Mycobacterium avium subspecies paratuberculosis infection of cattle does not diminish peripheral blood-derived macrophage mycobactericidal activity

Ruminants infected with Mycobacterium avium subspecies paratuberculosis consistently develop a multibacillary form of disease that is centered on the ileum. Mechanisms responsible for failure of macrophage function during multibacillary disease are incompletely characterized. Our data suggest that mycobactericidal functions are present, and potentially enhanced, in monocyte-derived macrophages from M. avium subsp. paratuberculosis infected cattle. Addition of CD4+ T cells from infected animals to autologous in vitro infected macrophages did not increase bacterial killing. In contrast, CD4+ T cells from non-infected animals did increase bacterial killing in autologous macrophages. In macrophages from both infected and non-infected cattle, bacterial killing appeared to be independent of interferon-γ (IFN-γ) and nitric oxide production.