Filterability of leukocytes in purified suspensions and in diluted whole blood

The transit time of adult leukocytes through 5 μm Nuclepore membranes has been calculated for subpopulations both in isolation and in co-suspensions. The results agree with previous findings that granulocytes and lymphocytes have similar properties. In suspensions of unfractionated leukocytes these subpopulations can not be distinguished and have a mean transit time of 1.17±0.11 s at 5 cm H₂O pressure. In all cases the number of pore-blocking cells corresponds approximately to the number of monocytes, being 1.1%, 11.8% and 4.8% respectively in the granulocyte, mononuclear and unfractionated suspensions. The transit time of purified red cells and the mean transit time for the majority of leukocytes, calculated for diluted but unfractionated blood, are 1.21±0.08 ms and 0.85±0.06 s respectively at a pressure of 10 cm H₂O. Under the same conditions, the mean transit time for isolated but unfractionated leukocytes is 0.51±0.06 s. Density centrifugation therefore seems to be an acceptable, but not essential, prerequisite to studying the filterability of human leukocytes.