Redundant function of macrophage inflammatory protein-2 and KC in tumor necrosis factor-alpha-induced extravasation of neutrophils in vivo.

Tumor necrosis factor-alpha (TNF-alpha) stimulates the expression CXC chemokines, i.e. macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (KC), and neutrophil extravasation. However, the individual role of MIP-2 and KC in the recruitment process of neutrophils in vivo remains elusive. By use of intravital microscopy in the mouse cremaster muscle, we analyzed the effect of specific inhibition of CXC chemokines, alone and together, on TNF-alpha-induced leukocyte rolling, firm adhesion and recruitment. After stimulation with TNF-alpha, the mRNA levels of both MIP-2 and KC were increased. Notably, separate administration of antibodies directed against MIP-2 and KC had no effect on TNF-alpha-induced neutrophil extravasation. In contrast, combined injection of anti-MIP-2 and anti-KC antibodies markedly inhibited extravascular migration of neutrophils. Moreover, MIP-2 and KC dose-dependently increased neutrophil recruitment, however, no synergistic effect of combined stimulation with MIP-2 and KC on the neutrophil response was found. Taken together, these data suggest that MIP-2 and KC are functionally redundant in TNF-alpha-induced neutrophil accumulation and that neutralization of both MIP-2 and KC may be necessary in order to reduce accumulation of neutrophils in cytokine-activated tissues.