Evaluation of the immunogenicity of recombinant stress-associated proteins during Mycobacterium avium subsp. paratuberculosis infection: Implications for pathogenesis and diagnosis

Immuno-reactivity evaluation of Mce-truncated subunit candidate vaccine against Mycobacterium avium subspecies paratuberculosis challenge in the goat models

BACKGROUND

Detection of an appropriate antigen with high immunogenicity can be a big step in the production of an effective vaccine for control of Johne's disease (JD). The aim of this study was to evaluate the efficacy of Mce-truncated protein as a subunit vaccine candidate for the control of JD in experimentally challenged goats.

MATERIALS AND METHODS

Six healthy goat kids were immunized with Mce-truncated protein, and two goats were kept as controls. All kids were twice challenged orally with live Mycobacterium avium subspecies paratuberculosis(MAP) strain and half the goats from both the categories were sacrificed at 7 and 10 months after start of challenge study. Culture of MAP was performed from all the necropsied tissues to determine the true JD infection status.

RESULTS

Mce-truncated protein only reacted with pooled vaccinated goat sera in western-blot. A significant increase in humoral immune response against Mce protein was also observed in vaccinated goats. Compared to the control group, vaccinated goats gained higher body weights and none of them shed MAP or showed histopatological lesions or colonization of MAP in their necropsy tissues.

CONCLUSIONS

The new Mce protein based vaccine provided significant immunity in goats as they could meet the challenge with live MAP bacilli. Although the vaccine used in this study showed the high potential as a new effective vaccine for the control of JD, further validation study is still required to successfully implement the vaccine for JD control program.

Novel recombinant Mce-truncated protein based ELISA for the diagnosis of Mycobacterium avium subsp. paratuberculosis infection in domestic livestock

Johne’s disease (JD) is an infectious wasting condition of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP) in domestic livestock of every country that has been investigated. Controlling JD is problematic due to the lack of sensitive, specific, efficient, and cost-effective diagnostic tests. A major challenge in the development of diagnostics like ELISA is the selection of an ideal antigen/(s) that is pathogen-specific and allows sensitive recognition. Therefore, the purpose of this study was to identify and use Mce-truncated protein-based ELISA assay for the diagnosis of MAP infection with high sensitivity and specificity. In silico epitope prediction by epitope mapping throughout the whole length of MAP2191 protein revealed that C-terminal portion of this protein presented potential T- and B-cell epitopes. Therefore, a novel Mce-truncated protein encoded by the selected region of MAP2191 gene was expressed, purified with Ni-NTA gel matrix and confirmed by SDS PAGE and western blot. A profiling ELISA assay was developed to evaluate sera from MAP infected and non-infected ruminant species for antibodies against Mce-truncated protein to infer the immunogenicity of this protein in the host. Using this Mce protein-based ELISA, 251 goats, 53 sheep, 117 buffaloes, and 33 cattle serum samples were screened and 49.4, 51.0, 69.2, and 54.6% animals, respectively, were found positive. Comparing with i-ELISA, the new Mce-based ELISA kit showed a relatively higher specificity but suffered from slightly reduced sensitivity. Mce-based ELISA excluded apparently false positive results of i-ELISA. Mce protein was found to be antigenic and Mce-ELISA test could be employed as a diagnostic test for JD in domestic livestock in view of the a relatively higher specificity and accuracy. The antigenic potential of Mce antigen can also be exploited for the development of a new vaccine for the control of MAP infection.

Identification of Sero-Diagnostic Antigens for the Early Diagnosis of Johne's Disease using MAP Protein Microarrays

Considerable effort has been directed toward controlling Johne’s disease (JD), a chronic granulomatous intestinal inflammatory disease caused by Mycobacterium avium subsp. paratuberculosis (MAP) in cattle and other ruminants. However, progress in controlling the spread of MAP infection has been impeded by the lack of reliable diagnostic tests that can identify animals early in the infection process and help break the transmission chain. To identify reliable antigens for early diagnosis of MAP infection, we constructed a MAP protein array with 868 purified recombinant MAP proteins, and screened a total of 180 well-characterized serum samples from cows assigned to 4 groups based on previous serological and fecal test results: negative low exposure (NL, n = 30); negative high exposure (NH, n = 30); fecal-positive, ELISA-negative (F + E−, n = 60); and both fecal- and ELISA-positive (F + E+, n = 60). The analyses identified a total of 49 candidate antigens in the NH, F + E−, and F + E+ with reactivity compared with the NL group (p < 0.01), a majority of which have not been previously identified. While some of the antigens were identified as reactive in only one of the groups, others showed reactivity in multiple groups, including NH (n = 28), F + E− (n = 26), and F + E+ (n = 17) groups. Using combinations of top reactive antigens in each group, the results reveal sensitivities of 60.0%, 73.3%, and 81.7% in the NH, F + E−, and F + E+, respectively at 90% specificity, suggesting that early detection of infection in animals may be possible and enable better opportunities to reduce within herd transmission that may be otherwise missed by traditional serological assays that are biased towards more heavily infected animals. Together, the results suggest that several of the novel candidate antigens identified in this study, particularly those that were reactive in the NH and F + E− groups, have potential utility for the early sero-diagnosis of MAP infection.

An update on Mycobacterium avium subspecies paratuberculosis antigens and their role in the diagnosis of Johne's disease

Mycobacterium avium subsp. paratuberculosis (MAP) is responsible for Johne's disease (JD) or paratuberculosis. Diagnosis of MAP infection by measuring host cell-mediated and humoral immune responses has been a major focus in MAP research. For this purpose, several MAP antigens such as secreted protein, cell envelope protein, cell-mediated immune and lipoprotein antigens have been identified and tested to measure their diagnostic utility with varying degree of success. Identifying the optimal antigen or antigen combinations for diagnosis of infected animals is hindered by the complex nature of the disease, prolonged subclinical infection, the differential expression of antigens and scarcity of well characterized MAP-specific epitopes making selection of a single MAP antigen very difficult. Thus, multiplexing of antigens with larger scale and longitudinal studies may lead to development of cost-effective next generation serodiagnostics. This mini review focuses on the role of different MAP antigens in the diagnosis of JD.

Early detection of Mycobacterium avium subsp. paratuberculosis infection in cattle with multiplex-bead based immunoassays

Johne’s Disease (JD), caused by Mycobacterium avium subspecies paratuberculosis (MAP), results in significant economic loss to livestock production. The early detection of MAP infection in animals with extant serological assays has remained challenging due to the low sensitivity of commercially available ELISA tests, a fact that has hampered the development of effective JD control programs. Our recent protein microarray-based studies identified several promising candidate antigens that are immunogenic during different stages of MAP infection. To evaluate these antigens for use in diagnostic assays and reliably identify animals with MAP infection, a multiplex (Luminex^®) assay was developed using color-coded flourescent beads coupled to 6 MAP recombinant proteins and applied to screen 180 serum and 90 milk samples from cows at different stages of MAP infection including negative (NL), fecal test positive/ELISA negative (F+E-), and fecal positive/ELISA positive (F+E+). The results show that while serum antibody reactivities to each of the 6 antigens were highest in F+E+ group, antibody reactivity to three of the six antigens were identified in the F+E- group, suggesting that these three antigens are expressed and provoke antibody responses during the early infection stages with MAP. Further, antibodies against all six antigens were elevated in milk samples from both the F+E- and F+E+ groups in comparison to the NL group (p<0.01). Taken together, the results of our investigation suggest that multiplex bead-based assays are able to reliably identify MAP infection, even during early stages when antibody responses in animals are undetectable with widely used commercial ELISA tests.

Identification of sero-reactive antigens for the early diagnosis of Johne's disease in cattle

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD), a chronic intestinal inflammatory disease of cattle and other ruminants. JD has a high herd prevalence and causes serious animal health problems and significant economic loss in domesticated ruminants throughout the world. Since serological detection of MAP infected animals during the early stages of infection remains challenging due to the low sensitivity of extant assays, we screened 180 well-characterized serum samples using a whole proteome microarray from Mycobacterium tuberculosis (MTB), a close relative of MAP. Based on extensive testing of serum and milk samples, fecal culture and qPCR for direct detection of MAP, the samples were previously assigned to one of 4 groups: negative low exposure (n = 30, NL); negative high exposure (n = 30, NH); fecal positive, ELISA negative (n = 60, F+E-); and fecal positive, ELISA positive (n = 60, F+E+). Of the 740 reactive proteins, several antigens were serologically recognized early but not late in infection, suggesting a complex and dynamic evolution of the MAP humoral immune response during disease progression. Ordinal logistic regression models identified a subset of 47 candidate proteins with significantly different normalized intensity values (p<0.05), including 12 in the NH and 23 in F+E- groups, suggesting potential utility for the early detection of MAP infected animals. Next, the diagnostic utility of four MAP orthologs (MAP1569, MAP2942c, MAP2609, and MAP1272c) was assessed and reveal moderate to high diagnostic sensitivities (range 48.3% to 76.7%) and specificity (range 96.7% to 100%), with a combined 88.3% sensitivity and 96.7% specificity. Taken together, the results of our analyses have identified several candidate MAP proteins of potential utility for the early detection of MAP infection, as well individual MAP proteins that may serve as the foundation for the next generation of well-defined serological diagnosis of JD in cattle.

Development of vaccines to Mycobacterium avium subsp. paratuberculosis infection

Johne's disease or paratuberculosis is a chronic debilitating disease in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease causes significant economic losses in livestock industries worldwide. There are no effective control measures to eradicate the disease because there are no appropriate diagnostic methods to detect subclinically infected animals. Therefore, it is very difficult to control the disease using only test and cull strategies. Vaccination against paratuberculosis has been considered as an alternative strategy to control the disease when combined with management interventions. Understanding host-pathogen interactions is extremely important to development of vaccines. It has long been known that Th1-mediated cellular immune responses are play a crucial role in protection against MAP infection. However, recent studies suggested that innate immune responses are more closely related to protective effects than adaptive immunity. Based on this understanding, several attempts have been made to develop vaccines against paratuberculosis. A variety of ideas for designing novel vaccines have emerged, and the tests of the efficacy of these vaccines are conducted constantly. However, no effective vaccines are commercially available. In this study, studies of the development of vaccines for MAP were reviewed and summarized.

Trends and advances in the diagnosis and control of paratuberculosis in domestic livestock

Paratuberculosis (pTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP) in a wide variety of domestic and wild animals. Control of pTB is difficult due to the lack of sensitive, efficacious and cost-effective diagnostics and marker vaccines. Microscopy, culture, and PCR have been used for the screening of MAP infection in animals for quite a long time. Besides, giving variable sensitivity and specificity, these tests have not been considered ideal for large-scale screening of domestic livestock. Serological tests like ELISA easily detects anti-MAP antibodies. However, it cannot differentiate between the vaccinated and infected animals. Nanotechnology-based diagnostic tests are underway to improve the sensitivity and specificity. Newer generation diagnostic tests based on recombinant MAP secretory proteins would open new paradigm for the differentiation between infected and vaccinated animals and for early detection of the infection. Due to higher seroreactivity of secretory proteins vis-à-vis cellular proteins, the secretory proteins may be used as marker vaccine, which may aid in the control of pTB infection in animals. Secretory proteins can be potentially used to develop future diagnostics, surveillance and monitoring of the disease progression in animals and the marker vaccine for the control and eradication of pTB.

Proteome-wide B and T cell epitope repertoires in outer membrane proteins of Mycobacterium avium subsp. paratuberculosis have vaccine and diagnostic relevance: a holistic approach

Mycobacterium avium subsp. paratuberculosis (MAP) is an etiological agent of chronic inflammation of the intestine among ruminants and humans. Currently, there are no effective vaccines and sensitive diagnostic tests available for its control and detection. For this, it is of paramount importance to identify the MAP antigens, which may be immunologically recognized by the host immune system. To address this challenge, we performed identification of the immunogenic epitopes in the MAP outer membrane proteins (OMPs). We have previously identified 57 MAP proteins as OMPs [Rana A, Rub A, Akhter Y. 2014. Molecular BioSystems, 10:2329-2337] and have evaluated them for the epitope selection and analysis employing a computational approach. Thirty-five MAP OMPs are reported with nine-mer peptides showing high binding affinity to major histocompatibility complex (MHC) class I molecules and 28 MAP OMPs with 15-mer peptides of high binding affinity for MHC class II molecules. The presence of MHC binding epitopes indicates the potential cell-mediated immune response inducing capacity of these MAP OMPs in infected host. To further investigate the humoral response inducing properties of OMPs of MAP, we report potential B cell epitopes based on the sequences of peptide antigens and their molecular structures. We also report 10 proteins having epitopes for both B and T cells representing potential candidates which may invoke both humoral and cellular immune responses in the host. These findings will greatly accelerate and expedite the formulation of effective and cost-efficient vaccines and diagnostic tests against MAP infection.

Antigenicity of recombinant maltose binding protein-Mycobacterium avium subsp. paratuberculosis fusion proteins with and without factor Xa cleaving

Mycobacterium avium subsp. paratuberculosis causes Johne's disease (JD) in ruminants. Proteomic studies have shown that M. avium subsp. paratuberculosis expresses certain proteins when exposed to in vitro physiological stress conditions similar to the conditions experienced within a host during natural infection. Such proteins are hypothesized to be expressed in vivo, are recognized by the host immune system, and may be of potential use in the diagnosis of JD. In this study, 50 recombinant maltose binding protein (MBP)-M. avium subsp. paratuberculosis fusion proteins were evaluated using serum samples from sheep infected with M. avium subsp. paratuberculosis, and 29 (58%) were found to be antigenic. Among 50 fusion proteins, 10 were evaluated in MBP fusion and factor Xa-cleaved forms. A total of 31 proteins (62%) were found to be antigenic in either MBP fusion or factor Xa-cleaved forms. Antigenicity after cleavage and removal of the MBP tag was marginally enhanced.

Detection of antibody responses against Mycobacterium avium subsp. paratuberculosis stress-associated proteins within 30 weeks after infection in cattle

In this study, humoral immune responses in cattle against Mycobacterium avium subsp. paratuberculosis (MAP) stress-associated recombinant proteins were assessed longitudinally by ELISA during the first 30 weeks after MAP infection. A total of 11 MAP genes previously identified by proteomic analysis were selected for cloning and expression. These included possible general stress-associated proteins of MAP and proteins expressed in vivo in MAP-infected sheep at an early stage of infection. An increase in the antibody levels against 5 recombinant antigen preparations (MAP1027c, MAP1339, MAP1588c, MAP1589c and MAP2411) was seen in MAP-infected calves (n=16) but not in control calves (n=3) over the time examined. Antibody responses were recorded as early as two weeks post-inoculation, and 87.5% of the inoculated cattle responded to at least one of the five immunogenic antigen preparations within the first 30 weeks of infection, suggesting that these proteins identified in the in vitro models of stress were also expressed in vivo in MAP-infected cattle at a relatively early stage after infection and therefore stimulate the host's immune system. It has been assumed that the sensitivity of antibody ELISA tests is dependent on the stage of infection and the age of the animals. However, we have provided some evidence that humoral immunity occurs at an early stage of paratuberculosis and can be detected using appropriate antigens such as MAP stress-associated proteins.

In silico screened Mycobacterium avium subsp. paratuberculosis (MAP) recombinant proteins upregulated under stress conditions are immunogenic in sheep

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD) in ruminants. MAP is known to enter a dormant phase outside the host, typically on soil. In vitro experiments have reported regulation of certain MAP genes when exposed to stressors similar to what is thought to produce dormancy. It is believed that in vivo regulation of dormancy genes and associated proteins by MAP may play a role in evading the host defence mechanisms and induce the host immune response against these dormancy-related proteins. Five proteins encoded by dormancy-related genes that were previously found to be upregulated under stress conditions and predicted through in silico analysis to possess immune epitopes (three hypothetical proteins and two proteins involved in fatty acid metabolism) were selected. Recombinant proteins were produced, purified and evaluated by indirect enzyme-linked immunosorbent assay (ELISA) for immunogenicity using a panel of sera obtained from sheep unexposed and exposed to MAP. The antibody levels of the exposed group were significantly higher than the unexposed group (P<0.001). Individually, the five proteins were found to discriminate between sera from sheep exposed to MAP compared to unexposed sheep. At 91% diagnostic specificity, the diagnostic sensitivity of the recombinant antigen ELISA ranged from 24% to 42% and AUC(ROC) from 0.7015 to 0.8405.

Recent research on bovine paratuberculosis in South Korea

Bovine paratuberculosis (Johne's disease), a chronic and debilitating disease of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP), is a major cause of chronic ruminant enteritis. A national eradication program has been in place in South Korea since the first report of the disease in 1967; however, only limited data on bovine paratuberculosis in South Korea are available. Some research, such as investigations of the reactivity of animal sera against MAP antigens, has been done in localized areas and in limited animal species. Compared with the worldwide situation, the development of diagnostic methods in South Korea has shown similar results even though some data were obtained from international collaborative studies. MAP is considered by some to be zoonotic, noting an association with Crohn's disease, although this issue is still controversial; however, research into this association is limited. Decisions based on disease priorities have hampered active progress in research on the disease. In this paper, we reviewed the available results generated from South Korea compared with global research. Finally, we propose a theme for future research.

In silico identification of epitopes in Mycobacterium avium subsp. paratuberculosis proteins that were upregulated under stress conditions

Johne's disease in ruminants is caused by Mycobacterium avium subsp. paratuberculosis. Diagnosis of M. avium subsp. paratuberculosis infection is difficult, especially in the early stages. To date, ideal antigen candidates are not available for efficient immunization or immunodiagnosis. This study reports the in silico selection and subsequent analysis of epitopes of M. avium subsp. paratuberculosis proteins that were found to be upregulated under stress conditions as a means to identify immunogenic candidate proteins. Previous studies have reported differential regulation of proteins when M. avium subsp. paratuberculosis is exposed to stressors which induce a response similar to dormancy. Dormancy may be involved in evading host defense mechanisms, and the host may also mount an immune response against these proteins. Twenty-five M. avium subsp. paratuberculosis proteins that were previously identified as being upregulated under in vitro stress conditions were analyzed for B and T cell epitopes by use of the prediction tools at the Immune Epitope Database and Analysis Resource. Major histocompatibility complex class I T cell epitopes were predicted using an artificial neural network method, and class II T cell epitopes were predicted using the consensus method. Conformational B cell epitopes were predicted from the relevant three-dimensional structure template for each protein. Based on the greatest number of predicted epitopes, eight proteins (MAP2698c [encoded by desA2], MAP2312c [encoded by fadE19], MAP3651c [encoded by fadE3_2], MAP2872c [encoded by fabG5_2], MAP3523c [encoded by oxcA], MAP0187c [encoded by sodA], and the hypothetical proteins MAP3567 and MAP1168c) were identified as potential candidates for study of antibody- and cell-mediated immune responses within infected hosts.

Partial proteome of Mycobacterium avium subsp. paratuberculosis under oxidative and nitrosative stress

The growth pattern and protein expression profiles of sheep (S) and cattle (C) strains of Mycobacterium avium subsp. paratuberculosis (MAP) under oxidative and nitrosative stress were characterised. Oxidative stress was induced using 0.05% (v/v) H(2)O(2) in BACTEC medium, and was lethal for an inoculum of 10(4) cells. However, an inoculum of 10(7) cells survived and proteomic changes were observed at 7 days. Nitrosative stress was induced using 1mM NaNO(2); it slowed the growth of an inoculum of 10(4) cells, but both strains recovered quickly when resuscitated in fresh media. Silver staining showed higher sensitivity for detection of 2D spots compared to SYPRO Ruby staining. A total of 18 proteins were regulated under oxidative and/or nitrosative stress. The expression of four antioxidant enzymes (AhpC, AhpD, OxcA and SodA) and four proteins involved in fatty acid metabolism (DesA2, FadA6_3, FabG and FadE19) was altered, together with a range of other proteins. Only one protein, AhpC was differentially regulated in both strains of MAP. Seven proteins (DesA2, AhpC, AhpD, Ppa, FabG, and hypothetical proteins MAP2411 and MAP 1885c) were identified in previous in vitro studies with temperature, hypoxia and/or nutrient starvation stressors and may be general stress response proteins of MAP. Prior studies have identified immune responses directed against AhpC and Ppa in animals with Johne's disease, expression of sodA and ppa within macrophages, and reduced virulence of impA mutants in mice, highlighting the relevance of proteomic studies using these in vitro stress models for pathogenesis studies.