A closed continuous flow centrifuge was used to separate and collect large quantities of buffy coat cells from the dog. One hundred fifty-five separate centrifugations of 2-12 hours duration were performed. Up to 61.0 liters of blood, representing 2.2-52 donor blood volumes, were processed. Buffy coat cells with a preponderance of granulocytes or lymphocytes, were collected while plasma and red blood cells were returned to the donor without change in flow or gravitational field. The mean total number of leukocytes, granulocytes, mononuclear cells and platelets removed was 24.0, 17.0, 7.0 and 197.0 x 10,9 respectively, which was 34.0, 28.0, 66.0 and 36.0 percent, respectively, of each cell population entering the centrifuge.

The effect of centrifugation on blood components was evaluated. Granulocytes from buffy coat collections exhibited normal phagocytic ability in vitro. The transfusion of large quantities of granulocytes (15.0 x 109) into leukopenic dogs produced an increment in peripheral granulocyte count (2.7 x 103 per mm.3). Granulocytes labeled with 3H-DFP were also infused with a recovery of 38.6 percent at one hour and a T-½ of 4-6 hours. Machine-separated lymphocytes responded normally to phytohemagglutinin. Prolonged passage of blood through the pumps, tubing and bowl without centrifugation resulted in a decrease in circulating platelet levels (21 percent). A greater decrease in platelets occurred with centrifugation at high g. forces (49 percent). Hemolysis of red blood cells was not a serious problem.

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