The Extracellular Matrix of Candida albicans Biofilms Impairs Formation of Neutrophil Extracellular Traps

Abstract

Neutrophils release extracellular traps (NETs) in response to planktonic C. albicans. These complexes composed of DNA, histones, and proteins inhibit Candida growth and dissemination. Considering the resilience of Candida biofilms to host defenses, we examined the neutrophil response to C. albicans during biofilm growth. In contrast to planktonic C. albicans, biofilms triggered negligible release of NETs. Time lapse imaging confirmed the impairment in NET release and revealed neutrophils adhering to hyphae and migrating on the biofilm. NET inhibition depended on an intact extracellular biofilm matrix as physical or genetic disruption of this component resulted in NET release. Biofilm inhibition of NETosis could not be overcome by protein kinase C activation via phorbol myristate acetate (PMA) and was associated with suppression of neutrophil reactive oxygen species (ROS) production. The degree of impaired NET release correlated with resistance to neutrophil attack. The clinical relevance of the role for extracellular matrix in diminishing NET production was corroborated in vivo using a rat catheter model. The C. albicans pmr1Δ/Δ, defective in production of matrix mannan, appeared to elicit a greater abundance of NETs by scanning electron microscopy imaging, which correlated with a decreased fungal burden. Together, these findings show that C. albicans biofilms impair neutrophil response through an inhibitory pathway induced by the extracellular matrix.

Peptidylarginine deiminase 2 is required for tumor necrosis factor alpha-induced citrullination and arthritis, but not neutrophil extracellular trap formation

“…In contrast, PAD2 −/− neutrophils were able to make NETs (Figure 4C and 4D). NETs can kill a variety of pathogens including Candida albicans [41, 44]. To test if PAD2 −/− neutrophils could kill Candida , we subjected PAD2 +/+ and PAD2 −/− neutrophils to a modified XTT assay.…”

“…A modified XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay was performed [40, 41]. Candida albicans strain SC5314 [42] was stored in 15% glycerol stock at −80°C and maintained on yeast extract-peptone-dextrose (YPD) medium supplemented with uridine (1% yeast extract, 2% peptone, 2% dextrose medium, 0.08% uridine) prior to experiments.…”

Development and regulation of single- and multi-species Candida albicans biofilms

“…In the presence of biofilm cells, neutrophils also fail to trigger a reactive oxygen species response, although the mechanisms for this are unknown 118 . Building on this observation, it has also been shown that the extracellular matrix of C. albicans biofilms helps to block the release of neutrophil extracellular traps (NETs), thus reducing neutrophil- mediated killing 119 . In support of this, decreased production of the extracellular matrix leads to increased NET levels and decreased fungal proliferation 119 .…”

Mechanisms involved in the triggering of neutrophil extracellular traps (NETs) by Candida glabrata during planktonic and biofilm growth

“…However, a recent investigation revealed that neutrophils fail to release NETs in response to biofilms produced by C . albicans 12 . This explains, in part, why neutrophils are ineffective at controlling C .…”