Monoclonal antibody that inhibits infection of HeLa and rhabdomyosarcoma cells by selected enteroviruses through receptor blockade

Multivalent norovirus vaccines induce strong mucosal and systemic blocking antibodies against multiple strains

Noroviruses are important agents of human gastroenteritis characterized by extensive sequence variation in the major capsid structural protein that likely encodes critical antigenic determinants of protective immunity. The lack of an infection model has limited detailed characterizations of viral antigenic relationships and identification of the essential components for protective immunity. This information would contribute to efficacious vaccine design against a broad array of norovirus strains. To understand the extent of heterotypic norovirus antibody specificity to inter- and intra-genogroup strains and its applicability to vaccine design, we collected sera from humans infected with different norovirus strains and from mice inoculated with alphavirus vectors expressing strain-specific recombinant norovirus-like particles (VLPs). We used VLPs that were assembled from Norwalk virus (NV), Hawaii virus (HV), Snow Mountain virus (SM) and Lordsdale virus (LV) as antigens to define and compare heterotypic antibody responses in humans and mice. We also examined if these heterotypic antibodies could block specific binding of ABH histo-blood group antigens, putative receptors for norovirus binding and entry, to norovirus VLPs. Furthermore, we examined the effect of multivalent inocula on the specificity, titer, and ligand blockade properties of systemic and mucosal norovirus-specific antibodies in mice. Our studies suggest that infection with one of several different genogroup I (GI) strains in humans induces heterotypic antibodies that block NV binding to ABH antigens, although comparable findings were not evident following infection with genogroup (GII) strains. Additionally, inoculating mice with vaccine cocktails encoding multiple norovirus VLPs enhances heterotypic and ligand attachment-blocking antibody responses against the LV strain not included in the cocktail. These data suggest that multivalent vaccination may provide better protection from a broader range of noroviruses than monovalent vaccination.

Cytolytic replication of coxsackievirus B2 in CAR-deficient rhabdomyosarcoma cells

The six coxsackievirus B serotypes (CVB1-6) use the coxsackie- and adenovirus receptor (CAR) for host cell entry. Four of these serotypes, CVB1, 3, 5 and 6, have also shown the capacity to replicate and cause cytolysis in rhabdomyosarcoma (RD) cells, a CAR-deficient cell line. This extended tropism has been associated with an acquired ability to bind decay accelerating factor (DAF). In this study, we have adapted the CVB2 prototype strain Ohio-1 (CVB2/O) to replicate in RD cells. Two types of infection were identified: (I) an enterovirus-typical, lytic infection, and (II) a non-lytic infection. Both CVB2/O-RD variants retained the prototype-ability to cause cytopathic effect in HeLa cells using CAR as receptor. Phenotypic and genotypic changes in the CVB2/O-RD-variants were determined and compared to the prototype cultured in HeLa cells. Inhibition studies using antibodies against CAR and DAF revealed a maintained ability of the CVB2/O-RD-variants to bind CAR, but no binding to DAF was observed. In addition, neither the prototype nor the CVB2/O-RD-variants were able to cause hemagglutination in human red blood cells, an enterovirus feature associated with affinity for DAF. Sequence analysis of the CVB2/O-RD-variants showed acquired mutations in the capsid region, suggesting extended receptor usage towards an alternative, yet unidentified, receptor for CVB2.

Cellular receptor for Pixuna virus in chicken embryonic fibroblasts

In this study, we describe the isolation and partial characterization of a Pixuna virus receptor, which is a component of a plasma membrane fraction of chicken embryo fibroblast (CEF). Polyclonal antiserum was prepared from rabbits immunized with the membrane fraction. Said polyclonal antiserum reacted in a similar way as monoclonal antibodies raised against the membrane fraction. Both antisera were able to prevent CEF and Vero cells from infection with Pixuna virus. Immunofluorescence studies suggested that the receptors found in the fibroblasts and in the Vero cells shared at least some epitopes. The Western blot analysis of the purified membrane fraction antigens, which reacted with the monoclonal and polyclonal antibodies, detected a double band with a molecular mass of approximately 60 kDa. Not only immunofluorescence staining but also electron and immunoelectron microscopy studies evidenced the receptor localization in the plasma membrane. In this manner, we reported the isolation and partial characterization of a new Pixuna virus receptor in the plasma membrane of chicken embryo fibroblasts in culture. The data obtained demonstrated the receptor significance for the penetration of Pixuna virus into fibroblasts and mammalian cell and the related importance of designing new antiviral drugs by blocking the mechanism of receptor penetration of the virus into the cells.

A novel cell entry pathway for a DAF-using human enterovirus is dependent on lipid rafts

The glycosylphosphatidylinositol (GPI)-anchored complement regulatory protein decay-accelerating factor (DAF) is used by a number of enteroviruses as a receptor during infection. DAF and other GPI-anchored proteins can be found in cholesterol-rich ordered domains within the plasma membrane that are known as "lipid rafts." We have shown, by using drugs to specifically inhibit various endocytosis routes, that infection by a DAF-using strain of echovirus 11 (EV11) is dependent upon cholesterol and an intact cytoskeleton, whereas a non-DAF-using mutant derived from it was unaffected by these drugs. Using RNA transfection and virus-binding assays, we have shown that this requirement for cholesterol, the actin cytoskeleton, and the microtubule network occurs postbinding of the virus but prior to uncoating of the RNA, indicating a role during virus entry. Confocal microscopy of virus infection supported the role of cholesterol and the cytoskeleton during entry. In addition, [(35)S]methionine-labeled DAF-using EV11, but not the non-DAF-using EV11, could be copurified with lipid raft components during infection after Triton X-100 extraction. These data indicate that DAF usage by EV11 enables the virus to associate with lipid rafts and enter cells through this novel route.

Differences in inhibition of replication between Coxsackie B4 virus strains in various cell lines by antibodies to some cell surface proteins

Monoclonal antibodies that interact with the decay accelerating factor (DAF, CD55), the lymphocyte homing receptor (CD44) or the intercellular adhesion molecule I (ICAM- 1) were found to inhibit the replication of different strains of Coxsackievirus serotype B4 (CBV-4) to various extent. By adding antibodies to CD55 the replication of two (V345 and VD2921) of seven strains in HeLa cells, three (V89-4557, VD2921 and T318) of seven in A549-10C cells and one (VD2921) of five strains in RD cells was blocked totally. Consequently, the replication of one strain (VD2921) was blocked in all cells indicating that this strain uses CD55 as a receptor or as a co-receptor on all cell lines and is unable to use another cell surface protein. The binding of this strain to the cell surface was inhibited by the antibodies to CD55. None of the CBV-4 strains was blocked totally by adding antibodies to CD44 to HeLa and A549-10C cells, whereas in RD cells the replication of one (T318) of the CBV-4 strains was blocked totally. The antibodies to ICAM-1 did not inhibit totally the replication of any strain in HeLa and RD cells, but it blocked totally the replication of one strain (CBV-4-E) in A549-10C cells. In HeLa and A549-10C cells the degree of replication correlated highly with the degree of cytopathic effect (CPE). In RD cells, four of the strains replicated without CPE. The adding of antibodies to the integrin alpha(v)beta(3) led to slightly enhanced replication of three of the CBV-4 strains in all cell lines. It is concluded that the receptor usage by different strains of CBV-4 varies not only within the same cells but also between different cell lines.

Attachment of coxsackievirus B3 variants to various cell lines: mapping of phenotypic differences to capsid protein VP1

The coxsackievirus B3 (CVB3) strain Nancy P establishes a persistent carrier-state infection without visible cytopathic effect in primary human fibroblasts (HuFi H), whereas the derivative variant PD induces a complete lysis of the cell monolayer. To define the molecular basis of this exceptional growth property, the complete genomes of both viruses were sequenced and compared to all published sequences of CVB3. As a result, six unique amino acid substitutions in the VP1 capsid protein were observed. Via hybrid virus construction, the lytic phenotype was transferred to a nonlytic cDNA-generated CVB3. Mapping experiments indicate that the presence of amino acid residues K78, A80, A91, and I92 in VP1 is sufficient to induce "lytic" infections in HuFi H cells. Binding assays demonstrate that CVB3 Nancy P preferentially binds to the human coxsackievirus-adenovirus receptor (CAR), while PD exhibits a very weak interaction with CAR but strong binding to the decay accelerating factor (DAF). These results suggest that the mutated amino acid residues in VP1 are involved in receptor recognition/binding. Moreover, the lytic replication of CVB3 PD and the hybrid virus in various nonpermissive rodent cell lines indicates that cell surface molecules other than CAR and DAF may be involved in attachment of this variant to cell surfaces.

The coxsackie-adenovirus receptor (CAR) is used by reference strains and clinical isolates representing all six serotypes of coxsackievirus group B and by swine vesicular disease virus

Group B coxsackieviruses are etiologically linked to many human diseases, and cell surface receptors are postulated to play an important role in mediating their pathogenesis. The coxsackievirus adenovirus receptor (CAR) has been shown to function as a receptor for selected strains of coxsackievirus group B (CVB) serotypes 3, 4, and 5 and is postulated to serve as a receptor for all six serotypes. In this study, we demonstrate that CAR can serve as a receptor for laboratory reference strains and clinical isolates of all six CVB serotypes. Infection of CHO cells expressing human CAR results in a 1000-fold increase in CVB progeny virus titer compared to mock transfected cells. CAR was shown to be a functional receptor for swine vesicular disease virus (SVDV), as CHO-CAR cells but not CHO mock transfected controls were susceptible to SVDV infection, produced progeny SVDV, and developed cytopathic effects. Moreover, SVDV infection could be specifically blocked by monoclonal antibody to CAR (RmcB). SVDV infection of HeLa cells was also inhibited by an anti-CD55 MAb, suggesting that this virus, like some CVB, may interact with CD55 (decay accelerating factor) in addition to CAR. Finally, pretreatment of CVB or SVDV with soluble CAR effectively blocks virus infection of HeLa cell monolayers.

Secondary heterotypic versus homotypic infection by Coxsackie B group viruses: impact on early and late histopathological lesions and virus genome prominence

The impact of prior exposure to a different or identical strain of Coxsackievirus B (CVB) on murine CVB myocarditis was studied using a susceptible murine host (A/J[H-2a]) and myocarditic CVB3 or avirulent CVB2 as primary or secondary infectants. The effects of secondary heterotypic infection (CVB2 followed by CVB3) and homotypic infection (CVB3 followed by CVB3) 28 days after primary inoculation, versus CVB2 or CVB3 alone, on injury and viral genomic replication, both early (day 7) and late (days 28 and 56), were evaluated. After the primary infection by CVB2, trivial viral RNA was present in the heart and other organs, and a substantial positivity was observed with CVB3 infection. Seven days after secondary heterotypic (CVB2-CVB3) infection, the quantity of CVB genome in heart, pancreas, liver, and spleen was increased compared with the virus genome in the CVB3-CVB3 group and in the group with primary CVB3 infection alone. This phenomenon was seen in the heart and spleen up to day 28 postsecondary infection. Tissue inflammation and necrosis in heart and pancreas were prominent 7 days postsecondary infection with CVB2-CVB3 and correlated well with an increased quantity of CVB genome. Virus genome was present in heart and spleen 28 days after CVB3 infection alone. Serum CVB3 neutralization titer was increased to 1:128 in CVB2-CVB3 group at days 7 and 28 postsecondary infection, and serum completely neutralized cytopathological effects of CVB3 in the CVB3-CVB3 group at day 7 and 28 postsecondary infection. Our results indicate that secondary heterotypic infection by CVB causes increased injury, inflammation, and CVB replication in target organs such as the heart and pancreas, as well as in immune compartments like the spleen. Compared with CVB3 alone, the intense inflammatory infiltriate in the CVB2-CVB3 group is as not due solely to postviral sensitization of the immune system, but rather to the inability of the host to eradicate the virus.

Integrin alpha v beta 6 enhances coxsackievirus B1 lytic infection of human colon cancer cells

Viral entry into host cells depends upon specific interactions between virus attachment proteins and cell surface receptors that enable virus binding and internalization of virus and/or the virus-receptor complex. We have recently reported that the ubiquitous cell surface molecule, decay-accelerating factor (DAF), is a major cell attachment receptor for Coxsackieviruses B1, B3, and B5. However, DAF permits only virus binding and not virus internalization, invoking the presence of secondary or accessory receptors. Among the known receptors for enteroviruses are members of the cell adhesion molecule family known as integrins. In the present study, we found that expression of the epithelial-restricted integrin, alpha v beta 6, on colonic epithelial cells significantly enhanced Coxsackievirus B1-mediated cell lysis. Importantly, the viral-mediated cell killing required the presence of the 11-amino-acid C-terminal cytoplasmic extension unique to the beta 6 subunit, providing the first evidence of regulation of viral infectivity by integrin cytoplasmic domains. These results indicate that alpha v beta 6 expression on intestinal epithelial cells critically affects Coxsackievirus B1 infectivity. This may be essential in the conversion of asymptomatic enterovirus infection into clinically apparent disease.

A decay-accelerating factor-binding strain of coxsackievirus B3 requires the coxsackievirus-adenovirus receptor protein to mediate lytic infection of rhabdomyosarcoma cells

The composition of the cellular receptor complex for coxsackievirus B3 (CVB3) has been an area of much contention for the last 30 years. Recently, two individual components of a putative CVB3 cellular receptor complex have been identified as (i) decay-accelerating factor (DAF) and (ii) the coxsackievirus-adenovirus receptor protein (CAR). The present study elucidates the individual roles of DAF and CAR in cell entry of CVB3 Nancy. First, we confirm that the DAF-binding phenotype of CVB3 correlates to the presence of key amino acids located in the viral capsid protein, VP2. Second, using antibody blockade, we show that complete protection of permissive cells from infection by high input multiplicities of CVB3 requires a combination of both anti-DAF and anti-CAR antibodies. Finally, it is shown that expression of the CAR protein on the surface of nonpermissive DAF-expressing RD cells renders them highly susceptible to CVB3-mediated lytic infection. Therefore, although the majority of CVB3 Nancy attaches to the cell via DAF, only virus directly interacting with the CAR protein mediates lytic infection. The role of DAF in CVB3 cell infection may be analogous to that recently described for coxsackievirus A21 (D. R. Shafren, D. J. Dorahy, R. A. Ingham, G. F. Burns, and R. D. Barry, J. Virol. 71:4736-4743, 1997), in that DAF may act as a CVB3 sequestration site, enhancing viral presentation to the functional CAR protein.

Complement component 3 interactions with coxsackievirus B3 capsid proteins: innate immunity and the rapid formation of splenic antiviral germinal centers

Innate immunity is central to the clearance of pathogens from hosts as well as to the definition of acquired immune responses (D. T. Fearon, and R. M. Locksley, Science 272:50-53, 1996). Coxsackievirus B3 (CVB3), a human cardiopathic virus, was evaluated for the ability to activate the alternative and classical pathway of complement. CVB3 proteins interact with complement component 3 (C3, a soluble protein effector of innate immunity) after either in vitro exposure to mouse serum or in vivo murine infection and activate the alternative pathway of complement. In addition, we demonstrate that viral antigen retention and localization in germinal centers is dependent on C3, while virus antigen retention in extrafollicular regions in the spleen is not. In vivo depletion of native C3 abolished the rapid formation of virus-specific germinal centers (by day 3 post-CVB3 infection) in the absence of serum anti-CVB3 antibodies. These studies demonstrate that innate immune mechanisms, such as C3 interaction with CVB3, are essential for splenic antiviral germinal center formation in naive (antigen nonsensitized) mice resistant (C57BL/6J strain) and susceptible (A/J strain) to CVB3-induced myocarditis.

Coxsackievirus A21 binds to decay-accelerating factor but requires intercellular adhesion molecule 1 for cell entry

It is becoming increasingly apparent that many viruses employ multiple receptor molecules in their cell entry mechanisms. The human enterovirus coxsackievirus A21 (CAV21) has been reported to bind to the N-terminal domain of intercellular adhesion molecule 1 (ICAM-1) and undergo limited replication in ICAM-1-expressing murine L cells. In this study, we show that in addition to binding to ICAM-1, CAV21 binds to the first short consensus repeat (SCR) of decay-accelerating factor (DAF). Dual antibody blockade using both anti-ICAM-1 (domain 1) and anti-DAF (SCR1) monoclonal antibodies (MAbs) is required to completely abolish binding and replication of high-titered CAV21. However, the binding of CAV21 to DAF, unlike that to ICAM-1, does not initiate a productive cell infection. The capacity of an anti-DAF (SCR3) MAb to block CAV21 infection but not binding, coupled with immunoprecipitation data from chemical cross-linking studies, indicates that DAF and ICAM-1 are closely associated on the cell surface. It is therefore suggested that DAF may function as a low-affinity attachment receptor either enhancing viral presentation or providing a viral sequestration site for subsequent high-affinity binding to ICAM-1.

Expression and distribution of the receptors for coxsackievirus B3 during fetal development of the Balb/c mouse and of their brain cells in culture

This study was designed mainly to determine the relationships between the expression and distribution of the cellular receptor proteins for coxsackievirus B3 (CVB3) and susceptibility of mouse brain cells during fetal development of Balb/c mice. Immunoblot analysis of fetal extracts demonstrated that the CVB3 receptor proteins were first expressed at day 14 of the fetal stage, and that maximal expression of the cellular receptor occurred at near term or newborn stage. Results also suggested that newborn mouse brain tissue expressed much larger quantities of viral receptor proteins, compared to other tissues. In vitro studies showed that both mouse neurons and astrocytes could be infected by two CVB3 strains, pantropic CVB3 Nancy strain (CVB3N) and myocardiotropic CVB3 Woodruff strain (CVB3W). CVB3N, however, replicated and grew to high titer in primary astrocyte cultures and in primary neuron cultures, whereas, primary astrocyte cultures were relatively resistant to CVB3W. Virus binding assays revealed that CVB3N bound faster and in greater amounts to mouse brain cells than CVBW. These two virus strains, however, were found to share the same receptor specificity by virus competition assays. The number of virus binding sites for CVB3 on newborn mouse brain cells was approximately 1.8 x 10(4) per cell. The data suggested that preferential expression of the cellular receptors on newborn mouse brain cells may be related to their high susceptibilities to CVB3 infection.

Coxsackieviruses B1, B3, and B5 use decay accelerating factor as a receptor for cell attachment

Receptor binding and subsequent cell-mediated internalization or disassembly are the initial steps in virus replication. Cell surface molecules that participate in this process are the primary determinants of virus tissue tropism. Monoclonal antibody blockade, immunoprecipitation, and DNA transfection were used to identify decay accelerating factor as a major cell attachment receptor for coxsackieviruses B1, B3, and B5. However, expression of human decay acceleration factor on the surface of nonpermissive murine fibroblasts led only to virus attachment without subsequent replication, and it was concluded that an additional cellular cofactor(s) is required to facilitate cell entry and subsequent replication.

Receptor proteins on newborn Balb/c mouse brain cells for coxsackievirus B3 are immunologically distinct from those on HeLa cells

Newborn Balb/c mice are highly susceptible to infection by the six coxsackievirus serotypes of group B (CVB) and it is known that receptor for these viruses are in highest concentration in the brain as compared to other tissues. Therefore, proteins from the brain tissues of these animals were solubilized (Brain-Ext) and characterized for the identification of mouse brain receptor (MBR) proteins. Virus-blot analyses of Brain-Ext suggested that each of three virus variants of CVB3-(N, W and RD) recognized four receptor proteins designated p46, p44, p36 and p33 according to their molecular size. Similar analyses of cultured neurons from newborn Balb/c mice revealed the presence of the same four receptor proteins, while astrocytes appeared to possess only p46 and/or p44. Isoelectric focusing of Brain-Ext, focused MBR proteins in the pH range 4.0-8.5, with a peak around pH 5.7. P46 was found to be neuraminidase sensitive. A polyclonal rat antiserum (anti-MBR) protected cultured neurons and astrocytes against infection by CVB3, inhibited virus binding to these cells and recognized the same four receptor proteins on western-blots as detected on virus-blots by CVB3. However, a rabbit polyclonal anti-HeLa cell antiserum, which strongly binds to HeLa cells and protects them from CVB3 infection, neither recognized any of the receptor proteins in western-blot analyses of Brain-Ext nor inhibited CVB3 infection on cultured neurons and astrocytes. Conversely, anti-MBR did not recognize any of the receptor proteins by western-blot analysis of HeLa cell extracts nor did it inhibit CVB3 infection of HeLa cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Coxsackievirus B3 adapted to growth in RD cells binds to decay-accelerating factor (CD55)

A coxsackievirus B3 (CB3) isolate adapted to growth in RD cells shows an alteration in cell tropism as a result of its capacity to bind a 70-kDa cell surface molecule expressed on these cells. We now show that this molecule is the complement regulatory protein, decay-accelerating factor (DAF) (CD55). Anti-DAF antibodies prevented CB3 attachment to the cell surface. Radiolabeled CB3 adapted to growth in RD cells bound to CHO cells transfected with human DAF, whereas CB3 (strain Nancy), the parental strain, did not bind to DAF transfectants. These results indicate that growth of CB3 in RD cells selected for a virus strain that uses DAF for cell surface attachment.

Isolation of a monoclonal antibody which blocks vaccinia virus infection

We have isolated a monoclonal antibody, B2, that neutralizes vaccinia virus infection. B2 reacts with a trypsin-sensitive cell surface epitope. B2 does not neutralize infection of herpes simplex virus, suggesting that the B2-reactive epitope is specifically involved in vaccinia virus entry. A survey of 12 different cell lines reveals a correlation between B2 reactivity and susceptibility to vaccinia virus infection. In addition, B2 interferes with vaccinia virus adsorption to target cells. Taken together, the B2-reactive epitope is part of a receptor that appears important for vaccinia virus entry.

VCAM-1 is a receptor for encephalomyocarditis virus on murine vascular endothelial cells

Murine VCAM-1 has been identified as a receptor for the D variant of encephalomyocarditis (EMC-D) virus on vascular endothelial cells from the heart. Monoclonal antibodies to VCAM-1 inhibited infection and lysis of endothelial cells with EMC-D virus. CHO cells transfected with the VCAM-1 gene were susceptible to EMC-D virus lysis, while control CHO cells transfected with the ELAM-1 gene were resistant. Similarly, 35S-labeled EMC-D virus bound to CHO-VCAM cells, and binding was inhibited with anti-VCAM-1 antibodies. Little or no radiolabeled virus bound to CHO-ELAM-1 cells.

Attempts to purify a second cellular receptor for a coxsackievirus B3 variant, CB3-RD from HeLa cells

A coxsackievirus B3 variant, CB3-RD, isolated on rhabdomyosarcoma (RD) cells is known to bind HeLa cells at two different receptor protein sites, HR1 and HR2. Since HR2 occurs in almost 50 fold excess of HR1 in HeLa cells, purification of HR2 was attempted, to obtain its partial N-terminal amino acid sequence and its further characterization. This study describes the purification of HR2 from octylthioglucoside solubilized HeLa cell membranes (HeLa-OTG) by preparative isoelectric focusing (IEF) followed by either preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) or affinity chromatography on immobilized receptor monoclonal antibody, RmcA (RmcA-agarose). IEF of HeLA-OTG showed that both HR2 and HR1 could be well separated by this technique and focused with peak maxima around pH 3.7 and 6.7, respectively. Both RmcA and CB3-RD recognized HR2 as doublet bands (60 kD major polypeptide and a minor 55 kD polypeptide) on electroblots under non-reducing conditions. Preparative SDS-PAGE of the pool of IEF fractions containing HR2 (IEF pool) and simultaneous elution of polypeptides from the bottom of the gel during electrophoresis, is shown to be a useful technique in purifying HR2 with only one contaminating polypeptide (65 kD). However, affinity chromatography of the IEF pool on RmcA-agarose yielded HR2 without any detectable contaminating polypeptide. A quantitative chemiluminescence assay was developed to estimate the amount of HR2 on HeLa cells and in solution, when dot blotted on polyvinylidene difluoride (PVDF) membranes and probed with RmcA. Assays revealed that about 1.2% of the total HR2 present on HeLa cells could be obtained by IEF followed by affinity chromatography. Efforts are continuing to obtain sufficient quantities of purified HR2 for partial N-terminal amino acid sequencing.

Protective effect of a monoclonal antibody specific for an echovirus cellular receptor in human fibroblast and simian kidney cell lines

We previously reported that infection of KB cells by echoviruses (EV) was inhibited by a KB-derived EV receptor murine monoclonal antibody (mAb 143). This antibody enabled the identification of a cellular receptor common to all echoviruses (with the exception of EV-22 and -23) and coxsackievirus (CV) A9, but different from the receptor of other picornaviruses. We now present results of cell protection assays conducted with human and simian cell lines different from the KB cell line used for production of mAb 143. When human embryonic lung fibroblasts were pretreated with 150 micrograms/ml of mAb 143, EV-11 and CV-A9 were completely inhibited (more than a 2-log difference compared to untreated cells). When the cell protection experiments were performed with Vero cells, the same results were observed with EV-33, but not with EV-22. The protection afforded human fibroblast cells by mAb 143 persisted for at least 5 days after 2-h exposure to 100 TCID50 of EV-11. These results suggest that EV receptors can be effectively blocked for prolonged periods in susceptible cells.

Mapping of the RD phenotype of the Nancy strain of coxsackievirus B3

The RD variants of group B coxsackieviruses differ from their parental strains in having the ability to replicate in a human rhabdomyosarcoma cell line, RD. The nucleotide sequence of the P1 region of the RD variant of coxsackievirus B3 strain Nancy (CB3NRD) was determined by sequencing cloned cDNAs, obtained by PCR amplification. A comparison between the established nucleotide sequence and that of the P1 region from the parental virus revealed 12 point mutations which corresponded to six amino acid replacements. To identify if the P1 region is responsible for the phenotype of CB3NRD, a chimeric virus was constructed, using an infectious cDNA clone of CB3. The P1 region of the infectious cDNA was replaced by cDNA fragments from CB3N (parental strain Nancy) or CB3NRD and the resulting recombinants were assayed for their ability to infect and replicate in RD cells. The results showed that the RD phenotype of CB3NRD maps in the P1 region. Furthermore, a chimera which only contained the 5' part of the P1 region derived from CB3NRD and the remaining P1 sequence from CB3N was able to replicate in RD cells, suggesting that the VP2 polypeptide contains at least one determinant for the RD phenotype.

Functional diversity in vascular endothelial cells: role in coxsackievirus tropism

Six plaque-purified virus isolates were obtained from liver and heart tissues of a DBA/2 mouse infected 7 days earlier with 10(4) PFU of coxsackievirus group B type 3. Each virus isolate was assayed in vitro for infectivity to vascular endothelial cells (VEC) of the liver, lungs, and heart. Both the percentage of VEC infected and the mean progeny PFU produced per infected VEC were determined. Virus isolates from the heart showed greater infectivity and replication in heart VEC than in VEC derived from either the liver or lungs. Similarly, virus isolated from the liver preferentially infected liver VEC. Virus receptor expression varied between VEC populations, as demonstrated by binding studies with a [35S]methionine-radiolabeled heart virus and by enzyme-linked immunoadsorption assay studies with a monoclonal antibody to the coxsackievirus group B type 3 receptor on heart tissue. Finally, the heart and liver virus isolates were injected (10(4) PFU) intraperitoneally into BALB/c mice. After 7 days, the animals were sacrificed, and the hearts, livers, and lungs were evaluated for tissue injury and virus concentrations. Viruses originally isolated from the heart preferentially infected the heart when reinjected into animals and caused severe myocarditis. Viruses originally derived from the liver most consistently reinfected the liver, although significant virus concentrations were also detected in the heart. The liver virus isolates, however, were incapable of causing myocarditis. Thus, selective tropism of viruses for particular organs in vivo corresponds to the ability of these isolates to infect VEC in vitro.

Poliovirus permissivity and specific receptor expression on human endothelial cells

To test the role of the endothelial cells (EC) in the poliomyelitis pathogenesis, their sensitivity to poliovirus infection was determined at different times after isolation from the human umbilical vein. While 80% of EC were permissive for poliovirus after 4 days of in vitro primary cultures, only 6% of freshly isolated EC were susceptible to poliovirus infection. A progressive development of this susceptibility was observed during the first 3 days of culture. In an attempt to explain the mechanism of the appearance of cell permissivity for poliovirus, the expression of the poliovirus receptor on EC was studied by cytofluorometric analysis using an anti-receptor monoclonal antibody. The number of poliovirus receptor molecules in the EC population was found to increase with time. This paralleled the increase of the poliovirus-binding capacity of EC cultures. In contrast, the efficiency of viral internalization did not appear to be dependent on the age of culture. These results indicate that the development of EC permissivity for poliovirus in vitro is mainly dependent on the expression of poliovirus receptor on the cell surface.

Coxsackievirus-induced disease. CD4+ cells initiate both myocarditis and pancreatitis in DBA/2 mice

DBA/2 male mice inoculated intraperitoneally with 1.8 X 10(5) plaque-forming units (PFU) coxsackievirus B-3 (CVB3) showed extensive inflammatory cell infiltration of the myocardium and acinar tissue of the pancreas in 7 days. Selective depletion of T lymphocyte subpopulations indicated that CD4 cells were either completely or partially responsible for cell damage in both organs. Other organs such as the liver were infected and contained virus titers equivalent to those seen in the heart and pancreas but showed no apparent tissue injury. The role of the CD4 cell was confirmed by positive selection of either T cell subpopulation from CVB3-immune lymphocytes in vitro and adoptive transfer of these cells into T cell-deficient (thymectomized, irradiated, bone marrow reconstituted, TXBM) DBA/2 recipients. Lymphocytes from CVB3-infected donor mice were adsorbed to myocyte, skin fibroblast, or liver vascular endothelial cell (VEC) monolayers. The adherent population was retrieved and adoptively transferred into uninfected syngeneic recipients. When killed 7 days later, the animals receiving unfractionated immune lymphocytes or cells eluted from heart monolayers developed both myocarditis and pancreatitis. Anti-Thy 1.2 and C' treatment of the unfractionated cells completely abrogated transfer of disease. Cells eluted from either fibroblast or liver VEC monolayers showed no pathogenicity. Adsorption of immune cells to heart monolayers in the presence of anti-IAd (class II major histocompatibility complex antigen, MHC) inhibited attachment of the pathogenic T cell, whereas anti KdDd (a class I MHC antigen) had no effect.

Genetic diversity of enterovirus subgroups

Enterovirus serotypes were studied using nucleic acid hybridization and nucleotide sequence analysis. A great majority of enteroviruses could be roughly divided into two larger subgroups the first consisting of poliovirus and certain coxsackievirus A serotypes. The second subgroup included coxsackie B viruses, most ECHO viruses, enterovirus 71 and representatives of coxsackie A viruses. Enterovirus 70 showed low homology to the viruses in both groups. Interestingly, ECHO virus 22 failed to react with any of the hybridization probes indicating a relatively distant relationship. The close relationship between coxsackie B and ECHO viruses as well as between polio and certain coxsackie A viruses was also evident when nucleotide sequences of the 3' end noncoding parts were compared.

Characterization of a YAC-1 mouse cell receptor for group B coxsackieviruses

A receptor on YAC-1 cells, a mouse T-lymphoma cell line, bound all six serotypes of the group B coxsackieviruses (CVB). In addition, the cells produced infectious virus. Each of the CVB competed for the same receptor on YAC-1 cells. CVB3 bound relatively slowly to YAC-1 cells (k = 4 x 10(-11) min-1 cell-1), and there were only 500 attachment sites per cell. A rabbit antiserum prepared against the HeLa cell receptor protein Rp-a specifically inhibited the binding of CVB1 and CVB3. A virus-receptor complex with CVB3 could be isolated from detergent (0.5% sodium deoxycholate, 1% Triton X-100)-solubilized YAC-1 plasma membranes. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the iodinated virus-receptor complex revealed a band with the same mobility as Rp-a. The results suggested that the YAC-1 receptor for CVB resembles that of the HeLa cell receptor.

Clinical and experimental aspects of viral myocarditis

Picornaviruses are frequently implicated as the etiological agents of acute myocarditis. This association is based historically on serological evidence of rising antibody titers to specific pathogens and more recently on identification of viral genomic material in endocardial biopsy specimens through in situ hybridization. Only rarely is infectious virus isolated from either the patient or the heart during periods of maximum myocardial inflammation and injury. Thus, despite a probable viral etiology, much interest centers on the role of the immune system in cardiac damage and the likelihood that the infection triggers an autoimmune response to heart-specific antigens. Heart-reactive antibodies and T cells are found in most myocarditis patients, and immunosuppressive therapy has proven beneficial in many, though not all, cases. Furthermore, murine models of coxsackievirus group B type 3-induced myocarditis also demonstrate that virus infection initiates autoimmunity and that these autoimmune effectors are predominately responsible for tissue injury. How virus-host interactions overcome presumed self-tolerance to heart antigens is discussed, and evidence supporting various theories of virus-initiated autoimmunity and disease pathogenesis are delineated.

The major human rhinovirus receptor is ICAM-1

The major human rhinovirus receptor has been identified with monoclonal antibodies that inhibit rhinovirus infection. These monoclonal antibodies recognize a 95 kd cell surface glycoprotein on human cells and on mouse transfectants expressing a rhinovirus binding phenotype. Purified 95 kd protein binds to rhinovirus in vitro. Protein sequence from the 95 kd protein showed an identity with that of intercellular adhesion molecule-1 (ICAM-1); a cDNA clone obtained from mouse transfectants expressing the rhinovirus receptor had essentially the same sequence as ICAM-1. Thus, the major human rhinovirus receptor is ICAM-1. The gene for this receptor maps to human chromosome 19, which also contains the genes for a number of other picornavirus receptors.

Monoclonal antibody identification of a 100-kDa membrane protein in HeLa cells and human spinal cord involved in poliovirus attachment

Unique receptor sites for poliovirus are considered to be the primary determinant of the virus' cell and tissue-type specificity. To study the poliovirus-cell interaction, eight monoclonal antibodies that specifically block the cytopathic effects of poliovirus were generated by using HeLa cell preparations as immunogen and a newly developed colorimetric screening assay. Plaque-inhibition assays confirmed the viral specificity of the antibodies, and when one antibody, AF3, was used as a probe in immunoblots of cell membrane preparations, it detected a 100-kDa band in only those cell lines and tissues permissive for poliovirus infection. AF3 also specifically inhibited radiolabeled poliovirus binding to cells. In terms of tissue specificity, AF3 detected the 100-kDa band in membrane preparations from human spinal cord but not in organ homogenates of human kidney or in murine tissue, including the central nervous system. Furthermore, AF3 detected the band in a human-mouse hybrid cell line containing human chromosome 19, which confers permissivity for poliovirus infection, but the antibody did not detect the band in a human chromosome 19-deficient subclone. In an immunohistochemical study of the human brainstem, AF3 stained neurons in the reticular formation and clusters of brainstem neurons, consistent with the known pattern of damage caused by poliovirus infection in the brainstem. Furthermore, AF3 reacted with human peripheral mononuclear cells, consistent with the known replication of poliovirus in Peyer's patches and tonsils. These results strongly suggest that the 100-kDa band detected by antibody AF3 is, or is closely associated with, the poliovirus receptor site.

Mice immunized with measles virus develop antibodies to a cell surface receptor for binding virus

Mice were immunized with measles virus to determine whether an auto-anti-idiotypic antireceptor response could be generated as a probe for measles virus receptors. Mice initially responded to viral antigens (days 11 to 18) and subsequently developed antibodies to a putative measles virus receptor (peak at day 30 to 35) by three criteria: the sera (1) agglutinated erythrocytes which virus agglutinates, (2) reacted with Vero cells, and (3) inhibited virus attachment to Vero cells. Additionally, select sera inhibited virus infection of Vero cells. The cell-reactive activity was identified as immunoglobulin G antibody and was neutralized by sera reacting with virus (idiotype). The application of this anti-idiotypic antibody to identify measles virus-binding sites on Vero cells was revealed by the ability of sera to immunoprecipitate 20- and 30.5-kilodalton proteins from metabolically labeled ([35S]methionine) Vero cells.

A monoclonal antibody specific for the cellular receptor for the group B coxsackieviruses

A 50-kilodalton receptor protein (Rp-a) for the group B coxsackieviruses (CB) was isolated in a virus-receptor complex from detergent-solubilized HeLa cells (J. E. Mapoles, D. L. Krah, and R. L. Crowell, J. Virol. 55:560-566, 1985). It was used as an immunogen for preparation of a mouse monoclonal antibody (RmcB) which protected HeLa cells and Buffalo green monkey kidney cells from infection by all six serotypes of CB. RmcB did not protect HeLa cells from infection by poliovirus, echovirus 6, or coxsackievirus A18. This monoclonal antibody differed in receptor epitope specificity from a previously isolated antibody (RmcA) (R. L. Crowell, A. K. Field, W. A. Schleif, W. L. Long, R. J. Colonno, J. E. Mapoles, and E. A. Emini, J. Virol. 57:438-445, 1986) which blocked receptors only for type 1 CB (CB1), CB3, CB5, and echovirus 6. RmcA and RmcB recognized two distinct saturable receptors on HeLa cells, designated HR2 and HR1, respectively. Human rhabdomyosarcoma (RD) cells have the HR2 receptor for CB3-RD (a variant of CB3), but lack the HR1 receptor for CB3. Therefore, RD cells were resistant to infection by CB3. Although binding of CB3-RD to the HR2 receptor on RD cells can lead to infection, binding of CB3-RD to the HR2 receptor on HeLa cells did not lead to infection. Apparently, both CB3 and CB3-RD use only the HR1 receptor for infection of HeLa cells. Thus, a given virus may use two distinct receptors to bind to cells when only one virus-receptor interaction leads to infection.

Characteristics of the minor group receptor of human rhinoviruses

The receptor for the minor group of human rhinoviruses was solubilized from HeLa cell membranes with various detergents. Virus binding activity was determined in a filter binding assay using 35S-labeled human rhinovirus 2 (HRV2) as a probe. The receptor protein was enriched on Lens culinaris lectin columns and the active fractions were further purified by gel permeation and anion exchange chromatography. The receptor has an apparent molecular weight of 450 kDa in the presence of detergent. The binding activity is sensitive to trypsin, sulfhydryl modifying agents, but insensitive to neuraminidase. Divalent cations are essential for virus binding.

Cell-protective monoclonal antibodies to bovine enterovirus-3 and partial or no activity against other serotypes

Preparation of monoclonal antibodies to bovine virus diarrhea virus (BVDV) yielded some hybridoma cells that secreted monoclonal antibodies against the Madin-Darby bovine kidney cells. The anti-cellular monoclonal antibodies reacted with other bovine cells (bovine turbinate and testicle) but not with cell lines derived from other animal species. Subclones derived from one hybridoma partially blocked the infectivity of BVDV, possibly through the binding of the monoclonal antibodies with an epitope close to the receptor site of BVDV and not by way of steric hindrance. Unexpectedly, these same subclones completely blocked the infectivity of bovine enterovirus-3 (BEV-3) strain 240A and partially blocked the infectivity of BEV-2 and BEV-3 (ATCC strain) but not that of other serotypes. Other subclones derived from two other hybridomas, although cell membrane specific, did not have a protective activity against BEV or BVDV.