Simple methods for measurement of bovine mucosal antibody responses in vivo

A curated multivariate approach to study efficacy and optimisation of a prototype vaccine against teladorsagiasis in sheep

This work discusses and demonstrates the novel use of multivariate analysis and data dimensionality reduction techniques to handle the variety and complexity of data generated in efficacy trials for the development of a prototype vaccine to protect sheep against the Teladorsagia circumcincta nematode. A curated collection of data dimension reduction and visualisation techniques, in conjunction with sensible statistical modelling and testing which explicitly model key features of the data, offers a synthetic view of the relationships between the multiple biological parameters measured. New biological insight is gained into the patterns and associations involving antigen-specific antibody levels, antibody avidity and parasitological parameters of efficacy that is not achievable by standard statistical practice in the field. This approach can therefore be used to guide vaccine refinement and simplification through identifying the most immunologically relevant antigens, and it can be analogously implemented for similar studies in other areas. To facilitate this, the associated data and computer codes written for the R open system for statistical computing are made freely available.

Mucosal IFNγ production and potential role in protection in Escherichia coli O157:H7 vaccinated and challenged cattle

Shiga-toxin producing Escherichia coli O157:H7 (O157)-based vaccines can provide a potential intervention strategy to limit foodborne zoonotic transmission of O157. While the peripheral antibody response to O157 vaccination has been characterized, O157-specific cellular immunity at the rectoanal junction (RAJ), a preferred site for O157 colonization, remains poorly described. Vaccine induced mucosal O157-specific antibodies likely provide some protection, cellular immune responses at the RAJ may also play a role in protection. Distinct lymphoid follicles were increased in the RAJ of vaccinated/challenged animals. Additionally, increased numbers of interferon (IFN)γ-producing cells and γδ + T cells were detected in the follicular region of the RAJ of vaccinated/challenged animals. Likewise, adjuvanted-vaccine formulation is critical in immunogenicity of the O157 parenteral vaccine. Local T cell produced IFNγ may impact epithelial cells, subsequently limiting O157 adherence, which was demonstrated using in vitro attachment assays with bovine epithelial cells. Thus, distinct immune changes induced at the mucosa of vaccinated and challenged animals provide insight of mechanisms associated with limiting O157 fecal shedding. Enhancing mucosal immunity may be critical in the further development of efficacious vaccines for controlling O157 in ruminants and thus limiting O157 transmission to humans.

Comparison of Lethal and Nonlethal Sampling Methods for the Detection of Largemouth Bass Virus (LMBV) from Largemouth Bass in the Upper Mississippi River

Traditional methodologies to identify fish pathogens require euthanasia before the collection of tissue samples. While these methods are standardized and proven, there are instances where nonlethal alternatives would be preferred. Despite the need to develop nonlethal sampling techniques, few publications have focused on them and even fewer have used these approaches to identify viruses from infections occurring in wild fish populations. In this study, we compared the ability of nonlethal sampling techniques with traditional methods for the detection of Largemouth Bass virus (LMBV) from a wild population of Largemouth Bass Micropterus salmoides from the upper Mississippi River. Largemouth bass virus was isolated from 30% of the Largemouth Bass sampled using traditional methods where tissue samples were inoculated on Bluegill fry (BF-2) cells. Furthermore, when using tissue cell culture to isolate LMBV, there was no significant difference observed in the overall proportion that was positive between the mucus samples and the kidney and spleen samples. Mucus swabs analyzed with molecular methods (conventional PCR and quantitative PCR) were more sensitive than traditional tissue cell culture-based methods as they detected LMBV from >70% of the samples; limitations to these methods (i.e., carryover contamination) were also identified. The results of this study suggest that nonlethal sampling may be a useful option for detecting LMBV from fish populations.

Identification of epitopes recognised by mucosal CD4(+) T-cell populations from cattle experimentally colonised with Escherichia coli O157:H7

Vaccines targeting enterohaemorrhagic Escherichia coli (EHEC) O157:H7 shedding in cattle are only partially protective. The correlates of protection of these vaccines are unknown, but it is probable that they reduce bacterial adherence at the mucosal surface via the induction of blocking antibodies. Recent studies have indicated a role for cellular immunity in cattle during colonisation, providing an impetus to understand the bacterial epitopes recognised during this response. This study mapped the epitopes of 16 EHEC O157:H7 proteins recognised by rectal lymph node CD4(+) T-cells from calves colonised with Shiga toxin producing EHEC O157:H7 strains. 20 CD4(+) T-cell epitopes specific to E. coli from 7 of the proteins were identified. The highly conserved N-terminal region of Intimin, including the signal peptide, was consistently recognised by mucosal CD4(+) T-cell populations from multiple animals of different major histocompatibility complex class II haplotypes. These T-cell epitopes are missing from many Intimin constructs used in published vaccine trials, but are relatively conserved across a range of EHEC serotypes, offering the potential to develop cross protective vaccines. Antibodies recognising H7 flagellin have been consistently identified in colonised calves; however CD4(+) T-cell epitopes from H7 flagellin were not identified in this study, suggesting that H7 flagellin may act as a T-cell independent antigen. This is the first time that the epitopes recognised by CD4(+) T-cells following colonisation with an attaching and effacing pathogen have been characterised in any species. The findings have implications for the design of antigens used in the next generation of EHEC O157:H7 vaccines.

Fecal antibody levels as a noninvasive method for measuring immunity to gastrointestinal nematodes in ecological studies

Among‐individual variation in antibody‐associated immunity to gastrointestinal nematode parasites (GIN) is known be associated with life‐history traits and vital rates in wild vertebrate systems. To date, measurement of levels of antibodies against GIN antigens in natural populations has exclusively been based on invasive blood sampling techniques. Previous work in laboratory rodents and ruminant livestock suggests that antibody measures from feces may provide a viable noninvasive approach. We measured total and anti‐GIN antibodies of different isotypes (immunoglobulin (Ig) G, IgA and IgE) from paired samples of plasma and feces from free‐living Soay sheep of different ages and sexes. We tested the correlations among these measures as well as their associations with body mass and Strongyle nematode fecal egg counts (FEC). Significant positive correlations were present among plasma and fecal anti‐GIN antibody levels for IgG and IgA. Generally, correlations between total antibody levels in plasma and feces were weaker and not significant. No significant relationships were found between any antibody measures and body mass; however, fecal anti‐GIN antibody levels were significantly negatively correlated with FEC. Our data clearly demonstrate the feasibility of measuring anti‐GIN antibodies from fecal samples collected in natural populations. Although associations of fecal antibody levels with their plasma counterparts and FEC were relatively weak, the presence of significant correlations in the predicted direction in a relatively small and heterogeneous sample suggests fecal antibody measures could be a useful, noninvasive addition to current eco‐immunological studies.

Regional immune response to immunization with Escherichia coli O157:H7-derived intimin in cattle

Escherichia coli O157:H7 is an enteric pathogen of animals and humans that can result in deadly sequelae. Cattle are asymptomatic carriers and shedders of the bacteria and serve as an important reservoir of human infection. E. coli O157:H7 colonizes the gastrointestinal tract, most frequently at the rectoanal junction mucosa in cattle. Vaccination is a potentially highly effective means of decreasing cattle colonization and shedding and thereby decreasing human infections. Currently available vaccines are administered subcutaneously or intramuscularly, and immune responses have been evaluated solely by systemic immunoglobulin responses. This study evaluated local and systemic lymphoproliferative responses in addition to immunoglobulin responses following subcutaneous or mucosal (rectal) immunization with E. coli O157:H7 outer membrane protein intimin over three trials. In all three trials, significant local and systemic lymphoproliferative responses (P < 0.05) occurred following immunization in the majority of animals, as well as significant immunoglobulin responses (P < 0.001) in all animals. Surprisingly, local responses in the mesorectal lymph nodes were very similar between the subcutaneous and mucosal immunization groups. Moreover, the responses in mesorectal lymph nodes appeared targeted rather than generalized, as minimal or no significant responses were observed in the associated prescapular lymph nodes of subcutaneously immunized animals. The results indicate that both subcutaneous and mucosal immunizations are effective methods of inducing immune responses against E. coli O157:H7 in cattle.

Immunization of cattle with a combination of purified intimin-531, EspA and Tir significantly reduces shedding of Escherichia coli O157:H7 following oral challenge

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a human pathogen that can cause gastrointestinal disease with potentially fatal consequences as a result of systemic Shiga toxin activity. Cattle are the main reservoir host of EHEC O157 and interventions need to be developed that prevent cattle colonization or limit shedding of the organism from this host. EHEC O157 predominately colonizes the bovine terminal rectum and requires a type III secretion system (T3SS) for adherence and persistence at this site. A vaccine based on concentrated bacterial supernatant that contains T3S proteins has shown some efficacy. Here we have demonstrated that vaccination with a combination of antigens associated with T3S-mediated adherence; the translocon filament protein, EspA, the extracellular region of the outer membrane adhesin, intimin, and the translocated intimin receptor (Tir) significantly reduced shedding of EHEC O157 from experimentally infected animals. Furthermore, this protection may be augmented by addition of H7 flagellin to the vaccine preparation that has been previously demonstrated to be partially protective in cattle. Protection correlates with systemic and mucosal antibody responses to the defined antigens and validates the targeting of these colonization factors.

The Escherichia coli O157:H7 EhaB autotransporter protein binds to laminin and collagen I and induces a serum IgA response in O157:H7 challenged cattle

Enterohaemorrhagic Escherichia coli (EHEC) are a subgroup of Shiga toxin-producing E.  coli that cause gastrointestinal disease with the potential for life-threatening sequelae. Cattle serve as the natural reservoir for EHEC and outbreaks occur sporadically as a result of contaminated beef and other farming products. While certain EHEC virulence mechanisms have been extensively studied, the factors that mediate host colonization are poorly defined. Previously, we identified four proteins (EhaA,B,C,D) from the prototypic EHEC strain EDL933 that belong to the autotransporter (AT) family. Here we characterize the EhaB AT protein. EhaB was shown to be located at the cell surface and overexpression in E.  coli K-12 resulted in significant biofilm formation under continuous flow conditions. Overexpression of EhaB in E.  coli K12 and EDL933 backgrounds also promoted adhesion to the extracellular matrix proteins collagen I and laminin. An EhaB-specific antibody revealed that EhaB is expressed in E.  coli EDL933 following in vitro growth. EhaB also cross-reacted with serum IgA from cattle challenged with E.  coli O157:H7, indicating that EhaB is expressed in vivo and elicits a host IgA immune response.

Escherichia coli O157:H7 colonization in small domestic ruminants

Enterohaemorrhagic Escherichia coli O157:H7 was first implicated in human disease in the early 1980s, with ruminants cited as the primary reservoirs. Preliminary studies indicated cattle to be the sole source of E. coli O157:H7 outbreaks in humans; however, further epidemiological studies soon demonstrated that E. coli O157:H7 was widespread in other food sources and that a number of transmission routes existed. More recently, small domestic ruminants (sheep and goats) have emerged as important sources of E. coli O157:H7 human infection, particularly with the widespread popularity of petting farms and the increased use of sheep and goat food products, including unpasteurized cheeses. Although the colonization and persistence characteristics of E. coli O157:H7 in the bovine host have been studied intensively, this is not the case for small ruminants. Despite many similarities to the bovine host, the pathobiology of E. coli O157:H7 in small domestic ruminants does appear to differ significantly from that described in cattle. This review aims to critically review the current knowledge regarding colonization and persistence of E. coli O157:H7 in small domestic ruminants, including comparisons with the bovine host where appropriate.

An investigation of the expression and adhesin function of H7 flagella in the interaction of Escherichia coli O157 : H7 with bovine intestinal epithelium

Enterohaemorrhagic Escherichia coli O157 : H7 is a bacterial pathogen that can cause haemorrhagic colitis and haemolytic uremic syndrome. In the primary reservoir host, cattle, the terminal rectum is the principal site of E. coli O157 colonization. In this study, bovine terminal rectal primary epithelial cells were used to examine the role of H7 flagella in epithelial adherence. Binding of a fliC(H7) mutant O157 strain to rectal epithelium was significantly reduced as was binding of the flagellated wild-type strain following incubation with H7-specific antibodies. Complementation of fliC(H7) mutant O157 strain with fliC(H7) restored the adherence to wild-type levels; however, complementation with fliC(H6) did not restore it. High-resolution ultrastructural and imunofluorescence studies demonstrated the presence of abundant flagella forming physical contact points with the rectal epithelium. Binding to terminal rectal epithelium was specific to H7 by comparison with other flagellin types tested. In-cell Western assays confirmed temporal expression of flagella during O157 interaction with epithelium, early expression was suppressed during the later stages of microcolony and attaching and effacing lesion formation. H7 flagella are expressed in vivo by individual bacteria in contact with rectal mucosa. Our data demonstrate that the H7 flagellum acts as an adhesin to bovine intestinal epithelium and its involvement in this crucial initiating step for colonization indicates that H7 flagella could be an important target in intervention strategies.

Responses of cattle to gastrointestinal colonization by Escherichia coli O157:H7

Recent research has established that the terminal rectum is the predominant colonization site of enterohemorrhagic Escherichia coli O157:H7 in cattle. The main aim of the present work was to investigate pathological changes and associated immune responses at this site in animals colonized with E. coli O157:H7. Tissue and gastrointestinal samples from a total of 22 weaned Holstein-cross calves challenged with E. coli O157:H7 were analyzed for bacterial colonization and pathology. Five unexposed age-matched calves were used as comparative negative controls. E. coli O157:H7 bacteria induced histopathological alterations of the rectal mucosa with enterocyte remodeling. This was often associated with removal of the colonized epithelial layer. Immunogold labeling and transmission electron microscopy (TEM) showed E. coli O157 bacteria on pedestals, as part of attaching and effacing lesions. These pathological changes induced a local infiltration of neutrophils that was quantified as larger in infected animals. Rectal mucosal immunoglobulin A responses were detected against the E. coli O157:H7 antigen. This work presents evidence that E. coli O157:H7 is not a commensal bacteria in the bovine host and that the mucosal damage produced by E. coli O157:H7 colonization of the terminal rectum induces a quantifiable innate immune response and production of specific mucosal antibodies.

Escherichia coli O157:H7 colonization in cattle following systemic and mucosal immunization with purified H7 flagellin

Escherichia coli O157:H7 is an important pathogen of humans. Cattle are most frequently identified as the primary source of infection, and therefore, reduction in E. coli O157:H7 prevalence in cattle by vaccination represents an attractive strategy for reducing the incidence of human disease. H7 flagella have been implicated in intestinal-epithelial colonization of E. coli O157:H7 and may represent a useful target for vaccination. In this study, calves were immunized either systemically with H7 flagellin by intramuscular injection or mucosally via the rectum with either H7 or H7 incorporated into poly(DL-lactide-co-glycolide) microparticles (PLG:H7). Systemic immunization resulted in high levels of flagellin-specific immunoglobulin G (IgG) and IgA in both serum and nasal secretions and detectable levels of both antibody isotypes in rectal secretions. Rectal administration of flagellin resulted in levels of rectal IgA similar to those by the intramuscular route but failed to induce any other antibody response, whereas rectal immunization with PLG:H7 failed to induce any H7-specific antibodies. Following subsequent oral challenge with E. coli O157:H7, reduced colonization rates and delayed peak bacterial shedding were observed in the intramuscularly immunized group compared to nonvaccinated calves, but no reduction in total bacterial shedding occurred. Rectal immunization with either H7 or PLG:H7 had no effect on subsequent bacterial colonization or shedding. Furthermore, purified H7-specific IgA and IgG from intramuscularly immunized calves were shown to reduce intestinal-epithelial binding in vitro. These results indicate that H7 flagellin may be a useful component in a systemic vaccine to reduce E. coli O157:H7 colonization in cattle.