Isolation of a 19-kDa mycobacterium, bovis-specific antigen, different from MPB70/80, by chromatofocusing

Two antigens, 19-kDa each, were purified from Mycobacterium bovis culture filtrate protein extract by chromatofocusing. Antigen I had a 4.5 pI, and its amino terminal (DPVDAVINTTCNYGQVVAALNATDP) showed a 100% homology with the hypothetical protein Rv1174c. Antigen II had a pI of 6.0 pI and its amino terminal (GDLVGPGCAEYAAANPTGPASVQGM) showed a 100% homology with M. bovis MPB70/80. Antigen I is a hetero-dimer formed by a glycosylated, 10.5-kDa, monomer and a non-glycosylated 8-kDa monomer with identical amino terminal sequences. Both antigens were recognized by the sera of PPD+ animals, but antigen I did not crossreact with sera of human PPD+ individuals. Antigen I was a weak inducer of lymphocyte proliferation and IFN-gamma production. Our results show that M. bovis expresses a 19 kDa glycoprotein, homologue to the product of M. tuberculosis gen Rv1174c, which may prove useful for bovine TB diagnostic assays.