Elimination of platelets from mononuclear cell preparations using heat-killed yeast

A new method for reducing platelet contamination in mononuclear cell preparations using heat killed yeast is presented. Yeast cells are added to the buffy coat of peripheral blood, incubated at 37 degrees C for 1 hour, layered over a Ficoll-Hypaque gradient, and centrifuged at 700 g for 30 minutes at room temperature. The cells at the interface are collected and evaluated for platelet count, lymphocyte surface markers, and mononuclear cell recovery. With increasing yeast concentration, the platelet count decreases to 93% over control values. No detectable lymphocyte subset is removed by this method. Cell recovery varies, but seems to decrease with the addition of higher concentrations of yeast cells. Normal plasma is required for the successful removal of platelets. Heat-inactivated plasma significantly reduces the efficiency of platelet removal.