Immunoreactivity of the <it>Mycobacterium avium </it>subsp. <it>paratuberculosis </it>19-kDa lipoprotein

<p>Abstract</p> <p>Background</p> <p>The <it>Mycobacterium tuberculosis </it>19-kDa lipoprotein has been reported to stimulate both T and B cell responses as well as induce a number of Th1 cytokines. In order to evaluate the <it>Mycobacterium avium </it>subsp. <it>paratuberculosis </it>(<it>M. avium </it>subsp. <it>paratuberculosis</it>) 19-kDa lipoprotein as an immunomodulator in cattle with Johne's disease, the gene encoding the 19-kDa protein (MAP0261c) was analyzed.</p> <p>Results</p> <p>MAP0261c is conserved in mycobacteria, showing a 95% amino acid identity in <it>M. avium </it>subspecies <it>avium</it>, 84% in <it>M. intracellulare </it>and 76% in <it>M. bovis </it>and <it>M. tuberculosis</it>. MAP0261c was cloned, expressed, and purified as a fusion protein with the maltose-binding protein (MBP-19 kDa) in <it>Escherichia coli</it>. IFN-γ production was measured from 21 naturally infected and 9 control cattle after peripheral blood mononuclear cells (PBMCs) were stimulated with a whole cell lysate (WCL) of <it>M. avium </it>subsp. <it>paratuberculosis </it>or the recombinant MBP-19 kDa. Overall, the mean response to MBP-19 kDa was not as strong as the mean response to the WCL. By comparison, cells from control, non-infected cattle did not produce IFN-γ after stimulation with either WCL or MBP-19 kDa. To assess the humoral immune response to the 19-kDa protein, sera from cattle with clinical Johne's disease were used in immunoblot analysis. Reactivity to MBP-19 kDa protein, but not MBP alone, was observed in 9 of 14 infected cattle. Antibodies to the 19-kDa protein were not observed in 8 of 9 control cows.</p> <p>Conclusions</p> <p>Collectively, these results demonstrate that while the 19-kDa protein from <it>M. avium </it>subsp. <it>paratuberculosis </it>stimulates a humoral immune response and weak IFN-γ production in infected cattle, the elicited responses are not strong enough to be used in a sensitive diagnostic assay.</p>