Immunogenicity and protective efficacy of the WI-1 adhesin of Blastomyces dermatitidis

Abstract

People infected with Blastomyces dermatitidis develop strong immunity to the yeast surface adhesin WI-1, including antibody responses to the adhesive domain, a 25-amino-acid repeat, and cellular responses to the N terminus. We studied the immunogenicity of WI-1 and the ability of anti-WI-1 immune responses to protect against lethal pulmonary infection in mice. WI-1 immunization, given in Freund's adjuvant subcutaneously in two doses 2 weeks apart, evoked delayed hypersensitivity responses in a concentration-dependent manner. Immunized mice also had anti-WI-1 antibody responses, with titers reaching an endpoint dilution of approximately 1:800,000. Anti-WI-1 immunoglobulin G (IgG) antibody subclasses were IgG1 > IgG2b > IgG2a > IgG3, indicating a mixed T helper 1 and T helper 2 immune response. In protection experiments, WI-1 immunization significantly prolonged the survival of C57BL/6 and BALB/c mice compared to controls following intranasal administration of a lethal dose of B. dermatitidis yeasts (Kaplan-Meier survival curve P values of 0.027 to 0.0002) and also protected a proportion of the animals from death due to progressive pulmonary blastomycosis. Taken together, our results suggest that administration of WI-1 raises antibody and cell-mediated immune responses, which enhance resistance against pulmonary infection with B. dermatitidis. Mechanisms of vaccine-induced resistance require further investigation.

FIG. 1

Immunization with WI-1 induces delayed-type hypersensitivity responses in a concentration-dependent manner. Groups of three C57BL/6 mice were immunized with various doses of WI-1 or live yeast according to the protocol described in Materials and Methods. Mice were tested 2 weeks after the second immunization for delayed-type hypersensitivity by administration of 10 μg of WI-1 in saline into one footpad and saline alone into the other footpad. Measurements were taken 24 h later. Error bars represent standard errors of the mean.

FIG. 2

Anti-WI-1 IgG subclasses in four C57BL/6 mice per group immunized with either 100 μg of WI-1, 10⁶ heat-killed yeasts (HK Yst), or 4 × 10⁴ live yeast (Live Yst) subcutaneously (A) and three C57BL/6 mice per group immunized with various doses of WI-1 as shown (B). In each experiment, sera were obtained 2 weeks after the second immunization and analyzed for anti-WI-1 IgG subclass by ELISA. Error bars indicate standard error of the mean. OD, optical density. NMS, normal mouse serum.

FIG. 3

Protective efficacy of WI-1 immunization against lethal pulmonary blastomycosis. Groups of C57BL/6 mice were immunized subcutaneously either with 100 μg of WI-1 or with BSA according to the protocol described in Materials and Methods. Two weeks after a second immunization, the mice were challenged with a lethal dose of 10⁴ B. dermatitidis ATCC 60636 yeasts and observed for survival. Kaplan-Meier survival curves were generated for WI-1-immunized mice and control mice during an observation interval of 30 days after experimental infection.