The effect of the inflammatory response against smooth and mucoid switch variants of Cryptococcus neoformans on the outcome of infection

Abstract

Cryptococcus neoformans is an encapsulated pathogenic fungus that causes meningoencephalitis in HIV infected individuals. The RC-2 strain of C. neoformans can undergo a process, known as phenotypic switching. In this process the RC-2 smooth parental strain switches to the hypervirulent mucoid strain. The inflammatory response in SM infected mice is associated with higher production levels of IL-10 cytokine. Compared to the inflammatory response elicited in the lungs of MC infected mice, which is associated with enhanced recruitment of macrophages. In this thesis we describe experiments designed to link the host inflammatory response to the differences in the outcome of infection.;First, we determined the role of IL-10 during SM and MC infection by infecting IL-10-/- mice with the switch variants. SM infected IL-10-/- mice survived significantly longer than SM infected control mice. In contrast to SM infected mice, no survival benefit was documented between MC infected IL-10-/- and wild type mice. The inflammatory response in the lungs of MC infected mice was associated with higher production of IL-6, TGF-beta, IFN-gamma type cytokines. Compared to SM infected mice was associated with enhanced recruitment of CD4+ cells and TNF-alpha production.;Next, we examined the role of macrophages during SM and MC infection. RTPCR of mRNA from isolated macrophages of SM and MC infected mice demonstrated higher arginase expression in the macrophages isolated from MC infected mice compared to SM infected mice. In addition, PD-L2 and MHC II gene expression was higher in alveolar macrophages isolated from MC infected mice compared to SM infected mice. It was determined by intracellular staining and ELISA that Th17 cells and IL-17 cytokine was higher in the lungs of MC infected mice compared to SM infected mice. Furthermore, IL-17 cytokine protein levels were lower in alveolar macrophage depleted mice infected with MC cells compared to control infected mice, which were not depleted of macrophages. We propose a model, which links differences in macrophage activation during MC infection to the emergence of IL-17 producing Th17 cells. The production of IL-17 cytokine maintains an uncontrolled inflammatory response resulting in death in MC infected mice.