Stepping Up to the Plate(let) against Candida albicans.

Candida albicans is a pervasive commensal fungus that is the most common pathogen responsible for invasive fungal infection (IFI). With incidence of IFI on the rise due to increasing susceptible populations, it is imperative that we investigate how Candida albicans interacts with blood components. When stimulating either human or mouse whole blood with thrombin, we saw a significant decrease in C. albicans survival. We then repeated Candida killing assays with thrombin-stimulated or unstimulated washed platelets and saw a similar decrease in CFU. To investigate whether killing was mediated through surface components or releasable products, platelets were pretreated with an inhibitor of actin polymerization (cytochalasin D [CytoD]). CytoD was able to abrogate C. albicans killing. Moreover, dilution of releasates from thrombin-stimulated platelets showed that the toxicity of the releasates on C. albicans is concentration dependent. We then investigated C. albicans actions on platelet activation, granule release, and aggregation. While C. albicans does not appear to affect alpha or dense granule release, C. albicans exerts a significant attenuation of platelet aggregation to multiple agonists. These results illustrate for the first time that platelets can directly kill C. albicans through release of their granular contents. Additionally, C. albicans can also exert inhibitory effects on platelet aggregation.