[Evaluation of ELISA using A60 antigen from Mycobacterium bovis BCG: specific IGG and IGM in mycobacterial...

The authors have evaluated an ELISA (A60-Tb, Anda biologicals) allowing the detection of specific IgG and IgM against A60 antigen from Mycobacterium bovis BCG during mycobacterial infections. This study included sera from 110 african subjects and from 71 French subjects distributed in 4 clinical groups: 55 tuberculous patients (I), 41 leprous patients (II), 33 pneumopathies (III) and 52 healthy subjects (IV). Serological results were compared taking as reference for the diagnosis of tuberculosis the positivity of culture and/or that of a direct examination, and for leprosy the positivity of a direct examination associated either with a Mitsuda's reaction or with an histopathological examination. IgG were found to be more discriminative than IgM. Considering together the results of groups I and II, the authors found a sensitivity of 95.8 p. cent and a specificity of 75.3 p. cent with threshold of 200 U/ml for specific IgG. Anti-A60 antigen antibodies obtained for groups I and II were significantly higher (IgG: p less than 0.0001; IgM: p less than 0.001) than those observed in other groups. African subjects presented IgG titers higher than those obtained by French subjects (p less than 0.0001). IgM response was more frequent among group II (97.6 p. cent) than group I (21.8 p. cent). However, IgG (26.9 p. cent) and IgM titers (30.8 p. cent) were detected among group IV. This test would allow a control of therapeutic efficacy with an additional interest for classifying borderline forms of leprosy.