Rotavirus acceleration of murine type 1 diabetes is associated with a T helper 1-dependent specific serum antibody response and virus effects in regional lymph nodes.

AIMS/HYPOTHESIS: Rotavirus infection in at-risk children correlates with production of serum autoantibodies indicative of type 1 diabetes progression. Oral infection with rhesus monkey rotavirus (RRV) accelerates diabetes onset in mice. This relates to their rotavirus-specific serum antibody titre and local pro-inflammatory cytokine induction without pancreatic infection. Our aim was to further investigate the roles of serum antibodies and viral extra-intestinal spread in diabetes acceleration by rotavirus. METHODS: Rotavirus-specific serum antibody production was detected by ELISA in diabetes-prone mice given either inactivated or low-dose RRV, in relation to their diabetes development. Serum anti-rotavirus antibody titres and infectious virus in lymph nodes were measured in mice given RRV or porcine rotavirus CRW-8. In lymph node cells, rotavirus antigen presence and immune activation were determined by flow cytometry, in conjunction with cytokine mRNA levels. RESULTS: Acceleration of diabetes by RRV required virus replication, which correlated with antibody presence. CRW-8 induced similar specific total immunoglobulin and IgA titres to those induced by RRV, but did not accelerate diabetes. RRV alone elicited specific serum IgG antibodies with a T helper (Th)1 bias, spread to regional lymph nodes and activated antigen-presenting cells at these sites. RRV increased Th1-specific cytokine expression in pancreatic lymph nodes. Diabetes onset was more rapid in the RRV-infected mice with the greater Th1 bias. CONCLUSIONS/INTERPRETATION: Acceleration of murine diabetes by rotavirus is virus strain-specific and associated with virus spread to regional lymph nodes, activation of antigen-presenting cells at these sites and induction of a Th1-dominated antibody and cytokine response.

Association between rotavirus infection and pancreatic islet autoimmunity in children at risk of developing type 1 diabetes.

Pancreatic islet autoimmunity leading to type 1 diabetes could be triggered by viruses in genetically susceptible individuals. Rotavirus (RV), the most common cause of childhood gastroenteritis, contains peptide sequences highly similar to T-cell epitopes in the islet autoantigens GAD and tyrosine phosphatase IA-2 (IA-2), suggesting T-cells to RV could trigger islet autoimmunity by molecular mimicry. We therefore sought an association between RV infection and islet autoantibody markers in children at risk for diabetes who were followed from birth. There was a specific and highly significant association between RV seroconversion and increases in any of these antibodies: 86% of antibodies to IA-2, 62% to insulin, and 50% to GAD first appeared or increased with increases in RV IgG or IgA. RV infection may therefore trigger or exacerbate islet autoimmunity in genetically susceptible children.

VP4 and VP7 typing using monoclonal antibodies.

Both rotavirus outer capsid proteins, VP4 and VP7, elicit neutralizing antibodies. Neutralizing mouse monoclonal antibodies (N-MAbs) to VP7 are easily derived and have been used widely and successfully to serotype both stool-derived and culture-adapted rotaviruses by enzyme immunoassay (EIA). Generally, approximately 70% of rotaviruses in stool samples are typable by VP7 EIA, an inexpensive and practical method. Variations in antigenic regions between strains within human rotavirus serotypes 1, 2, 4, and 9 have been recorded. These have been termed monotypes because they are detected with N-MAbs. The molecular basis for monotypes has been determined by mapping mutations selected in N-MAb-resistant antigenic variants, and by sequence analysis of the gene encoding VP7 in newly recognized monotypes. Antigenic regions A, B and C in VP7 are involved. In order to detect all members of a particular VP7 serotype, it is necessary to type with a panel of N-MAbs specific for that serotype. N-MAbs to VP4 of human rotavirus are difficult to raise and few have proven suitable for VP4 serotyping by EIA. The specificity of the assay for each P type is highest when the VP7 serotype specificity of the capture antiserum is matched to the G type of the rotavirus in the test sample. The VP4 EIA gives similar typing rates to the VP7 typing EIA. N-MAbs directed to VP8, the smaller subunit of VP4 generated by proteolytic cleavage, are more likely to show serotype specificity. Some N-MAbs that select mutations in the putative fusion region of VP5, the larger subunit of VP4, show cross-reactivity with extracts of normal, uninfected MA 104 cells and with fetal bovine serum. These N-MAbs also give elevated EIA OD readings with rotavirus-positive, but previously non-reactive fecal samples which have been frozen and thawed repeatedly. Overall, VP8-reactive N-MAbs appear most suitable for VP4 typing by EIA.

An improved enzyme-linked immunosorbent assay for the detection of rotavirus in faeces of neonates.

A direct enzyme-linked immunosorbent assay (EIA) for the detection of rotavirus in neonatal stools was developed. Rabbit antiserum against SA 11 rotavirus was incorporated as both coating and detector antibody, and rotavirus-negative rabbit serum was applied as a coating antibody control to eliminate false positive results. Pretreatment of stools with EDTA was found to increase both the sensitivity and specificity of the assay. This effect was greatest when 0.25 M EDTA (tetrasodium salt) was included in homogenized stool suspensions before the removal of solid debris by centrifugation. By electron microscopy, this EDTA pretreatment appeared to partly uncoat human rotavirus particles in faeces. Potentially suitable solid phase supports and horseradish peroxidase substrates were evaluated in the development of the assay. Screening of stool samples revealed that repeated freezing and thawing of stools eliminated positive EIA reactions. The SA 11 coating antibody compared favourably with a reference coating antiserum prepared against human faecal rotavirus strains. This EIA showed greater sensitivity for rotavirus detection than electron microscopy of stool concentrates prepared by ultracentrifugation, on testing 143 stools from 99 neonates and children. The assay has been applied successfully to detection of rotavirus in stools of neonates containing meconium, smaller amounts of viral antigen than in older children, and lacteal antirotaviral antibody. It is likely to be particularly useful for cross-infection studies in hospital wards and neonatal nurseries.

Evaluation of end-point titration, single dilution and capture enzyme immunoassays for measurement of antirotaviral IgA and IgM in infantile secretions and serum.

In order to facilitate measurement of antirotaviral IgA in large collections of faeces and secretions, adaptations of enzyme immunoassay methods for estimating antirotaviral IgA and IgM in duodenal fluid, saliva, faeces and serum were studied. To quantitate specific IgA, a single dilution of each sample was assayed. Results were expressed as antirotaviral IgA units derived from a standard curve. Units were calculated by log-logit analysis on computer. There was strong correlation between antirotaviral IgA units and end-point titres in 257 faecal samples (correlation coefficient r = 0.92) and in 182 duodenal fluids and salivary samples (correlation coefficient r = 0.74). The assay was validated using acute and convalescent faeces from children with or without rotavirus infection. Immune conversions in IgA were detected in 33 (75%) of the children by units and 34 (77%) by titres. None of nine children with gastroenteritis due to other infectious agents showed immune conversions to rotavirus. A monoclonal capture IgM assay showed similar end-point titres and numbers of immune conversions when compared with a direct assay for antirotaviral IgM in serum and secretions. Use of the capture method eliminated false-positive reactions with the cell control. The assay for antirotaviral IgA units in secretions is simple, rapid, reproducible and reliable, and has proven of value in longitudinal epidemiological studies of rotavirus coproIgA profiles. Both the capture IgM technique and the single dilution IgA method permit analysis of large numbers of specimens and are appropriate for examination of immune responses to natural rotavirus infection or during vaccine trials.

Rotavirus-neutralizing antibodies inhibit virus binding to integrins alpha 2 beta 1 and alpha 4 beta 1.

Rotavirus outer capsid proteins VP5(*), VP8(*) and VP7 elicit neutralizing, protective antibodies. The alpha 2 beta 1 integrin is a cellular receptor for rotavirus that is bound by VP5(*). Some rotaviruses also recognize the alpha 4 beta 1 integrin. In this study, the effects of antibodies to rotavirus on virus binding to recombinant alpha 2 beta 1 and alpha 4 beta 1 expressed on K562 cells were determined. All neutralizing monoclonal antibodies to VP5(*) tested (YO-2C2, 2G4, 1A10) and two to VP7 (RV-3:2, RV-4:2) inhibited rotavirus binding to alpha 2 beta 1. Rotavirus binding to alpha 4 beta 1 was reduced by 2G4 and neutralizing antibody F45:2, directed to VP7. However, a neutralizing antibody to VP8(*) (RV-5:2) and one to VP7 (RV-3:1) did not affect rotavirus binding to these integrins. Virus-cell binding was unaffected by non-neutralizing antibody RVA to the rotavirus inner capsid protein VP6. The attachment of human rotavirus strain Wa to these integrins was inhibited by infection sera with neutralizing activity collected from two children hospitalised with severe rotavirus gastroenteritis. A negative reference serum did not affect rotavirus-cell attachment. As the binding of rotaviruses to alpha 2 beta 1 and alpha 4 beta 1 is inhibited by neutralizing antibodies to VP5(*) and VP7, and serum from children with rotavirus disease, rotavirus recognition of these integrins may be important for host infection.

Variation in neutralization epitopes of human rotaviruses in relation to genomic RNA polymorphism.

Fecal rotaviruses collected from October 1983 to September 1984 from outpatients and inpatients attending the Royal Children's Hospital, Melbourne, Australia, with acute gastroenteritis were serotyped by enzyme immunoassay using rotavirus-neutralizing mouse monoclonal antibodies specific for serotypes 1 to 4. Application of three different serotype 1-neutralizing antibodies indicated variations in neutralization epitopes between serotype 1 rotaviruses on the major outer capsid glycoprotein, including a site shared with serotype 3 rotaviruses. The three different binding patterns observed were termed "monotypes." Comparison of monotype and serotype with genomic RNA profiles generated by gel electrophoresis of ds viral RNA indicated that each RNA electropherotype corresponded to only one monotype (1a, 1b, 1c) or serotype (3, 4). However, serotypes 1 (a and c) and 4 contained multiple electropherotypes. Greater numbers of RNA segment variations, including alteration in mobility of gene segments 7, 8, and 9, were evident between rotaviruses of different serotype or monotype than within those groups. Within limits of time and location, rotavirus neutralization epitope variations appear to correlate with RNA polymorphism. Where rotavirus epidemiology has been analyzed by year using RNA electropherotypes, only limited numbers of each RNA pattern need to be serotyped to ascertain the major serotypes in circulation.

Typing of human rotavirus VP4 by an enzyme immunoassay using monoclonal antibodies.

Two different neutralization specificities exist on the outer capsid of group A rotaviruses. At least seven VP7 (G) antigenic types are distinguishable among human rotaviruses. Four distinct antigenic (P) types of human rotavirus VP4 corresponding to separate rotavirus gene 4 groups have been described. The aim of this study was to identify P types in clinical specimens by developing an enzyme immunoassay, using P-type-specific neutralizing monoclonal antibodies (N-MAbs). Three N-MAbs primarily or solely recognizing each of P types 4, 6, and 8 and binding to VP4 or its subunit VP5* were derived. These N-MAbs served as detector antibodies in an enzyme immunoassay P-typing system similar to that in use for G typing. P-type specificity was highest when the G-type specificity of the capture antiserum was matched to the G type of the rotavirus in the test sample. The method correctly identified the P types of 13 well-characterized, cell culture-adapted human rotaviruses and was used to classify a further six strains. P typing of 118 rotavirus-positive stools gave results consistent with the P type inferred from the G type for 98 (83%) samples. Twelve (10%) of the stools showed no reaction with any N-MAb and eight (7%) samples were untypeable because of cross-reactivity between N-MAbs or high background readings. This P-typing enzyme immunoassay system is economical and amenable to large-scale use in epidemiological studies. Its use will facilitate assessment of the distribution of P types worldwide and of the role of VP4 in eliciting protective immune responses.

Longitudinal studies of neutralizing antibody responses to rotavirus in stools and sera of children following severe rotavirus gastroenteritis.

Rotavirus-neutralizing antibody responses in sera and stools of children hospitalized with rotavirus gastroenteritis and then monitored longitudinally were optimally detected by using local rotavirus strains. Stool responses were highest on days 5 to 8 after the onset of diarrhea. Longitudinal monitoring suggested that serum neutralizing antibody responses were a more useful measure of severely symptomatic rotavirus infection than stool responses but that stool antibody responses may be a useful measure of rotavirus immunity.

Measurement of rotavirus-neutralizing coproantibody in children by fluorescent focus reduction assay.

A fluorescent focus reduction assay suitable for the measurement of rotavirus-neutralizing antibodies in the feces of children was developed. Of 408 stools tested, 7% showed false-positive neutralization, and the number of rotavirus serotypes neutralized by a fecal extract was proportional to the levels of antirotaviral immunoglobulin A in the extract.

Relation of VP7 amino acid sequence to monoclonal antibody neutralization of rotavirus and rotavirus monotype.

The neutralization epitopes of the VP7 of human rotavirus RV-4 were studied by using five neutralizing mouse monoclonal antibodies to select virus variants resistant to neutralization by each of the antibodies. Antibody resistance patterns and sequence analysis of the RV-4 variants revealed that at least four sites on VP7, located at amino acids 94 (region A), 147 to 148 (region B), 213 (region C), and 291, are involved in neutralization of the human G1 rotavirus RV-4. The A-region site elicited antibody cross-reactive between G types and showed species-restricted immunodominance not related to carbohydrate attachment. The monotype 1b rotavirus M37 lacked this site. The B region contained strain-specific and cross-reactive sites, absent in monotype 1c rotaviruses. The C-region site was present in all G1 rotaviruses tested. Monotype 1a rotaviruses contained all these sites of neutralization. Virus monotype and sensitivity to monoclonal antibody neutralization usually related to the presence of a particular amino acid(s) at or next to the positions at which the mutations were selected in the virus variants.

Experience with an enzyme immunoassay for serotyping human group A rotaviruses.

An enzyme immunoassay utilizing neutralizing monoclonal antibodies to VP7 of four human group A rotavirus serotypes successfully typed rotaviruses in 71.4% (568 of 796) of fecal specimens. Sensitivity was enhanced by using homologous capture and detector antibodies. Serotyping was most successful with specimens stored for less than 3 years and containing 10(4) or more particles per ml.

Rotavirus contains integrin ligand sequences and a disintegrin-like domain that are implicated in virus entry into cells.

Rotavirus contains two outer capsid viral proteins, the spike protein VP4 and major capsid component VP7, both of which are implicated in cell entry. We show that VP4 and VP7 contain tripeptide sequences previously shown to act as recognition sites for integrins in extracellular matrix proteins. VP4 contains the alpha2beta1 integrin ligand site DGE. In VP7, the alphaxbeta2 integrin ligand site GPR and the alpha4beta1 integrin ligand site LDV are embedded in a novel disintegrin-like domain that also shows sequence similarity to fibronectin and the tie receptor tyrosine kinase. Microorganism sequence homology to these ligand motifs and to disintegrins has not been reported previously. In our experiments, peptides including these rotaviral tripeptides and mAbs directed to these integrins specifically blocked rotavirus infection of cells shown to express alpha2beta1 and beta2 integrins. Rotavirus VP4-mediated cell entry may involve the alpha2beta1 integrin, whereas VP7 appears to interact with alphaxbeta2 and alpha4beta1 integrins.

Phorbol dibutyrate-induced megakaryocytic differentiation increases susceptibility of K562 cells to SA11 rotavirus infection.

The role of integrins previously implicated as rotavirus receptors in determining cellular susceptibility to SA11 rotavirus was studied, using phorbol dibutyrate (PDB) treatment of K562 cells to induce megakaryocytic differentiation. Expression of alpha2beta1 integrin was detected after 2 days in PDB, and peaked after PDB treatment for 4-7 days. SA11 titres were increased by 1.8- to 10.8-fold over untreated cells after PDB treatment for 2-7 days, and correlated with levels of alpha2beta1 integrin expression in PDB-treated K562 cells.

Attachment and growth of human rotaviruses RV-3 and S12/85 in Caco-2 cells depend on VP4.

Studies with human neonatal rotaviruses RV-3 and S12/85 and their reassortants showed that VP4 is a determinant of rotavirus attachment to and growth in Caco-2 cells. The binding of these viruses to MA104 and Caco-2 cells correlated with their growth ability. Virus sensitivity to trypsin and the VP4 fusion region may be implicated in these processes.

G3P2 rotaviruses causing diarrhoeal disease in neonates differ in VP4, VP7 and NSP4 sequence from G3P2 strains causing asymptomatic neonatal infection.

During longitudinal epidemiological studies of rotavirus infections in children in Melbourne, Australia human G3P2 rotavirus strains causing asymptomatic or symptomatic infections have been identified. Eleven strains (AS strains) associated with asymptomatic infection of newborn babies from 1974-1984, and five strains (S strains) associated with symptomatic infection of newborn babies (4) or a 22 week old infant (1) during 1980-1986 were studied. The entire nucleotide sequences of genes coding for VP4, VP7, NSP4 and VP6 were derived for representative AS and S strains. The nucleotide sequences of neutralization epitope regions present on the outer capsid proteins VP4 and VP7 (regions C and F) showed extensive conservation of nucleotide and deduced amino acid sequence in all strains. Minor variations were observed over the 12 year period in VP7 epitope regions A and B in some strains. Specific conserved amino acids differences between the asymptomatic and symptomatic strains were observed in the genes encoding VP4 at aa133 and 303 (asparagine or threonine) and 380 (serine or isoleucine), VP7 at aa27 (threonine or isoleucine), aa29 (isoleucine or threonine), aa42 (valine or alanine) and aa238 (asparagine or aspartic acid/serine) and NSP4 at aa135 (isoleucine or valine). No amino acid changes were identified in gene 6. The observed amino acid differences occurred in proteins that have been implicated in virulence, and correlate with differences in clinical symptoms of infants infected with these strains. These results permit speculation about the genetic basis for virulence of human strains.

Characteristics and location of cross-reactive and serotype-specific neutralization sites on VP7 of human G type 9 rotaviruses.

The neutralization antigens of human rotavirus VP7 were studied by producing eight neutralizing monoclonal antibodies to G type 9 rotaviruses F45 and WI61 and selecting antigenic variants resistant to neutralization by these monoclonal antibodies. Neutralization resistance patterns and sequence analysis of the antigenic variants indicated the presence of overlapping serotype-specific and serotype cross-reactive epitopes in antigenic region A, and one distinct type-specific epitope. Cross-reactive monoclonal antibodies were more tolerant of amino acid sequence change than type-specific monoclonal antibodies. The existence of a new antigenic region, F, including amino acids 235 to 242 was confirmed. This region contained a cross-reactive epitope not detectable in the presence of glycosylation at amino acid 238. This glycosylation also affected neutralization by a cross-reactive monoclonal antibody directed to antigenic region C. Antigenic regions A, B, C, and F all contain epitopes shared between G types, of which at least two (C and F) are affected by glycosylation.

Human rotavirus VP4 contains strain-specific, serotype-specific and cross-reactive neutralization sites.

The neutralization epitopes of human rotavirus VP4 were studied by using a panel of neutralization monoclonal antibodies previously shown to be strain-specific (RV-3:3), serotype-specific (RV-5:2, ST-3:3) or cross-reactive (F45:4). Antigenic variants of human rotaviruses RV-3, ST-3, RV-5 and F45 resistant to neutralization by the appropriate of VP4 specific monoclonal antibodies (RV-3:3, ST-3:3, RV-5:2 and F45:4 respectively) were selected. By nucleotide sequence analysis and single strand conformational polymorphism analysis of these variants, three sites of neutralization on VP5* and one site on VP8* were identified. At or near to the putative fusion region on VP5*, a strain-specific site (aa383), a serotype P1A-P2 cross-reactive site (aa392) and a serotype P2-specific site (aa397) were found. On VP8*, a serotype P1B-specific site at aa148 was detected. These results confirmed the importance of the putative fusion region in neutralization and have identified a new neutralization site in the hypervariable region of VP8* which is specific for serotype P1B human rotaviruses.

Integrins alpha2beta1 and alpha4beta1 can mediate SA11 rotavirus attachment and entry into cells.

Most mammalian rotaviruses contain tripeptide amino acid sequences in outer capsid proteins VP4 and VP7 which have been shown to act as ligands for integrins alpha2beta1 and alpha4beta1. Peptides containing these sequences and monoclonal antibodies directed to these integrins block rotavirus infection of cells. Here we report that SA11 rotavirus binding to and infection of K562 cells expressing alpha2beta1 or alpha4beta1 integrins via transfection is increased over virus binding to and infection of cells transfected with alpha3 integrin or parent cells. The increased binding and growth were specifically blocked by a monoclonal antibody to the transfected integrin subunit but not by irrelevant antibodies. In our experiments, integrin activation with phorbol ester did not affect virus binding to cells. However, phorbol ester treatment of K562 parent and transfected cells induced endogenous gene expression of alpha2beta1 integrin, which was detectable by flow cytometry 16 h after treatment and quantitatively correlated with the increased level of SA11 virus growth observed after this time. Virus binding to K562 cells treated with phorbol ester 24 h previously and expressing alpha2beta1 was elevated over binding to control cells and was specifically blocked by the anti-alpha2 monoclonal antibody AK7. Virus growth in alpha4-transfected K562 cells which had also been induced to express alpha2beta1 integrin with phorbol ester occurred at a level approaching that in the permissive MA104 cell line. We therefore have demonstrated that two integrins, alpha2beta1 and alpha4beta1, are capable of acting as cellular receptors for SA11 rotavirus.

Simple and specific enzyme immunoassay using monoclonal antibodies for serotyping human rotaviruses.

An enzyme immunoassay for serotyping human rotaviruses in stools and in cell culture was developed. Hyperimmune rabbit antisera to rotaviruses were used as capture antibodies, and rotavirus-neutralizing mouse monoclonal antibodies specific for serotypes 1, 2, 3, and 4 were used as detection reagents. Partial purification of monoclonal antibodies and inclusion of skim milk powder in antibody diluents contributed to assay specificity. The sensitivity of this assay was greater than that of a direct enzyme immunoassay in which rotaviruses of the appropriate serotype were adsorbed directly to the solid phase. When fecal extracts were concentrated threefold, this serotyping enzyme immunoassay was of equal specificity and approached the sensitivity of electron microscopy for rotavirus detection. This assay is simple and rapid and is suitable for serotyping the large numbers of isolates obtained from epidemiological studies and vaccine trials.