HCC-1 is a CC chemokine that signals through the CCR1 receptor and chemoattracts blood monocytes. It is secreted by various tissues including skeletal muscle, heart, spleen, liver, bone marrow and plasma. Mature HCC-1 is found in four different forms, which are distinguished by differential N-terminal truncation and contain 74, 72, 71, or 66 amino acid residues. Recombinant human HCC-1 (66 a.a.) is a 7.8 kDa protein consisting of 66 amino acids including the four highly conserved residues present in CC chemokines.