Nucleotide Sequence Analysis and Serologic Characterization of a 27-kilodalton Mycobacterium Intracellulare Lipoprotein

Disseminated mycobacteremia resulting from Mycobacterium avium-Mycobacterium intracellulare complex (MAC) infections frequently contribute to the morbidity and mortality seen in AIDS patients. To better understand the immunopathology of MAC disease and to identify molecules that may have potential diagnostic and vaccine utility, an immunoreactive M. intracellulare protein (MI43) and the gene encoding this antigen were characterized. Southern blot hybridizations demonstrated that MI43 gene probes reacted only with genomic DNA from M. intracellulare, M. avium, and Mycobacterium asiaticum and not with DNA isolated from 11 other mycobacterial species. Nucleotide sequence analysis showed that the MI43 gene encodes a 27-kDa protein which contains a consensus bacterial lipoprotein processing sequence. Detergent-phase separations and metabolic labeling with [3H]palmitate also suggested that MI43 is a lipoprotein. Serological assays demonstrated that recombinant MI43 fusion proteins react with sera from M. avium-infected mice, sera from patients with MAC disease, and sera from patients with active tuberculosis. These results further suggest that mycobacterial lipoproteins are important immunogens that should be considered in the development of improved mycobacterial vaccines and diagnostic reagents.