Immunological characterization of antigens encoded by the RD1 region of the Mycobacterium tuberculosis genome

Development of immunoassays specific for the diagnosis of tuberculosis requ ires antigens unique to Mycobacterium tuberculosis. In a search for such an tigens we tested six proteins encoded by RD1, a region present in M. tuberc ulosis and virulent M. bovis genomes but missing from the DNA of all substr ains of M. bovis Bacillus Calmette-Guerin (BCG). The six proteins (Rv3871, Rv3872, Rv3873, MTSA-10, ESAT-6 and Rv3878) were purified to near-homogenei ty from recombinant Escherichia coli. When tested for the ability to elicit antibody responses and delayed type hypersensitivity in tuberculous guinea pigs, only two of six antigens, ESAT-6 and MTSA-10, elicited strong skin r eactions, while vigorous antibody responses were observed to all six protei ns. When antibody responses to RD1 antigens were evaluated in sera from pat ients having pulmonary tuberculosis and from control subjects (patients hav ing mycobacterioses other than tuberculosis, and healthy persons), a sizeab le proportion (25%) of tuberculosis patients but none of the control subjec ts, had antibodies against MTSA-10 and/or ESAT-6. We conclude that MTSA-10 and ESAT-6 are promising candidates for immunodiagnostic assays specific fo r tuberculosis.