Vaccination sequence effects on immunological response and tissue bacterial burden in paratuberculosis infection in a rabbit model

Modeling Paratuberculosis in Laboratory Animals, Cells, or Tissues: A Focus on Their Applications for Pathogenesis, Diagnosis, Vaccines, and Therapy Studies

Paratuberculosis is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. Paratuberculosis that affects a wide variety of domestic and wild animals. It is considered one of the diseases with the highest economic impact on the ruminant industry. Despite many efforts and intensive research, paratuberculosis control still remains controversial, and the existing diagnostic and immunoprophylactic tools have great limitations. Thus, models play a crucial role in understanding the pathogenesis of infection and disease, and in testing novel vaccine candidates. Ruminant animal models can be restricted by several reasons, related to space requirements, the cost of the animals, and the maintenance of the facilities. Therefore, we review the potential and limitations of the different experimental approaches currently used in paratuberculosis research, focusing on laboratory animals and cell-based models. The aim of this review is to offer a vision of the models that have been used, and what has been achieved or discovered with each one, so that the reader can choose the best model to answer their scientific questions and prove their hypotheses. Also, we bring forward new approaches that we consider worth exploring in the near future.

Peripheral IFN-ɣ Production after Blood Stimulation with Different Mycobacterial Antigens in Goats Vaccinated against Paratuberculosis

Vaccination can be an efficient method for the control of paratuberculosis in ruminants. However, the official tuberculosis control tests cross-interfere with the animals vaccinated against paratuberculosis. In order to test and compare new antigens that could solve this problem, the production of interferon-gamma (IFN-γ) in peripheral blood at different post-vaccination days in experimental kids and adult goats, in field conditions, using the avian and bovine purified protein derivative (PPD), the johnin, two peptide cocktails of Mycobacterium bovis (PC-EC and PC-HP) and the antigens VK 055 and VK 067 of Mycobacterium avium subspecies paratuberculosis (Map) has been analyzed in vitro. The non-specific production of IFN-γ was observed after blood stimulation with the PC-EC and PC-HP cocktail in any sample from vaccinated animals, whereas it was detected when bovine PPD was used. These results support the possible use of these new Mycobacterium bovis antigens in the in the differentiation of animals vaccinated against paratuberculosis or infected with tuberculosis by improving the specificity of bovine PPD. In contrast, the two Map antigens tested in this study did not improve the sensitivity of johnin or avian PPD in the detection of vaccinated or Map-infected goats.

Oral vaccination stimulates neutrophil functionality and exerts protection in a Mycobacterium avium subsp. paratuberculosis infection model

Mycobacterium avium subsp. paratuberculosis (Map) causes paratuberculosis (PTB), a granulomatous enteritis in ruminants that exerts high economic impact on the dairy industry worldwide. Current vaccines have shown to be cost-effective against Map and in some cases confer beneficial non-specific effects against other pathogens suggesting the existence of trained immunity. Although Map infection is mainly transmitted by the fecal-oral route, oral vaccination has not been deeply studied. Therefore, the aim of this study was to compare the oral route with a set of mycobacterial and non-mycobacterial vaccines with a subcutaneously administered commercially available vaccine. Training effects on polymorphonuclear neutrophils (PMNs) and homologous and heterologous in vivo protection against Map were investigated in the rabbit infection model. Oral vaccination with inactivated or live vaccines was able to activate mucosal immunity as seen by elevation of serum IgA and the expression of IL4 in peripheral blood mononuclear cells (PBMCs). In addition, peripheral PMN phagocytosis against Map was enhanced by vaccination and extracellular trap release against Map and non-related pathogens was modified by both, vaccination and Map-challenge, indicating trained immunity. Finally, PBMCs from vaccinated animals stimulated in vitro with Map antigens showed a rapid innate activation cytokine profile. In conclusion, our data show that oral vaccination against PTB can stimulate neutrophil activity and both innate and adaptive immune responses that correlate with protection.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Inducing cellular immune responses with a marked Mycobacterium avium subsp. paratuberculosis strain in dairy calves

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne's disease, a chronic granulomatous enteritis with a high global prevalence in dairy cattle. This disease causes significant economic loss in the dairy industry and has been challenging to control, as current diagnostic assays are low in sensitivity and specificity, and previously developed vaccines do not prevent infection and face regulatory concerns due to interference with bovine tuberculosis diagnostics. To remediate this issue, positive and negative immune markers were created in a MAP strain as a step towards a vaccine capable of differentiating infected from vaccinated animals (DIVA). A gene coding for an immunogenic protein (MAP1693c) in the MAP genome was replaced with a library of epitope-tagged immunogenic genes (pepA) via a stable allelic exchange method. These markers were evaluated in a calf infection trial, where Holstein-Friesian dairy calves were inoculated at two weeks of age with either the marked strain or the parent strain, or remained uninfected controls. Cellular immune responses to the markers were measured using an interferon gamma release assay (IGRA). There were no MAP1693c marker-specific differences in cellular immune responses between infection groups. A scrambled version of the HA (human influenza hemagglutinin) epitope, but not the actual HA epitope, induced a significant IFN-γ response in marker-infected calves compared to WT-infected and uninfected groups at 4.5 months post-inoculation. This scrambled HA epitope thus holds potential as a diagnostic tool as part of a DIVA vaccine for Johne's disease.

Alternative Vaccination Routes against Paratuberculosis Modulate Local Immune Response and Interference with Tuberculosis Diagnosis in Laboratory Animal Models

Paratuberculosis (PTB) is an enteric granulomatous disease caused by Mycobacterium avium subsp. paratuberculosis (MAP) that mainly affects ruminants. Current vaccines have shown to be cost–effective control reagents, although they are restricted due to cross-interference with bovine tuberculosis (bTB). Therefore, novel vaccination strategies are needed and this study is focused on evaluating alternative vaccination routes and their effect on the local immune response. The MAP oral challenge rabbit model was used to evaluate and compare an experimental inactivated MAP vaccine through oral (VOR) and intradermal (VID) routes. The VID group presented the highest proportion of animals with no visible lesions and the lowest proportion of animals with MAP positive tissues. Immunohistochemistry analysis revealed that the VID group presented a dominantly M1 polarized response indicating an ability to control MAP infection. In general, all vaccinated groups showed lower calprotectin levels compared to the non-vaccinated challenged group suggesting less active granulomatous lesions. The VID group showed some degree of skin test reactivity, whereas the same vaccine through oral administration was completely negative. These data show that PTB vaccination has an effect on macrophage polarization and that the route influences infection outcome and can also have an impact on bTB diagnosis. Future evaluation of new immunological products against mycobacterial diseases should consider assaying different vaccination routes.

Effectiveness of an inactivated paratuberculosis vaccine in Iranian sheep flocks using the Mycobacterium avium subsp paratuberculosis 316F strain

BACKGROUND AND OBJECTIVES

Paratuberculosis (PTb) (John's disease) is an incurable chronic intestinal infection that mainly affects ruminants. PTb is caused by Mycobacterium avium subspecies paratuberculosis (MAP) with a global distribution. Despite evidences on MAP contribution in Crohn's disease its causal role is still a matter of controversy. In ruminant farming, vaccination is broadly accepted as an effective control measure of PTb. This article describes preparation and field trial of an inactivated PTb vaccine made from the MAP 316F strain.

MATERIALS AND METHODS

Formulation of the vaccine was conducted based on the method traditionally used in the UK. Identity of the MAP strain was authenticated by PCR-IS900 and PCR-F57 tests. In the field, a group of 100 lambs (3-8 weeks old) were subcutaneously inoculated with the vaccine preparation under study. These animals, pre-vaccination, were all PTb ELISA negative. Serum level of antibody was determined by ELISA on days 0, 30, 60, 120 and 240, post-vaccination.

RESULTS

In PCR-900 and PCR-F57, the MAP 316F strain produced two fragments of 560 and 704 bp length respectively, a confirmation of its identity as MAP bacterium. In the field trial and at the arranged time intervals, the achieved blood serum levels of antibody, attributable to the vaccine formulation, displayed considerably high values.

CONCLUSION

Given that the PTb-caused economical losses in the Iranian environment are dramatically high and also the fact that future of state policy on control of PTb remains unknown, we belive vaccination of animals is the best recommendable practice.