Serum antibody responses to mycobacteria in leprosy patients and their contacts

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Abstract
The aim of this descriptive study was to investigate the relationships between serum antibody responses to different mycobacteria in leprosy patients and contacts. The results of ELISAs for serum antibody against whole mycobacteria (Mycobacterium leprae, M. tuberculosis, and M. scrofulaceum) were compared with the results of an M. leprae-specific ELISA for antibody against an epitope of PGL1. The IgG response was found to be predominant in ELISAs for antibody directed against whole M. leprae, while the IgM response was greatest in the assay for antibody against PGL1. Some healthy hospital workers were found to have appreciable levels of IgM anti-PGL1. Since infection in this group is unlikely, chronic exposure may result in humoral responses to PGL1 in addition to subclinical leprosy. None of the ELISAs studied were able to give greater than a 55% sensitivity at 95% specificity and none were considered suitable for serodiagnostic use. Significant correlation was found between the results from the whole mycobacterial ELISAs, which could be explained on the basis of cross-reaction between antibodies directed against common antigens. However, similar correlations were found between the results of the M. leprae-specific ELISA and the assay for antibody against whole M. tuberculosis and M. scrofulaceum which were greater than those for antibody against whole M. leprae. Infection with M. leprae may produce general stimulation of immunological memory for common mycobacterial antigens resulting in responses to antigens belonging to other mycobacteria to which the host has been exposed previously.