Evaluation of the gamma interferon test for diagnosis of paratuberculosis in goats

Influence of Heterologous and Homologous Vaccines, and Their Components, on the Host Immune Response and Protection Against Experimental Caprine Paratuberculosis

Vaccination against paratuberculosis, a chronic disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map), has been considered as the most effective control method. However, protection is incomplete, and the mechanisms operating in the response of the animals to vaccination are not fully understood. Therefore, this study analyzed the immune response and the effects on protection against Map infection, elicited by paratuberculosis (Silirum®) and tuberculosis (heat-inactivated M. bovis [HIMB]) vaccines and their components in a caprine experimental model. Fifty goat kids were divided into 10 groups (n = 5) according to their vaccination (Silirum®, HIMB and nonvaccinated), immunization (inactivated bacteria or adjuvant), and/or infection. Oral challenge with Map was performed 45 days postvaccination/immunization (dpv), and animals were euthanized at 190 dpv. Peripheral immune response and proportion of lymphocyte subpopulations were assessed monthly by enzyme-linked immunosorbent assay and flow cytometry analysis, respectively. Local immune response, proportion of tissue lymphocyte subpopulations, Map detection (polymerase chain reaction), and histological examination were conducted in gut-associated lymphoid tissues. All infected groups developed paratuberculosis granulomatous lesions despite vaccination or immunization. The Silirum® and HIMB-vaccinated groups showed a considerable lesion reduction consistent with a significant peripheral cellular and humoral immune response. Besides, a lower number of granulomas were observed in groups immunized with inactivated bacteria and adjuvants in comparison to nonvaccinated and infected group. However, despite not being significant, this reduction was even higher in adjuvant immunized groups, which developed milder granulomatous lesion with no detectable peripheral immune responses associated with immunization. No changes in the peripheral and local proportion of lymphocyte subsets or local immune response were detected in relation to either vaccination/immunization or infection. Despite that paratuberculosis and tuberculosis vaccination showed a partial and cross-protection against Map infection, respectively, only histological examination could assess the progression of infection in these animals. In addition, the pattern observed in the reduction of the lesions in adjuvant immunized groups suggests the possible involvement of a nonspecific immune response that reduces the development of granulomatous lesions.

Using Omics Approaches in the Discovery of Biomarkers for Early Diagnosis of Johne's Disease in Sheep and Goats

Simple Summary

Johne’s disease (JD) is caused by Mycobacterium avium subsp. paratuberculosis (MAP) and is an important and emerging problem in livestock. Most JD research has been carried out on cattle, but interest in the pathogenesis and diagnosis of this disease in sheep and goats is greatest in developing countries. Sheep and goats are also a relevant part of livestock production in Europe and Australia, and these species provide an excellent resource to study and better understand the mechanism of survival of MAP and gain insights into possible approaches to control this disease. This review gives an overview of the literature on paratuberculosis in sheep and goats, highlighting the immunological aspects and the potential for “omics” approaches to identify effective biomarkers for the early detection of infection.

Abstract

Johne’s disease (JD) is caused by Mycobacterium avium subsp. paratuberculosis (MAP) and is an important and emerging problem in livestock; therefore, its control and prevention is a priority to reduce economic losses and health risks. Most JD research has been carried out on cattle, but interest in the pathogenesis and diagnosis of this disease in sheep and goats is greatest in developing countries. Sheep and goats are also a relevant part of livestock production in Europe and Australia, and these species provide an excellent resource to study and better understand the mechanism of survival of MAP and gain insights into possible approaches to control this disease. This review gives an overview of the literature on paratuberculosis in sheep and goats, highlighting the immunological aspects and the potential for “omics” approaches to identify effective biomarkers for the early detection of infection. As JD has a long incubation period before the disease becomes evident, early diagnosis is important to control the spread of the disease.

Effects of Age and Environment on Adaptive Immune Responses to Mycobacterium avium subsp. paratuberculosis (MAP) Vaccination in Dairy Goats in Relation to Paratuberculosis Control Strategies

Paratuberculosis infection is caused by Mycobacterium avium subsp. paratuberculosis (MAP). In the Netherlands, 75% herd level prevalence of caprine paratuberculosis has been estimated, and vaccination is the principal control strategy applied. Most goat dairy farms with endemic paratuberculosis systematically vaccinate goat kids in the first months of life with a commercially available whole cell MAP vaccine. We hypothesized that the development of adaptive immune responses in goats vaccinated at young age depends on the environment they are raised in, and this has implications for the application of immune diagnostic tests in vaccinated dairy goats. We evaluated the early immune response to vaccination in young goat kids sourced from a MAP unsuspected non-vaccinated herd and raised in a MAP-free environment. Subsequently we compared these with responses observed in birth year and vaccination matched adult goats raised on farms with endemic paratuberculosis. Results indicated that initial adaptive immune responses to vaccination are limited in a MAP-free environment. In addition, adult antibody positive vaccinated goats raised in a MAP endemic environment are less likely to be IS900 PCR-positive as compared to antibody negative herd mates. We conclude that test-and-cull strategies in a vaccinated herd are currently not feasible using available immune diagnostic tests.

Identification of new antigen candidates for the early diagnosis of Mycobacterium avium subsp. paratuberculosis infection in goats

Currently Mycobacterium avium subsp. paratuberculosis (MAP) infection is diagnosed through indirect tests based on the immune response induced by the infection. The antigens commonly used in IFN-γ release assays (IGRA) are purified protein derivative tuberculins (PPD). However, PPDs, lack both specificity (Sp) and sensitivity (Se) in the early phase of infection. This study investigated the potential of 16 MAP recombinant proteins and five lipids to elicit the release of IFN-γ in goats from herds with or without a history of paratuberculosis. Ten recombinant proteins were selected as potential candidates for the detection of MAP infection in young goats. They were found to detect 25 to 75% of infected shedder (IS) and infected non-shedder (INS) kids younger than 10months of age. In comparison, PPD was shown to detect only 10% of INS and no IS kids. For seven antigens, Se (21-33%) and Sp (≥90%) of IGRA were shown to be comparable with PPD at 20months old. Only three antigens were suitable candidates to detect IS adult goats, although Se was lower than that obtained with PPD. In paratuberculosis-free herds, IGRA results were negative in 97% of indoor goats and 86% of outdoor goats using the 10 antigens. However, 22 to 44% of one-year-old outdoor goats were positive suggesting that they may be infected. In conclusion, this study showed that ten MAP recombinant proteins are potential candidates for early detection of MAP infected goats. Combining these antigens could form a possible set of MAP antigens to optimize the Se of caprine IGRA.

A longitudinal study of the Mycobacterium avium subspecies paratuberculosis infection status in young goats and their mothers

The dynamics between Mycobacterium avium subspecies paratuberculosis (MAP) infection and the immune response of goats naturally exposed to MAP were studied in a herd where the clinical expression of paratuberculosis had been observed. Four generations of goats were observed over a 33-month period: mothers of three different generations (G1, G2, G3) and their daughters, generation 4 (G4). A MAP infection status was defined according to the combined results of an IFN-γ assay, antibody response, faecal culture and post-mortem examination. Goats were defined as non-infected (NI), infected and non-shedder (INS), infected and shedder (IS) or atypical (A). Twenty-nine percent of goats were NI, 66% were infected and either shedding (14%) or not shedding (52%) MAP, and 5% were atypical. IFN-γ responses were detected first, followed by faecal shedding and antibody responses. The results showed that in goats naturally exposed to MAP, IFN-γ responses were regularly detected earlier in non-shedders than in young infected shedder goats and were stronger in shedder than in non-shedder goats. They were also higher in the mother goats than in their daughters. Goats shedding MAP or with positive antibody response at the beginning of their pregnancy are more likely to have an infected daughter positive to an IFN-γ assay by the age of 15 months.

Production and proteomic characterisation of purified protein derivative from Mycobacterium avium subsp. paratuberculosis

Background

Effective diagnosis of Johne's disease (JD), particularly at the stage of early subclinical infection, remains one of the greatest challenges for the control of JD worldwide. The IFN-γ test of cell mediated immunity is currently one of the most suitable diagnostics for subclinical infections, however a major limitation of this test is the lack of a standardised purified protein derivative (PPD) antigen (also referred to as Johnin PPD or PPDj). While attempting to replace PPDj with more specific individual antigens is an attractive proposition, bacterial culture derived PPDj remains the most effective antigen preparation for the diagnosis of subclinical JD. It may be possible to increase the reproducibility and specificity of PPDj preparations by further characterising and standardising the PPDj production.

Results

Using a standardised protocol, five in-house preparations of PPDj were prepared from cultures of Mycobacterium avium subsp. paratuberculosis (MAP). Compared to PPDs obtained from other institutes/laboratories, these preparations appeared to perform similarly well in the IFN-γ test. Although the broad proteomic composition of all PPDj preparations was remarkably similar, the absolute abundance of individual proteins varied markedly between preparations. All PPDj preparations contained common immunogenic proteins which were also observed in PPD preparations from Mycobacterium avium subsp. avium (PPDa) and Mycobacterium bovis (PPDb). Temporal difference in protein secretion of in vitro cultured MAP was observed between 20 and 34 weeks suggesting that the age of MAP culture used for PPDj preparations may markedly influence PPDj composition.

Conclusions

This study describes a protocol for the production of PPDj and its subsequent proteomic characterisation. The broad proteomic composition of different preparations of PPDj was, for the most part, highly similar. Compositional differences between PPDj preparations were found to be a direct reflection of genetic differences between the MAP strain types used to produce these preparations and the age of MAP cultures they were derived from. A number of conserved immunogenic proteins, such as members of the cutinase-like protein family, were found to be more abundant in PPDj compared to PPDa and should be considered as possible diagnostic antigens for the future.

Effect of an inactivated paratuberculosis vaccine on the intradermal testing of goats for tuberculosis

The effect of an inactivated paratuberculosis vaccine on the diagnosis of tuberculosis (TB) in goats was investigated in a herd with a history of clinical paratuberculosis but which was free of TB. Cohorts of animals in 2006, 2008 and 2009, were vaccinated once at 1 month of age, and 50% of the 2006 cohort served as unvaccinated controls. The goats were aged 8 months, 20 months and 3.5 years old at the time of the survey. All animals were assessed using a single intradermal injection of bovine tuberculin purified protein derivative (PPD) (SID test), or using both bovine and avian PPD (CID test). An interferon (IFN)-γ assay using both bovine and avian PPD was carried out on the 2006 cohort and was interpreted according to three different 'cut-off' points. No unvaccinated (control) animals tested positive to any of the assays, confirming that the herd was TB-free. The SID test had a low specificity in vaccinated animals at 8 and 20 months of age, whereas the CID test demonstrated 100% specificity in animals ≥20 months-old. The specificity of IFN-γ assay was less than maximal for vaccinated animals 3.5 years old as small numbers of false positives were detected, although this depended on the chosen cut-off point. The study findings demonstrate that the use of an inactivated paratuberculosis vaccine in goats <1 month-old in a TB-free herd does not result in false positives to a CID test for TB when performed in animals ≥20 months-old.

Neutralization of interleukin-10 from CD14(+) monocytes enhances gamma interferon production in peripheral blood mononuclear cells from Mycobacterium avium subsp. paratuberculosis-infected goats

The gamma interferon assay is used to identify Mycobacterium avium subsp. paratuberculosis-infected animals. It has been suggested that regulatory mechanisms could influence the sensitivity of the test when it is performed with cells from cattle and that the neutralization of interleukin-10 (IL-10) in vitro would increase the gamma interferon responses. To investigate the regulatory mechanisms affecting the gamma interferon assay with cells from goats, blood was collected from M. avium subsp. paratuberculosis-infected, M. avium subsp. paratuberculosis-exposed, and noninfected goats. Neutralization of IL-10 by a monoclonal antibody resulted in increased levels of gamma interferon production in M. avium subsp. paratuberculosis purified protein derivative (PPDj)-stimulated samples from both infected and exposed goats. However, the levels of gamma interferon release were also increased in unstimulated cells and in PPDj-stimulated cells from some noninfected animals following neutralization. Depletion of putative regulatory CD25(high) T cells had no clear effect on the number of gamma-interferon-producing cells. The IL-10-producing cells were identified to be mainly CD14(+) major histocompatibility complex class II-positive monocytes in both PPDj-stimulated and control cultures and not regulatory T cells. However, possible regulatory CD4(+) CD25(+) T cells produced IL-10 in response to concanavalin A stimulation. The numbers of CD4(+), CD8(+), and CD8(+) gammadelta T-cell receptor-positive cells producing gamma interferon increased following IL-10 neutralization. These results provide insight into the source and the role of IL-10 in gamma interferon assays with cells from goats and suggest that IL-10 from monocytes can regulate both innate and adaptive gamma interferon production from several cell types. Although IL-10 neutralization increased the sensitivity of the gamma interferon assay, the specificity of the test could be compromised.

Development and use of a partial Mycobacterium avium subspecies paratuberculosis protein array

As an initial step toward systematically characterizing all antigenic proteins produced by a significant veterinary pathogen, 43 recombinant Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) expression clones were constructed, cataloged, and stored. NC filters were spotted with purified proteins from each clone along with a whole cell lysate of M. paratuberculosis. Spots on the resulting dot array consisted of hypothetical proteins (13), metabolic proteins (3), cell envelope proteins (7), known antigens (4), and unique proteins with no similarity in public sequence databases (16). Dot blot arrays were used to profile antibody responses in a rabbit and mouse exposed to M. paratuberculosis as well as in cattle showing clinical signs of Johne's disease. The M. paratuberculosis heat shock protein DnaK, encoded by ORF MAP3840 and a membrane protein (MAP2121c), were identified as the most strongly immunoreactive in both the mouse and rabbit hosts, respectively. MAP3155c, which encodes a hypothetical protein, was most strongly immunoreactive in sera from Johne's disease cattle. This study has enabled direct comparisons of antibody reactivity for an entire panel of over 40 proteins and has laid the foundation for future high throughput production and arraying of M. paratuberculosis surface proteins for immune profiling experiments in cattle.

Impact of protein shedding on detection of Mycobacterium avium subsp. paratuberculosis by a whole-cell immunoassay incorporating surface-enhanced Raman scattering

The etiological agent of Johne's disease is Mycobacterium avium subsp. paratuberculosis. Controlling the spread of this disease is hindered by the lack of sensitive, selective, and rapid detection methods for M. avium subsp. paratuberculosis. By using a recently optimized sandwich immunoassay (B. J. Yakes, R. J. Lipert, J. P. Bannantine, and M. D. Porter, Clin. Vaccine Immunol. 15:227-234, 2008), which incorporates a new monoclonal antibody for the selective capture and labeling of M. avium subsp. paratuberculosis and surface-enhanced Raman scattering for sensitive readout, detection limits of approximately 630 and approximately 740 M. avium subsp. paratuberculosis cells/ml are achieved in phosphate-buffered saline and whole milk samples, respectively, after spiking with heat-treated M. avium subsp. paratuberculosis. Surprisingly, these detection limits are 3 orders of magnitude lower than expected based on theoretical predictions. Experiments designed to determine the origin of the improvement revealed that the major membrane protein targeted by the monoclonal antibody was present in the sample suspensions as shed protein. This finding indicates that the capture and labeling of shed protein function as a facile amplification strategy for lowering the limit of detection for M. avium subsp. paratuberculosis that may also be applicable to the design of a wide range of highly sensitive assays for other cells and viruses.

Detection of Mycobacterium avium subsp. paratuberculosis by a sonicate immunoassay based on surface-enhanced Raman scattering

A sandwich immunoassay for the rapid, low-level detection of Mycobacterium avium subsp. paratuberculosis has been developed. M. avium subsp. paratuberculosis is the causative agent of Johne's disease in cattle, and one of the major obstacles in controlling the spread of this disease is the inability to rapidly detect small amounts of bacteria or other diagnostic markers shed during the subclinical stage of infection. This paper details the development and performance of an assay for sonicated M. avium subsp. paratuberculosis lysate that is based on surface-enhanced Raman scattering (SERS). There are two key components of the assay: (i) an immobilized layer of monoclonal antibodies that target a surface protein on the microorganism; and (ii) extrinsic Raman labels (ERLs) that are designed to selectively bind to captured proteins and produce large SERS signals. By correlating the number of M. avium subsp. paratuberculosis bacilli present prior to sonication to the amount of total protein in the resulting sonicate, the detection limit determined for total protein can be translated to the microorganism concentration. These findings yield detection limits of 100 and 200 ng/ml (estimated to be 500 and 1,000 M. avium subsp. paratuberculosis bacilli/ml) for sonicate spiked in phosphate buffer and sonicate spiked in whole milk, respectively. Moreover, the time required to complete the assay, which includes sample preparation, antigen extraction, ERL incubation, and readout, is less than 24 h. The potential for incorporation of this novel assay into diagnostic laboratories is also briefly discussed.

Profiling bovine antibody responses to Mycobacterium avium subsp. paratuberculosis infection by using protein arrays

With the genome sequence of Mycobacterium avium subsp. paratuberculosis determined, technologies are now being developed for construction of protein arrays to detect the presence of antibodies against M. avium subsp. paratuberculosis in host serum. The power of this approach is that it enables a direct comparison of M. avium subsp. paratuberculosis proteins to each other in relation to their immunostimulatory capabilities. In this study, 93 recombinant proteins, produced in Escherichia coli, were arrayed and spotted onto nitrocellulose. These proteins include unknown hypothetical proteins and cell surface proteins as well as proteins encoded by large sequence polymorphisms present uniquely in M. avium subsp. paratuberculosis. Also included were previously reported or known M. avium subsp. paratuberculosis antigens to serve as a frame of reference. Sera from healthy control cattle (n = 3) and cattle infected with either M. avium subsp. avium and Mycobacterium bovis were exposed to the array to identify nonspecific or cross-reactive epitopes. These data demonstrated a degree of cross-reactivity with the M. avium subsp. avium proteins that was higher than the degree of cross-reactivity with the more distantly related M. bovis proteins. Finally, sera from naturally infected cattle (n = 3) as well as cattle experimentally infected with M. avium subsp. paratuberculosis (n = 3) were used to probe the array to identify antigens in the context of Johne's disease. Three membrane proteins were the most strongly detected in all serum samples, and they included an invasion protein, an ABC peptide transport permease, and a putative GTPase protein. This powerful combination of genomic information, molecular tools, and immunological assays has enabled the identification of previously unknown antigens of M. avium subsp. paratuberculosis.

Evaluation of the gamma interferon ELISA in sheep subclinically infected with Mycobacterium avium subspecies paratuberculosis using a whole-cell sonicate or a johnin purified-protein derivative

The aim of the study reported here was to estimate the sensitivity and specificity of the gamma interferon (IFN-gamma) ELISA for paratuberculosis in sheep using receiver-operating characteristic analysis. Bacteriologic culture of tissues was used to define the reference positive population (n = 33). Two reference negative populations were used: culture-negative sheep from infected flocks (n = 77), and sheep from noninfected flocks (n = 358). We also evaluated the accuracy of 2 Mycobacterium avium subspecies paratuberculosis (MAP) antigen preparations, a whole-cell sonicate (MpS) and a johnin purified-protein derivative (PPDj). The source of the reference negative sheep used in the analysis affected overall accuracy of the IFN-gamma ELISA. The area under the curve was 0.683 (95% confidence interval 0.574-0.787), using culture-negative sheep from infected flocks, was 0.831 (0.764-0.889), using sheep from noninfected flocks for the MpS, and was 0.809 (0.726-0.881) and 0.897 (0.862-0.925) for the PPDj, respectively. Using the MpS, the cut point that classified the most sheep correctly was an optical density reading of 0.20, for sensitivity of 40.7% (19.4-57.6) and specificity of 88.7% (77.0-95.7) or 97.6% (93.04-99.5), depending on the reference negative population used. Using the PPDj, the cut point that classified the most sheep correctly was 0.25 for sensitivity of 66.7% (47.2-82.7) and specificity of 93.5% (85.5-97.9) or 98.3% (96.4-99.4), respectively. The PPDj was more accurate at identifying MAP-infected sheep than was the MpS (P = 0.034).