Activation of mechanical responses in leukocytes.

Different kinds of leukocytes undergo cytoskeleton-dependent mechanical responses associated with their specific physiological functions. We have investigated cellular stiffening of several types of leukocytes using a method which measures the force resisting cellular indentation. We have found that lymphocytes stiffen in response to crosslinking cell surface antigens in a process associated with the much studied capping and patching processes. Further studies of myosin-deficient mutants of the ameba Dictyostelium discoideum suggest that this stiffening process results from a myosin dependent contractile process. Rat basophilic leukemia cells and pancreatic islet cells stiffen when triggered to secrete. The function of these cytoskeleton dependent processes is now unknown, but, at least in the islet cells, may be related to a regulation of the rate of secretion. Primary neutrophils stiffen in response to the chemotactic agent, fMet-Leu-Phe. This stiffening may be responsible for retention of these cells in the pulmonary microcirculation during response to inflammation. These observations pose the challenge of determining the structural basis, mechanism, and physiological function of each of these cellular responses.