Relative importance of rotavirus-specific effector and memory B cells in protection against challenge

Development and function of tissue-resident memory B cells

Barrier tissues are the primary site of infection for pathogens likely to cause future pandemics. Tissue-resident lymphocytes can rapidly detect pathogens upon infection of barrier tissues and are critical in preventing viral spread. However, most vaccines fail to induce tissue-resident lymphocytes and are instead reliant on circulating antibodies to mediate protective immunity. Circulating antibody titers wane over time following vaccination leaving individuals susceptible to breakthrough infections by variant viral strains that evade antibody neutralization. Memory B cells were recently found to establish tissue residence following infection of barrier tissues. Here, we summarize emerging evidence for the importance of tissue-resident memory B cells in the establishment of protective immunity against viral and bacterial challenge. We also discuss the role of tissue-resident memory B cells in regulating the progression of non-infectious diseases. Finally, we examine new approaches to develop vaccines capable of eliciting barrier immunity.

Microbial-Driven Immunological Memory and Its Potential Role in Microbiome Editing for the Prevention of Colorectal Cancer

Over the last several years, many advances have been made in understanding the role of bacteria in the pathogenesis of gastrointestinal cancers. Beginning with Helicobacter pylori being recognized as the first bacterial carcinogen and the causative agent of most gastric cancers, more recent studies have examined the role of enteric microbes in colorectal cancer. In the digestive tract, these communities are numerous and have a complex interrelationship with local immune/inflammatory responses that impact the health of the host. As modifying the microbiome in the stomach has decreased the risk of gastric cancer, modifying the distal microbiome may decrease the risk of colorectal cancers. To date, very few studies have considered the notion that mucosal lymphocyte-dependent immune memory may confound attempts to change the microbial components in these communities. The goal of this review is to consider some of the factors impacting host-microbial interactions that affect colorectal cancer and raise questions about how immune memory responses to the local microbial consortium affect any attempt to modify the composition of the intestinal microbiome.

Surface Display of Antigen Protein VP8* of Porcine Rotavirus on Bacillus Subtilis Spores Using CotB as a Fusion Partner

Porcine rotavirus is a major cause of acute viral gastroenteritis in suckling piglets, and vaccination is considered to be an effective measure to control these infections. The development of a live mucosal vaccine using Bacillus subtilis spores as an antigen delivery vehicle is a convenient and attractive vaccination strategy against porcine rotavirus. In this study, a shuttle vector was constructed for the spore surface display of the spike protein VP8* from porcine rotavirus (the genotype was G5P[7]). A successful display of the CotB-VP8* fusion protein on the spore surface was confirmed by Western blot and immunofluorescence microscopy analysis. The capacity for immune response generated after immunization with the recombinant strain was evaluated in a mouse model. The intestinal fecal IgA and serum IgG were detected by enzyme-linked-immunosorbent serologic assay (ELISA). Importantly, recombinant strain spores could elicit strong specific mucosal and humoral immune responses. These encouraging results suggest that recombinant B. subtilis BV could provide a strategy for a potential novel application approach to the development of a new and safe mucosal subunit vaccine against porcine rotavirus.

Enhancement of VP6 immunogenicity and protective efficacy against rotavirus by VP2 in a genetic immunization

VP2/VP6 virus like particles (VLPs) are very effective in inducing protection against the rotavirus infection in animal models. Individually, VP6 can also induce protection. However, there is no information about the immunogenicity of VP2. The aim of this work was to evaluate the efficacy of DNA vaccines codifying for VP2 or VP6, alone or combined, to induce protection against the rotavirus infection. Murine rotavirus VP2 and VP6 genes were cloned into the pcDNA3 vector. Adult BALB/c mice were inoculated three times by intramuscular (i.m.) injections with 100 or 200µg of pcDNA3-VP2 or pcDNA3-VP6 alone or co-administered with 100µg of pcDNA3-VP2/100µg of pcDNA3-VP6. Two weeks after the last inoculation, mice were challenged with the wild type murine rotavirus strain epizootic diarrhea of infant mice (EDIM_wt). We found that both plasmids, pcDNA3-VP2 and pcDNA3-VP6, were able to induce rotavirus-specific serum antibodies, but not intestinal rotavirus-specific IgA; only 200µg of pcDNA3-VP6 induced 35% protection against the infection. A similar level of protection was found when mice were co-administered with 100µg of pcDNA3-VP2/100µg of pcDNA3-VP6 (1:1 ratio). However, the best protection (up to 58%) occurred when mice were inoculated with 10µg of pcDNA3-VP2/100µg of pcDNA3-VP6 (1:10 ratio). These results indicate that the DNA plasmid expressing VP6 is a better vaccine candidate that the one expressing VP2. However, when co-expressed, VP2 potentiates the immunogenicity and protective efficacy of VP6.

Challenges to Developing a Rotavirus Vaccine

Rotavirus is the most important cause of gastroenteritis worldwide. In developing countries, the virus is a major cause of death in infants and young children. In the United States, before the licensure of vaccines, rotavirus infections accounted for ∼2.7 million cases of gastroenteritis annually. Here are described the history and challenges surrounding the development of a rotavirus vaccine.

Rotavirus infection of infant and young adult nonobese diabetic mice involves extraintestinal spread and delays diabetes onset

Rotaviruses have been implicated as a possible viral trigger for exacerbations in islet autoimmunity, suggesting they might modulate type 1 diabetes development. In this study, the ability of rotavirus strain RRV to infect the pancreas and affect insulitis and diabetes was examined in nonobese diabetic (NOD) mice, an experimental model of type 1 diabetes. Mice were inoculated either orally or intraperitoneally as infants or young adults. In infant mice inoculated orally, rotavirus antigen was detected in pancreatic macrophages outside islets and infectious virus was found in blood cells, pancreas, spleen, and liver. Extraintestinal RRV spread and pancreatic presence of infectious virus also occurred in intraperitoneally inoculated infant and adult mice. The initiation of insulitis was unaltered by infection. The onset of diabetes was delayed in infant mice inoculated orally and infant and adult mice inoculated intraperitoneally. In contrast, adult mice inoculated orally showed no evidence of pancreatic RRV, the lowest rate of detectable RRV replication, and no diabetes modulation. Thus, the ability of RRV infection to modulate diabetes development in infant and young adult NOD mice was related to the overall extent of detectable virus replication and the presence of infectious virus extraintestinally, including in the pancreas. These studies show that RRV infection of infant and young adult NOD mice provides significant protection against diabetes. As these findings do not support the hypothesis that rotavirus triggers autoimmunity related to type 1 diabetes, further research is needed to resolve this issue.

Induction of mucosal B-cell memory by intranasal immunization of mice with respiratory syncytial virus

The capacity of live or inactivated respiratory syncytial virus (RSV) to induce B-cell memory in respiratory-associated lymphoid tissues of mice was examined. Eight weeks after primary inoculation with either live or inactivated RSV, adult BALB/c mice were challenged with 4x10(5) PFU of RSV. Protection from viral shedding and mucosal production of RSV-specific antibodies were examined at various time points after challenge. We found that primary immunization with live, but not inactivated, RSV induced complete and durable protection upon challenge within the upper and lower respiratory tract. Also, primary immunization with live, but not inactivated, RSV enhanced the production of mucosal RSV-specific immunoglobulin A (IgA) upon challenge. Secondary mucosal IgA responses were characterized by (i) the early production of mucosal IgA by B cells that reside in organized nasal-associated lymphoid tissues, cervical lymph nodes, and bronchial lymph nodes, and (ii) the subsequent production of RSV-specific IgA by mucosal effector tissues, such as the tracheal lamina propria and lung. These findings suggest that primary infection of mice with live RSV might induce mucosal IgA-committed memory B cells. A greater understanding of the characteristics of RSA-specific mucosal memory B cells may facilitate the development of an RSV vaccine.

Inability to evoke a long-lasting protective immune response to respiratory syncytial virus infection in mice correlates with ineffective nasal antibody responses

Long-lasting protective antibody is not normally generated in children following primary respiratory syncytial virus (RSV) infection, frequently leading to reinfection. We used the BALB/c mouse model to examine the role of the nasal-associated lymphoid tissue and the bone marrow in the generation of RSV-specific long-lasting plasma cells, with a view to further understanding the mechanisms responsible for the poorly sustained RSV antibody levels following primary infection. We show here that substantial numbers of RSV-specific plasma cells were generated in the bone marrow following challenge, which were maintained thereafter. In contrast, in the nasal-associated lymphoid tissue, RSV-specific plasma cell numbers waned quickly both after primary infection and after challenge and were not maintained at a higher level after boosting. These data indicate that the inability to generate a robust local mucosal response in the nasal tissues may contribute substantially to the likelihood of subsequent reinfection and that the presence of serum anti-RSV antibody without local protection is not enough to protect against reinfection.

Possible mechanisms of protection elicited by candidate rotavirus vaccines as determined with the adult mouse model

Rotaviruses cause extensive morbidity and mortality worldwide each year, supporting the need for a vaccine that is effective against rotavirus disease in all socioeconomic environments. Vaccines evaluated in clinical trials have all been live viruses that are delivered orally to mimic the excellent protection against severe rotavirus disease consistently observed after natural infection. The mechanisms by which either these vaccine candidates or natural rotavirus infections elicit protection are poorly understood. Therefore, it is not surprising that several of these candidate vaccines have provided little or no protection and have been discontinued. Two candidate vaccines are presently in phase III trials. These two were developed on the basis of very different views regarding the importance of one specific immune effector, that is, serotype-specific neutralizing antibody. One of these candidates (RotaTeq) is composed of five bovine/human reassortant rotavirus strains containing neutralization proteins representative of dominant human serotypes. The other candidate (Rotarix) is composed of only a single strain of human rotavirus. Very recent data obtained with Rotarix support the suggestion that factors other than neutralizing antibody can play important roles in protection against rotavirus disease after live rotavirus immunization. These results must be confirmed in subsequent studies in different locales with circulating rotaviruses belonging to a variety of serotypes in order to establish there overall applicability. Mechanisms by which rotavirus immunization with live viruses or other immunogens elicit protection have been most extensively examined in an adult mouse model and were reported to be multi-factorial. That is, CD8 and CD4 T cells as well as B cells were all found to play significant roles. The importance of each lymphocyte population as effectors of protection was found to be dependent on the immunogen and the route of immunization. The results of studies in the adult mouse model that appear to be most pertinent to the present vaccine candidates are presented and discussed.

Growth of rotaviruses in primary pancreatic cells

Rotavirus infection in children at risk of developing type 1 diabetes has been temporally associated with development of pancreatic islet autoantibodies. In this study, nonobese diabetic mice were shown to be susceptible to rhesus rotavirus infection and pancreatic islets from nonobese diabetic mice, nonobese diabetes-resistant mice, fetal pigs, and macaque monkeys supported various degrees of rotavirus growth. Human rotaviruses replicated in monkey islets only. This islet susceptibility shows that rotavirus infection of the pancreas in vivo might be possible.

Differences between the large and small intestine in the immunodominant amoebic proteins recognized by IgG and IgA antibodies in BALB/c mice

We have previously reported that there are differences in the number of predominant amoebic antigens recognized by serum and small intestinal antibodies induced after local and systemic immunization with glutarldehyde-fixed Entamoeba histolytica trophozoites (GFT) in BALB/c mice, by an immunoblot analysis. Moreover, by enzyme-linked immunosorbent assay (ELISA) analysis, we found differences in the antiamoebic antibody isotype patterns elicited at the large and small intestines. To further characterize the antiamoebic immune response induced in BALB/c mice, after local (oral and rectal) and systemic (intraperitoneal and intramuscular) immunization with GFT, we performed an immunoblot analysis of the amoebic proteins predominantly recognized by immunoglobulins (Ig)G, IgA and IgM in the serum and in the small and large intestines. The present work shows differences between the large and small intestine in the IgG- and IgA-antibody recognition pattern of amoebic proteins, thus confirming and extending our previous findings supporting the compartmentalization of the intestinal immune response. Furthermore, our reported observation that there are differences in the amoebic proteins predominantly recognized by antibodies of different isotypes was extended to the intestines, as some proteins with relative molecular weights of 24-25, 66, 140 kDa are strongly recognized by IgG but not by other antibody isotypes.

Distribution of rotavirus-specific memory B cells in gut-associated lymphoid tissue after primary immunization

We found previously that mice inoculated orally with simian rotavirus strain RRV developed virus-specific memory B cell responses 16 weeks after immunization that were greater than those found 6 weeks after immunization. Memory B cell responses were defined as the quantity of virus-specific IgA detected in small intestinal lamina propria (LP) fragment cultures of immunized mice at various intervals after challenge. Enhanced memory B cell responses correlated with enhanced protection against shedding. In order to understand better the delayed onset of rotavirus-specific memory B cell responses, a method was developed to determine the frequencies of rotavirus-specific memory B cells in gut-associated lymphoid tissues (GALT). We found that protection against rotavirus challenge was determined by the frequency of rotavirus-specific memory B cells in GALT LP.

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.

Short-term immunoglobulin A B-cell memory resides in intestinal lymphoid tissues but not in bone marrow of gnotobiotic pigs inoculated with Wa human rotavirus

Immunological memory is important for protecting the host from reinfection. To investigate the development and sites of residence of intestinal memory B cells, and their role in protective immunity to reinfection with an enteric virus, we assessed the association between memory B cell and antibody-secreting cell (ASC) responses and protection using a gnotobiotic pig model for human rotavirus (HRV) infection and diarrhoea. The isotypes, quantities and tissue distribution of rotavirus-specific memory B cells and ASC were evaluated prechallenge (28 and 83 postinoculation days [PID]) and postchallenge (7 postchallenge days [PCD]), using enzyme-linked immunospot (ELISPOT) assay, in gnotobiotic pigs inoculated once with virulent or three times with attenuated HRV and challenged at PID 28 with the corresponding virulent HRV. Complete protection against HRV shedding and diarrhoea was associated with significantly higher numbers of immunoglobulin A (IgA) and immunoglobulin G (IgG) memory B cells and ASC in the ileum of virulent HRV-inoculated pigs at challenge. In contrast, pigs inoculated with attenuated HRV had lower numbers of IgA and IgG memory B cells and ASC in intestinal lymphoid tissues, but higher numbers in the spleen. The bone marrow had the lowest mean numbers of IgA and IgG memory B cells and ASC prechallenge in both groups of HRV-inoculated pigs. Therefore, bone marrow was not a site for IgA and IgG rotavirus-specific antibody production or for memory B cells after inoculation with live rotavirus, from 28 PID up to at least 83 PID. The effect of in vitro antigen dose was examined and it was determined to play an important role in the development of ASC from memory B cells for the different tissues examined.

T-cell-independent responses to Borrelia burgdorferi are critical for protective immunity and resolution of lyme disease

The humoral immune response to Borrelia burgdorferi during persistent infection is critical to both protective and disease-resolving immunity. This study examined the role of B cells in the absence of T cells during these events, using mice with selected immune dysfunctions. At 6 weeks postinfection, an interval at which arthritis resolves in immunocompetent mice, arthritis severity was equivalent among immunocompetent mice, alphabeta(+)-T-cell-deficient mice, and mice lacking both alphabeta(+) and gammadelta(+) T cells. Arthritis severity was worse in SCID mice, which lack T and B lymphocytes. Carditis regressed in immunocompetent mice and those lacking both alphabeta(+) and gammadelta(+) T cells but remained active in mice lacking only alphabeta(+) T cells and in SCID mice. Mice lacking only alphabeta(+) T cells and those lacking both alphabeta(+) and gammadelta(+) T cells generated immunoglobulin M (IgM) and IgG3 B. burgdorferi-reactive antibodies. Sera from infected immunocompetent mice, mice lacking only alphabeta(+) T cells, and mice lacking both alphabeta(+) and gammadelta(+) T cells passively protected naive mice against challenge inoculation with B. burgdorferi. However, only sera from infected immunocompetent mice, but not sera from infected T-cell-deficient mice, were able to resolve arthritis when passively transferred to actively infected SCID mice. These data demonstrate that B-cell activation during a T-cell-independent response may be critical for resolution of arthritis and carditis and that protective antibodies are generated during this response.

Primary murine small intestinal epithelial cells, maintained in long-term culture, are susceptible to rotavirus infection

We describe a method for long-term culture of primary small intestinal epithelial cells (IEC) from suckling mice. IEC were digested from intestinal fragments as small intact units of epithelium (organoids) by using collagenase and dispase. IEC proliferated from organoids on a basement-membrane-coated culture surface and remained viable for 3 weeks. Cultured IEC had the morphologic and functional characteristics of immature enterocytes, notably sustained expression of cytokeratin and alkaline phosphatase. Few mesenchymal cells were present in the IEC cultures. IEC were also cultured from adult BALB/c mice and expressed major histocompatibility complex (MHC) class II antigens for at least 48 h in vitro. Primary IEC supported the growth of rhesus rotavirus (RRV) to a greater extent than a murine small intestinal cell line, m-IC(cl2). Cell-culture-adapted murine rotavirus strain EDIM infected primary IEC and m-IC(cl2) cells to a lesser extent than RRV. Wild-type EDIM did not infect either cell type. Long-term culture of primary murine small intestinal epithelial cells provides a method to study (i) virus-cell interactions, (ii) the capacity of IEC to act as antigen-presenting cells using a wide variety of MHC haplotypes, and (iii) IEC biology.

Rotavirus Vaccines: Current Controversies and Future Directions

Rotaviruses are the most important cause of pediatric gastroenteritis worldwide. In August 1998, a new rotavirus vaccine was licensed for general use in the United States. However, 14 months later, the vaccine was withdrawn from the market because of serious gastrointestinal side effects. This paper discusses the need for a rotavirus vaccine, the development of the first rotavirus vaccine, and the safety issues that led to the recall of that vaccine.

Rotavirus infections: guidelines for treatment and prevention

The classification of rotaviruses as well as the pathogenesis and the diagnosis of rotavirus infections are briefly reviewed. Treatment of rotavirus disease consists mainly of oral or intravenous rehydration, using World Health Organization-recommended oral rehydration solutions or lactated Ringer's solutions, respectively. Specific antivirals have been tried in animal models but are not used for human treatment at present. The epidemiology of rotaviruses is complex as at any one time and in any geographical area different types co-circulate. The development of rotavirus candidate vaccines is reviewed, one of which, the tetravalent, rhesus rotavirus-based human reassortant vaccine, was licensed for universal use in the US in 1998. Its implementation requires careful surveillance of co-circulating rotavirus types (molecular epidemiology) as well as of any potential adverse effects not previously detected.

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.

Antibody responses and protection stimulated by sequential oral-parenteral immunization of mice with rotavirus

Antibody responses and protection against shedding following oral challenge with murine rotavirus (EDIM) were determined in mice after sequential oral parenteral immunization. Oral immunization of 4-day-old BALB/c mice with live, heterologous rotavirus (RRV) stimulated serum rotavirus IgG but little serum or intestinal rotavirus IgA and small but significant (P < 0.001) reductions in EDIM shedding. Intraperitoneal immunization with inactivated EDIM at 29 days of age had similar effects. Sequential oral-parenteral immunization under these conditions stimulated small but significant (P < 0.001) increases in both rotavirus IgG and IgA titers and reduced shedding (P < 0.001) compared to individual immunizations. However, these responses were essentially additive, indicative of separate inductive/effector sites for mucosal and systemic immunity.

T-cell-independent antiviral antibody responses

Recent work has shown that viruses can act in vivo as T-cell-independent antigens, eliciting protective, isotype-switched antibodies in the absence of conventional TCR alpha beta+ T cell help. Inactivated virus or virus-like particles can stimulate IgM production, but factors induced during live virus infection appear to be required to induce the isotype switch that leads to IgG or IgA responses.

Effect of water-based microencapsulation on protection against EDIM rotavirus challenge in mice

We determined the capacity of microcapsules formed by the combination of sodium alginate, an aqueous anionic polymer, and spermine hydrochloride, an aqueous cationic amine, to enhance protection against rotavirus challenge in mice. Adult BALB/c mice were orally inoculated with either free or microencapsulated rotavirus (simian rotavirus strain RRV) and challenged 6 or 16 weeks later with murine rotavirus strain EDIM. Virus-specific humoral immune responses were determined at the time of challenge and 4 days after challenge by intestinal fragment culture. We found that spermine-alginate microcapsules enhanced protection against challenge 16 weeks after immunization but not 6 weeks after immunization. Quantities of virus-specific immunoglobulin A produced by small intestinal lamina propria lymphocytes were correlated with the degree of protection against challenge afforded by spermine-alginate microcapsules. Possible mechanisms by which microcapsules enhance protection against rotavirus challenge are discussed.