Aggregated platelets enhance adherence of Candida yeasts to endothelium

The adherence of Candida albicans yeasts to human umbilical vein endothelium to subendothelial extracellular matrix (ECM) was investigated. Yeasts added to confluent endothelium in citrated platelet-poor plasma adhered on the average of 1 colony forming unit (cfu) per culture well. When platelets were added as platelet-rich plasma, a significant increase of yeast adherence was not seen. However, when endothelium was contracted by treatment with 2 mM EDTA, resulting in exposure of ECM, yeast adherence was increased to 10 cfu/well. When platelets were added with these yeasts, the number of adhering yeasts was further increased to 23 cfu/well (P less than .01). This represented an increase in adherence of yeasts of 230%. When the endothelial cells were completely removed and ECM exposed, platelets were found to likewise augment yeast adherence. Platelets, when added to the ECM, formed aggregates to which the yeasts firmly adhered. Likewise, when platelets were aggregated by adenosine diphosphate and mixed with yeasts, yeasts were shown to bind avidly to aggregated platelets, whereas yeasts did not adhere to unactivated, discoid platelets. Thus, exposed subendothelial ECM induces the aggregation of platelets and yeasts bind avidly to these platelet aggregates.