Immunological properties of M. leprae culture isolates ICRC bacilli: hypothesis on relationship between M. leprae and ML-culture isolates.

The M. leprae-culture isolate, being a culture, is identified by biochemical criteria. Majority belong to either M. avium-intracellulare-scrofulacieum complex, or corynobacterium group. The identification is also determined by serological methods using soluble sonicates. Skin tests with heat-killed suspension often give positive Mitsuda response and hence the isolates are discarded as non-M. leprae. The data on ICRC strains show that Dharmendra type antigen prepared from ICRC bacilli compares very well with lepromin in lepromatous patients. The CMI/DTH tests in mice by FPE and LMI technique have experimentally demonstrated that ICRC bacillus is the first cultivable mycobacterium that can sensitize mice against lepromin. These data also brought out antigenic differences between the ICRC strains. The clinical trial on ICRC vaccine has shown that the ICRC bacilli is immunogenic in Man. The biochemical data on ICRC strain show that they possess DOPA-Oxidase and can express biochemical character of 9/10 similarity index with M. leprae with appropriate substrates in the medium. Thus, the ICRC strains possess both M. leprae and M. avium characters. An hypothesis is proposed to explain these observations--The 'Janus face' of M. leprae--by proposing a relationship between M. leprae and its culture isolates, e.g. ICRC bacilli (1). The M. leprae-culture isolate may by a recombinent of M. leprae with M. avium background (2). The ML-isolate may express the CMI related antigenic determinants corresponding to that of M. leprae in the biopsy (3). The CMI related antigens of whole bacilli in the ML-culture isolate may be inducing type as against only eliciting antigen expressed by M. leprae (4). Recombination may provide immunogenicity as well as 'in vitro' growth potential to the ML-culture isolate (5). Absence or failure to express inducing antigen by M. leprae maybe alternate biological escape mechanism from immune surveillance for survival in vivo, with or without suppressor mechanisms.