CC chemokines induce P-selectin-dependent neutrophil rolling and recruitment in vivo: intermediary role of mast cells.

1. Based on in vitro chemotaxis experiments, it is widely held that CC chemokines, such as macrophage inflammatory protein-1alpha (MIP-1alpha) and macrophage chemotactic protein-1 (MCP-1) mainly support lymphocyte trafficking. 2. The objective of the present study was to examine the role of MIP-1alpha and MCP-1 in neutrophil recruitment in vivo by use of intravital microscopy of the mouse cremaster microcirculation. 3. MIP-1alpha and MCP-1 caused a dose-dependent increase in leukocyte rolling, adhesion and recruitment. Indeed, neutrophils comprised more than 85% of the leukocyte response to MIP-1alpha and MCP-1. An anti-P-selectin antibody reduced MIP-1alpha and MCP-1-provoked leukocyte rolling by more than 94%. Concomitantly, firm adhesion and extravasation of neutrophils in response to MIP-1alpha and MCP-1 challenge were significantly decreased by more than 78 and 84%, respectively. In contrast, an anti-E-selectin antibody had no influence on CC chemokine-induced neutrophil recruitment. 4. Flow cytometric analysis revealed that MIP-1alpha and MCP-1 had no effect on P-selectin expression on endothelial cells, suggesting that neutrophil recruitment elicited by CC chemokines in vivo is not mediated via a direct effect on the endothelium but rather via an indirect effect involving activation of an intermediary tissue cell. Indeed, it was found that MIP-1alpha-induced neutrophil accumulation was significantly decreased by 58% in mast cell-deficient mice. 5. These findings demonstrate that CC chemokines trigger P-selectin-dependent rolling and tissue recruitment of neutrophils via tissue mast cells in vivo and suggest that CC chemokines may also be important targets in neutrophil-mediated tissue damage in multicellular organs.