The WI-1 adhesin is indispensable for pathogenicity of Blastomyces dermatitidis and is thought to promote pulmonary infection by fixing yeast to lung tissue and cells. Recent findings suggest that WI-1 confers pathogenicity by mechanisms in addition to adherence. Here, we investigated whether WI-1 modulates host immunity by altering production of pro-inflammatory cytokines. Production of TNF-α in lung alveolar fluids of mice infected with B. dermatitidis was severalfold higher for WI-1 knockout yeast compared with wild-type yeast, and in vitro coculture of unseparated lung cells with these isogenic yeast disclosed similar differences. Upon coculture with purified macrophages and neutrophils, wild-type yeast blocked TNF-α production, yet WI-1 knockout yeast stimulated production. Coating knockout yeast with purified WI-1 converted them from stimulating TNF-α production to inhibiting production. Addition of purified WI-1 into stimulated phagocyte cultures led to concentration-dependent inhibition of TNF-α production. Neutralization of TNF-α in vivo exacerbated experimental pulmonary infection, particularly for the nonpathogenic WI-1 knockout yeast. Inducing increased TNF-α levels in the lung by adenovirus-vectored gene therapy controlled infection with wild-type yeast. Thus, the WI-1 adhesin on yeast modulates host immunity through blocking TNF-α production by phagocytes, which fosters progression of pulmonary infection.

TNF-α is crucial in defense against intracellular microbes. Host immune cells use type 3 complement receptors (CR3) to regulate excess TNF-α production during physiological clearance of apoptotic cells. BAD1, a virulence factor of Blastomyces dermatitidis, is displayed on yeast and released during infection. BAD1 binds yeast to macrophages (Mφ) via CR3 and CD14 and suppresses TNF-α, which is required for resistance. We investigated whether blastomyces adhesin 1 (BAD1) exploits host receptors for immune deviation and pathogen survival. Soluble BAD1 rapidly entered Mφ, accumulated intracellularly by 10 min after introduction to cells, and trafficked to early and late endosomes. Inhibition of receptor recycling by monodansyl cadaverine blocked association of BAD1 with Mφ and reversed TNF-α suppression in vitro. Inhibition of BAD1 uptake with cytochalasin D and FcR-redirected delivery of soluble BAD1 as Ag-Ab complexes or of wild-type yeast opsonized with IgG similarly reversed TNF-α suppression. Hence, receptor-mediated entry of BAD1 is requisite in TNF-α suppression, and the route of entry is critical. Binding of soluble BAD1 to Mφ of CR3−/− and CD14−/− mice was reduced to 50 and 33%, respectively, of that in wild-type mice. Mφ of CR3−/− and CD14−/− mice resisted soluble BAD1 TNF-α suppression in vitro, but, in contrast to CR3−/− cells, CD14−/− cells were still subject to suppression mediated by surface BAD1 on wild-type yeast. CR3−/− mice resisted both infection and TNF-α suppression in vivo, in contrast to wild-type and CD14−/− mice. BAD1 of B. dermatitidis thus co-opts normal host cell physiology by exploiting CR3 to subdue TNF-α production and foster pathogen survival.