Cryptococcus gattii alters immunostimulatory potential in response to the environment

Abstract

Cryptococcus gattii is a capsular fungal pathogen, which causes life-threatening cryptococcosis in immunocompetent individuals. This emerging pathogen is less likely to be recognized by innate immunity compared to traditional Cryptococcus neoformans strains. Previous studies indicate that C-type lectin receptors (CLRs), including dectin-1 and dectin-2, play a role in recognizing cryptococcal cells; however, it remains to be elucidated whether the receptors physically associate with C . gattii yeast cell surfaces. Based on the previous findings, we hypothesized that culture conditions influence the expression or exposure of CLR ligands on C . gattii . Therefore, in the present study, we first investigated the culture conditions that induce exposure of CLR ligands on C . gattii yeast cells via the binding assay using recombinant fusion proteins of mouse CLR and IgG Fc, Fc dectin-1 and Fc dectin-2. Common fungal culture media, such as yeast extract–peptone–dextrose (YPD) broth, Sabouraud broth, and potato dextrose agar, did not induce the exposure of dectin-1 ligands, including β-1,3-glucan, on both capsular and acapsular C . gattii strains, in contrast to Fc dectin-1 and Fc dectin-2 bound to C . gattii cells growing in the conventional synthetic dextrose (SD) medium [may also be referred to as a yeast nitrogen base with glucose medium]. The medium also induced the exposure of dectin-1 ligands on C . neoformans , whereas all tested media induced dectin-1 and dectin-2 ligands in a control fungus Candida albicans . Notably, C . gattii did not expose dectin-1 ligands in SD medium supplemented with yeast extract or neutral buffer. In addition, compared to YPD medium-induced C . gattii , SD medium-induced C . gattii more efficiently induced the phosphorylation of Syk, Akt, and Erk1/2 in murine dendritic cells (DCs). Afterwards, the cells were considerably engulfed by DCs and remarkably induced DCs to secrete the inflammatory cytokines. Overall, the findings suggest that C . gattii alters its immunostimulatory potential in response to the environment.

Pro-inflammatory response ensured by LPS and Pam3CSK4 in RAW 264.7 cells did not improve a fungistatic effect on Cryptococcus gattii infection

“…Macrophage polarization occurs in different sources of macrophages and the microenvironment and innate immune receptors are major inductors in differentiation to M1 or M2 subsets ( Mantovani et al, 2004 ; Wang, Liang & Zen, 2014 ). The modulation of M1- and M2-type macrophage polarization can be orchestrated by C. gattii compounds through interactions with receptors on the cell surface ( Ueno et al, 2019 ). In this context, carbohydrates located in the C. gattii capsule can inhibit TLR2 and TLR4 signaling, which is a mechanism to subvert the host immune response.…”

Cryptococcus gattii evades CD11b‐mediated fungal recognition by coating itself with capsular polysaccharides

“…In brief, BM cells were cultivated in GM-CSF-containing medium for 6 days to induce BMDC deferentiation [15][16][17]. In some experiments, peritoneal exudate cells (PECs), including resident macrophages or the macrophage-like cell line J774A.1, were used instead of BMDCs.…”

Vaccines and Protective Immune Memory against Cryptococcosis

“…35,36) We demonstrated that capsular cryptococcal cells could not be recognized by immune cells without opsonization and that acapsular mutants are immediately engulfed by innate immune cells. 14,37,38) Cryptococcal cells can be opsonized with anti-GXM antibody, and opsonized capsular cells are phagocytized by innate immune cells. 39,40) Thus, it is reasonable to use GXM or GalXM as vaccine antigens to induce specific antibodies and AMI.…”

“…69) It was shown that C. neoformans Cda2 recombinant protein prepared in Pichia pastoris was recognized by dectin-2 in B3Z reporter cells and DCs, and recombinant soluble dectin-2 physically bound to C. gattii cells. 38,70) Antigen-presenting cells (APCs) such as DCs can uptake MPs via PRRs and process MPs for antigen presentation to naive T cells. 71,72) Recombinant proteins generated in Escherichia coli (rCda1, rCda2, rCda3, rd25, and rSod1) are likely lacking glycosylation and similar to CPs are less recognizable as foreign antigens.…”