Inhibition of leukocyte locomotion by hyaluronic acid

The effect of hyaluronate on neutrophil motility in vitro was studied by the micropore filter technique and by direct visual analysis of the locomotion of neutrophils on glass. Both directed and random locomotion of neutrophils was inhibited by physiological concentrations (0.5-6.0 mg ml(-1)) of hyaluronate in a dose- and molecular weight-dependent manner. Inhibition of cell movement was more pronounced for high molecular weight chemoattractants such as casein than for small chemotactic peptides such as f-Met-Leu-Phe. Chemotactic factor gradient formation in filter chambers was profoundly retarded by hyaluronate, which may partly explain the inhibitory effects of hyaluronate on directed neutrophil locomotion. In addition, hyaluronate inhibited the binding of chemotactic factor to the neutrophil surface. This effect, together with a reduction in cell-to-substratum adhesion, may provide an additional explanation for hyaluronate-induced inhibition of random neutrophil locomotion. Inhibition of locomotion by hyaluronate was easily reversed by washing the cells free of hyaluronate; thus competition by hyaluronate for cell-surface binding sites is unlikely, and physical effects such as steric exclusion or molecular sieving by the large hyaluronate polymer provide the most probable explanations of its inhibitory effect on cell locomotion. Since hyaluronate is a major constituent of tissue matrices, these results draw attention to the importance of the extracellular environment in regulating inflammatory cell movement in vivo.