Serologic and mucosal immune response to rotavirus infection in the rabbit model

Rotavirus reverse genetics systems: Development and application

Rotaviruses (RVs) cause acute gastroenteritis in infants and young children. Since 2006, live-attenuated vaccines have reduced the number of RV-associated deaths; however, RV is still responsible for an estimated 228,047 annual deaths worldwide. RV, a member of the family Reoviridae, has an 11-segmented double-stranded RNA genome contained within a non-enveloped, triple layered virus particle. In 2017, a long-awaited helper virus-free reverse genetics system for RV was established. Since then, numerous studies have reported the generation of recombinant RVs; these studies verify the robustness of reverse genetics systems. This review provides technical insight into current reverse genetics systems for RVs, as well as discussing basic and applied studies that have used these systems.

Fecal Components Modulate Human Astrovirus Infectivity in Cells and Reconstituted Intestinal Tissues

To ensure transmission, enteric viruses must maintain their infectivity during the various environmental challenges that they face in transit within and between hosts. Increased knowledge of the factors affecting enteric virus survival may help to control their transmission. This study reveals that specific fecal bacterial components preserve classic human astrovirus infectivity by stabilizing viral particles. However, the outcomes of stool-virus interactions are very variable, ranging from protection to a reduction of viral infectivity, depending on the viral genotype and the individual from whom the stool has been collected. We show that the transmissibility of enteric viruses is dependent on the intestinal contents of the infected individual and highlight the complex multiple interactions that could explain the stochastic nature of enteric virus transmission in humans.

Human astroviruses (HAstV) are among the most common causative agents of viral gastroenteritis, especially in children, and extraintestinal manifestations have also been described. These viruses are transmitted by the fecal-oral route, implying that stool composition and the gut microbiota may impact their ability to remain infectious. For some enteric viruses, individual bacterial envelope components and other polysaccharide-containing molecules, which are abundant in stools, have been shown to enhance capsid stability. However, the role of the complex stool environment and, most importantly, the role of interindividual differences have been poorly studied. We used HAstV as a model to investigate how the stool environment in itself, its interindividual variability, and some specific stool components could affect HAstV stability and infectivity. Using two different HAstV genotypes, we found that stools as a whole modulate astrovirus infectivity not only in an individual-dependent manner but also in a manner that depends on the viral genotype. A virus-protective effect was observed after incubation with various Gram-positive and Gram-negative bacteria as well as with bacterial components, such as lipopolysaccharide and peptidoglycan. These results were further confirmed in human intestinal tissues, a more physiologically relevant system. Astrovirus infectivity was also preserved by mucin, a major component of intestinal mucus. We further confirmed that these components stabilize the viral capsid. These results show that although HAstV benefits from the stabilizing effect of fecal components, the complexity and variability of the stool composition and the multiple potential interactions may explain the interindividual differences in viral transmission observed in real life.

IMPORTANCE To ensure transmission, enteric viruses must maintain their infectivity during the various environmental challenges that they face in transit within and between hosts. Increased knowledge of the factors affecting enteric virus survival may help to control their transmission. This study reveals that specific fecal bacterial components preserve classic human astrovirus infectivity by stabilizing viral particles. However, the outcomes of stool-virus interactions are very variable, ranging from protection to a reduction of viral infectivity, depending on the viral genotype and the individual from whom the stool has been collected. We show that the transmissibility of enteric viruses is dependent on the intestinal contents of the infected individual and highlight the complex multiple interactions that could explain the stochastic nature of enteric virus transmission in humans.

Development of Stable Rotavirus Reporter Expression Systems

Engineered recombinant viruses expressing reporter genes have been developed for real-time monitoring of replication and for mass screening of antiviral inhibitors. Recently, we reported using a reverse genetics system to develop the first recombinant reporter rotaviruses (RVs) that expressed NanoLuc (NLuc) luciferase. Here, we describe a strategy for developing stable reporter RVs expressing luciferase and green or red fluorescent proteins. The reporter genes were inserted into the open reading frame of NSP1 and expressed as a fusion with an NSP1 peptide consisting of amino acids 1 to 27. The stability of foreign genes within the reporter RV strains harboring a shorter chimeric NSP1-reporter gene was greater than that of those in the original reporter RV strain, independent of the transgene inserted. The improved reporter RV was used to screen for neutralizing monoclonal antibodies (MAbs). Sequence analysis of escape mutants from one MAb clone (clone 29) identified an amino acid substitution (arginine to glycine) at position 441 in the VP4 protein, which resides within neutralizing epitope 5-1 in the VP5* fragment. Furthermore, to express a native reporter protein lacking NSP1 amino acids 1 to 27, the 5'- and 3'-terminal region sequences were modified to restore the predicted secondary RNA structure of the NSP1-reporter chimeric gene. These data demonstrate the utility of reporter RVs for live monitoring of RV infections and also suggest further applications (e.g., RV vaccine vectors, which can induce mucosal immunity against intestinal pathogens).IMPORTANCE Development of reporter RVs has been hampered by the lack of comprehensive reverse genetics systems. Recently, we developed a plasmid-based reverse genetics system that enables generation of reporter RVs expressing NLuc luciferase. The prototype reporter RV had some disadvantages (i.e., the transgene was unstable and was expressed as a fusion protein with a partial NSP1 peptide); however, the improved reporter RV overcomes these problems through modification of the untranslated region of the reporter-NSP1 chimeric gene. This strategy for generating stable reporter RVs could be expanded to diverse transgenes and be used to develop RV transduction vectors. Also, the data improve our understanding of the importance of 5'- and 3'-terminal sequences in terms of genome replication, assembly, and packaging.

Rotavirus Double Infection Model to Study Preventive Dietary Interventions

Rotaviruses are the main cause of acute diarrhea among young children worldwide with an increased frequency of reinfection. Several life style factors, such as dietary components, may influence such processes by affecting the outcome of the first rotavirus infection and therefore having a beneficial impact on the anti-rotavirus immune responses during any subsequent reinfections. The aim of this research was to develop a double-infection model in rat that mimics real-life clinical scenarios and would be useful in testing whether nutritional compounds can modulate the rotavirus-associated disease and immune response. Three experimental designs and a preventive dietary-like intervention were conducted in order to achieve a differential response in the double-infected animals compared to the single-infected ones and to study the potential action of a modulatory agent in early life. Diarrhea was only observed after the first infection, with a reduction of fecal pH and fever. After the second infection an increase in body temperature was also found. The immune response against the second infection was regulated by the preventive effect of the dietary-like intervention during the first infection in terms of specific antibodies and DTH. A rotavirus-double-infection rat model has been developed and is suitable for use in future preventive dietary intervention studies.

[A plasmid-based reverse genetics system for rotaviruses]

Rotavirus (RV), a non-enveloped icosahedral virus containing eleven gene segments of double-stranded RNA, is the leading cause of severe, acute diarrhea among infants and young children worldwide. Safe and effective rotavirus vaccines have been available since 2006, and have markedly reduced the number of deaths by severe gastroenteritis. However, rotaviruses are still responsible for approximately 200,000 deaths annually worldwide. Reverse genetics systems for the manipulation of viral genomes are a powerful approach for studying viral replication and pathogenesis, and for developing vaccines and viral vectors. The understanding of the molecular mechanisms underlying RV pathogenesis, or development of next generation vaccines, has been hampered by the lack of a complete reverse genetics system. Recently, we developed a novel reverse genetics system which enabled recovery of recombinant RVs entirely from cloned cDNAs. This new strategy requires co-expression of a small transmembrane protein that accelerates cell-to-cell fusion and vaccinia virus capping enzyme. In this review, the strategies and history of the development of reverse genetics systems for the family Reoviridae are described.

The gastrointestinal frontier: IgA and viruses

Viral gastroenteritis is one of the leading causes of diseases that kill ~2.2 million people worldwide each year. IgA is one of the major immune effector products present in the gastrointestinal tract yet its importance in protection against gastrointestinal viral infections has been difficult to prove. In part this has been due to a lack of small and large animal models in which pathogenesis of and immunity to gastrointestinal viral infections is similar to that in humans. Much of what we have learned about the role of IgA in the intestinal immune response has been obtained from experimental animal models of rotavirus infection. Rotavirus-specific intestinal IgA appears to be one of the principle effectors of long term protection against rotavirus infection. Thus, there has been a focus on understanding the immunological pathways through which this virus-specific IgA is induced during infection. In addition, the experimental animal models of rotavirus infection provide excellent systems in which new areas of research on viral-specific intestinal IgA including the long term maintenance of viral-specific IgA.

Characterization of a novel G3P[3] rotavirus isolated from a lesser horseshoe bat: a distant relative of feline/canine rotaviruses

Bats are considered important animal reservoirs for many viruses pathogenic to humans. An approach based on viral metagenomics was used to study gut specimens from 78 insectivorous bats in Yunnan Province, China. Seventy-four reads were found to be related to group A rotavirus (RVA). Further reverse transcription-PCR screening and viral isolation on cell cultures confirmed the presence of a novel RVA strain, named RVA/Bat-tc/MSLH14/2012/G3P[3], in 1 (6%) of 16 lesser horseshoe bats. Full genomic sequencing analyses showed that MSLH14 possessed the genotype constellation G3-P[3]-I8-R3-C3-M3-A9-N3-T3-E3-H6, which is akin to human and animal rotaviruses believed to be of feline/canine origin. Phylogenetic analysis indicated that VP7 was most closely related to bovine RVA strains from India, whereas VP4 was most closely related to an unusual human RVA strain, CMH222, with animal characteristics isolated in Thailand. The remaining gene segments were only distantly related to a range of animal RVA strains, most of which are believed to be related to feline/canine RVAs. Experimental infection showed that bat RVA strain MSLH14 was highly pathogenic to suckling mice, causing 100% mortality when they were inoculated orally with a titer as low as 5 × 10² 50% tissue culture infective doses. As this virus is not closely related to any known RVA strain, it is tempting to speculate that it is a true bat RVA strain rather than a virus transmitted between species. However, further screening of bat populations, preferably juvenile animals, will be crucial in determining whether or not this virus is widely distributed in the bat population.

A gastrointestinal rotavirus infection mouse model for immune modulation studies

BACKGROUND

Rotaviruses are the single most important cause of severe diarrhea in young children worldwide. The current study was conducted to assess whether colostrum containing rotavirus-specific antibodies (Gastrogard-R®) could protect against rotavirus infection. In addition, this illness model was used to study modulatory effects of intervention on several immune parameters after re-infection.

METHODS

BALB/c mice were treated by gavage once daily with Gastrogard-R® from the age of 4 to 10 days, and were inoculated with rhesus rotavirus (RRV) at 7 days of age. A secondary inoculation with epizootic-diarrhea infant-mouse (EDIM) virus was administered at 17 days of age. Disease symptoms were scored daily and viral shedding was measured in fecal samples during the post-inoculation periods. Rotavirus-specific IgM, IgG and IgG subclasses in serum, T cell proliferation and rotavirus-specific delayed-type hypersensitivity (DTH) responses were also measured.

RESULTS

Primary inoculation with RRV induced a mild but consistent level of diarrhea during 3-4 days post-inoculation. All mice receiving Gastrogard-R® were 100% protected against rotavirus-induced diarrhea. Mice receiving both RRV and EDIM inoculation had a lower faecal-viral load following EDIM inoculation then mice receiving EDIM alone or Gastrogard-R®. Mice receiving Gastrogard-R® however displayed an enhanced rotavirus-specific T-cell proliferation whereas rotavirus-specific antibody subtypes were not affected.

CONCLUSIONS

Preventing RRV-induced diarrhea by Gastrogard-R® early in life showed a diminished protection against EDIM re-infection, but a rotavirus-specific immune response was developed including both B cell and T cell responses. In general, this intervention model can be used for studying clinical symptoms as well as the immune responses required for protection against viral re-infection.

Identification of Rotavirus VP6-Specific CD4+ T Cell Epitopes in a G1P[8] Human Rotavirus-Infected Rhesus Macaque

A non-human primate model was used to evaluate its potential for identification of rotavirus viral protein 6 (VP6) CD4+ T cell epitopes. Four juvenile rhesus macaques were inoculated with a mixed inoculum (G1P[8] and G9P[8]) of human rotaviruses. Infection accompanied by G1P[8] shedding was achieved in the two macaques that had no rotavirus immunoglobulin A (IgA) in plasma. To measure the interferon gamma (IFN-γ) and tumor necrosis factor (TNF) anti-viral cytokines produced by peripheral CD4+ cells that recognize VP6 epitopes, whole blood cells from one infected macaque were stimulated in vitro with VP6 peptides. Stimulation with peptide pools derived from the simian rotavirus VP6(161-395) region revealed reactivity of CD4+ T cells with the VP6(281-331) domain. A VP6(301-315) region was identified as the epitope responsible for IFN-γ production while a broader VP6(293-327) domain was linked to TNF production. These results suggest that human rotavirus-infected macaques can be used for identification of additional epitopes and domains to address specific questions related to the development of pediatric vaccines.

Rotavirus viremia and extraintestinal viral infection in the neonatal rat model

Rotaviruses infect mature, differentiated enterocytes of the small intestine and, by an unknown mechanism, escape the gastrointestinal tract and cause viremia. The neonatal rat model of rotavirus infection was used to determine the kinetics of viremia, spread, and pathology of rotavirus in extraintestinal organs. Five-day-old rat pups were inoculated intragastrically with an animal (RRV) or human (HAL1166) rotavirus or phosphate-buffered saline. Blood was collected from a subset of rat pups, and following perfusion to remove residual blood, organs were removed and homogenized to analyze rotavirus-specific antigen by enzyme-linked immunosorbent assay and infectious rotavirus by fluorescent focus assay or fixed in formalin for histology and immunohistochemistry. Viremia was detected following rotavirus infection with RRV and HAL1166. The RRV 50% antigenemia dose was 1.8 x 10(3) PFU, and the 50% diarrhea dose was 7.7 x 10(5) PFU, indicating that infection and viremia occurred in the absence of diarrhea and that detecting rotavirus antigen in the blood was a more sensitive measure of infection than diarrhea. Rotavirus antigens and infectious virus were detected in multiple organs (stomach, intestines, liver, lungs, spleen, kidneys, pancreas, thymus, and bladder). Histopathological changes due to rotavirus infection included acute inflammation of the portal tract and bile duct, microsteatosis, necrosis, and inflammatory cell infiltrates in the parenchymas of the liver and lungs. Colocalization of structural and nonstructural proteins with histopathology in the liver and lungs indicated that the histological changes observed were due to rotavirus infection and replication. Replicating rotavirus was also detected in macrophages in the lungs and blood vessels, indicating a possible mechanism of rotavirus dissemination. Extraintestinal infectious rotavirus, but not diarrhea, was observed in the presence of passively or actively acquired rotavirus-specific antibody. These findings alter the previously accepted concept of rotavirus pathogenesis to include not only gastroenteritis but also viremia, and they indicate that rotavirus could cause a broad array of systemic diseases in a number of different organs.

Protection against rotavirus shedding after intranasal immunization of mice with a chimeric VP6 protein does not require intestinal IgA

Intranasal immunization of mice with chimeric VP6 and the adjuvant LT(R192G) consistently elicits >95% reductions in fecal rotavirus shedding following challenge. To determine the association between mucosal antibody and protection, we immunized BALB/c wt and J chain knockout (Jch-/-) mice with VP6 and either LT(R192G) or cholera toxin (CT). Both strains developed nearly equal levels of serum rotavirus IgG, but Jch-/- mice, which cannot transport dimeric IgA across epithelial cell surfaces, developed >4-fold higher levels of serum rotavirus IgA. Stool rotavirus IgA was present in wt but undetectable in Jch-/- mice. When challenged with rotavirus strain EDIM, reductions in rotavirus shedding were nearly identical in VP6-immunized wt and Jch-/- mice (i.e., 97% and 92%, respectively; P > 0.01). Th1 CD4 T cell responses were also detected in VP6-immunized animals based on high levels of IFN-gamma and IL-2 found after in vitro VP6 stimulation of spleen cells. Therefore, protection induced by intranasal immunization of mice with VP6 and adjuvant does not depend on intestinal rotavirus IgA antibody but appears to be associated with CD4 T cells.

Experimental infection of pigtailed macaques with a simian rotavirus, YK-1

Experimental rotavirus infection was investigated in pigtailed macaques to study the infectivity, immunity, and pathogenesis of rotavirus. A challenge virus, YK-1, was administered intragastrically to four seronegative macaques (age: 11-16 months). Although none of the monkeys developed diarrhea, an active infection occurred with high titers of rotavirus antigen detected in stools 2-10 days after challenge. These animals developed rotavirus-specific antibody responses similar to those seen following primary exposure to rotavirus. YK-1 was then inoculated in four seropositive macaques (age: 14-16 months). All animals shed viral antigen in their stool, but the titers and duration were significantly less when compared to seronegative macaques. When rechallenged 28 days after initial YK-1 challenge, the macaques demonstrated significant protection against reinfection. All seropositive animals developed a rise in rotavirus-specific serum and fecal antibodies during YK-1 challenge and rechallenge. To independently assess the role of age and preexisting IgG titers to rotavirus, a 4-month-old seronegative and 6-month-old seropositive macaque were inoculated with YK-1. The seronegative macaque shed high titers of virus for 9 days, while the seropositive macaque shed only 3 days and in low titer. These data suggest that a primate model of rotavirus infection using the YK-1 strain may be useful in examining the immune response and protection from infection in pigtailed macaques and indicate that levels and duration of shedding may provide a good measure of protection from natural infection and from that induced by oral or parenteral vaccines.

Early response to rotavirus infection involves massive B cell activation

Rotavirus is an acute enteric pathogen which induces severe diarrhea in infants and children. To determine the immune response to rotavirus in vivo, we used a mouse model of rotavirus infection. We observed dramatic increases in the sizes of both Peyer's patches and mesenteric lymph nodes, but not spleen, between 1 and 6 days after infection with a homologous strain of murine rotavirus, EC wild type. Histological analysis showed large increases in the numbers of lymphocytes in these same tissues in rotavirus-infected mice. Flow cytometric analysis confirmed the increase in numbers of lymphocytes and revealed a large increase in the percentage of activated B, but not T, lymphocytes in both Peyer's patches and mesenteric lymph nodes of rotavirus-infected mice compared with control mice. Fragment cultures from these tissues established at 3-4 days postinfection contain rotavirus-specific IgM but not IgA Ab. A similar degree of lymphoid hyperplasia and percentage of activated B cells were observed in rotavirus-infected TCR knockout mice. Taken together, our findings show that rotavirus infection, in the context of a normal immune response, induces a large increase in the percentages of activated B cells in the absence of any detectable increase in the percentage of activated T cells, implicating a T cell-independent B cell response as the primary mechanism for initial rotavirus clearance.

Group A rotavirus infection and age-dependent diarrheal disease in rats: a new animal model to study the pathophysiology of rotavirus infection

Group A rotaviruses are major pathogens causing acute gastroenteritis in children and animals. To determine if group A rotavirus replicates and induces disease in rats, antibody-negative Lewis neonatal or adult rats were inoculated orally with tissue culture-adapted human (Wa, WI61, and HAL1166), simian (rhesus rotavirus [RRV] and SA11), bovine (WC3), lapine (ALA), or porcine (OSU) rotavirus strains, wild-type murine (EC(wt)) rotavirus strain, or phosphate-buffered saline (PBS). Rotavirus infection in rats was evaluated by (i) clinical findings, (ii) virus antigen shedding or infectious virus titers in the feces or intestinal contents measured by enzyme-linked immunosorbent assay or fluorescent-focus assay, (iii) histopathological changes in the small intestine, (iv) distribution of rotavirus antigen in small-intestine sections by immunofluorescence, and (v) growth rate. Rotavirus infection of 5-day-old but not > or =21-day-old rats resulted in diarrhea that lasted from 1 to 10 days postinoculation. The severity of disease and spread of infection to naIve littermates differed depending on the virus strain used for inoculation. The duration of virus antigen shedding following infection was considerably prolonged (up to 10 days) in neonatal rats compared to that in 21-day-old rats (1 or 2 days). Based on lack of virus antigen shedding and disease induction, the murine EC(wt) rotavirus was the only strain tested that did not infect rats. Histopathological changes in the small-intestine mucosa of 5-day-old RRV-inoculated rats but not of PBS-inoculated rats was limited to extensive enterocyte vacuolation in the ileum. In RRV-inoculated neonatal rats, rotavirus antigen was detected in the epithelial cells on the upper half of the intestinal villi of the jejunum and ileum. In addition, infection of neonatal rats with RRV but not with PBS resulted in reduced weight gain. Rats infected with group A rotaviruses provide a new animal model with unique features amenable to investigate rotavirus pathogenesis and the molecular mechanisms of intestinal development, including physiological factors that may regulate age-dependent rotavirus-induced diarrhea.

Intranasal administration of 2/6-rotavirus-like particles with mutant Escherichia coli heat-labile toxin (LT-R192G) induces antibody-secreting cell responses but not protective immunity in gnotobiotic pigs

We investigated the immunogenicity of recombinant double-layered rotavirus-like particle (2/6-VLPs) vaccines derived from simian SA11 or human (VP6) Wa and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were administered to gnotobiotic pigs intranasally (i.n.) with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT), as mucosal adjuvant. Pigs were challenged with virulent Wa (P1A[8],G1) human rotavirus at postinoculation day (PID) 21 (two-dose VLP regimen) or 28 (three-dose VLP regimen). In vivo antigen-activated antibody-secreting cells (ASC) (effector B cells) and in vitro antigen-reactivated ASC (derived from memory B cells) from intestinal and systemic lymphoid tissues (duodenum, ileum, mesenteric lymph nodes [MLN], spleen, peripheral blood lymphocytes [PBL], and bone marrow lymphocytes) collected at selected times were quantitated by enzyme-linked immunospot assays. Rotavirus-specific immunoglobulin M (IgM), IgA, and IgG ASC and memory B-cell responses were detected by PID 21 or 28 in intestinal and systemic lymphoid tissues after i.n. inoculation with two or three doses of 2/6-VLPs with or without mLT. Greater mean numbers of virus-specific ASC and memory B cells in all tissues prechallenge were induced in pigs inoculated with two doses of SA11 2/6-VLPs plus mLT compared to SA11 2/6-VLPs without mLT. After challenge, anamnestic IgA and IgG ASC and memory B-cell responses were detected in intestinal lymphoid tissues of all VLP-inoculated groups, but serum virus-neutralizing antibody titers were not significantly enhanced compared to the challenged controls. Pigs inoculated with Wa-RF 2/6-VLPs (with or without mLT) developed higher anamnestic IgA and IgG ASC responses in ileum after challenge compared to pigs inoculated with SA11 2/6-VLPs (with or without mLT). Three doses of SA 11 2/6-VLP plus mLT induced the highest mean numbers of IgG memory B cells in MLN, spleen, and PBL among all groups postchallenge. However, no significant protection against diarrhea or virus shedding was evident in any of the 2/6-VLP (with or without mLT)-inoculated pigs after challenge with virulent Wa human rotavirus. These results indicate that 2/6-VLP vaccines are immunogenic in gnotobiotic pigs when inoculated i.n. and that the adjuvant mLT enhanced their immunogenicity. However, i.n. inoculation of gnotobiotic pigs with 2/6-VLPs did not confer protection against human rotavirus challenge.

Simian rhesus rotavirus is a unique heterologous (non-lapine) rotavirus strain capable of productive replication and horizontal transmission in rabbits

Simian rhesus rotavirus (RRV) is the only identified heterologous (non-lapine) rotavirus strain capable of productive replication at a high inoculum dose of virus (>10(8) p.f.u.) in rabbits. To evaluate whether lower doses of RRV would productively infect rabbits and to obtain an estimate of the 50% infectious dose, rotavirus antibody-free rabbits were inoculated orally with RRV at inoculum doses of 10(3), 10(5) or 10(7) p.f.u. Based on faecal virus antigen or infectious virus shedding, RRV replication was observed with inoculum doses of 10(7) and 10(5) p.f.u., but not 10(3) p.f.u. Horizontal transmission of RRV to one of three mock-inoculated rabbits occurred 4-5 days after onset of virus antigen shedding in RRV-infected rabbits. Rabbits infected at 10(7) and 10(5), but not 10(3), p.f.u. of RRV developed rotavirus-specific immune responses and were completely (100%) protected from lapine ALA rotavirus challenge. These data confirm that RRV can replicate productively and spread horizontally in rabbits. In attempts to elucidate the genetic basis of the unusual replication efficacy of RRV in rabbits, the sequence of the gene encoding the lapine non-structural protein NSP1 was determined. Sequence analysis of the NSP1 of three lapine rotaviruses revealed a high degree of amino acid identity (85-88%) with RRV. Since RRV and lapine strains also share similar VP7s (96-97%) and VP4s (69-70%), RRV might replicate efficiently in rabbits because of the high relatedness of these three gene products, each implicated in host range restriction.

Heterotypic protection and induction of a broad heterotypic neutralization response by rotavirus-like particles

The recognition that rotaviruses are the major cause of life-threatening diarrheal disease and significant morbidity in young children has focused efforts on disease prevention and control of these viruses. Although the correlates of protection in children remain unclear, some studies indicate that serotype-specific antibody is important. Based on this premise, current live attenuated reassortant rotavirus vaccines include the four predominant serotypes of virus. We are evaluating subunit rotavirus vaccines, 2/6/7-VLPs and 2/4/6/7-VLPs, that contain only a single VP7 of serotype G1 or G3. In mice immunized parenterally twice, G3 virus-like particles (VLPs) induced a homotypic, whereas G1 VLPs induced a homotypic and heterotypic (G3) serum neutralizing immune response. Administration of three doses of G1 or G3 VLPs induced serum antibodies that neutralized five of seven different serotype test viruses. The inclusion of VP4 in the VLPs was not essential for the induction of heterotypic neutralizing antibody in mice. To confirm these results in another species, rabbits were immunized parenterally with two doses of 2/4/6/7-VLPs containing a G3 or G1 VP7, sequentially with G3 VLPs followed by G1 (G3/G1) VLPs, or with live or psoralen-inactivated SA11. High-titer homotypic serum neutralizing antibody was induced in all rabbits, and low-level heterotypic neutralizing antibody was induced in a subset of rabbits. The rabbits immunized with the G1 or G3/G1 VLPs in QS-21 were challenged orally with live G3 ALA rotavirus. Protection levels were similar in rabbits immunized with homotypic G3 2/4/6/7-VLPs, heterotypic G1 2/4/6/7-VLPs, or G3/G1 2/4/6/7-VLPs. Therefore, G1 2/4/6/7-VLPs can induce protective immunity against a live heterotypic rotavirus challenge in an adjuvant with potential use in humans. Following challenge, broad serum heterotypic neutralizing antibody responses were detected in rabbits parenterally immunized with G1, G3/G1, or G3 VLPs but not with SA11. Immunization with VLPs may provide sufficient priming of the immune system to induce protective anamnestic heterotypic neutralizing antibody responses upon subsequent rotavirus infection. Therefore, a limited number of serotypes of VLPs may be sufficient to provide a broadly protective subunit vaccine.

Rotavirus disease, but not infection and development of intestinal histopathological lesions, is age restricted in rabbits

The rabbit model of rotavirus infection has proved to be useful for assessing active immunity and protection after infection or vaccination with virus or virus-like particles. One limitation of the rabbit model is that after experimental infection of rabbits, clinical diarrhea is not routinely induced. Lack of diarrhea in the rabbit model has been proposed to be due to the fluid absorptive capability of the cecum or attenuation of virus strains through tissue culture adaptation. To test whether a wild-type lapine rotavirus strain BAP (BAPwt) isolated from diarrheic rabbits would cause disease on passage in rabbits, 1-, 2-, 10-, and 16-week-old rabbits were orally inoculated with BAPwt, its tissue culture-adapted counterpart strain (BAP-2), tissue culture-adapted lapine strain ALA, or PBS. Lapine rotavirus infection in 1-week-old, but not >/=2-week-old, rabbits resulted in the development of disease characterized by soft, wet, yellow-to-brownish-green partially formed-to-liquid stools observed only at the time of virus antigen shedding. The level and duration of virus shedding after infection were prolonged in 1-week-old rabbits compared with rabbits >/=2 weeks of age. Although diarrhea was not observed beyond the first 2 weeks of life, histopathological changes, including villus shortening and fusion, increased vacuolation of epithelial cells, and mononuclear infiltration of the lamina propria, were observed throughout the small intestine between 12 and 120 h after ALA infection in 1-week-old, 1- to 2-month-old, and 11-month-old rabbits. In 11-month-old rabbits, onset of intestinal damage appeared to be slightly delayed, was less severe, and was not observed in the duodenum. There were no differences in the immune responses to rotavirus infection in rabbits of different age groups (1 week to 5 years of age). All lapine rotavirus-inoculated rabbits seroconverted and were protected from virus challenge at 28 days postinoculation. Like in mice, rotavirus disease is age restricted in rabbits.

Subunit rotavirus vaccine administered parenterally to rabbits induces active protective immunity

Virus-like particles (VLPs) are being evaluated as a candidate rotavirus vaccine. The immunogenicity and protective efficacy of different formulations of VLPs administered parenterally to rabbits were tested. Two doses of VLPs (2/6-, G3 2/6/7-, or P[2], G3 2/4/6/7-VLPs) or SA11 simian rotavirus in Freund's adjuvants, QS-21 (saponin adjuvant), or aluminum phosphate (AlP) were administered. Serological and mucosal immune responses were evaluated in all vaccinated and control rabbits before and after oral challenge with 10(3) 50% infective doses of live P[14], G3 ALA lapine rotavirus. All VLP- and SA11-vaccinated rabbits developed high levels of rotavirus-specific serum and intestinal immunoglobulin G (IgG) antibodies but not intestinal IgA antibodies. SA11 and 2/4/6/7-VLPs afforded similar but much higher mean levels of protection than 2/6/7- or 2/6-VLPs in QS-21. The presence of neutralizing antibodies to VP4 correlated (P < 0.001, r = 0.55; Pearson's correlation coefficient) with enhanced protection rates, suggesting that these antibodies are important for protection. Although the inclusion of VP4 resulted in higher mean protection levels, high levels of protection (87 to 100%) from infection were observed in individual rabbits immunized with 2/6/7- or 2/6-VLPs in Freund's adjuvants. Therefore, neither VP7 nor VP4 was absolutely required to achieve protection from infection in the rabbit model when Freund's adjuvant was used. Our results show that VLPs are immunogenic when administered parenterally to rabbits and that Freund's adjuvant is a better adjuvant than QS-21. The use of the rabbit model may help further our understanding of the critical rotavirus proteins needed to induce active protection. VLPs are a promising candidate for a parenterally administered subunit rotavirus vaccine.

Characterisation of the primary local and systemic immune response in gnotobiotic lambs against rotavirus infection

This study characterised the primary immune response in gnotobiotic lambs after infection with a lamb rotavirus (RV). Lambs were infected and killed over a 7 week period together with controls. RV-ELISA and neutralising antibodies were determined in serum, nasal secretions, and intestinal scrapings. RV-antibody secreting cells (ASC) were enumerated in blood. Lymphocyte proliferations were determined in blood and gut-associated lymphoid tissues and cytokine expression was analysed in jejunal Peyer's patches (JPPs) and mesenteric lymph nodes (MLNs). Infected lambs cleared the virus by 8-9 days after infection without showing any clinical signs. The first indication of a specific immune response to RV was an increased expression of IL-4 mRNA in the JPPs in the infected group compared to the control group 3 days after infection. Rotavirus-specific IgA ASC in blood and IgA antibodies in serum and nasal secretions were detected from 7 days after infection followed at 10 days after infection by RV-specific IgG ASC and antibodies. Rotavirus-specific IgA antibodies were not detected in intestinal scrapings in the first 10 days after infection, but were detected by 52 days after infection. No RV-specific neutralising antibodies were seen in the intestine during the course of the experiment.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Analysis of host range restriction determinants in the rabbit model: comparison of homologous and heterologous rotavirus infections

The main limitation of both the rabbit and mouse models of rotavirus infection is that human rotavirus (HRV) strains do not replicate efficiently in either animal. The identification of individual genes necessary for conferring replication competence in a heterologous host is important to an understanding of the host range restriction of rotavirus infections. We recently reported the identification of the P type of the spike protein VP4 of four lapine rotavirus strains as being P[14]. To determine whether VP4 is involved in host range restriction in rabbits, we evaluated infection in rotavirus antibody-free rabbits inoculated orally with two P[14] HRVs, PA169 (G6) and HAL1166 (G8), and with several other HRV strains and animal rotavirus strains of different P and G types. We also evaluated whether the parental rhesus rotavirus (RRV) (P5B[3], G3) and the derived RRV-HRV reassortant candidate vaccine strains RRV x D (G1), RRV x DS-1 (G2), and RRV x ST3 (G4) would productively infect rabbits. Based on virus shedding, limited replication was observed with the P[14] HRV strains and with the SA11 Cl3 (P[2], G3) and SA11 4F (P6[1], G3) animal rotavirus strains, compared to the homologous ALA strain (P[14], G3). However, even limited infection provided complete protection from rotavirus infection when rabbits were challenged orally 28 days postinoculation (DPI) with 10(3) 50% infective doses of ALA rabbit rotavirus. Other HRVs did not productively infect rabbits and provided no significant protection from challenge, in spite of occasional seroconversion. Simian RRV replicated as efficiently as lapine ALA rotavirus in rabbits and provided complete protection from ALA challenge. Live attenuated RRV reassortant vaccine strains resulted in no, limited, or productive infection of rabbits, but all rabbits were completely protected from heterotypic ALA challenge. The altered replication efficiency of the reassortants in rabbits suggests a role for VP7 in host range restriction. Also, our results suggest that VP4 may be involved in, but is not exclusively responsible for, host range restriction in the rabbit model. The replication efficiency of rotavirus in rabbits also is not controlled by the product of gene 5 (NSP1) alone, since a reassortant rotavirus with ALA gene 5 and all other genes from SA11 was more severely replication restricted than either parental rotavirus strain.

Rotavirus virus-like particles administered mucosally induce protective immunity

We have evaluated the immunogenicity and protective efficacy of rotavirus subunit vaccines administered by mucosal routes. Virus-like particles (VLPs) produced by self-assembly of individual rotavirus structural proteins coexpressed by baculovirus recombinants in insect cells were the subunit vaccine tested. We first compared the immunogenicities and protective efficacies of VLPs containing VP2 and VP6 (2/6-VLPs) and G3 2/6/7-VLPs mixed with cholera toxin and administered by oral and intranasal routes in the adult mouse model of rotavirus infection. VLPs administered orally induced serum antibody and intestinal immunoglobulin A (IgA) and IgG. The highest oral dose (100 microg) of VLPs induced protection from rotavirus challenge (> or = 50% reduction in virus shedding) in 50% of the mice. VLPs administered intranasally induced higher serum and intestinal antibody responses than VLPs administered orally. All mice receiving VLPs intranasally were protected from challenge; no virus was shed after challenge. Since there was no difference in immunogenicity or protective efficacy between 2/6- and 2/6/7-VLPs, protection was achieved without inclusion of the neutralization antigens VP7 and VP4. We also tested the immunogenicities and protective efficacies of 2/6-VLPs administered intranasally without the addition of cholera toxin. 2/6-VLPs administered intranasally without cholera toxin induced lower serum and intestinal antibody titers than 2/6-VLPs administered with cholera toxin. The highest dose (100 microg) of 2/6-VLPs administered intranasally without cholera toxin resulted in a mean reduction in shedding of 38%. When cholera toxin was added, higher levels of protection were achieved with 10-fold less immunogen. VLPs administered mucosally offer a promising, safe, nonreplicating vaccine for rotavirus.

Comparative studies of the pathogenesis, antibody immune responses, and homologous protection to porcine and human rotaviruses in gnotobiotic piglets

Gnotobiotic piglets serve as a useful animal model for studies of rotavirus pathogenesis and immunity. An advantage over laboratory animal models is the prolonged susceptibility of piglets to rotavirus-induced disease, permitting an analysis of cross-protection and active immunity. Studies from our laboratory of the pathogenesis of human rotavirus infections in gnotobiotic piglets have confirmed that villous atrophy is induced in piglets given virulent but not attenuated human rotavirus (Wa strain) and have revealed that factors other than villous atrophy may contribute to the early diarrhea induced. To facilitate and improve rotavirus vaccination strategies, it is important to identify correlates of protective immunity. Comparison of antibody immune responses induced by infection with virulent porcine and human rotaviruses (mimic host response to natural infection) with those induced by live attenuated human rotavirus (mimic attenuated oral vaccines) in the context of homotypic protection has permitted an analysis of correlates of protective immunity. Our results indicate that the magnitude of the immune response is greatest in lymphoid tissues adjacent to the site of viral replication (small intestine). Secondly there was a direct association between the degree of protection induced and the level of the intestinal immune response, with primary exposure to virulent rotaviruses inducing significantly higher numbers of IgA ASC and complete protection against challenge. These studies thus have established basic parameters related to immune protection in the piglet model of rotavirus-induced disease, verifying the usefulness of this model to apply new strategies for the design and improvement of rotavirus vaccines.

Effects of the route of infection on immunoglobulin G subclasses and specificity of the reovirus-specific humoral immune response

Reovirus serotype 1, strain Lang (T1/L), a well characterized enteric virus, elicits humoral and cellular immune responses in mice. Although orally and intradermally induced infections generate comparable reovirus-specific serum antibody titers, little is known about the effects of the route of infection on the systemic immunoglobulin G (IgG) response. To assess whether the route of exposure affects virus-specific humoral immunity, we infected various strains of mice with reovirus T1/L by the oral or intradermal routes. At day 10 following infection, virus-specific serum antibody titers and IgG subclasses were determined by enzyme-linked immunosorbent assay. Serum IgG2a and IgG2b antibodies were detected in all mouse strains independent of the route of infection. Mice of the H-2d haplotype that received an intradermal infection also had high levels of reovirus-specific serum IgG1. This dichotomy of responses was not associated with differences in the types of cytokine produced by draining peripheral lymph nodes. However, peripheral lymph node lymphocytes from C3H mice produced significantly higher levels of gamma interferon than did BALB/c, C57BL/6, and B10.D2 mice. Additionally, peripheral lymph node lymphocytes from all strains of mice produced only low levels of interleukin-5, with no detectable level of interleukin-4 or interleukin-6. Analysis of specific antibody at inductive sites of the immune response showed that orally infected Peyer's patches produced predominantly IgA and intradermally infected peripheral lymph nodes produced predominantly IgG2a. Western blot (immunoblot) analysis showed that virus-specific IgA, IgG1, and IgG2a reacted with reovirus structural proteins. These data suggest that the route of infection affects the isotype and IgG subclasses, but not the antigen specificity, of the local antibody response. In addition, virus-specific IgG1 generated following an intradermally induced infection is linked to the H-2d major histocompatibility complex haplotype.

A simplified procedure for studies of intestinal immunity in rabbits

As interest in the development of oral vaccines continues to rise, alternative animal models for studies of mucosal immunity are needed. The present study examines a simplified procedure for delivering antigen to rabbit Peyer's patches via an indwelling cannula. The cannula was placed 3-4 cm proximal to the Peyer's patch, and was used to deliver four weekly doses of the potent mucosal immunogen, cholera toxin (CT). Anti-CT specific fecal secretory IgA (S-IgA), serum IgG and serum IgA were found in essentially equal amounts in rabbits with cannulas and in rabbits fitted with Thiry-Vella (T-V) isolated ileal loops. In contrast to animals with T-V loops, the intestinal flora of animals with cannulas contained less bacterial overgrowth with Pseudomonas sp. Further, the villus architecture remained histologically normal in appearance and there were fewer post-surgical complications associated with this technique than with T-V loops. This simplified technique should allow wider use of rabbits in studies of mucosal immunity.

Systematic and intestinal antibody-secreting cell responses and correlates of protective immunity to human rotavirus in a gnotobiotic pig model of disease

Neonatal gnotobiotic pigs orally inoculated with virulent (intestinal-suspension) Wa strain human rotavirus (which mimics human natural infection) developed diarrhea, and most pigs which recovered (87% protection rate) were immune to disease upon homologous virulent virus challenge at postinoculation day (PID) 21. Pigs inoculated with cell culture-attenuated Wa rotavirus (which mimics live oral vaccines) developed subclinical infections and seroconverted but were only partially protected against challenge (33% protection rate). Isotype-specific antibody-secreting cells (ASC were enumerated at selected PID in intestinal (duodenal and ileal lamina propria and mesenteric lymph node [MLN]) and systemic (spleen and blood) lymphoid tissues by using enzyme-linked immunospot assays. At challenge (PID 21), the numbers of virus-specific immunoglobulin A (IgA) ASC, but not IgG ASC, in intestines and blood were significantly greater in virulent-Wa rotavirus-inoculated pigs than in attenuated-Wa rotavirus-inoculated pigs and were correlated (correlation coefficients: for duodenum and ileum, 0.9; for MLN, 0.8; for blood, 0.6) with the degree of protection induced. After challenge, the numbers of IgA and IgG virus-specific ASC and serum-neutralizing antibodies increased significantly in the attenuated-Wa rotavirus-inoculated pigs but not in the virulent-Wa rotavirus-inoculated pigs (except in the spleen and except for IgA ASC in the duodenum). The transient appearance of IgA ASC in the blood mirrored the IgA ASC responses in the gut, albeit at a lower level, suggesting that IgA ASC in the blood of humans could serve as an indicator for IgA ASC responses in the intestine after rotavirus infection. To our knowledge, this is the first report to study and identify intestinal IgA ASC as a correlate of protective active immunity in an animal model of human-rotavirus-induced disease.

The gnotobiotic piglet as a model for studies of disease pathogenesis and immunity to human rotaviruses

Gnotobiotic piglets serve as a useful animal model for studies of human rotavirus infections, including disease pathogenesis and immunity. An advantage of piglets over laboratory animal models is their prolonged susceptibility to human rotavirus-induced disease, permitting cross-protection studies and an analysis of active immunity. Major advances in rotavirus research resulting from gnotobiotic piglet studies include: 1) the adaptation of the first human rotavirus to cell culture after passage and amplification in piglets; 2) delineation of the independent roles of the two rotavirus outer capsid proteins (VP4 and VP7) in induction of neutralizing antibodies and cross-protection; and 3) recognition of a potential role for a nonstructural protein (NSP4) in addition to VP4 and VP7, in rotavirus virulence. Current studies of the pathogenesis of group A human rotavirus infections in gnotobiotic piglets in our laboratory have confirmed that villous atrophy is induced in piglets given virulent but not cell culture attenuated human rotavirus (G1, P1A, Wa strain) and have revealed that factors other than villous atrophy may contribute to the early diarrhea induced. A comprehensive examination of these factors, including a proposed role for NSP4 in viral-induced cytopathology, may reveal new mechanisms for induction of viral diarrhea. Finally, to facilitate and improve rotavirus vaccination strategies, our current emphasis is on the identification of correlates of protective active immunity in the piglet model of human rotavirus-induced diarrhea. Comparison of cell-mediated and antibody immune responses induced by infection with a virulent human rotavirus (to mimic host response to natural infection) with those induced by a live attenuated human rotavirus (to mimic attenuated oral vaccines) in the context of homotypic protection has permitted an analysis of correlates of protective immunity. Results of these studies have indicated that the magnitude of the immune response is greatest in lymphoid tissues adjacent to the local site of viral replication (small intestine). Secondly, there was a direct correlation between the degree of protection induced and the level of the intestinal immune response, with significantly higher local immune responses and complete protection induced only after primary exposure to virulent human rotavirus. These studies thus have established basic parameters related to immune protection in the piglet model of human rotavirus-induced disease, verifying the usefulness of this model to examine new strategies for the design and improvement of human rotavirus vaccines.

Rotavirus subunit vaccines

We evaluated rotavirus subunit vaccines for use in humans and animals. Insect cells were co-infected with combinations of individual baculovirus recombinants expressing human, bovine or simian rotavirus VP2, VP4, VP6 or VP7 to produce virus-like particles (VLPs). To determine whether immunization with VLPs could induce active protective immunity, VLPs were administered parenterally to rabbits, and the immune response and protection from rabbit ALA rotavirus challenge were evaluated. Complete or partial protection was attained, showing that parenteral immunization with VLPs induces active protective immunity. We also examined whether heterotypic immune responses could be induced with a limited number of broadly reactive VP7 proteins or with chimeric particles (multiple VP7 types on individual particles). The feasibility of this approach was determined by immunizing mice with VLPs containing a G3 VP7 or G1 VP7 and chimeric G1/G3 VLPs. Broadly reactive neutralizing antibody was induced by the G1 VLPs. VLPs also have been successfully used to boost lactogenic (colostral and milk) immunity in dairy cows. Taken together, these results show that VLPs can be effective immunogens in rabbits, mice and dairy cattle when administered parenterally, a limited number of VLPs may be sufficient to produce a broadly protective vaccine, and G3 VLPs may serve as an effective subunit vaccine for use in bovines.

Intestinal cellular immunity after primary rotavirus infection

Infection of neonatal gnotobiotic lambs with a bovine strain of rotavirus was used to characterize the kinetics of the primary cellular intestinal immune response to this agent. At 2-3 days after infection virus was first detected in the faeces and increased numbers of CD45R+ cells were observed in peripheral blood. These cells persisted in significantly increased numbers in the circulation until 7-8 days after infection. At this time, virus was no longer detectable in the faeces. The increase in CD45R+ cells preceded the appearance of virus-neutralizing antibodies in the serum at 1 week after infection. Maximal antibody titres were reached 2 weeks after infection. Virus-primed cells were first observed 1 week after infection in the jejunal and ileal Peyer's patches, mesenteric lymph nodes and peripheral blood, and persisted in the mesenteric lymph nodes and jejunal Peyer's patches for a further 4 weeks. Analysis of lymphocyte surface antigens indicated that different sub-populations of lymphocytes were responding in the various lymphoid tissues; a majority of CD4+ cells was observed in the mesenteric lymph nodes, whereas B cells predominated in the ileal Peyer's patches.

Enumeration of isotype-specific antibody-secreting cells derived from gnotobiotic piglets inoculated with porcine rotaviruses

In order to evaluate mucosal antibody responses to rotavirus, an enzyme-linked immunospot (ELISPOT) assay was adapted to enumerate antibody-secreting cells (ASC) in the mesenteric lymph nodes (MLN), lamina propria (LP) of the small intestine and spleens of gnotobiotic pigs orally inoculated with porcine rotaviruses (SB1A and Gottfried). Rotavirus-specific IgM ASC occurred by post-inoculation day (PID) 3, and numbers peaked in spleen and MLN tissues by PID 7 and in intestinal LP by PID 7-14. Numbers of rotavirus specific IgA and IgG ASC in these tissues peaked at PID 14-21. Rotavirus specific IgA ASC were predominant in the gut and IgA to IgG rotavirus specific ASC ratios were highest for all rotavirus antigen coatings in the gut LP. However, the relative ratios of specific IgA to IgG ASC were lower (ratios of 5 to 7) against combined structural and nonstructural viral antigens (rotavirus-infected fixed cell ELISPOT plates) than ratios (13 to 46) against only viral structural antigens (rotavirus-coated ELISPOT plates), indicating that there were proportionately more specific IgG ASC to the nonstructural viral antigens in the LP, the tissue adjacent to the site of rotavirus replication in the intestine. In the node cells (spleen and MLN) rotavirus-specific IgA to IgG ASC ratios were lowest and against the various ELISPOT rotavirus coatings ranged from 0.7 to 4. Gnotobiotic piglets inoculated at different ages with porcine rotaviruses generally showed similar specific immunoglobulin (Ig) ASC responses to rotavirus infection, along with similar diarrhea and virus shedding patterns in the different age groups. However, the numbers of specific IgA ASC in the MLN of 3-4 week old pigs were higher than those of 3-5 day old pigs. Although challenge of SB1A or Gottfried rotavirus-inoculated pigs with SB1A (G4P7) or Gottfried (G4P6) rotavirus revealed a high degree of protection from diarrhea and virus shedding, greater numbers of specific IgM ASC were observed in spleen after challenge of SB1A-inoculated pigs with Gottfried rotavirus (same G type, distinct P type). Thus, by using the ELISPOT technique, we successfully measured intestinal mucosal antibody-related responses to rotavirus in gnotobiotic pigs. Moreover, our results support the use of gnotobiotic piglets as an animal model to evaluate active antibody responses and protection against rotavirus infection and disease.

Rotaviruses: immunological determinants of protection against infection and disease

Although studies of rotavirus immunity in experimental animals and humans have often yielded conflicting data, a preponderance of evidence supports the following answers to the questions initially posed. 1. What is the importance of virus serotype in formulating an optimal vaccine? Both vp4 and vp7 induce virus-neutralizing antibodies after either natural infection or immunization; the capacity of vp4 to induce rotavirus-specific neutralizing antibodies is probably greater than that of vp7. However, protection against disease after immunization of infants and young children is induced by strains heterotypic to the challenge virus (e.g., immunization with WC3 induces protection against disease induced by serotypically distinct human G1 strains). In addition, oral inoculation of infants with primate or bovine reassortant rotaviruses containing genes that encode human vp7 has not consistently induced a higher level of protection against challenge than that induced by parent animal rotaviruses (see Table I). Therefore, although vp4 or vp7 or both are probably important in inducing protection against challenge, it has not been clearly demonstrated that inclusion of the epidemiologically important human (as distinct from animal) P or G type is important in protection against human disease. 2. Which immunological effector arm most likely protects against rotavirus disease? No immunological effector arm clearly explains protection against heterotypic challenge. Protection against disease is not predicted by rotavirus-specific neutralizing antibodies in serum. Rotavirus-specific, binding sIgA in feces [detected by enzyme-linked immunosorbent assay (ELISA)] induced after natural infection does correlate with protection against disease induced by subsequent infection. However, protection after immunization with WC3 may occur in the absence of a detectable fecal sIgA response. The relationship between rotavirus-binding sIgA and sIgA-mediated neutralizing activity directed against the challenge virus remains to be determined. Binding rotavirus-specific sIgA in feces detected by ELISA may only be a correlate of other events occurring at the intestinal mucosal surface. The presence of broadly cross-reactive, rotavirus-specific CTLs at the intestinal mucosal surface of mice acutely after infection is intriguing. It would be of interest to determine the degree to which the presence of cross-reactive, rotavirus-specific CTLs in the circulation is predictive of the presence of virus-specific CTLs among intestinal lymphocytes and protection against challenge. Unfortunately, studies of virus-specific CTLs are difficult to perform in children. 3. By what means is virus antigen best presented to the host to elicit a protective immune response? Oral inoculation may not be necessary to induce a protective, virus-specific immune response at the intestinal mucosal surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Rotavirus vaccines and vaccination potential

The development of a successful rotavirus vaccine is a complex problem. Our review of rotavirus vaccine development shows that many challenges remain, and priorities for future studies need to be established. For example, the evaluation of administration of a vaccine with OPV or breast milk might receive less emphasis until a vaccine is made that shows clear efficacy against all virus serotypes. Samples remaining from previous trials should be analyzed to determine epitope-specific serum and coproantibody responses to clarify why only some trials were successful. Detailed evaluation of the antigenic properties of the viruses circulating and causing illness in vaccinated children also should be performed for comparisons with the vaccine strains. In future trials, sample collection should include monitoring for asymptomatic infections and cellular immune responses should be analyzed. The diversity of rotavirus serotype distribution must be monitored before, during, and after a trial in the study population and placebo recipients must be matched carefully to vaccine recipients. Epidemiologic and molecular studies should be expanded to document, or disprove, the possibility of animal to human rotavirus transmission, because, if this occurs, vaccine protection may be more difficult in those areas of the world where cohabitation with animals occurs. We also need to have an accurate assessment of the rate of protection that follows natural infections. Is it realistic to try to achieve 90% protective efficacy with a vaccine if natural infections with these enteric pathogens only provide 60% or 70% protection? Subunit vaccines should be considered to be part of vaccine strategies, especially if maternal antibody interferes with the take of live vaccines. The constraints on development of new vaccines are not likely to come from molecular biology. The challenge remains whether the biology and immunology of rotavirus infections can be understood and exploited to permit effective vaccination. Recent advances in developing small animal models for evaluation of vaccine efficacy should facilitate future vaccine development and understanding of the protective immune response(s) (Ward et al. 1990b; Conner et al. 1993).

Rotavirus vaccine administered parenterally induces protective immunity

We performed experiments to determine whether parenteral immunization with SA11 rotavirus can induce active protective immunity in a rabbit model of rotavirus infection. After one or two intramuscular injections of 1 ml of live or formalin-inactivated SA11 virus, we evaluated the mucosal and serologic immune response and protection from challenge with a high dose of live, virulent rabbit (Ala) rotavirus. Inactivated SA11 virus preparations, evaluated by enzyme-linked immunosorbent assay (ELISA) with a panel of VP4- and VP7-specific neutralizing and nonneutralizing monoclonal antibodies, did not show a loss of epitopes from the inactivation procedure compared with live virus. Administration of two doses of vaccine, one at zero days postvaccination (DPV) and a booster shot at 49 DPV, followed by challenge at 71 DPV with 3.5 x 10(5) PFU of Ala virus resulted in protection from challenge. None of the two-dose virus-vaccinated rabbits shed virus after challenge, while virus shedding was detected in all control rabbits (P = 0.001, Fisher's exact two-tailed test). Differences in total serum immunoglobulin (Ig) antirotavirus ELISA titers (P < 0.05, Wilcoxon's rank sum test) were observed between groups vaccinated with virus in aluminum phosphate or Freund's adjuvant but not between groups vaccinated with live or inactivated virus in either adjuvant. All rabbits given two doses of vaccine had detectable antirotavirus intestinal antibody of the IgG, but not IgA, isotype. After challenge, fourfold or greater increases in intestinal IgG antibody responses were observed in three rabbits, whereas all controls and all but one virus-vaccinated rabbit had an intestinal IgA antibody response. In contrast, vaccination of rabbits with one dose of SA11 followed by challenge at 21 DPV did not protect from challenge; no difference in the mean number of days of virus shedding between any of the vaccinated groups and controls was observed. A serologic, but not a mucosal, antibody response was observed after the one-dose vaccination regimen. Differences in serologic antibody titers were not observed between any of the one-dose virus-vaccinated groups. These data indicate that parenteral vaccination with two, but not one, doses of rotavirus in either Freund's adjuvant or aluminum phosphate can induce active protection from challenge.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunodominant neutralizing antigens depend on the virus strain during a primary immune response in calves to bovine rotaviruses

Sera obtained from gnotobiotic calves (GC antisera) infected with bovine rotavirus strain NCDV or B223 from a previous study (Woode et al., 1987), which have different G (G6 and G10 respectively) and P serotypes, were compared for their neutralization (NT) properties to a number of human and animal rotaviruses (representing G serotype 1-6, 8-10). Two distinct patterns of neutralization were identified from these GC antisera. Of all the serotypes tested, NCDV GC antisera neutralized only B641 to a relatively high titer compared with the homologous titer, implying a narrow pattern of NT response. Analysis with reassortants indicated that the response was primarily to VP4. In contrast, B223 GC antisera neutralized most of the G serotypes tested to titers within 3-7 fold of the homologous titer, demonstrating a broad pattern of NT response. In the earlier study B223 was shown to induce a heterotypic protection against bovine rotavirus B641 (G serotype 6), and the serologic data obtained from this study indicates that a B223 vaccine might provide broad protection against several different serotypes of human and animal rotaviruses.

Characterization of an oligomerization domain and RNA-binding properties on rotavirus nonstructural protein NS34

Intermolecular interactions between polypeptide chains often play essential roles in such biological phenomena as replication, transcription, translation, transport, ligand binding, and assembly. We have initiated studies of the functions of the rotavirus SA114F gene 7 product by sequence analysis and expression in insect cells. This nonstructural protein, NS34, is a slightly acidic protein, and its secondary structure is predicted to be 78% alpha-helix, with several heptad repeats of hydrophobic amino acids being present in its carboxy half. NS34 was found in oligomers when analyzed in insect cells, in SA11-infected MA104 cells, and in cell-free translation reactions. Investigation of the multiple electrophoretically distinct forms of NS34 showed they were all composed of homooligomers. Deletion mutants constructed and tested for oligomerization showed that the carboxy terminus of the protein, containing the predicted heptad repeats, was responsible for oligomerization. A basic region present in NS34 of group A rotaviruses, found to be 40% conserved in NS34 of group C rotavirus, is a candidate for a functional domain of this protein. NS34, which was found to be associated with the cytoskeleton fraction of cells, also interacts with viral RNA. These results make it likely that NS34 plays a central role in the replication and assembly of genomic RNA structures.