Immunology of leprosy: new findings, future perspectives

Abstract

Leprosy affects more than 15 million people in the world primarily in the developing countries (summarized in ref. 1). The etiologic agent, Mycobacterium leprae, is an intracellular microorganism, perfectly adopted to survival within human mononuclear phagocytes. It is an extreme slow grower with an estimated doubling time of 13 d. The slow growth somehow seems to reflect the latency by which advances have proceeded in leprosy research. Although M. leprae was discovered by G. H. Armauer Hansen as early as 1873, 2 at a time when the concept that certain diseases are caused and transmitted by microorganisms was not generally accepted, it took nearly 100 years until an animal could be experimentally infected with M. leprae 3 and its in vitro cultivation has still not been achieved. Recently, however, achievements have progressed more rapidly including (i) identification of M. leprae-specific antigens and monoclonal antibodies, (ii) elucidation of mechanisms involved in M. leprae-specific unresponsiveness, (iii) establishment of M. leprae-reactive T-cell clones and (iv) cloning of M. leprae antigens in E. coli. Thus, the information is now at hand for better understanding how M. leprae deals with the immune system and how the immune system can be manipulated to better deal with M. leprae. Hopefully, this will ultimately lead to the development of an anti-leprosy vaccine of reliable effectiveness. Before reviewing more recent findings let us briefly consider some facts about leprosy of relevance to the succeeding discussion.