Mycobacterial Antigen Complex A60-specific T-cell Repertoire During the Course of Pulmonary Tuberculosis

The Mycobacterium bovis antigen complex A60 is known to be immunodominant in tuberculosis and to have a protective effect against experimental infection in vitro and in vivo. To identify immunodominant and possibly protective antigens in pulmonary tuberculosis, the T-cell repertoire directed to nitrocellulose-bound fractions of A60 antigen was analyzed in active tuberculosis patients during the course of the infection and after recovery. The results show that patients infected with Mycobacterium tuberculosis acquired reactivity only in the late phases of infection. At disease onset, patients with active tuberculosis were characterized by (i) T-cell unresponsiveness to most A60 fractions, (ii) high tumor necrosis factor alpha production, and (iii) low gamma interferon (IFN-gamma) release. Several weeks after chemotherapy, the unresponsive state disappeared and the following reverse situation was observed: (i) high blastogenic response to almost all A60 fractions, (ii) low tumor necrosis factor alpha release, and (iii) high IFN-gamma production. In addition, 60% of these patients significantly responded against seven A60 fractions (61 to 58, 56 to 53, 49 to 46, 46 to 44, 35 to 33, 33 to 30, and 30 to 28 kDa), indicating that they included immunodominant antigens. Furthermore, only the fractions within the molecular mass ranges of 56 to 44 and 35 to 28 kDa induced IFN-gamma synthesis. One year after complete recovery from infection, more than 60% of past-active tuberculosis subjects had memory T cells specific for the immunodominant fractions of 61 to 58, 56 to 53, 49 to 46, and 33 to 30 kDa. Since the same fractions induced the strongest IFN-gamma production, known to exhibit antimycobacterial effects, it is suggested that these may represent the inducers of a protective immune response.