Role of the capsule in microglial cell-Cryptococcus neoformans interaction: impairment of antifungal activity but not of secretory functions.

Using two isogenic strains of Cryptococcus neoformans, we studied the influence of the capsule in C. neoformans microglial-cell interaction. We demonstrate that the acapsular mutant yeasts (CAP67) are more susceptible to phagocytosis and killing than encapsulated yeasts (B3501) by the murine microglial cells, BV-2. RT-PCR analysis showed that the pattern of gene transcripts for tumour necrosis factor alpha (TNF-a), interleukin (IL)-1beta, IL-6, IL-12p40 and granulocyte macrophage colony stimulating factor remains unchanged following BV-2 cell infection with CAP67 or B3501 yeasts. Moreover, no induction of TNF-alpha secretion occurs in BV-2 cells infected with either B3501 or CAP67 yeasts or exposed to glucuronoxylomannan (GXM) or galactoxylomannan (GalXM). Nevertheless, lipopolysaccharide-induced TNF-alpha secretion is downregulated by cell infection with B3501 or CAP67 yeasts or exposure to GXM or GalXM. Overall, by means of a continuous cell line, it appears that the C. neoformans capsule is detrimental to microglial cell antifungal activity, while no effect can be attributed to the capsule as trend of cytokine gene expression and TNF-alpha secretion.