Aggregated Platelets Enhance Adherence of Candida Yeasts to Endothelium

Abstract

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.

Adherence of Platelets toCandidaSpecies In Vivo

“…There is some discrepancy between our results and those of Klotz et al, who concluded that whole C. albicans cells are unable to aggregate platelets in vitro (15).…”

“…These results have been confirmed by Yeaman et al in a flow cytometric analysis of C. albicans adherence to platelets in vitro, which indicated that these organisms bind directly to platelets in the absence of plasma (31). Our present results may be compared to those reported by Klotz et al, who showed that blastoconidia of C. albicans bound firmly to the surfaces of platelets aggregated by ADP whereas inactivated platelets did not adhere to yeast cells (15).…”

“…There is circumstantial evidence that platelets may interact with Candida (15,24,25,29). Although numerous studies have investigated the ability of yeast cells and yeast cell components to aggregate platelets in PRP (22,29,30), little is known concerning the adherence of platelets to yeast cells, which could be a critical initial event in inducing the activation and aggregation of platelets.…”

“…Previously, we reported that resting platelets adhere to C. albicans germ tubes and that this attachment is associated with morphological changes (24,25). Klotz et al studied the adherence of C. albicans to the endothelium and to the subendothelial extracellular matrix and demonstrated that the interaction between yeast and platelets occurred after platelet aggregation (14,15). However, although these authors detected platelet aggregation with yeast cytosol, they were unable to produce platelet aggregation with viable whole yeast.…”

Genetic Loci of Streptococcus mitis That Mediate Binding to Human Platelets

“…The relative importance of these host binding factors to colonization is uncertain. However, since a variety of endocarditisassociated organisms, including streptococci and staphylococci, can bind platelets directly in vitro (16,36,42,43), it is likely that direct binding to platelets in vivo contributes to the initiation of endocardial infection.…”