T-Cell Epitopes and Human Leukocyte Antigen Restriction Elements of an Immunodominant Antigen ofBlastomyces dermatitidis

Abstract

Humans infected with the dimorphic fungus Blastomyces dermatitidis develop strong T-lymphocyte responses to WI-1, an immunodominant antigen that has been shown to elicit protective immunity in mice. In the present study, the T-cell epitopes of WI-1 and human leukocyte antigen (HLA) restricting elements that display them were investigated. Peripheral blood mononuclear cells (PBMC) from 37 patients with a confirmed history of blastomycosis were tested for a response to WI-1 in primary proliferation assays; PBMC from 35 (95%) responded. Six patients whose PBMC proliferated strongly in response to WI-1 (defined as a stimulation index greater than 50) were tested further for responses to subcloned, recombinant fragments of the antigen. These patients responded chiefly to sequences within the N terminus and the 25-amino-acid tandem repeat. Cloned CD4 ؉ T cells from an infected individual were used to delineate more precisely the peptide epitopes in the fragments and HLA restricting elements that present them. A majority of the T-cell clones recognized an epitope spanning amino acids 149 to 172 within the N terminus, displayed by HLA-DR 15. A minority of the clones, which have been shown to perform a cytolytic function in vitro, recognized an epitope in the tandem repeat displayed by HLA-DPw4, an uncommon restricting element. Tandem repeat epitopes required display by the ␤ chain of DPw4 heterodimers. Thus, human T cells with different functions in vitro also recognize distinct regions of WI-1, raising the possibility that HLA restricting elements that present them could modulate immunity during blastomycosis by selection and display of WI-1 peptides.Blastomyces dermatitidis is a dimorphic fungus that causes disease in both healthy and immunodeficient hosts. The fungus is endemic to the Mississippi and Ohio River valleys and northern Wisconsin. The spectrum of infection includes asymptomatic disease, acute or chronic pneumonia, and disseminated disease, especially in immunodeficient patients, who are at higher risk for developing widely disseminated blastomycosis (19,20).The growing frequency of invasive fungal diseases and the challenge of treating them have stimulated interest in developing ways to prevent fungal infections. The immunodominant and protective antigens for many fungal pathogens have not been elucidated and are actively being investigated (7). For B. dermatitidis, we previously described a 120-kDa protein antigen, WI-1, expressed abundantly on yeast phase cells. WI-1 is an adhesin that binds the fungus to receptors on human macrophages (17) and confers virulence on the yeast (2) and is also an immunodominant antigen that stimulates humoral and cellmediated immune responses during natural infection (11,12). Immunization of mice with WI-1 significantly enhances their resistance against a lethal pulmonary challenge with B. dermatitidis (25), an indication that anti-WI-1 immune responses benefit the host. Thus, WI-1 may serve as a candidate for developing a vaccine against blastomycosis.Studies of mice and ...

Identification of Novel Immunodominant CD4+Th1-Type T-Cell Peptide Epitopes from Herpes Simplex Virus Glycoprotein D That Confer Protective Immunity

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