Molecular and immunological characterization of Mycobacterium tuberculosisCFP-10, an immunodiagnostic antigen missing in Mycobacterium bovis BCG

In order to identify antigens that may be used in the serodiagnosis of acti ve tuberculosis (TB), we screened a Mycobacterium tuberculosis genomic expr ession library with a pool of sera from patients diagnosed with active pulm onary TB. The sera used lacked reactivity with a recombinant form of the M. tuberculosis 38-kDa antigen (r38kDa), and the goal was to identify antigen s that might complement r38kDa in a serodiagnostic assay, Utilizing this st rategy, we identified a gene, previously designated lhp, which encodes a 10 0-amino-acid protein referred to as culture filtrate protein 10 (CFP-10), T he lhp gene is located directly upstream of esat-6, within a region missing in M. bovis BCG, Immunoblot analysis demonstrated that CFP-10 is present i n M. tuberculosis CFP, indicating that it is likely a secreted or shed anti gen. Purified recombinant CFP-10 (rCFP-10) was shown to be capable of detec ting specific antibody in a percentage of TB patients that lack reactivity with r38kDa, most notably in smear-negative cases, where sensitivity was in creased from 21% for r38kDa alone to 40% with the inclusion of rCFP-10. In smear-positive patient sera, sensitivity was increased from 49% for r38kDa alone to 58% with the inclusion of rCFP-10, In addition, rCFP-10 was shown to be a potent T-cell antigen, eliciting proliferative responses and gamma interferon production from peripheral blood mononuclear cells in 70% of pur ified protein derivative-positive individuals without evident disease. The responses to this antigen argue for the inclusion of rCFP-10 in a polyvalen t serodiagnostic test for detection of active TB infection. rCFP-10 could a lso contribute to the development of a recombinant T-cell diagnostic test c apable of detecting exposure to M. tuberculosis.