Lipocalin 2 Protects Against Escherichia coli Infection by Modulating Neutrophil and Macrophage Function

CXCR2 perturbation promotes Staphylococcus aureus implant-associated infection

Introduction. Staphylococcus aureus is the leading cause of acute medical implant infections, representing a significant modern medical concern. The success of S. aureus as a pathogen in these cases resides in its arsenal of virulence factors, resistance to multiple antimicrobials, mechanisms of immune modulation, and ability to rapidly form biofilms associated with implant surfaces. S. aureus device-associated, biofilm-mediated infections are often persistent and notoriously difficult to treat, skewing innate immune responses to promote chronic reoccurring infections. While relatively little is known of the role neutrophils play in response to acute S. aureus biofilm infections, these effector cells must be efficiently recruited to sites of infection via directed chemotaxis. Here we investigate the effects of modulating CXC chemokine receptor 2 (CXCR2) activity, predominantly expressed on neutrophils, during S. aureus implant-associated infection.Hypothesis. We hypothesize that modulation of CXCR2 expression and/or signalling activities during S. aureus infection, and thus neutrophil recruitment, extravasation and antimicrobial activity, will affect infection control and bacterial burdens in a mouse model of implant-associated infection.Aim. This investigation aims to elucidate the impact of altered CXCR2 activity during S. aureus biofilm-mediated infection that may help develop a framework for an effective novel strategy to prevent morbidity and mortality associated with implant infections.Methodology. To examine the role of CXCR2 during S. aureus implant infection, we employed a mouse model of indwelling subcutaneous catheter infection using a community-associated methicillin-resistant S. aureus (MRSA) strain. To assess the role of CXCR2 induction or inhibition during infection, treatment groups received daily intraperitoneal doses of either Lipocalin-2 (Lcn2) or AZD5069, respectively. At the end of the study, catheters and surrounding soft tissues were analysed for bacterial burdens and dissemination, and Cxcr2 transcription within the implant-associated tissues was quantified.Results. Mice treated with Lcn2 developed higher bacterial burdens within the soft tissue surrounding the implant site, which was associated with increased Cxcr2 expression. AZD5069 treatment also resulted in increased implant- and tissues-associated bacterial titres, as well as enhanced Cxcr2 expression.Conclusion. Our results demonstrate that CXCR2 plays an essential role in regulating the severity of S. aureus implant-associated infections. Interestingly, however, perturbation of CXCR2 expression or signalling both resulted in enhanced Cxcr2 transcription and elevated implant-associated bacterial burdens. Thus, CXCR2 appears finely tuned to efficiently recruit effector cells and mediate control of S. aureus biofilm-mediated infection.

Dynamic changes and clinical value of lipocalin 2 in liver diseases caused by microbial infections

Lipocalin 2 (LCN2) plays a pivotal role in iron metabolism, particularly in the context of microbial infection resistance (e.g., viruses, bacteria, parasites, etc.). LCN2 combats microbial infection by directly assisting the body in competing with microorganisms for iron, inducing immune cells to secrete various cytokines to enhance systemic immune responses, or recruiting neutrophils to infectious sites. The liver serves as the primary organ for LCN2 secretion during microbial infections. This review encapsulates recent advances in dynamic changes, clinical values, and the effects of LCN2 in infectious liver diseases caused by various microbial microorganisms.

Tick bite-induced alpha-gal syndrome and immunologic responses in an alpha-gal deficient murine model

Introduction

Alpha-Gal Syndrome (AGS) is a delayed allergic reaction due to specific IgE antibodies targeting galactose-α-1,3-galactose (α-gal), a carbohydrate found in red meat. This condition has gained significant attention globally due to its increasing prevalence, with more than 450,000 cases estimated just in the United States alone. Previous research has established a connection between AGS and tick bites, which sensitize individuals to α-gal antigens and elevate the levels of specific IgE. However, the precise mechanism by which tick bites influence the host's immune system and contribute to the development of AGS remains poorly understood. This study investigates various factors related to ticks and the host associated with the development of AGS following a tick bite, using mice with a targeted disruption of alpha-1,3-galactosyltransferase (AGKO) as a model organism.

Methods

Lone-star tick (Amblyomma americanum) and gulf-coast tick (Amblyomma maculatum) nymphs were used to sensitize AGKO mice, followed by pork meat challenge. Tick bite site biopsies from sensitized and non-sensitized mice were subjected to mRNA gene expression analysis to assess the host immune response. Antibody responses in sensitized mice were also determined.

Results

Our results showed a significant increase in the total IgE, IgG1, and α-gal IgG1 antibodies titers in the lone-star tick-sensitized AGKO mice compared to the gulf-coast tick-sensitized mice. Pork challenge in Am. americanum -sensitized mice led to a decline in body temperature after the meat challenge. Gene expression analysis revealed that Am. americanum bites direct mouse immunity toward Th2 and facilitate host sensitization to the α-gal antigen.

Conclusion

This study supports the hypothesis that specific tick species may increase the risk of developing α-gal-specific IgE and hypersensitivity reactions or AGS, thereby providing opportunities for future research on the mechanistic role of tick and host-related factors in AGS development.

Role of Lipocalin-2 in N1/N2 Neutrophil Polarization After Stroke

BACKGROUND

Neutrophils and Lipocalin-2 (LCN2) play pivotal roles in cerebral ischemiareperfusion (I/R) injury. However, their contribution is not fully clarified.

OBJECTIVE

This study aimed to explore the role of LCN2 and its association with neutrophil polarization in I/R injury.

METHODS

A mouse model of middle cerebral artery occlusion (MCAO) was used to induce cerebral ischemia. LCN2mAb was administered 1 h and Anti-Ly6G was administered for 3d before MCAO. The role of LCN2 in the polarity transition of neutrophils was explored using an in vitro HL-60 cell model.

RESULTS

LCN2mAb pretreatment had neuroprotective effects in mice. The expression of Ly6G was not significantly different, but the expression of N2 neutrophils was increased. In the in vitro study, LCN2mAb-treated N1-HL-60 cells induced N2-HL-60 polarization.

CONCLUSION

LCN2 may affect the prognosis of ischemic stroke by mediating neutrophil polarization.

Lcn2 deficiency accelerates the infection of Escherichia coli O157:H7 by disrupting the intestinal barrier function

Bacterial infections result in intestinal inflammation and injury, which affects gut health and nutrient absorption. Lipocalin 2 (Lcn2) is a protein that reacts to microbial invasion, inflammatory responses, and tissue damage. However, it remains unclear whether Lcn2 has a protective effect against bacterial induced intestinal inflammation. Therefore, this study endeavors to investigate the involvement of Lcn2 in the intestinal inflammation of mice infected with Enterohemorrhagic Escherichia coli O157:H7 (E. coli O157:H7). Lcn2 knockout (Lcn2-/-) mice were used to evaluate the changes of inflammatory responses. Lcn2 deficiency significantly exacerbated clinical symptoms of E. coli O157:H7 infection by reducing body weight and encouraging bacterial colonization of. Compared to infected wild type mice, infected Lcn2-/- mice had significantly elevated levels of pro-inflammatory cytokines in serum and ileum, including interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α), as well as severe villi destruction in the jejunum. Furthermore, Lcn2 deficiency aggravated intestinal barrier degradation by significantly reducing the expression of tight junction proteins occludin and claudin 1, the content of myeloperoxidase (MPO) in the ileum, and the number of goblet cells in the colon. Our findings indicated that Lcn2 could alleviate inflammatory damage caused by E. coli O157:H7 infection in mice by enhancing intestinal barrier function.

Tick bite-induced Alpha-Gal Syndrome and Immunologic Responses in an Alpha-Gal Deficient Murine Model

Introduction

Alpha-Gal Syndrome (AGS) is a delayed allergic reaction due to specific IgE antibodies targeting galactose-α-1,3-galactose (α-gal), a carbohydrate found in red meat. This condition has gained significant attention globally due to its increasing prevalence, with more than 450,000 cases estimated in the United States alone. Previous research has established a connection between AGS and tick bites, which sensitize individuals to α-gal antigens and elevate the levels of α-gal specific IgE. However, the precise mechanism by which tick bites influence the hosťs immune system and contribute to the development of AGS remains poorly understood. This study investigates various factors related to ticks and the host associated with the development of AGS following a tick bite, using mice with a targeted disruption of alpha-1,3-galactosyltransferase (AGKO) as a model organism.

Methods

Lone-star tick (Amblyomma americanum) and gulf-coast tick (Amblyomma maculatum) nymphs were used to sensitize AGKO mice, followed by pork meat challenge. Tick bite site biopsies from sensitized and non-sensitized mice were subjected to mRNA gene expression analysis to assess the host immune response. Antibody responses in sensitized mice were also determined.

Results

Our results showed a significant increase in the titer of total IgE, IgG1, and α-gal IgG1 antibodies in the lone-star tick-sensitized AGKO mice compared to the gulf-coast tick-sensitized mice. Pork challenge in Am. americanum -sensitized mice led to a decline in body temperature after the meat challenge. Gene expression analysis revealed that Am. americanum bites direct mouse immunity toward Th2 and facilitate host sensitization to the α-gal antigen, while Am. maculatum did not.

Conclusion

This study supports the hypothesis that specific tick species may increase the risk of developing α-gal-specific IgE and hypersensitivity reactions or AGS, thereby providing opportunities for future research on the mechanistic role of tick and host-related factors in AGS development.

Heme oxygenase-1 increases intracellular iron storage and suppresses inflammatory response of macrophages by inhibiting M1 polarization

Heme oxygenase-1 (HO-1) catalyzes the first and rate-limiting enzymatic step of heme degradation, producing carbon monoxide, biliverdin, and free iron. Most iron is derived from aged erythrocytes by the decomposition of heme, which happened mainly in macrophages. However, the role of HO-1 on iron metabolism and function of macrophage is unclear. The present study investigated the effect of HO-1 on iron metabolism in macrophages, and explored the role of HO-1 on inflammatory response, polarization, and migration of macrophages. HO-1 inducer Hemin or HO-1 inhibitor zinc protoporphyrin was intravenously injected to C57BL/6 J mice every 4 d for 28 d. We found that HO-1 was mainly located in the cytoplasm of splenic macrophages of mice. Activation of HO-1 by Hemin significantly increased iron deposition in the spleen, up-regulated the gene expression of ferritin and ferroportin, and down-regulated gene expression of divalent metal transporter 1 and hepcidin. Induced HO-1 by Hemin treatment increased intracellular iron levels of macrophages, slowed down the absorption of extracellular iron, and accelerated the excretion of intracellular iron. In addition, activation of HO-1 significantly decreased the expression of pro-inflammatory cytokines including interleukin (IL)-6, IL-1β, and inducible nitric oxide synthase, but increased the expression of anti-inflammatory cytokines such as IL-10. Furthermore, activation of HO-1 inhibited macrophages to M1-type polarization, and increased the migration rate of macrophages. This study demonstrated that HO-1 was able to regulate iron metabolism, exert anti-inflammatory effects, and inhibit macrophages polarization to M1 type.

Iron Chelator Deferoxamine Alleviates Progression of Diabetic Nephropathy by Relieving Inflammation and Fibrosis in Rats

Diabetic nephropathy (DN) is one of the most devastating diabetic microvascular complications. It has previously been observed that iron metabolism levels are abnormal in diabetic patients. However, the mechanism by which iron metabolism levels affect DN is poorly understood. This study was designed to evaluate the role of iron-chelator deferoxamine (DFO) in the improvement of DN. Here, we established a DN rat model induced by diets high in carbohydrates and fat and streptozotocin (STZ) injection. Our data demonstrated that DFO treatment for three weeks greatly attenuated renal dysfunction as evidenced by decreased levels of urinary albumin, blood urea nitrogen, and serum creatinine, which were elevated in DN rats. Histopathological observations showed that DFO treatment improved the renal structures of DN rats and preserved podocyte integrity by preventing the decrease of transcripts of nephrin and podocin. In addition, DFO treatment reduced the overexpression of fibronectin 1, collagen I, IL-1β, NF-κB, and MCP-1 in DN rats, as well as inflammatory cell infiltrates and collagenous fibrosis. Taken together, our findings unveiled that iron chelation via DFO injection had a protective impact on DN by alleviating inflammation and fibrosis, and that it could be a potential therapeutic strategy for DN.

The regulation of TRPA1 expression and function by Th1 and Th2-type inflammation in human A549 lung epithelial cells

BACKGROUND

Transient Receptor Potential Ankyrin 1 (TRPA1) is a cation channel that mediates pain, itch, cough, and neurogenic inflammation in response to pungent compounds such as acrolein in cigarette smoke. TRPA1 is also activated by endogenous factors and promotes inflammation in asthma models. We have recently shown that TRPA1 is upregulated by inflammatory cytokines in A549 human lung epithelial cells. Here, we explored the effects of Th1 and Th2-type inflammation on TRPA1.

METHODS AND RESULTS

TRPA1 expression and function was studied in A549 human lung epithelial cells. To induce inflammation, the cells were exposed to a combination of cytokines TNF-α and IL-1β; and to model Th1 or Th2-type responses, IFN-γ or IL-4/IL-13 was added, respectively. TRPA1 expression (measured by RT-PCR and Western blot) and function (assessed by Fluo-3AM intracellular calcium measurement) was enhanced under the influence of TNF-α + IL-1β. IFN-γ further enhanced TRPA1 expression and function, whereas IL-4 and IL-13 suppressed them. The effects of IFN-γ and IL-4 on TRPA1 expression were reversed by the Janus kinase (JAK) inhibitors baricitinib and tofacitinib, and those of IL-4 also by the STAT6 inhibitor AS1517499. The glucocorticoid dexamethasone downregulated TRPA1 expression, whereas the PDE4 inhibitor rolipram had no effect. Under all conditions, TRPA1 blockade was found to reduce the production of LCN2 and CXCL6.

CONCLUSIONS

TRPA1 expression and function in lung epithelial cells was upregulated under inflammatory conditions. IFN-γ further increased TRPA1 expression while IL-4 and IL-13 suppressed that in a JAK-STAT6 dependent manner which is novel. TRPA1 also modulated the expression of genes relevant to innate immunity and lung disease. We propose that the paradigm of Th1 and Th2 inflammation is a major determinant of TRPA1 expression and function, which should be considered when targeting TRPA1 for pharmacotherapy in inflammatory (lung) disease.

Lipocalin-2 deletion attenuates lipopolysaccharide-induced acute lung inflammation via downregulating chemotaxis-related genes

Lipocalin-2 (LCN2) is an acute phase protein used as a biomarker for acute lung injury (ALI). Although the innate immune functions of LCN2 have been studied, how LCN2 contributes to ALI induced by lipopolysaccharide (LPS) remains unknown. In this study, we investigated the effect of LCN2 deletion on LPS-induced ALI using RNA-sequencing. LPS-treated LCN2 knockout (KO) mice had a decreased histopathological score and reduced neutrophil and macrophage infiltration in lung tissue compared with LPS-treated WT mice. RNA-sequencing analysis identified 38 differentially expressed genes (DEGs), including Cxcl5, Cxcl13, Xcl1, Saa1, and Cd14. In particular, Gene Ontology analysis of DEGs revealed a significant reduction in the inflammatory response, neutrophil chemotaxis, and chemokine-mediated signaling in LPS-treated LCN2KO mice compared with LPS-treated WT mice. Thus, these results suggest that LCN2 deletion alleviates LPS-induced ALI and that LCN2 may be involved in chemotaxis-related gene expression.

Iron in infectious diseases friend or foe?: The role of gut microbiota

Iron is a trace element involved in metabolic functions for all organisms, from microorganisms to mammalians. Iron deficiency is a prevalent health problem that affects billions of people worldwide, and iron overload could have some hazardous effect. The complex microbial community in the human body, also called microbiota, influences the host immune defence against infections. An imbalance in gut microbiota, dysbiosis, changes the host's susceptibility to infections by regulating the immune system. In recent years, the number of studies on the relationship between infectious diseases and microbiota has increased. Gut microbiota is affected by different parameters, including mode of delivery, hygiene habits, diet, drugs, and plasma iron levels during the lifetime. Gut microbiota may influence iron levels in the body, and iron overload and deficiency can also affect gut microbiota composition. Novel researches on microbiota shed light on the fact that the bidirectional interactions between gut microbiota and iron play a role in the pathogenesis of many diseases, especially infections. A better understanding of these interactions may help us to comprehend the pathogenesis of many infectious and metabolic diseases affecting people worldwide and following the development of more effective preventive and/or therapeutic strategies. In this review, we aimed to present the iron-mediated host-gut microbiota interactions, susceptibility to bacterial infections, and iron-targeted therapy approaches for infections.

Lipocalin-2 promotes acute lung inflammation and oxidative stress by enhancing macrophage iron accumulation

Lipocalin-2 (LCN2) is an acute-phase protein that regulates inflammatory responses to bacteria or lipopolysaccharide (LPS). Although the bacteriostatic role of LCN2 is well studied, the function of LCN2 in acute lung damage remains unclear. Here, LCN2 knockout (KO) mice were used to investigate the role of LCN2 in LPS-treated mice with or without recombinant LCN2 (rLCN2). In addition, we employed patients with pneumonia. RAW264.7 cells were given LCN2 inhibition or rLCN2 with or without iron chelator deferiprone. LCN2 KO mice had a higher survival rate than wild-type (WT) mice after LPS treatment. In addition to elevated LCN2 levels in serum and bronchoalveolar lavage fluid (BALF), LPS treatment also increased LCN2 protein in alveolar macrophage lysates of BALF. LCN2 deletion attenuated neutrophil and macrophage infiltration in the lungs of LPS-treated mice as well as serum and BALF interleukin-6 (IL-6). Circulating proinflammatory cytokines and LCN2-positive macrophages were prominently increased in the BALF of pneumonia patients. In addition to increase of iron-stained macrophages in pneumonia patients, increased iron-stained macrophages and oxidative stress in LPS-treated mice were inhibited by LCN2 deletion. In contrast, rLCN2 pretreatment aggravated lung inflammation and oxidative stress in LPS-treated WT mice and then resulted in higher mortality. In RAW264.7 cells, exogenous LCN2 treatment also increased inflammation and oxidative stress, whereas LCN2 knockdown markedly diminished these effects. Furthermore, deferiprone inhibited inflammation, oxidative stress, and phagocytosis in RAW264.7 cells with high LCN2 levels, as well as LPS-induced acute lung injury in WT and LCN2 KO mice. Thus, these findings suggest that LCN2 plays a key role in inflammation and oxidative stress following acute lung injury and that LCN2 is a potential therapeutic target for pneumonia or acute lung injury.

Iron Dyshomeostasis in COVID-19: Biomarkers Reveal a Functional Link to 5-Lipoxygenase Activation

Coronavirus disease 2019 (COVID-19) is characterized by a broad spectrum of clinical symptoms. After acute infection, some subjects develop a post-COVID-19 syndrome known as long-COVID. This study aims to recognize the molecular and functional mechanisms that occur in COVID-19 and long-COVID patients and identify useful biomarkers for the management of patients with COVID-19 and long-COVID. Here, we profiled the response to COVID-19 by performing a proteomic analysis of lymphocytes isolated from patients. We identified significant changes in proteins involved in iron metabolism using different biochemical analyses, considering ceruloplasmin (Cp), transferrin (Tf), hemopexin (HPX), lipocalin 2 (LCN2), and superoxide dismutase 1 (SOD1). Moreover, our results show an activation of 5-lipoxygenase (5-LOX) in COVID-19 and in long-COVID possibly through an iron-dependent post-translational mechanism. Furthermore, this work defines leukotriene B4 (LTB4) and lipocalin 2 (LCN2) as possible markers of COVID-19 and long-COVID and suggests novel opportunities for prevention and treatment.

The role of lipocalin 2 in brain injury and recovery after ischemic and hemorrhagic stroke

Ischemic and hemorrhagic stroke (including intracerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage) is the dominating cause of disability and death worldwide. Neuroinflammation, blood–brain barrier (BBB) disruption, neuronal death are the main pathological progress, which eventually causes brain injury. Increasing evidence indicated that lipocalin 2 (LCN2), a 25k-Da acute phase protein from the lipocalin superfamily, significantly increased immediately after the stroke and played a vital role in these events. Meanwhile, there exists a close relationship between LCN2 levels and the worse clinical outcome of patients with stroke. Further research revealed that LCN2 elimination is associated with reduced immune infiltrates, infarct volume, brain edema, BBB leakage, neuronal death, and neurological deficits. However, some studies revealed that LCN2 might also act as a beneficial factor in ischemic stroke. Nevertheless, the specific mechanism of LCN2 and its primary receptors (24p3R and megalin) involving in brain injury remains unclear. Therefore, it is necessary to investigate the mechanism of LCN2 induced brain damage after stroke. This review focuses on the role of LCN2 and its receptors in brain injury and aiming to find out possible therapeutic targets to reduce brain damage following stroke.

Lipocalin-2 is an essential component of the innate immune response to Acinetobacter baumannii infection

Acinetobacter baumannii is an opportunistic pathogen and an emerging global health threat. Within healthcare settings, major presentations of A. baumannii include bloodstream infections and ventilator-associated pneumonia. The increased prevalence of ventilated patients during the COVID-19 pandemic has led to a rise in secondary bacterial pneumonia caused by multidrug resistant (MDR) A. baumannii. Additionally, due to its MDR status and the lack of antimicrobial drugs in the development pipeline, the World Health Organization has designated carbapenem-resistant A. baumannii to be its priority critical pathogen for the development of novel therapeutics. To better inform the design of new treatment options, a comprehensive understanding of how the host contains A. baumannii infection is required. Here, we investigate the innate immune response to A. baumannii by assessing the impact of infection on host gene expression using NanoString technology. The transcriptional profile observed in the A. baumannii infected host is characteristic of Gram-negative bacteremia and reveals expression patterns consistent with the induction of nutritional immunity, a process by which the host exploits the availability of essential nutrient metals to curtail bacterial proliferation. The gene encoding for lipocalin-2 (Lcn2), a siderophore sequestering protein, was the most highly upregulated during A. baumannii bacteremia, of the targets assessed, and corresponds to robust LCN2 expression in tissues. Lcn2^-/- mice exhibited distinct organ-specific gene expression changes including increased transcription of genes involved in metal sequestration, such as S100A8 and S100A9, suggesting a potential compensatory mechanism to perturbed metal homeostasis. In vitro, LCN2 inhibits the iron-dependent growth of A. baumannii and induces iron-regulated gene expression. To elucidate the role of LCN2 in infection, WT and Lcn2^-/- mice were infected with A. baumannii using both bacteremia and pneumonia models. LCN2 was not required to control bacterial growth during bacteremia but was protective against mortality. In contrast, during pneumonia Lcn2^-/- mice had increased bacterial burdens in all organs evaluated, suggesting that LCN2 plays an important role in inhibiting the survival and dissemination of A. baumannii. The control of A. baumannii infection by LCN2 is likely multifactorial, and our results suggest that impairment of iron acquisition by the pathogen is a contributing factor. Modulation of LCN2 expression or modifying the structure of LCN2 to expand upon its ability to sequester siderophores may thus represent feasible avenues for therapeutic development against this pathogen.

A lack of therapeutic options has prompted the World Health Organization to designate multidrug-resistant Acinetobacter baumannii as its priority critical pathogen for research into new treatment strategies. The mechanisms employed by A. baumannii to cause disease and the host tactics exercised to constrain infection are not fully understood. Here, we further characterize the innate immune response to A. baumannii infection. We identify nutritional immunity, a process where the availability of nutrient metals is exploited to restrain bacterial growth, as being induced during infection. The gene encoding for lipocalin-2 (Lcn2), a protein that can impede iron uptake by bacteria, is highly upregulated in infected mice, and corresponds to robust LCN2 detection in the tissues. We find that LCN2 is crucial to reducing mortality from A. baumannii bacteremia and inhibits dissemination of the pathogen during pneumonia. In wild-type and Lcn2-deficient mice, broader transcriptional profiling reveals expression patterns consistent with the known response to Gram-negative bacteremia. Although the role of LCN2 in infection is likely multifactorial, we find its antimicrobial effects are at least partly exerted by impairing iron acquisition by A. baumannii. Facets of nutritional immunity, such as LCN2, may be exploited as novel therapeutics in combating A. baumannii infection.

A zero-sum game or an interactive frame? Iron competition between bacteria and humans in infection war

ABSTRACT

Iron is an essential trace element for both humans and bacteria. It plays a vital role in life, such as in redox reactions and electron transport. Strict regulatory mechanisms are necessary to maintain iron homeostasis because both excess and insufficient iron are harmful to life. Competition for iron is a war between humans and bacteria. To grow, reproduce, colonize, and successfully cause infection, pathogens have evolved various mechanisms for iron uptake from humans, principally Fe 3+ -siderophore and Fe 2+ -heme transport systems. Humans have many innate immune mechanisms that regulate the distribution of iron and inhibit bacterial iron uptake to help resist bacterial invasion and colonization. Meanwhile, researchers have invented detection test strips and coupled antibiotics with siderophores to create tools that take advantage of this battle for iron, to help eliminate pathogens. In this review, we summarize bacterial and human iron metabolism, competition for iron between humans and bacteria, siderophore sensors, antibiotics coupled with siderophores, and related phenomena. We also discuss how competition for iron can be used for diagnosis and treatment of infection in the future.

Escherichia coli 0157:H7 virulence factors and the ruminant reservoir

PURPOSE OF REVIEW

This review updates recent findings about Escherichia coli O157:H7 virulence factors and its bovine reservoir. This Shiga toxin (Stx)-producing E. coli belongs to the Enterohemorrhagic E. coli (EHEC) pathotype causing hemorrhagic colitis. Its low infectious dose makes it an efficient, severe, foodborne pathogen. Although EHEC remains in the intestine, Stx can translocate systemically and is cytotoxic to microvascular endothelial cells, especially in the kidney and brain. Disease can progress to life-threatening hemolytic uremic syndrome (HUS) with hemolytic anemia, acute kidney failure, and thrombocytopenia. Young children, the immunocompromised, and the elderly are at the highest risk for HUS. Healthy ruminants are the major reservoir of EHEC and cattle are the primary source of human exposure.

RECENT FINDINGS

Advances in understanding E. coli O157:H7 pathogenesis include molecular mechanisms of virulence, bacterial adherence, type three secretion effectors, intestinal microbiome, inflammation, and reservoir maintenance.

SUMMARY

Many aspects of E. coli O157:H7 disease remain unclear and include the role of the human and bovine intestinal microbiomes in infection. Therapeutic strategies involve controlling inflammatory responses and/or intestinal barrier function. Finally, elimination/reduction of E. coli O157:H7 in cattle using CRISPR-engineered conjugative bacterial plasmids and/or on-farm management likely hold solutions to reduce infections and increase food safety/security.

Interplay Between the Immune and Endocrine Systems in the Lung: Implications for TB Susceptibility

The role of the endocrine system on the immune response, especially in the lung, remains poorly understood. Hormones play a crucial role in the development, homeostasis, metabolism, and response to the environment of cells and tissues. Major infectious and metabolic diseases, such as tuberculosis and diabetes, continue to converge, necessitating the development of a clearer understanding of the immune and endocrine interactions that occur in the lung. Research in bacterial respiratory infections is at a critical point, where the limitations in identifying and developing antibiotics is becoming more profound. Hormone receptors on alveolar and immune cells may provide a plethora of targets for host-directed therapy. This review discusses the interactions between the immune and endocrine systems in the lung. We describe hormone receptors currently identified in the lungs, focusing on the effect hormones have on the pulmonary immune response. Altered endocrine responses in the lung affect the balance between pro- and anti-inflammatory immune responses and play a role in the response to infection in the lung. While some hormones, such as leptin, resistin and lipocalin-2 promote pro-inflammatory responses and immune cell infiltration, others including adiponectin and ghrelin reduce inflammation and promote anti-inflammatory cell responses. Furthermore, type 2 diabetes as a major endocrine disease presents with altered immune responses leading to susceptibility to lung infections, such as tuberculosis. A better understanding of these interactions will expand our knowledge of the mechanisms at play in susceptibility to infectious diseases and may reveal opportunities for the development of host-directed therapies.

Lipocalin 2 Participates in the Epidermal Differentiation and Inflammatory Processes of Psoriasis

As a multifunctional cytokine, lipocalin 2 is weakly expressed in skin and serum under normal conditions. However, it is over-expressed by neutrophils and keratinocytes in the skin lesions and sera in several skin diseases. Recent studies demonstrated that lipocalin 2 participates in the pathogenesis of psoriasis by exerting versatile effects on skin resident cells and infiltrating immune cells. Lipocalin 2 inhibits the synthesis of keratin, involucrin, and loricrin in keratinocytes, leading to epidermal parakeratosis via the Tcf7l1-lipocalin 2 signaling axis. It also recruits inflammatory cells such as T cells and neutrophils into skin lesions via the IL-23/IL17, p38-MAPK, and ERK-1/2 signaling pathways. Additionally, lipocalin 2 and other cytokines such as IL-17 have the synergetic effects on skin cells. The neutralization of lipocalin 2 or relevant cytokines can alleviate psoriasis, verifying that lipocalin 2 is an effective interfering target for psoriasis. In this review, we summarize the roles of lipocalin 2 in the processes of psoriatic inflammation and the promising therapeutic strategies based on lipocalin 2-related molecules.

Antimicrobial production by perifollicular dermal preadipocytes is essential to the pathophysiology of acne

Innate immune defense against deep tissue infection by Staphylococcus aureus is orchestrated by fibroblasts that become antimicrobial when triggered to differentiate into adipocytes. However, the role of this process in noninfectious human diseases is unknown. To investigate the potential role of adipogenesis by dermal fibroblasts in acne, a disorder triggered by Cutibacterium acnes, single-cell RNA sequencing was performed on human acne lesions and mouse skin challenged by C. acnes. A transcriptome consistent with adipogenesis was observed within specific fibroblast subsets from human acne and mouse skin lesions infected with C. acnes. Perifollicular dermal preadipocytes in human acne and mouse skin lesions showed colocalization of PREF1, an early marker of adipogenesis, and cathelicidin (Camp), an antimicrobial peptide. This capacity of C. acnes to specifically trigger production of cathelicidin in preadipocytes was dependent on TLR2. Treatment of wild-type mice with retinoic acid (RA) suppressed the capacity of C. acnes to form acne-like lesions, inhibited adipogenesis, and enhanced cathelicidin expression in preadipocytes, but lesions were unresponsive in Camp^-/- mice, despite the anti-adipogenic action of RA. Analysis of inflamed skin of acne patients after retinoid treatment also showed enhanced induction of cathelicidin, a previously unknown beneficial effect of retinoids in difficult-to-treat acne. Overall, these data provide evidence that adipogenic fibroblasts are a critical component of the pathogenesis of acne and represent a potential target for therapy.

Application of Stem Cell-Derived Extracellular Vesicles as an Innovative Theranostics in Microbial Diseases

Extracellular vesicles (EVs), as nano-/micro-scale vehicles, are membranous particles containing various cargoes including peptides, proteins, different types of RNAs and other nucleic acids, and lipids. These vesicles are produced by all cell types, in which stem cells are a potent source for them. Stem cell-derived EVs could be promising platforms for treatment of infectious diseases and early diagnosis. Infectious diseases are responsible for more than 11 million deaths annually. Highly transmissible nature of some microbes, such as newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), drives researcher's interest to set up different strategies to develop novel therapeutic strategies. Recently, EVs-based diagnostic and therapeutic approaches have been launched and gaining momentum very fast. The efficiency of stem cell-derived EVs on treatment of clinical complications of different viruses and bacteria, such as SARS-CoV-2, hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), Staphylococcus aureus, Escherichia coli has been demonstrated. On the other hand, microbial pathogens are able to incorporate their components into their EVs. The microbe-derived EVs have different physiological and pathological impacts on the other organisms. In this review, we briefly discussed biogenesis and the fate of EVs. Then, EV-based therapy was described and recent developments in understanding the potential application of stem cell-derived EVs on pathogenic microorganisms were recapitulated. Furthermore, the mechanisms by which EVs were exploited to fight against infectious diseases were highlighted. Finally, the deriver challenges in translation of stem cell-derived EVs into the clinical arena were explored.

Chronic mineral oil administration increases hepatic inflammation in wild type mice compared to lipocalin 2 null mice

Lipocalin 2 (LCN2), an acute-phase protein produced during acute liver injury, plays an important role in the innate immune response against bacterial infection via iron scavenging. LCN2 further influences neutrophil development and physiology leading to increased inflammatory responses. We investigated the roles of LCN2 in chronic inflammation and fibrosis, using repeated carbon tetrachloride (CCl4) in mineral-oil injection. Surprisingly, mice treated with the mineral oil vehicle alone showed liver inflammation, evidenced by neutrophil and monocyte-macrophage infiltration. Fluorescence-activated cell sorting (FACS) of isolated liver leukocytes showed significantly high CD45+ leukocyte concentrations in CCl4 mice, but no difference of Ly6G+ neutrophils between mineral oil and CCl4 application. Liver CD11b+ F4/80+ cells counted higher in CCl4 mice, but the proportions of Gr1high, an indicator of inflammation, were significantly higher in mineral oil groups. Liver myeloperoxidase (MPO), expressed in neutrophils and monocytes, showed higher levels in wild type mice compared to Lcn2-/- in both mineral-oil and CCl4 treated groups. Hepatic and serum LCN2 levels were remarkably higher in the mineral oil-injected wild type group compared to the CCl4. Wild type animals receiving mineral oil showed significantly higher inflammatory cytokine- and chemokine mRNA levels compared to Lcn2-/- mice, with no differences in the CCl4 treated groups. RNA sequencing (RNA-Seq) confirmed significant downregulation of gene sets involved in myeloid cell activation and immune responses in Lcn2 null mice receiving chronic mineral oil versus wild-type. We observed significant upregulation of gene sets and proteins involved in cell cycle DNA replication, with downregulation of collagen-containing extracellular matrix genes in Lcn2-/- mice receiving CCl4, compared to the wild type. Consequently, the wild type mice developed slightly more liver fibrosis compared to Lcn2-/- mice, evidenced by higher levels of collagen type I in the CCl4 groups and no liver fibrosis in mineral oil-treated mice. Our findings indicate that serum and hepatic LCN2 levels correlate with hepatic inflammation rather than fibrosis.

Lipocalin 2 Is a Regulator During Macrophage Polarization Induced by Soluble Worm Antigens

Caused by schistosomes, the human schistosomiasis is a tropical zoonotic parasitic disease. Pathologically, it occurs most often in the intestines and the liver, the sites of Schistosoma japonicum egg accumulation. The parasites' produced eggs cause the main pathology in patients. Deposited parasite eggs in the liver induce the production of multiple cytokines that mediate the immune response, which in turn leads to granulomatous responses and liver fibrosis. These impact the hosts' quality of life and health status, resulting in severe morbidity and even mortality. In this study, differentially expressed genes (DEGs) between ordinary samples and three 6- week infected mice were mined from microarray analysis based on the limma package. In total, we excavated the differential expression LCN2 was exhibited high expressions profile in GSE59276, GSE61376 demonstrated the result. Furthermore, CIBERSORT suggested detailed analysis of the immune subtype distribution pattern. In vivo experiments like real-time quantitative PCR, immunohistochemical (IHC) staining, and immunofluorescence (IF) demonstrated the expressions of LCN2 was significantly upregulated in S. japonicum-infected mice liver tissues and located in macrophages. Previous studies have shown that macrophages act as the first line of defense during schistosome infection and are an important part of liver granuloma. We used S. japonicum soluble worm antigens (SWA) to induce RAW264.7 cells to construct an in vitro inflammatory model. The current study aimed to investigate whether the NF-κB signaling network is involved in LCN2 upregulation induced by SWA and whether LCN2 can promote M1 polarization of macrophages under SWA treatment. Our research work suggests that LCN2 is significant in the development of early infection caused by S. japonicum and is of great value for further exploration. Collectively, the findings indicated that SWA promoted the expression of LCN2 and promoted M1 polarization of macrophages via the upregulation of NF-κB signaling pathway. Our findings demonstrate that NF-κB/LCN2 is necessary for migration and phagocytosis of M1 macrophages in response to SWA infection. Our study highlights the essential role of NF-κB/LCN2 in early innate immune response to infection.

Epigenetic induction of lipocalin 2 expression drives acquired resistance to 5-fluorouracil in colorectal cancer through integrin β3/SRC pathway

The therapeutic efficacy of 5-fluorouracil (5-FU) is often reduced by the development of drug resistance. We observed significant upregulation of lipocalin 2 (LCN2) expression in a newly established 5-FU-resistant colorectal cancer (CRC) cell line. In this study, we demonstrated that 5-FU-treated CRC cells developed resistance through LCN2 upregulation caused by LCN2 promoter demethylation and that feedback between LCN2 and NF-κB further amplified LCN2 expression. High LCN2 expression was associated with poor prognosis in CRC patients. LCN2 attenuated the cytotoxicity of 5-FU by activating the SRC/AKT/ERK-mediated antiapoptotic program. Mechanistically, the LCN2-integrin β3 interaction enhanced integrin β3 stability, thus recruiting SRC to the cytomembrane for autoactivation, leading to downstream AKT/ERK cascade activation. Targeting LCN2 or SRC compromised the growth of CRC cells with LCN2-induced 5-FU resistance. Our findings demonstrate a novel mechanism of acquired resistance to 5-FU, suggesting that LCN2 can be used as a biomarker and/or therapeutic target for advanced CRC.

Lipocalin-2 Alleviates LPS-Induced Inflammation Through Alteration of Macrophage Properties

Purpose

Lipocalin-2 (Lcn2) is an acute-phase protein and elevated in several inflammatory diseases. This study aimed to determine whether Lcn2 alleviates inflammation and explore the underlying cellular mechanisms.

Methods

C57BL/6 Lcn2-deficient (Lcn2^−/-) male mice were intraperitoneally injected with lipopolysaccharide (LPS) to build systemic inflammation model. The inflammatory processes were investigated. The morphology of villi was measured by scanning electron microscopy (SEM). The levels of inflammatory factors were detected by ELISA and qPCR analysis. The production of Lcn2 was determined with immunofluorescence staining by confocal microscope. The molecular mechanism of Lcn2 in bone marrow-derived macrophages (BMDMs) was analyzed by mass spectrometry (MS)-based quantitative proteomic analysis.

Results

Compared to wild-type (WT) mice injected with LPS, Lcn2^−/- mice injected with LPS showed increased inflammatory damage in jejunum and ileum, and significantly elevated the levels of multiple pro-inflammatory cytokines. After determining that Lcn2 was mainly located in the cytoplasm of macrophages, we isolated BMDMs from Lcn2^−/- mice to evaluate their function. During LPS challenge, transcripts of pro-inflammatory cytokines were all significantly increased in BMDMs from Lcn2^−/- mice, while those of anti-inflammatory cytokines were significantly decreased when compared with the cytokines in BMDMs from WT mice. A label-free relative quantitation proteomics analysis showed that LPS-treated BMDMs from Lcn2^−/- mice had elevated levels of pro-inflammatory pathways, but reduced phagocytosis and autophagy when compared with LPS-treated BMDMs from WT mice.

Conclusion

These findings demonstrated that Lcn2 was a potent protective factor in response to systemic inflammation and might be an indispensable factor for macrophage functions.

Lipocalin 2 as a link between ageing, risk factor conditions and age-related brain diseases

Chronic (neuro)inflammation plays an important role in many age-related central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease and vascular dementia. Inflammation also characterizes many conditions that form a risk factor for these CNS disorders, such as physical inactivity, obesity and cardiovascular disease. Lipocalin 2 (Lcn2) is an inflammatory protein shown to be involved in different age-related CNS diseases, as well as risk factor conditions thereof. Lcn2 expression is increased in the periphery and the brain in different age-related CNS diseases and also their risk factor conditions. Experimental studies indicate that Lcn2 contributes to various neuropathophysiological processes of age-related CNS diseases, including exacerbated neuroinflammation, cell death and iron dysregulation, which may negatively impact cognitive function. We hypothesize that increased Lcn2 levels as a result of age-related risk factor conditions may sensitize the brain and increase the risk to develop age-related CNS diseases. In this review we first provide a comprehensive overview of the known functions of Lcn2, and its effects in the CNS. Subsequently, this review explores Lcn2 as a potential (neuro)inflammatory link between different risk factor conditions and the development of age-related CNS disorders. Altogether, evidence convincingly indicates Lcn2 as a key constituent in ageing and age-related brain diseases.

Functions and potential of lipocalin-2 as fecal biomarker for acute gastrointestinal infections (review of literature)

Despite the visible progress in reducing morbidity and mortality from intestinal infections and acute diarrhea associated with them, especially in childhood, the problem of their diagnosis and treatment remains relevant. The article discusses the structure, function and application of lipocalin-2 in infectious diseases as a non-invasive biomarker of bacterial inflammation in the intestine.

Serial Lipocalin 2 and Oncostatin M levels reflect inflammation status and treatment response in axial spondyloarthritis

Background

Informative serum biomarkers for monitoring inflammatory activity and treatment responses in axial spondyloarthritis (axSpA) are lacking. We assessed whether Lipocalin 2 (LCN2) and Oncostatin M (OSM), both having roles in inflammation and bone remodeling, may accurately reflect chronic joint inflammation and treatment response in axSpA. Previous reports in animal models showed involvement of LCN2 and OSM in joint/gut inflammation. We asked whether they also play a role in human axSpA.

Methods

We analyzed a longitudinal observational axSpA cohort (286 patients) with yearly clinical assessments and concurrent measurements of serum LCN2 and OSM (1204 serum samples) for a mean of 4 years. Biomarker levels were correlated with MRI scoring and treatment response.

Results

Persistent and transient elevation of LCN2 and OSM were observed in axSpA patients. Persistent elevation of LCN2 or OSM, but not CRP, correlated with sacroiliac joint (SIJ) MRI SPARCC scores (Pearson’s correlation p = 0.0005 and 0.005 for LCN2 and OSM respectively), suggesting that LCN2/OSM outperforms CRP as reflective of SIJ inflammation. We observed both concordant and discordant patterns of LCN2 and OSM in relationship to back pain, the cardinal clinical symptom in axSpA. Twenty-six percent (73/286) of the patients remained both clinically and serologically active (CASA). Sixty percent (173/286) of the patients became clinically quiescent, with back pain resolved, but 53% (92/173) of them were serologically active (CQSA), indicating that pain control may not indicate control of joint inflammation, as reflected by positive MRI imaging of SIJ. With respect to treatment responses, transient elevation of LCN2 or OSM over time was predictive of better response to all treatments.

Conclusion

In axSpA, persistent LCN2 and/or OSM elevation reflects chronic SIJ inflammation and suboptimal treatment response. In our cohort, half of the currently deemed clinically quiescent patients with back pain resolved continued to demonstrate chronic joint inflammation. LCN2 and OSM profiling outperforms CRP as a predictive measure and provides an objective assessment of chronic local inflammation in axSpA patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02521-y.

Ironing Out the Details: How Iron Orchestrates Macrophage Polarization

Iron fine-tunes innate immune responses, including macrophage inflammation. In this review, we summarize the current understanding about the iron in dictating macrophage polarization. Mechanistically, iron orchestrates macrophage polarization through several aspects, including cellular signaling, cellular metabolism, and epigenetic regulation. Therefore, iron modulates the development and progression of multiple macrophage-associated diseases, such as cancer, atherosclerosis, and liver diseases. Collectively, this review highlights the crucial role of iron for macrophage polarization, and indicates the potential application of iron supplementation as an adjuvant therapy in different inflammatory disorders relative to the balance of macrophage polarization.

Galectin-3 plays an important pro-inflammatory role in A. fumigatus keratitis by recruiting neutrophils and activating p38 in neutrophils

PURPOSE

To determine the role of galectin-3 (Gal-3) in cornea infected by Aspergillus fumigatus (A. fumigatus).

METHODS

Gal-3 was tested in normal and infected corneas of C57BL/6 mice. Mice corneas were pretreated with or without rmGal-3 or Gal-3 siRNA and infected with A. fumigatus. Recombinant mouse (rm) Gal-3 stimulated polymorphonuclear neutrophilic leukocytes (PMNs). PMNs were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of Gal-3 siRNA. Disease severity was documented by clinical score and photographs with a slit lamp. PCR, Western blot, and ELISA tested expression of Gal-3, interleukin (IL)-1β, IL-6, macrophage inflammatory protein 2 (MIP-2) and p-p38. PMNs infiltration was assessed by flow cytometry and myeloperoxidase (MPO) assay.

RESULTS

Gal-3 expression was significantly elevated by A. fumigatus in mice corneas. rmGal-3 treatment increased clinical scores, PMNs infiltration, and cytokines expression, which were decreased by Gal-3 siRNA treatment. In PMNs, Gal-3 expression was also significantly increased by A. fumigatus. The rmGal-3 treatment upregulated proinflammatory cytokines secretion and p-p38 expression, which was significantly inhibited by Gal-3 siRNA.

CONCLUSION

These data proved that A. fumigatus increased Gal-3 expression and elevated disease clinical scores, PMNs infiltration and cytokines expression through Gal-3. In PMNs, A. fumigatus upregulated IL-1β and IL-6 secretion through the Gal-3 / p38 pathway.

Cyclic GMP-AMP promotes the acute phase response and protects against Escherichia coli infection in mice

The acute phase response, as a component of the innate immune system, is part of the first line of defense against invading pathogens. The Stimulator of Interferon Genes (STING) pathway initiates innate immune responses upon recognition of exogenous bacterial and viral DNA. However, whether STING signaling pathway plays any roles in regulating acute phase response during bacterial infection remains unknown. In this study, we used STING-deficient (Tmem173^gt) and wildtype mice to investigate acute phase responses to bacterial infection (Escherichia coli, E. coli) and test the effect of exogenous cyclic GMP-AMP (cGAMP, a STING agonist) treatment. Bacterial infection of STING-deficient mice resulted in an increase in mortality and bacterial dissemination. Also, inflammation-induced acute phase response was drastically reduced in STING-deficient mice, showing significant reduction in expression of cytokine TNF-α and acute phase proteins. In contrast, exogenous cGAMP treatment enhanced inflammation-induced acute phase response by increasing the expression of TNF-α and acute phase proteins. Also, cGAMP accelerated bacterial clearance and improved survival rate of wildtype mice, but not STING-deficient mice. Interestingly, cGAMP treatment mitigated bacterial infection induced liver injury in both wildtype and STING-deficient mice. Further in vitro evidence showed that cGAMP treatment retarded TNF-α-mediated hepatocyte apoptosis, potentially accelerating autophagy. Taken together, our results indicated that cGAMP/STING signaling pathway is critical for organism to initiate blood-borne innate immune-responses to defend bacterial infection, and cGAMP is envisaged as a drug candidate for further clinical trial.

Higher Aqueous Levels of Resistin and Lipocalin-2 Indicated Worse Visual Improvement following anti-VEGF Therapy in Patients with Retinal Vein Occlusion

PURPOSE

The aim of this study was to investigate the aqueous humor levels of elastase-2, lactoferrin, lipocalin-2 (LCN-2), resistin, and thrombospondin-1 (TSP-1) in patients with retinal vein occlusion (RVO) and their relationship with visual prognosis following intravitreal anti-vascular endothelial growth factor (VEGF) therapy.

MATERIALS AND METHODS

52 RVO patients (23 cases of central retinal vein occlusion (CRVO) and 29 cases of branch retinal vein occlusion (BRVO)) and 20 cases of senile cataract were enrolled in this study. All RVO patients underwent fundus examinations before and 6-8 months after intravitreal anti-VEGF treatment. Five milliliters of blood were collected from RVO patients before treatment for the measurement of lipids and coagulation factors. Sixty microliters of aqueous humor were collected during intravitreal injection of anti-VEGF or during cataract surgery. The levels of elastase-2, lactoferrin, LCN-2, resistin, and TSP-1 in aqueous humor were determined by Luminex xMAP multiple analysis.

RESULTS

The aqueous levels of resistin and LCN-2 were significantly higher but the level of TSP-1 was significantly lower in RVO patients compared to controls. Further, sub-group analysis showed that CRVO patients had significantly higher levels of resistin and LCN-2 than controls. The aqueous levels of resistin and LCN-2 were negatively correlated with visual improvement following anti-VEGF therapy in CRVO but not in BRVO patients. Visual improvement in RVO patients was not associated with blood lipid levels or any of the coagulation factors.

CONCLUSION

CRVO patients had significantly higher aqueous levels of resistin and LCN-2, which negatively impacted on visual improvement after anti-VEGF therapy.

Subtilase cytotoxin induces a novel form of Lipocalin 2, which promotes Shiga-toxigenic Escherichia coli survival

Shiga-toxigenic Escherichia coli (STEC) infection causes severe bloody diarrhea, renal failure, and hemolytic uremic syndrome. Recent studies showed global increases in Locus for Enterocyte Effacement (LEE)-negative STEC infection. Some LEE-negative STEC produce Subtilase cytotoxin (SubAB), which cleaves endoplasmic reticulum (ER) chaperone protein BiP, inducing ER stress and apoptotic cell death. In this study, we report that SubAB induces expression of a novel form of Lipocalin-2 (LCN2), and describe its biological activity and effects on apoptotic cell death. SubAB induced expression of a novel LCN2, which was regulated by PRKR-like endoplasmic reticulum kinase via the C/EBP homologous protein pathway. SubAB-induced novel-sized LCN2 was not secreted into the culture supernatant. Increased intracellular iron level by addition of holo-transferrin or FeCl₃ suppressed SubAB-induced PARP cleavage. Normal-sized FLAG-tagged LCN2 suppressed STEC growth, but this effect was not seen in the presence of SubAB- or tunicamycin-induced unglycosylated FLAG-tagged LCN2. Our study demonstrates that SubAB-induced novel-sized LCN2 does not have anti-STEC activity, suggesting that SubAB plays a crucial role in the survival of LEE-negative STEC as well as inducing apoptosis of the host cells.

Iron in infection and immunity

Iron is an essential micronutrient for virtually all living cells. In infectious diseases, both invading pathogens and mammalian cells including those of the immune system require iron to sustain their function, metabolism and proliferation. On the one hand, microbial iron uptake is linked to the virulence of most human pathogens. On the other hand, the sequestration of iron from bacteria and other microorganisms is an efficient strategy of host defense in line with the principles of 'nutritional immunity'. In an acute infection, host-driven iron withdrawal inhibits the growth of pathogens. Chronic immune activation due to persistent infection, autoimmune disease or malignancy however, sequesters iron not only from infectious agents, autoreactive lymphocytes and neoplastic cells but also from erythroid progenitors. This is one of the key mechanisms which collectively result in the anemia of chronic inflammation. In this review, we highlight the most important interconnections between iron metabolism and immunity, focusing on host defense against relevant infections and on the clinical consequences of anemia of inflammation.

Does an Apple a Day Also Keep the Microbes Away? The Interplay Between Diet, Microbiota, and Host Defense Peptides at the Intestinal Mucosal Barrier

A crucial mechanism of intestinal defense includes the production and secretion of host defense peptides (HDPs). HDPs control pathogens and commensals at the intestinal interface by direct killing, by sequestering vital ions, or by causing bacterial cells to aggregate in the mucus layer. Accordingly, the combined activity of various HDPs neutralizes gut bacteria before reaching the mucosa and thus helps to maintain the homeostatic balance between the host and its microbes at the mucosal barrier. Defects in the mucosal barrier have been associated with various diseases that are on the rise in the Western world. These include metabolic diseases, such as obesity and type 2 diabetes, and inflammatory intestinal disorders, including ulcerative colitis and Crohn's disease, the two major entities of inflammatory bowel disease. While the etiology of these diseases is multifactorial, highly processed Western-style diet (WSD) that is rich in carbohydrates and fat and low in dietary fiber content, is considered to be a contributing lifestyle factor. As such, WSD does not only profoundly affect the resident microbes in the intestine, but can also directly alter HDP function, thereby potentially contributing to intestinal mucosal barrier dysfunction. In this review we aim to decipher the complex interaction between diet, microbiota, and HDPs. We discuss how HDP expression can be modulated by specific microbes and their metabolites as well as by dietary factors, including fibers, lipids, polyphenols and vitamins. We identify several dietary compounds that lead to reduced HDP function, but also factors that stimulate HDP production in the intestine. Furthermore, we argue that the effect of HDPs against commensal bacteria has been understudied when compared to pathogens, and that local environmental conditions also need to be considered. In addition, we discuss the known molecular mechanisms behind HDP modulation. We believe that a better understanding of the diet-microbiota-HDP interdependence will provide insights into factors underlying modern diseases and will help to identify potential dietary interventions or probiotic supplementation that can promote HDP-mediated intestinal barrier function in the Western gut.

Diabetes-Mediated Toxicity Resulted in the Expression of CD80 and CD86 on Neutrophils after Delayed Wound Healing in Male Rats

Background

Polymorphonuclear neutrophils (PMNs) play an essential role in the innate immune response, and their number increases after prolonged inflammatory diabetic wounds and prolonged wounds in older rats. The expression of CD80 and CD86 on PMNs confirms their participation in acquired immunity, wherein these molecules are involved in antigen presentation.

Materials and Methods

We investigated CD80 and CD86 expression on PMNs by flow cytometry and analyzed the mRNA expression of neutrophil chemoattractants macrophage inflammatory protein-2 (MIP-2) and MIP-1α by real-time polymerase chain reaction (PCR) in diabetic wound, which was healed by a camel milk peptide (CMP). The animals were allocated to the following wounded groups: control, diabetic (DM), and diabetic treated with CMP (DM-CMP).

Results

Alkaline phosphatase, gamma-glutamyl transpeptidase, and lactate dehydrogenase levels were elevated in DM rats but decreased in peptide-treated rats. The expression of CD80 and CD86 was significantly higher in DM rats with prolonged wounds than in control rats. The expression of both markers was restored to normal levels in diabetic rats treated with CMP. RT-PCR analysis revealed the upregulation in MIP-2 mRNA expression in DM rats. However, neutrophil number at wounded sites of DM rats declined at day 1 after wounding as compared to that in control rats. MIP-2 mRNA expression and neutrophil number were restored in CMP-treated diabetic rats.

Conclusion

Prolonged wound stress induced toxicity in DM rats and significantly increased the expression of CD80 and CD86 on PMNs. CMP peptide ameliorated the levels of toxicity markers, CD80 and CD86, and chemoattractant molecules in diabetic rats.