Introduction: Polymorphonuclear granulocytes (PMN) provide a rapid innate immune response against fungal infections. Using an ex vivo human whole blood model, we confirmed their central role in immune responses against Candida albicans. In this model, a fraction of C. albicans cells escaped phagocytosis and extracellular killing.

Goals: We aimed to identify the mechanisms by which C. albicans cells escape from phagocytosis.

Materials & Methods: PMNs were isolated from whole blood with the MACSxpress Whole Blood Neutrophil Isolation Kit (Miltenyi) and confronted with opsonized C. albicans. Using flow cytometry, we investigated remodelling of the surface of C. albicans after incubation with PMNs or extracellular vesicles (EVs) released by PMNs. EVs were isolated by high-speed centrifugation. EVs released by PMNs after contact with C. albicans (CaEVs) were compared with those released from mock-infected PMNs (sponEVs) using nanoparticle tracking analysis and mass spectrometry.

Results: After 1 h of confrontation, 90 % of C. albicans cells had been phagocytosed by neutrophils. Extracellular C. albicans acquired PMN markers (e.g. CD66b) and Annexin V, suggesting that EVs may be involved in surface remodelling of the extracellular fungi. Incubation of C. albicans with isolated EVs confirmed transfer of host cell markers by EVs. Both sponEVs and CaEVs transferred host cell markers. The size and protein content of sponEVs and CaEVs were similar, but confrontation of PMNs with C. albicans increased the amount of EVs released. Pre-incubating C. albicans with EVs decreased the percentage of fungal cells phagocytosed by neutrophils.

Summary: EVs released by PMNs may contribute to the escape of C. albicans from phagocytosis by transfer of host cell proteins. These results increase our understanding of host-cell interactions with C. albicans in the blood.