Lung and salivary scavenger receptor glycoprotein-340 contribute to the host defense against influenza A viruses

Protein-bound sialic acid in saliva contributes directly to salivary anti-influenza virus activity

The oral cavity is an entrance for respiratory viruses, such as influenza. Recently, saliva has been shown to exert both antimicrobial and antiviral activities. Thus, saliva may be a biological factor that contributes to the prevention of influenza infection. However, the actual salivary anti-influenza A virus (IAV) activity in individuals and its determinant factors are unknown. By assessing individual variations in salivary anti-IAV activity in 92 people using an established new high-throughput system in this study, we found that the anti-IAV activity varied widely between individuals and showed a significant positive correlation with protein-bound sialic acid (BSA) level (ρ = 0.473; p < 0.001). Furthermore, the anti-IAV activity of saliva with enzymatically reduced BSA content was significantly lower. These results indicate that BSA is a direct regulator of salivary anti-IAV activity and is a determinant of individual differences. Additionally, after comparing the anti-IAV activity across the groups by age, anti-IAV activity in young people (aged 5–19 years) were lower than in adults aged 20–59 years and elderly people aged 60–79 years. Our study suggests that BSA levels in saliva may be important in preventing influenza infection.

Exosome therapeutics for COVID-19 and respiratory viruses

Respiratory viral diseases are a leading cause of mortality in humans. They have proven to drive pandemic risk due to their complex transmission factors and viral evolution. However, the slow production of effective antiviral drugs and vaccines allows for outbreaks of these diseases, emphasizing a critical need for refined antiviral therapeutics. The delivery of exosomes, a naturally secreted extracellular vesicle, yields therapeutic effects for a variety of diseases, including viral infection. Exosomes and viruses utilize similar endosomal sorting pathways and mechanisms, providing exosomes with the potential to serve as a therapeutic that can target, bind, and suppress cellular uptake of various viruses including the novel severe acute respiratory syndrome coronavirus 2. Here, we review the relationship between exosomes and respiratory viruses, describe potential exosome therapeutics for viral infections, and summarize progress toward clinical translation for lung-derived exosome therapeutics.

Glycosylation and Aging

Human lifespan has increased significantly in the last 200 years, emphasizing our need to age healthily. Insights into molecular mechanisms of aging might allow us to slow down its rate or even revert it. Similar to aging, glycosylation is regulated by an intricate interplay of genetic and environmental factors. The dynamics of glycopattern variation during aging has been mostly explored for plasma/serum and immunoglobulin G (IgG) N-glycome, as we describe thoroughly in this chapter. In addition, we discuss the potential functional role of agalactosylated IgG glycans in aging, through modulation of inflammation level, as proposed by the concept of inflammaging. We also comment on the potential to use the plasma/serum and IgG N-glycome as a biomarker of healthy aging and on the interventions that modulate the IgG glycopattern. Finally, we discuss the current knowledge about animal models for human plasma/serum and IgG glycosylation and mention other, less explored, instances of glycopattern changes during organismal aging and cellular senescence.

Intestinal SALSA/dmbt1 levels are decreased in prematurely born infants

The first months of life represent a crucial time period for an infant. Alongside establishing the early microbiome, the mucosal immunological homeostasis is being developed. Both processes may be perturbed in prematurely born infants. The glycoprotein SALSA plays a role in mucosal inflammation and microbial clearance. It is one of the most abundant molecules on the intestinal mucosal surfaces in early life. SALSA binds to many types of microbes and host defence molecules like IgA, C1q and collectin molecules. We here describe the development in faecal SALSA levels during the first three months of life. During these 90 days, the median SALSA level in full-term babies decreased from 1100 μg/mL (range 49-17 000 μg/mL) to 450 μg/mL (range 33-1000 μg/mL). Lower levels of SALSA were observed in prematurely born infants in the same time period. Our novel observation thus indicates an impact of prematurity on an important component of the infant intestinal immune system. Changes in SALSA in early life may have an effect on the early establishment of the human microbiome.

DMBT1 is upregulated in lung epithelial cells after hypoxia and changes surfactant ultrastructure

BACKGROUND

Hypoxia and asphyxia are known to induce surfactant inactivation in newborns. Deleted in Malignant Brain Tumors 1 (DMBT1) is an innate immunity protein with functions in epithelial differentiation and angiogenesis. It was detected in hyaline membranes of infants with respiratory distress syndrome. Human recombinant DMBT1 is able to increase the surface tension of exogenous surfactant preparations in a dose-dependent manner.

METHODS

Immunohistochemistry was performed on lung sections of infants who died due to pre-, peri- or postnatal hypoxia. The lung epithelial cell line A549 was stably transfected with a DMBT1 (DMBT1+ cells) expression plasmid or with an empty plasmid (DMBT1- cells). The cells were cultured in normoxic or hypoxic conditions, and then DMBT1 as well as HIF-1α RNA expression were analyzed by using real-time-polymerase chain reaction. Human recombinant DMBT1 was added to the modified porcine natural surfactant Curosurf to examine the effect of DMBT1 on surfactant ultrastructure with electron microscopy.

RESULTS

DMBT1 expression was upregulated in human lung tissue after fetal/peri-/postnatal hypoxia. In addition, in vitro experiments showed increased DMBT1 RNA expression in A549 cells after hypoxia. HIF-1α was upregulated in both DMBT1+ and DMBT1- cells in response to hypoxia. The addition of human recombinant DMBT1 to Curosurf caused an impaired surfactant ultrastructure.

CONCLUSIONS

DMBT1 is upregulated in response to hypoxia and there seems to be a link between hypoxia and surfactant inactivation.

Innate Immunity and Influenza A Virus Pathogenesis: Lessons for COVID-19

There is abundant evidence that the innate immune response to influenza A virus (IAV) is highly complex and plays a key role in protection against IAV induced infection and illness. Unfortunately it also clear that aspects of innate immunity can lead to severe morbidity or mortality from IAV, including inflammatory lung injury, bacterial superinfection, and exacerbation of reactive airways disease. We review broadly the virus and host factors that result in adverse outcomes from IAV and show evidence that inflammatory responses can become damaging even apart from changes in viral replication per se, with special focus on the positive and adverse effects of neutrophils and monocytes. We then evaluate in detail the role of soluble innate inhibitors including surfactant protein D and antimicrobial peptides that have a potential dual capacity for down-regulating viral replication and also inhibiting excessive inflammatory responses and how these innate host factors could possibly be harnessed to treat IAV infection. Where appropriate we draw comparisons and contrasts the SARS-CoV viruses and IAV in an effort to point out where the extensive knowledge existing regarding severe IAV infection could help guide research into severe COVID 19 illness or vice versa.

Structures of SALSA/DMBT1 SRCR domains reveal the conserved ligand-binding mechanism of the ancient SRCR fold

The structures of SALSA SRCR domains 1 and 8 reveal a cation-dependent mechanism for ligand recognition, contributing to important roles in the immune system and cellular signalling. The cation-binding sites are conserved across all SRCR domains, suggesting conserved functional mechanisms.

The scavenger receptor cysteine-rich (SRCR) family of proteins comprises more than 20 membrane-associated and secreted molecules. Characterised by the presence of one or more copies of the ∼110 amino-acid SRCR domain, this class of proteins have widespread functions as antimicrobial molecules, scavenger receptors, and signalling receptors. Despite the high level of structural conservation of SRCR domains, no unifying mechanism for ligand interaction has been described. The SRCR protein SALSA, also known as DMBT1/gp340, is a key player in mucosal immunology. Based on detailed structural data of SALSA SRCR domains 1 and 8, we here reveal a novel universal ligand-binding mechanism for SALSA ligands. The binding interface incorporates a dual cation-binding site, which is highly conserved across the SRCR superfamily. Along with the well-described cation dependency on most SRCR domain–ligand interactions, our data suggest that the binding mechanism described for the SALSA SRCR domains is applicable to all SRCR domains. We thus propose to have identified in SALSA a conserved functional mechanism for the SRCR class of proteins.

Inhibition of Influenza A Virus by Human Infant Saliva

Innate antiviral factors in saliva play a role in protection against respiratory infections. We tested the anti-influenza virus activities of saliva samples taken from human infants, 1–12 months old, with no history of prior exposure to influenza. In contrast to the inhibitory activity we observed in mouse and ferret saliva, the activity of human infant saliva was complex, with both sialic acid-dependent and independent components, the proportion of which differed between individuals. Taken as a whole, we showed that the major anti-influenza activity of infant saliva is acquired over the first year of life and is associated with sialic acid-containing molecules. The activity of sialic acid-independent inhibitors was lower overall, more variable between individuals, and less dependent on age. The results show that the saliva of very young infants can provide a degree of protection against influenza, which may be critical in the absence of adaptive immunity.

The association of PM2.5 with airway innate antimicrobial activities of salivary agglutinin and surfactant protein D

Fine particulate matter ≤2.5 μm (PM_2.5) is a prominent global public health risk factor that can cause respiratory infection by downregulating the amounts of antimicrobial proteins and peptides (AMPs). Both salivary agglutinin (SAG) and surfactant protein D (SPD) are important AMPs in respiratory mucosal fluid, providing protection against airway pathogen invasion and infection by inducing microbial aggregation and enhancing pathogen clearance. However, the relationship between PM_2.5 and these AMPs is unclear. To better understand the relationship between PM_2.5 and airway innate immune defenses, we review the respiratory antimicrobial activities of SAG and SPD, as well as the adverse effects of PM_2.5 on airway innate antimicrobial defense. We speculate there exists a dual effect between PM_2.5 and respiratory antimicrobial activity, which means that PM_2.5 suppresses respiratory antimicrobial activity through downregulating airway AMPs, while airway AMPs accelerate PM_2.5 clearance by inducing PM_2.5 microbial aggregation. We propose further research on the relationship between PM_2.5 and these AMPs.

The Role and Molecular Mechanism of Action of Surfactant Protein D in Innate Host Defense Against Influenza A Virus

Influenza A viruses (IAVs) continue to pose major risks of morbidity and mortality during yearly epidemics and periodic pandemics. The genomic instability of IAV allows it to evade adaptive immune responses developed during prior infection. Of particular concern are pandemics which result from wholesale incorporation of viral genome sections from animal sources. These pandemic strains are radically different from circulating human strains and pose great risk for the human population. For these reasons, innate immunity plays a strong role in the initial containment of IAV infection. Soluble inhibitors present in respiratory lining fluids and blood provide a level of early protection against IAV. In general, these inhibitors act by binding to the viral hemagglutinin (HA). Surfactant protein D (SP-D) and mannose-binding lectin (MBL) attach to mannosylated glycans on the HA in a calcium dependent manner. In contrast, surfactant protein A, ficolins, and other inhibitors present sialic acid rich ligands to which the HA can bind. Among these inhibitors, SP-D seems to be the most potent due to its specific mode of binding to viral carbohydrates and its ability to strongly aggregate viral particles. We have studied specific properties of the N-terminal and collagen domain of SP-D that enable formation of highly multimerized molecules and cooperative binding among the multiple trimeric lectin domains in the protein. In addition, we have studied in depth the lectin activity of SP-D through expression of isolated lectin domains and targeted mutations of the SP-D lectin binding site. Through modifying specific residues around the saccharide binding pocket, antiviral activity of isolated lectin domains of SP-D can be markedly increased for seasonal strains of IAV. Wild-type SP-D causes little inhibition of pandemic IAV, but mutated versions of SP-D were able to inhibit pandemic IAV through enhanced binding to the reduced number of mannosylated glycans present on the HA of these strains. Through collaborative studies involving crystallography of isolated lectin domains of SP-D, glycomics analysis of the HA, and molecular modeling, the mechanism of binding of wild type and mutant forms of SP-D have been determined. These studies could guide investigation of the interactions of SP-D with other pathogens.

Lectin-mediated binding and sialoglycans of porcine surfactant protein D synergistically neutralize influenza A virus

Innate immunity is critical in the early containment of influenza A virus (IAV) infection, and surfactant protein D (SP-D) plays a crucial role in the pulmonary defense against IAV. In pigs, which are important intermediate hosts during the generation of pandemic IAVs, SP-D uses its unique carbohydrate recognition domain (CRD) to interact with IAV. An N-linked CRD glycosylation provides interactions with the sialic acid-binding site of IAV, and a tripeptide loop at the lectin-binding site facilitates enhanced interactions with IAV glycans. Here, to investigate both mechanisms of IAV neutralization in greater detail, we produced an N-glycosylated neck-CRD fragment of porcine SP-D (RpNCRD) in HEK293 cells. X-ray crystallography disclosed that the N-glycan did not alter the CRD backbone structure, including the lectin site conformation, but revealed a potential second nonlectin-binding site for glycans. IAV hemagglutination inhibition, IAV aggregation, and neutralization of IAV infection studies showed that RpNCRD, unlike the human analogue RhNCRD, exhibits potent neutralizing activity against pandemic A/Aichi/68 (H3N2), enabled by both porcine-specific structural features of its CRD. MS analysis revealed an N-glycan site-occupancy of >98% at Asn-303 of RpNCRD with complex-type, heterogeneously branched and predominantly α(2,3)-sialylated oligosaccharides. Glycan-binding array data characterized both RpNCRD and RhNCRD as mannose-type lectins. RpNCRD also bound Lewis^Y structures, whereas RhNCRD bound polylactosamine-containing glycans. The presence of the N-glycan in the CRD increases the glycan-binding specificity of RpNCRD. These insights increase our understanding of porcine-specific innate defense against pandemic IAV and may inform the design of recombinant SP-D-based antiviral drugs.

Microparticle and anti-influenza activity in human respiratory secretion

Respiratory secretions, such as saliva and bronchoalveolar fluid, contain anti-influenza activity. Multiple soluble factors have been described that exert anti-influenza activity and are believed to be responsible for the anti-influenza activity in respiratory secretions. It was previously shown that a bronchial epithelial cell culture could produce exosome-like particles with anti-influenza activity. Whether such extracellular vesicles in respiratory secretions have anti-influenza activity is unknown. Therefore, we characterized bronchoalveolar lavage fluid and found microparticles, which mostly stained positive for epithelial cell markers and both α2,3- and α2,6-linked sialic acid. Microparticles were purified from bronchoalveolar lavage fluid and shown to exhibit anti-influenza activity by a hemagglutination inhibition (HI) assay and a neutralization (NT) assay. In addition, physical binding between influenza virions and microparticles was demonstrated by electron microscopy. These findings indicate that respiratory microparticles containing viral receptors can exert anti-viral activity by probably trapping viral particles. This innate mechanism may play an important role in the defense against respiratory viruses.

Salivary Blockade Protects the Lower Respiratory Tract of Mice from Lethal Influenza Virus Infection

It is possible to model the progression of influenza virus from the upper respiratory tract to the lower respiratory tract in the mouse using viral inoculum delivered in a restricted manner to the nose. In this model, infection with the A/Udorn/307/72 (Udorn) strain of virus results ultimately in high viral titers in both the trachea and lungs. In contrast, the A/Puerto Rico/8/34 (PR8) strain causes an infection that is almost entirely limited to the nasal passages. The factors that govern the progression of virus down the respiratory tract are not well understood. Here, we show that, while PR8 virus grows to high titers in the nose, an inhibitor present in the saliva blocks further progression of infection to the trachea and lungs and renders an otherwise lethal dose of virus completely asymptomatic. In vitro, the salivary inhibitor was capable of potent neutralization of PR8 virus and an additional 20 strains of type A virus and two type B strains that were tested. The exceptions were Udorn virus and the closely related H3N2 strains A/Port Chalmers/1/73 and A/Victoria/3/75. Characterization of the salivary inhibitor showed it to be independent of sialic acid and other carbohydrates for its function. This and other biochemical properties, together with its virus strain specificity and in vivo function, indicate that the mouse salivary inhibitor is a previously undescribed innate inhibitory molecule that may have evolved to provide pulmonary protection of the species from fatal influenza virus infection.IMPORTANCE Influenza A virus occasionally jumps from aquatic birds, its natural host, into mammals to cause outbreaks of varying severity, including pandemics in humans. Despite the laboratory mouse being used as a model to study influenza virus pathogenesis, natural outbreaks of influenza have not been reported in the species. Here, we shed light on one mechanism that might allow mice to be protected from influenza in the wild. We show that virus deposited in the mouse upper respiratory tract will not progress to the lower respiratory tract due to the presence of a potent inhibitor of the virus in saliva. Containing inhibitor-sensitive virus to the upper respiratory tract renders an otherwise lethal infection subclinical. This knowledge sheds light on how natural inhibitors may have evolved to improve survival in this species.

Mouse Saliva Inhibits Transit of Influenza Virus to the Lower Respiratory Tract by Efficiently Blocking Influenza Virus Neuraminidase Activity

We previously identified a novel inhibitor of influenza virus in mouse saliva that halts the progression of susceptible viruses from the upper to the lower respiratory tract of mice in vivo and neutralizes viral infectivity in MDCK cells. Here, we investigated the viral target of the salivary inhibitor by using reverse genetics to create hybrid viruses with some surface proteins derived from an inhibitor-sensitive strain and others from an inhibitor-resistant strain. These viruses demonstrated that the origin of the viral neuraminidase (NA), but not the hemagglutinin or matrix protein, was the determinant of susceptibility to the inhibitor. Comparison of the NA sequences of a panel of H3N2 viruses with differing sensitivities to the salivary inhibitor revealed that surface residues 368 to 370 (N2 numbering) outside the active site played a key role in resistance. Resistant viruses contained an EDS motif at this location, and mutation to either EES or KDS, found in highly susceptible strains, significantly increased in vitro susceptibility to the inhibitor and reduced the ability of the virus to progress to the lungs when the viral inoculum was initially confined to the upper respiratory tract. In the presence of saliva, viral strains with a susceptible NA could not be efficiently released from the surfaces of infected MDCK cells and had reduced enzymatic activity based on their ability to cleave substrate in vitro. This work indicates that the mouse has evolved an innate inhibitor similar in function, though not in mechanism, to what humans have created synthetically as an antiviral drug for influenza virus.

IMPORTANCE Despite widespread use of experimental pulmonary infection of the laboratory mouse to study influenza virus infection and pathogenesis, to our knowledge, mice do not naturally succumb to influenza. Here, we show that mice produce their own natural form of neuraminidase inhibitor in saliva that stops the virus from reaching the lungs, providing a possible mechanism through which the species may not experience severe influenza virus infection in the wild. We show that the murine salivary inhibitor targets the outer surface of the influenza virus neuraminidase, possibly occluding entry to the enzymatic site rather than binding within the active site like commercially available neuraminidase inhibitors. This knowledge sheds light on how the natural inhibitors of particular species combat infection.

The scavenging capacity of DMBT1 is impaired by germline deletions

The Scavenger Receptor Cysteine-Rich (SRCR) proteins are an archaic group of proteins characterized by the presence of multiple SRCR domains. They are membrane-bound or secreted proteins, which are generally related to host defense systems in animals. Deleted in Malignant Brain Tumors 1 (DMBT1) is a SRCR protein which is secreted in mucosal fluids and involved in host defense by pathogen binding by its SRCR domains. Genetic polymorphism within DMBT1 leads to DMBT1-alleles giving rise to polypeptides with interindividually different numbers of SRCR domains, ranging from 8 SRCR domains (encoded by 6 kb DMBT1 variant) to 13 SRCR domains (encoded by the 8 kb DMBT1 variant). In the present study, we have investigated whether reduction from 13 to 8 amino-terminal SRCR domains leads to reduction of bacterial binding. The 6 kb variant bound ~20–45% less bacteria compared to the 8 kb variant. These results support the hypothesis that genetic variation in DMBT1 may influence microbial defense.

Neuraminidase Activity and Resistance of 2009 Pandemic H1N1 Influenza Virus to Antiviral Activity in Bronchoalveolar Fluid

Human bronchoalveolar fluid is known to have anti-influenza activity. It is believed to be a frontline innate defense against the virus. Several antiviral factors, including surfactant protein D, are believed to contribute to the activity. The 2009 pandemic H1N1 influenza virus was previously shown to be less sensitive to surfactant protein D. Nevertheless, whether different influenza virus strains have different sensitivities to the overall anti-influenza activity of human bronchoalveolar fluid was not known. We compared the sensitivities of 2009 pandemic H1N1, seasonal H1N1, and seasonal H3N2 influenza virus strains to inhibition by human bronchoalveolar lavage (BAL) fluid. The pandemic and seasonal H1N1 strains showed lower sensitivity to human BAL fluid than the H3N2 strains. The BAL fluid anti-influenza activity could be enhanced by oseltamivir, indicating that the viral neuraminidase (NA) activity could provide resistance to the antiviral defense. In accordance with this finding, the BAL fluid anti-influenza activity was found to be sensitive to sialidase. The oseltamivir resistance mutation H275Y rendered the pandemic H1N1 virus but not the seasonal H1N1 virus more sensitive to BAL fluid. Since only the seasonal H1N1 but not the pandemic H1N1 had compensatory mutations that allowed oseltamivir-resistant strains to maintain NA enzymatic activity and transmission fitness, the resistance to BAL fluid of the drug-resistant seasonal H1N1 virus might play a role in viral fitness.

IMPORTANCE

Human airway secretion contains anti-influenza activity. Different influenza strains may vary in their susceptibilities to this antiviral activity. Here we show that the 2009 pandemic and seasonal H1N1 influenza viruses were less sensitive to human bronchoalveolar lavage (BAL) fluid than H3N2 seasonal influenza virus. The resistance to the pulmonary innate antiviral activity of the pandemic virus was determined by its neuraminidase (NA) gene, and it was shown that the NA inhibitor resistance mutation H275Y abolished this resistance of the pandemic H1N1 but not the seasonal H1N1 virus, which had compensatory mutations that maintained the fitness of drug-resistant strains. Therefore, the innate respiratory tract defense may be a barrier against NA inhibitor-resistant mutants, and evasion of this defense may play a role in the emergence and spread of drug-resistant strains.

SALSA: A Regulator of the Early Steps of Complement Activation on Mucosal Surfaces

Complement is present mainly in blood. However, following mechanical damage or inflammation, serous exudates enter the mucosal surfaces. Here, the complement proteins interact with other endogenous molecules to keep microbes from entering the parenteral tissues. One of the mucosal proteins known to interact with the early complement components of both the classical and the lectin pathway is the salivary scavenger and agglutinin (SALSA). SALSA is also known as deleted in malignant brain tumors 1 and gp340. It is found both attached to the epithelium and secreted into the surrounding fluids of most mucosal surfaces. SALSA has been shown to bind directly to C1q, mannose-binding lectin, and the ficolins. Through these interactions SALSA regulates activation of the complement system. In addition, SALSA interacts with surfactant proteins A and D, secretory IgA, and lactoferrin. Ulcerative colitis and Crohn's disease are examples of diseases, where complement activation in mucosal tissues may occur. This review describes the latest advances in our understanding of how the early complement components interact with the SALSA molecule. Furthermore, we discuss how these interactions may affect disease propagation on mucosal surfaces in immunological and inflammatory diseases.

Proteomic analysis of pediatric sinonasal secretions shows increased MUC5B mucin in CRS

BACKGROUND

Chronic rhinosinusitis (CRS) is characterized by mucous overproduction and submucosal gland hyperplasia. The global protein profile of sinonasal secretions in pediatric CRS has not been studied. We hypothesized that MUC5B, a glandular mucin, would be relatively increased in CRS secretions compared to other mucins.

METHODS

Secretions were collected at Children's National Health System (Children's National) from CRS patients undergoing sinus surgery and from control patients without CRS undergoing craniofacial procedures. Proteins were extracted, digested to peptides, and analyzed by mass spectometry. Fold change significance was calculated using the QSpec algorithm. Western blot analysis was performed to validate proteomic findings.

RESULTS

In total, 294 proteins were identified. Although both MUC5B and MUC5AC were identified in a majority of samples, the relative abundance of MUC5B was found to be significantly higher (P < 0.05). Western blot data validated these findings. Other proteins with the highest significant positive-fold change in CRS samples were BP1 fold-containing family A member 1, chitinase-3-like protein 1, plastin-2, serpin 10, and BP1 fold-containing family B member 1.

CONCLUSION

Overall, our data demonstrate an increase of MUC5B abundance in the sinus secretions of pediatric patients with CRS.

Playing hide and seek: how glycosylation of the influenza virus hemagglutinin can modulate the immune response to infection

Seasonal influenza A viruses (IAV) originate from pandemic IAV and have undergone changes in antigenic structure, including addition of glycans to the hemagglutinin (HA) glycoprotein. The viral HA is the major target recognized by neutralizing antibodies and glycans have been proposed to shield antigenic sites on HA, thereby promoting virus survival in the face of widespread vaccination and/or infection. However, addition of glycans can also interfere with the receptor binding properties of HA and this must be compensated for by additional mutations, creating a fitness barrier to accumulation of glycosylation sites. In addition, glycans on HA are also recognized by phylogenetically ancient lectins of the innate immune system and the benefit provided by evasion of humoral immunity is balanced by attenuation of infection. Therefore, a fine balance must exist regarding the optimal pattern of HA glycosylation to offset competing pressures associated with recognition by innate defenses, evasion of humoral immunity and maintenance of virus fitness. In this review, we examine HA glycosylation patterns of IAV associated with pandemic and seasonal influenza and discuss recent advancements in our understanding of interactions between IAV glycans and components of innate and adaptive immunity.

Innate immunity to influenza virus: implications for future therapy

Innate immunity is critical in the early containment of influenza virus infection. The innate response is surprisingly complex. A variety of soluble innate inhibitors in respiratory secretions provide an initial barrier to infection. Dendritic cells, phagocytes and natural killer cells mediate viral clearance and promote further innate and adaptive responses. Toll-like receptors 3 and 7 and cytoplasmic RNA sensors are critical for activating these responses. In general, the innate response restricts viral replication without injuring the lung; however, the 1918 pandemic and H5N1 strains cause more profound, possibly harmful, innate responses. In this review, we discuss the implications of burgeoning knowledge of innate immunity for therapy of influenza.

Influenza A penetrates host mucus by cleaving sialic acids with neuraminidase

Background

Influenza A virus (IAV) neuraminidase (NA) cleaves sialic acids (Sias) from glycans. Inhibiting NA with oseltamivir suppresses both viral infection, and viral release from cultured human airway epithelial cells. The role of NA in viral exit is well established: it releases budding virions by cleaving Sias from glycoconjugates on infected cells and progeny virions. The role of NA in viral entry remains unclear. Host respiratory epithelia secrete a mucus layer rich in heavily sialylated glycoproteins; these could inhibit viral entry by mimicking sialylated receptors on the cell surface. It has been suggested that NA allows influenza to penetrate the mucus by cleaving these sialylated decoys, but the exact mechanism is not yet established.

Methods

We tested IAV interaction with secreted mucus using frozen human trachea/bronchus tissue sections, and bead-bound purified human salivary mucins (HSM) and purified porcine submaxillary mucins (PSM). The protective effect of mucus was analyzed using MDCK cells coated with purified HSM and PSM with known Sia content. Oseltamivir was used to inhibit NA activity, and the fluorescent reporter substrate, 4MU-Neu5Ac, was used to quantify NA activity.

Results

IAV binds to the secreted mucus layer of frozen human trachea/bronchus tissues in a Sia dependent manner. HSM inhibition of IAV infection is Sia dose-dependent, but PSM cannot inhibit infection of underlying cells. HSM competitively inhibits NA cleavage of 4MU-Neu5Ac, reporter substrate. Human IAV effectively cleaves Sias from HSM but not from PSM, and binds to HSM but not to PSM.

Conclusion

IAV interacts with human mucus on frozen tissue sections and mucus-coated beads. Inhibition of IAV infection by sialylated human mucus is dose-dependent, and enhanced when NA is inhibited with oseltamivir. Thus NA cleaves sialylated decoys during initial stages of infection. Understanding IAV interactions with host mucins is a promising new avenue for drug development.

The amazing innate immune response to influenza A virus infection

Influenza A viruses (IAVs) remain a major health threat and a prime example of the significance of innate immunity. Our understanding of innate immunity to IAV has grown dramatically, yielding new concepts that change the way we view innate immunity as a whole. Examples include the role of p53, autophagy, microRNA, innate lymphocytes, endothelial cells and gut commensal bacteria in pulmonary innate immunity. Although the innate response is largely beneficial, it also contributes to major complications of IAV, including lung injury, bacterial super-infection and exacerbation of reactive airways disease. Research is beginning to dissect out which components of the innate response are helpful or harmful. IAV uses its limited genetic complement to maximum effect. Several viral proteins are dedicated to combating innate responses, while other viral structural or replication proteins multitask as host immune modulators. Many host innate immune proteins also multitask, having roles in cell cycle, signaling or normal lung biology. We summarize the plethora of new findings and attempt to integrate them into the larger picture of how humans have adapted to the threat posed by this remarkable virus. We explore how our expanded knowledge suggests ways to modulate helpful and harmful inflammatory responses, and develop novel treatments.

Susceptibility of human and avian influenza viruses to human and chicken saliva

Oral cavity can be an entry site of influenza virus and saliva is known to contain innate soluble anti-influenza factors. Influenza strains were shown to vary in their susceptibility to those antiviral factors. Whether the susceptibility to the saliva antiviral factors plays any role in the host species specificity of influenza viruses is not known. In this study, the antiviral activity of human and chicken saliva against human and the H5N1 avian influenza viruses were investigated by hemagglutination inhibition (HI) and neutralization (NT) assays. In comparison to human influenza viruses, H5N1 isolates showed reduced susceptibility to human saliva as measured by HI and NT assays. Interestingly, an H5N1 isolate that bind to both α2,3- and α2,6-linked sialic acid showed much higher HI titers with human saliva, suggesting that the susceptibility profile was linked to the receptor-binding preference and the presence of α2,6-linked sialic in human saliva. On the other hand, the H5N1 isolates showed increased HI titers but reduced NT titers to chicken saliva as compared to human influenza isolates. The human salivary antiviral components were characterized by testing the sensitivity to heat, receptor destroying enzyme (RDE), CaCl₂/EDTA dependence, and inhibition by mannan, and shown to be α- and γ-inhibitors. These data suggest that the H5N1 HPAI influenza virus had distinctive susceptibility patterns to human and chicken saliva, which may play some roles in its infectivity and transmissibility in these hosts.

Identification of human immunodeficiency virus type 1 (HIV-1) gp120-binding sites on scavenger receptor cysteine rich 1 (SRCR1) domain of gp340

BACKGROUND

gp340, a member of scavenger receptor cysteine rich family encoded by Deleted in Malignant Brain Tumors 1 (DMBT1), is an important component in innate immune defense. The first scavenger receptor cysteine rich domain (SRCR1) of gp340 has been shown to inhibit HIV-1 infection through binding to the N-terminal flank of the V3 loop of HIV-1 gp120.

RESULTS

Through homology modeling and docking analysis of SRCR1 to a gp120-CD4-X5 antibody complex, we identified three loop regions containing polar or acidic residues that directly interacted with gp120. To confirm the docking prediction, a series of over-lapping peptides covering the SRCR1 sequence were synthesized and analyzed by gp120-peptide binding assay. Five peptides coincide with three loop regions showed the relative high binding index. An alanine substitution scan revealed that Asp34, Asp35, Asn96 and Glu101 in two peptides with the highest binding index are the critical residues in SRCR1 interaction with gp120.

CONCLUSION

We pinpointed the vital gp120-binding regions in SRCR1 and narrowed down the amino acids which play critical roles in contacting with gp120.

Serum amyloid P is a sialylated glycoprotein inhibitor of influenza A viruses

Members of the pentraxin family, including PTX3 and serum amyloid P component (SAP), have been reported to play a role in innate host defence against a range of microbial pathogens, yet little is known regarding their antiviral activities. In this study, we demonstrate that human SAP binds to human influenza A virus (IAV) strains and mediates a range of antiviral activities, including inhibition of IAV-induced hemagglutination (HA), neutralization of virus infectivity and inhibition of the enzymatic activity of the viral neuraminidase (NA). Characterization of the anti-IAV activity of SAP after periodate or bacterial sialidase treatment demonstrated that α(2,6)-linked sialic acid residues on the glycosidic moiety of SAP are critical for recognition by the HA of susceptible IAV strains. Other proteins of the innate immune system, namely human surfactant protein A and porcine surfactant protein D, have been reported to express sialylated glycans which facilitate inhibition of particular IAV strains, yet the specific viral determinants for recognition of these inhibitors have not been defined. Herein, we have selected virus mutants in the presence of human SAP and identified specific residues in the receptor-binding pocket of the viral HA which are critical for recognition and therefore susceptibility to the antiviral activities of SAP. Given the widespread expression of α(2,6)-linked sialic acid in the human respiratory tract, we propose that SAP may act as an effective receptor mimic to limit IAV infection of airway epithelial cells.

Identification and characterization of a cell surface scavenger receptor cysteine-rich protein of Sciaenops ocellatus: bacterial interaction and its dependence on the conserved structural features of the SRCR domain

The scavenger receptor cysteine-rich (SRCR) proteins are secreted or membrane-bound receptors with one or multiple SRCR domains. Members of the SRCR superfamily are known to have diverse functions that include pathogen recognition and immunoregulation. In teleost, although protein sequences with SRCR structure have been identified in some species, very little functional investigation has been carried out. In this study, we identified and characterized a teleost SRCR protein from red drum Sciaenops ocellatus. The protein was named S. ocellatus SRCR1 (SoSRCRP1). SoSRCRP1 is 410-residue in length and was predicted to be a transmembrane protein, with the extracellular region containing a collagen triple helix repeat and a SRCR domain. The SRCR domain has six conserved cysteines, of which, C338 and C399, C351 and C409, and C379 and C389 were predicted to form three disulfide bonds. SoSRCRP1 expression was detected mainly in immune-relevant tissues and upregulated by bacterial and viral infection. In head kidney leukocytes, bacterial infection stimulated the expression of SoSRCRP1, and the expressed SoSRCRP1 was localized on cell surface. Recombinant SoSRCRP1 (rSoSRCRP1) corresponding to the SRCR domain was purified from Escherichia coli and found to be able to bind Gram-negative and Gram-positive bacteria. To examine the structure-function relationship of SoSRCRP1, the mutant proteins SoSRCRP1M1, SoSRCRP1M2, SoSRCRP1M3, and SoSRCRP1M4 were created, which bear C351S and C409S, C338S, C379S, and R325A mutations respectively. Compared to rSoSRCRP1, all mutants were significantly reduced in the ability of bacterial interaction, with the highest reduction observed with SoSRCRP1M4. Taken together, these results indicate that SoSRCRP1 is a cell surface-localized SRCR protein that binds bacterial ligands in a manner that depends on the conserved structural features of the SRCR domain.

Bacterial neuraminidase rescues influenza virus replication from inhibition by a neuraminidase inhibitor

Influenza virus neuraminidase (NA) cleaves terminal sialic acid residues on oligosaccharide chains that are receptors for virus binding, thus playing an important role in the release of virions from infected cells to promote the spread of cell-to-cell infection. In addition, NA plays a role at the initial stage of viral infection in the respiratory tract by degrading hemagglutination inhibitors in body fluid which competitively inhibit receptor binding of the virus. Current first line anti-influenza drugs are viral NA-specific inhibitors, which do not inhibit bacterial neuraminidases. Since neuraminidase producing bacteria have been isolated from oral and upper respiratory commensal bacterial flora, we posited that bacterial neuraminidases could decrease the antiviral effectiveness of NA inhibitor drugs in respiratory organs when viral NA is inhibited. Using in vitro models of infection, we aimed to clarify the effects of bacterial neuraminidases on influenza virus infection in the presence of the NA inhibitor drug zanamivir. We found that zanamivir reduced progeny virus yield to less than 2% of that in its absence, however the yield was restored almost entirely by the exogenous addition of bacterial neuraminidase from Streptococcus pneumoniae. Furthermore, cell-to-cell infection was severely inhibited by zanamivir but restored by the addition of bacterial neuraminidase. Next we examined the effects of bacterial neuraminidase on hemagglutination inhibition and infectivity neutralization activities of human saliva in the presence of zanamivir. We found that the drug enhanced both inhibitory activities of saliva, while the addition of bacterial neuraminidase diminished this enhancement. Altogether, our results showed that bacterial neuraminidases functioned as the predominant NA when viral NA was inhibited to promote the spread of infection and to inactivate the neutralization activity of saliva. We propose that neuraminidase from bacterial flora in patients may reduce the efficacy of NA inhibitor drugs during influenza virus infection. (295 words).

Differential gene expression between skin and cervix induced by the E7 oncoprotein in a transgenic mouse model

HPV16 E7 oncoprotein expression in K14E7 transgenic mice induces cervical cancer after 6 months of treatment with the co-carcinogen 17β-estradiol. In untreated mice, E7 also induces skin tumors late in life albeit at low penetrance. These findings indicate that E7 alters cellular functions in cervix and skin so as to predispose these organs to tumorigenesis. Using microarrays, we determined the global genes expression profile in cervical and skin tissue of young adult K14E7 transgenic mice without estrogen treatment. In these tissues, the E7 oncoprotein altered the transcriptional pattern of genes involved in several biological processes including signal transduction, transport, metabolic process, cell adhesion, apoptosis, cell differentiation, immune response and inflammatory response. Among the E7-dysregulated genes were ones not previously known to be involved in cervical neoplasia including DMBT1, GLI1 and 17βHSD2 in cervix, as well as MMP2, 12, 14, 19 and 27 in skin.

Human H-ficolin inhibits replication of seasonal and pandemic influenza A viruses

The collectins have been shown to have a role in host defense against influenza A virus (IAV) and other significant viral pathogens (e.g., HIV). The ficolins are a related group of innate immune proteins that are present at relatively high concentrations in serum, but also in respiratory secretions; however, there has been little study of the role of ficolins in viral infection. In this study, we demonstrate that purified recombinant human H-ficolin and H-ficolin in human serum and bronchoalveolar lavage fluid bind to IAV and inhibit viral infectivity and hemagglutination activity in vitro. Removal of ficolins from human serum or bronchoalveolar lavage fluid reduces their antiviral activity. Inhibition of IAV did not involve the calcium-dependent lectin activity of H-ficolin. We demonstrate that H-ficolin is sialylated and that removal of sialic acid abrogates IAV inhibition, while addition of the neuraminidase inhibitor oseltamivir potentiates neutralization, hemagglutinin inhibition, and viral aggregation caused by H-ficolin. Pandemic and mouse-adapted strains of IAV are generally not inhibited by the collectins surfactant protein D or mannose binding lectin because of a paucity of glycan attachments on the hemagglutinin of these strains. In contrast, H-ficolin inhibited both the mouse-adapted PR-8 H1N1 strain and a pandemic H1N1 strain from 2009. H-ficolin also fixed complement to a surface coated with IAV. These findings suggest that H-ficolin contributes to host defense against IAV.

The salivary scavenger and agglutinin binds MBL and regulates the lectin pathway of complement in solution and on surfaces

The salivary scavenger and agglutinin (SALSA), also known as gp340, salivary agglutinin and deleted in malignant brain tumor 1, is a 340-kDa glycoprotein expressed on mucosal surfaces and secreted into several body fluids. SALSA binds to a broad variety of microbes and endogenous ligands, such as complement factor C1q, surfactant proteins D and A, and IgA. Our search for novel ligands of SALSA by direct protein-interaction studies led to the identification of mannan-binding lectin (MBL) as a new binding partner. We observed that surface-associated SALSA activates complement via binding of MBL. On the other hand, soluble SALSA was found to inhibit Candida albicans-induced complement activation. Thus, SALSA has a dual complement activation modifying function. It activates the lectin pathway when bound to a surface and inhibits it when free in the fluid phase. These activities are mediated via a direct interaction with MBL. This suggests that SALSA could target the innate immune responses to certain microorganisms and simultaneously limit complement activation in the fluid phase.

Soluble host defense lectins in innate immunity to influenza virus

Host defenses against viral infections depend on a complex interplay of innate (nonspecific) and adaptive (specific) components. In the early stages of infection, innate mechanisms represent the main line of host defense, acting to limit the spread of virus in host tissues prior to the induction of the adaptive immune response. Serum and lung fluids contain a range of lectins capable of recognizing and destroying influenza A viruses (IAV). Herein, we review the mechanisms by which soluble endogenous lectins mediate anti-IAV activity, including their role in modulating IAV-induced inflammation and disease and their potential as prophylactic and/or therapeutic treatments during severe IAV-induced disease.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

Detection of Influenza A virus in porcine oral fluid samples

Porcine oral fluids have been used for the detection of Porcine reproductive and respiratory syndrome virus and Porcine circovirus-2. The objective of the present study was to determine whether Influenza A virus (FLUAV) is present in porcine oral fluids at detectable levels and to validate a standard FLUAV molecular diagnostic test for porcine oral fluids. Pen-based oral fluid samples were collected on 3, 4, 5, and 6 days postinfection (DPI) from 4 groups of 6 pigs each that were inoculated intratracheally with A/Swine/Iowa/00239/2004 H1N1 and from 2 untreated or mock-inoculated groups of 6 pigs each that served as negative controls. Individual nasal swabs were also collected from these 36 pigs on 3 and 7 DPI. All oral fluid samples were examined for the presence of FLUAV by matrix gene real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and virus isolation. Nasal swabs were tested initially by virus isolation followed by retest of negative samples with real-time RT-PCR. No oral fluid sample from virus-inoculated pigs was positive by virus isolation, but 15 of 16 positive (94%) oral fluids were positive by real-time RT-PCR. In contrast, virus was isolated from 32 of 48 (67%) nasal swabs collected from virus-inoculated pigs. In addition, 382 of 910 porcine oral fluids collected from pigs in the field between August 1, 2009, and January 31, 2010, were positive by real-time RT-PCR. The results of the present study indicate that pen-based oral fluids provide an easy, effective, and safe collection method for the detection of FLUAV with rapid testing methods such as real-time RT-PCR.

An overview of influenza A virus receptors

Influenza A viruses are spherical particles that attach to cells through bonds between hemagglutinin and specific cellular receptors. Numerous studies performed have recently revealed that Sialic acid (SA) is a crucial component of influenza A virus receptors. This brief review summarizes recent advances in our understanding of influenza A virus receptors. The introduction describes the classification of influenza A virus receptors and the review continues with a survey of the distribution of SA in different tissue and host. This is followed by research applications of influenza A virus receptors, and explanation of why receptor studies are so important on a world-wide scale.

Deleted in malignant brain tumors-1 protein (DMBT1): a pattern recognition receptor with multiple binding sites

Deleted in Malignant Brain Tumors-1 protein (DMBT1), salivary agglutinin (DMBT1(SAG)), and lung glycoprotein-340 (DMBT1(GP340)) are three names for glycoproteins encoded by the same DMBT1 gene. All these proteins belong to the scavenger receptor cysteine-rich (SRCR) superfamily of proteins: a superfamily of secreted or membrane-bound proteins with SRCR domains that are highly conserved down to sponges, the most ancient metazoa. In addition to SRCR domains, all DMBT1s contain two CUB domains and one zona pellucida domain. The SRCR domains play a role in the function of DMBT1s, which is the binding of a broad range of pathogens including cariogenic streptococci, Helicobacter pylori and HIV. Mucosal defense proteins like IgA, surfactant proteins and lactoferrin also bind to DMBT1s through their SRCR domains. The binding motif on the SRCR domains comprises an 11-mer peptide in which a few amino acids are essential for binding (GRVEVLYRGSW). Adjacent to each individual SRCR domain are glycosylation domains, where the attached carbohydrate chains play a role in the binding of influenza A virus and Helicobacter pylori. The composition of the carbohydrate chains is not only donor specific, but also varies between different organs. These data demonstrate a role for DMBT1s as pattern recognition molecules containing various peptide and carbohydrate binding motifs.

The essentiality of alpha-2-macroglobulin in human salivary innate immunity against new H1N1 swine origin influenza A virus

A novel strain of influenza A H1N1 emerged in the spring of 2009 and has spread rapidly throughout the world. Although vaccines have recently been developed that are expected to be protective, their availability was delayed until well into the influenza season. Although anti-influenza drugs such as neuraminidase inhibitors can be effective, resistance to these drugs has already been reported. Although human saliva was known to inhibit viral infection and may thus prevent viral transmission, the components responsible for this activity on influenza virus, in particular, influenza A swine origin influenza A virus (S-OIV), have not yet been defined. By using a proteomic approach in conjunction with beads that bind alpha-2,6-sialylated glycoprotein, we determined that an alpha-2-macroglobulin (A2M) and an A2M-like protein are essential components in salivary innate immunity against hemagglutination mediated by a clinical isolate of S-OIV (San Diego/01/09 S-OIV). A model of an A2M-based "double-edged sword" on competition of alpha-2,6-sialylated glycoprotein receptors and inactivation of host proteases is proposed. We emphasize that endogenous A2M in human innate immunity functions as a natural inhibitor against S-OIV.

SP-D and regulation of the pulmonary innate immune system in allergic airway changes

The airway mucosal surfaces are constantly exposed to inhaled particles that can be potentially toxic, infectious or allergenic and should elicit inflammatory changes. The proximal and distal air spaces, however, are normally infection and inflammation free due to a specialized interplay between cellular and molecular components of the pulmonary innate immune system. Surfactant protein D (SP-D) is an epithelial-cell-derived immune modulator that belongs to the small family of structurally related Ca(2+)-dependent C-type collagen-like lectins. While collectins can be detected in mucosal surfaces of various organs, SP-A and SP-D (the 'lung collectins') are constitutively expressed in the lung at high concentrations. Both proteins are considered important players of the pulmonary immune responses. Under normal conditions however, SP-A-/- mice display no pathological features in the lung. SP-D-/- mice, on the other hand, show chronic inflammatory alterations indicating a special importance of this molecule in regulating immune homeostasis and the function of the innate immune cells. Recent studies in our laboratory and others implied significant associations between changes in SP-D levels and the presence of airway inflammation both in animal models and patients raising a potential usefulness of this molecule as a disease biomarker. Research on wild-type and mutant recombinant molecules in vivo and in vitro showed that SP-D binds carbohydrates, lipids and nucleic acids with a broad spectrum specificity and initiates phagocytosis of inhaled pathogens as well as apoptotic cells. Investigations on gene-deficient and conditional over expressor mice in addition, provided evidence that SP-D directly modulates macrophage and dendritic cell function as well as T cell-dependent inflammatory events. Thus, SP-D has a unique, dual functional capacity to induce pathogen elimination on the one hand and control of pro-inflammatory mechanisms on the other, suggesting a potential suitability for therapeutic prevention and treatment of chronic airway inflammation without compromising the host defence function of the airways. This paper will review recent findings on the mechanisms of immune-protective function of SP-D in the lung.

Identification of a DMBT1 polymorphism associated with increased breast cancer risk and decreased promoter activity

According to present estimations, the unfavorable combination of alleles with low penetrance but high prevalence in the population might account for the major part of hereditary breast cancer risk. Deleted in Malignant Brain Tumors 1 (DMBT1) has been proposed as a tumor suppressor for breast cancer and other cancer types. Genomewide mapping in mice further identified Dmbt1 as a potential modulator of breast cancer risk. Here, we report the association of two frequent and linked single-nucleotide polymorphisms (SNPs) with increased breast cancer risk in women above the age of 60 years: DMBT1 c.-93C>T, rs2981745, located in the DMBT1 promoter; and DMBT1 c.124A>C, p.Thr42Pro, rs11523871(odds ratio [OR]=1.66, 95% confidence interval [CI]=1.21-2.29, P=0.0017; and OR=1.66; 95% CI=1.21-2.28, P=0.0016, respectively), based on 1,195 BRCA1/2 mutation-negative German breast cancer families and 1,466 unrelated German controls. Promoter studies in breast cancer cells demonstrate that the risk-increasing DMBT1 -93T allele displays significantly decreased promoter activity compared to the DMBT1 -93C allele, resulting in a loss of promoter activity. The data suggest that DMBT1 polymorphisms in the 5'-region are associated with increased breast cancer risk. In accordance with previous results, these data link decreased DMBT1 levels to breast cancer risk.

Systems biology of influenza: understanding multidimensional interactions for personalized prevention and treatment

Influenza virus infection is a public health threat worldwide. It is urgent to develop effective methods and tools for the prevention and treatment of influenza. Influenza vaccines have significant immune response variability across the population. Most of the current circulating strains of influenza A virus are resistant to anti-influenza drugs. It is necessary to understand how genetic variants affect immune responses, especially responses to the HA and NA transmembrane glycoproteins. The elucidation of the underlying mechanisms can help identify patient subgroups for effective prevention and treatment. New personalized vaccines, adjuvants, and drugs may result from the understanding of interactions of host genetic, environmental, and other factors. The systems biology approach is to simulate and model large networks of the interacting components, which can be excellent targets for antiviral therapies. The elucidation of host-influenza interactions may provide an integrative view of virus infection and host responses. Understanding the host-influenza-drug interactions may contribute to optimal drug combination therapies. Insight of the host-influenza-vaccine interactions, especially the immunogenetics of vaccine response, may lead to the development of better vaccines. Systemic studies of host-virus-vaccine-drug-environment interactions will enable predictive models for therapeutic responses and the development of individualized therapeutic strategies. A database containing such information on personalized and systems medicine for influenza is available at http://flu.pharmtao.com.

gp340 promotes transcytosis of human immunodeficiency virus type 1 in genital tract-derived cell lines and primary endocervical tissue

The human scavenger receptor gp340 has been identified as a binding protein for the human immunodeficiency virus type 1 (HIV-1) envelope that is expressed on the cell surface of female genital tract epithelial cells. This interaction allows such epithelial cells to efficiently transmit infective virus to susceptible targets and maintain viral infectivity for several days. Within the context of vaginal transmission, HIV must first traverse a normally protective mucosa containing a cell barrier to reach the underlying T cells and dendritic cells, which propagate and spread the infection. The mechanism by which HIV-1 can bypass an otherwise healthy cellular barrier remains an important area of study. Here, we demonstrate that genital tract-derived cell lines and primary human endocervical tissue can support direct transcytosis of cell-free virus from the apical to basolateral surfaces. Further, this transport of virus can be blocked through the addition of antibodies or peptides that directly block the interaction of gp340 with the HIV-1 envelope, if added prior to viral pulsing on the apical side of the cell or tissue barrier. Our data support a role for the previously described heparan sulfate moieties in mediating this transcytosis but add gp340 as an important facilitator of HIV-1 transcytosis across genital tract tissue. This study demonstrates that HIV-1 actively traverses the protective barriers of the human genital tract and presents a second mechanism whereby gp340 can promote heterosexual transmission.

Leucine-rich repeats of bacterial surface proteins serve as common pattern recognition motifs of human scavenger receptor gp340

Scavenger receptors are innate immune molecules recognizing and inducing the clearance of non-host as well as modified host molecules. To recognize a wide pattern of invading microbes, many scavenger receptors bind to common pathogen-associated molecular patterns, such as lipopolysaccharides and lipoteichoic acids. Similarly, the gp340/DMBT1 protein, a member of the human scavenger receptor cysteine-rich protein family, displays a wide ligand repertoire. The peptide motif VEVLXXXXW derived from its scavenger receptor cysteine-rich domains is involved in some of these interactions, but most of the recognition mechanisms are unknown. In this study, we used mass spectrometry sequencing, gene inactivation, and recombinant proteins to identify Streptococcus pyogenes protein Spy0843 as a recognition receptor of gp340. Antibodies against Spy0843 are shown to protect against S. pyogenes infection, but no function or host receptor have been identified for the protein. Spy0843 belongs to the leucine-rich repeat (Lrr) family of eukaryotic and prokaryotic proteins. Experiments with truncated forms of the recombinant proteins confirmed that the Lrr region is needed in the binding of Spy0843 to gp340. The same motif of two other Lrr proteins, LrrG from the Gram-positive S. agalactiae and BspA from the Gram-negative Tannerella forsythia, also mediated binding to gp340. Moreover, inhibition of Spy0843 binding occurred with peptides containing the VEVLXXXXW motif, but also peptides devoid of the XXXXW motif inhibited binding of Lrr proteins. These results thus suggest that the conserved Lrr motif in bacterial proteins serves as a novel pattern recognition motif for unique core peptides of human scavenger receptor gp340.

Multiple components contribute to ability of saliva to inhibit influenza viruses

INTRODUCTION

Saliva is a potentially important barrier against respiratory viral infection but its mechanism of action is not well studied.

METHODS

We tested the antiviral activities of whole saliva, specific salivary gland secretions, and purified salivary proteins against strains of influenza A virus (IAV) in vitro.

RESULTS

Whole saliva or parotid or submandibular/sublingual secretions from healthy donors inhibited IAV based on hemagglutination inhibition and neutralization assays. This differs from human immunodeficiency virus (HIV), for which only submandibular/sublingual secretions are reported to be inhibitory. Among purified salivary proteins, MUC5B, scavenger receptor cysteine-rich glycoprotein 340 (salivary gp-340), histatins, and human neutrophil defensins (HNPs) inhibited IAV at the concentrations present in whole saliva. In contrast, some abundant salivary proteins (acidic proline-rich proteins and amylase) had no activity, nor did several other less abundant salivary proteins with known activity against HIV (e.g. thrombospondin or serum leukocyte protease inhibitor). Whole saliva and MUC5B did not inhibit neuraminidase activity of IAV and viral neutralizing and aggregating activity of MUC5B was potentiated by the neuraminidase inhibitor oseltamivir. Hence, MUC5B inhibits IAV by presenting a sialic acid ligand for the viral hemagglutinin. The mechanism of action of histatins requires further study.

CONCLUSIONS

These findings indicate that saliva represents an important initial barrier to IAV infection and underline the complexity of host defense activity of oral secretions. Of interest, antiviral activity of saliva against IAV and HIV differs in terms of specific glandular secretions and proteins that are inhibitory.