ELISA method for evaluation of anti-A60 IgG in patients with pulmonary and extrapulmonary tuberculosis

Several studies on the IgG mediated humoral immune response against the mycobacterial antigen A60 are available in the literature. However extensive variability in observed responses has been reported. In the present study we measured by ELISA the titers of IgG antibodies against A60 in 50 tuberculin negative healthy subjects, (Group I); 44 tuberculin positive healthy subjects, (Group II); 13 patients with healed Tuberculosis (Group III); 22 patients with a defined acute or chronic Non Tuberculous Pulmonary Pathology (Group IV); 42 patients suffering from sputum positive Active Pulmonary Tuberculosis, (Group V); 15 patients with sputum negative Active Pulmonary Tuberculosis (Group VI) and 16 patients with Active Extrapulmonary Tuberculosis (Group VII). The assay was performed at the time of recruitment into the study, corresponding for patients of Groups IV to VII to the day of hospital admission; in patients from Groups III to VII the assay was repeated two weeks later. The cut-off point was defined as mean +2SD of values found in Groups I-IV and was 0.372 (expressed in Optical Density). By using this cut-off, the test on first blood samples was positive in 1/50 subjects from Group I, 1/44 from Group II, 0/13 from Group III, 3/22 patients from Group IV, 35/42 from Group V, 9/15 from Group VI, 9/16 from Group VII. On second blood samples, kept 9-12 days after starting anti-TB chemotherapy in Groups V, VI and VII, the test resulted positive in 0/13 patients from Group III, 3/22 from Group IV, 39/42 from Group V, 13/15 from Group VI and 14/16 from Group VII.