In vitro cellular immune responses to recombinant antigens of Mycobacterium avium subsp. paratuberculosis

Five recombinant antigens (Ags; 85A, 85B, 85C, superoxide dismutase [SOD], and 35-kDa protein) were purified from Mycobacterium avium subsp. paratuberculosis and evaluated for their ability to stimulate peripheral blood mononuclear cells (PMBCs) from fecal-culture-positive cows (low and medium shedders) and culture-negative healthy cows. Recombinant Ags 85A, 85B, and 85C induced significant lymphocyte proliferation as well as the production of gamma interferon (IFN-γ), interleukin-2 (IL-2), IL-12, and tumor necrosis factor alpha (TNF-α), but not IL-4, from low and medium shedders. The 85 antigen complex did not stimulate PMBC proliferation from culture-negative healthy cows. The 35-kDa protein also induced significant lymphocyte proliferation as well as the production of IFN-γ and IL-4 from low and medium shedders. CD4⁺ T cells and CD25⁺ (IL-2R) T cells were stimulated the most by 85A and 85B, while the 35-kDa protein primarily stimulated CD21 ⁺ B cells involved in humoral immune responses. Interestingly, SOD was less immunostimulatory than other antigens but strongly induced γδ⁺ T cells, which are thought to be important in the early stages of infection, such as pathogen entry. These data provide important insight into how improved vaccines against mycobacterial infections might be constructed.