Early immune markers associated with experimental Mycobacterium avium subsp. paratuberculosis (MAP) infection in a neonatal calf model.

Infection models are useful for studying host responses to infection to aid in the development of diagnostic tools and vaccines. The current study compared experimental oral and intraperitoneal MAP infection on early host immune responses. Twenty neonatal Holstein calves were assigned to 5 treatments:1) Control (C), 2) Oral, 3) Oral with dexamethasone pretreatment (Oral/DXM), 4) Intraperitoneal (IP), and 5) Oral/mucosal (Oral/M). The oral group was inoculated with 2 × 10¹⁰ cfu of live MAP, laboratory strain K-10, whereas the Oral/M calves received a recent clinical isolate of MAP. The Oral/DXM calves were given 0.25 mg/kg BW dexamethasone IV for 3 d prior to bacterial challenge to induce immunosuppression. Alternatively, Oral/M calves were inoculated with mucosal scrapings from a clinically infected cow. Lymphocyte proliferation and iNOS were upregulated in experimentally infected calves. Further, experimental infection of calves by either the oral or IP method induced significantly higher antigen-specific IFN-γ responses as compared to C calves and responses were noted as early as 7 d post-infection. T cell activation markers CD25, CD26, CD5, and CD45RO were upregulated in CD4, CD8, and γΔ T cell subpopulations after antigen stimulation in infected calves. These results demonstrate that immunologic markers such as cytokine secretion and T cell markers may be useful tools for diagnosis of MAP infection. [ABSTRACT FROM AUTHOR]