In vitro responses to purified protein derivate of caprine T lymphocytes following vaccination with live strains of Mycobacterium avium subsp. paratuberculosis

Live attenuated vaccines provide protection against intestinal lesions in goats infected with Mycobacterium avium subsp. paratuberculosis. To examine the role of different T lymphocyte subsets in the development of this protective immunity, CD4+, CD8+ and γδ T cell receptor (TCR)+ cells from peripheral blood of goat kids vaccinated with live attenuated strains of M. a. paratuberculosis were studied. After in vitro stimulation with purified protein derivate, the expression of γ-interferon (IFN-γ) and the activation marker interleukin-2 receptor (IL-2R) was analysed by flow cytometry. A depletion experiment was performed, where the phenotypes and IL-2R expression was studied after stimulation of cultures depleted of a T lymphocyte subpopulation. Close to all of the IFN-γ producing cells were of the CD4+ subset, while only a small number were CD8+ cells. The γδ TCR+ cells were highly activated, but did not produce IFN-γ after in vitro stimulation. Depletion of CD4+ cells lead to a decrease in the percentage of total γδ TCR+ cells and γδ TCR+IL2-R+ cells. Removing the γδ TCR+ cells increased the relative numbers of CD4+, but not the CD4+IL-2R+ cells. Insight into the in vitro recall responses of T cell subsets from animals vaccinated with live paratuberculosis vaccines is essential in the development of more efficient vaccines.