The two variants of the Macrophage Inflammatory Protein 1, designated MIP-1α and MIP-1β, belong to the β or CC chemokine subfamily. The two chemokines were originally purified from lipopolysaccharidetreated murine monocytic cell lines, hence their designation as "Macrophage Inflammatory Protein".

MIP-1α and MIP-1β are produced by stimulated leukocytes as well as other tissue cells and tumor cells. At least seven variants of rat MIP-1β, corresponding to the products of independantly cloned cDNA, including Act-2, G-26, HC-21, HIMAP, H400, pAT 744 and MAD-5, have been described. At the protein levels, mature rat MIP-1β has a length of 69 amino acids and shows a homology of 70% with MIP-1α. MIP-1β is a natural ligand for the chemokine receptors CCR3, CCR5 and CCR8.