Production and characterization of a monoclonal antibody to the complement fixation antigen of Coccidioides immitis

Detection of complement-fixing antibody to coccidioidin by using the complement fixation test or an immunodiffusion assay for complement-fixing antibody (IDCF) is widely viewed as the most useful immunodiagnostic test for coccidioidomycosis. In this investigation, we report the production of an immunoglobulin G subclass 1 (IgG1) monoclonal antibody (MAb) to the IDCF antigen for use as a biospecific ligand for purifying the IDCF antigen on solid-phase immunosorbents and for use as a reagent for screening genomic or cDNA expression libraries from Coccidioides immitis. BALB/c mice were immunized by intramuscular injections of coccidioidin in adjuvant, followed by an intrasplenic booster injection of coccidioidin in saline. The spleen cells were fused with SP2/0 Ag14 myeloma cells, and the fusion products were screened for IgG antibody to coccidiodin by using an enzyme-linked immunosorbent assay. Positive hybridomas were cloned and evaluated for reactivity to the IDCF antigen by two-dimensional immunoelectrophoresis and by immunoblotting. An IgG1 Mab was produced that was specific for the IDCF antigen when evaluated by two-dimensional immunoelectrophoresis and immunoblotting. The epitope recognized by the MAb was heat labile (60 degrees C, 30 min) and susceptible to enzymatic digestion with pronase but was resistant to treatment with lipase, alpha-mannosidase, glucose oxidase, and endoglycosidase H. This heat-labile peptide epitope appears to be specific to C. immitis, as judged by the fact that the MAb was not reactive in immunoblots or enzyme-linked immunosorbent assays of histoplasmin or blastomycin.