Serological Comparison of the Two Morphological Phases of Paracoccidioides brasiliensis

The antigenic relationship of six different strains of Paracoccidioides brasiliensis was investigated by the agar-gel immunodiffusion test. Soluble antigens prepared from the two morphological phases of the fungus were diffused against human sera obtained from eight patients with paracoccidioidomycosis (South American blastomycosis). The mycelial phase showed common antigenic determinants as revealed by the formation of identical precipitin bands. The yeast phase proved to be more complex. Most of the strains produced a common antigen, but reactions of partial identity and of nonidentity were recorded for two strains. Antigens common to both mycelial and yeast phases were observed in five strains. The remaining strains, however, contained different antigenic determinants. The results of the experiment suggest that P. brasiliensis in its yeast form is not an antigenically homogeneous organism.