Alterations by leukocytes of erythrocyte flow in microchannels

The effects of leukocytes on blood rheology in the microcirculation may be predicted to result from the rheological characteristics of the individual white blood cell types and their behavior at entrances of small vessels; their influence on flow resistance of blood due to their disturbance of erythrocyte flow; and the obstruction caused by their adherence to endothelial cells or geometrical hindrance of their flow at irregular or narrow regions. Deformation of leukocytes in micropipettes indicates the relative rigidity of lymphocytes and blast cells from leukemias in contrast to granulocyte viscoelastic properties, and entry times for lymphocytes in 2.6-4.6-microns channels were 11-151 s but milliseconds in 9.1-micron tubes. Lymphocytes and erythrocytes rarely (less than 1%) adhered to cultured endothelium; however, granulocytes adhered avidly at shear stresses of 10-100 dyn/cm2, typical of microcirculation. In the 9.1-microns flow tube at Hct = 17.7 +/- 2.6%, increasing [WBC] caused a linear increase in flow resistance, but above [WBC] = 1000/mm3 resistance tended to plateau. These data support the interpretation that granulocyte adherence to endothelial cells with the potential for obstruction of flow may be a more significant rheological consequence of leukocytes in blood than their resistance to flow because of their relative rigidity or their influence on flow resistance by perturbation of the erythrocyte flow.