Eosinophil extracellular traps (EETs) fail to kill Candida albicans hyphae in vitro

The release of DNA extracellular traps is a leukocyte activation mechanism frequently observed in the neutrophil response against fungi. Despite eosinophils being the main granulocytes involved in several fungal allergic conditions, such as asthma, allergic bronchopulmonary mycoses (ABPM) and allergic fungal rhinosinusitis (AFRS), the release of eosinophil extracellular traps (EETs) in response to fungal species and their different morphotypes is still not fully understood. Therefore, we investigated the release of EETs in response to Candida albicans, a dimorphic species found in human mucosa that can cause both superficial and deadly invasive infections, besides being the second most common cause of ABPM. Using eosinophils from human peripheral blood and C. albicans yeasts and hyphae (strain SC5314) as well as the yeast-locked strain efg^-/-, we assessed the release of EETs induced by both fungal morphotypes through fluorometric assays, fluorescence confocal microscopy and scanning electron microscopy. We also investigated the role of reactive oxygen species (ROS) and histone citrullination (events commonly associated with DNA extracellular traps release) in C. albicans-induced EETs using similar techniques. Finally, fungal viability was assessed through a metabolic activity assay (XTT sodium salt) and along a fluorescence microscopic time-lapse. All experiments were conducted under institutional review board approved protocols (CAAE 31968020.9.0000.5257). We found that eosinophils release EETs in response to C. albicans hyphae (opsonized or not) through a mechanism that is dependent on ROS production and histone citrullination. However, EETs effects on fungal viability are not sufficient to kill or impair fungal growth. This suggests that EETs do not control fungal burden during allergic inflammation but might instead contribute to exacerbate inflammation.

REFERENCES

J Leukoc Biol (2018) 104:49

J Allergy Clin Immunol. (2018) 141:571