Mycobacterium avium Subspecies paratuberculosis Recombinant Proteins Modulate Antimycobacterial Functions of Bovine Macrophages

It has been shown that Mycobacterium avium subspecies paratuberculosis ( M . paratuberculosis ) activates the Mitogen Activated Protein Kinase (MAPK) p38 pathway, yet it is unclear which components of M . paratuberculosis are involved in the process. Therefore, a set of 42 M . paratuberculosis recombinant proteins expressed from coding sequences annotated as lipoproteins were screened for their ability to induce IL-10 expression, an indicator of MAPKp38 activation, in bovine monocyte-derived macrophages. A recombinant lipoprotein, designated as MAP3837c, was among a group of 6 proteins that strongly induced IL-10 gene transcription in bovine macrophages, averaging a 3.1-fold increase compared to non-stimulated macrophages. However, a parallel increase in expression of IL-12 and TNF-α was only observed in macrophages exposed to a subset of these 6 proteins. Selected recombinant proteins were further analyzed for their ability to enhance survival of M . avium within bovine macrophages as measured by recovered viable bacteria and nitrite production. All 6 IL-10 inducing MAP recombinant proteins along with M . paratuberculosis cells significantly enhanced phosphorylation of MAPK-p38 in bovine macrophages. Although these proteins are likely not post translationally lipidated in E . coli and thus is a limitation in this study, these results form the foundation of how the protein component of the lipoprotein interacts with the immune system. Collectively, these data reveal M . paratuberculosis proteins that might play a role in MAPK-p38 pathway activation and hence in survival of this organism within bovine macrophages.