Mycobacterium tuberculosis and Mycobacterium bovis derived proteins induce caspase-independent apoptosis in bovine macrophages

Species of the genus Mycobacterium are capable of inducing cell apoptosis. Infected cells with M. tuberculosis undergo apoptosis through a caspase-dependent pathway. We have previously shown that whole Mycobacterium bovis cells and derived crude protein extracts were able to trigger apoptosis through a caspase independent mechanism. However, the identity of the protein or protein fractions capable of inducing apoptosis has not been determined. In this study, bovine macrophages were incubated in the presence of Mycobacterium tuberculosis recombinant proteins and Mycobacterium bovis protein extracts to identify proteins capable of inducing apoptosis. A subgroup of proteins and protein extracts from strains of the Mycobacterium tuberculosis complex were shown to induce DNA fragmentation in bovine macrophages through a caspase independent pathway. Our findings suggest that bovine macrophages may elicit a different response to mycobacterium infection than that displayed by murine or human cells.