Phagocyte-mediated killing of Candida tropicalis

Candida tropicalis induces pro-inflammatory cytokine production, NF-κB and MAPKs pathways regulation, and dectin-1 activation

The prevalence of Candida infection induced by non-albicans Candida (NAC) species is increasing. However, as a common NAC species, C. tropicalis has received much less study in terms of host immunity than C. albicans has. In this study, we evaluated the pro-inflammatory cytokine responses evoked by C. tropicalis and determined whether dectin-1 and downstream NF-κB and mitogen-activated protein kinases (MAPKs) signaling pathways played roles in inflammation in human peripheral blood mononuclear cells (PBMCs) and THP-1 macrophage-like cells. Exposure of PBMCs and THP-1 macrophage-like cells to C. tropicalis led to the enhanced gene expression and secretion of TNF-α and IL-6 in a time- and dose-dependent manner. THP-1 macrophage-like cells being challenged by C. tropicalis resulted in the activation of the NF-κB, p38, and ERK1/2 MAPK signaling pathways. We also found that the expression of dectin-1 was increased with C. tropicalis treatment. These data reveal that dectin-1 may play a role in sensing the inflammation response induced by C. tropicalis and that NF-κB and MAPK are involved in the downstream signaling pathways in macrophages.

Delinking CARD9 and IL-17: CARD9 Protects against Candida tropicalis Infection through a TNF-α-Dependent, IL-17-Independent Mechanism

Candida is the third most common cause of bloodstream infections in hospitalized patients. Immunity to C. albicans, the most frequent species to be isolated in candidiasis, involves a well-characterized Dectin-1/caspase-associated recruitment domain adaptor 9 (CARD9)/IL-17 signaling axis. Infections caused by non-albicans Candida species are on the rise, but surprisingly little is known about immunity to these pathogens. In this study, we evaluated a systemic infection model of C. tropicalis, a clinically relevant, but poorly understood, non-albicans Candida. Mice lacking CARD9 were profoundly susceptible to C. tropicalis, displaying elevated fungal burdens in visceral organs and increased mortality compared with wild-type (WT) controls. Unlike C. albicans, IL-17 responses were induced normally in CARD9(-/-) mice following C. tropicalis infection. Moreover, there was no difference in susceptibility to C. tropicalis infection between WT and IL-23p19(-/-), IL-17RA(-/-), or Act1(-/-) mice. However, TNF-α expression was markedly impaired in CARD9(-/-) mice. Consistently, WT mice depleted of TNF-α were more susceptible to C. tropicalis, and CARD9-deficient neutrophils and monocytes failed to produce TNF-α following stimulation with C. tropicalis Ags. Both neutrophils and monocytes were necessary for defense against C. tropicalis, because their depletion in WT mice enhanced susceptibility to C. tropicalis. Disease in CARD9(-/-) mice was not due to defective neutrophil or monocyte recruitment to infected kidneys. However, TNF-α treatment of neutrophils in vitro enhanced their ability to kill C. tropicalis. Thus, protection against systemic C. tropicalis infection requires CARD9 and TNF-α, but not IL-17, signaling. Moreover, CARD9-dependent production of TNF-α enhances the candidacidal capacity of neutrophils, limiting fungal disease during disseminated C. tropicalis infection.

The role of tumour necrosis factor-alpha (TNF-alpha) and platelet-activating factor (PAF) interaction on murine candidosis

Tumour necrosis factor-alpha (TNF-alpha) is related to some other factors in addition to being the essential cytokine of the sepsis which results from Candida infections. In our study, we investigated serum TNF-alpha levels, measured by enzyme-linked immunosorbent assay (ELISA), and platelet-activating factor (PAF)-like activity, measured by high-pressure liquid chromatography (HPLC) of the mice infected with Candida species. The PAF antagonist, ginkgolide BN 52021 was used to evaluate the possible interaction between TNF-alpha and PAF. The average TNF-alpha levels were found to be 396, 489, 699 and 803 pg ml(-1) on the 4th, 5th, 6th and 19th days of Candida albicans infection, respectively (P<0.05). There was no statistically significant difference between the serum TNF-alpha levels of the groups infected with other Candida species, such as C. kefyr, C. krusei and C. tropicalis (P>0.05). Serum TNF-alpha levels were found to be more significantly different in mice with C. albicans infection that were injected with PAF antagonists on the 6th day (23 pg ml(-1)). It was therefore thought that PAF antagonists have an inhibitory effect on TNF-alpha production. No significant difference was found between PAF levels in the three groups: healthy control mice, C. albicans-infected mice and C. albicans-infected mice given PAF antagonists (466 milli-absorbance unit (mAU), 475 mAU and 329 mAU, respectively). It was noticed that the positive interaction between PAF and TNF-alpha was not important after the first 4 days of the infection had passed.

Enhanced oxidative killing of azole-resistant Candida glabrata strains with ERG11 deletion

The susceptibility of genetically defined Candida glabrata strains to killing by H2O2 and neutrophils was assessed. Fluconazole-susceptible L5L and L5D strains demonstrated survival rates higher than those of two fluconazole-resistant strains lacking the ERG11 gene coding for 14 alpha-demethylase. Fluconazole resistance can occur by mechanisms which increase fungal susceptibility to oxidative killing by H2O2 and neutrophils.

Effect of TNF alpha production inhibitors BRL 61063 and pentoxifylline on the response of rats to poly I:C

BRL 61063 is a novel xanthine phosphodiesterase (PDE) type IV inhibitor with selective inhibitory activity for tumor necrosis factor (TNF) alpha production. This compound inhibits TNF alpha production by activated human blood monocytes in vitro and in animal models of endotoxemia and influenza infection. Inhibition of TNF alpha may be beneficial in many diseases; however, little is known about potential adverse effects of such inhibition on host defense. In an ex vivo study, we examined the effect of BRL 61,063 on the microbicidal and tumoricidal activity of pulmonary lavage cells during a local inflammatory response in rats challenged with Poly I:C. Pentoxifylline, a PDE inhibitor which also blocks TNF alpha production, was used for comparison. Treatment with BRL 61063 or pentoxifylline did not block the inflammatory response to Poly I:C or the activation of bronchoalveolar lavage (BAL) cells but reduced the level of tumoricidal activity attained. At the dosages used, pentoxifylline was more inhibitory than BRL 61063. Drug treatment did not prevent further stimulation of tumoricidal activity by LPS in vitro. LPS-stimulated cells from BRL 61063-treated rats reached a level of activation similar to the control group while the LPS-stimulated activity of BAL cells from pentoxifylline treated rats remained lower than control. Although pentoxifylline was more inhibitory for tumoricidal activity than BRL 61063, the latter was a more potent inhibitor of TNF alpha release as measured in vivo in LPS-challenged rats. This finding indicates that TNF alpha is not the main mediator involved in the activation of pulmonary macrophage tumoricidal function. Treatment with either BRL 61063 or pentoxifylline had little or no effect on the Poly I:C-induced candidacidal activity of BAL cells indicating that these compounds are unlikely to compromise non-specific host defense against infection.