Equilibrium binding studies on canine mononuclear and granulocytic cells allow the identification of a single high affinity receptor for the human C-C chemokine RANTES (dissociation constant, 14 +/- 8 pM), that, in contrast to the human RANTES receptor, has no affinity for human macrophage inflammatory protein 1 alpha (hMIP-1 alpha). A single intradermal injection of hRANTES in dog resulted in eosinophil- and macrophage-rich inflammatory sites within 4 h. Cell infiltration peaked at 16-24 h after hRANTES injection. There was histological evidence of intravascular activation of eosinophils at 4 h, although eosinophils in the vasculature and interstitium contained apparently intact granules. Monocytes were the predominant cells adherent to venular endothelium at 16-24 h. Human MIP-1 alpha elicited no response in canine dermis, whereas monocyte chemoattractant protein 1 caused mild perivascular cuffing with monocytes. In contrast, human interleukin 8 induced a neutrophilic dermal infiltrate that was maximal by 4 h after challenge. This provides the first direct evidence in vivo that RANTES has significant proinflammatory activity and, in addition, could be a mediator in atopic pathologies characterized by eosinophilic and monocytic inflammatory responses.