Immunofluorescent detection of Histoplasma capsulatum in primate experimental ocular histoplasmosis

We have developed a polyclonal anti-Histoplasma capsulatum antibody to detect H. capsulatum antigens in ocular tissue. Antibodies were specific for H. capsulatum as determined by enzyme linked immunosorbent assay and immunoprecipitation. A total of 21 choroidal histoplasmic lesions in 4 primate eyes (Macaca speciosa and Macaca mulatta), taken at various times from 14 to 60 days after the internal carotid artery injection of yeast phase organisms, were evaluated. Using an indirect immunofluorescent technique, these antibodies stained yeast phase organisms within acute choroidal lesions at 14 days after infection. By 60 days intact organisms were no longer detected; occasional cells, however, contained intracellular inclusions that stained with these antibodies. Although yeast phase organisms are rapidly cleared from the primate choroid, these data indicate that residual H. capsulatum antigens may remain in choroidal lesions after the acute infectious stage. These findings are consistent with the hypothesis that H. capsulatum antigens play a role in the immunologic reactivation of atrophic choroidal scars in ocular histoplasmosis.