Abstract
European badgers are a wildlife reservoir of bovine tuberculosis in parts of Great Britain. Accurate diagnosis of tuberculosis in badgers is important for the development of strategies for the control of the disease. Sensitive serological tests for badger TB are needed for reasons such as cost and simplicity. Assay of mucosal IgA could be useful for diagnosing respiratory pathogens such as Mycobacterium bovis and for monitoring the response to mucosal vaccination. To develop an IgA assay, we purified secretory IgA from badger bile, identifying secretory component (SC), heavy chain (HC) and light chain (LC), at 66, 46 and 27 Kda, respectively, on the basis of size comparison with other species. Monoclonal antibodies (mAbs) were generated to purified IgA. We selected two for ELISA development. The detection limit of the IgA-specific mAbs was found to be approximately 20 ng/mL when titrated against purified badger bile. One monoclonal antibody specific for badger IgA was used to detect IgA in serum and tracheal aspirate with specificity to an immunodominant antigen of M. bovis. An M. bovis infection dose-dependent IgA response was observed in experimentally infected badgers. IgA was also detected by immunohistochemistry in the lungs of bTB-infected badgers. With further characterisation, these represent new reagents for the study of the IgA response in badgers.
Highlights
In parts of Great Britain and Ireland, the European badger (Meles meles) constitutes a reservoir of infection for Mycobacterium bovis and a potential source of infection to cattle [1,2,3]
We have developed an interferon-gamma (IFNγ) release assay (IGRA) for bTB detection in badgers [4]
We have separately evaluated the amount of IgA present in tracheal aspirate samples from different badgers by direct ELISA and found the amounts to be extremely variable
Summary
In parts of Great Britain and Ireland, the European badger (Meles meles) constitutes a reservoir of infection for Mycobacterium bovis and a potential source of infection to cattle [1,2,3]. Accurate diagnosis of M. bovis infection in badgers is an important component of strategies to control bTB in this species. Culture isolation of M. bovis remains the “gold-standard” diagnostic test but this is only sensitive when post-mortem tissue samples are used. Sensitive in vitro diagnostics that can be used to test live animals are still required. Assays based on measurement of a cellular immune response are commonly used for the diagnosis of TB in cattle, humans and other mammals. With a sensitivity of up to 81% and a specificity of 94% [5,6], it is the most accurate bTB test that can be performed on live badgers. As an alternative diagnostic approach, assays measuring serological responses offer several advantages
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