MDC (macrophage-derived chemokine) is a 69-amino acid CC chemokine with an NH2-terminalsequence of 24 residues as a signal sequence. It was originally cloned from human monocyte-derived macrophages1. Recombinant MDC attracts monocyte-derived dendritic cells, activated lymphocytes and natural killer cells1,2. MDC has anti-HIV-1 activity2. Expression of MDC mRNA in macrophages is enhanced by LPS, IL-1ß and TNFa 3. MDC is a functional ligand for CCR44.