Insights into the Mechanisms of Protective Immunity against Cryptococcus neoformans Infection Using a Mouse Model of Pulmonary Cryptococcosis

Abstract

Cryptococcus neoformans is an opportunistic fungal pathogen that causes life-threatening pneumonia and meningoencephalitis in immune compromised individuals. Previous studies have shown that immunization of BALB/c mice with an IFN-γ-producing C. neoformans strain, H99γ, results in complete protection against a second pulmonary challenge with an otherwise lethal cryptococcal strain. The current study evaluated local anamnestic cell-mediated immune responses against pulmonary cryptococcosis in mice immunized with C. neoformans strain H99γ compared to mice immunized with heat-killed C. neoformans (HKC.n.). Mice immunized with C. neoformans strain H99γ had significantly reduced pulmonary fungal burden post-secondary challenge compared to mice immunized with HKC.n. Protection against pulmonary cryptococcosis was associated with increased pulmonary granulomatous formation and leukocyte infiltration followed by a rapid resolution of pulmonary inflammation, which protected the lungs from severe allergic bronchopulmonary mycosis (ABPM)-pathology that developed in the lungs of mice immunized with HKC.n. Pulmonary challenge of interleukin (IL)-4 receptor, IL-12p40, IL-12p35, IFN-γ, T cell and B cell deficient mice with C. neoformans strain H99γ demonstrated a requirement for Th1-type T cell-mediated immunity, but not B cell-mediated immunity, for the induction of H99γ-mediated protective immune responses against pulmonary C. neoformans infection. CD4+ T cells, CD11c+ cells, and Gr-1+ cells were increased in both proportion and absolute number in protected mice. In addition, significantly increased production of Th1-type/pro-inflammatory cytokines and chemokines, and conversely, reduced Th2-type cytokine production was observed in the lungs of protected mice. Interestingly, protection was not associated with increased production of cytokines IFN-γ or TNF-α in lungs of protected mice. In conclusion, immunization with C. neoformans strain H99γ results in the development of protective anti-cryptococcal immune responses that may be measured and subsequently used in the development of immune-based therapies to combat pulmonary cryptococcosis.

Dendritic Cell-Based Immunization Ameliorates Pulmonary Infection with Highly Virulent Cryptococcus gattii

“…engulf fungal cells in granulomas is associated with protection from cryptococcosis due to C. neoforomans, which is also associated with an increase in cytokine-producing T cells, such as Th1 and Th17 cells (30)(31)(32)(33). Because DC-based vaccines reportedly augmented cytokine-producing effector T cells (17,34), we assessed cytokine-producing T cells in the spleen and lungs after vaccination.…”

Interleukin-17 Is Not Required for Classical Macrophage Activation in a Pulmonary Mouse Model ofCryptococcus neoformansInfection

“…Conversely, we observed increases in the expression of hallmark markers of aaMac (arginase, CD206, FIZZ1, and Ym1), uncontrolled microbial growth, and Th2-type cytokine secretion in the lungs of mice during infection with wild-type cryptococci (15). In addition to a robust Th1-type cytokine response, infection with C. neoformans strain H99␥ is also associated with a significant increase in IL-17A cytokine expression in the lungs (15,38).…”

“…Previous studies demonstrated that experimental pulmonary infection with a C. neoformans strain engineered to express IFN-␥, strain H99␥, results in the generation of a polarized Th1-type cytokine response in mice (36). Mice given a pulmonary infection with C. neoformans strain H99␥ resolve the acute infection and are completely protected from a secondary infection with wild-type (WT) cryptococci (36,38,40). Recently, we demonstrated that clearance of infection with C. neoformans strain H99␥ is associated with the induction of inducible nitric oxide synthase (iNOS) expression, caMac, and pulmonary Th1-type cytokine production (15).…”

Cryptococcus inositol utilization modulates the host protective immune response during brain infection

“…During cryptococcal infection, engagement of surface receptors, such as TLR-4, has been reported to signal TNF-α production, activation of macrophages and dendritic cells as well as other immune cells that are important not only for the early control of infection, but also essential for IFN-γ production by the T-cells and establishing an effective adaptive immunity [29]. Together, IFN-γ and TNF-α regulate several downstream cellular networks/pathways involved in the host protective Th-1 type immune response against infecting pathogen [30,31]. This is evident by the increased cryptococcosis among humans and experimental animals that are either defective in producing these cytokines or lacking sufficient T cells [32,33].…”