Abstract
Detection of IgG antibodies against purified protein derivative (PPD) prepared fromMycobacterium tuberculosis strain Aoyama B and alpha antigen, a homogeneous proteinprepared from M. tuberculosis strain H37Rv by immunosorbent affinity chromatography, was done by a method of enzyme-linked immunosorbent assay (ELISA) and its diagnosticusefulness was also evaluated in this study. Sera from 80 patients with active pulmonarytuberculosis, 25 patients with inactive tuberculosis, 200 healthy adults, 117 healthy children, 84 patients with diseases other than tuberculosis and seven patients due to atypicalmycobacteria were examined. The titer of each test serum was calculated by a computersystem using the standard curve obtained by serial dilution of a standard serum. Use ofphosphate buffer saline (PBS) with gelatin as blocking buffer in ELISA showed considerablyuseful results than the use of PBS with bovine serum albumin.
Patients with active pulmonary tuberculosis showed statistically higher amount of IgGantibodies against PPD or alpha antigen than other groups (p<0.001). The sensitivitywas 73.8% and the specificity was 97.0% at a cut-off titer of 1: 330 in and-PPD antibodyassay. On the other hand, the sensitivity was 77.5% and the specificity was 93.3% at acut-off titer of 1: 540 in and-alpha antibody assay. However, the sensitivity of 91.3% and the specificity of 91.7% could be obtained with parallel application of both assays.
Slight elevation of antibody titers was observed in the first or second month afteradministration of some anti-tuberculosis drugs and then these titers decreased gradually.
Seven false-negative cases in active tuberculosis were observed in two patients with hypogamma-globulinemia, two casts with diabetes mellitus and three cases of fresh pulmonarytuberculosis without chemotherapy, and five of these false negative cases were positive onsmear stained by Ziehl-Neelsen's method.
From these results, it is concluded that judgment by combination of several antibodyassays using different antigens of M. tuberculosis is helpful in the diagnosis of activepulmonary tuberculosis when compared with any assay using single antigen. In addition toabove, the measurement of antibody to M. tuberculosis will be also a useful marker for thejudgment of the chemotherapeutic efficacy or clinical improvement.
