Hemofiltrate CC chemokine (HCC-1/NCC-2/CK/M/ M-CIF) is a beta chemokine family member that shares highest structural similarity with macrophage inflammatory protein (MlP)-1 alfa. Cross-desensitization experiments suggest that HCC-1 and MIP-lo share a common receptor. CCR1 was identified as a functional HCC-1 receptor upon analysis of transfectants expressing various cloned chemokine receptors. Functionally. HCC-1 displays calcium mobilization and chemotactic activity toward monocytes, but with 100-fold reduced potency compared with MlP-la. HCC-1 fails to activate T lymphocytes, neutrophils, and eosinophils, but displays activity on myeloid progenitors. Unlike most CC chemokines. it is con-stitutively expressed in many tissues without activation and is present in nanomolar concentrations in normal human plasma.