A quantitative enzyme-linked immunoassay (ELISA) to approximate complement-fixing antibody titers in serum from patients with coccidioidomycosis.

Coccidioidomycosis is most frequently diagnosed serologically, and the quantitative test for complement-fixing antibodies is considered prognostically useful. Because complement-fixing antibody testing is complex, labor-intensive, and poorly standardized, an enzyme-linked immunoassay (ELISA) alternative would be attractive. In this report, we restrict the complement-fixing, antibody-binding domain to a 200-amino-acid recombinant peptide of the known antigen. Over-lapping truncations of this peptide do not bind complement-fixing antibodies, suggesting that the responsible epitope(s) are conformational. Further, anchoring the antigenic peptide to the ELISA plate by means of a C-terminal biotin-mimic peptide tag instead of allowing the peptide to randomly adhere to the plastic plate improves sensitivity of antibody detection by 1-2 logs in different sera. The newly developed ELISA shows a significant quantitative correlation with complement-fixing antibody titers. This ELISA shows potential as the basis for a new quantitative assay for coccidioidal antibodies.