Bovine Immunoinhibitory Receptors Contribute to Suppression of Mycobacterium avium subsp. paratuberculosis-Specific T-Cell Responses
Johne's disease (paratuberculosis) is a chronic enteritis in cattle that is caused by intracellular infection withMycobacterium aviumsubsp.paratuberculosis. This infection is characterized by the functional exhaustion of T-cell responses toM. aviumsubsp.paratuberculosisantigens during late subclinical and clinical stages, presumably facilitating the persistence of this bacterium and the formation of clinical lesions. However, the mechanisms underlying T-cell exhaustion in Johne's disease are poorly understood. Thus, we performed expression and functional analyses of the immunoinhibitory molecules programmed death-1 (PD-1)/PD-ligand 1 (PD-L1) and lymphocyte activation gene 3 (LAG-3)/major histocompatibility complex class II (MHC-II) inM. aviumsubsp.paratuberculosis-infected cattle during the late subclinical stage. Flow cytometric analyses revealed the upregulation of PD-1 and LAG-3 in T cells in infected animals, which suffered progressive suppression of interferon gamma (IFN-γ) responses to theM. aviumsubsp.paratuberculosisantigen. In addition, PD-L1 and MHC-II were expressed on macrophages from infected animals, consistent with PD-1 and LAG-3 pathways contributing to the suppression of IFN-γ responses during the subclinical stages ofM. aviumsubsp.paratuberculosisinfection. Furthermore, dual blockade of PD-L1 and LAG-3 enhancedM. aviumsubsp.paratuberculosis-specific IFN-γ responses in blood from infected animals, andin vitroLAG-3 blockade enhanced IFN-γ production fromM. aviumsubsp.paratuberculosis-specific CD4+and CD8+T cells. Taken together, the present data indicate thatM. aviumsubsp.paratuberculosis-specific T-cell exhaustion is in part mediated by PD-1/PD-L1 and LAG-3/MHC-II interactions and that LAG-3 is a molecular target for the control ofM. aviumsubsp.paratuberculosis-specific T-cell responses.