BackgroundBovine purified protein derivative (bPPD) and avian purified protein derivative (aPPD) are widely used for bovine tuberculosis diagnosis. However, little is known about their qualitative and quantitative characteristics, which makes their standardisation difficult. In addition, bPPD can give false-positive tuberculosis results because of sequence homology between Mycobacterium bovis (M. bovis) and M. avium proteins. Thus, the objective of this study was to carry out a proteomic characterisation of bPPD, aPPD and an immunopurified subcomplex from bPPD called P22 in order to identify proteins contributing to cross-reactivity among these three products in tuberculosis diagnosis.MethodsTrypsin digests of bPPD, aPPD and P22 were analysed by nanoscale liquid chromatography-electrospray ionization tandem mass spectrometry. Mice were immunised with bPPD or aPPD, and their serum was tested by indirect ELISA for reactivity against these preparations as well as against P22.ResultsA total of 456 proteins were identified in bPPD, 1019 in aPPD and 118 in P22; 146 of these proteins were shared by bPPD and aPPD, and 43 were present in all three preparations. Candidate proteins that may cause cross-reactivity between bPPD and aPPD were identified based on protein abundance and antigenic propensity. Serum reactivity experiments indicated that P22 may provide greater specificity than bPPD with similar sensitivity for ELISA-type detection of antibodies against M. tuberculosis complex.ConclusionThe subpreparation from bPPD called P22 may be an alternative to bPPD for serodiagnosis of bovine tuberculosis, since it shares fewer proteins with aPPD than bPPD does, reducing risk of cross-reactivity with anti-M. avium antibodies.Electronic supplementary materialThe online version of this article (10.1186/s12014-017-9171-z) contains supplementary material, which is available to authorized users.
Background
Serum antibody detection has potential as a complementary diagnostic tool in animal tuberculosis (TB) control, particularly in multi-host systems. The objective of the present study was to assess the specificity (Sp) of an enzyme-linked immunosorbent assay (ELISA) based on the new multiprotein complex P22 for the detection of specific antibodies against the
Mycobacterium tuberculosis
complex (MTC) in the four most relevant domestic animals acting as MTC hosts: cattle, goat, sheep and pig. We used sera from an officially TB-free (OTF) country, Norway, and from a non-OTF one, Spain. The samples included sera from goats that had been vaccinated against
M. avium
subsp.
paratuberculosis
(MAP) and sheep from a herd in which
Corynebacterium pseudotuberculosis
had been isolated.
Results
In cattle, the Sp ranged from 92.5 (IC95% 90.7–94) to 99.4% (IC95% 98.3–99.8) depending on the cut-off used and the origin of the samples (Spain or Norway). Sp in cattle (cut-off point 100) was significantly higher (
P
< 0.05) for Norwegian samples. By contrast, Sp in goats was consistently low at the 100 cut-off [30.9 (CI95%23.4–39.5)-78% (CI95% 68.9–85)]. A higher cut-off of 150 improved Sp in Norwegian goats [97% (CI95% 91.6–99)], but still yielded a poor Sp of 56.1% (CI95% 47.3–64.6) in Spanish goats. In Norway at the 100 cut-off the Sp was 58.3 (CI95% 42.2–72.9) and 90.6% (CI95% 81–95.6) in MAP vaccinated and non-vaccinated goats, respectively, indicating interference due to MAP vaccination. Sp in sheep was between 94.4 (CI95% 91.7–96.3) and 100% (CI95% 96.3–100) depending on the cut-off and country, and no diagnostic interference due to infection with
C. pseudotuberculosis
was recorded. Sp in pigs was 100%, regardless the cut-off point applied, and no significant differences were observed between pigs from Norway and from Spain.
Conclusions
Due to its excellent Sp in pigs and acceptable Sp in cattle and sheep, this ELISA may constitute a suitable option for TB screening at herd level, particularly in OTF-countries.
Effective vaccines against tuberculosis (TB) are needed in order to prevent TB transmission in human and animal populations. Evaluation of TB vaccines may be facilitated by using reliable animal models that mimic host pathophysiology and natural transmission of the disease as closely as possible. In this study, we evaluated the immunogenicity and efficacy of two attenuated vaccines, BCG and MTBVAC, after each was given to 17 goats (2 months old) and then exposed for 9 months to goats infected with M. caprae. In general, MTBVAC-vaccinated goats showed higher interferon-gamma release than BCG vaccinated goats in response to bovine protein purified derivative and ESAT-6/CFP-10 antigens and the response was significantly higher than that observed in the control group until challenge. All animals showed lesions consistent with TB at the end of the study. Goats that received either vaccine showed significantly lower scores for pulmonary lymph nodes and total lesions than unvaccinated controls. Both MTBVAC and BCG vaccines proved to be immunogenic and effective in reducing severity of TB pathology caused by M. caprae. Our model system of natural TB transmission may be useful for evaluating and optimizing vaccines.
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