Removal of Plasmodium falciparum-infected red blood cells from whole blood by leukoreduction filters.

摘要

BACKGROUND: There has been an unexplained decrease in the incidence of transfusion-transmitted malaria in recent years. The decrease in incidence has paralleled the increasing use of leukoreduction filters. Malaria-infected red blood cells (RBCs) share surface characteristics of hemoglobin S-containing cells. Because units collected from donors with sickle trait do not filter optimally due to adherence of RBCs to the filters, the possibility that malaria-infected RBCs may also adhere to filters was investigated. STUDY DESIGN AND METHODS: Malaria-infected whole blood or calcium ionophore (A25187)-treated and control RBCs were filtered with leukoreduction filters. Quantitation of malaria-infected RBCs before and after filtration was performed by flow cytometry to determine the presence of DNA within RBCs, indicating malaria infection. Annexin V binding was also determined before and after filtration of RBCs treated with A25187. Immediately after filtration, filters were fixed and examined by scanning and transmission electron microscopy. RESULTS: There were at least three configurations of adherence of malaria-infected RBCs demonstrated within the filters. The first was direct adherence of infected RBCs to filter fibers; the second involved adherence of malaria-infected RBCs to platelets, which were adherent to filter fibers; and the third was adherence of infected RBCs to other RBCs. Filtration also resulted in preferential removal of phosphatidylserine (PS)-expressing cells as seen by the reduction of annexin V binding after filtration. This was further confirmed by electron micrographic examination of the filters in which untreated RBCs sit within the filter resting on top of filter fibers; however, calcium ionophore-treated RBCs are seen to cling tightly to the fibers. CONCLUSIONS: PS expression by RBCs leads to their adherence within leukoreduction filters. Malaria-infected RBCs are retained via more than one mechanism. The efficiency of removal requires further study.