The epithelial cell response to rotavirus infection

Rotavirus is the most important worldwide cause of severe gastroenteritis in infants and young children. Intestinal epithelial cells are the principal targets of rotavirus infection, but the response of enterocytes to rotavirus infection is largely unknown. We determined that rotavirus infection of HT-29 intestinal epithelial cells results in prompt activation of NF-kappaB (<2 h), STAT1, and ISG F3 (3 h). Genetically inactivated rotavirus and virus-like particles assembled from baculovirus-expressed viral proteins also activated NF-kappaB. Rotavirus infection of HT-29 cells induced mRNA for several C-C and C-X-C chemokines as well as IFNs and GM-CSF. Mice infected with simian rotavirus or murine rotavirus responded similarly with the enhanced expression of a profile of C-C and C-X-C chemokines. The rotavirus-stimulated increase in chemokine mRNA was undiminished in mice lacking mast cells or lymphocytes. Rotavirus induced chemokines only in mice <15 days of age despite documented infection in older mice. Macrophage inflammatory protein-1beta and IFN-stimulated protein 10 mRNA responses occurred, but were reduced in p50-/- mice. Macrophage inflammatory protein-1beta expression during rotavirus infection localized to the intestinal epithelial cell in murine intestine. These results show that the intestinal epithelial cell is an active component of the host response to rotavirus infection.

The Epithelial Cell Response to Rotavirus Infection

Rotavirus is the most important worldwide cause of severe gastroenteritis in infants and young children. Intestinal epithelial cells are the principal targets of rotavirus infection, but the response of enterocytes to rotavirus infection is largely unknown. We determined that rotavirus infection of HT-29 intestinal epithelial cells results in prompt activation of NF-κB (&lt;2 h), STAT1, and ISG F3 (3 h). Genetically inactivated rotavirus and virus-like particles assembled from baculovirus-expressed viral proteins also activated NF-κB. Rotavirus infection of HT-29 cells induced mRNA for several C-C and C-X-C chemokines as well as IFNs and GM-CSF. Mice infected with simian rotavirus or murine rotavirus responded similarly with the enhanced expression of a profile of C-C and C-X-C chemokines. The rotavirus-stimulated increase in chemokine mRNA was undiminished in mice lacking mast cells or lymphocytes. Rotavirus induced chemokines only in mice &lt;15 days of age despite documented infection in older mice. Macrophage inflammatory protein-1β and IFN-stimulated protein 10 mRNA responses occurred, but were reduced in p50−/− mice. Macrophage inflammatory protein-1β expression during rotavirus infection localized to the intestinal epithelial cell in murine intestine. These results show that the intestinal epithelial cell is an active component of the host response to rotavirus infection.

Viral infections of the gastrointestinal tract

Viral gastroenteritis is a major worldwide public health problem. The number of identified pathogens continues to increase, and characterization of the viral structures and functions must be inexorably pursued. Investigators have made considerable progress toward understanding the mechanisms of virus-cell interactions, host responses, and pathogenesis, but the application of this knowledge to improve disease treatment and prevention awaits further key discoveries. Despite deficiencies in knowledge of many aspects of these important issues, a vaccine for the most important pathogen, rotavirus, has been submitted to the US Food and Drug Administration for approval.

Detection of serum antibodies to Helicobacter pylori by an immunochromatographic method

OBJECTIVES

FlexsureHP is a bi-directional immunochromatographic device for detection of IgG antibodies to Helicobacter pylori in human serum. This test, requiring only three steps and a 4-min incubation, can be used as an office-based diagnostic test. The goal of this study was to compare the sensitivity and specificity of the FlexsureHP, when performed by a clinician, with the established ELISA in the evaluation of clinical samples in an office setting.

RESULTS

The sensitivity and specificity of the FlexsureHP, compared with the biopsy, is 92.4% and 83.0%, respectively, with a positive predictive value of 88.4%. This was not significantly different from the results obtained when the ELISA was compared with biopsy data.

CONCLUSION

The immunochromatographic device, FlexsureHP, is a rapid, highly sensitive, and moderately specific office-based diagnostic test for H. pylori infection.

Replication as a determinant of the intestinal response to rotavirus

Mucosal antibody induction by otherwise identical replication-competent and replication-incompetent rhesus monkey rotaviruses was compared. Although psoralen-inactivated virus induced diarrhea, the magnitude of the intestinal antibody response was severely attenuated compared with that of replicating rotavirus, as determined by assay of mucosal antibody-secreting cells. Rotavirus that was neutralized by monoclonal antibodies (anti-VP4 and -VP7) prior to inoculation was similarly ineffective at induction of specific antibodies in intestinal secretions. In contrast to genetically inactivated virus, antibody-neutralized virus did not induce diarrhea. In this murine model, viral replication is an important determinant of antibody induction. The diarrhea response is blocked by neutralizing antibodies, but the mechanism of action is not exclusively the inhibition of viral replication.

Rotavirus stimulates IL-8 secretion from cultured epithelial cells

Rotavirus is the most important cause of severe gastroenteritis in children worldwide. We have investigated cytokine responses to rotavirus infection of cultured intestinal epithelial cells. Interleukin 8 (IL-8) is a chemotactic and cell-activating cytokine that is synthesized by epithelial cells and induced in response to bacterial enteric pathogens. Rotavirus inoculation increased IL-8 mRNA levels in cultured intestinal epithelial cells within 2 hr of infection. IL-8 secretion increased 10(2)- to 10(3)-fold by 8 hr postinfection. Secretion of TNF alpha or IL-1 beta, cytokines which themselves increase IL-8 secretion, was not induced by rotavirus, nor was that of TNF alpha, IFN alpha, IFN gamma, or IL-6. Neutralizing antibodies to TNF alpha or IL-1 alpha/beta did not affect the IL-8 response. Secretion of IL-8 was dependent on an intact viral capsid, as single-shell particles were inert. Neutralizing monoclonal antibodies (vp7-specific) that do not block cell attachment did block rotavirus stimulation of IL-8 secretion, indicating that attachment to the cell surface is not a sufficient stimulus to induce IL-8. Genetically inactivated rotavirus was also effective for IL-8 induction, indicating that viral replication was not required. These data suggest that epithelial cytokine IL-8 may be an important mediator of the host response to viral gastroenteritis pathogens such as rotavirus.

Rotavirus diarrhea is caused by nonreplicating viral particles

Rotaviruses infect the villous epithelium of the small intestine and cause severe diarrhea in young children. The mechanism by which rotavirus causes diarrhea has not been elucidated. It has been hypothesized that rotavirus replication in the intestinal epithelium causes a loss of viable absorptive cells, leading to an imbalance of intestinal secretion and absorption. Cell destruction has generally been thought to result from rotavirus transcription and replication. However, the widely used heterologous murine model of rotavirus infection demonstrates minimal viral replication and histological changes limited to epithelial vacuolation on the distal villus despite the simultaneous occurrence of voluminous liquid diarrhea. We have genetically inactivated rotaviruses to test the importance of viral replication in the pathogenesis of rotavirus-induced diarrhea. We present direct evidence that transcription- and replication-defective rotaviruses cause diarrhea in an animal model. These findings suggest that rotavirus attachment or entry into cells is sufficient for the induction of diarrhea. The mechanism of rotavirus-induced diarrhea is therefore consistent with a viral toxin-like effect exerted during virus-cell contact.

Effects of rotavirus on epithelial transport in rabbit small intestine

The present study investigated changes in small intestinal epithelial transport in rabbits infected with rotavirus. The crypt depth-villus height ratio was increased in infected ileal tissue as a result of a significant increase in crypt depth and patchy shortening of the villi. Similar villus damage was seen in the jejunum. Despite these histological changes, basal fluid absorption by both the ileum and jejunum of infected animals was unaltered. Values for basal short-circuit current and resistance were similar; however, the increase in short-circuit current evoked by prostaglandin E2 was significantly smaller in rotavirus-infected tissues than in controls. The apparent Vmax for electrogenic glucose and alanine uptake by the jejunum was significantly increased following inoculation with rotavirus. Reduced responsiveness to the secretory effect of prostaglandin E2 and increased nutrient uptake may limit diarrhea that would otherwise be expected to occur as a result of the changes in mucosal architecture. This has important implications on the clinical treatment of rotavirus diarrhea, suggesting that oral rehydration therapy, which depends on the active transport of nutrients, may provide a more effective treatment than the use of cyclooxygenase inhibitors.

Infectious diarrhoea. Viruses

Increased knowledge has been gained into the aetiology and pathogenesis of viral gastroenteritis during the past two decades. There are now thought to be four major subclassifications of gastroenteritis-causing viruses; these include rotavirus, enteric adenovirus, calicivirus, including Norwalk and Norwalk-like viruses, and astrovirus. The association of these agents with gastroenteritis has been made by their electron microscopic detection in stool and intestinal biopsy specimens from affected patients, the inability to detect the viruses after recovery from disease, and the subsequent development of immunoglobulin responses after infection; in some instances disease transmission was achieved in human volunteers. The association of these viral agents with gastroenteritis has facilitated the study of classification, epidemiology, immunity, diagnostic tests, methods of treatment and, most importantly, disease prevention strategies such as vaccine development for rotavirus. This chapter highlights the major features of these agents, with special attention being given to the pertinent molecular biology as well as current and future prospects for vaccination. Enteric viral infections of the gastrointestinal tract in patients with AIDS are also discussed.

Persistence of intestinal antibody response to heterologous rotavirus infection in a murine model beyond 1 year

We used an ELISPOT (enzyme-linked immunosorbent spot) assay to quantitate the long-term rotavirus-specific intestinal antibody response in a murine model. The frequency of murine intestinal antibody-secreting cells (ASCs) was followed for a period of 1 year after a single dose of rhesus rotavirus (10(6) PFU) was administered at 10 days of age. Some animals were boosted at that time with a second dose. One year after infection, virus-specific ASCs declined from acute-phase levels, but they were still present at significant levels (1.32 x 10(4) virus-specific ASCs per 10(6) intestinal mononuclear cells; approximately 17% of the previously reported response at 1 month after infection). A booster dose 1 year after the primary infection produced a 100% increase in virus-specific ASCs but did not restore the response to that of the primary infection.

Psoralen preparation of antigenically intact noninfectious rotavirus particles

The use of the synthetic psoralen 4'-aminomethyl-4,5',8-trimethylpsoralen hydrochloride (AMT) is described for the inactivation of infectious rotavirus, a member of the viral family Reoviradae with a double-stranded RNA genome. This method not only provides complete inactivation of the virus but leaves antigenically intact particles. The lack of viral replication following inactivation was determined with an immunohistochemical focus assay. The antigenic authenticity of the particles was determined by monoclonal antibody ELISA and a viral hemagglutination assay.

Kayaking as a risk factor for leptospirosis

Leptospirosis is a common zoonosis present throughout Missouri. Previously regarded as an occupational illness of farmers and sewer workers, it is now primarily acquired from exposure to water polluted with the bacteria Leptospira. We present a case report of leptospirosis acquired through kayaking and review both the disease and the risk factor associated with kayaking.

Recombinant baculovirus-expressed rotavirus protein (VP4) in an ELISPOT assay of antibody secretion

Studies on the protein specificity of the intestinal antibody response to rotavirus infection have been hampered by lack of antigenically conserved isolated proteins to serve as antigens in immunochemical assays. In this report, the use of an antigenically conserved baculovirus-expressed rotavirus protein (VP4) as a capture antigen in the ELISPOT assay is described. Anti-VP4 antibody-secreting hybridoma cells are used as a test population to show that expressed VP4 as the capture antigen detects numbers of antibody secreting cells comparable to intact rotavirus particles. Hybridoma cells specific for other rotavirus proteins are used to ensure the specificity of the expressed VP4 in the assay. The flexibility and ease of use of a recombinant expressed protein product as a capture antigen in this assay dramatically enhances the ability to quantitate intestinal antibody responses to specific viral proteins.

Murine intestinal antibody response to heterologous rotavirus infection

Rotavirus is the most important worldwide cause of severe gastroenteritis. Extensive efforts have been devoted to the design of a vaccine that will prevent disease, but development of a more effective vaccine strategy may require progress in the understanding of the mucosal immune response to replicating viral antigens. In this article, we report the characterization of the intestinal antibody response of a murine model to heterologous infection with the rhesus rotavirus vaccine strain. We have adapted the enzyme-linked immunospot assay to measure this response without the difficulties associated with measurement of antibodies in intestinal contents or the artifacts associated with culturing of lymphocytes. The predominant response in terms of antibody-secreting cells (ASC) is seen in the small intestine lamina propria, which can be measured within 4 days of infection, peaks 3 weeks after infection, and remains near that level for longer than 8 weeks. The magnitude of the immunoglobulin A (IgA) cell response is approximately 10 times greater than the intestinal IgG cell response, and IgM cells are rare. Virus-specific ASC constitute approximately 50% of all ASC in the gut at the peak of the virus-specific response. This response is considerably greater than responses to nonreplicating mucosal antigens measured by similar techniques. Enteral infection engenders minimal virus-specific ASC response in the spleen. Rhesus rotavirus-specific enzyme-linked immunosorbent assay and neutralization assays of serum and intestinal contents did not correlate with virus-specific ASC response.

VP4-specific intestinal antibody response to rotavirus in a murine model of heterotypic infection

We have adapted a murine model of heterotypic rotavirus infection for the purpose of evaluating the intestinal antibody response to an infection that mimics human vaccination. Neonatal mice were infected with the rhesus rotavirus (RRV). The enzyme-linked immunospot assay was used in order to avoid common artifacts in the quantitation of intestinal immune responses inherent in measurements of luminal or serum immunoglobulins and to obtain easily quantifiable data in a flexible and convenient format. Functionally active lymphocytes were harvested from the spleen, small intestinal lamina propria, Peyer's patches, and mesenteric lymph nodes and processed into single-cell suspensions. Antibody-secreting cells (ASC) were quantitated from 5 to 50 days after infection for total, RRV-specific, baculovirus-expressed VP4-specific, and single-shell RRV-specific ASC secreting either immunoglobulin G (IgG), IgM, or IgA. The response to VP4 constituted less than 1.5% of the total virus-specific response, which was located almost exclusively in the gut and was 90% IgA. Intestinal ASC were directed overwhelmingly toward proteins incorporated in the single-shell particle, predominantly VP2 and VP6. We conclude that the antibody response to VP4, thought to be the site of the important neutralization sites conserved among several rotavirus serotypes, is an extremely small portion of the overall antibody response in the intestinal tract.

Passive protection against rotavirus-induced diarrhea by monoclonal antibodies to the heterotypic neutralization domain of VP7 and the VP8 fragment of VP4

A murine model was used to determine whether neutralizing monoclonal antibodies (MAbs) with heterotypic specificity directed to VP7 (MAb 57-8) or to the VP8 fragment of VP4 (MAb M14) passively protect mice against challenge with various strains of rotavirus. (The gene 4 product, an outer capsid protein, has traditionally been called VP3. It has been proposed, however, that the rotavirus gene 4 product be named VP4. The gene 3 product, a core protein, has been identified recently and named VP3 [M. Liu, P. A. Offit, and M. K. Estes, Virology 163:28-32, 1988]). Suckling mice orally inoculated with MAb 57-8 did not develop diarrhea when challenged with virulent serotype 3, 4, or 6 rotaviruses, while those inoculated with MAb M14 were passively protected from challenge with serotype 3 or 6 rotaviruses, as predicted by in vitro neutralization tests. These MAbs, however, did not protect mice from infection when the mice were challenged with rotaviruses of other serotypes. We conclude that specific neutralization epitopes on each surface protein are capable of mediating protection against one or several rotavirus serotypes.

Serotypic analysis of VP3 and VP7 neutralization escape mutants of rhesus rotavirus

Neutralization escape mutants of simian rotaviruses (rhesus rotavirus and SA11) were tested in hemagglutination inhibition and neutralization assays against hyperimmune and infection sera to determine if mutation in an immunodominant epitope could enable neutralization escape. An SA11 mutant with a new glycosylation site at amino acid 211 of VP7 was shown to escape neutralization by hyperimmune but not infection sera.

Characterization of homotypic and heterotypic VP7 neutralization sites of rhesus rotavirus

The gene 9 nucleotide sequence was determined for rhesus rotavirus and each of 14 viral variants selected for their resistance to neutralizing monoclonal antibodies. Each variant contains a single gene 9, VP7, mutation which permits viral growth in the presence of the antibody. Variant mutations were identified in two distinct neutralization regions. Region A was identified by monoclonal antibodies that are involved in both serotype-specific and serotype cross-reactive neutralization. Region C was identified by serotype-specific neutralizing monoclonal antibodies. Heterotypic neutralizing monoclonal antibody 57-8 selected variants with a mutation at amino acid 94 in the A region, the same amino acid location selected by serotype-specific monoclonal antibodies. Monoclonal antibody 3 selected a VP7 mutation at amino acid 99 resulting in additional N-linked glycosylation of the VP7 protein. Despite the added VP7 glycosylation, variant v3 was not broadly resistant to additional VP7-specific neutralizing monoclonal antibodies.

Functional and topographical analyses of epitopes on the hemagglutinin (VP4) of the simian rotavirus SA11

An immunochemical analysis of the hemagglutinin (VP4) of the simian rotavirus SA11 was performed to better understand the structure and function of this molecule. Following immunization of mice with double-shelled virus particles and VP4-enriched fractions from CsCl gradients, a battery of anti-SA11 hybridomas was generated. A total of 13 clones secreting high levels of anti-VP4 monoclonal antibody (MAb) was characterized and compared with two cross-reactive anti-VP4 MAbs generated against heterologous rhesus (RRV) and porcine (OSU) rotavirus strains. These cross-reactive MAbs effectively neutralized SA11 infectivity in vitro. The epitopes recognized by these 15 MAbs were grouped into six antigenic sites on the SA11 hemagglutinin. These sites were identified following analysis of the MAbs by using a simple competitive binding enzyme-linked immunosorbent assay (ELISA) and biological assays. Three of the antigenic sites were involved in neutralization of virus infectivity in vitro. All the MAbs with neutralization activity and two nonneutralizing MAbs were able to inhibit viral hemagglutination of human erythrocytes. Competitive binding ELISA data showed a positive cooperative binding effect with some pairs of the anti-VP4 MAbs, apparently due to a conformational change induced by the binding of the first MAb. Some of the MAbs also bound better to trypsin-treated virus than to non-trypsin-treated virus. A topographic map for VP4 is proposed on the basis of the observed properties of each antigenic site.

Infectious rotavirus enters cells by direct cell membrane penetration, not by endocytosis

Rotaviruses are icosahedral viruses with a segmented, double-stranded RNA genome. They are the major cause of severe infantile infectious diarrhea. Rotavirus growth in tissue culture is markedly enhanced by pretreatment of virus with trypsin. Trypsin activation is associated with cleavage of the viral hemagglutinin (viral protein 3 [VP3]; 88 kilodaltons) into two fragments (60 and 28 kilodaltons). The mechanism by which proteolytic cleavage leads to enhanced growth is unknown. Cleavage of VP3 does not alter viral binding to cell monolayers. In previous electron microscopic studies of infected cell cultures, it has been demonstrated that rotavirus particles enter cells by both endocytosis and direct cell membrane penetration. To determine whether trypsin treatment affected rotavirus internalization, we studied the kinetics of entry of infectious rhesus rotavirus (RRV) into MA104 cells. Trypsin-activated RRV was internalized with a half-time of 3 to 5 min, while nonactivated virus disappeared from the cell surface with a half-time of 30 to 50 min. In contrast to trypsin-activated RRV, loss of nonactivated RRV from the cell surface did not result in the appearance of infection, as measured by plaque formation. Endocytosis inhibitors (sodium azide, dinitrophenol) and lysosomotropic agents (ammonium chloride, chloroquine) had a limited effect on the entry of infectious virus into cells. Purified trypsin-activated RRV added to cell monolayers at pH 7.4 medicated 51Cr, [14C]choline, and [3H]inositol released from prelabeled MA104 cells. This release could be specifically blocked by neutralizing antibodies to VP3. These results suggest that MA104 cell infection follows the rapid entry of trypsin-activated RRV by direct cell membrane penetration. Cell membrane penetration of infectious RRV is initiated by trypsin cleavage of VP3. Neutralizing antibodies can inhibit this direct membrane penetration.

The rhesus rotavirus gene encoding protein VP3: location of amino acids involved in homologous and heterologous rotavirus neutralization and identification of a putative fusion region

The complete gene 4 nucleotide sequence was determined for rhesus rotavirus and each of 11 viral variants selected by neutralizing monoclonal antibodies. Gene 4 is 2362 bases in length and encodes a protein, VP3, of 776 amino acids with a calculated Mr of 86,500. A conserved trypsin cleavage site, located at amino acid 247, divides VP3 into VP8 and VP5. Neutralizing monoclonal antibodies directed at VP3 were used to select variants that escaped neutralization. Each variant contains a single gene 4 mutation that permits viral growth in the presence of the antibody. Variant mutations were identified in six distinct neutralization regions in VP8 and VP5. Five of the six neutralization regions were found in VP8. The VP8 regions were primarily associated with strain-specific or limited heterotypic rotavirus neutralization. One region was identified in VP5 by three monoclonal antibodies that neutralize a broad range of rotavirus serotypes. The VP5 neutralization region is largely hydrophobic and is similar to putative fusion sequences of Sindbis and Semliki Forest viruses.

Epitope-specific immune responses to rotavirus vaccination

Rotavirus gastroenteritis is a leading cause of infant mortality in developing countries and an important cause of morbidity in children under 2 yr of age in the United States. Vaccine programs have evaluated animal rotavirus strains that are attenuated in humans but antigenically similar to some human strains. Whether a single vaccine strain can elicit protective immunity in humans to rotaviruses of the same or different serotypes is an important question in determining vaccine efficacy. We used characterized serotype-specific monoclonal antibodies directed at VP7 in a competitive solid-phase immunoassay to measure epitope-specific immune responses to serotypes 1, 2, and 3 in sera of children who received a candidate serotype-3 rotavirus vaccine. Antibodies to serotype 3 were detected in 72% of sera samples, and to serotype 1 and 2 in only 11% each. Also, a VP3-specific monoclonal antibody which neutralizes three serotypically distinct strains of rotavirus was used to detect the presence of similar antibodies in 56% of the test sera. This finding suggests a mechanism of heterotypic immunity.

Examination of sexually abused adolescents

The care of the sexually assaulted adolescent demands an integrated, sensitive approach to psychologic and medical needs, along with careful follow-up. This care is best provided by knowledgeable and supportive individuals. This discussion has reviewed definitions of sexual assault terms, potential psychologic reactions, physical evaluation of these individuals, and therapy considerations.

Antigenic mapping of the surface proteins of rhesus rotavirus

Monoclonal antibodies have been produced and used to map the functional topography of the surface proteins of rhesus rotavirus (RRV) that mediate viral neutralization. Ten monoclonal antibodies directed to VP7 were studied in neutralization assays and competitive binding studies. A large neutralization domain with several interrelated epitopes on VP7 was apparent. Twelve monoclonal antibodies directed to VP3 were used in similar studies and delineated at least 2 distinct neutralization domains on that protein. Neutralizing monoclonal antibodies directed at both VP3 and VP7 were used to isolate viral antigenic variants, which were than studied in neutralization and hemagglutination inhibition assays. The viral variant studies, while confirming the general conclusions obtained from the competitive binding studies, allowed the apparent distinction of two separate neutralization domains on VP7 and three on VP3. All VP7-specific monoclonal antibodies (mAb) mediated serotype-specific neutralization, but a VP3-specific mAb was identified that neutralized rotaviruses of three distinct serotypes. No alteration of viral virulence was apparent in studies of suckling mice orally inoculated with antigenic variant viruses selected with our panel of neutralizing VP3 or VP7-specific mAbs.