Mucosal immunity to mycobacteria in leprosy patients and their contacts

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Abstract
Since the development of leprosy may follow the formation of an initial lesion in the nose, mucosal immune responses might be important in the protective immune response to Mycobacterium leprae. Salivary antibody responses to M. leprae and other mycobacteria were therefore investigated in leprosy patients and healthy contacts using ELISAs against whole mycobacteria and an M. leprae-specific glycolipid constituent (PGL1) of the external surface of M. leprae. Lower levels of salivary IgA directed against M. leprae were found in household contacts (at high risk of developing leprosy) than in hospital contacts (low risk of leprosy). Samples from the local indigenous population with no known leprosy contact showed an intermediate number of positive salivary IgA responses against M. leprae and untreated patients were less likely to be positive than treated patients. Correlation was found between salivary antibody responses to M. leprae, M. scrofulaceum and M. tuberculosis, suggesting the presence of some cross-reacting antibody. Few patients and no healthy subjects had detectable antibody responses against an epitope of PGL1, suggesting that this important serum antibody response is not a major component of the mucosal immune response to M. leprae. Since there appears to be a secretory IgA response to M. leprae which is least likely to be found amongst those with the disease and in those individuals with increased risk of developing leprosy, we suggest that the mucosal immune system might be of importance in a putative protective response to infection by the leprosy bacillus.