Methods for Measuring Leukocyte Locomotion

The most direct way to study the movement of any object or living thing would seem to be to watch it moving. Strangely, where leukocytes are concerned, watching cells move has been something of a minority interest. The reasons for this are partly historical, partly that more people have been interested in the way that chemical substances modify leukocyte locomotion than in the locomotion itself, and the direct approach has not always been the most helpful for answering questions about such modifications. In this methodological review, we have deliberately placed much emphasis on visual assays. We feel that an understanding of locomotory behavior is fundamental to an understanding of cellular reactions such as chemotaxis and chemokinesis, and that some of the conceptual confusions which arise in the study of these reactions can be avoided if results obtained with filter assays or agarose assays are interpreted in the context of a detailed knowledge of the way leukocytes actually move. The use of a variety of assays, each of which provides information which is not fully provided by the others, seems increasingly important if balance is to be maintained in a field which is becoming highly popular. The study of leukocyte chemotaxis is attracting workers from a range of disciplines—both basic and clinical—some of whom may be fairly unfamiliar with the locomotory behavior of cells. We hope that this review will give them a feeling for the possible experimental approaches that can be used to answer questions about leukocyte locomotion.