A filtration model for study of leukocyte transit in the microcirculation

In order to study characteristics of leukocytes which would be important determinants of their flow in the microcirculation, a model system was tested which utilizes in vitro filtration of leukocytes. Normal human peripheral blood leukocytes (85-90% granulocytes) were studied with filters with uniform 8 mum pore size. Studies were performed to determine the effects of EDTA, temperature, hydrostatic pressure, pH, and osmolarity on filtration. Filterability was optimal at 0.2% EDTA, 10 cm hydrostatic pressure, neutral pH, isotonicity, and at room temperature. Filtration was slowed greatly at leukocyte concentrations exceeding 25 X 10(9)/liter. When leukocyte membranes were altered by formalin fixation, filtration slowed greatly, indicating that deformability is an important determinant of flow through small orifices. When mixtures of erythrocytes and leukocytes were filtered, there was a paradoxically enhanced transit of leukocytes compared to filtration of leukocytes alone, indicating interactions between these cells which alter flow. These studies serve to characterize this model system which can be used to study the contribution to flow in the microcirculation of both normal and pathological leukocytes.