Mannose Receptor Is Required for Optimal Induction of Vaccine-Induced T-Helper Type 17 Cells and Resistance to Blastomyces dermatitidis Infection

Abstract

We investigated how innate sensing by the mannose receptor (MR) influences the development of antifungal immunity. We demonstrate that MR senses mannan on the surface of attenuated Blastomyces dermatitidis vaccine yeast and that MR(-/-) mice demonstrate impaired vaccine immunity against lethal experimental blastomycosis, compared with wild-type control mice. Using naive Blastomyces-specific transgenic CD4(+) T cells, we found that MR regulates differentiation of naive T cells into T-helper type 17 (Th17) effector cells, which are essential in vaccine immunity against systemic dimorphic fungi. Thus, MR regulates differentiation of Th17 cells and is required to induce vaccine immunity against lethal pulmonary blastomycosis.

Keywords: T-cell differentiation; fungi; mannose receptor; vaccine immunity.

Figure 1.

Fungal mannan drives T-helper type 17 (Th17) responses through mannose receptor (MR). A, ConA-FITC staining of Blastomyces dermatitidis yeast. B, Soluble mannan derived from Candida albicans blocks vaccine yeast–induced interleukin 17 (IL-17) production by 1807 cells in a dose-dependent manner. In the absence of yeast, mannan did not trigger an IL-17 response by 1807 cells (data not shown). *P < .05 vs non–mannan-treated controls. C, Naive 1807 cells primed by bone marrow–derived dendritic cells (BMDCs) to become Th17 cells. Wild-type and MR^−/− dendritic cells (DCs), yeast, and naive 1807 cells were cocultured for 3 days, and supernatants were analyzed by an enzyme-linked immunosorbent assay. *P < .05 vs wild-type control. Data are representative of 3 independent experiments. D, mCherry-expressing yeast were cocultured with BMDCs at a multiplicity of infection of 1:1 (yeast to BMDCs; for cytokine production) and 1:10 (for antigen uptake). Cytokine levels in the cell culture supernatant were measured at 16 hours, and yeast ingestion was measured at 5 hours and 48 hours. To distinguish intracellular yeast from extracellular yeast, cocultures were stained with Uvitex. CD11b⁺ events were gated on and assessed for the frequencies of mCherry- and Uvitex-positive events. Data are expressed as mean values ± standard errors of the mean (n = cells raised from 4 mice/group) and are representative of 2 independent experiments. *P < .05 vs wild-type controls.

Figure 2.

Mannose receptor (MR) drives protective T-helper type 1 (Th1) and Th17 cells and vaccine-induced resistance. A and B, Wild-type and MR^−/− mice adoptively received 10⁶ CD4⁺ purified, naive 1807 transgenic (Tg) cells (Thy1.1⁺) and were or were not vaccinated with 10⁶ heat-killed vaccine yeast. Four weeks after vaccination, mice were challenged intratracheally with 2 × 10⁴ strain 26199 yeast, and the number of activated (CD44⁺) and cytokine-producing lung CD4⁺ T cells were enumerated at day 4 after infection. Dot plots show concatenated samples of 4–6 mice/group. The numbers indicate mean values ± standard errors of the mean (SEMs) of activated (CD44^hi) endogenous CD4⁺ and transferred 1807 Tg (Thy1.1⁺) T cells. Data are representative of 2 independent experiments. *P < .05 vs yeast-stimulated, non–mannan-treated controls. C, Cytokine transcripts in lung homogenates were analyzed at day 4 after infection, and cytokine levels were measured in ex vivo–stimulated splenocytes. D, The lung burden was assessed at day 4 and 2 weeks after infection. Data are the average and SEMs of 3 independent experiments. *P < .05 vs infected wild-type controls. Abbreviations: CFUs, colony-forming units; IFN-γ, interferon γ; IL-17, interleukin 17.