Different patterns of deactivation of chemotaxis and haptotaxis of human peripheral blood mononuclear leukocytes by soluble and surface-bound attractants.

Soluble mediators and inducible cell-surface and matrix-bound molecules coordinate the cascade of events giving rise to leukocyte emigration. Knowledge of the specific mechanisms underlying the attraction of cells into a local site, however, remains sketchy. In particular, it is unclear how chemoattractants cause rapidly moving immune cells to adhere to the blood vessel wall and to enter tissues. Here we show that the neuroendocrine human growth hormone, a chemoattractant for monocytes and lymphocytes in vitro, promotes haptotaxis, the migration of the cells induced by surface-bound gradients. Combination of soluble growth hormone with soluble attractants, RANTES or formyl peptide, deactivates the migratory responses, as do combinations of surface-bound growth hormone with surface-bound RANTES or formyl peptide. In contrast, exposure of mononuclear leukocytes to combinations of soluble chemotactic with surface-bound haptotactic gradients of attractants does not deactivate migration. The findings suggest that growth hormone may act as haptotactic agent, on the one hand, and that soluble attractants do not appear to affect haptotaxis when acting in concert with a surface-bound attractant, on the other. This observation may have implications for the differential regulation of leukocyte accumulation in the vessel wall at systemic and local sites.