Assay for evaluation of rotavirus-cell interactions: identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition

Whey Protein Lipid Concentrate High in Milk Fat Globule Membrane Components Inhibit Porcine and Human Rotavirus in vitro

Background: The milk fat globule membrane (MFMG) is a complex milk component that has been shown to inhibit rotavirus (RV) binding to cell membranes in vitro. Herein, a whey protein lipid concentrate high in MFGM components (WPLC) and whey protein concentrate (WPC; control) were screened for anti-infective activity against porcine OSU and human Wa strains of RV in both the African Green Monkey kidney (MA104) and the human colorectal adenocarcinoma (Caco-2) cell lines. Materials and Methods: Confluent cells were exposed to OSU or Wa RV in the presence of WPLC or WPC (control) at 0, 0.1, 0.5, 1.0, 2.5, or 5 mg/ml. Infectivity was detected by immunohistochemistry and expressed as % inhibition relative to 0 mg/ml. WPLC efficacy over WPC was expressed as fold-change. One-way ANOVA analyzed data for the independent and interactive effects of concentration, test material, and RV strain. Results: Both WPLC and WPC exhibited concentration-dependent inhibition of human Wa and porcine OSU RV infectivity in MA104 and Caco-2 cells (p < 0.0001). WPLC was 1.5-4.8-fold more effective in reducing infectivity than WPC. WPLC efficacy was independent of RV strains, but varied between cell lines. WPLC and WPC at concentrations ≥0.5 mg/mL were most effective in reducing human Wa RV infectivity in MA104 cells (p < 0.0001). Conclusions: WPLC decreased infectivity of two strains for RV which differ in their dependency on sialic acid for binding to cells. Inhibition was observed in the most commonly used cell type for RV infectivity assays (MA104) and an intestinal cell line (Caco-2). An effect on virus infectivity might be a potential mechanisms of action contributing to beneficial effects of supplementation of infant formula with MGFM reducing the risk of infections and consequently diarrhea incidence in infants.

Sialoglycovirology of Lectins: Sialyl Glycan Binding of Enveloped and Non-enveloped Viruses

On the cell sur "face", sialoglycoconjugates act as receptionists that have an important role in the first step of various cellular processes that bridge communication between the cell and its environment. Loss of Sia production can cause the developmental of defects and lethality in most animals; hence, animal cells are less prone to evolution of resistance to interactions by rapidly evolved Sia-binding viruses. Obligative intracellular viruses mostly have rapid evolution that allows escape from host immunity, leading to an epidemic variant, and that allows emergence of a novel strain, occasionally leading to pandemics that cause health-social-economic problems. Recently, much attention has been given to the mutual recognition systems via sialosugar chains between viruses and their host cells and there has been rapid growth of the research field "sialoglycovirology." In this chapter, the structural diversity of sialoglycoconjugates is overviewed, and enveloped and non-enveloped viruses that bind to Sia are reviewed. Also, interactions of viral lectins-host Sia receptors, which determine viral transmission, host range, and pathogenesis, are presented. The future direction of new therapeutic routes targeting viral lectins, development of easy-to-use detection methods for diagnosis and monitoring changes in virus binding specificity, and challenges in the development of suitable viruses to use in virus-based therapies for genetic disorders and cancer are discussed.

Pathophysiological Mechanisms of Gastrointestinal Toxicity

Humans swallow a great variety and often large amounts of chemicals as nutrients, incidental food additives and contaminants, drugs, and inhaled particles and chemicals, thus exposing the gastrointestinal tract to many potentially toxic substances. It serves as a barrier in many cases to protect other components of the body from such substances and infections. Fortunately, the gastrointestinal tract is remarkably robust and generally is able to withstand multiple daily assaults by the chemicals to which it is exposed. Some chemicals, however, can affect one or more aspects of the gastrointestinal tract to produce abnormal events that reflect toxicity. It is the purpose of this chapter to evaluate the mechanisms by which toxic chemicals produce their deleterious effects and to determine the consequences of the toxicity on integrity of gastrointestinal structure and function. Probably because of the intrinsic ability of the gastrointestinal tract to resist toxic chemicals, there is a paucity of data regarding gastrointestinal toxicology. It is therefore necessary in many cases to extrapolate toxic mechanisms from infectious processes, inflammatory conditions, ischemia, and other insults in addition to more conventional chemical sources of toxicity.

Glycosphingolipid-Protein Interaction in Signal Transduction

Glycosphingolipids (GSLs) are a class of ceramide-based glycolipids essential for embryo development in mammals. The synthesis of specific GSLs depends on the expression of distinctive sets of GSL synthesizing enzymes that is tightly regulated during development. Several reports have described how cell surface receptors can be kept in a resting state or activate alternative signalling events as a consequence of their interaction with GSLs. Specific GSLs, indeed, interface with specific protein domains that are found in signalling molecules and which act as GSL sensors to modify signalling responses. The regulation exerted by GSLs on signal transduction is orthogonal to the ligand–receptor axis, as it usually does not directly interfere with the ligand binding to receptors. Due to their properties of adjustable production and orthogonal action on receptors, GSLs add a new dimension to the control of the signalling in development. GSLs can, indeed, dynamically influence progenitor cell response to morphogenetic stimuli, resulting in alternative differentiation fates. Here, we review the available literature on GSL–protein interactions and their effects on cell signalling and development.

Influence of Epicuticular Physicochemical Properties on Porcine Rotavirus Adsorption to 24 Leafy Green Vegetables and Tomatoes

Foodborne diseases are a persistent problem in the United States and worldwide. Fresh produce, especially those used as raw foods like salad vegetables, can be contaminated, causing illness. In this study, we determined the number of rotaviruses adsorbed on produce surfaces using group A porcine rotaviruses and 24 cultivars of leafy vegetables and tomato fruits. We also characterized the physicochemical properties of each produce's outermost surface layer, known as the epicuticle. The number of rotaviruses found on produce surfaces varied among cultivars. Three-dimensional crystalline wax structures on the epicuticular surfaces were found to significantly contribute to the inhibition of viral adsorption to the produce surfaces (p = 0.01). We found significant negative correlations between the number of rotaviruses adsorbed on the epicuticular surfaces and the concentrations of alkanes, fatty acids, and total waxes on the epicuticular surfaces. Partial least square model fitting results suggest that alkanes, ketones, fatty acids, alcohols, contact angle and surface roughness together can explain 60% of the variation in viral adsorption. The results suggest that various fresh produce surface properties need to be collectively considered for efficient sanitation treatments. Up to 10.8% of the originally applied rotaviruses were found on the produce surfaces after three washing treatments, suggesting a potential public health concern regarding rotavirus contamination.

Solar and temperature treatments affect the ability of human rotavirus wa to bind to host cells and synthesize viral RNA

Rotavirus, the leading cause of diarrheal diseases in children under the age of five, is often resistant to conventional wastewater treatment and thus can remain infectious once released into the aquatic environment. Solar and heat treatments can inactivate rotavirus, but it is unknown how these treatments inactivate the virus on a molecular level. To answer this question, our approach was to correlate rotavirus inactivation with the inhibition of portions of the virus life cycle as a means to identify the mechanisms of solar or heat inactivation. Specifically, the integrity of the rotavirus NSP3 gene, virus-host cell interaction, and viral RNA synthesis were examined after heat (57°C) or solar treatment of rotavirus. Only the inhibition of viral RNA synthesis positively correlated with a loss of rotavirus infectivity; 57°C treatment of rotavirus resulted in a decrease of rotavirus RNA synthesis at the same rate as rotavirus infectivity. These data suggest that heat treatment neutralized rotaviruses primarily by targeting viral transcription functions. In contrast, when using solar disinfection, the decrease in RNA synthesis was responsible for approximately one-half of the decrease in infectivity, suggesting that other mechanisms, including posttranslational, contribute to inactivation. Nevertheless, both solar and heat inactivation of rotaviruses disrupted viral RNA synthesis as a mechanism for inactivation.

Interactions between rotavirus and natural organic matter isolates with different physicochemical characteristics

Interaction forces between rotavirus and Suwanee River natural organic matter (SRNOM) or Colorado River NOM (CRNOM) were studied by atomic force microscopy (AFM) in NaCl solutions and at unadjusted pH (5.7-5.9). Compared to CRNOM, SRNOM has more aromatic carbon and phenolic/carboxylic functional groups. CRNOM is characterized with aliphatic structure and considerable presence of polysaccharide moieties rich in hydroxyl functional groups. Strong repulsive forces were observed between rotavirus and silica or mica or SRNOM. The interaction decay length derived from the approaching curves for these systems involving rotavirus in high ionic strength solution was significantly higher than the theoretical Debye length. While no adhesion was observed for rotavirus and SRNOM, attraction was observed between CRNOM and rotavirus during approach and adhesion during retraction. Moreover, these adhesion forces decreased with increasing ionic strength. Interactions due to ionic hydrogen bonding between deprotonated carboxyl groups on rotavirus and hydroxyl functional groups on CRNOM were suggested as the dominant interaction mechanisms between rotavirus and CRNOM.

Human milk oligosaccharides inhibit rotavirus infectivity in vitro and in acutely infected piglets

Human milk (HM) is rich in oligosaccharides (HMO) that exert prebiotic and anti-infective activities. HM feeding reduces the incidence of rotavirus (RV) infection in infants. Herein, the anti-RV activity of oligosaccharides was tested in an established in vitro system for assessing cellular binding and viral infectivity/replication, and also tested in a newly developed, acute RV infection, in situ piglet model. For the in vitro work, crude HMO isolated from pooled HM, neutral HMO (lacto-N-neotetraose, LNnT; 2'-fucosyllactose) and acidic HMO (aHMO, '-sialyllactose, 3'-SL; -sialyllactose, -SL) were tested against the porcine OSU strain and human RV Wa strain. The RV Wa strain was not inhibited by any oligosaccharides. However, the RV OSU strain infectivity was dose-dependently inhibited by sialic acid (SA)-containing HMO. 3'-SL and 6'-SL concordantly inhibited (125)I-radiolabelled RV cellular binding and infectivity/replication. For the in situ study, a midline laparotomy was performed on 21-d-old formula-fed piglets and six 10 cm loops of ileum were isolated in situ. Briefly, 2 mg/ml of LNnT, aHMO mixture (40% 6'-SL/10 % 3'-SL/50 % SA) or media with or without the RV OSU strain (1 x 10(7) focus-forming units)were injected into the loops and maintained for 6 h. The loops treated with HMO treatments þ RV had lower RV replication, as assessed by non-structural protein-4 (NSP4) mRNA expression, than RV-treated loops alone. In conclusion, SA-containing HMO inhibited RV infectivity in vitro; however, both neutral HMO and SA with aHMO decreased NSP4 replication during acute RV infection in situ.

Gangliosides have a functional role during rotavirus cell entry

Cell entry of rotaviruses is a complex process, which involves sequential interactions with several cell surface molecules. Among the molecules implicated are gangliosides, glycosphingolipids with one or more sialic acid (SA) residues. The role of gangliosides in rotavirus cell entry was studied by silencing the expression of two key enzymes involved in their biosynthesis--the UDP-glucose:ceramide glucosyltransferase (UGCG), which transfers a glucose molecule to ceramide to produce glucosylceramide GlcCer, and the lactosyl ceramide-α-2,3-sialyl transferase 5 (GM3-s), which adds the first SA to lactoceramide-producing ganglioside GM3. Silencing the expression of both enzymes resulted in decreased ganglioside levels (as judged by GM1a detection). Four rotavirus strains tested (human Wa, simian RRV, porcine TFR-41, and bovine UK) showed a decreased infectivity in cells with impaired ganglioside synthesis; however, their replication after bypassing the entry step was not affected, confirming the importance of gangliosides for cell entry of the viruses. Interestingly, viral binding to the cell surface was not affected in cells with inhibited ganglioside synthesis, but the infectivity of all strains tested was inhibited by preincubation of gangliosides with virus prior to infection. These data suggest that rotaviruses can attach to cell surface in the absence of gangliosides but require them for productive cell entry, confirming their functional role during rotavirus cell entry.

Interactions between rotavirus and Suwannee River organic matter: aggregation, deposition, and adhesion force measurement

Interactions between rotavirus and Suwannee River natural organic matter (NOM) were studied by time-resolved dynamic light scattering, quartz crystal microbalance, and atomic force microscopy. In NOM-containing NaCl solutions of up to 600 mM, rotavirus suspension remained stable for over 4 h. Atomic force microscopy (AFM) measurement for interaction force decay length at different ionic strengths showed that nonelectrostatic repulsive forces were mainly responsible for eliminating aggregation in NaCl solutions. Aggregation rates of rotavirus in solutions containing 20 mg C/L increased with divalent cation concentration until reaching a critical coagulation concentration of 30 mM CaCl(2) or 70 mM MgCl(2). Deposition kinetics of rotavirus on NOM-coated silica surface was studied using quartz crystal microbalance. Experimental attachment efficiencies for rotavirus adsorption to NOM-coated surface in MgCl(2) solution were lower than in CaCl(2) solution at a given divalent cation concentration. Stronger adhesion force was measured for virus-virus and virus-NOM interactions in CaCl(2) solution compared to those in MgCl(2) or NaCl solutions at the same ionic strength. This study suggested that divalent cation complexation with carboxylate groups in NOM and on virus surface was an important mechanism in the deposition and aggregation kinetics of rotavirus.

Role of temperature and Suwannee River natural organic matter on inactivation kinetics of rotavirus and bacteriophage MS2 by solar irradiation

Although the sunlight-mediated inactivation of viruses has been recognized as an important process that controls surface water quality, the mechanisms of virus inactivation by sunlight are not yet clearly understood. We investigated the synergistic role of temperature and Suwannee River natural organic matter (SRNOM), an exogenous sensitizer, for sunlight-mediated inactivation of porcine rotavirus and MS2 bacteriophage. Upon irradiation by a full spectrum of simulated sunlight in the absence of SRNOM and in the temperature range of 14-42 °C, high inactivation rate constants, k(obs), of MS2 (k(obs) ≤ 3.8 h(-1) or 1-log(10) over 0.6 h) and rotavirus (k(obs) ≤ 11.8 h(-1) or ∼1-log(10) over 0.2 h) were measured. A weak temperature (14-42 °C) dependence of k(obs) values was observed for both viruses irradiated by the full sunlight spectrum. Under the same irradiation condition, the presence of SRNOM reduced the inactivation of both viruses due to attenuation of lower wavelengths of the simulated sunlight. For rotavirus and MS2 solutions irradiated by only UVA and visible light in the absence of SRNOM, inactivation kinetics were slow (k(obs) < 0.3 h(-1) or <1-log(10) unit reduction over 7 h) and temperature-independent for the range considered. Conversely, under UVA and visible light irradiation and in the presence of SRNOM, temperature-dependent inactivation of MS2 was observed. For rotavirus, the SRNOM-mediated exogenous inactivation was only important at temperatures >33 °C, with low rotavirus k(obs) values (k(obs) ≈ 0.2 h(-1); 1-log(10) unit reduction over 12 h) for the temperature range of 14-33 °C. These k(obs) values increased to 0.5 h(-1) at 43 °C and 1.5 h(-1) (1-log(10) reduction over 1.6 h) at 50 °C. While SRNOM-mediated exogenous inactivation of MS2 was triggered by singlet oxygen, the presence of hydrogen peroxide was important for rotavirus inactivation in the 40-50 °C range.

Iron oxide amended biosand filters for virus removal

Laboratory studies were performed to determine if the addition of iron oxides throughout biosand filter (BSF) media would increase virus removal due to adsorption. The proposed mechanism is electrostatic adsorption of negatively charged virion particles to positively charged iron oxides formed during the corrosion of zerovalent iron. Initial tests conducted using continuous flow, small-scale glass columns showed high MS2 bacteriophage removal in an iron-amended sand column (5log10) compared to a sand-only column (0.5log10) over 20 pore volumes. Additionally, two experiments with a column containing iron particles revealed 4log10 and 5log10 removal of rotavirus in the presence of 20 mg/L total organic carbon. Full-scale BSFs with iron particles removed>4log10 MS2 for the duration of the experiment (287 days), while BSF with steel wool removed>4log10 MS2 for the first 160 days. Plug flow for the BSF was shown to depend on uniformity between the iron oxide material and sand media grains. The results suggest that the duration of effective virus removal by iron-amended biosand filtration depends on source water conditions and the quantity and composition of iron material added. Overall, this study provides evidence that iron-amended BSFs may advance the field of point-of-use technologies and bring relief to millions of people suffering from waterborne diseases.

Novel structural insights into rotavirus recognition of ganglioside glycan receptors

Rotaviruses ubiquitously infect children under the age of 5, being responsible for more than half a million diarrhoeal deaths each year worldwide. Host cell oligosaccharides containing sialic acid(s) are critical for attachment by rotaviruses. However, to date, no detailed three-dimensional atomic model showing the exact rotavirus interactions with these glycoconjugate receptors has been reported. Here, we present the first crystallographic structures of the rotavirus carbohydrate-recognizing protein VP8* in complex with ganglioside G(M3) glycans. In combination with assessment of the inhibition of rotavirus infectivity by N-acetyl and N-glycolyl forms of this ganglioside, our results reveal key details of rotavirus-ganglioside G(M3) glycan recognition. In addition, they show a direct correlation between the carbohydrate specificities exhibited by VP8* from porcine and by monkey rotaviruses and the respective infectious virus particles. These novel results also indicate the potential binding interactions of rotavirus VP8* with other sialic acid-containing gangliosides.

Inhibition of rotavirus infectivity by a neoglycolipid receptor mimetic

Group A rotaviruses are a major cause of diarrhea in the young of many mammalian species. In rotavirus infected piglets mortality can be as high as 60%. Previous research in this laboratory has identified a porcine intestinal GM₃ ganglioside receptor that is required for sialic acid-dependent rotavirus recognition of host cells. In addition, we previously demonstrated exogenously added GM₃ can competitively inhibit porcine rotavirus binding and infectivity of host cells in vitro. Sialyllactose, the carbohydrate moiety of GM₃, is approximately 3 orders of magnitude less effective than GM₃ at inhibiting rotavirus binding to cells. Furthermore, production of therapeutic quantities of GM₃ ganglioside for use as an oral carbomimetic in swine is cost prohibitive. In an effort to circumvent these problems, a sialyllactose-containing neoglycolipid was synthesized and evaluated for its ability to inhibit rotavirus binding and infectivity of host cells. Sialyllactose was coupled to dipalmitoylphosphatidylethanolamine (PE) by reductive amination and the product (SLPE) purified by HPLC. Characterization of the product showed a single primulin (lipid) and resorcinol (sialic acid) positive band by thin layer chromatography and quantification of phosphate and sialic acid yielded a 1:1 molar ratio. Mass spectroscopy confirmed a molecular weight coinciding with SLPE. Concentration-dependent binding of rotavirus to SLPE was demonstrated using a thin-layer overlay assay. Using concentrations comparable to GM₃, SLPE was also shown to inhibit rotavirus binding to host cells by 80%. Furthermore, SLPE was shown to decrease rotavirus infection of host cells by over 90%. Finally, preliminary results of in vivo animal challenge studies using newborn piglets in their natural environment, demonstrated SLPE afforded complete protection from rotavirus disease. The efficacy of SLPE in inhibiting rotavirus binding and infection in vitro and in vivo, coupled with its relatively low-cost, large-scale production capabilities make SLPE a promising candidate for further exploration as a possible prophylactic or therapeutic nutriceutical for combating rotavirus disease in animals. Most importantly, the results presented here provide proof of concept that the nutriceutical approach of providing natural or synthetic dietary receptor mimetics for protection against gastrointestinal virus infectious disease in all species is plausible.

Deposition and aggregation kinetics of rotavirus in divalent cation solutions

Aggregation kinetics of rotavirus in aqueous solutions and its deposition kinetics on silica surface in the presence of divalent (Ca(2+), Mg(2+)) cations were studied using complementary techniques of time-resolved dynamic light scattering (TR-DLS) and quartz crystal microbalance (QCM). Within a reasonable temporal window of 4 h, aggregation could be observed at levels as low as 10 mM of Ca(2+) and 20 mM of Mg(2+). Attachment efficiencies were always greater in Ca(2+) solutions of the same concentration, and the critical coagulation concentration (CCC) for rotavirus in Ca(2+) solutions was slightly smaller than that in Mg(2+) solutions. No aggregation was detected in Na(+) solution within the temporal window of 4 h. Deposition experiments showed higher attachment coefficients in solutions containing Ca(2+) compared to those obtained in Mg(2+) solution. The classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory failed to predict both the aggregation behavior of rotavirus and its deposition on silica surface. Besides electrostatic interactions, steric repulsions and specific interactions with divalent cations were important mechanisms in controlling rotavirus deposition and aggregation. Experimental results presented here suggest that rotavirus is not expected to aggregate in groundwater with typical hardness (up to 6 mM Ca(2+)) and rotavirus deposition on silica soil would be more favorable in the presence of Ca(2+) than Mg(2+).

Glycosphingolipids as receptors for non-enveloped viruses

Glycosphingolipids are ubiquitous molecules composed of a lipid and a carbohydrate moiety. Their main functions are as antigen/toxin receptors, in cell adhesion/recognition processes, or initiation/modulation of signal transduction pathways. Microbes take advantage of the different carbohydrate structures displayed on a specific cell surface for attachment during infection. For some viruses, such as the polyomaviruses, binding to gangliosides determines the internalization pathway into cells. For others, the interaction between microbe and carbohydrate can be a critical determinant for host susceptibility. In this review, we summarize the role of glycosphingolipids as receptors for members of the non-enveloped calici-, rota-, polyoma- and parvovirus families.

Adsorption of rotavirus and bacteriophage MS2 using glass fiber coated with hematite nanoparticles

Batch and flow-through experiments were conducted to investigate the removal and inactivation of rotavirus (RV) and bacteriophage MS2 using glass fiber coated with hematite nanoparticles. Batch tests showed a high removal of MS2 (2.49x10(11) plaque forming unit/g) and RV (8.9x10(6) focal forming unit/g) at a low concentration of hematite nanoparticles in solution (0.043g/L and 0.26g/L, respectively). Virus adsorption was, however, decreased in the presence of bicarbonate ions and natural organic matter (NOM) in solution, suggesting a great affinity of iron oxide nanoparticles for these competitors. Adsorption on hematite nanoparticles by MS2 and RV was also tested with aquifer groundwater under saturated flow conditions to mimic environmental conditions with promising results (8x10(8) plaque forming unit/g and 3x10(4) focal forming unit/g, respectively). Desorption of up to 63% of infectious MS2 and only 2% of infectious RV from hematite nanoparticles were achieved when an eluant solution containing beef extract and glycine was used. Transmission electron microscopy (TEM) images showed evidence of electrostatic adsorption of apparently intact MS2 and structurally damaged RV particles to hematite nanoparticles. Results from this research suggest that a cartridge made of glass fiber coated with hematite nanoparticles could be used as a point-of-use device for virus removal for drinking water treatment.

Isoflavones at concentrations present in soy infant formula inhibit rotavirus infection in vitro

Rotavirus (RV) infections are a major cause of acute gastroenteritis in children and domestic animals, infecting virtually all children within their first 5 y of life. Infants consuming soy-based infant formula (SBIF) are exposed to high levels of isoflavones that exhibit antiviral activity on numerous viruses in vitro and in vivo. Thus, the hypothesis that isoflavones would inhibit RV infection was tested. All isoflavones at SBIF concentrations were tested individually and as a mixture (MIX). Virus infectivity was assessed in MA-104 cells using a focus forming unit assay. Genistin and MIX significantly reduced RV infectivity by 33-62% and 66-74%, respectively, compared with the control and across a wide range of RV concentrations. When tested without genistin, the MIX lost its anti-RV activity, suggesting that genistin is the biologically active isoflavone in our model. In a dose response assay, genistin significantly reduced RV infectivity at a concentration as low as 30 mumol/L. We investigated several possible mechanisms of action. Isoflavones decreased RV infectivity by modulating virion attachment to the host cells and by modulating a postbinding step. Isoflavones did not alter RV triple-layered structure and genistin did not act through inhibition of protein tyrosine kinases and topoisomerase II or by mimicking the effect of estrogens. To our knowledge, this is the first study showing the inhibition of RV infectivity by isoflavones present in SBIF. The modulation of SBIF isoflavone composition and concentration represents novel nutritional approaches to potentially reduce the severity of RV infection in human and production animals.

Role of sialic acids in rotavirus infection

Rotaviruses are the leading cause of childhood diarrhea. The entry of rotaviruses into the host cell is a complex process that includes several interactions of the outer layer proteins of the virus with different cell surface molecules. The fact that neuraminidase treatment of the cells, or preincubation of the virus with sialic acid-containing compounds decrease the infectivity of some rotavirus strains, suggested that these viruses interact with sialic acid on the cell surface. The infectivity of some other rotavirus strains is not affected by neuraminidase treatment of the cells, and therefore they are considered neuraminidase-resistant. However, the current evidence suggests that even these neuraminidase-resistant strains might interact with sialic acids located in context different from that of the sialic acids used by the neuraminidase-sensitive strains. This review summarizes our current knowledge of the rotavirus-sialic acid interaction, its structural basis, the specificity with which distinct rotavirus isolates interact with sialic acid-containing compounds, and also the potential use of these compounds as therapeutic agents.

STD NMR spectroscopy and molecular modeling investigation of the binding of N-acetylneuraminic acid derivatives to rhesus rotavirus VP8* core

The VP8* subunit of rotavirus spike protein VP4 contains a sialic acid (Sia)-binding domain important for host cell attachment and infection. In this study, the binding epitope of the N-acetylneuraminic acid (Neu5Ac) derivatives has been characterized by saturation transfer difference (STD) nuclear magnetic resonance (NMR) spectroscopy. From this STD NMR data, it is proposed that the VP8* core recognizes an identical binding epitope in both methyl alpha-D-N-acetylneuraminide (Neu5Acalpha2Me) and the disaccharide methyl S-(alpha-D-N-acetylneuraminosyl)-(2-->6)-6-thio-beta-D-galactopyranoside (Neu5Ac-alpha(2,6)-S-Galbeta1Me). In the VP8*-disaccharide complex, the Neu5Ac moiety contributes to the majority of interaction with the protein, whereas the galactose moiety is solvent-exposed. Molecular dynamics calculations of the VP8*-disaccharide complex indicated that the galactose moiety is unable to adopt a conformation that is in close proximity to the protein surface. STD NMR experiments with methyl 9-O-acetyl-alpha-D-N-acetylneuraminide (Neu5,9Ac(2)alpha2Me) in complex with rhesus rotavirus (RRV) VP8* revealed that both the N-acetamide and 9-O-acetate moieties are in close proximity to the Sia-binding domain, with the N-acetamide's methyl group being saturated to a larger extent, indicating a closer association with the protein. RRV VP8* does not appear to significantly recognize the unsaturated Neu5Ac derivative [2-deoxy-2,3-didehydro-D-N-acetylneuraminic acid (Neu5Ac2en)]. Molecular modeling of the protein-Neu5Ac2en complex indicates that key interactions between the protein and the unsaturated Neu5Ac derivative when compared with Neu5Acalpha2Me would not be sustained. Neu5Acalpha2Me, Neu5Ac-alpha(2,6)-S-Galbeta1Me, Neu5,9Ac(2)alpha2Me, and Neu5Ac2en inhibited rotavirus infection of MA104 cells by 61%, 35%, 30%, and 0%, respectively, at 10 mM concentration. NMR spectroscopic, molecular modeling, and infectivity inhibition results are in excellent agreement and provide valuable information for the design of inhibitors of rotavirus infection.

Attachment factors

As obligate intracellular parasites, viruses must bind to, and enter, permissive host cells in order to gain access to the cellular machinery that is required for their replication. The very large number of mammalian viruses identified to date is reflected in the fact that almost every human and animal cell type is a target for infection by one, or commonly more than one, species of virus. As viruses have adapted to target certain cell types for their propagation, there is exquisite specificity in cellular tropism. This specificity is frequently, but not always, mediated by the first step in the viral replication cycle: attachment of viral surface proteins to receptors expressed on susceptible cells. Viral receptors may be protein, carbohydrate, and/or lipid. Many viruses can use more than one attachment receptor, and indeed may sequentially engage multiple receptors to infect a cell. Thus, it is useful to differentiate between attachment receptors, that simply allow viruses a foothold at the limiting membrane of a cell, and entry receptors that mediate delivery the viral genome into the cytoplasm. For some viruses the attachment factors that promote binding to permissive cells are very well defined, but the sequence of events that triggers viral entry is only now beginning to be understood. For other viruses, despite many efforts, the receptors remain elusive. In this chapter we will confine our review to viruses that infect mammals, with particular focus on human pathogens. We do not intend that this will be an exhaustive overview of viral attachment receptors; instead we will take a number of examples of well-characterized virus-receptor interactions, discuss supporting evidence, and highlight any controversies and uncertainties in the field. We will then conclude with a reflection on general principles of viral attachment, consider some exceptions to these principles, and make some suggestion for future research.

Microbial adhesion of Cryptosporidium parvum sporozoites: purification of an inhibitory lipid from bovine mucosa

Cryptosporidium parvum is a protozoan pathogen of humans and livestock worldwide. Its ability to infect a wide range of species raises questions as to the involvement of a specific host cell receptor for parasite-host recognition. To investigate the mechanism of parasite-host cell recognition, we have developed an in vitro cell suspension binding assay to investigate adhesion of C. parvum sporozoites to host cells. Morphologic features of binding events observed with this assay were identical to those described in natural infections. Glycoconjugates, Madin Darby bovine kidney (MDBK) cell fractions, and plasma membrane vesicles (PMVs) were screened for their ability to block binding of sporozoites to MDBK cells. Mucins, MDBK cell fractions, and PMVs exhibited dose-dependent inhibition of sporozoite binding. The major inhibitory fraction from MDBK cells was found to be insoluble in aqueous medium, nonsaponifiable, and lacking carbohydrate moieties, nitrogen, and phosphorus. Its inhibitory effect was resistant to heat, protease digestion, and glycosidase treatment, suggesting that the inhibitory activity is a lipid or a lipid-like component. The inhibitory activity was purified from MDBK cells, and in larger amounts from bovine small intestinal mucosa, by organic solvent extraction, semipreparative high-pressure liquid chromatography, and preparative high-performance thin-layer chromatography. Biochemical analyses, thin-layer chromatography staining techniques, mass spectrometry, and elemental analysis were used to partially characterize the purified lipid. These results indicate that a host intestinal lipid(s) or a lipid-like component(s) may play an important role in the early stages of host cell invasion by C. parvum.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

Oligosaccharides as receptors for JC virus

JC virus (JCV) belongs to the polyomavirus family of double-stranded DNA viruses and in humans causes a demyelinating disease of the central nervous system, progressive multifocal leukoencephalopathy. Its hemagglutination activity and entry into host cells have been reported to depend on an N-linked glycoprotein containing sialic acid. In order to identify the receptors of JCV, we generated virus-like particles (VLP) consisting of major viral capsid protein VP1. We then developed an indirect VLP overlay assay to detect VLP binding to glycoproteins and a panel of glycolipids. We found that VLP bound to sialoglycoproteins, including alpha1-acid glycoprotein, fetuin, and transferrin receptor, and that this binding depended on alpha2-3-linked sialic acids and N-linked sugar chains. Neoglycoproteins were synthesized by using ovalbumin and conjugation with oligosaccharides containing the terminal alpha2-3- or alpha2-6-linked sialic acid or the branched alpha2-6-linked sialic acid. We show that the neoglycoprotein containing the terminal alpha2-6-linked sialic acid had the highest affinity for VLP, inhibited the hemagglutination activity of VLP and JCV, and inhibited the attachment of VLP to cells. We also demonstrate that VLP bound to specific glycolipids, such as lactosylceramide, and gangliosides, including GM3, GD2, GD3, GD1b, GT1b, and GQ1b, and that VLP bound weakly to GD1a but did not bind to GM1a, GM2, or galactocerebroside. Furthermore, the neoglycoprotein containing the terminal alpha2-6-linked sialic acid and the ganglioside GT1b inhibited JCV infection in the susceptible cell line IMR-32. These results suggest that the oligosaccharides of glycoproteins and glycolipids work as JCV receptors and may be feasible as anti-JCV agents.

Initial interaction of rotavirus strains with N-acetylneuraminic (sialic) acid residues on the cell surface correlates with VP4 genotype, not species of origin

We examined 41 human and animal rotavirus strains representative of all known P genotypes for their dependency on cellular N-acetylneuraminic (sialic) acid (SA) residues for infectivity. Our results showed that all rotaviruses studied, whether of animal or human origin, belonging to P genotypes [1], [2], [3], and [7] depended on SA residues on the cell surface for efficient infectivity but that all human and animal rotavirus strains representative of the remaining known P genotypes were SA independent. The SA residue requirement for efficient infectivity did not change for reassortant rotavirus strains with altered VP4-VP7 combinations. The initial interaction of rotavirus strains with SA residues on the cell surface correlated with VP4 genotype specificity, not with species of origin or VP7 G serotype specificity (P = 0.001; r2 = 1.00, Pearson's correlation coefficient). In addition to being a requirement for infectivity, the presence of SA residues on the cell surface is a requirement for efficient growth in cell culture; recognition of the association of specific P genotypes with the binding of rotavirus to SA residues will facilitate our understanding of the molecular basis of the early events of rotavirus-cell interactions in cell culture models and of pathogenicity in vivo.

Selection of rotavirus VP4 cell receptor binding domains for MA104 cells using a phage display library

Rotavirus infection of host cells, like other viruses, is a complex process that has not been fully elucidated, and much attention has been focused on the regions of the viral attachment protein, VP4, that are involved in binding to the cellular receptor. In this study, phage display technology was employed to generate a g3p VP4 gene-targeted phage display peptide library using the porcine rotavirus strain CRW8, and a method was optimised for panning this library on adherent MA104 cells to identify receptor binding domains. Recombinant phage that displayed expressed peptides from both the rotavirus VP4 trypsin cleavage products VP8* and VP5* were selected, and while some of the phage clones contained insert sequences from regions of VP4 implicated previously in cell binding and infection, new domains were also identified. In all, four regions within VP8* and six regions of VP5* were selected by panning. To our knowledge, this paper is the first description of using a gene-targeted phage display library to identify receptor binding domains on viral proteins.

Glycosphingolipid binding specificities of rotavirus: identification of a sialic acid-binding epitope

The glycosphingolipid binding specificities of neuraminidase-sensitive (simian SA11 and bovine NCDV) and neuraminidase-insensitive (bovine UK) rotavirus strains were investigated using the thin-layer chromatogram binding assay. Both triple-layered and double-layered viral particles of SA11, NCDV, and UK bound to nonacid glycosphingolipids, including gangliotetraosylceramide (GA1; also called asialo-GM1) and gangliotriaosylceramide (GA2; also called asialo-GM2). Binding to gangliosides was observed with triple-layered particles but not with double-layered particles. The neuraminidase-sensitive and neuraminidase-insensitive rotavirus strains showed distinct ganglioside binding specificities. All three strains bound to sialylneolactotetraosylceramide and GM2 and GD1a gangliosides. However, NeuAc-GM3 and the GM1 ganglioside were recognized by rotavirus strain UK but not by strains SA11 and NCDV. Conversely, NeuGc-GM3 was bound by rotaviruses SA11 and NCDV but not by rotavirus UK. Thus, neuraminidase-sensitive strains bind to external sialic acid residues in gangliosides, while neuraminidase-insensitive strains recognize gangliosides with internal sialic acids, which are resistant to neuraminidase treatment. By testing a panel of gangliosides with triple-layered particles of SA11 and NCDV, the terminal sequence sialyl-galactose (NeuGc/NeuAcalpha3-Galbeta) was identified as the minimal structural element required for the binding of these strains. The binding of triple-layered particles of SA11 and NCDV to NeuGc-GM3, but not to NeuAc-GM3, suggested that the sequence NeuGcalpha3Galbeta is preferred to NeuAcalpha3Galbeta. Further dissection of this binding epitope showed that the carboxyl group and glycerol side chain of sialic acid played an important role in the binding of such triple-layered particles.

Biochemical characterization of rotavirus receptors in MA104 cells

We have tested the effect of metabolic inhibitors, membrane cholesterol depletion, and detergent extraction of cell surface molecules on the susceptibility of MA104 cells to infection by rotaviruses. Treatment of cells with tunicamycin, an inhibitor of protein N glycosylation, blocked the infectivity of the SA-dependent rotavirus RRV and its SA-independent variant nar3 by about 50%, while the inhibition of O glycosylation had no effect. The inhibitor of glycolipid biosynthesis d, l-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) blocked the infectivity of RRV, nar3, and the human rotavirus strain Wa by about 70%. Sequestration of cholesterol from the cell membrane with beta-cyclodextrin reduced the infectivity of the three viruses by more than 90%. The involvement of N-glycoproteins, glycolipids, and cholesterol in rotavirus infection suggests that the virus receptor(s) might be forming part of lipid microdomains in the cell membrane. MA104 cells incubated with the nonionic detergent octyl-beta-glucoside (OG) showed a ca. 60% reduction in their ability to bind rotaviruses, the same degree to which they became refractory to infection, suggesting that OG extracts the potential virus receptor(s) from the cell surface. Accordingly, when preincubated with the viruses, the OG extract inhibited the virus infectivity by more than 95%. This inhibition was abolished when the extract was treated with either proteases or heat but not when it was treated with neuraminidase, indicating the protein nature of the inhibitor. Two protein fractions of around 57 and 75 kDa were isolated from the extract, and these fractions were shown to have rotavirus-blocking activity. Also, antibodies to these fractions efficiently inhibited the infectivity of the viruses in untreated as well as in neuraminidase-treated cells. Five individual protein bands of 30, 45, 57, 75, and 110 kDa, which exhibited virus-blocking activity, were finally isolated from the OG extract. These proteins are good candidates to function as rotavirus receptors.

Rotavirus infection of MA104 cells is inhibited by Ricinus lectin and separately expressed single binding domains

Various lectins were tested for blocking rotavirus infection of MA104 cells and it was observed that galactose-specific lectins were the most inhibitory. Of these Ricinus agglutinin was able to inhibit infection (by human and animal strains) at concentrations as low as 10(-9) M. In addition, in a virus overlay protein blot assay Ricinus agglutinin competed with simian rotavirus SA11 for binding to solubilized MA104 proteins. Amino acid sequence comparisons revealed similarity between the ricin toxin B subunit (which contains two separate carbohydrate-binding motifs: single binding domains (SBD) 1 and 2) and rotavirus spike protein VP4. A filamentous phage display system was used to independently express the two binding domains and while SBD1 inhibited infection of MA104 cells by CRW8, NCDV, and to a lesser extent Wa, SBD2 blocked only CRW8 and NCDV infection. Furthermore inhibition of CRW8 infection was a direct result of phage inhibiting virus attachment to cells. When amino acid 248 within SBD2 was mutated from the ricin toxin to the Ricinus agglutinin sequence this phage clone showed reduced binding to galactose and was no longer able to inhibit virus infection. Thus, rotavirus recognizes galactose as an important component of the receptor on MA104 cells.

Sialic acid dependence and independence of group A rotaviruses

We have found (1), in contrast to previous reports, the human rotavirus Wa strain is sialic acid-dependent for binding to and infectivity of MA-104 cells and (2), a dual carbohydrate binding specificity is associated with both human Wa and Porcine OSU rotaviruses. One carbohydrate binding activity is associated with triple-layered virus particles (TLP) and the other with double-layered virus particles (DLP). In binding and infectivity studies, we found that gangliosides were the most potent inhibitors of both the human and procine rotavirus TLP. Furthermore, glycosylation mutant cells deficient in sialylation or neuraminidase-treated MA104 cells, did not bind rotavirus TLP from either strain. Our results show that human Wa binding and infectivity cannot be distinguished from the porcine OSU strain and appears to be sialic acid-dependent. Direct binding of human or porcine TLP to a variety of intact gangliosides was demonstrated in an thin-layer chromatographic (TLC) overlay assay. Human or porcine rotavirus DLP did not bind to any of the intact gangliosides but surprisingly bound asialogangliosides. This binding was abolished by prior treatment of the glycolipids with ceramide glycanase suggesting the intact asialoglycolipid was required for DLP binding. After treatment of either human or porcine TLP with EDTA to remove the outer shell, virus particles bound only to the immobilized asialogangliosides. These results suggest that rotavirus sugar binding specificity can be interpreted either as sialic acid-dependent or independent based on whether the virus preparation consists primarily of triple-layered or double-layered particles. Of perhaps greater interest is the possibility that sialic acid-independent carbohydrate binding activity plays a role in virus maturation or assembly.

Structure and function of a ganglioside receptor for porcine rotavirus

A ganglioside fraction isolated from pooled intestines from newborn to 4-week-old piglets, which we previously partially characterized and showed to specifically inhibit the binding of porcine rotavirus (OSU strain) to host cells (M. D. Rolsma, H. B. Gelberg, and M. S. Kuhlenschmidt, J. Virol. 68:258-268, 1994), was further purified and found to contain two major monosialogangliosides. Each ganglioside was purified to apparent homogeneity, and their carbohydrate structure was examined by high-pH anion-exchange chromatography coupled with pulsed amperometric detection and fast atom bombardment mass spectroscopy. Both gangliosides possessed a sialyllactose oligosaccharide moiety characteristic of GM3 gangliosides. Compositional analyses indicated that each ganglioside was composed of sialic acid, galactose, glucose, and sphingosine in approximately a 1:1:1:1 molar ratio. Each ganglioside differed, however, in the type of sialic acid residue it contained. An N-glycolylneuraminic acid (NeuGc) moiety was found in the more polar porcine GM3, whereas the less polar GM3 species contained N-acetylneuraminic acid (NeuAc). Both NeuGcGM3 and NeuAcGM3 displayed dose-dependent inhibition of virus binding to host cells. NeuGcGM3 was approximately two to three times more effective than NeuAcGM3 in blocking virus binding. Inhibition of binding occurred with as little as 400 pmol of NeuGcGM3/50 ng of virus (approximately 2 x 10(7) virions) and 2 x 10(6) cells/ml. Fifty percent inhibition of binding was achieved with 0.64 and 1.5 microM NeuGcGM3 and NeuAcGM3, respectively. The free oligosaccharides 3'- and 6'-sialyllactose inhibited binding 50% at millimolar concentrations, which were nearly 1,000 times the concentration of intact gangliosides required for the same degree of inhibition. Direct binding of infectious, triple-layer rotavirus particles, but not noninfectious, double-layered rotavirus particles, to NeuGcGM3 and NeuAcGM3 was demonstrated by using a thin-layer chromatographic overlay assay. NeuGcGM3 and NeuAcGM3 inhibited virus infectivity of MA-104 cells by 50% at concentrations of 3.97 and 9. 84 microM, respectively. NeuGcGM3 (700 nmol/g [dry weight] of intestine) was found to be the predominant enterocyte ganglioside (comprising 75% of the total lipid-bound sialic acid) in neonatal piglets, followed by NeuAcGM3 (200 nmol/g [dry weight] of intestine). NeuGcGM3 and NeuAcGM3 together comprised nearly 100% of the lipid-bound sialic acid in the neonatal intestine, but their quantities rapidly diminished during the first 5 weeks of life. These data support the hypothesis that porcine NeuGcGM3 and NeuAcGM3 are physiologically relevant receptors for porcine rotavirus (OSU strain). Further support for this hypothesis was obtained from virus binding studies using mutant or neuraminidase-treated cell lines. Lec-2 cells, a mutant clone of CHO cells characterized by a 90% reduction in sialyllation of its glycoconjugates, bound less than 5% of the virus compared to control cell binding. In contrast, Lec-1 cells, a mutant CHO clone characterized by a deficiency in glycosylation of N-linked oligosaccharides, still bound rotavirus. Furthermore, exogenous addition of NeuGcGM3 to the Lec-2 mutant cells restored their ability to bind rotavirus in amounts equivalent to that of their parent (CHO) cell line. In the virus-permissive MA-104 cell line, NeuGcGM3 was also able to partially restore rotavirus infectivity in neuraminidase-treated cells. These data suggest that gangliosides play a major role in recognition of host cells by porcine rotavirus (OSU strain).

Characterization of the interaction between VP8 of bovine rotavirus C486 and cellular components on MA-104 cells and erythrocytes

Rotavirus VP8*, the N-terminal trypsin cleavage product of VP4, has been shown to bind to MA-104 cells and human O type erythrocytes. To examine whether bacterially expressed VP8* binds to cellular components of MA-104 cells, the VP8* (aa 1-247) was expressed in E. coli and radiolabelled with 35S-methionine. The radiolabelled rVP8* was immunoprecipitated with antiserum to bovine rotavirus C486 (BRV). The rVP8* was found to bind to MA-104 cells and its binding was competed by BRV. To study the interaction between VP8* and receptors of erythrocytes, hemagglutination (HA) and hemagglutination inhibition (HI) assays were carried out using solubilized rVP8*. rVP8* showed HA which could be inhibited by antiserum to BRV. This interaction was also inhibited by gangliosides, demonstrating a sialic acid dependent interaction. To study the contribution of the C-terminal region of VP8* to HA, a number of approaches were used. First, a peptide spanning aa 230-247 was synthesized and antisera was raised against the peptide to see whether it could inhibit HA of rVP8*. Second, a truncated form of VP8* (tVP8*: aa 1-229) was expressed to examine its hemagglutinating activity. Third, the dimerization of rVP8* and tVP8* was compared by Western-blotting following electrophoresis using native SDS-PAGE. The results indicated that antibody to aa 230-247 inhibits hemagglutination by preventing dimerization of VP8* which in turn allows the molecule to cause HA. To characterize the interaction between the HA domain and sialic acid receptors, erythrocytes were treated with sialidases of different specificities. Arthrobacter ureafaciens, Clostridium perfringens and alpha 2-8 linkage-specific neuraminidase destroyed the ability of sialic acid of erythrocytes to interact with rVP8*, indicating that bovine rotavirus C486 binding requires an alpha 2-8 linkage but acetylation of the sialic acid is not necessary.

Rotavirus is released from the apical surface of cultured human intestinal cells through nonconventional vesicular transport that bypasses the Golgi apparatus

Rotaviruses are nonenveloped viruses that infect enterocytes of the small intestine and cause severe infantile gastroenteritis. It was previously thought that rotavirus exits cells by lysis, but this behavior does not match the local pathogenesis of the virus. In this study, we have investigated the release of the simian rotavirus strain (RRV) from the polarized intestinal Caco-2 cells. We found that RRV is released almost exclusively from the apical pole of Caco-2 cells before any cells lyse. Using confocal laser scanning microscopy and drugs that inhibit vesicular transport, we studied the RRV transport route from the endoplasmic reticulum (ER) to the apical side of intestinal cells. We demonstrated that RRV exits from the ER through a carbonyl cyanide m-chlorophenylhydrazone-sensitive vesicular transport. RRV staining was never found within the Golgi apparatus or lysosomes, suggesting that the RRV intracellular pathway does not involve these organelles. This finding was confirmed by treatment with monensin or NH4Cl, which do not affect release of RRV. Electron microscopic analysis revealed RRV containing small smooth vesicles in the apical area and free virions outside the cell in the brush border, consistent with a vesicular vectorial transport of virus. These results may provide, for the first time, a cellular explanation of the pathogenesis of rotavirus.

Sialic acids in molecular and cellular interactions

Sialic acids (Sias) are terminal components of many glycoproteins and glycolipids especially of higher animals. In this exposed position they contribute significantly to the structural properties of these molecules, both in solution and on cell surfaces. Therefore, it is not surprising that Sias are important regulators of cellular and molecular interactions, in which they play a dual role. They can either mask recognition sites or serve as recognition determinants. Whereas the role of Sias in masking and in binding of pathogens to host cells has been documented over many years, their role in nonpathological cellular interaction has only been shown recently. The aim of this chapter is to summarize our knowledge about Sias in masking, for example, galactose residues, and to review the progress made during the past few years with respect to Sias as recognition determinants in the adhesion of pathogenic viruses, bacteria, and protozoa, and particularly as binding sites for endogenous cellular interaction molecules. Finally, perspectives for future research on these topics are discussed.

Virus-receptor interactions in the enteric tract. Virus-receptor interactions

Expression of specific virus receptors on the surface of intestinal epithelial cells or M cells can determine whether or not a animal is susceptible to infection with an enterotropic virus. Receptors for many animal viruses have been identified. The specificity of virus-receptor interactions clearly affects the species specificity of virus infection, and in some instances may be an important determinant of viral tissue tropism. In this paper, the specificity of coronavirus-receptor interactions is summarized. Porcine and human coronaviruses utilize aminopeptidase N as their receptors, but in a species-specific manner. Mouse hepatitis virus uses several rodent glycoproteins in the carcinoembryonic antigen family as receptors. In addition, some coronaviruses can interact with carbohydrate moieties on the cell surface. Understanding the molecular mechanisms of virus-receptor interactions may lead to development of novel strategies for the control of enteric viral diseases.

Characterization of a porcine enterocyte receptor for group A rotavirus

We have identified, purified to apparent homogeneity and chemically characterized a biologically-relevant porcine enterocyte receptor for group A porcine rotavirus. Ceramide glycanase digestion followed by acid hydrolysis and monosaccharide compositional analyses indicated the receptor is a family of two GM, gangliosides, one containing N-glycolyl-neuraminic acid and the other N-acetylneuraminic acid. Both gangliosides displayed dose-dependent inhibition of rotavirus binding to, and infectivity of, host cells. Inhibition of infectivity in a focus-forming-unit-reduction assay was achieved with as little as 2 nmols of NeuGcGM3 (50% inhibition with 3.97 nmol) or NeuAcGM3 (50% inhibition with 9.84 nmol) per 10(4) FFU of virus. Preliminary data suggest specific porcine GM3 carbohydrate fine structure or spatial orientation of the sialyloligosaccharide epitopes of the holoGM3 gangliosides may be crucial to enterocyte receptor recognition by rotavirus. We have quantified both NeuGcGM3 and NeuAcGM3 in enterocytes of various-aged pigs from newborn through 16 weeks and have found with increasing age the amount of both GM3 derivatives, especially NeuGcGM3 per gram (dry weight) intestinal brush border decreases rapidly from newborn through 4 weeks of age. These results may help explain the age-sensitivity of piglets to severe rotavirus diarrhea.

Human serum immunoglobulin counteracts rotaviral infection in Caco-2 cells

Oral administration of human serum immunoglobulin reduces the duration of diarrhea and of rotaviral excretion in children. To investigate the in vitro effects of immunoglobulin on virus-enterocyte interaction, Caco-2 cells were infected with Rotavirus strain SA11. Immunoglobulin was added prior to and at various times postinfection. Indirect immunofluorescence was performed with an antibody against VP-6 rotaviral antigen. Cell viability and monolayer transepithelial electrical resistance (TEER) were monitored. Immunofluorescence showed a perinuclear distribution in 90% of cells. Rotavirus infection induced a progressive decrease in TEER and a parallel reduction in cell viability, depending on viral load. Preincubation of the virus with immunoglobulin prevented cell infection as judged by immunofluorescence. Immunoglobulin addition to infected cells partially prevented the decrease in TEER and induced a later shift of TEER toward increasing values, suggesting restoration of monolayer's integrity. The efficacy of immunoglobulin depended on its concentration and on the time of its addition. These results indicate that immunoglobulin is effective in preventing infection and in reducing cell damage, through a direct anti-Rotavirus action and may indicate that immunoglobulin should be administered in the early phase of diarrhea, to reduce the severity of Rotavirus infection.

Genetic mapping indicates that VP4 is the rotavirus cell attachment protein in vitro and in vivo

To identify the rotavirus protein which mediates attachment to cells in culture, viral reassortants between the simian rotavirus strain RRV and the murine strains EHP and EW or between the simian strain SA-11 and the human strain DS-1 were isolated. These parental strains differ in the requirement for sialic acid to bind and infect cells in culture. Infectivity and binding assays with the parental and reassortant rotaviruses indicate that gene 4 encodes the rotavirus protein which mediates attachment to cells in culture for both sialic acid-dependent and -independent strains. Using ligated intestinal segments of newborn mice and reassortants obtained between the murine strain EW and RRV, we developed an in vivo infectivity assay. In this system, the infectivity of EW was not affected by prior treatment of the enterocytes with neuraminidase, while neuraminidase treatment reduced the infectivity of a reassortant carrying gene 4 from RRV on an EW background more than 80% relative to the controls. Thus, VP4 appears to function as the cell attachment protein in vivo as well as in vitro.

Characterization of SA-11 rotavirus receptorial structures on human colon carcinoma cell line HT-29

The involvement of different cell membrane components in the receptor structures for SA-11 rotavirus was investigated. As experimental model, the human enterocyte-like HT-29 cell line, was used because of its closer resemblance to the in vivo viral cellular target as compared to other in vitro systems. Rotavirus was incubated with whole membranes or their separated protein and lipid fractions before infection. Either isolated cell membranes or lipid components were capable of binding to the virus and to prevent infection, whereas proteins did not show any inhibitory activity. Among lipids, the glycolipid fraction was shown to impede rotaviral antigen synthesis with a dose-dependent relationship, whereas phospholipids failed to prevent viral infection. To confirm these findings, membranes and target cells were subjected to different enzymatic treatments prior to infection. In addition, HT-29 cells were also incubated with different lectins before infection. The blocking activity of membranes was inhibited by treatment with ceramide glycanase, neuraminidase, and beta-galactosidase but not by treatment with proteases or heat (100 degrees C). Viral infection was prevented by preincubation of target cells with lectins specific for sialic acid and galactose or with ceramide glycanase, neuraminidase, and beta-galactosidase, whereas protease treatments were not active. The results of these experimental procedures indicate that glycolipids containing specific carbohydrate moieties, such as sialic acid and galactose, contribute to the SA-11 rotavirus receptor structure on HT-29 cells.