Specific antibody in the subclasses of immunoglobulin G in patients with smear-positive pulmonary tuberculosis.

Discrimination between patients with smear-positive pulmonary tuberculosis and healthy adults achieved by the assay of serum anti-mycobacterial antibodies in the major immunoglobulin class (IgG) was greatly improved by assay of antibodies in its four subclasses. By the former method, only 55 of 107 (51%) patients had antibody levels above the upper limit of 31 control sera, but 96 (90%) patients had levels above the upper control level in one or more of the IgG subclasses. Antibody levels in the IgA and IgM classes were less discriminative, but four patients with no elevated levels in the IgG subclasses had elevated IgA antibody levels, bringing the total of patients with significant serological changes compatible with tuberculosis to 100 (93.5%).