Biomolecular events involved in anticryptococcal resistance in the brain

Abstract

We have recently shown that intracerebral (i.c.) administration of heat-killed Cryptococcus neoformans (HCN) enhances mouse resistance to a subsequent local challenge with lethal doses of viable yeast cells. Here we show that i.c. administration of HCN is also effective in significantly delaying brain colonization of mice intravenously infected with viable C. neoformans. PCR analysis revealed that interleukin 6 (IL-6) and IL-1␤ gene expression occurs in brains of HCN-treated mice but not in brains of saline-treated controls. In contrast, no differences are observed in terms of tumor necrosis factor alpha and IL-1␣ gene transcripts, which are slightly and highly detectable, respectively, in saline-treated mice and which remain such also following HCN treatment. Furthermore, i.c. administration of exogenous IL-6 or IL-1␤, but not tumor necrosis factor alpha, before local challenge with viable C. neoformans results in significantly reduced microbial counts in the brain and blood and in increased mouse survival. Taken together, these observations provide initial evidence that brain anticryptococcal resistance involves elicitation of a local cytokine response, involving primarily IL-6 and IL-1␤.

Urease Expression by Cryptococcus neoformans Promotes Microvascular Sequestration, Thereby Enhancing Central Nervous System Invasion

“…Only laccase (an other extracellular enzymatic factor produced by C. neoformans) has been clearly demonstrated to facilitate intracerebral growth of this organism. 8,42 Consistent with the requirement for laccase in CNS infection, our laboratory has performed experiments demonstrating that a laccase-deficient strain produces a minimal CNS infection after intratracheal infection. 43 All C. neoformans strains used in this study (H99, ure1, ure1ϩURE1Ϫ1) were laccase-positive.…”

The ABC transporter-encoding geneAFR1affects the resistance ofCryptococcus neoformansto microglia-mediated antifungal activity by delaying phagosomal maturation

“…Macrophages play a key role in host defence against virtually all pathogenic microorganisms. In particular, microglia, the resident brain macrophages, directly act as a local defence barrier against the neurotropic yeast C. neoformans (Blasi et al, 1990(Blasi et al, , 1992(Blasi et al, , 1995a(Blasi et al, , 2004Mazzolla et al, 1997;Barluzzi et al, 2000). Phagocytosis and killing occur to a different extent, depending on the activation state of the effector cell and on the opsonization of the fungal target or its exposure to protease inhibitors.…”

“…Microglia may either allow C. neoformans intracellular survival and replication (Lee et al, 1995) or exert anticryptococcal activity, whose levels are enhanced upon exposure to IFN-g or chloroquine (Blasi et al, 1995b;Mazzolla et al, 1997;Saleppico et al, 1999). Furthermore, C. neoformans resistance to microglia is partially reduced by yeast cell preopsonization with fresh serum or by pretreatment with protease inhibitors (Blasi et al, 1992(Blasi et al, , 1995aLipovsky et al, 1997). Thus, both the early yeast-to-microglia recognition step(s) and the postphagocytosis intracellular events seem to be relevant in the outcome of such pathogen-host cell interplay.…”

“…Specific virulence factors of C. neoformans, including polysaccharide capsule (Bhattacharjee et al, 1984;Cherniak & Sundstrom, 1994), melanin (Shaw & Kapica, 1972) or mannitol production (Wong et al, 1990), superoxidase dismutase (Jacobson et al, 1994), proteases (Brueske, 1986;Blasi et al, 2004), phospholipase B and lysophospholipase (Chen et al, 1997a, b), have been described; among all, capsule formation and melanin production appear as crucial elements to elude host defences at the brain level (Blasi et al, 1992(Blasi et al, , 1995a. Recently, the antifungal resistance 1 (AFR1) gene has been identified and characterized (Posteraro et al, 2003;Sanguinetti et al, 2006): it encodes an ATP binding cassette transporter protein, involved in the in vitro resistance to fluconazole (Posteraro et al, 2003).…”

The human immunodeficiency virus (HIV) protease inhibitor indinavir directly affects the opportunistic fungal pathogenCryptococcus neoformans

“…Since it is proposed that C. neoformans produces proteases, as biochemical devise(s) for nutritional recruitment [16,19], we suggest that such a pathway is critically disturbed upon exposure to the PI indinavir. By a murine model of experimental meningoencephalitis, it has been demonstrated that the brain phagocytic compartment is an important defence barrier against C. neoformans [27,[30][31][32]. Accordingly, in vitro studies reveal that microglial cells are endowed with direct antifungal activity and their efficacy may further increase, under appropriate conditions [27,28,33].…”