Proliferative haemorrhagic enteropathy

Development and validation of a flow cytometry antibody test for Lawsonia intracellularis

Lawsonia intracellularis is the etiologic agent of porcine proliferative enteropathy (PPE), an inflammatory bowel disease with a major economic impact on the pig industry. The serological diagnosis of PPE can be performed using Blocking or Indirect ELISA, Immunoperoxidase Monolayer Assay (IPMA) and Indirect Fluorescence Antibody Test (IFAT). Here, we designed a most sophisticated immunological method for the detection of porcine anti-L. intracellularis IgGs, named Flow Cytometry Antibody Test - FCAT. This assay uses whole, live-attenuated L. intracellularis bacteria derived from a commercial vaccine. For the assay, we set up the optimal antigen concentration (10⁶ bacterium/assay), primary antibody dilution (1:100), time of incubation (20 min), antigen stability (15 days), precision (coefficient of variation - CV < 10%), reproducibility (CV ≤ 13%) and Receiver Operating Characteristic (ROC). When using a cut-off of >15.15% for FCAT, we determined that it showed a sensitivity of 98.8% and specificity of 100%. The rate of agreement with IPMA was 84.09% with a kappa index of 0.66. FCAT was used to screen 1,000 sera from non-vaccinated pigs housed in 22 different farms and we found that 730 pigs (73%) from 16 farms (72.7%) had L. intracellularis IgG. This high prevalence confirms that L. intracellularis is endemic on Brazilian pig farms. Finally, we determined that FCAT is an easy to perform diagnostic assay and we would highly recommend it for: i) seroepidemiological studies; ii) evaluation of infection dynamics; and iii) characterization of the humoral response profile induced by vaccines.

Evaluation of immunogenicity and protection mediated by Lawsonia intracellularis subunit vaccines

Lawsonia intracellularis is an economically important bacterium that causes ileitis in pigs. Current vaccines for L. intracellularis do not allow for differentiation between infected and vaccinated animals (DIVA), which is beneficial for disease tracking and surveillance. Previously, we identified five putative surface L. intracellularis proteins that were targeted by antibodies from pigs infected with L. intracellularis which could serve as antigens in a subunit vaccine. We conducted two trials to determine whether these antigens were immunogenic and provided protection against infectious challenge and whether truncated glycoprotein D could be used as a DIVA antigen. For Trial 1, 5 week-old piglets were administered intramuscular monovalent vaccines comprised of a recombinant (r) flagella subunit protein (rFliC,) and DIVA antigen (truncated glycoprotein D (TgD), a herpes virus antigen) both formulated with a combination adjuvant consisting of polyinosinic:polycytidylic acid(poly I:C), host defense peptide 1002 and polyphosphazene, referred to as Triple Adjuvant (TriAdj). Relative to control animals, animals vaccinated with rFliC and rTgD had significantly elevated antigen-specific humoral immunity in sera suggesting that rFliC and TgD are immunogenic. Control animals had negligible anti-TgD titres suggesting that TgD may be a suitable DIVA antigen for pigs. For Trial 2, piglets were immunized with a trivalent vaccine (FOG vaccine consisting of rFLiC, rOppA protein (a ABC Type dipeptide transport system) and rGroEL (a stress response protein)) and a divalent vaccine (CM vaccine consisting of rClpP (an ATP-dependent Clp protease proteolytic subunit) and rMetK (a S-adenosyl methionine synthase)) formulated with Emulsigen®. Relative to the control pigs, pigs immunized with the FOG vaccine produced robust and significantly higher serum IgG antibodies against rFliC and rGroEL, and significantly higher anti-FliC and anti-GroEL IgA antibodies in jejunal (GroEL only) and ileal intestinal mucosa. Pigs immunized with CM vaccine produced significantly higher serum antibodies against rClpP and rMetK and significantly higher anti-rClpP IgA antibodies in the ileum relative to the control pigs. Quantitative polymerase chain reaction (qPCR) analysis showed that 18 days after challenge with infectious L. intracellularis, challenged/control pigs and pigs that received the CM vaccine, but not the pigs vaccinated with the FOG vaccine, shed significantly more bacteria in feces than the unchallenged controls pigs. These data suggest that the FOG vaccinated pigs showed limited protection. While promising, more work is needed to enhance the efficiency of the intramuscular vaccine to show significant disease protection.

Review of methods for the detection of Lawsonia intracellularis infection in pigs

Lawsonia intracellularis is an obligate intracellular bacterium associated with enteric disease in pigs. Clinical signs include weight loss, diarrhea, and, in some cases, sudden death. The hallmark lesion is the thickening of the intestinal mucosa caused by increased epithelial cell replication, known as proliferative enteropathy. The immune response to L. intracellularis is not well defined, and detection of the infection, especially in the early stages, is still a significant challenge. We review here the main approaches used to identify this important but poorly understood pathogen. Detection of L. intracellularis infection as the cause of clinical disease is confounded by the high prevalence of the pathogen in many countries and that several other pathogens can produce similar clinical signs. A single L. intracellularis–specific ELISA and several amplification assays are available commercially to aid detection and surveillance, although histopathology remains the primary way to reach a conclusive diagnosis. There are major gaps in our understanding of L. intracellularis pathogenesis, especially how the host responds to infection and the factors that drive infection toward different clinical outcomes. Knowledge of pathogenesis will increase the predictive value of antemortem tests to guide appropriate interventions, including identification and treatment of subclinically affected pigs in the early stages of disease, given that this important manifestation reduces pig productivity and contributes to the economic burden of L. intracellularis worldwide.

Use of flow cytometry and PCR analysis to detect 5-carboxyfluoroscein-stained obligate intracellular bacteria Lawsonia intracellularis invasion of McCoy cells

In this study, we describe a method to quantify invasion of obligate intracellular bacteria, Lawsonia intracellularis, inside McCoy cells. In immunological research, the cell-permeable fluorescent dye 5'-carboxyfluoroscein succidyl ester (CFSE) is commonly used to quantify eukaryotic cellular proliferation. Instead of using it in this traditional way, we stained L. intracellularis with CFSE dye prior to infection of McCoy cells. Flow cytometry was performed to quantify the percentage of eukaryotic cells which had taken up or were associated with fluorescent bacteria. As obligate intracellular bacteria, they cannot replicate outside of eukaryotic cells and thus qPCR analysis was used to quantify bacterial growth. Indirectly, PCR analysis confirmed invasion rather than adherence to the McCoy cell surface. Fluorescent activated cell sorting (FACS) was used to sort the CFSE(+) (i.e. infected) McCoy cells from the CFSE(-) (i.e. non-infected) McCoy cells and confocal microscopy was used to confirm bacterial invasion and cytosolic localization of CFSE-L. intracellularis. To show that this approach could be used in conjunction with functional assays, we investigated the effect that serum antibodies had on CFSE-bacterial invasion and growth. Instead of blocking invasion, rabbit hyperimmune serum augmented invasion of the bacteria inside McCoy cells and qPCR analysis confirmed bacterial growth over the course of 5days. We conclude that CFSE-labeling of bacteria and qPCR can be used to track and quantify bacterial invasion and may be a valuable tool for studying the invasive properties of bacteria, especially if commercial antibodies are not available. This approach may be adapted for use in other obligate intracellular bacteria and intracellular pathogens.

Down-regulation of mechanisms involved in cell transport and maintenance of mucosal integrity in pigs infected with Lawsonia intracellularis

Lawsonia intracellularis is an obligate intracellular bacterium, responsible for the disease complex known as proliferative enteropathy (PE). L. intracellularis is associated with intestinal crypt epithelial cell proliferation but the mechanisms responsible are yet to be defined. Microarray analysis was used to investigate the host-pathogen interaction in experimentally infected pigs to identify pathways that may be involved. Ileal samples originating from twenty-eight weaner pigs experimentally challenged with a pure culture of L. intracellularis (strain LR189/5/83) were subjected to microarray analysis. Microarray transcriptional signatures were validated using immunohistochemistry and quantitative real time PCR of selected genes at various time points post challenge. At peak of infection (14 days post challenge) 86% of altered transcripts were down regulated, particularly those involved in maintenance of mucosal integrity and regulation of cell transport. Among the up-regulated transcripts, CD163 and CDK1 were novel findings and considered to be important, due to their respective roles in innate immunity and cellular proliferation. Overall, targeted cellular mechanisms included those that are important in epithelial restitution, migration and protection; maintenance of stable inter-epithelial cell relationships; cell transport of nutrients and electrolytes; innate immunity; and cell cycle.

Cell-mediated and humoral immune responses in pigs following primary and challenge-exposure to Lawsonia intracellularis

To investigate immune responses upon re-infection with Lawsonia intracellularis, local and peripheral humoral and cell-mediated immune responses to primary and challenge inoculations were studied in 22 pigs. Pigs were orally inoculated with virulent L. intracellularis at the age of 5-6 weeks, treated with antibiotics and challenged with a re-inoculation (RE) at the age of 12 weeks. Treatment control (TC) pigs received only the primary inoculation and challenge control (CC) pigs received only the secondary inoculation at 12 weeks of age. Following this regimen, all RE pigs were protected against the re-infection as defined by reduced colonisation and pathology of intestinal mucosa, absence of bacterial shedding and without increase in serum acute phase protein response. In the protected RE pigs, serum IgG responses were variable with both high and low responders. Serum IgA responses were not boosted by the re-inoculation, since identical intestinal IgA responses developed in response to the inoculation in both the susceptible CC pigs and the protected RE pigs. A memory recall cell-mediated immune response developed in RE pigs which was significantly stronger compared to the primary response in age-matched CC pigs as assessed by whole blood IFN-γ assay and by calculation of IFN-γ integrated median fluorescence intensity (iMFI) after flow cytometry. The major IFN-γ producing cells were identified as CD8⁺ and CD4⁺CD8⁺ double positive lymphocytes. The results indicate that cell-mediated immune responses are likely mediators of protective immunity against L. intracellularis, with CD8⁺ effector cells and CD4⁺CD8⁺ double positive memory T cells as main contributors to the antigen-specific IFN-γ production.

Proliferative enteropathy: a global enteric disease of pigs caused byLawsonia intracellularis

Proliferative enteropathy (PE; ileitis) is a common intestinal disease affecting susceptible pigs raised under various management systems around the world. Major developments in the understanding of PE and its causative agent,Lawsonia intracellularis, have occurred that have led to advances in the detection of this disease and methods to control and prevent it. Diagnostic tools that have improved overall detection and early onset of PE in pigs include various serological and molecular-based assays. Histological tests such as immunohistochemistry continue to be the gold standard in confirmingLawsonia-specific lesions in pigspost mortem. Despite extreme difficulties in isolatingL. intracellularis, innovations in the cultivation and the development of pure culture challenge models, have opened doors to better characterization of the pathogenesis of PE throughin vivoandin vitro L. intracellularis–host interactions. Advancements in molecular research such as the genetic sequencing of the entireLawsoniagenome have provided ways to identify various immunogens, metabolic pathways and methods for understanding the epidemiology of this organism. The determinations of immunological responsiveness in pigs to virulent and attenuated isolates ofL. intracellularisand identification of various immunogens have led to progress in vaccine development.

Reproductive performance of gilts following an outbreak of acute proliferative enteropathy due to Lawsonia intracellularis

After a sudden outbreak of clinical porcine proliferative enteropathy (PPE) in a Croatian indoor breeding unit, the farm experienced decreased reproductive performance of Lawsonia intracellularis positive gilts. Conception-, farrowing-, and adjusted farrowing rates were lower (P<0.001) in gilts with positive L. intracellularis status. The number of live born and the total born litter size were significantly lower (P<0.001) in L. intracellularis positive gilts compared to seronegative ones. No differences were observed in numbers of stillborn and mummified pigs between the L. intracellularis positive and negative gilts.

Immunopathogenesis of experimentally induced proliferative enteropathy in pigs

To characterize the immune response associated with Lawsonia intracellularis infection, twenty-eight, 7-week-old pigs were dosed orally with a pure culture of L. intracellularis. Animals were killed 3, 7, 14, 21, 28, 35, and 42 days postinfection. Light microscopic studies were undertaken to immunophenotype the immunologic response using specific antibodies to T-cell subsets (CD3, CD4, and CD8), B cells, major histocompatibility complex class II, cadherin, and macrophages over the course of time. The results indicate that there is a direct association between the presence of L. intracellularis and reduced T-cell and B-cell numbers. For the first time, this provides evidence of the presence of an immunosuppressive mechanism operating in this disease. Furthermore, macrophage marker studies indicated that macrophages may play a more complex and significant role in the disease process than has been previously reported, with activated macrophages accumulating in infected hyperplastic crypts.

Lawsonia intracellularis: getting inside the pathogenesis of proliferative enteropathy

Although proliferative enteropathy (PE) has been recognised for several decades, Lawsonia intracellularis, the aetiological agent, was identified formally in only 1995. This organism is both highly fastidious and obligately intracellular bacterium, characteristics which have inevitably restricted investigations in all aspects of its biology. Despite these limitations, advances have been made in characterising and understanding L. intracellularis-host interaction both in vivo and in vitro. Based upon evidence provided by mainly pathological and histological investigations conducted to date, we review salient features of our current understanding of processes involved throughout the course of infection by this unique pathogen.

Intracellular bacteria of porcine proliferative enteropathy: cultivation and maintenance in vitro

An obligate intracellular bacterium was isolated from the intestines of all 10 cases of porcine proliferative enteropathy from four different pig farms. The organism grew in a rat enterocyte cell line (IEC-18) and was maintained over 20 passages. The growth of the bacteria was assessed by immunostaining of cells exposed to infection. Infection was not associated with morphological cell change, and growth was confined to cells infected at the time of each transfer of infection and the progeny of these cells. The bacterium is a microaerophilic, cell dependent, curved or rod-shaped, gram-negative bacillus that multiplies freely in the enterocyte cytoplasm. Cell cultures containing the intracellular bacteria appear to be free of other microorganisms, including chlamydiae and viruses.

Production of a monoclonal antibody that recognizes the lipopolysaccharide of a Campylobacter-like organism

A monoclonal antibody was produced to a Campylobacter-like organism (RMIT 32A) which was isolated from the terminal ileum of a pig with proliferative enteritis. Isotyping of the antibody revealed that it was an IgG2a with kappa light chains. Immunoblots using the antibody against proteinase-K-treated whole cell lysates of RMIT 32A, a selection of Campylobacter species and other enteric bacteria showed that the antibody was specific for RMIT 32A and was directed against the lipopolysaccharide. This antibody can be used for the specific detection of RMIT 32A.

Southern blot analysis of strain variation in Campylobacter mucosalis

A panel of three DNA probes were derived at random from a genomic DNA library of Campylobacter mucosalis strain E8384-4. Each probe hybridized specifically to C. mucosalis DNA from bacteria fixed to nylon membranes. The probes did not hybridize to DNA from other Campylobacter species or to other bacteria even at 100-fold higher amounts. Each probe hybridized to all of 24 isolates of C. mucosalis which had been collected over time from different geographic locations. Southern blot analysis of selected C. mucosalis isolates was carried out to determine if the probes would be useful for differentiating among various isolates. It indicated that restriction fragment length polymorphisms (RFLPs) exist at the loci identified by our probes. These differences were used to characterize seven C. mucosalis isolates recovered from pigs in Minnesota. The results suggest that RFLP analysis may be a useful tool for epidemiological studies of C. mucosalis.

Enterocecocolitis associated with intraepithelial Campylobacter-like bacteria in rabbits (Oryctolagus cuniculus)

We examined 28 suckling, weanling, and young adult rabbits with lethargy, inappetence, and mucinous, semifluid feces. Sixteen of the rabbits had intestinal lesions. In eight of these rabbits, the primary changes were multifocal to diffuse epithelial proliferation and accumulation of lymphocytes, macrophages, or both in the lamina propria of the small intestine, cecum, and sacculated colon. In two of these rabbits, the accumulation of macrophages in the lamina propria was extensive. The other eight rabbits had erosive and suppurative cecocolitis, and four of the rabbits with proliferative lesions also had suppurative cecocolitis. In Warthin-Starry-stained sections of affected intestine, curved or spiral bacteria were visible within degenerated or hyperplastic epithelium, in luminal exudate, or in both. Such organisms were sparse or not found in the other 12 rabbits, which did not have intestinal lesions. The bacteria ultrastructurally resembled intraepithelial Campylobacter-like bacteria previously observed in proliferative enteritis in a variety of species and in acute typhlitis in young rabbits. In immunofluorescence tests, Campylobacter-like bacteria in epithelial cells, crypt lumina, and in luminal exudates in both proliferative and erosive lesions bound monoclonal antibodies and polyclonal antisera prepared against intracellular bacteria found in proliferative enteritis in pigs, hamsters, and ferrets. These observations indicate that a condition similar to proliferative enteritis of swine, hamsters, and other species also occurs in laboratory rabbits.

Demonstration of a new intracellular antigen in porcine intestinal adenomatosis and hamster proliferative ileitis

In the proliferate enteropathies of the pig, intracellular Campylobacter-like organisms can be demonstrated in the apical cytoplasm of affected cells. A new antigen (omega) can be visualised at the site of bacterial parasitism using certain rabbit sera in a sandwich immunofluorescence test; the rabbit sera tested were largely derived from rabbits immunised with bacterial antigens including Campylobacter spp., but it appeared that the reaction was not related to the immunisation procedure and was also present in at least one "normal" rabbit serum. Rabbits immunised with bacteria extracted from the tissues sero-converted to omega-antigen yet did not react with Campylobacter spp., cultured from pig intestine. The omega-antigen was also present in the lesions of hamster proliferative ileitis.