Monocytes are a rheologically heterogeneous population of cells

The effect of increased adhesiveness and decreased deformability of leukocytes following activation can have a profound effect on flow through the microcirculation. Measurement of leukocyte deformability is therefore an important tool in the study of the pathology of vascular diseases. Although much work has been done on the rheological properties of lymphocytes and granulocytes, there is little information available on the larger mononuclear cells, the monocytes. To investigate monocyte rheology, attempts were made to purifiy monocytes by a variety of methods. Purified monocytes were then filtered through 5 μm polycarbonate filters, with flow profiles (change in volume with time) recorded over 300 seconds. The profiles were analysed by least squares fitting to an appropriate mathematical model. Analysis of filtration data demonstrated 3 distinct sub-populations of monocytes with differing rheological properties. Other workers have characterised monocytes into defined subsets on the basis of their size, phagocytic ability or expression of cell surface markers. The definition of monocytes into defined rheological subsets is a new and useful addition to these studies.