Cell-mediated immunity to mycobacteria: a double-sided sword?

Mycobacteria are intracellular pathogens capable of replicating in resting macrophages. Specific helper T lymphocytes which activate antimycobacterial capacities in infected macrophages represent an important constituent of acquired resistance. In addition, cytolytic T lymphocytes may contribute to resistance. On the other hand, lysis of infected host cells may also comprise autoaggressive consequences. Recent evidence suggest that T cells with specificity for mycobacterial heat shock proteins are involved in the antimycobacterial immune response. Heat shock proteins are evolutionarily highly conserved and cross-reactivity between microbial and mammalian molecules may occur on the B-cell and T-cell level. Thus, T cells directed against shared epitopes of mycobacterial and autologous origin could initiate autoimmune reactions.