Immunoblot analysis of antibody responses to Sporothrix schenckii

The serologic response to Sporothrix schenckii was investigated in patients with sporotrichosis by solid-phase enzyme-linked immunosorbent assays (ELISAs) and Western immunoblot techniques. A soluble antigen preparation derived from an S. schenckii isolate contained 15 protein staining components ranging in molecular size from 22 to 70 kilodaltons (kDa) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sera from 40 patients with sporotrichosis demonstrated Sporothrix immunoglobulin G antibody by ELISA with titers between 128 and 65,200. No sera from 300 healthy individuals or 100 patients with various systemic mycoses other than sporotrichosis had ELISA titers greater than 64. By Western immunoblotting of the antigens separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, sera from 10 patients with cutaneous sporotrichosis reacted with 8 to 10 antigen components (range, 40 to 70 kDa), while sera from 15 patients with extracutaneous sporotrichosis reacted with a greater number of antigen components (15 to 20 bands) over a wider range of molecular sizes (22 to 70 kDa). Antibody to 40- and 70-kDa antigen components was detected by immunoblots in all sera tested from patients with sporotrichosis. Antibody to 22- to 36-kDa antigen components was present in sera from 13 of 15 patients with extracutaneous sporotrichosis, but these lower-molecular-weight components were not detected by sera from patients with cutaneous sporotrichosis. Antibody to these components was not detected by Western blotting in sera from 19 of 20 patients with other fungal diseases or from 30 healthy individuals. Purification of these specific antigen fractions could provide the basis of a sensitive and specific serodiagnostic test to indicate the presence and activity of extracutaneous sporotrichosis.