Innate IFN-gamma production in cattle in response to MPP14, a secreted protein from Mycobacterium avium subsp Paratuberculosis

Calves experimentally infected with Mycobacterium avium subsp. paratubercul osis and uninfected calves were tested for interferon(IFN)-gamma production after stimulation with purified protein derivative from M. avium subsp. pa ratuberculosis (PPDp) or a secreted 14 kDa protein (MPP14) specific for the M. avium-intracellulare-scrofulaceum (MAIS) complex. Several calves in bot h groups responded strongly up to about 5 months to both antigens. Two unin fected calves responded repeatedly, but not always, to MPP14 and PPDp throu ghout the study. The responses in the uninfected animals seemed to be indep endent of cell contact between the antigen presenting cells (APC) and the r esponding population. The supernatant from adherent cells stimulated with M PP14 induced similar levels of IFN-gamma production in CD14(+)/B-cell deple ted peripheral blood mononuclear cells (PBMC) as when the antigen was used directly on PBMC. In contrast, APC/T-cell contact was necessary to induce t he IFN-gamma production in infected animals, suggesting that both innate an d adaptive IFN-gamma production in response to MPP14 could occur. CD8(+) ce lls contributed to some of the IFN-gamma production in response to MPP14, b ut the rest could not be explained, while CD4(+) cells were responsible for the adaptive response to PPDp. This study showed that secreted proteins co uld induce innate IFN-gamma production that interferes with diagnostic test ing using the IFN-gamma -test.