Mapping of a Coccidioides immitis-specific epitope that reacts with complement-fixing antibody

Abstract

We have previously cloned the cDNA fragment that encodes the complement fixation antigen of Coccidioides immitis. The recombinant protein was highly sensitive in detecting CF antibody in sera from patients with coccidioidomycosis but was not specific to C. immitis, as evidenced by its reactivity with sera from patients with histoplasmosis and, to lesser extent, blastomycosis. We undertook this study to determine if the epitope(s) that reacts with CF antibody is the same or differs from the epitopes that are shared with Histoplasma capsulatum and Blastomyces dermatitidis. PCR-generated CF/chitinase cDNA fragments were cloned and examined for their reactivity in enzyme-linked immunosorbent assays using sera from patients with coccidioidomycosis, histoplasmosis, or blastomycosis. A peptide domain comprised of amino acid residues 20 through 310 was shown to express an epitope(s) that is specific to anti-Coccidioides CF antibody. The peptide detected serum antibody in 21 (95%) of 22 patients with active coccidioidomycosis and was without reactivity with sera from 20 patients with histoplasmosis, 15 patients with blastomycosis, and 14 healthy subjects. Antibody titers to the recombinant peptide directly correlated with CF antibody titers (P < 0.01), and preadsorption of reference CF antiserum with the peptide ablated the reactivity of the antiserum in the immunodiffusion assay for CF antibody. The delineation of a recombinant peptide that has both sensitivity and specificity will provide a valuable tool for detecting CF antibody and for evaluating the role of CF antibody in the host response to C. immitis.

Clinical Laboratory Utility of a Humanized Antibody in Commercially Available Enzyme Immunoassays for Coccidioidomycosis

“…The use of recombinant CTS1 (rCTS1) and truncations of rCTS1 have been tested to measure anti-CF antibodies in VF patient serum using an EIA format ( 15 , 17 , 18 ). Currently, there are two Food and Drug Administration (FDA)-approved EIAs used for the qualitative detection of anti-coccidioidal IgG and IgM, Premier Coccidioides EIA (Meridian Bioscience, Cincinnati, OH) and clarus Coccidioides antibody EIA (Immuno-Mycologics, Inc. [IMMY], Norman, OK).…”

Development of a quantitative antigen assay to detect coccidioidal chitinase-1 (CTS1) in human serum

“…CTS1 is also known as the "CF" antigen used in serodiagnostics, namely complement fixation (CF) assays and its immunodiffusion correspondent (IDCF) [16,17]. It has since been produced recombinantly by several groups, and truncations of CTS1 have been explored to map antibodybinding sites to increase sensitivity and specificity for detecting antibodies to Coccidioides in patients [19][20][21][22][23].…”