Leprosy as a Model of Immunity

Yang Degang; Kazuaki Nakamura; Takeshi Akama; Yuko Ishido; Yuqian Luo; Norihisa Ishii; Koichi Suzuki


Future Microbiol. 2014;9(1):43-54. 

In This Article

Conclusion & Future Perspective

Leprosy was eliminated without chemotherapy in Norway, although the impact of isolation remains uncertain. Effective immunity against M. leprae was recovered using improvements in public health and nutrition. Therefore, consistent with the Ridley–Jopling model, M. leprae-related immunity may stand as a key factor in the elimination of leprosy. The high incidence of type I reactions towards cure or relief of the disease was attributed to reactivated or excessive cellular immunity. Type II reactions have now been associated with cellular immunity in addition to the complement system. Reactivated cellular immune responses are more prevalent with MDT (compared with public health and nutrition) as suggested by the aggregated occurrence of both type II and type I reactions during and following MDT. In addition, the duration of MDT has been shortened again and again with no significant effectiveness at the end of treatment, and eventual success usually occurring several years later. Chemotherapy in vivo is believed to reduce bacilli viability as well as morphological integrity, and experiments in vitro reveal that live M. leprae is a suppressor of the immune response, while dead M. leprae is a trigger for activated cellular immune responses. Persistence of M. leprae within the immune-tolerated liver in the so-called 'graveyard of T cells' could be one possible route for the induction of M. leprae-specific cellular immune deficiency in the presence of a significant humoral response. This theory may help decipher the dose- or bacilli load-related immunopathology model of M. leprae infection.