Confirmation of a false-positive result associated with a competition inhibition assay used for detecting antibodies to a protein epitope of Mycobacterium leprae.

A competitive antibody-binding assay (CABA) was developed to detect antibodies in infected armadillos and leprosy patients which compete with an M. leprae-specific 125I monoclonal antibody IIIE9 for the species-specific M. leprae-IIIE9 epitope on the 65-kD protein. The results suggest armadillos and leprosy patients produce antibodies that inhibit the binding of 125I-IIIE9 monoclonal antibody to the IIIE9 epitope on crude, native 65-kD protein preparations. When purified, recombinant 65-kD protein was substituted for crude antigen, there was no evidence in the CABA of antibody to the IIIE9 epitope. False-positive results, possibly induced by steric hindrance, are likely to be associated with CABA which incorporate crude cell wall extracts as solid-phase antigen.