The Role of Collectins and Galectins in Lung Innate Immune Defense

Are the class 18 myosins Myo18A and Myo18B specialist sarcomeric proteins?

Initially, the two members of class 18 myosins, Myo18A and Myo18B, appeared to exhibit highly divergent functions, complicating the assignment of class-specific functions. However, the identification of a striated muscle-specific isoform of Myo18A, Myo18Aγ, suggests that class 18 myosins may have evolved to complement the functions of conventional class 2 myosins in sarcomeres. Indeed, both genes, Myo18a and Myo18b, are predominantly expressed in the heart and somites, precursors of skeletal muscle, of developing mouse embryos. Genetic deletion of either gene in mice is embryonic lethal and is associated with the disorganization of cardiac sarcomeres. Moreover, Myo18Aγ and Myo18B localize to sarcomeric A-bands, albeit the motor (head) domains of these unconventional myosins have been both deduced and biochemically demonstrated to exhibit negligible ATPase activity, a hallmark of motor proteins. Instead, Myo18Aγ and Myo18B presumably coassemble with thick filaments and provide structural integrity and/or internal resistance through interactions with F-actin and/or other proteins. In addition, Myo18Aγ and Myo18B may play distinct roles in the assembly of myofibrils, which may arise from actin stress fibers containing the α-isoform of Myo18A, Myo18Aα. The β-isoform of Myo18A, Myo18Aβ, is similar to Myo18Aα, except that it lacks the N-terminal extension, and may serve as a negative regulator through heterodimerization with either Myo18Aα or Myo18Aγ. In this review, we contend that Myo18Aγ and Myo18B are essential for myofibril structure and function in striated muscle cells, while α- and β-isoforms of Myo18A play diverse roles in nonmuscle cells.

Cancer cells and viruses share common glycoepitopes: exciting opportunities toward combined treatments

Aberrant glycosylation patterns of glycoproteins and glycolipids have long been recognized as one the major hallmarks of cancer cells that has led to numerous glycoconjugate vaccine attempts. These abnormal glycosylation profiles mostly originate from the lack of key glycosyltransferases activities, mutations, over expressions, or modifications of the requisite chaperone for functional folding. Due to their relative structural simplicity, O-linked glycans of the altered mucin family of glycoproteins have been particularly attractive in the design of tumor associated carbohydrate-based vaccines. Several such glycoconjugate vaccine formulations have generated potent monoclonal anti-carbohydrate antibodies useful as diagnostic and immunotherapies in the fight against cancer. Paradoxically, glycoproteins related to enveloped viruses also express analogous N- and O-linked glycosylation patterns. However, due to the fact that viruses are not equipped with the appropriate glycosyl enzyme machinery, they need to hijack that of the infected host cells. Although the resulting N-linked glycans are very similar to those of normal cells, some of their O-linked glycan patterns often share the common structural simplicity to those identified on tumor cells. Consequently, given that both cancer cells and viral glycoproteins share both common N- and O-linked glycoepitopes, glycoconjugate vaccines could be highly attractive to generate potent immune responses to target both conditions.

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Molecular Impact of Conventional and Electronic Cigarettes on Pulmonary Surfactant

The alveolar epithelium is covered by a non-cellular layer consisting of an aqueous hypophase topped by pulmonary surfactant, a lipo-protein mixture with surface-active properties. Exposure to cigarette smoke (CS) affects lung physiology and is linked to the development of several diseases. The macroscopic effects of CS are determined by several types of cell and molecular dysfunction, which, among other consequences, lead to surfactant alterations. The purpose of this review is to summarize the published studies aimed at uncovering the effects of CS on both the lipid and protein constituents of surfactant, discussing the molecular mechanisms involved in surfactant homeostasis that are altered by CS. Although surfactant homeostasis has been the topic of several studies and some molecular pathways can be deduced from an analysis of the literature, it remains evident that many aspects of the mechanisms of action of CS on surfactant homeostasis deserve further investigation.

3D Inkjet-Bioprinted Lung-on-a-Chip

There is an urgent need for physiologically relevant and customizable biochip models of human lung tissue to provide a niche for lung disease modeling and drug efficacy. Although various lung-on-a-chips have been developed, the conventional fabrication method has been limited in reconstituting a very thin and multilayered architecture and spatial arrangements of multiple cell types in a microfluidic device. To overcome these limitations, we developed a physiologically relevant human alveolar lung-on-a-chip model, effectively integrated with an inkjet-printed, micron-thick, and three-layered tissue. After bioprinting lung tissues inside four culture inserts layer-by-layer, the inserts are implanted into a biochip that supplies a flow of culture medium. This modular implantation procedure enables the formation of a lung-on-a-chip to facilitate the culture of 3D-structured inkjet-bioprinted lung models under perfusion at the air-liquid interface. The bioprinted models cultured on the chip maintained their structure with three layers of tens of micrometers and achieved a tight junction in the epithelial layer, the critical properties of an alveolar barrier. The upregulation of genes involved in the essential functions of alveoli was also confirmed in our model. Our culture insert-mountable organ-on-a-chip is a versatile platform that can be applied to various organ models by implanting and replacing culture inserts. It is amenable to mass production and the development of customized models through the convergence with bioprinting technology.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

Avian surfactant protein (SP)-A2 first arose in an early tetrapod before the divergence of amphibians and gradually lost the collagen domain

The air-liquid interface of the mammalian lung is lined with pulmonary surfactants, a mixture of specific proteins and lipids that serve a dual purpose-enabling air-breathing and protection against pathogens. In mammals, surfactant proteins A (SP-A) and D (SP -D) are involved in innate defence of the lung. Birds seem to lack the SP-D gene, but possess SP-A2, an additional SP-A-like gene. Here we investigated the evolution of the SP-A and SP-D genes using computational gene prediction, homology, simulation modelling and phylogeny with published avian and other vertebrate genomes. PCR was used to confirm the identity and expression of SP-A analogues in various tissue homogenates of zebra finch and turkey. In silico analysis confirmed the absence of SP-D-like genes in all 47 published avian genomes. Zebra finch and turkey SP-A1 and SP-A2 sequences, confirmed by PCR of lung homogenates, were compared with sequenced and in silico predicted vertebrate homologs to construct a phylogenetic tree. The collagen domain of avian SP-A1, especially that of zebra finch, was dramatically shorter than that of mammalian SP-A. Amphibian and reptilian genomes also contain avian-like SP-A2 protein sequences with a collagen domain. NCBI Gnomon-predicted avian and alligator SP-A2 proteins all lacked the collagen domain completely. Both avian SP-A1 and SP-A2 sequences form separate clades, which are most closely related to their closest relatives, the alligators. The C-terminal carbohydrate recognition domain (CRD) of zebra finch SP-A1 was structurally almost identical to that of rat SP-A. In fact, the CRD of SP-A is highly conserved among all the vertebrates. Birds retained a truncated version of mammalian type SP-A1 as well as a non-collagenous C-type lectin, designated SP-A2, while losing the large collagenous SP-D lectin, reflecting their evolutionary trajectory towards a unidirectional respiratory system. In the context of zoonotic infections, how these evolutionary changes affect avian pulmonary surface protection is not clear.

Vitamin D3 enhances the antibacterial ability in head-kidney macrophages of turbot (Scophthalmus maximus L.) through C-type lectin receptors

It has been known that vitamin D₃ (VD₃) not only plays an important role in regulating calcium and phosphorus metabolism in animals, but also has extensive effects on immune functions. In this study, the mechanism how VD₃ influences bactericidal ability in turbot was explored. The transcriptomic analysis identified that dietary VD₃ significantly upregulated the gene expression of C-type lectin receptors (CLRs), including mannose receptors (mrc1, mrc2, pla2r1) and collectins (collectin 11 and collectin 12) in turbot intestine. Further results obtained from in vitro experiments confirmed that the gene expression of mannose receptors and collectins in head-kidney macrophages (HKMs) of turbot was induced after the cells were incubated with different concentrations of VD₃ (0, 1, 10 nM) or 1,25(OH)₂D₃ (0, 10, 100 pM). Meanwhile, both phagocytosis and bactericidal functions of HKMs were significantly improved in VD₃ or 1,25(OH)₂D₃-incubated HKMs. Furthermore, phagocytosis and bacterial killing of HKMs decreased after collectin 11 was knocked down. Moreover, VD₃-enhanced antibacterial activities diminished in collectin 11-interfered cells. Interestingly, the evidence was provided in the present study that inactive VD₃ could be metabolized into active 1,25(OH)₂D₃ via hydroxylases encoded by cyp27a1 and cyp27b1 in fish macrophages. In conclusion, VD₃ could be metabolized to 1,25(OH)₂D₃ in HKMs, which promoted the expression of CLRs in macrophages, leading to enhanced bacterial clearance.

Lung and Plasma Metabolome in HIV-Associated Obstructive Lung Disease

BACKGROUND

HIV is a risk factor for obstructive lung disease (OLD), independent of smoking. We used mass spectrometry (MS) approaches to identify metabolomic biomarkers that inform mechanistic pathogenesis of OLD in persons with HIV (PWH).

METHODS

We obtained bronchoalveolar lavage fluid (BALF) samples from 52 PWH, in case:control (+OLD/-OLD) pairs matched on age, smoking status, and antiretroviral treatment. Four hundred nine metabolites from 8 families were measured on BALF and plasma samples using a MS-based Biocrates platform. After filtering metabolites with a high proportion of missing values and values below the level of detection, we performed univariate testing using paired t tests followed by false discovery rate corrections. We used distance-weighted discrimination (DWD) to test for an overall difference in the metabolite profile between cases and controls.

RESULTS

After filtering, there were 252 BALF metabolites for analysis from 8 metabolite families. DWD testing found that collectively, BALF metabolites differentiated cases from controls, whereas plasma metabolites did not. In BALF samples, we identified 3 metabolites that correlated with OLD at the false discovery rate of 10%; all were in the phosphatidylcholine family. We identified additional BALF metabolites when analyzing lung function as a continuous variable, and these included acylcarnitines, triglycerides, and a cholesterol ester.

CONCLUSIONS

Collectively, BALF metabolites differentiate PWH with and without OLD. These included several BALF lipid metabolites. These findings were limited to BALF and were not found in plasma from the same individuals. Phosphatidylcholine, the most common lipid component of surfactant, was the predominant lipid metabolite differentially expressed.

Big Data for Tiny Patients: A Precision Medicine Approach to Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of extreme prematurity. Despite more than 50 years of research, current treatments are ineffective, and clinicians are largely unable to accurately predict which neonates the condition will develop in. A deeper understanding of the molecular mechanisms underlying the characteristic arrest in lung development are warranted. Integrating high-fidelity technology from precision medicine approaches may fill this gap and provide the tools necessary to identify biomarkers and targetable pathways. In this review, we describe insights garnered from current studies using omics for BPD prediction and stratification. We conclude by describing novel programs that will integrate multi-omics in efforts to better understand and treat the pathogenesis of BPD. [Pediatr Ann. 2022;51(10):e396-e404.].

Cooperative action of SP-A and its trimeric recombinant fragment with polymyxins against Gram-negative respiratory bacteria

The exploration of therapies combining antimicrobial lung proteins and conventional antibiotics is important due to the growing problem of multidrug-resistant bacteria. The aim of this study was to investigate whether human SP-A and a recombinant trimeric fragment (rfhSP-A) have cooperative antimicrobial activity with antibiotics against pathogenic Gram-negative bacteria. We found that SP-A bound the cationic peptide polymyxin B (PMB) with an apparent dissociation constant (K D) of 0.32 ± 0.04 µM. SP-A showed synergistic microbicidal activity with polymyxin B and E, but not with other antibiotics, against three SP-A-resistant pathogenic bacteria: Klebsiella pneumoniae, non-typable Haemophilus influenzae (NTHi), and Pseudomonas aeruginosa. SP-A was not able to bind to K. pneumoniae, NTHi, or to mutant strains thereof expressing long-chain lipopolysaccharides (or lipooligosaccharides) and/or polysaccharide capsules. In the presence of PMB, SP-A induced the formation of SP-A/PMB aggregates that enhance PMB-induced bacterial membrane permeabilization. Furthermore, SP-A bound to a molecular derivative of PMB lacking the acyl chain (PMBN) with a K D of 0.26 ± 0.02 μM, forming SP-A/PMBN aggregates. PMBN has no bactericidal activity but can bind to the outer membrane of Gram-negative bacteria. Surprisingly, SP-A and PMBN showed synergistic bactericidal activity against Gram-negative bacteria. Unlike native supratrimeric SP-A, the trimeric rfhSP-A fragment had small but significant direct bactericidal activity against K. pneumoniae, NTHi, and P. aeruginosa. rfhSP-A did not bind to PMB under physiological conditions but acted additively with PMB and other antibiotics against these pathogenic bacteria. In summary, our results significantly improve our understanding of the antimicrobial actions of SP-A and its synergistic action with PMB. A peptide based on SP-A may aid the therapeutic use of PMB, a relatively cytotoxic antibiotic that is currently being reintroduced into clinics due to the global problem of antibiotic resistance.

The collectin SP-A and its trimeric recombinant fragment protect alveolar epithelial cells from the cytotoxic and proinflammatory effects of human cathelicidin in vitro

Human cathelicidin (LL-37) is a defense peptide with antimicrobial activity against various pathogens. However, LL-37 can also trigger tissue injury by binding to host cell membranes. The cytotoxic effects of LL-37 may be especially relevant in chronic respiratory diseases characterized by increased LL-37. The aim of this study was to investigate whether the human collectin SP-A and a trimeric recombinant fragment thereof (rfhSP-A) can regulate the activities of LL-37. To this end, we studied the interaction of LL-37 with SP-A and rfhSP-A by intrinsic fluorescence, dynamic light scattering, and circular dichroism, as well as the effects of these proteins on the antimicrobial and cytotoxic activities of LL-37. Both SP-A and rfhSP-A bound LL-37 with high affinity at physiological ionic strength (K_D = 0.45 ± 0.01 nM for SP-A and 1.22 ± 0.7 nM for rfhSP-A). Such interactions result in the reduction of LL-37-induced cell permeability and IL-8 release in human pneumocytes, mediated by P2X7 channels. Binding of LL-37 to SP-A did not modify the properties of SP-A or the antibacterial activity of LL-37 against respiratory pathogens (Klebsiella pneumoniae, Pseudomonas aeruginosa, and nontypeable Haemophilus influenzae). SP-A/LL-37 complexes showed a greater ability to aggregate LPS vesicles than LL-37, which reduces endotoxin bioactivity. These results reveal the protective role of native SP-A in controlling LL-37 activities and suggest a potential therapeutic effect of rfhSP-A in reducing the cytotoxic and inflammatory actions of LL-37, without affecting its microbicidal activity against Gram-negative pathogens.

A Dynamic Interplay of Circulating Extracellular Vesicles and Galectin-1 Reprograms Viral Latency during HIV-1 Infection

Combined Antiretroviral therapy (cART) suppresses HIV replication but fails to eradicate the virus, which persists in a small pool of long-lived latently infected cells. Immune activation and residual inflammation during cART are considered to contribute to viral persistence. Galectins, a family of β-galactoside-binding proteins, play central roles in host-pathogen interactions and inflammatory responses. Depending on their structure, glycan binding specificities and/or formation of distinct multivalent signaling complexes, different members of this family can complement, synergize, or oppose the function of others. Here, we identify a regulatory circuit, mediated by galectin-1 (Gal-1)–glycan interactions, that promotes reversal of HIV-1 latency in infected T cells. We found elevated levels of circulating Gal-1 in plasma from HIV-1-infected individuals, which correlated both with inflammatory markers and the transcriptional activity of the reservoir, as determined by unspliced-RNA (US-RNA) copy number. Proinflammatory extracellular vesicles (EVs) isolated from the plasma of HIV-infected individuals induced Gal-1 secretion by macrophages. Extracellularly, Gal-1 interacted with latently infected resting primary CD4⁺ T cells and J-LAT cells in a glycan-dependent manner and reversed HIV latency via activation of the nuclear factor κB (NF-κB). Furthermore, CD4⁺ T cells isolated from HIV-infected individuals showed increased HIV-1 transcriptional activity when exposed to Gal-1. Thus, by modulating reservoir dynamics, EV-driven Gal-1 secretion by macrophages links inflammation with HIV-1 persistence in cART-treated individuals.

Small Peptide Derivatives Within the Carbohydrate Recognition Domain of SP-A2 Modulate Asthma Outcomes in Mouse Models and Human Cells

Surfactant Protein-A (SP-A) is an innate immune modulator that regulates a variety of pulmonary host defense functions. We have shown that SP-A is dysfunctional in asthma, which could be partly due to genetic heterogeneity. In mouse models and primary bronchial epithelial cells from asthmatic participants, we evaluated the functional significance of a particular single nucleotide polymorphism of SP-A2, which results in an amino acid substitution at position 223 from glutamine (Q) to lysine (K) within the carbohydrate recognition domain (CRD). We found that SP-A 223Q humanized mice had greater protection from inflammation and mucin production after IL-13 exposure as compared to SP-A-2 223K mice. Likewise, asthmatic participants with two copies the major 223Q allele demonstrated better lung function and asthma control as compared to asthmatic participants with two copies of the minor SP-A 223K allele. In primary bronchial epithelial cells from asthmatic participants, full-length recombinant SP-A 223Q was more effective at reducing IL-13-induced MUC5AC gene expression compared to SP-A 223K. Given this activity, we developed 10 and 20 amino acid peptides of SP-A2 spanning position 223Q. We show that the SP-A 223Q peptides reduce eosinophilic inflammation, mucin production and airways hyperresponsiveness in a house dust mite model of asthma, protect from lung function decline during an IL-13 challenge model in mice, and decrease IL-13-induced MUC5AC gene expression in primary airway epithelial cells from asthmatic participants. These results suggest that position 223 within the CRD of SP-A2 may modulate several outcomes relevant to asthma, and that short peptides of SP-A2 retain anti-inflammatory properties similar to that of the endogenous protein.

Advancing Lung Immunology Research: An Official American Thoracic Society Workshop Report

The mammalian airways and lungs are exposed to a myriad of inhaled particulate matter, allergens, and pathogens. The immune system plays an essential role in protecting the host from respiratory pathogens, but a dysregulated immune response during respiratory infection can impair pathogen clearance and lead to immunopathology. Furthermore, inappropriate immunity to inhaled antigens can lead to pulmonary diseases. A complex network of epithelial, neural, stromal, and immune cells has evolved to sense and respond to inhaled antigens, including the decision to promote tolerance versus a rapid, robust, and targeted immune response. Although there has been great progress in understanding the mechanisms governing immunity to respiratory pathogens and aeroantigens, we are only beginning to develop an integrated understanding of the cellular networks governing tissue immunity within the lungs and how it changes after inflammation and over the human life course. An integrated model of airway and lung immunity will be necessary to improve mucosal vaccine design as well as prevent and treat acute and chronic inflammatory pulmonary diseases. Given the importance of immunology in pulmonary research, the American Thoracic Society convened a working group to highlight central areas of investigation to advance the science of lung immunology and improve human health.

Role of surfactant protein-D in ocular bacterial infection

Purpose

Our review explains the role of surfactant protein D (SP-D) in different kinds of bacterial infection based on its presence in different ocular surface tissues. We discuss the potential role of SP-D against invasion by pathogens, with the aim of identifying new prospects for the possible mechanism of SP-D-mediated immune processes, and the diagnosis, prognosis, or treatment of ocular bacterial infection.

Methods

We reviewed articles about the role of SP-D in various ocular bacterial infections or infection-related ocular diseases through PubMed, Google Scholar, and the Web of Science databases.

Results

SP-D acts as an important immune factor that can resemble molecules in different polymerization states and that defends against pathogen invasion. The increased SP-D production and secretion in tear fluid and the cornea after ocular bacterial infections such as Staphylococcus aureus, Pseudomonas aeruginosa keratitis, and infection-related ocular diseases, was shown to have potential anti-inflammatory effects. The mechanisms of SP-D’s action against ocular bacterial infections include presenting, aggregating, opsonizing, and phagocytizing antigens, as well as regulating anti-bacterial immunity processes, including toll-like receptor-5 (TLR-5) pathway and IL-8 effect, TLR-4 and TLR-2 pathways and other possible ways remained to be elucidated in more detail. The findings demonstrate the potential of SP-D as an important clinical diagnostic biomarker prognosis predictor, and target for ocular immunotherapy.

Conclusion

SP-D participates in invasion by different ocular bacteria and infection-related ocular diseases through multiple immune mechanisms. This finding provides new prospects for the diagnosis, prognosis and treatment of ocular bacterial infection.

Signaling Pathways That Mediate Alveolar Macrophage Activation by Surfactant Protein A and IL-4

Activation of tissue repair program in macrophages requires the integration of IL-4/IL-13 cytokines and tissue-specific signals. In the lung, surfactant protein A (SP-A) is a tissue factor that amplifies IL-4Rα-dependent alternative activation and proliferation of alveolar macrophages (AMs) through the myosin18A receptor. However, the mechanism by which SP-A and IL-4 synergistically increase activation and proliferation of AMs is unknown. Here we show that SP-A amplifies IL-4-mediated phosphorylation of STAT6 and Akt by binding to myosin18A. Blocking PI3K activity or the myosin18A receptor abrogates SP-A´s amplifying effects on IL-4 signaling. SP-A alone activates Akt, mTORC1, and PKCζ and inactivates GSK3α/β by phosphorylation, but it cannot activate arginase-1 activity or AM proliferation on its own. The combined effects of IL-4 and SP-A on the mTORC1 and GSK3 branches of PI3K-Akt signaling contribute to increased AM proliferation and alternative activation, as revealed by pharmacological inhibition of Akt (inhibitor VIII) and mTORC1 (rapamycin and torin). On the other hand, the IL-4+SP-A-driven PKCζ signaling axis appears to intersect PI3K activation with STAT6 phosphorylation to achieve more efficient alternative activation of AMs. Consistent with IL-4+SP-A-driven activation of mTORC1 and mTORC2, both agonists synergistically increased mitochondrial respiration and glycolysis in AMs, which are necessary for production of energy and metabolic intermediates for proliferation and alternative activation. We conclude that SP-A signaling in AMs activates PI3K-dependent branched pathways that amplify IL-4 actions on cell proliferation and the acquisition of AM effector functions.

Bacterial Microarrays for Examining Bacterial Glycosignatures and Recognition by Host Lectins

The surface of bacteria displays diverse carbohydrate structures that may significantly differ among bacteria with the same cell wall architecture and even among strains of a given bacterial species. These structures are often recognized by lectins of the innate immune system for triggering defense responses, although some bacterial pathogens exploit recognition by host lectins for favoring infection. Bacterial microarrays are a useful tool for profiling accessible bacterial surface glycans and for exploring their recognition by innate immune lectins. The use of array-printed bacterial cells enables evaluation of the recognition of the glycan epitopes in their natural presentation, i.e., preserving their real density and accessibility. Glycosylation patterns of bacterial surfaces can be examined by testing the binding to the bacterial arrays of a panel of lectins with known carbohydrate-binding preferences, and the recognition of surface glycans by innate immune lectins can easily be assessed using similar binding assays.

A recipe for a good clinical pulmonary surfactant

The lives of thousands premature babies have been saved along the last thirty years thanks to the establishment and consolidation of pulmonary surfactant replacement therapies (SRT). It took some time to close the gap between the identification of the biophysical and molecular causes of the high mortality associated with respiratory distress syndrome in very premature babies and the development of a proper therapy. Closing the gap required the elucidation of some key questions defining the structure–function relationships in surfactant as well as the particular role of the different molecular components assembled into the surfactant system. On the other hand, the application of SRT as part of treatments targeting other devastating respiratory pathologies, in babies and adults, is depending on further extensive research still required before enough amounts of good humanized clinical surfactants will be available. This review summarizes our current concepts on the compositional and structural determinants defining pulmonary surfactant activity, the principles behind the development of efficient natural animal-derived or recombinant or synthetic therapeutic surfactants, as well as a the most promising lines of research that are already opening new perspectives in the application of tailored surfactant therapies to treat important yet unresolved respiratory pathologies.

Physicochemical properties of nanoparticles affecting their fate and the physiological function of pulmonary surfactants

Pulmonary drug delivery has drawn great attention due to its targeted local lung action, reduced side effects, and ease of administration. However, inhaled nanoparticles (NPs) could adsorb different pulmonary surfactants depending on their physicochemical properties, which may impair the physiological function of the pulmonary surfactants or alter the fate of the NPs. Thus, the objective of this review is to summarize how the physicochemical properties of NPs affecting the physiological function of pulmonary surfactants and their fate. First of all, the composition and characteristics of pulmonary surfactants, methods for studying pulmonary surfactant interaction with NPs are introduced. Thereafter, the influence of physicochemical properties of NPs on hydrophobic protein adsorption and strategies to decrease the interaction of NPs with pulmonary surfactants are discussed. Finally, the influence of physicochemical properties of NPs on lipids and hydrophilic protein adsorption and consequently their fate is described. In conclusion, a better understanding of the interaction of NPs with pulmonary surfactants will promote the faster development of safe and effective nanomedicine for pulmonary drug delivery. STATEMENT OF SIGNIFICANCE: Drug delivery carriers often face complex body fluid components after entering the human body. Pulmonary surfactants diffuse at the lung gas-liquid interface, and particles inevitably interact with pulmonary surfactants after pulmonary nanomedicine delivery. This review presents an overview of how the physicochemical properties of nanoparticles affecting their fate and physiological function of pulmonary surfactants. We believe that the information included in this review can provide important guiding for the development of safe and effective pulmonary delivery nanocarriers.

Glycosylation of SARS-CoV-2: structural and functional insights

The COVID-19 pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Similar to other coronaviruses, its particles are composed of four structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. S, E, and M proteins are glycosylated, and the N protein is phosphorylated. The S protein is involved in the interaction with the host receptor human angiotensin-converting enzyme 2 (hACE2), which is also heavily glycosylated. Recent studies have revealed several other potential host receptors or factors that can increase or modulate the SARS-CoV-2 infection. Interestingly, most of these molecules bear carbohydrate residues. While glycans acquired by the viruses through the hijacking of the host machinery help the viruses in their infectivity, they also play roles in immune evasion or modulation. Glycans play complex roles in viral pathobiology, both on their own and in association with carrier biomolecules, such as proteins or glycosaminoglycans (GAGs). Understanding these roles in detail can help in developing suitable strategies for prevention and therapy of COVID-19. In this review, we sought to emphasize the interplay of SARS-CoV-2 glycosylated proteins and their host receptors in viral attachment, entry, replication, and infection. Moreover, the implications for future therapeutic interventions targeting these glycosylated biomolecules are also discussed in detail.

Pulmonary surfactant inactivation by β-D-glucan and protective role of surfactant protein A

Pulmonary fungal infections lead to damage of the endogenous lung surfactant system. However, the molecular mechanism underlying surfactant inhibition is unknown. β-D-glucan is the major component of pathogenic fungal cell walls and is also present in organic dust, which increases the risk of respiratory diseases. The objective of this study was to characterize the interaction of this D-glucopyranose polymer with pulmonary surfactant. Our results show that β-D-glucan induced a concentration-dependent inhibition of the surface adsorption, respreading, and surface tension-lowering activity of surfactant preparations containing surfactant proteins SP-B and SP-C. Our data support a new mechanism of surfactant inhibition that consists in the extraction of phospholipid molecules from surfactant membranes by β-D-glucan. As a result, surfactant membranes became more fluid, as demonstrated by fluorescence anisotropy, and showed decreased T_m and transition enthalpy. Surfactant preparations containing surfactant protein A (SP-A) were more resistant to β-D-glucan inhibition. SP-A bound to different β-D-glucans with high affinity (K_d = 1.5 ± 0.1 nM), preventing and reverting β-D-glucan inhibitory effects on surfactant interfacial adsorption and partially abrogating β-D-glucan inhibitory effects on surfactant's reduction of surface tension. We conclude that β-D-glucan inhibits the biophysical function of surfactant preparations lacking SP-A by subtraction of phospholipids from surfactant bilayers and monolayers. The increased resistance of SP-A-containing surfactant preparations to β-D-glucan reinforces its use in surfactant replacement therapy.

Surfactant protein A enhances the degradation of LPS-induced TLR4 in primary alveolar macrophages involving Rab7, β-arrestin2, and mTORC1

Respiratory infections by Gram-negative bacteria are a major cause of global morbidity and mortality. Alveolar macrophages (AMs) play a central role in maintaining lung immune homeostasis and host defense by sensing pathogens via pattern recognition receptors (PRR). The PRR Toll-like receptor (TLR) 4 is a key sensor of lipopolysaccharide (LPS) from Gram-negative bacteria. Pulmonary surfactant is the natural microenvironment of AMs. Surfactant protein A (SP-A), a multifunctional host defense collectin, controls LPS-induced pro-inflammatory immune responses at the organismal and cellular level via distinct mechanisms. We found that SP-A post-transcriptionally restricts LPS-induced TLR4 protein expression in primary AMs from healthy humans, rats, wild-type and SP-A^-/- mice by further decreasing cycloheximide-reduced TLR4 protein translation and enhances the co-localization of TLR4 with the late endosome/lysosome. Both effects as well as the SP-A-mediated inhibition of LPS-induced TNFα release are counteracted by pharmacological inhibition of the small GTPase Rab7. SP-A-enhanced Rab7 expression requires β-arrestin2 and, in β-arrestin2^-/- AMs and after intratracheal LPS challenge of β-arrestin2^-/- mice, SP-A fails to enhance TLR4/lysosome co-localization and degradation of LPS-induced TLR4. In SP-A^-/- mice, TLR4 levels are increased after pulmonary LPS challenge. SP-A-induced activation of mechanistic target of rapamycin complex 1 (mTORC1) kinase requires β-arrestin2 and is critically involved in degradation of LPS-induced TLR4. The data suggest that SP-A post-translationally limits LPS-induced TLR4 expression in primary AMs by lysosomal degradation comprising Rab7, β-arrestin2, and mTORC1. This study may indicate a potential role of SP-A-based therapeutic interventions in unrestricted TLR4-driven immune responses to lower respiratory tract infections caused by Gram-negative bacteria.

Synergistic Action of Antimicrobial Lung Proteins against Klebsiella pneumoniae

As key components of innate immunity, lung antimicrobial proteins play a critical role in warding off invading respiratory pathogens. Lung surfactant protein A (SP-A) exerts synergistic antimicrobial activity with the N-terminal segment of the SP-B proprotein (SP-B^N) against Klebsiella pneumoniae K2 in vivo. However, the factors that govern SP-A/SP-B^N antimicrobial activity are still unclear. The aim of this study was to identify the mechanisms by which SP-A and SP-B^N act synergistically against K. pneumoniae, which is resistant to either protein alone. The effect of these proteins on K. pneumoniae was studied by membrane permeabilization and depolarization assays and transmission electron microscopy. Their effects on model membranes of the outer and inner bacterial membranes were analyzed by differential scanning calorimetry and membrane leakage assays. Our results indicate that the SP-A/SP-B^N complex alters the ultrastructure of K. pneumoniae by binding to lipopolysaccharide molecules present in the outer membrane, forming packing defects in the membrane that may favor the translocation of both proteins to the periplasmic space. The SP-A/SP-B^N complex depolarized and permeabilized the inner membrane, perhaps through the induction of toroidal pores. We conclude that the synergistic antimicrobial activity of SP-A/SP-B^N is based on the capability of this complex, but not either protein alone, to alter the integrity of bacterial membranes.

Status of mannose-binding lectin (MBL) and complement system in COVID-19 patients and therapeutic applications of antiviral plant MBLs

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.

A Machine-Generated View of the Role of Blood Glucose Levels in the Severity of COVID-19

SARS-CoV-2 started spreading toward the end of 2019 causing COVID-19, a disease that reached pandemic proportions among the human population within months. The reasons for the spectrum of differences in the severity of the disease across the population, and in particular why the disease affects more severely the aging population and those with specific preconditions are unclear. We developed machine learning models to mine 240,000 scientific articles openly accessible in the CORD-19 database, and constructed knowledge graphs to synthesize the extracted information and navigate the collective knowledge in an attempt to search for a potential common underlying reason for disease severity. The machine-driven framework we developed repeatedly pointed to elevated blood glucose as a key facilitator in the progression of COVID-19. Indeed, when we systematically retraced the steps of the SARS-CoV-2 infection, we found evidence linking elevated glucose to each major step of the life-cycle of the virus, progression of the disease, and presentation of symptoms. Specifically, elevations of glucose provide ideal conditions for the virus to evade and weaken the first level of the immune defense system in the lungs, gain access to deep alveolar cells, bind to the ACE2 receptor and enter the pulmonary cells, accelerate replication of the virus within cells increasing cell death and inducing an pulmonary inflammatory response, which overwhelms an already weakened innate immune system to trigger an avalanche of systemic infections, inflammation and cell damage, a cytokine storm and thrombotic events. We tested the feasibility of the hypothesis by manually reviewing the literature referenced by the machine-generated synthesis, reconstructing atomistically the virus at the surface of the pulmonary airways, and performing quantitative computational modeling of the effects of glucose levels on the infection process. We conclude that elevation in glucose levels can facilitate the progression of the disease through multiple mechanisms and can explain much of the differences in disease severity seen across the population. The study provides diagnostic considerations, new areas of research and potential treatments, and cautions on treatment strategies and critical care conditions that induce elevations in blood glucose levels.

Air particulate matter pollution and circulating surfactant protein: A systemic review and meta-analysis

OBJECTIVE

Air particulate matter (PM) pollution is associated with the alterations in circulating pulmonary damage proteins. But there are not consistent results among the epidemiological studies. The aim of this study is to investigate the alteration of surfactant protein (SP) from PM exposure.

METHODS

We conducted a comprehensive meta-analysis by searching the databases of PubMed, Medline, EMBASE, Web of Science and CNKI before October 2020 which reported PM pollutants and surfactant protein in the population. The sources of heterogeneity were assessed by subgroup (smoking, particulate matter with different aerodynamic diameter, exposure duration) analysis. We also used the publication bias tests for the comprehensive assessment.

RESULTS

This meta-analysis consisted of 10 studies with 1985 subjects. The results showed that the combined standardized mean difference (SMD) value was 0.05, 95% confidence interval (CI) was -0.07 to 0.17 for serum SP-A and -0.81 (95% CI: -1.41 to -0.21) for circulating SP-D. Among smokers, the combined SMD value of SP-A were 0.29 (95% CI: 0.05 to 0.52). We did not find the correlation between publication year of SP-A and SP-D and study heterogeneity.

CONCLUSIONS

Circulating SP-D was significantly decreased by air particulate matter. Serum SP-A was significantly increased by PM exposure among smokers. Circulating surfactant protein may be considered as a biomarker for respiratory injury caused by air particulate matter.

Exploration of Galectin Ligands Displayed on Gram-Negative Respiratory Bacterial Pathogens with Different Cell Surface Architectures

Galectins bind various pathogens through recognition of distinct carbohydrate structures. In this work, we examined the binding of four human galectins to the Gram-negative bacteria Klebsiella pneumoniae (Kpn) and non-typeable Haemophilus influenzae (NTHi), which display different surface glycans. In particular, Kpn cells are covered by a polysaccharide capsule and display an O-chain-containing lipopolysaccharide (LPS), whereas NTHi is not capsulated and its LPS, termed lipooligosacccharide (LOS), does not contain O-chain. Binding assays to microarray-printed bacteria revealed that galectins-3, -4, and -8, but not galectin-1, bind to Kpn and NTHi cells, and confocal microscopy attested binding to bacterial cells in suspension. The three galectins bound to array-printed Kpn LPS. Moreover, analysis of galectin binding to mutant Kpn cells evidenced that the O-chain is the docking point for galectins on wild type Kpn. Galectins-3, -4, and -8 also bound the NTHi LOS. Microarray-assisted comparison of the binding to full-length and truncated LOSs, as well as to wild type and mutant cells, supported LOS involvement in galectin binding to NTHi. However, deletion of the entire LOS oligosaccharide chain actually increased binding to NTHi cells, indicating the availability of other ligands on the bacterial surface, as similarly inferred for Kpn cells devoid of both O-chain and capsule. Altogether, the results illustrate galectins’ versatility for recognizing different bacterial structures, and point out the occurrence of so far overlooked galectin ligands on bacterial surfaces.

A Plausible Role for Collectins in Skin Immune Homeostasis

The skin is a complex organ that faces the external environment and participates in the innate immune system. Skin immune homeostasis is necessary to defend against external microorganisms and to recover from stress to the skin. This homeostasis depends on interactions among a variety of cells, cytokines, and the complement system. Collectins belong to the lectin pathway of the complement system, and have various roles in innate immune responses. Mannose-binding lectin (MBL), collectin kidney 1, and liver (CL-K1, CL-L1) activate the lectin pathway, while all have multiple functions, including recognition of pathogens, opsonization of phagocytosis, and modulation of cytokine-mediated inflammatory responses. Certain collectins are localized in the skin, and their expressions change during skin diseases. In this review, we summarize important advances in our understanding of how MBL, surfactant proteins A and D, CL-L1, and CL-K1 function in skin immune homeostasis. Based on the potential roles of collectins in skin diseases, we suggest therapeutic strategies for skin diseases through the targeting of collectins and relevant regulators.

Genetic variation in surfactant protein-A2 alters responses to ozone

BACKGROUND

Increased exposure to Ozone (O3) is associated with adverse health effects in individuals afflicted with respiratory diseases. Surfactant protein-A (SP-A), encoded by SP-A1 and SP-A2, is the largest protein component in pulmonary surfactant and is functionally impaired by O3-oxidation.

OBJECTIVE

We used humanized SP-A2 transgenic mice with allelic variation corresponding to a glutamine (Q) to lysine (K) amino acid substitution at position 223 in the lectin domain to determine the impact of this genetic variation in regards to O3 exposure.

METHODS

Mice were exposed to 2ppm O3 or Filtered Air (FA) for 3 hours and 24 hrs post-challenge pulmonary function tests and other parameters associated with inflammation were assessed in the bronchoalveolar lavage (BAL) fluid and lung tissue. Additionally, mouse tracheal epithelial cells were cultured and TEER measurements recorded for each genotype to determine baseline epithelial integrity.

RESULTS

Compared to FA, O3 exposure led to significantly increased sensitivity to methacholine challenge in all groups of mice. SP-A2 223Q variant mice were significantly protected from O3-induced AHR compared to SP-A-/- and SP-A2 223K mice. Neutrophilia was observed in all genotypes of mice post O3-exposure, however, SP-A2 223Q mice had a significantly lower percentage of neutrophils compared to SP-A-/- mice. Albumin levels in BAL were unchanged in O3-exposed SP-A2 223Q mice compared to their FA controls, while levels were significantly increased in all other genotypes of O3-exposed mice. SP-A 223Q MTECS has significant higher TEER values than all other genotypes, and WT MTECS has significantly higher TEER than the SP-A KO and SP-A 223K MTECS.

SIGNIFICANCE

Taken together, our study suggests that expression of a glutamine (Q) as position 223 in SP-A2, as opposed to expression of lysine (K), is more protective in acute exposures to ozone and results in attenuated O3-induced AHR, neutrophilia, and vascular permeability.

Role of Surfactant Protein D in Experimental Otitis Media

Surfactant protein D (SP-D) is a C-type collectin and plays an important role in innate immunity and homeostasis in the lung. This study studied SP-D role in the nontypeable Haemophilus influenzae (NTHi)-induced otitis media (OM) mouse model. Wild-type C57BL/6 (WT) and SP-D knockout (KO) mice were used in this study. Mice were injected in the middle ear (ME) with 5 μL of NTHi bacterial solution (3.5 × 105 CFU/ear) or with the same volume of sterile saline (control). Mice were sacrificed at 3 time points, days 1, 3, and 7, after treatment. We found SP-D expression in the Eustachian tube (ET) and ME mucosa of WT mice but not in SP-D KO mice. After infection, SP-D KO mice showed more intense inflammatory changes evidenced by the increased mucosal thickness and inflammatory cell infiltration in the ME and ET compared to WT mice (p < 0.05). Increased bacterial colony-forming units and cytokine (IL-6 and IL-1β) levels in the ear washing fluid of infected SP-D KO mice were compared to infected WT mice. Molecular analysis revealed higher levels of NF-κB and NLRP3 activation in infected SP-D KO compared to WT mice (p < 0.05). In vitro studies demonstrated that SP-D significantly induced NTHi bacterial aggregation and enhanced bacterial phagocytosis by macrophages (p < 0.05). Furthermore, human ME epithelial cells showed a dose-dependent increased expression of NLRP3 and SP-D proteins after LPS treatment. We conclude that SP-D plays a critical role in innate immunity and disease resolution through enhancing host defense and regulating inflammatory NF-κB and NLRP3 activation in experimental OM mice.

Collagen Binding Proteins of Gram-Positive Pathogens

Collagens are the primary structural components of mammalian extracellular matrices. In addition, collagens regulate tissue development, regeneration and host defense through interaction with specific cellular receptors. Their unique triple helix structure, which requires a glycine residue every third amino acid, is the defining structural feature of collagens. There are 28 genetically distinct collagens in humans. In addition, several other unrelated human proteins contain a collagen domain. Gram-positive bacteria of the genera Staphylococcus, Streptococcus, Enterococcus, and Bacillus express cell surface proteins that bind to collagen. These proteins of Gram-positive pathogens are modular proteins that can be classified into different structural families. This review will focus on the different structural families of collagen binding proteins of Gram-positive pathogen. We will describe how these proteins interact with the triple helix in collagens and other host proteins containing a collagenous domain and discuss how these interactions can contribute to the pathogenic processes.

Pulmonary Surfactant and Drug Delivery: An Interface-Assisted Carrier to Deliver Surfactant Protein SP-D Into the Airways

This work is focused on the potential use of pulmonary surfactant to deliver full-length recombinant human surfactant protein SP-D (rhSP-D) using the respiratory air-liquid interface as a shuttle. Surfactant protein D (SP-D) is a collectin protein present in the pulmonary surfactant (PS) system, involved in innate immune defense and surfactant homeostasis. It has been recently suggested as a potential therapeutic to alleviate inflammatory responses and lung diseases in preterm infants suffering from respiratory distress syndrome (RDS) or bronchopulmonary dysplasia (BPD). However, none of the current clinical surfactants used for surfactant replacement therapy (SRT) to treat RDS contain SP-D. The interaction of SP-D with surfactant components, the potential of PS as a respiratory drug delivery system and the possibility to produce recombinant versions of human SP-D, brings the possibility of delivering clinical surfactants supplemented with SP-D. Here, we used an in vitro setup that somehow emulates the respiratory air-liquid interface to explore this novel approach. It consists in two different compartments connected with a hydrated paper bridge forming a continuous interface. We firstly analyzed the adsorption and spreading of rhSP-D alone from one compartment to another over the air-liquid interface, observing low interfacial activity. Then, we studied the interfacial spreading of the protein co-administered with PS, both at different time periods or as a mixed formulation, and which oligomeric forms of rhSP-D better traveled associated with PS. The results presented here demonstrated that PS may transport rhSP-D long distances over air-liquid interfaces, either as a mixed formulation or separately in a close window time, opening the doors to empower the current clinical surfactants and SRT.

Galectins in allergic inflammatory diseases

Allergic inflammatory diseases are a global public health concern affecting millions of people. Although there are several potential hypotheses, details regarding their molecular mechanisms are still ambiguous. Recently, a group of β-galactoside-binding proteins, galectins, have been revealed as important factors in altering allergic chronic inflammatory diseases. In this review, we describe the molecular and cellular basis of how galectins modulate inflammatory reactions. We also provide an overview of clinical features related to galectins. Finally, we discuss the potential issues that might lead to misrepresentation of the exact biological functions of galectins.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.

Phosphatidylglycerol and surfactant: A potential treatment for COVID-19?

A hypothesis concerning the potential utility of surfactant supplementation for the treatment of critically ill patients with COVID-19 is proposed, along with a brief summary of the data in the literature supporting this idea. It is thought that surfactant, which is already approved by the Food and Drug Administration for intratracheal administration to treat neonatal respiratory distress syndrome in pre-term infants, could benefit COVID-19-infected individuals by: (1) restoring surfactant damaged by lung infection and/or decreased due to the virus-induced death of the type II pneumocytes that produce it and (2) reducing surface tension to decrease the work of breathing and limit pulmonary edema. In addition, a constituent of surfactant, phosphatidylglycerol, could mitigate COVID-19-induced lung pathology by: (3) decreasing excessive innate immune system stimulation via its inhibition of toll-like receptor-2 and -4 activation by microbial components and cellular proteins released by damaged cells, thereby limiting inflammation and the resultant pulmonary edema, and (4) possibly blocking spread of the viral infection to non-infected cells in the lung. Therefore, it is suggested that surfactant preparations containing phosphatidylglycerol be tested for their ability to improve lung function in critically ill patients with COVID-19.

Analysis of the SARS-CoV-2 spike protein glycan shield reveals implications for immune recognition

Here we have generated 3D structures of glycoforms of the spike (S) glycoprotein from SARS-CoV-2, based on reported 3D structures and glycomics data for the protein produced in HEK293 cells. We also analyze structures for glycoforms representing those present in the nascent glycoproteins (prior to enzymatic modifications in the Golgi), as well as those that are commonly observed on antigens present in other viruses. These models were subjected to molecular dynamics (MD) simulation to determine the extent to which glycan microheterogeneity impacts the antigenicity of the S glycoprotein. Lastly, we have identified peptides in the S glycoprotein that are likely to be presented in human leukocyte antigen (HLA) complexes, and discuss the role of S protein glycosylation in potentially modulating the innate and adaptive immune response to the SARS-CoV-2 virus or to a related vaccine. The 3D structures show that the protein surface is extensively shielded from antibody recognition by glycans, with the notable exception of the ACE2 receptor binding domain, and also that the degree of shielding is largely insensitive to the specific glycoform. Despite the relatively modest contribution of the glycans to the total molecular weight of the S trimer (17% for the HEK293 glycoform) they shield approximately 40% of the protein surface.

Quantitative Impact of Cell Membrane Fluorescence Labeling on Phagocytosis Measurements in Confrontation Assays

Phagocytosis is series of steps where the pathogens and the immune cells interact during an invasion. This starts with the adhesion process between the host and pathogen cells, and is followed by the engulfment of the pathogens. Many analytical methods that are applied to characterize phagocytosis based on imaging the host-pathogen confrontation assays rely on the fluorescence labeling of cells. However, the potential effect of the membrane labeling on the quantitative results of the confrontation assays has not been studied in detail. In this study, we determine whether the fluorescence labeling processes themselves influence the results of the phagocytosis measurements. Here, alveolar macrophages, which form one of the most important compartments of the innate immune system, were used as an example of host cells, whereas Aspergillus fumigatus and Lichtheimia corymbifera that cause aspergillosis and mucormycosis, respectively, were studied as examples for pathogens. At first, our study investigated the importance of the sequence of steps of the fixation process when preparing the confrontation assay sample for microscopy studies. Here we showed that applying the fixation agent before the counter-staining causes miscalculations during the determination of the phagocytic measures. Furthermore, we also found that staining the macrophages with various concentrations of DID, as a typical membrane label, in most cases altered the capability of macrophages to phagocytose FITC-stained A. fumigatus and L. corymbifera spores in comparison with unlabeled macrophages. This effect of the DID staining showed a differential character dependent upon the labeling status and the specific type of pathogen. Moreover, labeling the spores of A. fumigatus and L. corymbifera with FITC increased the phagocytic measures during confrontation with unlabeled macrophages when compared to label-free spores. Overall, our study confirms that the staining process itself may significantly manipulate the quantitative outcome of the confrontation assay. As a result of our study, we also developed a user-friendly image analysis tool that analyses confrontation assays both with and without fluorescence labeling of the host cells and of the pathogens. Our image analysis algorithm saves experimental work effort and time, provides more precise results when calculating the phagocytic measures, and delivers a convenient analysis tool for the biologists to monitor host-pathogen interactions as they happen without the artifacts that fluorescence labeling imposes on biological interactions.

Lipid-Protein and Protein-Protein Interactions in the Pulmonary Surfactant System and Their Role in Lung Homeostasis

Pulmonary surfactant is a lipid/protein complex synthesized by the alveolar epithelium and secreted into the airspaces, where it coats and protects the large respiratory air–liquid interface. Surfactant, assembled as a complex network of membranous structures, integrates elements in charge of reducing surface tension to a minimum along the breathing cycle, thus maintaining a large surface open to gas exchange and also protecting the lung and the body from the entrance of a myriad of potentially pathogenic entities. Different molecules in the surfactant establish a multivalent crosstalk with the epithelium, the immune system and the lung microbiota, constituting a crucial platform to sustain homeostasis, under health and disease. This review summarizes some of the most important molecules and interactions within lung surfactant and how multiple lipid–protein and protein–protein interactions contribute to the proper maintenance of an operative respiratory surface.

Analysis of the SARS-CoV-2 spike protein glycan shield: implications for immune recognition

Here we have generated 3D structures of glycoforms of the spike (S) glycoprotein from SARS-CoV-2, based on reported 3D structures and glycomics data for the protein produced in HEK293 cells. We also analyze structures for glycoforms representing those present in the nascent glycoproteins (prior to enzymatic modifications in the Golgi), as well as those that are commonly observed on antigens present in other viruses. These models were subjected to molecular dynamics (MD) simulation to determine the extent to which glycan microheterogeneity impacts the antigenicity of the S glycoprotein. Lastly, we have identified peptides in the S glycoprotein that are likely to be presented in human leukocyte antigen (HLA) complexes, and discuss the role of S protein glycosylation in potentially modulating the adaptive immune response to the SARS-CoV-2 virus or to a related vaccine. The 3D structures show that the protein surface is extensively shielded from antibody recognition by glycans, with the exception of the ACE2 receptor binding domain, and also that the degree of shielding is largely insensitive to the specific glycoform. Despite the relatively modest contribution of the glycans to the total molecular weight (17% for the HEK293 glycoform) the level of surface shielding is disproportionately high at 42%.

Co-expression of surfactant protein A and chicken lung lectin in chicken respiratory system

Chicken surfactant protein A (cSP-A) and chicken lung lectin (cLL) are C-type lectins that play important roles in pulmonary host defense responses. Herein, we explored the localization of cSP-A and cLL in the chicken respiratory system. Six tissues from 30-days-old SPF chickens were used to quantify the expression of cSP-A and cLL using the quantitative real-time reverse transcriptional polymerase chain reaction (qRT-PCR) and fluorescence multiplex immunohistochemistry staining (fluorescence mIHC staining). Results showed that cSP-A and cLL mRNA were highly expressed in lungs compared to other tissues. cSP-A mRNA expression levels in all tissues were higher compared with cLL expression levels as analyzed using qRT-PCR. Fluorescence mIHC co-expression of cSP-A and cLL were mainly detected in lung parabronchial epithelia, and mucosal epithelia of larynx, trachea, syrinx, bronchus and air sac, with cSP-A showing a stronger positive staining compared with cLL. cLL is expressed on both mucosal surfaces, some individual lung epithelial cells and cartilage cells, while cSP-A is mainly restricted to mucosal surfaces of the respiratory tract. These histological findings may be useful for understanding the biological significance of this pulmonary lectins in future studies.

Microarray Strategies for Exploring Bacterial Surface Glycans and Their Interactions With Glycan-Binding Proteins

Bacterial surfaces are decorated with distinct carbohydrate structures that may substantially differ among species and strains. These structures can be recognized by a variety of glycan-binding proteins, playing an important role in the bacteria cross-talk with the host and invading bacteriophages, and also in the formation of bacterial microcolonies and biofilms. In recent years, different microarray approaches for exploring bacterial surface glycans and their recognition by proteins have been developed. A main advantage of the microarray format is the inherent miniaturization of the method, which allows sensitive and high-throughput analyses with very small amounts of sample. Antibody and lectin microarrays have been used for examining bacterial glycosignatures, enabling bacteria identification and differentiation among strains. In addition, microarrays incorporating bacterial carbohydrate structures have served to evaluate their recognition by diverse host/phage/bacterial glycan-binding proteins, such as lectins, effectors of the immune system, or bacterial and phagic cell wall lysins, and to identify antigenic determinants for vaccine development. The list of samples printed in the arrays includes polysaccharides, lipopoly/lipooligosaccharides, (lipo)teichoic acids, and peptidoglycans, as well as sequence-defined oligosaccharide fragments. Moreover, microarrays of cell wall fragments and entire bacterial cells have been developed, which also allow to study bacterial glycosylation patterns. In this review, examples of the different microarray platforms and applications are presented with a view to give the current state-of-the-art and future prospects in this field.

Mannan-Binding Lectin Regulates Inflammatory Cytokine Production, Proliferation, and Cytotoxicity of Human Peripheral Natural Killer Cells

Natural killer (NK) cells represent the founding members of innate lymphoid cells (ILC) and play critical roles in inflammation and the immune response. NK cell effector functions are regulated and fine-tuned by various immune modulators. Mannan (or mannose)-binding lectin (MBL), a soluble C-type lectin, is traditionally recognized as an initiator of the complement pathway. Recently, it is also considered as an immunomodulator by its interaction with kinds of immune cells. However, the effect of MBL on NK cell function remains unexplored. In this study, we found that human plasma MBL could interact directly with peripheral NK cells partially via its collagen-like region (CLR). This MBL binding markedly suppressed the interleukin-2- (IL-2-) induced inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) production but increased the IL-10 production in NK cells. In addition, the expression of activation surface markers such as CD25 and CD69 declined after MBL treatment. Also, MBL impaired the proliferation and lymphokine-activated killing (LAK) of NK cells. Moreover, we demonstrated that MBL inhibited IL-2-induced signal transducers and activators of transcription 5 (STAT5) activation in NK cells. In conclusion, we have uncovered a far unknown regulatory role of MBL on NK cells, a new clue that could be important in the immunomodulatory networks of immune responses.

Galectin-3 Inhibits Paracoccidioides brasiliensis Growth and Impacts Paracoccidioidomycosis through Multiple Mechanisms

The thermodimorphic pathogenic fungi Paracoccidioides brasiliensis and Paracoccidioides lutzii are the etiologic causes of paracoccidioidomycosis (PCM), the most prevalent systemic mycosis in Latin America. Galectin-3 (Gal-3), an animal β-galactoside-binding protein, modulates important roles during microbial infections, such as triggering a Th2-polarized immune response in PCM. Herein, we demonstrate that Gal-3 also plays other important roles in P. brasiliensis infection. We verified that Gal-3 levels are upregulated in human and mice infections and established that Gal-3 inhibited P. brasiliensis growth by inhibiting budding. Furthermore, Gal-3 affected disruption and internalization of extracellular vesicles (EVs) from P. brasiliensis by macrophages. Our results suggest important protective roles for Gal-3 in P. brasiliensis infection, indicating that increased Gal-3 production during P. brasiliensis infection may affect fungal growth and EV stability, thus promoting beneficial effects that could influence the course of PCM. The finding that Gal-3 has effects against P. brasiliensis together with previously reported effects against Cryptococcus neoformans suggests that molecule has a general antifungal role in innate defenses against fungal pathogens.IMPORTANCE Paracoccidioidomycosis (PCM) is the most prevalent systemic mycosis in Latin America. Although the immune mechanisms to control PCM are still not fully understood, several events of the host innate and adaptive immunity are crucial to determine the progress of the infection. Mammalian β-galactoside-binding protein galectin-3 (Gal-3) plays significant roles during microbial infections and has been studied for its immunomodulatory roles, but it can also have direct antimicrobial effects. We asked whether this protein plays a role in Paracoccidioides brasiliensis We report herein that Gal-3 indeed has direct effects on the fungal pathogen, inhibiting fungal growth and reducing extracellular vesicle stability. Our results suggest a direct role for Gal-3 in P. brasiliensis infection, with beneficial effects for the mammalian host.

Galectins in the Pathogenesis of Cerebrovascular Accidents: An Overview

Due to limitations of neuroimaging, such as the isodense appearance of blood to neuronal tissue in subacute hemorrhagic stroke, a body of studies have been performed to evaluate candidate biomarkers which may aid in accurate determination of cerebrovascular accident type. Beyond aiding in the delineation of stroke cause, biomarkers could also confer useful prognostic information to help clinicians plan use of resources. One of the candidate biomarkers studied for detection of cerebrovascular accident (CVA) includes a class of proteins called galectins. Galectins bind β-galactoside through a highly conserved carbohydrate recognition domain, endowing an ability to interact with carbohydrate moieties on glycoproteins, some of which are relevant to CVA response. Furthermore, galectins-1, -2, -3, -9, and -12 are expressed in tissues relevant to CVA, and some exhibit characteristics (eg, extracellular secretion) that could render feasible their detection in serum. Galectins-1 and -3 appear to have the largest amounts of preclinical evidence, consistently demonstrating increased activity and expression levels during CVA. However, a lack of standardization of biochemical assays across cohort studies limits further translation of these basic science studies. This review aims to increase awareness of the biochemical roles of galectins in CVA, while also highlighting challenges and remaining questions preventing the translation of basic science observations into a clinically useful test.

Complement Dependent and Independent Interaction Between Bovine Conglutinin and Mycobacterium bovis BCG: Implications in Bovine Tuberculosis

Bovine conglutinin, the first animal collectin to be discovered, is structurally very similar to Surfactant Protein D (SP-D). SP-D is known to interact with Mycobacterium tuberculosis, and the closely-related M. bovis, the causative agent of bovine tuberculosis. We speculated that due to the overall similarities between conglutinin and SP-D, conglutinin is likely to have a protective influence in bovine tuberculosis. We set out to investigate the role of conglutinin in host-pathogen interaction during mycobacterial infection. We show here that a recombinant truncated form of conglutinin (rfBC), composed of the neck and C-type lectin domains, binds specifically and in a dose-dependent manner to the model organism Mycobacterium bovis BCG. rfBC showed a significant direct bacteriostatic effect on the growth of M. bovis BCG in culture. In addition, rfBC inhibited the uptake of M. bovis BCG by THP-1 macrophages (human monocyte lineage cell line) and suppressed the subsequent pro-inflammatory response. Conglutinin is well-known as a binder of the complement activation product, iC3b. rfBC was also able to inhibit the uptake of complement-coated M. bovis BCG by THP-1 macrophages, whilst modulating the pro-inflammatory response. It is likely that rfBC inhibits the phagocytosis of mycobacteria by two distinct mechanisms: firstly, rfBC interferes with mannose receptor-mediated uptake by masking lipoarabinomannan (LAM) on the mycobacterial surface. Secondly, since conglutinin binds iC3b, it can interfere with complement receptor-mediated uptake via CR3 and CR4, by masking interactions with iC3b deposited on the mycobacterial surface. rfBC was also able to modulate the downstream pro-inflammatory response in THP-1 cells, which is important for mobilizing the adaptive immune response, facilitating containment of mycobacterial infection. In conclusion, we show that conglutinin possesses complement-dependent and complement-independent anti-mycobacterial activities, interfering with both known mechanisms of mycobacterial uptake by macrophages. As mycobacteria are specialized intracellular pathogens, conglutinin may inhibit M. bovis and M. tuberculosis from establishing an intracellular niche within macrophages, and thus, negatively affect the long-term survival of the pathogen in the host.