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The innate immune system plays a critical role in the rapid recognition and elimination of pathogens through pattern recognition receptors (PRRs). Among these PRRs are the C-type lectins (CTLs) langerin, mannan-binding lectin (MBL), and surfactant protein D (SP-D), which recognize carbohydrate patterns on pathogens. Each represents proteins from different compartments of the body and employs separate effector mechanisms. We have investigated their interaction with the Gram-positive opportunistic pathogen Staphylococcus aureus , a bacterium whose cell wall contains two key glycopolymers: capsular polysaccharide (CP) and wall teichoic acid (WTA). Using a langerin-expressing cell line and recombinant langerin, MBL, and SP-D, we demonstrated that langerin, MBL, and SP-D all recognize nonencapsulated S . aureus . However, the bacterium may produce CP that effectively shields S. aureus from recognition by all three CTLs. Experiments utilizing mutant S. aureus strains confirmed that WTA is a ligand for MBL, but that langerin likely interacts with an additional unknown ligand. A competition assay revealed that MBL and SP-D inhibit langerin’s interaction with S. aureus , highlighting the intricate redundancy and cooperation within the innate immune system. This study highlights the dynamic interplay of langerin, MBL, and SP-D in recognizing specific surface structures on S. aureus and provides insight into how this pathogen evades innate immune recognition.

Sucralose is a noncaloric artificial sweetener that is widely consumed worldwide and has been associated with alteration in glucose and insulin homeostasis. Unbalance in monocyte subpopulations expressing CD11c and CD206 hallmarks metabolic dysfunction but has not yet been studied in response to sucralose. Our goal was to examine the effect of a single sucralose sip on serum insulin and blood glucose and the percentages of classical, intermediate, and nonclassical monocytes in healthy young adults subjected to an oral glucose tolerance test (OGTT). This study was a randomized, placebo-controlled clinical trial. Volunteers randomly received 60 mL water as placebo (n=20) or 48 mg sucralose dissolved in 60 mL water (n=25), fifteen minutes prior to an OGTT. Blood samples were individually drawn every 15 minutes for 180 minutes for quantifying glucose and insulin concentrations. Monocyte subsets expressing CD11c and CD206 were measured at -15 and 180 minutes by flow cytometry. As compared to controls, volunteers receiving sucralose exhibited significant increases in serum insulin at 30, 45, and 180 minutes, whereas blood glucose values showed no significant differences. Sucralose consumption caused a significant 7% increase in classical monocytes and 63% decrease in nonclassical monocytes with respect to placebo controls. Pearson’s correlation models revealed a strong association of insulin with sucralose-induced monocyte subpopulation unbalance whereas glucose values did not show significant correlations. Sucralose ingestion decreased CD11c expression in all monocyte subsets and reduced CD206 expression in nonclassical monocytes suggesting that sucralose does not only unbalance monocyte subpopulations but also alter their expression pattern of cell surface molecules. This work demonstrates for the first time that a 48 mg sucralose sip increases serum insulin and unbalances monocyte subpopulations expressing CD11c and CD206 in noninsulin-resistant healthy young adults subjected to an OGTT. The apparently innocuous consumption of sucralose should be reexamined in light of these results.

Key message Trimeric Galanthus nivalis agglutinin-related lectin of Orchidaceae with two conformational forms was first studied in Dendrobium pendulum . It was highly expressed by stress factors. Using mannan–agarose column chromatography, a mannose-binding protein was purified from Dendrobium pendulum Roxb. pseudobulb. After heating in the presence of sodium dodecyl sulfate (SDS) with or without 2-mercaptoethanol, the protein showed one band with molecular mass of 14.0 kDa on SDS-polyacrylamide gel electrophoresis (PAGE). Without heating, three bands were found at positions of 14.0, 39.4, and 41.5 kDa, but a higher amount of 39.4 and 41.5 kDa protein bands were seen in the presence of 2-mercaptoethanol. Liquid chromatography–tandem mass spectrometry and database search indicated that the 14.0 kDa protein band contained three peptide fragments identical to parts of a lectin precursor from Dendrobiu m findleyanum Parish & Rchb.f. Native-PAGE and Ferguson plot showed that the purified protein had two native forms with molecular masses of 44.2 and 45.3 kDa, indicating three 14.0 kDa polypeptide subunits. The purified protein exhibited the agglutination activity with trypsinized chicken erythrocytes. It was then recognized as a Galanthus nivalis agglutinin-related lectin and named D. pendulum agglutinin (DPA). Using reverse transcription-polymerase chain reaction and DNA sequencing, the deduced amino acid sequence of DPA precursor showed the highest homology (96.4 %) with a lectin precursor of D. findleyanum and contained three mannose-binding sites. Greater amounts of DPA were found when the pseudobulbs were treated with stress factors including ultraviolet light, abscisic acid, hydrogen peroxide, and acetylene gas.

The humoral arm of innate immunity includes diverse molecules with antibody-like functions, some of which serve as disease severity biomarkers in coronavirus disease 2019 (COVID-19). The present study was designed to conduct a systematic investigation of the interaction of human humoral fluid-phase pattern recognition molecules (PRMs) with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Of 12 PRMs tested, the long pentraxin 3 (PTX3) and mannose-binding lectin (MBL) bound the viral nucleocapsid and spike proteins, respectively. MBL bound trimeric spike protein, including that of variants of concern (VoC), in a glycan-dependent manner and inhibited SARS-CoV-2 in three in vitro models. Moreover, after binding to spike protein, MBL activated the lectin pathway of complement activation. Based on retention of glycosylation sites and modeling, MBL was predicted to recognize the Omicron VoC. Genetic polymorphisms at the MBL2 locus were associated with disease severity. These results suggest that selected humoral fluid-phase PRMs can play an important role in resistance to, and pathogenesis of, COVID-19, a finding with translational implications.Stravalaci et al. examined recognition of SARS-CoV-2 by human soluble innate pattern recognition receptor. They report that pentraxin 3 and mannose-binding protein recognize viral nucleoprotein and spike, respectively. Mannose-binding lectin has antiviral activity, and human genetic polymorphisms of MBL2 are associated with more severe COVID-19.

Phenotypic polarization of macrophages is regulated by a milieu of cues in the local tissue microenvironment. Although much is known about how soluble factors influence macrophage polarization, relatively little is known about how physical cues present in the extracellular environment might modulate proinflammatory (M1) vs. prohealing (M2) activation. Specifically, the role of cell shape has not been explored, even though it has been observed that macrophages adopt different geometries in vivo. We and others observed that macrophages polarized toward different phenotypes in vitro exhibit dramatic changes in cell shape: M2 cells exhibit an elongated shape compared with M1 cells. Using a micropatterning approach to control macrophage cell shape directly, we demonstrate here that elongation itself, without exogenous cytokines, leads to the expression of M2 phenotype markers and reduces the secretion of inflammatory cytokines. Moreover, elongation enhances the effects of M2-inducing cytokines IL-4 and IL-13 and protects cells from M1-inducing stimuli LPS and IFN-γ. In addition shape- but not cytokine-induced polarization is abrogated when actin and actin/myosin contractility are inhibited by pharmacological agents, suggesting a role for the cytoskeleton in the control of macrophage polarization by cell geometry. Our studies demonstrate that alterations in cell shape associated with changes in ECM architecture may provide integral cues to modulate macrophage phenotype polarization.

Regulation of the programming of tumour-associated macrophages (TAMs) controls tumour growth and anti-tumour immunity. We examined the role of FGF2 in that regulation. Tumours in mice genetically deficient in low-molecular weight FGF2 (FGF2 LMW ) regress dependent on T cells. Yet, TAMS not T cells express FGF receptors. Bone marrow derived-macrophages from Fgf2 LMW−/− mice co-injected with cancer cells reduce tumour growth and express more inflammatory cytokines. FGF2 is induced in the tumour microenvironment following fractionated radiation in murine tumours consistent with clinical reports. Combination treatment of in vivo tumours with fractionated radiation and a blocking antibody to FGF2 prolongs tumour growth delay, increases long-term survival and leads to a higher iNOS + /CD206 + TAM ratio compared to irradiation alone. These studies show for the first time that FGF2 affects macrophage programming and is a critical regulator of immunity in the tumour microenvironment. Macrophages contribute to tumour progression and response to therapy. Here, the authors show that absence of FGF2 in the tumour microenvironment reduces tumour growth and enhances the anti-tumour immune response by altering macrophage polarization. As a result, disruption of this macrophage programming by anti-FGF2 blocking antibodies enhances the outcome from radiotherapy. 

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by a virus called “Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).” In the majority of patients, infection with COVID-19 may be asymptomatic or may cause only mild symptoms. However, in some patients, there can also be immunological problems, such as macrophage activation syndrome (CSS) that results in cytokine storm syndrome (CSS) and acute respiratory distress syndrome (ARDS). Comprehension of host-microbe communications is the critical aspect in the advancement of new therapeutics against infectious illnesses. Endogenous animal lectins, a class of proteins, may perceive non-self glycans found on microorganisms. Serum mannose-binding lectin (sMBL), as a part of the innate immune framework, recognizes a wide range of microbial microorganisms and activates complement cascade via an antibody-independent pathway. Although the molecular basis for the intensity of SARS-CoV-2 infection is not generally understood, scientific literature indicates that COVID-19 is correlated with unregulated activation of the complement in terms of disease severity. Disseminated intravascular coagulation (DIC), inflammation, and immune paralysis contribute to unregulated complement activation. Pre-existing genetic defects in MBL and their association with complement play a major role in immune response dysregulation caused by SARS-CoV-2. In order to generate anti-complement-based therapies in Covid-19, an understanding of sMBL in immune response to SARS-CoV-2 and complement is therefore essential. This review highlights the role of endogenous sMBL and complement activation during SARS-CoV-2 infection and their therapeutic management by various agents, mainly plant lectins, since antiviral mannose-binding plant lectins (pMBLs) offer potential applications in the prevention and control of viral infections.

Single-cell mass cytometry was applied to comprehensively characterize postmortem and fresh human microglia. Using a hybrid workflow for multidimensional data analysis, a core signature and regional heterogeneity were identified.

PET imaging using 2-deoxy-2-[ 18 F]fluoro-d-glucose ([ 18 F]FDG) has been widely used for the detection of plaque inflammation. Here, however, Nobuhiro Tahara and colleagues explore the possibility of using 18 F-labeled mannose (2-deoxy-2-[ 18 F]fluoro-d-mannose, [ 18 F]FDM), a structural analog to FDG, as an alternative and potentially more specific PET tracer than FDG for assessing the risk of acute vascular events in patients. The approach targets the mannose receptor–bearing macrophages that are abundant in high-risk atherosclerotic plaques, with feasibility demonstrated in a rabbit model of atherosclerosis. Progressive inflammation in atherosclerotic plaques is associated with increasing risk of plaque rupture. Molecular imaging of activated macrophages with 2-deoxy-2-[ 18 F]fluoro- D -glucose ([ 18 F]FDG) has been proposed for identification of patients at higher risk for acute vascular events. Because mannose is an isomer of glucose that is taken up by macrophages through glucose transporters and because mannose receptors are expressed on a subset of the macrophage population in high-risk plaques, we applied 18 F-labeled mannose (2-deoxy-2-[ 18 F]fluoro- D -mannose, [ 18 F]FDM) for targeting of plaque inflammation. Here, we describe comparable uptake of [ 18 F]FDM and [ 18 F]FDG in atherosclerotic lesions in a rabbit model; [ 18 F]FDM uptake was proportional to the plaque macrophage population. Our FDM competition studies in cultured cells with 2-deoxy-2-[ 14 C]carbon- D -glucose ([ 14 C]2DG) support at least 35% higher [ 18 F]FDM uptake by macrophages in cell experiments. We also demonstrate that FDM restricts binding of anti–mannose receptor antibody to macrophages by approximately 35% and that mannose receptor targeting may provide an additional avenue for imaging of plaque inflammation.

Influenza virus infections cause a wide variety of outcomes, from mild disease to 3 to 5 million cases of severe illness and ∼290,000 to 645,000 deaths annually worldwide. The molecular mechanisms underlying these disparate outcomes are currently unknown. Glycosylation within the human host plays a critical role in influenza virus biology. However, the impact these modifications have on the severity of influenza disease has not been examined. Herein, we profile the glycomic host responses to influenza virus infection as a function of disease severity using a ferret model and our lectin microarray technology. We identify the glycan epitope high mannose as a marker of influenza virus-induced pathogenesis and severity of disease outcome. Induction of high mannose is dependent upon the unfolded protein response (UPR) pathway, a pathway previously shown to associate with lung damage and severity of influenza virus infection. Also, the mannan-binding lectin (MBL2), an innate immune lectin that negatively impacts influenza outcomes, recognizes influenza virus-infected cells in a high mannosedependent manner. Together, our data argue that the high mannose motif is an infection-associated molecular pattern on host cells that may guide immune responses leading to the concomitant damage associated with severity.