Enzyme-linked immunosorbent assay (ELISA): a study of antibodies to Mycobacterium tuberculosis in the IgG, IgA and IgM classes in tuberculosis, sarcoidosis and Crohn's disease.

Enzyme-linked immunosorbent assay (ELISA) has been used to study the levels of antibody binding to the soluble antigens of Mycobacterium tuberculosis (BCG) in the IgG, IgM and IgA classes in sera from patients with tuberculosis, sarcoidosis and Crohn's disease. Of the patients with tuberculosis, 75% had significantly elevated levels of anti-M. tuberculosis antibodies in the IgG class. The levels of antibodies in the IgM and IgA classes were much less discriminative. Many of the patients with sarcoidosis and Crohn's disease had significantly elevated levels of antimycobacterial antibodies, principally in the IgM and IgA classes. These elevated levels of antibody were not related to the total levels of the immunoglobulin classes. For the purpose of serodiagnosis, an estimation of the antimycobacterial antibodies in the IgG class gives the most discriminative results.