investigate the molecular mechanisms underlying the pulmonary toxicity induced by exposure to one form of multi-walled carbon nanotubes (MWCNT-7). Materials and methods: Rats were exposed, by whole-body inhalation, to air or an aerosol containing MWCNT-7 particles at target cumulative doses (concentration x time) ranging from 22.5 to 180 (mg/m3)h over a three-day (6 hours/day) period and toxicity and global gene expression profiles were determined in the lungs. Results: MWCNT-7 particles, associated with alveolar macrophages (AMs), were detected in rat lungs following the exposure. Mild to moderate lung pathological changes consisting of increased cellularity, thickening of the alveolar wall, alveolitis, fibrosis, and granuloma formation were detected. Bronchoalveolar lavage (BAL) toxicity parameters such as lactate dehydrogenase activity, number of AMs and polymorphonuclear leukocytes (PMNs), intracellular oxidant generation by phagocytes, and levels of cytokines were significantly (p < 0.05) increased in response to exposure to MWCNT-7. Global gene expression profiling identified several significantly differentially expressed genes (fold change >1.5 and FDR p value <0.05) in all the MWCNT-7 exposed rats. Bioinformatic analysis of the gene expression data identified significant enrichment of several diseases/biological function categories (for example, cancer, leukocyte migration, inflammatory response, mitosis, and movement of phagocytes) and canonical pathways (for example, kinetochore metaphase signaling pathway, granulocyte and agranulocyte adhesion and diapedesis, acute phase response, and LXR/RXR activation). The alterations in the lung toxicity parameters and gene expression changes exhibited a dose-response to the MWCNT exposure. Conclusions: Taken together, the data provided insights into the molecular mechanisms underlying the pulmonary toxicity induced by inhalation exposure of rats to MWCNT-7.

Chemokines and anionic phospholipids: new binding partners for microbial killing and apoptotic cell clearance

Abstract Chemokines constitute a large family of small cytokines that regulate leukocyte migration in immunity and inflammation, some of which also have direct bacteria-killing properties. While the molecular mechanism by which chemokines kill bacteria remains poorly understood, chemokines mediate cell migration by interacting with cell surface glycosaminoglycans (GAGs) and G protein-coupled receptors (GPCRs). We have discovered that many chemokines interact with high affinity with anionic membrane phospholipids, including phosphatidylserine (PS) and cardiolipin (CL) which are selectively exposed on the membrane of apoptotic cells and apoptotic extracellular vesicles (ApoEV), and bacteria, respectively. This adds to GPCRs and GAGs a third class of cell surface binding site for chemokines and expands the scope of chemokine action to the biological niches occupied by PS and CL. For instance, we found that ApoEV induce phagocyte migration for apoptotic cell clearance by presenting PS-binding chemokines on the vesicle surface to GPCRs expressed by phagocytes. This is a novel PS-dependent mechanism for chemokine delivery by extracellular vesicles potentially relevant to other areas of immunology and indicates that chemokines may play a more prominent role in the removal of dying cells than previously reported. On the other hand, we discovered that only CL-binding chemokines are antimicrobial and that CL-deficient bacteria are resistant to chemokine treatment, indicating that chemokines kill bacteria by targeting CL on the bacterial membrane. In short, we have identified chemokines as the first family of soluble cytokines whose bioactivities can be regulated by direct interaction with membrane phospholipids. Supported by NIAID/NIH intramural research program

Anionic membrane phospholipids: A New Class of Chemokine‐Binding Site Important for both Apoptotic Cell Clearance and Antibiotic Activity by Chemokines

Chemokines are small cytokines that orchestrate immune cell migration by binding to cell surface glycosaminoglycans (GAGs) and activating G protein‐couple receptors (GPCRs) expressed by leukocytes. We have discovered that chemokines selectively bind with high affinity to anionic membrane phospholipids, including phosphatidylserine (PS) and cardiolipin (CL). This adds to GPCRs and GAGs a third class of high affinity membrane binding site for chemokines and expands the scope of chemokine action to new areas of biology dictated by the specific biological niches occupied by their phospholipid binding partners. PS, for example, is usually restricted to the cytosolic face of the phospholipid bilayer of the plasma membrane of healthy eukaryotic cells, but it is flipped to the outer leaflet of the membrane of apoptotic cells and apoptotic extracellular vesicles (ApoEVs), where it acts as an ‘eat‐me’ signal recognized by phagocytes for apoptotic cell clearance. In this regard, we have recently demonstrated that ApoEVs generated in vivo from mouse thymus induce phagocyte migration using endogenous chemokines bound to the vesicle surface via PS. Our results indicate that PS‐bound chemokines on ApoEVs may serve as ‘find‐me’ signals that recruit phagocytes toward apoptotic cells for the removal of dying cells. This is a new PS‐dependent mechanism for chemokine delivery by extracellular vesicles. On the other hand, CL is absent in the plasma membrane of eukaryotic cells but it is a major and naturally exposed anionic phospholipid in the bacterial plasma membrane. As such, we have found that chemokines act as potent direct bacteria‐killing agents by binding to bacterial CL. This finding identifies the molecular mechanism for antimicrobial action by chemokines and launch new avenues of research in antimicrobial therapies and bacteria‐host interactions. In short, we have identified chemokines as the first example of a family of soluble cytokines whose functions are regulated by direct interaction with membrane phospholipids.

A non-bactericidal cathelicidin provides prophylactic efficacy against bacterial infection by driving phagocyte influx.

The roles of bactericidal cathelicidins against bacterial infection have been extensively studied. However, the antibacterial property and mechanism of action of non-bactericidal cathelicidins are rarely known. Herein, a novel naturally occurring cathelicidin (PopuCATH) from tree frog (Polypedates puerensis) did not't show any direct anti-bacterial activity in vitro. Intriguingly, intraperitoneal injection of PopuCATH before bacterial inoculation significantly reduced the bacterial load in tree frogs and mice, and reduced the inflammatory response induced by bacterial inoculation in mice. PopuCATH pretreatment also increased the survival rates of septic mice induced by a lethal dose of bacterial inoculation or cecal ligation and puncture (CLP). Intraperitoneal injection of PopuCATH significantly drove the leukocyte influx in both frogs and mice. In mice, PopuCATH rapidly drove neutrophil, monocyte/macrophage influx in mouse abdominal cavity and peripheral blood with a negligible impact on T and B lymphocytes, and neutrophils, monocytes/macrophages, but not T and B lymphocytes, were required for the preventive efficacy of PopuCATH. PopuCATH did not directly act as chemoattractant for phagocytes, but PopuCATH obviously drove phagocyte migration when it was cultured with macrophages. PopuCATH significantly elicited chemokine/cytokine production in macrophages through activating p38/ERK mitogen-activated protein kinases (MAPKs) and NF-κB p65. PopuCATH markedly enhanced neutrophil phagocytosis via promoting the release of neutrophil extracellular traps (NETs). Additionally, PopuCATH showed low side effects both in vitro and in vivo. Collectively, PopuCATH acts as a host-based immune defense regulator that provides prophylactic efficacy against bacterial infection without direct antimicrobial effects. Our findings reveal a non-bactericidal cathelicidin which possesses unique anti-bacterial action, and highlight the potential of PopuCATH to prevent bacterial infection.

Response biomarkers of inhalation exposure to cigarette smoke in the mouse lung.

Cigarette smoking is known to increase the risk of cancer and chronic obstructive pulmonary disease (COPD). In this study, we evaluated the effects of short-term nose-only inhalation exposure to cigarette smoke in mice. Male 10-week-old C57BL mice were exposed to clean air (control) or mainstream cigarette smoke for 1 h/day, 5 days/week, for 2 or 4 weeks. Exposure to cigarette smoke increased the number of inflammatory cells, especially neutrophils, in the bronchoalveolar lavage fluid, increased inflammatory cell infiltration foci, and caused an increase in the thickness of the peripheral bronchial epithelium. Microarray gene expression analysis indicated that smoke exposure induced inflammatory responses, including leukocyte migration and activation of phagocytes and myeloid cells, as early as two weeks after the initiation of exposure. Importantly, chemokine (C-C motif) ligand 17, resistin-like alpha, and lipocalin 2 were upregulated and may serve as useful markers of the toxic effects of exposure to cigarette smoke before pulmonary histological changes become evident.

Bacterial Infection-Mimicking Three-Dimensional Phagocytosis and Chemotaxis in Electrospun Poly(ε-caprolactone) Nanofibrous Membrane.

In this study, we developed a three-dimensional (3D) in vitro infection model to investigate the crosstalk between phagocytes and microbes in inflammation using a nanofibrous membrane (NM). Poly(ε-caprolactone) (PCL)-NMs (PCL-NMs) were generated via electrospinning of PCL in chloroform. Staphylococcus aureus and phagocytes were able to adhere to the nanofibers and phagocytes engulfed S. aureus in the PCL-NM. The migration of phagocytes to S. aureus was evaluated in a two-layer co-culture system using PCL-NM. Neutrophils, macrophages and dendritic cells (DCs) cultured in the upper PCL-NM layer migrated to the lower PCL-NM layer containing bacteria. DCs migrated to neutrophils that cultured with bacteria and then engulfed neutrophils in two-layer system. In addition, phagocytes in the upper PCL-NM layer migrated to bacteria-infected MLE-12 lung epithelial cells in the lower PCL-NM layer. S. aureus-infected MLE-12 cells stimulated the secretion of tumor necrosis factor-α and IL-1α in 3D culture conditions, but not in 2D culture conditions. Therefore, the PCL-NM-based 3D culture system with phagocytes and bacteria mimics the inflammatory response to microbes in vivo and is applicable to the biomimetic study of various microbe infections.

ISOLYQUIRITIGENIN AFFECTS PHAGOCYTES FUNCTIONS AND INCREASES MICE SURVIVAL RATE IN STAPHYLOCOCCAL INFECTION

The results of studying the effect of isoliquiritigenin on animal survival in the model of staphylococcal infection and the function of human and animal phagocytes are presented in this article.The aim of the investigation was to study the effect of an isoliquiritigenin preliminary administration on the survival of animals against the background of staphylococcal infection, as well as on the function of phagocytes in mice and humans.Materials and methods. To assess the survival of Balb/C mice, a model of infection caused by Staphylococcus aureus J49 ATCC 25923 with the construction of Kaplan-Meier curves, was used. The effect on the phagocytes functions was studied by assessing the peptone-induced migration of phagocytes into the abdominal cavity of Balb/C mice, the absorption activity of phagocytes (neutrophils and monocytes) of human blood, as well as their production of reactive oxygen intermediates (ROIs) using а flow cytometry.Results. It was found out that a preliminary triple intraperitoneal administration of isoliquiritigenin (30 mg/kg) increases the survival rate of Balb/C mice in staphylococcal infection caused by Staphylococcus aureus J49 ATCC 25923. At the same time, isoliquiritigenin dose-dependently activates the production of reactive oxygen intermediates by human neutrophils and monocytes without statistically significantly suppressing a phagocytic activity of monocytes and neutrophils against fluoresceinisothiocyanate-labeled S. aureus J 49 ATCC 25923, as well as peptone-induced migration of phagocytes into the abdominal cavity of mice.Conclusion. Thus, a preliminary administration of isoliquiritigenin increases the survival rate of mice with staphylococcal infection and increases the production of reactive oxygen intermediates by phagocytes. The data obtained, can become the basis for further research of antibacterial and immunotropic effects of isoliquiritigenin in order to find new drugs for the treatment of staphylococcal infection.