Eosinophilic differentiation of a pro-eosinophilic HL-60 cell line resulted in the induction of a high affinity RANTES/macrophage inflammatory protein-1 alpha receptor. The induced receptor is biochemically indistinguishable in RANTES equilibrium-binding studies from the monocytic receptor expressed on THP-1 cell membranes. Continued expression of the receptor requires the continuous presence of the inducing stimulus, and receptor site number declines without a loss of binding affinity with a t1/2 of 11.5 h on withdrawal of the inducing stimulus. The induced receptor is capable of three physiologic measures of receptor coupling, namely, ligand-induced Ca2+ fluxes, priming of the respiratory burst, and chemotaxis. Dose-dependent Ca2+ fluxes were elicited upon increasing concentrations of RANTES and MIP-1 alpha whereas no response was measured upon addition of MIP-1 beta or MCP-1. In addition, desensitization studies demonstrated that previous exposure to either RANTES or MIP-1 alpha almost completely inhibits a Ca2+ flux upon subsequent exposure to either ligand. Priming of the respiratory burst to PMA in differentiated cells by human rRANTES was more effective than priming by IL-5 or granulocyte-macrophage-CSF, whereas undifferentiated cells failed to secrete superoxide anion. In addition, differentiated cells underwent chemotaxis in response to RANTES. This provides the first evidence for the induction of a C-C chemokine receptor upon eosinophilic differentiation of a leukocyte cell line, and is in keeping with the demonstrated ability of human RANTES to induce the rapid formation of eosinophilic inflammatory sites.

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