Immunosuppression and treatment-associated inflammatory response in patients with Mycobacterium ulcerans infection (Buruli ulcer)

Buruli ulcer is a necrotizing skin disease caused by Mycobacterium ulcerans. Major necrosis with abundant clusters of extracellularly replicating mycobacteria and only minor leukocyte infiltration are characteristic histopathologic features of the disease. Mycolactone, a cytotoxic macrolide exotoxin of M. ulcerans, plays a key role in the development of this pathology. Antimicrobial therapy, such as rifampicin/streptomycin that was recently introduced, seems to lead to phagocytosis of mycobacteria and massive leukocyte infiltration, which culminates in the development of ectopic lymphoid structures in the lesions. Whereas the curative effect of the antibiotic treatment may be supported by immune defense mechanisms, persisting mycobacterial antigens and immunostimulators occasionally also seem to cause apparent reactivation of the disease. This seems to be related to excessive immunostimulation rather than to incomplete killing of the pathogen.