Rotavirus-specific cytotoxic T lymphocytes cross-react with target cells infected with different rotavirus serotypes

Antiviral effects of cyclosporine A in neonatal mice with rotavirus-induced diarrhea

OBJECTIVES

Because rotavirus gastroenteritis is associated with high morbidity and mortality especially in developing countries, it is necessary to develop antirotavirus drugs for the treatment of rotavirus infection. Previous studies have demonstrated that cyclosporin A (CsA) has antiviral properties against rotavirus. Its effect has not yet been evaluated against rotavirus diarrheal disease. The aim of this study was to assess the anti-rotavirus efficacy of CsA in neonatal mice after induction of rotavirus diarrhea.

METHODS

Suckling mice were inoculated with murine rotavirus. On the onset of diarrhea, mice were given different concentrations of CsA. To evaluate the effects of CsA on reduction of rotavirus diarrhea, diarrhea score, fecal virus shedding, and pathological lesion change in the small intestine, messenger RNA (mRNA) expression levels in the small intestine and spleen of mice were measured for type I interferon (IFN-α and IFN-β), inflammation-related cytokines (interleukin [IL]-8, IL-10, IFN-γ, and tumor necrosis factor-α), and inflammatory signaling pathways (p38, c-Jun N-terminal kinase, activator protein-1, and nuclear factor-kappa B).

RESULTS

Among virus-inoculated and CsA-treated groups, a dose of 5 mg · kg⁻¹ · day⁻¹ of CsA inhibited diarrhea and improved fecal virus shedding and intestinal lesion changes. IFN-β mRNA expression was significantly increased in rotavirus-induced diarrhea mice treated with 5 mg · kg⁻¹ · day⁻¹ of CsA, whereas the mRNA expression levels of inflammation-related cytokines (IL-8, IL-10, IFN-γ, and tumor necrosis factor-α) and inflammatory signaling pathways (p38, c-Jun N-terminal kinase, activator protein-1, and nuclear factor-kappa B) were markedly decreased. Antiviral effects of CsA were dose dependent.

CONCLUSIONS

CsA can inhibit rotavirus infection in neonatal mice through its antiviral properties. The mechanism for this may be through CsA suppression of inflammation by viral inhibition in animal models.

Detection of unusual G6 rotavirus strains in Italian children with diarrhoea during the 2011 surveillance season

Two rare G6 rotavirus A (RVA) strains, designated as RVA/human-wt/ITA/CEC06/2011/G6P[6] and RVA/human-wt/ITA/PG05/2011/G6P[9], were identified in stool specimens from children hospitalized in Central Italy. After PCR genotyping, the samples CEC06 and PG05 gave G-UD-P[6] and G-UD-P[9] genotypes, respectively. To determine the G-type and to characterize further the two strains, sequencing of 8 of the 11 genomic segments was performed. CEC06 and PG05 strains were found to possess unusual genotype constellations: G6-P[6]-I2-A2-N2-T2-E2-H2 and G6-P[9]-I2-A3-N2-T3-E3-H3, respectively. This study reports the first detection of rare G6P[6] and G6P[9] RVA strains in peninsular Italy. Phylogenetic analysis of VP4 (VP8*), VP7, VP6, and NSP1-5 showed no evidence of zoonosis or inter-species reassortment, revealing for both strains constellations previously associated to human cases.

Why does the world need another rotavirus vaccine?

A “Meeting on Upstream Rotavirus Vaccines and Emerging Vaccine Producers” was held at the World Health Organization in Geneva, Switzerland on March 28–30, 2006. The purpose was to discuss, evaluate, and weigh the importance of additional rotavirus vaccine candidates following the successful international licensure of rotavirus vaccines by two major pharmaceutical companies (GlaxoSmithKline and Merck) that had been in development for many years. Both licensed vaccines are composed of live rotaviruses that are delivered orally as have been all candidate rotavirus vaccines evaluated in humans. Each is built on the experience gained with previous candidates whose development had either been discontinued or, in the case of the previously licensed rhesus rotavirus reassortant vaccine (Rotashield), was withdrawn by its manufacturer after the discovery of a rare association with intussusception. Although which alternative candidate vaccines should be supported for development and where this should be done are controversial topics, there was general agreement expressed at the Geneva meeting that further development of alternative candidates is a high priority. This development will help insure that the most safe, effective and economic vaccines are available to children in Third World nations where the vast majority of the >600,000 deaths due to rotavirus occur each year. This review is intended to provide the history and present status of rotavirus vaccines as well as a perspective on the future development of candidate vaccines as a means of promulgating plans suggested at the Geneva meeting.

Rotavirus vaccines: how they work or don't work

In 2004 and 2006, two new rotavirus vaccines - Rotarixtrade mark and RotaTeqtrade mark - were licensed worldwide. Both are live virus vaccines and are composed of either a monovalent attenuated human rotavirus or five bovine-human reassortant rotaviruses, respectively. Studies in humans and animals have reported correlations between rotavirus antibody levels and protection, the most consistent of which has been with rotavirus IgA. Cellular immunity was also found to have a role in protection after live rotavirus immunisation, particularly in mice. However, the primary importance of CD8+ T cells may be in resolution of infection and that of CD4+ T cells may be their helper function, particularly for antibody production. CD4+ T cells have been reported to have a more direct role in protection after mucosal immunisation with non-living rotavirus vaccines, possibly because of direct or indirect effects of the cytokines they generate. Immune effectors have overlapping functions, and protection against rotavirus by either live or non-living vaccines is probably enhanced by this redundancy.

Stimulation History Dictates Memory CD8 T Cell Phenotype: Implications for Prime-Boost Vaccination

Heterologous prime-boost vaccination results in increased frequencies of memory T cells. Although these quantitative effects of reexposure to Ag are well documented, little is known about the impact of boosting on the functional qualities of memory T cells. To address this critical issue, we have used three different types of immunization regimens and examined how boosting effects the function and anatomic location of memory CD8 T cells. We found that memory T cell phenotype differed substantially depending on the number of immunizations and that secondary and tertiary responses resulted in the generation of memory CD8 T cells that retained effector-like properties and showed preferential accumulation in nonlymphoid tissues. These results show that memory differentiation is coupled to the history of Ag experience and that prime-boost vaccination strategies have important consequences on memory CD8 T cell quality and surveillance within mucosal tissues.

Characterization of homologous and heterologous rotavirus-specific T-cell responses in infant and adult mice

During primary rotavirus (RV) infection, CD8+ T cells play an important role in viral clearance as well as providing partial protection against reinfection. CD4+ T cells are essential for maximal development of RV-specific intestinal immunoglobulin A. In this study, we took advantage of the cytokine flow cytometry technique to obtain a detailed map of H-2b- and H-2d-restricted CD8+ and CD4+ T-cell epitopes from the RV proteins VP6 and VP7. Three new CD8+ T-cell epitopes (H-2d and H-2b restricted) and one new CD4+ T-cell epitope (H-2d and H-2b restricted) were identified. Using these newly identified targets, we characterized the development and specificity of cellular immune responses in C57BL/6 and BALB/c mice during acute infection of infants and adults. We found that both the CD4+ and CD8+ responses peaked on days 5 to 7 after infection and then declined rapidly. Interestingly, both the response kinetics and tissue distributions were different when epitopes on VP6 and VP7 were compared. VP6 elicited a response which predominated in the intestine, while the response to VP7 was more systemic. Additionally, the T-cell responses elicited after homologous versus heterologous infection differed substantially. We found that during homologous infection, there was a greater response toward VP6 than that toward VP7, especially in the intestine, while after heterologous infection, this was not the case. Finally, in suckling mice, we found two peaks in the CD8 response on days 7 and 14 postinfection, which differed from the single peak found in adults and likely mimics the biphasic pattern of rotavirus shedding in infant mice.

Cytokines as mediators for or effectors against rotavirus disease in children

Rotavirus is the most common cause of severe gastroenteritis in young children, but the pathogenesis and immunity of this disease are not completely understood. To examine the host response to acute infection, we collected paired serum specimens from 30 children with rotavirus diarrhea and measured the levels of nine cytokines (interleukin-1beta [IL-1beta], IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, gamma interferon [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]) using a microsphere-based Luminex Flowmetrix system. Patients with acute rotavirus infection had elevated median levels of seven cytokines in serum, and of these, the levels of three (IL-6, IL-10, and IFN-gamma) were significantly (P < 0.05) higher than those in serum from control children without diarrhea. Patients with fever had significantly (P < 0.05) higher levels of IL-6 in serum than control children, and those with fever and more episodes of diarrhea had significantly (P < 0.05) higher levels of TNF-alpha than those without fever and with fewer episodes of diarrhea. We further demonstrated a negative association (P < 0.05) between the levels of IL-2 and the number of stools on the day on which the first blood sample was collected. Finally, patients with vomiting had significantly (P < 0.05) lower levels of IFN-gamma than those without vomiting. Our pilot study provides evidence that the types and magnitudes of cytokine responses to rotavirus infection in children influence or reflect the clinical outcome of disease. These findings suggest that certain cytokines may play an important role in the pathogenesis of and the protection against rotavirus disease in children and, consequently, may provide directions and insights that could prove critical to the prevention or treatment of this important disease.

B2 but not B1 cells can contribute to CD4+ T-cell-mediated clearance of rotavirus in SCID mice

Studies utilizing various immunodeficient mouse models of rotavirus (RV) infection demonstrated significant roles of RV-specific secretory immunoglobulin A (IgA), CD4+ T cells, and CD8+ T cells in the clearance of RV and protection from secondary infection. Secretion of small but detectable amounts of IgA in RV-infected alphabeta T-cell receptor knockout mice (11) and distinctive anatomical localization and physiology of B1 cells suggested that B1 cells might be capable of producing RV-specific intestinal IgA in a T-cell-independent fashion and, therefore, be responsible for ablation of RV shedding. We investigated the role of B1 cells in the resolution of primary RV infection using a SCID mouse model. We found that the adoptive transfer of unseparated peritoneal exudate cells ablates RV shedding and leads to the production of high levels of RV-specific intestinal IgA. In contrast, purified B1 cells do not ablate RV shedding and do not induce a T-cell-independent or T-cell-dependent, RV-specific IgA response but do secrete large amounts of polyclonal (total) intestinal IgA. Cotransfer of mixtures of purified B1 cells and B1-cell-depleted peritoneal exudate cells differing in IgA allotypic markers also demonstrated that B2 cells (B1-cell-depleted peritoneal exudate cells) and not B1 cells produced RV-specific IgA. To our knowledge, this is the first observation that B1 cells are unable to cooperate with CD4+ T cells and produce virus-specific intestinal IgA antibody. We also observed that transferred CD4+ T cells alone are capable of resolving RV shedding, although no IgA is secreted. These data suggest that RV-specific IgA may not be obligatory for RV clearance but may protect from reinfection and that effector CD4+ T cells alone can mediate the resolution of primary RV infection. Reconstitution of RV-infected SCID mice with B1 cells results in the outgrowth of contaminating, donor CD4+ T cells that are unable to clear RV, possibly because their oligoclonal specificities may be ineffective against RV antigens.

Rotavirus-specific cytotoxic T lymphocytes recognize overlapping epitopes in the amino-terminal region of the VP7 glycoprotein

Rotavirus-specific cytotoxic T lymphocytes (CTL) play an important role in the resolution of rotavirus infection. The outer capsid glycoprotein, VP7, elicits a class I MHC-restricted CTL response. Vaccinia virus recombinants expressing the VP7 genes from simian rotavirus SA11 (serotype G3) and from the RF strain of bovine rotavirus (serotype G6) were used to analyze the CTL activity to this antigen in BALB/c (H-2(d)) and C57BL/6 (H-2(b)) mice neonatally infected with homologous and heterologous rotaviruses. A vaccinia virus recombinant expressing the first amino-terminal 88 amino acids of VP7 was constructed and used to search for cross-reactive CTL against this region of the protein. By using synthetic Kb, Db, and Kd motif-fitting peptides two overlapping CTL epitopes have been identified located in the first hydrophobic domain (H1) of VP7. Splenocytes obtained from rotavirus SA11-infected C57BL/6 mice induced the strongest CTL response against target cells sensitized with a peptide containing a Kb-restricted CTL epitope (amino acids 8-16). A second Kd-restricted epitope (residues 5-13) was recognized by splenocytes derived from rotavirus-infected BALB/c mice. These findings reveal the existence of CTL epitopes in the H1 signal sequence of the VP7 glycoprotein that coexist with a CTL epitope (residues 31-40) previously described within the H2 region.

Oral delivery of homologous and heterologous strains of rotavirus to BALB/c mice induces the same profile of cytokine production by spleen cells

In this work, we wanted to clarify if differences in antibody (Ab) and particularly in secretory immunoglobulin A (IgA) responses following homologous or heterologous rotavirus infection could be explained by different priming of specific T helper (Th) cells. We compared the Ab responses from suckling BALB/c mice orally inoculated with either a heterologous simian (SA11) or bovine (RF) rotavirus or a homologous murine rotavirus (EHPw), as well as the profile of cytokines produced by spleen cells after in vitro restimulation. Oral inoculation of EHPw and SA11 induced a similar pattern of Ab with mucosal and serum IgA associated with serum IgG with equal levels of IgG1 and IgG2a, whereas RF elicited a weak humoral response. We found that these strains induced the same mixed Th1/Th2 pattern of cytokine production by spleen cells with IFN-gamma and IL-5 as well as IL-10, but not IL-2 or IL-4. These findings suggest that the induction of immune response is probably not different between these strains. Other factors such as the amount of antigen, strain immunogenicity, and other cytokines, particularly produced in effector sites, remain to be considered in order to better explain the differences in secretory IgA following homologous or heterologous rotavirus infection.

The carboxyl-terminal 120-residue polypeptide of infectious bronchitis virus nucleocapsid induces cytotoxic T lymphocytes and protects chickens from acute infection

Specific cytotoxic T-lymphocyte (CTL) responses to nucleocapsid of infectious bronchitis virus (IBV) were identified by using target cells infected with a Semliki Forest virus (SFV) vector. Effector cells for CTL assays were collected from chickens infected with the Gray strain of IBV or inoculated with a DNA plasmid encoding nucleocapsid proteins. IBV-specific CTL epitopes were mapped within the carboxyl-terminal 120 amino acids of the nucleocapsid protein. CTL lysis of target cells infected with SFV encoding nucleocapsid was major histocompatibility complex restricted and mediated by CD8+ T cells. In addition, splenic T cells collected from chickens inoculated in the breast muscle with a DNA plasmid encoding this CTL epitope(s) recognized target cells infected with wild-type virus or an SFV vector encoding nucleocapsid proteins. CTL activity of splenic T cells collected from chicks immunized with a DNA plasmid encoding CTL epitopes was cross-reactive, in that lysis of target cells infected with serologically distinct strains of IBV was dose responsive in a manner similar to that for lysis of target cells infected with the homologous strain of IBV. Furthermore, chickens immunized with a DNA plasmid encoding a CTL epitope(s) were protected from acute viral infection.

Development of mucosal and systemic lymphoproliferative responses and protective immunity to human group A rotaviruses in a gnotobiotic pig model

Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group 1), attenuated Wa rotavirus (group 2) or diluent (controls) and were challenged with virulent Wa rotavirus 21 days later. On various postinoculation or postchallenge days, virus-specific responses of systemic (blood and spleen) and intestinal (mesenteric lymph node and ileal lamina propria) mononuclear cells (MNC) were assessed by lymphoproliferative assays (LPA). After inoculation, 100% of group 1 pigs and 6% of group 2 pigs shed virus. Diarrhea occurred in 95, 12, and 13% of group 1, group 2, and control pigs, respectively. Only groups 1 and 2 developed virus-specific LPA responses prior to challenge. Group 1 developed significantly greater mean virus-specific LPA responses prior to challenge and showed no significant changes in tissue mean LPA responses postchallenge, and 100% were protected against virulent virus challenge. By comparison, both group 2 and controls had significantly lower LPA responses at challenge and both groups showed significant increases in mean LPA responses postchallenge. Eighty-one percent of group 2 and 100% of control pigs shed challenge virus, and both groups developed diarrhea that was similar in severity postchallenge. The virus-specific LPA responses of blood MNC mirrored those of intestinal MNC, albeit at a reduced level and only at early times postinoculation or postchallenge in all pigs. In a separate study evaluating antibody-secreting-cell responses of these pigs (L. Yuan, L.A. Ward, B.I. Rosen, T.L. To, and L.J. Saif, J. Virol. 70:3075-3083, 1996), we found that the magnitude of a tissue's LPA response positively correlated with the numbers of virus-specific antibody-secreting cells for that tissue, supporting the hypothesis that the LPA assesses T-helper-cell function. The magnitude of LPA responses in systemic and intestinal tissues also strongly correlated with the degree of protective immunity elicited by the inoculum (p = 0.81). We conclude that blood may provide a temporary "window" for monitoring intestinal T cells and that the LPA can be used to assess protective immunity to human rotaviruses.

DNA vaccines against rotavirus infections

Plasmid DNA vaccines encoding for murine rotaviral proteins VP4, VP6, and VP7 were tested in adult BALB/c mice for their ability to induce immune responses and provide protection against rotavirus challenge. Serum antibodies were measured by virus neutralization and by ELISA. Cellular immunity was assessed by measuring cytotoxic T cell (CTL) responses. The vaccines were administered by inoculation into cells of the epidermis with an Accell gene gun (Auragen, Inc., Middleton, WI, USA). Each of the three vaccines elicited rotavirus-specific serum antibodies as measured by ELISA. Virus neutralizing antibodies were detected in mice receiving DNA vaccines encoding for VP4 and VP7, but not in those which received the plasmid encoding for VP6. Vaccines encoding for VP4, VP6, or VP7 generated virus-specific CTL responses in recipient mice. Efficacy of the vaccines was determined by challenge with homotypic rotaviruses. Each of the three vaccines was effective in protecting mice against infection after rotavirus (100 ID50) challenge. Significant reductions (p < 0.0002, analysis of variance) in viral excretion measured over a 9 day period were seen in mice receiving the DNA vaccines compared with mice that received control plasmids.

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.

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)

Serological response to rotavirus infection in newborn infants

We report the identification of rotavirus in stools of newborn infants at the "Hospital Materno Infantil de Caricuao" (HMIC) as well as the infants' serological responses to various rotavirus strains. The serological responses of another group of rotavirus-positive neonates studied previously at the "Maternidad Concepcion Palacios" (MCP) hospital was also evaluated. Fifty-four of 266 (20%) newborns examined at HMIC shed rotavirus. The infection rate was higher among infants admitted to the nursery (75%) than in those "rooming in" with their mothers (7%) (P < .01). Eleven of the 54 neonates (20%) had diarrhea; seven of them experienced mild, short-lived episodes, whereas five had frequent diarrhea bouts or diarrhea lasting for over 3 days; the remaining 43 infants were asymptomatic. Twenty-seven of 28 rotavirus specimens tested at HMIC had VP7 serotype 4 specificity and one belonged to VP7 serotype 1; VP4 typing performed on 24 of the viruses by RNA hybridization showed these viruses to be similar to the M37 strain, a rotavirus previously associated with asymptomatic infections in newborns at MCP. IgA seroresponses were detected in eight of 11 infants born at HMIC (73%), but most failed to developed neutralization responses to homologous or heterologous strains. Newborn infants who had shed the M37 rotavirus strain at MCP reacted similarly: 16 of 24 (67%) developed a rotavirus IgA rise, but only 29% developed a neutralization response.

Rotavirus antigen detection in patients with HIV infection and diarrhea

A wide variety of bacterial, viral, and parasitic pathogens can cause severe diarrhea in patients with advanced human immunodeficiency virus (HIV) infection. The role of enteric viruses, especially rotaviruses, in HIV-related diarrhea is still unclear. One hundred and six stool samples from 66 HIV-infected patients with otherwise unexplained diarrhea and 35 samples from 35 patients with advanced HIV infection but without diarrhea were tested for the presence of rotavirus antigen. Rotavirus was detected in 13 samples from 9 patients with diarrhea and in none of the samples from patients without diarrhea. Two patients had recurrence of rotavirus infection more than 6 months after the first episode. Rotavirus was associated with prolonged diarrhea, often accompanied by abdominal cramping. Symptoms were readily controlled with anti-diarrheal and pain-relieving measures. Illness was self-limited and did not require hospitalization. A seasonal variation, typical of infantile rotavirus infection, was not observed in this setting. While rotavirus infection has been infrequently detected in American HIV-infected patients, the prevalence in Australia and Europe appears to be considerably higher.

Outer capsid glycoprotein vp7 is recognized by cross-reactive, rotavirus-specific, cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) generated in mice orally inoculated with rotaviruses lyse target cells infected with different rotavirus serotypes (cross-reactive CTLs). Using vaccinia virus recombinants expressing individual rotavirus proteins from two different rotavirus serotypes, we found that cross-reactive CTLs recognize target cells expressing outer capsid protein vp7 better than those expressing outer capsid protein vp4 or inner capsid protein vp6. These findings may be relevant to vaccine strategies which include immunization with reassortant rotaviruses or viral or bacterial vectors expressing individual rotavirus proteins. The region or regions of vp7 which are antigenically conserved among different rotavirus serotypes and recognized by cross-reactive CTLs remain to be determined.

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.

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

We examined the humoral immune response to rotavirus infection in specific pathogen-free rabbits inoculated and challenged orally with rabbit Ala rotavirus (7.5 x 10(5) to 1 x 10(7) PFU). The humoral immune response in both serologic and mucosal samples was monitored by using total antibody enzyme-linked immunosorbent assays (ELISAs), isotype-specific ELISAs, and plaque reduction neutralization assays. Following a primary infection, all rabbits shed virus and serologic and mucosal antibody responses were initially detected by 1 week postinoculation. Intestinal immunoglobulin M was detected by 3 days postinoculation, and secretory immunoglobulin A was detected by 6 days postinoculation. Following challenge, rabbits were protected (no detectable virus shedding) from infection. An anamnestic immune response was observed only with mucosal neutralizing antibodies, and all serologic and mucosal immune responses persisted at high levels until at least 175 days postchallenge (204 days postinoculation). Detection of neutralization responses was influenced by the virus strain used in the neutralization assay; all inoculated rabbits developed detectable serum and intestinal neutralizing antibodies against the infecting (Ala) virus strain. Neutralization activity in both serum and mucosal samples was generally, but not exclusively, homotypic (VP7 serotype 3) after both primary and challenge inoculations with Ala virus. Heterotypic serum neutralization activity was observed with serotype 8 (9 of 12 rabbits) and 9 (12 of 12 rabbits) viruses and may be based on reactivity with the outer capsid protein VP4 or on a shared epitope in the C region of VP7. Comparisons of heterologous (serotype 3) and heterotypic neutralizing responses in mucosal and serologic samples revealed that 43% (21 of 49) of the responses were discordant. In 19 of 49 (39%) of these cases, a heterotypic serologic response was seen in the absence of a heterotypic mucosal response, but in 2 of 49 (4%) instances, a heterotypic mucosal response was seen in the absence of a concomitant serologic response. These results provide insight into factors which may affect detection of heterotypic responses.

Memory and distribution of virus-specific cytotoxic T lymphocytes (CTLs) and CTL precursors after rotavirus infection

The gastrointestinal tract is constantly exposed to a variety of potentially invasive bacteria, viruses, and parasites. The first line of defense against these pathogens is the intestinal mucosal surface, which consists of epithelial cells, intraepithelial lymphocytes (IELs), mucus, and secretory immunoglobulins. In addition, the intestine is a rich source of lymphocytes located within Peyer's patches and the lamina propria. Little is known about the function, memory, trafficking, or origin of intestinal T lymphocytes after intestinal infection. We studied the murine cytotoxic T-lymphocyte (CTL) response to the intestinal pathogen rotavirus (simian strain RRV). Adult mice were inoculated orally or via the hind footpad with RRV; virus-specific cytotoxic activities in intestinal and nonintestinal lymphocyte populations were determined by 51Cr release assays. In addition, virus-specific CTL precursor (CTLp) frequencies were determined by limiting-dilution analysis. IELs containing rotavirus-specific cytotoxic activity were detected after oral but not footpad inoculation and expressed alpha/beta but not gamma/delta cell surface protein; virus-specific CTLs did not appear to arise from CTLp among IELs. In addition, the site at which RRV was presented to the immune system determined the site at which RRV-specific CTLp first appeared. Frequencies of rotavirus-specific CTLp detected in Peyer's patches were 25- to 30-fold greater after oral than after footpad inoculation. However, regardless of the route of inoculation, rotavirus-specific CTLp were distributed throughout the lymphoid system 21 days after infection. Implications of these findings for vaccine design are discussed.

Clonal analysis of the cytotoxic T-lymphocyte response to reovirus

Reovirus has previously been classified into three serotypes based on hemagglutination inhibition assays. In the present study, the specificity of cytotoxic T lymphocytes (CTL) generated in reovirus type 3-infected C3H/HeN mice was investigated at the population and clonal levels. Short-term CTL lines generated in response to reovirus type 3 preferentially lysed cells infected with reovirus type 1 or 3 and, in some instances, type 2-infected cells as well. Eleven CTL clones established from the lines demonstrated two unique patterns of recognition. A single clone was exquisitely specific for reovirus type 3-infected cells and did not cross-react on reovirus type 1- or 2-infected cells. Ten of the clones recognized reovirus type 1- and type 3-infected cells. These clones had low levels of cross-reactivity on reovirus type 2-infected cells that was revealed only at high effector:target cell ratios. Precursor frequency analysis further revealed that the majority of the CTL generated against reovirus type 3 could cross-react on both reovirus type 1- and type 2-infected cells. Some CTL could be detected that had a more restricted pattern of recognition and recognized reovirus type 3-infected cells exclusively or recognized reovirus type 3-infected cells and either reovirus type 1- or type 2-infected cells. These results indicate that a minimum of four epitopes are recognized by reovirus-specific CTL and that the response is dominated by CTL that recognize an epitope common to all three serotypes of reovirus.

Rotavirus-specific cytotoxic T lymphocytes passively protect against gastroenteritis in suckling mice

Suckling mice are protected against murine rotavirus-induced gastroenteritis after adoptive transfer of splenic lymphocytes from immunized animals. Adoptive transfer of Thy1(+)-depleted or CD8(+)-depleted lymphocytes abrogated protection against challenge. (We previously found that depletion of Thy1+ or CD8+ lymphocytes from rotavirus-immunized mice decreased rotavirus-specific cytotoxic activity in vitro.) Protection against disease occurred in the absence of rotavirus-specific neutralizing antibodies in the sera of suckling mice. Rotavirus-specific cytotoxic T lymphocytes may be important in either amelioration of acute infection or protection against reinfection.

The immunogenicity of VP7, a rotavirus antigen resident in the endoplasmic reticulum, is enhanced by cell surface expression

The glycoprotein VP7, the major serotype antigen of rotaviruses, is localized to the endoplasmic reticulum (ER) of the cell, where it is retained as a membrane-associated protein before assembly into mature virus particles. Wild-type VP7 expressed by a recombinant vaccinia virus was also located internally and was poorly antigenic. Using recombinant techniques, a correctly processed, secreted form of VP7 (S.C. Stirzaker and G.W. Both, Cell 56:741-747, 1989) was modified by addition to its C terminus of the membrane anchor and cytoplasmic domains from the influenza virus hemagglutinin. The hybrid protein was directed to the surface of cells, where it was anchored in the plasma membrane. When expressed in mice and rabbits by a recombinant vaccinia virus, the surface-anchored antigen stimulated a level of rotavirus-specific antibodies that was greater than 100-fold above the level induced by wild-type VP7. T-cell responses to the novel antigen were also elevated in comparison with the wild-type, intracellular protein. Cell surface anchoring may provide a strategy to increase the immunogenicity of intracellular antigens from other parasites and viruses.

Natural killer cell activity of chicken intraepithelial leukocytes against rotavirus-infected target cells

Intraepithelial leukocytes (IEL) and splenocytes collected from uninfected and rotavirus-infected chickens were evaluated for cytotoxic activity against a natural killer (NK) cell-susceptible lymphoblastoid cell line (LSCC-RP9) and against rotavirus-infected chick kidney cells in 4-h chromium-release assays. Both splenocytes and IELs from uninfected and rotavirus-infected chickens were cytotoxic for LSCC-RP9, and the levels of this NK cell activity were not altered by infection of the host with rotavirus. IELs but not splenocytes from uninfected and rotavirus-infected chickens were cytotoxic for rotavirus-infected but not for uninfected chick kidney cell targets. Because this cytotoxic activity was not induced nor altered by rotavirus infection of the host, and was not major histocompatibility complex-restricted, it was considered to be due to NK cell activity. The cytotoxicity of IELs against rotavirus-infected target cells was dose-dependent; however, there was some suppression of cytotoxic activity at high effector to target cell ratios. There were no differences in the cytotoxic activities of IELs collected from the duodenum versus the jejunum. The in vitro cytotoxic activity of IELs against rotavirus-infected target cells suggested that NK cell activity may be an important immune response to rotavirus infections in vivo. The absence of cytotoxic activity by splenocytes against rotavirus-infected target cells indicated that there may be different subpopulations of NK cells in the spleen and intestinal epithelium of chickens.

Recovery from chronic rotavirus infection in mice with severe combined immunodeficiency: virus clearance mediated by adoptive transfer of immune CD8+ T lymphocytes

Severe combined immunodeficient (SCID) mice lack both functional T and B cells. These mice develop chronic rotavirus infection following an oral inoculation with the epizootic diarrhea of infant mice (EDIM) rotavirus. Reconstitution of rotavirus-infected SCID mice with T lymphocytes from immunocompetent mice allows an evaluation of a role of T-cell-mediated immunity in clearing chronic rotavirus infection. Complete rotavirus clearance was demonstrated in C.B-17/scid mice 7 to 9 days after the transfer of immune CD8+ splenic T lymphocytes from histocompatible BALB/c mice previously immunized intraperitoneally with the EDIM-w strain of murine rotavirus. The virus clearance mediated by T-cell transfer was restricted to H-2d-bearing T cells and occurred in the absence of rotavirus-specific antibody as determined by enzyme-linked immunosorbent assay, neutralization, immunohistochemistry, and radioimmunoprecipitation. Temporary clearance of rotavirus was observed after the transfer of immune CD8+ T cells isolated from the intestinal mucosa (intraepithelial lymphocytes [IELs]) or the spleens of BALB/c mice previously infected with EDIM by the oral route. Chronic virus shedding was transiently eliminated 7 to 11 days after spleen cell transfer and 11 to 12 days after IEL transfer. However, recurrence of rotavirus infection was detected 1 to 8 days later in all but one SCID recipient receiving cells from orally immunized donors. The viral clearance was mediated by IELs that were both Thy1+ and CD8+. These data demonstrated that the clearance of chronic rotavirus infection in SCID mice can be mediated by immune CD8+ T lymphocytes and that this clearance can occur in the absence of virus-specific antibodies.

Rotavirus induces proliferative response and augments non-specific cytotoxic activity of lymphocytes in humans

In vitro cell-mediated immune responses to rotavirus in humans were studied. Peripheral blood mononuclear cells (PBMC) of healthy adults proliferated in response to stimulation with the infectious and u.v.-inactivated Wa strain of human rotavirus, showing a maximum response on day 7 of culture; however, cord blood lymphocytes failed to respond to rotavirus. A cross-reactive proliferative response of PBMC detected by stimulation with the NCDV strain of bovine rotavirus suggests the existence of epitopes common to both human and bovine rotaviruses, which are recognized by human T lymphocytes. The phenotype of the majority of activated lymphocytes was CD3+4+8-, indicating that the cells mainly activated were helper T cells. Culture supernatants of PBMC stimulated with rotavirus contained interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In addition, PBMC stimulated with rotavirus demonstrated significantly enhanced cytotoxic activity against natural killer (NK) sensitive K562 cells as well as an NK-resistant Epstein-Barr virus-immortalized lymphoblastoid cell line (LCL). Treatment of PBMC with anti-CD16 or NKH1A monoclonal antibody, both of which react with most NK cells and lymphokine-activated killer cells and complement markedly reduced the cytotoxic activity against K562 and LCL. These results suggest that stimulation of human PBMC with rotavirus results in the production of lymphokines, such as IL-2 and IFN-gamma, by rotavirus-reactive helper T cells and that these lymphokines augment NK activity and generate other forms of non-specific cytotoxic human lymphocyte activity. These cell-mediated immune responses observed in the present in vitro study might play an important role in protection and recovery from rotavirus infection.

Evaluation of RIT 4237 bovine rotavirus vaccine in newborn infants: correlation of vaccine efficacy to season of birth in relation to rotavirus epidemic period

A single oral dose of bovine rotavirus vaccine RIT 4237 or placebo was given to 2 groups of 5-day-old infants, born in October 1984 (n = 244) and June 1985 (n = 245), who remained in follow-up for 2.8 and 2.0 years, respectively. The vaccine had no effect on the total number of detectable episodes of rotavirus diarrhoea: there were 22 cases in the vaccinees and 24 in the placebo recipients in the October group and 18 and 16 respectively in the June group. However, vaccination decreased significantly the clinical severity of rotavirus diarrhoea, as assessed by a numerical score 0-20; this vaccine effect was much greater in the infants born in October. The mean severity scores for vaccine and placebo recipients were 4.55 and 10.75 respectively in the October group (p less than 0.0001, t-test) and 8.2 and 11.6 respectively in the June group (p = 0.010, t-test). Vaccine-induced clinical protection against rotavirus diarrhoea did not correlate well with serological response after vaccination, but showed good correlation to the presence of rotavirus antibodies before the rotavirus epidemic season. It is concluded that bovine rotavirus vaccine is more efficacious when given immediately before the rotavirus epidemic season: the vaccine effect may be amplified by exposure to wild rotaviruses during the season.

Rotavirus gene structure and function

Knowledge of the structure and function of the genes and proteins of the rotaviruses has expanded rapidly. Information obtained in the last 5 years has revealed unexpected and unique molecular properties of rotavirus proteins of general interest to virologists, biochemists, and cell biologists. Rotaviruses share some features of replication with reoviruses, yet antigenic and molecular properties of the outer capsid proteins, VP4 (a protein whose cleavage is required for infectivity, possibly by mediating fusion with the cell membrane) and VP7 (a glycoprotein), show more similarities with those of other viruses such as the orthomyxoviruses, paramyxoviruses, and alphaviruses. Rotavirus morphogenesis is a unique process, during which immature subviral particles bud through the membrane of the endoplasmic reticulum (ER). During this process, transiently enveloped particles form, the outer capsid proteins are assembled onto particles, and mature particles accumulate in the lumen of the ER. Two ER-specific viral glycoproteins are involved in virus maturation, and these glycoproteins have been shown to be useful models for studying protein targeting and retention in the ER and for studying mechanisms of virus budding. New ideas and approaches to understanding how each gene functions to replicate and assemble the segmented viral genome have emerged from knowledge of the primary structure of rotavirus genes and their proteins and from knowledge of the properties of domains on individual proteins. Localization of type-specific and cross-reactive neutralizing epitopes on the outer capsid proteins is becoming increasingly useful in dissecting the protective immune response, including evaluation of vaccine trials, with the practical possibility of enhancing the production of new, more effective vaccines. Finally, future analyses with recently characterized immunologic and gene probes and new animal models can be expected to provide a basic understanding of what regulates the primary interactions of these viruses with the gastrointestinal tract and the subsequent responses of infected hosts.

Passive immunity modulates genetic reassortment between rotaviruses in mixedly infected mice

Genetic reassortment between simian rotavirus SA11 and rhesus rotavirus (RRV) occurs with high frequency following mixed infection of nonimmune suckling mice (J. L. Gombold and R. F. Ramig, J. Virol. 57:110-116, 1986). We examined the effects of passively acquired homotypic or heterotypic immunity on reassortment in vivo. Passively immune suckling mice obtained from dams immune to either serotype 3 simian rotavirus (SA11) or serotype 6 bovine rotavirus (NCDV) were infected orally with either SA11 or RRV or a mixture of SA11 and RRV (both serotype 3 viruses). At various times postinfection, signs of disease were noted and the intestines of individual mice were removed and homogenized for titration of infectious virus and isolation of progeny plaques. Electrophoresis of genomic RNA was used to identify reassortants among the viral progeny isolated from infected animals. No reassortants (less than 0.45%) were detected among 224 clones examined from mixedly infected, homotypically immune mice. Twenty-nine reassortants (10.66%) were identified among 272 progeny clones from mixedly infected, heterotypically immune mice. Thus, reassortment was reduced more than 50-fold by homotypic immunity and approximately threefold by heterotypic immunity compared with prior data obtained from mixed infections of nonimmune mice. In addition, reassortment between SA11 and RRV in nonimmune mice was shown to be dependent on the virus dose. Taken together, these results suggest that immune responses may modulate the frequency of reassortment by reducing the effective multiplicity of infection (by neutralization or other immune mechanisms), thereby preventing efficient mixed infection of enterocytes.

Comparative studies of the antigenic polypeptide species VP4, VP6, and VP7 of three strains of bovine rotavirus

Three bovine rotavirus strains belonging to two distinct serotype groups, serotype 6 (NCDV and B641) and B223, distinct from the other six mammalian rotavirus serotypes but not yet assigned to a serotype group, were compared with each other and with canine rotavirus (K9, serotype 3) by studying the properties of their cognate polypeptide species VP4, VP6, and VP7. The three viruses showed distinct differences in the polyacrylamide gel electrophoretic migration rates of protein species VP4 and VP7, with minor differences in VP6. Differences were also observed among the migration patterns of genome segments 4, 6, and the 7-8-9 triplet, which encode VP4, VP6, and VP7, respectively. Monoclonal antibodies (MAbs) to B223, which were directed against VP4 or VP7, showed homologous specificity for neutralization and immunofluorescence (IF), although one MAb reactive with VP4 also reacted by IF and by immunoprecipitation (IP) with all four viruses and weakly neutralized B641 and K9. This MAb may react with the epitope responsible for the B223-induced one-way neutralizing and protection response of calves against B641 observed in earlier studies. MAbs reactive with VP6 by IP showed enzyme-linked immunosorbent assay and IF reactivity with all three bovine viruses and the canine virus. The two serotype 6 viruses could be distinguished by the two B641 MAbs, B641-N2b reacting by neutralization and IF with both viruses and B641-N1 reacting with B641 and the serotype 3 canine rotavirus but not with NCDV. One nonneutralizing B641 MAb reacted by IP and IF with VP7 of all four rotaviruses examined, and one B223 MAb neutralized B223 and, to low titer, B641 and K9 although reacting by IP and IF with all four viruses. Three MAb-resistant mutants were selected by passage of B223 in the presence of one of three selected B223 MAbs at concentrations which only neutralized approximately 90% of the infectious virions. The resulting mutants were 100% resistant to neutralization with their respective MAb but remained neutralizable by the same selection of MAbs as the parent B223 virus.

Rotavirus-specific cytotoxic T lymphocytes appear at the intestinal mucosal surface after rotavirus infection

The gastrointestinal tract is constantly exposed to a variety of potentially invasive bacteria and viruses. The first line of defense of the host against these pathogens is the intestinal mucosal surface, which consists of epithelial cells, intraepithelial lymphocytes (IELs), mucus, and secretory immunoglobulins. Little is known about the function, memory, or trafficking of IELs after intestinal infection. We found that IELs obtained 6 days after oral inoculation of mice with the intestinal pathogen rotavirus (simian strain RRV) lysed rotavirus-infected target cells; cytotoxic T lymphocytes (CTLs) were responsible for rotavirus-specific cytotoxic activity. Rotavirus-specific cytotoxic activity by IELs was (i) eliminated by treatment with Thy 1.2-specific immunoglobulin M plus complement, (ii) restricted by proteins encoded at the major histocompatibility complex, and (iii) absent in mock-infected animals. Oral inoculation of mice with RRV also induced rotavirus-specific CTLs in splenic and intestinal lymphocytes (mesenteric lymph nodes, Peyer's patch). Parenteral inoculation induced rotavirus-specific CTLs in splenic, intestinal (IELs, mesenteric lymph nodes, Peyer's patch), and nonintestinal lymphocytes (inguinal nodes). Therefore, presentation of rotavirus to the intestinal mucosal surface was not necessary to induce IELs with virus-specific cytotoxic activity. At 4 weeks after oral or parenteral inoculation of mice with RRV, rotavirus-specific CTL precursors appeared among splenic, Peyer's patch, inguinal, and mesenteric node lymphocytes, but not among IELs. IELs with rotavirus-specific cytotoxic activity may be generated from precursors at a site other than the intestinal mucosal surface. Part of the response of the host to enteric infection may include surveillance and lysis of virus-infected villus epithelial cells by IELs.

Rotavirus-specific protein synthesis is not necessary for recognition of infected cells by virus-specific cytotoxic T lymphocytes

We found that rotavirus-specific protein synthesis was not necessary for recognition by virus-specific cytotoxic T lymphocytes (CTLs). In addition, CTLs lysed rotavirus-infected target cells prior to production of infectious virus. Target cell processing of rotavirus antigens for presentation to CTLs was enhanced by treatment of rotavirus with trypsin prior to infection; trypsin-induced cleavage of the viral hemagglutinin (vp4) has previously been found to facilitate rotavirus entry into target cells by direct penetration of virions through the plasma membrane. We conclude that sufficient quantities of exogenous viral proteins may be introduced into the cytoplasm for processing by target cells. The mechanism by which rotavirus proteins are processed for presentation to the target cell surface remains to be determined.

Noninfectious rotavirus (strain RRV) induces an immune response in mice which protects against rotavirus challenge

We found that female adult mice parenterally inoculated with noninfectious rotavirus (simian strain RRV) developed virus-specific neutralizing antibodies in the serum; newborn mice from these dams were protected against RRV-induced gastroenteritis. In addition, mice parenterally inoculated with noninfectious RRV developed virus-specific cytotoxic T-lymphocyte precursors in the spleen. Replication of rotavirus in intestinal epithelial cells was apparently not required to induce rotavirus-neutralizing antibodies or rotavirus-specific cytotoxic T lymphocytes. Parenteral immunization of infants and young children with noninfectious rotaviruses may induce an immune response which protects against rotavirus challenge.

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.

The reovirus-specific cytotoxic T cell response is not restricted to serotypically unique epitopes associated with the virus hemagglutinin

Reovirus, a virus that contains neither an envelope nor glycosylated polypeptides, has been found to induce virus-specific, major histocompatibility complex (MHC) class I antigen restricted, cytotoxic T lymphocyte (CTL) responses. The cytotoxic T cells require in vitro stimulation in the presence of virus to phenotypically express cytotoxic activity. Utilizing reovirus types 1 and 3, the CTLs derived from mice infected with one serotype can lyse target cells infected with a second serotype of reovirus. In addition, lymphocytes primed in vivo with one serotype develop into fully functional CTLs during in vitro stimulation with the other serotype of reovirus. Therefore, these results suggest that reovirus induced CTLs are virus, but not serotype specific. Common determinants shared by reovirus polypeptides from reovirus types 1 and 3 are most likely the stimuli for the majority of CTLs responses to reovirus.

Immunological aspects of interaction between rotavirus and the intestine in infancy

Rotaviruses are important pathogens causing severe diarrhoea in human infants and young animals. Available information on the pathogenic mechanisms of and the immune response to rotaviruses is reviewed here. Studies in our laboratory using the suckling mouse model have focused on elucidating the nature of interaction between the virus and the gut, and on the importance of T and B cell mediated immunity in protection and recovery from the disease. Our data suggest that the age dependence of mouse rotavirus (MRV) infection is related to the presence of virus-specific receptors on the enterocytes. The uptake of rotavirus antigens appears to be limited to the epithelium associated with Peyer's patches. The antigen is transported to local and regional lymph nodes. Recent studies have indicated that rotavirus infection also increases the uptake of other macromolecules in the intestine. Rotavirus-specific mucosal IgA response seems to be related to the location and magnitude of MRV antigen in the lymph follicles in different segments of the small intestine. Studies in mice with different types of immunodeficiency suggest that a specific immune response is required for complete resolution of virus infection. Several parameters of immunity to rotavirus infection have been examined and, similar to other reports, local immunity in the intestine appears to have the most important role in protection. It also has been observed that nutritional factors may be important in modifying disease. However, there are still many questions to be answered concerning the role of immunity in mediating the pathogenesis of rotavirus infection.