Histolyn CYL, the yeast phase
reagent, has been employed as the
antigen in an
enzyme immunoassay (ELISA) to detect antibody to Histoplasma capsulatum in sera from experimentally sensitized rabbits and from humans with
histoplasmosis. Three different lots of
Histolyn CYL were initially evaluated with respect to antibody detection in individual and pooled rabbit serum specimens. Optimal reactivity was obtained with 4.5 micrograms (total dry weight) per ml of lots 2 and 3 of the
reagent. The optimally diluted pooled
reagent detected antibody titers ranging from 1:16 to 1:8192 in 36 rabbit sera. In contrast, a marked decrease in sensitivity was evidenced when the same sera were assayed by
complement fixation and immunodiffusion tests with commercially available reference
reagents.
Complement fixation titers ranged from 0 to 1:128 and immunodiffusion tests on undiluted sera were positive with only 5 specimens. Twenty-five sera from patients with acute, chronic and
disseminated histoplasmosis were also assayed by the ELISA with the
reagent described above. Titers ranged from less than 1:16 to 1:20,480 or greater.
Complement fixation titers ranged from 0 to 1:1024 (mycelial
antigen) and from 0 to 1:256 (whole yeast cell
antigen). No antibody was detected in 7 specimens with mycelial
antigen or in 3 specimens with the yeast cell
antigen. Immunodiffusion tests on undiluted sera were positive with 9 of 11 specimens. Minimal cross reactivity was evidenced when
Histolyn CYL was used in the ELISA to detect anti-Coccidioides immitis antibody in sera from infected animals and humans. These data encourage the continued development of this method for the serodiagnosis of human histoplasmal
infection.