Optimization of antigen preparations from Coccidioides for diagnostic testing

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Summary: Coccidioidomycosis (Valley Fever, “VF”) is caused by a soil-dwelling fungus endemic to the southwestern U.S. and central valley in California. The Coccidioides fungus is a dimorphic organism with a mycelial form in soil and spherules (a yeast-like form) in a human host. When soil is disrupted, mycelial spores become airborne and can be inhaled into lungs where they transform into spherules. As spherules burst they release endospores, each of which can grow into a new spherule. Fungal pneumonia may mimic cancer or other community acquired pneumonias (bacterial and viral), but should be recognized as fungal and treated differently. Current diagnostic tests rely on a serologic (antibody) response to fungal antigens. For over 50 years, antigen preparations for detecting antibodies in patients suspected of having Valley Fever have been derived from mycelia which is rich with an antigen called CF (also called CTS-1 or chitinase-1). Serologic assays may be performed by enzyme immunoassay, immunodiffusion or a complement fixation assay to detect antibodies against the fungus. The clinical problem is that approximately 30-50% of patients who are acutely ill initially test sero- negative using current tests, leading to inappropriate treatment. We suggest that one of the reasons for sero-negativity is that mycelial antigen preparations, not spherule antigens, are used for detection of patient antibodies. Since spherules, not mycelia, are what grow in a host, we hypothesize that patients are more likely to make antibodies to antigens predominantly in spherules, the form that grows in the host. In fact, our analysis of the proteomes of Coccidioidal spherules and mycelia demonstrated that the CF (CTS-1, chitinase-1) antigen is highly expressed in mycelia, but not spherules (CF levels are 70-fold higher in mycelia than spherules). Continued proteomic analysis revealed that several other proteins are more highly expressed in spherules than mycelia. The objectives of this grant are to test sero-negative, sero-positive and control patient sera for reactivity and titers against 3 recombinant spherule proteins and to compare titers to commercially available antigen preparations. If sero-negative and sero-positive patient sera are more reactive with spherule antigens alone–or spiked into current diagnostic antigen preparations, this work could translate into a more sensitive, reliable, and consistent antigen preparation for accurate serologic diagnosis of patients with Valley Fever.