Recruitment Of Innate Immune Cells Research Articles

X-Linked Immunodeficient Mice With No Functional Bruton's Tyrosine Kinase Are Protected From Sepsis-Induced Multiple Organ Failure.

We previously reported the Bruton's tyrosine kinase (BTK) inhibitors ibrutinib and acalabrutinib improve outcomes in a mouse model of polymicrobial sepsis. Now we show that genetic deficiency of the BTK gene alone in Xid mice confers protection against cardiac, renal, and liver injury in polymicrobial sepsis and reduces hyperimmune stimulation (“cytokine storm”) induced by an overwhelming bacterial infection. Protection is due in part to enhanced bacterial phagocytosis in vivo, changes in lipid metabolism and decreased activation of NF-κB and the NLRP3 inflammasome. The inactivation of BTK leads to reduced innate immune cell recruitment and a phenotypic switch from M1 to M2 macrophages, aiding in the resolution of sepsis. We have also found that BTK expression in humans is increased in the blood of septic non-survivors, while lower expression is associated with survival from sepsis. Importantly no further reduction in organ damage, cytokine production, or changes in plasma metabolites is seen in Xid mice treated with the BTK inhibitor ibrutinib, demonstrating that the protective effects of BTK inhibitors in polymicrobial sepsis are mediated solely by inhibition of BTK and not by off-target effects of this class of drugs.

Treponema denticola stimulates Oncostatin M cytokine release and de novo synthesis in neutrophils and macrophages.

Oncostatin M (OSM) is a pleiotropic cytokine elevated in a number of inflammatory conditions including periodontal disease. OSM is produced by a variety of immune cells and has diverse functionality such as regulation of metabolic processes, cell differentiation, and the inflammatory response to bacterial pathogens. The oral cavity is under constant immune surveillance including complementary neutrophil and macrophage populations, due to a persistent symbiotic bacterial presence. Periodontal disease is characterized by a dysbiotic bacterial community, with an abundance of Treponema denticola. Despite strong associations with severe periodontal disease, the source and mechanism of the release of OSM have not been defined in the oral cavity. We show that OSM protein is elevated in the gingival epithelium and immune cell infiltrate during periodontal disease. Furthermore, salivary and oral neutrophil OSM is elevated in correlation with the presence of T. denticola. In an air pouch infection model, T. denticola stimulated higher levels of OSM than the oral pathogen Porphorymonas gingivalis, despite differential recruitment of innate immune cells suggesting T. denticola has distinct properties to elevate OSM levels. OSM release and transcription were increased in isolated human blood, oral neutrophils, or macrophages exposed to T. denticola in vitro as measured by ELISA, qPCR, and microscopy. Using transcription, translation, and actin polymerization inhibition, we found that T. denticola stimulates both OSM release through degranulation and de novo synthesis in neutrophils and also OSM release and synthesis in macrophages. Differential induction of OSM by T. denticola may promote clinical periodontal disease.

The Aspergillus fumigatus transcription factor RglT is important for gliotoxin biosynthesis and self-protection, and virulence.

Aspergillus fumigatus is an opportunistic fungal pathogen that secretes an array of immune-modulatory molecules, including secondary metabolites (SMs), which contribute to enhancing fungal fitness and growth within the mammalian host. Gliotoxin (GT) is a SM that interferes with the function and recruitment of innate immune cells, which are essential for eliminating A. fumigatus during invasive infections. We identified a C6 Zn cluster-type transcription factor (TF), subsequently named RglT, important for A. fumigatus oxidative stress resistance, GT biosynthesis and self-protection. RglT regulates the expression of several gli genes of the GT biosynthetic gene cluster, including the oxidoreductase-encoding gene gliT, by directly binding to their respective promoter regions. Subsequently, RglT was shown to be important for virulence in a chemotherapeutic murine model of invasive pulmonary aspergillosis (IPA). Homologues of RglT and GliT are present in eurotiomycete and sordariomycete fungi, including the non-GT-producing fungus A. nidulans, where a conservation of function was described. Phylogenetically informed model testing led to an evolutionary scenario in which the GliT-based resistance mechanism is ancestral and RglT-mediated regulation of GliT occurred subsequently. In conclusion, this work describes the function of a previously uncharacterised TF in oxidative stress resistance, GT biosynthesis and self-protection in both GT-producing and non-producing Aspergillus species.

Innate Immune Sensing of Influenza A Virus.

Influenza virus infection triggers host innate immune response by stimulating various pattern recognition receptors (PRRs). Activation of these PRRs leads to the activation of a plethora of signaling pathways, resulting in the production of interferon (IFN) and proinflammatory cytokines, followed by the expression of interferon-stimulated genes (ISGs), the recruitment of innate immune cells, or the activation of programmed cell death. All these antiviral approaches collectively restrict viral replication inside the host. However, influenza virus also engages in multiple mechanisms to subvert the innate immune responses. In this review, we discuss the role of PRRs such as Toll-like receptors (TLRs), Retinoic acid-inducible gene I (RIG-I), NOD-, LRR-, pyrin domain-containing protein 3 (NLRP3), and Z-DNA binding protein 1 (ZBP1) in sensing and restricting influenza viral infection. Further, we also discuss the mechanisms influenza virus utilizes, especially the role of viral non-structure proteins NS1, PB1-F2, and PA-X, to evade the host innate immune responses.

Innate Immune Components that Regulate the Pathogenesis and Resolution of hRSV and hMPV Infections.

The human respiratory syncytial virus (hRSV) and human Metapneumovirus (hMPV) are two of the leading etiological agents of acute lower respiratory tract infections, which constitute the main cause of mortality in infants. However, there are currently approved vaccines for neither hRSV nor hMPV. Moreover, despite the similarity between the pathology caused by both viruses, the immune response elicited by the host is different in each case. In this review, we discuss how dendritic cells, alveolar macrophages, neutrophils, eosinophils, natural killer cells, innate lymphoid cells, and the complement system regulate both pathogenesis and the resolution of hRSV and hMPV infections. The roles that these cells play during infections by either of these viruses will help us to better understand the illnesses they cause. We also discuss several controversial findings, relative to some of these innate immune components. To better understand the inflammation in the lungs, the role of the respiratory epithelium in the recruitment of innate immune cells is briefly discussed. Finally, we review the main prophylactic strategies and current vaccine candidates against both hRSV and hMPV.

Immune checkpoint inhibitors reverse tolerogenic mechanisms induced by melanoma targeted radionuclide therapy.

In line with the ongoing phase I trial (NCT03784625) dedicated to melanoma targeted radionuclide therapy (TRT), we explore the interplay between immune system and the melanin ligand [131I]ICF01012 alone or combined with immunotherapy (immune checkpoint inhibitors, ICI) in preclinical models. Here we demonstrate that [131I]ICF01012 induces immunogenic cell death, characterized by a significant increase in cell surface-exposed annexin A1 and calreticulin. Additionally, [131I]ICF01012 increases survival in immunocompetent mice, compared to immunocompromised (29 vs. 24days, p = 0.0374). Flow cytometry and RT-qPCR analyses highlight that [131I]ICF01012 induces adaptive and innate immune cell recruitment in the tumor microenvironment. [131I]ICF01012 combination with ICIs (anti-CTLA-4, anti-PD-1, anti-PD-L1) has shown that tolerance is a main immune escape mechanism, whereas exhaustion is not present after TRT. Furthermore, [131I]ICF01012 and ICI combination has systematically resulted in a prolonged survival (p < 0.0001) compared to TRT alone. Specifically, [131I]ICF01012 + anti-CTLA-4 combination significantly increases survival compared to anti-CTLA-4 alone (41 vs. 26days; p = 0.0011), without toxicity. This work represents the first global characterization of TRT-induced modifications of the antitumor immune response, demonstrating that tolerance is a main immune escape mechanism and that combining TRT and ICI is promising.

Novel paediatric presentation of COVID-19 with ARDS and cytokine storm syndrome without respiratory symptoms.

Novel paediatric presentation of COVID-19 with ARDS and cytokine storm syndrome without respiratory symptoms.

Glucocorticoids Promote the Onset of Acute Experimental Colitis and Cancer by Upregulating mTOR Signaling in Intestinal Epithelial Cells.

The therapeutic effects of glucocorticoids on colitis and colitis-associated cancer are unclear. In this study, we investigated the therapeutic roles of glucocorticoids in acute experimental ulcerative colitis and colitis-associated cancer in mice and their immunoregulatory mechanisms. Murine acute ulcerative colitis was induced by dextran sulfate sodium (DSS) and treated with dexamethasone (Dex) at different doses. Dex significantly exacerbated the onset and severity of DSS-induced colitis and potentiated mucosal inflammatory macrophage and neutrophil infiltration, as well as cytokine production. Furthermore, under inflammatory conditions, the expression of the glucocorticoid receptor (GR) did not change significantly, while mammalian target of rapamycin (mTOR) signaling was higher in colonic epithelial cells than in colonic immune cells. The deletion of mTOR in intestinal epithelial cells, but not that in myeloid immune cells, in mice significantly ameliorated the severe course of colitis caused by Dex, including weight loss, clinical score, colon length, pathological damage, inflammatory cell infiltration and pro-inflammatory cytokine production. These data suggest that mTOR signaling in intestinal epithelial cells, mainly mTORC1, plays a critical role in the Dex-induced exacerbation of acute colitis and colitis-associated cancer. Thus, these pieces of evidence indicate that glucocorticoid-induced mTOR signaling in epithelial cells is required in the early stages of acute ulcerative colitis by modulating the dynamics of innate immune cell recruitment and activation.

The Recruitment of Innate Immune Cells in Liver Diseases: Uncovering the Role of NK Cells and pDC in HCC and NASH

Background/ ObjectiveHepatocellular carcinoma (HCC) is the most common primary malignancy of the liver, with over half a million new cases diagnosed annually worldwide. The fatality of HCC is high despite administration of traditional chemotherapies. In recent years, immunotherapy has become a promising strategy to treat cancer, such as PD‐1/PDL‐1 immune checkpoint blockade. However, the interactions between immune cells and HCC and how immunotherapies work, in vivo, in HCC are still unclear. Non‐alcoholic steatohepatitis (NASH) is an extremely severe form of fatty liver disease and often associated with heavy infiltration of immune cells. Natural Killer (NK) cells and plasmacytoid dendritic cells (pDC) are critical in the innate immune response, and are known for their cytotoxic and interferon producing abilities in response to cancer cells and viral pathogens, respectively. To learn more about the role of innate immunity in liver diseases, we evaluated and characterized pDC and NK cells in HCC and NASH compared to their background hepatic tissue.MethodsNK cells and pDC were isolated from HCC, NASH and hepatic tissue, stained with CD3, CD56, and CXCR6 or BDCA2 and CD123, respectively. The flow cytometry data were acquired and analyzed using FlowJo. E2‐2 immunostain for pDC was performed on FFPE tissue of HCC and NASH.ResultsThe presence of pDC was identified in the lymphoid aggregates of HCC and background cirrhotic areas (6/9 cases). In contrast, in 3 HCC cases, no pDCs were appreciated either in tumors or their backgrounds, including two patients who were smokers and with a history of coronary artery disease. In addition, using flow cytometry we demonstrated that there were more pDC in tumor infiltrating lymphocytes (TILs) of HCC compared to adjacent and distant hepatic tissues (Figure 1). We also found that NK cells isolated from NASH livers do not express CXCR6, a marker for liver‐resident NK cells, in contrast to NK cells obtained from HCC that express high levels of CXCR6 in both tumor and non‐tumor areas. The NK cells from NASH appear similar to those isolated and expanded from peripheral blood as both show low levels of CXCR6 (Figure 2). This suggests that NK cells in NASH originated from the blood and completely outnumber those in the liver, while the NK cells in HCC are residents of the liver.ConclusionsWe have shown that both pDC and NK cells are recruited to the liver in patients with NASH or HCC. More pDC were found in HCC tumors compared to surrounding hepatic tissue. NK cells isolated from NASH do not express CXCR6, a marker for liver‐resident NK cells. This study will further uncover the roles of innate immunity in liver disease and assist in the establishment of novel immunotherapies.A. pDC were present in the lymphoid aggregates of HCC and infiltrating tumor tissue.B. The numbers of pDC in TILs of HCC, adjacent and distant hepatic tissue.Figure 1Reduced expression of CXCR6 in NASH liverFigure 2

Leishmania major degrades murine CXCL1

Leishmaniasis is a global health problem with an estimated report of 2 million new cases every year. Innate immune system plays a central role in controlling L. major infection by initiating a signaling cascade that results in the production of pro‐inflammatory cytokines and recruitment of both innate and adaptive immune cells. Upon infection with L. major, CXCL1 is produced locally and plays an important role in the recruitment of neutrophils and macrophages to the site of infection. Herein, we report that L. major specifically targets murine CXCL1 for degradation and this allows L. major to establish infection in the host. The degradation of CXCL1 is not dependent on host factors because L. major can directly degrade recombinant CXCL1 in a cell‐free system. This degradation is specific to murine CXCL1 as murine CXCL2 as well as human CXCL1 and CXCL2 are not degraded. Using mass spectrometry, we have determined that the unknown L. major protease cleaves at the C‐terminal end of murine CXCL1. Using protease inhibitors our data suggest that the L. major unknown protease is a metalloprotease involved in the direct degradation of CXCL1. Finally, we have tested a peptide spanning the cleavage site which can be used to inhibit L. major protease activity and pathogenesis.Support or Funding InformationThis work was supported by NIH K22, NIEHS P30 and University of Iowa Start‐up funds to P.G.Upon infection with L. major, CXCL1 is produced locally and plays an important role in the recruitment of neutrophils and macrophages to the site of infection. We have identified that a secreted L. major protease cleaves at the C‐terminal end of murine CXCL1. This protease is likely a metalloproteases as Zn2+ chelators inhibit degradation of CXCL1. The degradation of CXCL1 dampens the hosts ability to resolve infection.Figure 1

Tauopathy Analysis in P301S Mouse Model of Alzheimer Disease Immunized With DNA and MVA Poxvirus-Based Vaccines Expressing Human Full-Length 4R2N or 3RC Tau Proteins.

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by a progressive memory loss and cognitive decline that has been associated with an accumulation in the brain of intracellular neurofibrillary tangles (NFTs) formed by hyperphosphorylated tau protein, and extracellular senile plaques formed by β-amyloid peptides. Currently, there is no cure for AD and after the failure of anti β-amyloid therapies, active and passive tau immunotherapeutic approaches have been developed in order to prevent, reduce or ideally reverse the disease. Vaccination is one of the most effective approaches to prevent diseases and poxviruses, particularly modified vaccinia virus Ankara (MVA), are one of the most promising viral vectors used as vaccines against several human diseases. Thus, we present here the generation and characterization of the first MVA vectors expressing human tau genes; the full-length 4R2N tau protein or a 3RC tau fragment containing 3 tubulin-binding motifs and the C-terminal region (termed MVA-Tau4R2N and MVA-Tau3RC, respectively). Both MVA-Tau recombinant viruses efficiently expressed the human tau 4R2N or 3RC proteins in cultured cells, being detected in the cytoplasm of infected cells and co-localized with tubulin. These MVA-Tau vaccines impacted the innate immune responses with a differential recruitment of innate immune cells to the peritoneal cavity of infected mice. However, no tau-specific T cell or humoral immune responses were detected in vaccinated mice. Immunization of transgenic P301S mice, a mouse model for tauopathies, with a DNA-Tau prime/MVA-Tau boost approach showed no significant differences in the hyperphosphorylation of tau, motor capacity and survival rate, when compared to non-vaccinated mice. These findings showed that a well-established and potent protocol of T and B cell activation based on DNA/MVA prime/boost regimens using DNA and MVA vectors expressing tau full-length 4R2N or 3RC proteins is not sufficient to trigger tau-specific T and B cell immune responses and to induce a protective effect against tauopathy in this P301S murine model. In the pursuit of AD vaccines, our results highlight the need for novel optimized tau immunogens and additional modes of presentation of tau protein to the immune system.

Does Dysregulation of Redox State Underpin the Decline of Innate Immunity with Aging?

Significance: Antibacterial defense invokes the innate immune system as a first responder, with neutrophils phagocytozing and forming neutrophil extracellular traps around pathogens in a reactive oxygen species (ROS)-dependent manner. Increased NOX2 activity and mitochondrial ROS production in phagocytic, antigen-presenting cells (APCs) affect local cytokine secretion and proteolysis of antigens for presentation to T cells at the immune synapse. Uncontrolled oxidative post-translational modifications to surface and cytoplasmic proteins in APCs during aging can impair innate immunity. Recent Advances: NOX2 plays a role in the maturation of dendritic cells, but paradoxically NOX2 activity has also been shown to promote viral pathogenicity. Accumulating evidence suggests that a reducing environment is essential to inhibit pathogen proliferation, facilitate antigenic processing in the endosomal lumen, and enable an effective immune synapse between APCs and T cells. This suggests that the kinetics and location of ROS production and reducing potential are important for effective innate immunity. Critical Issues: During aging, innate immune cells are less well able to phagocytoze, kill bacteria/viruses, and process proteins into antigenic peptides-three key steps that are necessary for developing a specific targeted response to protect against future exposure. Aberrant control of ROS production and impaired Nrf2-dependent reducing potential may contribute to age-associated immune decline. Future Directions: Local changes in redox potential may be achieved through adjuvant formulations to improve innate immunity. Further work is needed to understand the timing of delivery for redox modulators to facilitate innate immune cell recruitment, survival, antigen processing and presentation activity without disrupting essential ROS-dependent bacterial killing.

A mouse ear skin model to study the dynamics of innate immune responses against Staphylococcus aureus biofilms

BackgroundStaphylococcus aureus is a human pathogen that is a common cause of nosocomial infections and infections on indwelling medical devices, mainly due to its ability to shift between the planktonic and the biofilm/sessile lifestyle. Biofilm infections present a serious problem in human medicine as they often lead to bacterial persistence and thus to chronic infections. The immune responses elicited by biofilms have been described as specific and ineffective. In the few experiments performed in vivo, the importance of neutrophils and macrophages as a first line of defence against biofilm infections was clearly established. However, the bilateral interactions between biofilms and myeloid cells remain poorly studied and analysis of the dynamic processes at the cellular level in tissues inoculated with biofilm bacteria is still an unexplored field. It is urgent, therefore, to develop biologically sound experimental approaches in vivo designed to extract specific immune signatures from the planktonic and biofilm forms of bacteria.ResultsWe propose an in vivo transgenic mouse model, used in conjunction with intravital confocal microscopy to study the dynamics of host inflammatory responses to bacteria. Culture conditions were created to prepare calibrated inocula of fluorescent planktonic and biofilm forms of bacteria. A confocal imaging acquisition and analysis protocol was then drawn up to study the recruitment of innate immune cells in the skin of LysM-EGFP transgenic mice. Using the mouse ear pinna model, we showed that inflammatory responses to S. aureus can be quantified over time and that the dynamics of innate immune cells after injection of either the planktonic or biofilm form can be characterized. First results showed that the ability of phagocytic cells to infiltrate the injection site and their motility is not the same in planktonic and biofilm forms of bacteria despite the cells being considerably recruited in both cases.ConclusionWe developed a mouse model of infection to compare the dynamics of the inflammatory responses to planktonic and biofilm bacteria at the tissue and cellular levels. The mouse ear pinna model is a powerful imaging system to analyse the mechanisms of biofilm tolerance to immune attacks.

Immune response to fungi in diabetic patients with invasive fungal rhinosinusitis.

This article aims to review the literature regarding the immune response to fungi in diabetic patients with invasive fungal rhinosinusitis. Systematic searches of Medline, EMBASE, and Cochrane Library databases were performed to include articles from 1988 to 2019 which assessed 'immune response to fungi in normal host', 'immune deficiency in diabetes mellitus', or 'immune response to fungi in diabetic patients'. Fungal cell wall activated pattern recognition receptors, resulting in recruitment of innate immune cells and an adaptive immune response. In diabetes mellitus, the expression of class I major histocompatibility complex was reduced. A hyperglycemic state decreased vascular dilation and the formation of neutrophil extracellular traps. The structure of complement was altered with consequent inhibition of complement fixation to bacteria. The balance between complement activation and restriction was broken. Hyperglycemia activated protein kinase C which inhibited neutrophil migration, decreased production of polymorphonuclear cells, decreased chemotaxis and decreased phagocytic activity. Germination and filamentous growth of the fungus within a diabetic host caused angioinvasion, vascular thrombosis and necrosis. Patients with diabetic ketoacidosis had elevated levels of serum iron which regulated endothelial cell damage. Iron and the overexpression of glucose-induced glucose-regulated protein 78 enhanced the susceptibility of endothelial cells to fungi and induced fungal invasion. In summary, associations among the immunopathology of diabetes, the pathophysiology of fungal infections, and the therapeutic outcomes must be considered in clinical practice. In diabetic patients, both the humoral and cellular immune responses of innate and adaptive immune systems were defective. Treatments should aim for the immune function restoration.

Lyophilizable and Multifaceted Toll-like Receptor 7/8 Agonist-Loaded Nanoemulsion for the Reprogramming of Tumor Microenvironments and Enhanced Cancer Immunotherapy.

The low therapeutic efficacy of current cancer immunotherapy is related to nonimmunogenic and immunosuppressive tumor microenvironments (TMEs). To overcome these limitations, both the immune priming of antitumoral lymphocytes and the reprogramming of immunosuppressive factors in TMEs are essential. Here, we suggest a nanoemulsion (NE)-based immunotherapeutic platform that can not only modulate tumor-induced suppression but also induce an effective cell-mediated immune response for T cell proliferation. Multifunctional NEs can be fabricated by integrating the efficacy of NEs as delivery systems and the multifaceted immunomodulation characteristics (i.e., immunostimulation and reprogramming of immunosuppression) of small molecule-based Toll-like receptor 7/8 agonists. Local in situ vaccination of melanoma and cervical tumor models with tumor antigens (protein and peptide) adjuvanted with NE loaded with TLR7/8 agonists [NE (TLR7/8a)] induced the recruitment and activation of innate immune cells, infiltration of lymphocytes, and polarization of tumor-associated M2 macrophages, which resulted in inhibition of tumor growth and prolonged survival in both primary and rechallenged tumor models. Antibody-depletion experiments also suggested that macrophages, type I IFN (IFN-α and IFN-β), CD8+ T cells, and NK1.1+ cells contributed to the antitumor effect of NE (TLR7/8a). The combination of antitumoral lymphocytes and reprogramming of immunosuppressive TMEs induced by NE (TLR7/8a) treatment evoked a synergistic antitumor immune response with immune checkpoint blockade therapy (anti-PD-1 and anti-PD-L1).

Identification of the CXCL12–CXCR4/CXCR7 axis as a potential therapeutic target for immunomodulating macrophage polarization and foreign body response to implanted biomaterials

Host recognition and immune-mediated foreign body response (FBR) to biomaterials can compromise the performance of implanted medical devices. Macrophage participation and polarization play vital roles in regulating the development of FBR; therefore, research is ongoing to use macrophages to regulate FBR. At the implantation site, the chemokine CXC chemokine ligand 12 (CXCL12) is upregulated and mediates the recruitment of innate immune cells (e.g., macrophages and monocytes) that participate in FBR. In this study, polymethyl methacrylate (PMMA) was used to induce FBR in vivo. The results indicated that PMMA induced macrophage M1 polarization, both in vitro and in vivo. The expression of CXC chemokine receptor type 7 (CXCR7), the receptor of CXCL12, was significantly higher on macrophages following PMMA implantation. In contrast, the expression of CXCR4 (another receptor of CXCL12) was significantly lower. The inhibition of CXCR7 and promotion of CXCR4 led to macrophage polarization switching from the M1 to M2 phenotype and prominent restriction of FBR. In terms of mechanism, Western blot results showed that STAT1/3/6, ERK1/2, p38 and NF-κB signaling pathways participated in the complex mechanism by which the CXCL12–CXCR4/CXCR7 axis mediated macrophage polarization. Overall, our results demonstrate that targeting the CXCL12–CXCR4/CXCR7 axis may allow for a more selective method of immunomodulating FBR, improving biomaterial biocompatibility without the need for broad immunosuppression.

Immune‐Informed Mucin Hydrogels Evade Fibrotic Foreign Body Response In Vivo

AbstractThe immune‐mediated foreign body response to biomaterial implants can trigger the formation of insulating fibrotic capsules that can compromise implant function. To address this challenge, the intrinsic bioactivity of the mucin biopolymer, a heavily glycosylated protein that forms the protective mucus gel covering mucosal epithelia, is leveraged. By using a bioorthogonal inverse electron demand Diels–Alder reaction, mucins are crosslinked into implantable hydrogels. It is shown that mucin hydrogels (Muc‐gels) modulate the immune response driving biomaterial‐induced fibrosis. Muc‐gels do not elicit fibrosis 21 days after implantation in the peritoneal cavity of C57Bl/6 mice, whereas medical‐grade alginate hydrogels are covered by fibrous tissues. Further, Muc‐gels dampen the recruitment of innate and adaptive immune cells to the gel and trigger a pattern of very mild activation marked by a noticeably low expression of the fibrosis‐stimulating transforming growth factor beta 1 cytokine. Macrophages recruited to Muc‐gels upregulate the gene expression of the protein inhibitor of activated STAT 1 (PIAS1) and SH2‐containing phosphatase 1 (SHP‐1) cytokine regulatory proteins, which likely contributes to their low cytokine expression profiles. With this advance in mucin materials, an essential tool is provided to better understand mucin bioactivities and to initiate the development of new mucin‐based and mucin‐inspired “immune‐informed” materials for implantable devices subject to fibrotic encapsulation.

Abstract 094: Adaptive Cardiac Remodeling to Chronic Pressure Overload Requires the Expression of Placental Growth Factor in the Spleen to Recruit Reparative Macrophages to the Left Ventricle

Cardiac remodeling is the process established by the left ventricle (LV) to respond to different challenging stimuli. Although immunity has been clearly shown to participate to LV remodeling in myocardial infarction, how immune response participates to hypertensive chronic stress is poorly understood. We found that Placental Growth Factor (PlGF), belonging to the VEGF family, is necessary for adaptive remodeling to pressure overload and modulates the recruitment of innate immune cells in the LV. Here we asked where PlGF does exert its effects: i) directly in the myocardium or ii) by modulating immune organs? As TAC induced PlGF both in cardiac tissue and in the spleen, we devised a strategy to assess the contribution of these two tissues. We generated chimeric mice by spleen transplantation between WT and KO mice, obtaining: 1) WT mice with PlGF KO spleen and 2) PlGF KO mice with WT spleen (EF% 78 ± 0,7), finding that only mice with PlGF expressed in the spleen (EF% 68 ± 1,5) established adaptive remodeling to pressure overload, as assessed by echocardiography (p&lt;0.01). Since in the absence of PlGF we observed a consistent reduction of LV macrophages, we characterized the subsets of innate immune cells by flow cytometry. While WT mice subjected to TAC showed early LV recruitment of non resident CD11b + CD64 + Timd4 - CCR2 low CX 3 CR1 hi macrophages, PlGF KO mice failed to show this response. To investigate the potential relevance of the spleen as reservoir of myeloid cells with adaptive/reparative functions for LV, we induced TAC in splenectomized mice, finding that they didn’t develop adaptive remodeling, exhibiting early HFrEF. To investigate the role of reparative macrophages, that are mostly characterized by the expression of the CX 3 CR1 receptor, and of pro-inflammatory monocytes that express high levels and accumulate through CCR2, we also subjected CCR2 KO and CX 3 CR1 KO mice to TAC. While CCR2 KO behaved similarly to WT mice, CX 3 CR1 KO were unable to establish adaptive remodeling and early developed HFrEF similarly to mice deprived of the spleen and to PlGF KO mice. Overall our results indicate that pressure overload induces PlGF in the spleen as an immunomodulator capable to deploy reparative macrophages that sustain adaptive remodeling of the LV.

The Dark Side of Fibroblasts: Cancer-Associated Fibroblasts as Mediators of Immunosuppression in the Tumor Microenvironment.

Cancer-associated fibroblasts (CAFs) are prominent components of the microenvironment in most types of solid tumors, and were shown to facilitate cancer progression by supporting tumor cell growth, extracellular matrix remodeling, promoting angiogenesis, and by mediating tumor-promoting inflammation. In addition to an inflammatory microenvironment, tumors are characterized by immune evasion and an immunosuppressive milieu. In recent years, CAFs are emerging as central players in immune regulation that shapes the tumor microenvironment. CAFs contribute to immune escape of tumors via multiple mechanisms, including secretion of multiple cytokines and chemokines and reciprocal interactions that mediate the recruitment and functional differentiation of innate and adaptive immune cells. Moreover, CAFs directly abrogate the function of cytotoxic lymphocytes, thus inhibiting killing of tumor cells. In this review, we focus on recent advancements in our understanding of how CAFs drive the recruitment and functional fate of tumor-infiltrating immune cells toward an immunosuppressive microenvironment, and provide outlook on future therapeutic implications that may lead to integration of preclinical findings into the design of novel combination strategies, aimed at impairing the tumor-supportive function of CAFs.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection.

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.