TheCryptococcus neoformans cap10 andcap59 mutant strains, affected in glucuronoxylomannan synthesis, differentially activate human dendritic cells

Abstract

The human pathogen Cryptococcus neoformans causes meningo-encephalitis. The polysaccharide capsule is one of the main virulence factors and consists of two distinct polysaccharides: glucuronoxylomannan and galactoxylomannan. The presence of this polysaccharide capsule was previously shown to interfere with maturation of human dendritic cells (DCs), possibly by shielding cell-wall components from interacting with these host immune cells. Here we show that two mutant strains of C. neoformans, both lacking a visible capsule due to a defect in glucuronoxylomannan synthesis, differentially activate human monocyte-derived DCs. Cells from a cap59 mutant, but not of a cap10 mutant strain, induce maturation of DCs as indicated by an increase in the expression of the costimulatory molecules CD80 and CD86, and production of the cytokines interleukin (IL)-10, IL-12p40 and tumor necrosis factor alpha. Interestingly, cap59 mutant cells reassociated with a concentrated culture medium of wild-type C. neoformans had lost their capacity to induce DC maturation. Summarizing, our data suggest that glucuronoxylomannan confers properties to the capsule that protect the fungus against activation of DCs; however, the presence of intact glucuronoxylomannan is not an absolute requirement to prevent activation of DCs.

Cryptococcus gattii Capsule Blocks Surface Recognition Required for Dendritic Cell Maturation Independent of Internalization and Antigen Processing

“…We chose two of the four CAP genes, CAP59 and CAP10, which are involved in biosynthesis of the polysaccharide capsule and are homologous to CMT1 and CXT1 (42). The corresponding mutants, cap10D and cap59D, are devoid of capsule components (42)(43)(44) and induced DC maturation as indicated by enhanced expression of costimulatory molecules, decreased phagocytic receptor expression, and induction of efficient T cell proliferation, whereas the encapsulated organisms (R265 and cap59 R ) failed to do so. Together, these observations showed that the polysaccharide capsule of C. gattii was responsible for evasion of DC maturation.…”

“…To determine whether the capsule of C. gattii was responsible for the effect on impaired DC maturation, we made use of capsuledeficient mutants. The cap10 and cap59 mutants were chosen because they are better characterized than other acapsular strains, and the mutation is specific for capsule synthesis and transport pathways (31,(37)(38)(39)(40)(41)(42)(43)(44) (Table I). The CAP59 mutant strain of R265 (cap59D) and reconstituted strain (cap59 R ) were produced by homologous recombination (Fig.…”

Cryptococcus neoformans Capsular Enlargement and Cellular Gigantism during Galleria mellonella Infection

“…There is indirect evidence that the inability of the host to clear the infection depends on the interaction with phagocytic cells and on the polysaccharide capsule surrounding the cryptococcal cells [7], [8], [9]. In this regard, capsular polysaccharides are potent immunomodulators that interfere with immune responses [10], [11], [12], [13], [14], [15], [16], and consequently the capsule is considered the major virulence factor [17].…”

Cryptococcus neoformansevades pulmonary immunity by modulating xylose precursor transport

“…We also tested single uxt Δ mutants: uxt1 Δ shows an intermediate level of Xyl utilization while uxt2 Δ is similar to WT (21). In these assays, we measured the ability of heat-killed fungi to stimulate the production of pro-inflammatory cytokines by DC, comparing WT, uxt1 Δ uxt2 Δ, single uxt mutants, uxs1 Δ (which lacks all Xyl modification because it cannot synthesize UDP-Xyl), and an acapsular control strain ( cap59 Δ) that induces a potent DC response (29). We found that bone marrow derived DCs (BMDCs) cultured with uxt1 Δ uxt2 Δ cells released high levels of IL-1β, IL-6, and TNF-α, similar to the levels observed following exposure to a completely acapsular control strain, cap59 Δ (Fig 4A-C).…”