Comparison of skin reactivity of spherule and mycelial coccidioidins produced by different strains of Coccidioides immitis

Coccidioidin produced from mycelial and spherule phases of growth of three strains of C. immitis were compared for skin reactivity. Spherule coccidioidin was about 17 times more active on a weight basis than mycelial coccidioidin. When each of the coccidioidins was adjusted to equipotency in guinea pigs sensitized with the homologous strain and form of organisms, all of the skin test preparations were virtually equivalent in reactivity in heterologously as well as homologously sensitized animals. Skin testing sometimes rendered animals less reactive to a second skin test.