Immunoglobulins G, M, and A against Sporothrix schenckii exoantigens in patients with sporotrichosis before and during treatment with itraconazole

Abstract

Sporotrichosis is an important subcutaneous mycosis, with an increasing worldwide incidence. However, few data are available regarding the immunological aspects of Sporothrix schenckii infection, particularly the humoral responses to the fungus. In this study we measured immunoglobulin G (IgG), IgM, and IgA in sera from 41 patients with sporotrichosis before antifungal treatment and from another 35 patients with sporotrichosis during itraconazole treatment by using a recently described S. schenckii exoantigen enzyme-linked immunosorbent assay (ELISA). More than 95% of patients had detectable IgA antibodies, and more than 85% had IgM and IgG antibodies before treatment. The number of patients with IgG antibodies increased to 91% during treatment. Conversely, significantly fewer samples from treated patients were positive for IgM (71%) and IgA (89%). Overall, 78% of patients had detectable levels of all isotypes tested at diagnosis, and this percentage dropped to 62.9% in patients receiving itraconazole. Testing of all three isotypes improved the sensitivity; at least two isotypes were detected in 93% of patients before and 89% after treatment. The reactivity of 94 sera from patients with other diseases and healthy individuals was also tested. Cross-reactivity occurred in 33% of the heterologous sera. Most of them were positive only in one isotype, 8.5% were positive for at least two isotypes, and only one serum (1.1%) was positive for the three isotypes. Antibodies produced during S. schenckii infection are diverse, and we demonstrate that an exoantigen ELISA for the detection of combinations of IgA, IgG, and IgM antibodies is a highly sensitive and specific diagnostic assay for sporotrichosis.

FIG. 1.

Antibody levels in patients with several clinical forms of sporotrichosis against mycelial phase S. schenckii exoantigens. IgG (A and B), IgM (C and D), and IgA (E and F) ELISA results in patients with sporotrichosis who were not yet treated (A, C, and E) and in those receiving itraconazole (B, D, and F) are shown. Dashed lines indicate cutoff values for each single ELISA. FC, fixed cutaneous sporotrichosis; LC, lymphocutaneous sporotrichosis; DC, disseminated cutaneous sporotrichosis; EC, extracutaneous sporotrichosis.

FIG. 2.

Comparison between IgG (A), IgM (B), and IgA (C) antibody levels in patients with sporotrichosis in the group not yet treated and in the group receiving itraconazole. *, P < 0.05.

FIG. 3.

Correlation between time of treatment and levels of IgG (A), IgM (B), and IgA (C) in sera from patients with sporotrichosis. Dashed lines indicate the 95% confidence interval for the linear regression (continuous line) of values.

FIG. 4.

Cross-reactions observed in IgG (A), IgM (B), and IgA (C) ELISAs using mycelial-phase S. schenckii exoantigens. Cross-reactions were studied in 94 sera from patients with histoplasmosis (Histo), tuberculosis (TB), leishmaniasis (Leish), aspergillosis (Asp), paracoccidioidomycosis (PCM), and cryptococcosis (Crypto) and with sera from normal human subjects (NHS). Dashed lines indicate the cutoff values for each ELISA. Samples above the cutoff were considered positive.

FIG. 5.

Correlation between the antibody levels of different isotypes in each patient with sporotrichosis. The OD values for one ELISA were plotted versus the OD values of another ELISA to detect another isotype. The linear regression line in the middle is bracketed by two dashed lines, which indicate the 95% confidence interval. R² values were calculated for each comparison by using SigmaPlot 2000. (A) Comparison between IgG and IgM levels; (B) comparison between IgG and IgA levels; (C) comparison between IgM and IgA levels.