Filterability of subpopulations of leukocytes: effect of pentoxifylline

Human leukocytes were separated by density into two fractions, one containing predominantly granulocytes (FI) and the other, lymphocytes and monocytes (FII). The filterability of these fractions and their mixture was determined from the pressure measured during constant flow through 5-microns Nuclepore filters. The pressure-time curve of FI indicates the behavior of a relatively homogeneous cell population. The FII pressure-time curve can be analyzed to distinguish the effect of the more numerous and more filterable lymphocytes from that of the sparser but less filterable monocytes. Pressure generated by mixed leukocytes, which had been treated with 1 and 10 mmol/L of pentoxifylline (PTX) or its metabolite I, was substantially less than untreated control; at 10 mmol/L, the pressure was reduced to about 50% of control. PTX appears to affect the filterability of monocytes and polymorphonuclear leukocytes but not lymphocytes. Scanning electron microscopy showed an inhibition of protopod formation in the treated granulocytes. The degree of cell adhesion to the filter, as measured by the number of cells remaining on the outflow side of the filter, was similar in all groups (FI and FII, treated and untreated). The results indicate that the variations in filterability between the leukocyte subpopulations and the improvement by PTX treatment reflect differences in the cells' ability to deform under the test conditions.