MIP-1 alpha (macrophage inflammatory protein 1 alpha) is a member of the CC or beta chemokine subfamily that was originally purified from the conditioned media of an LPS-stimulated murine macrophage cell line. MIP-1 alpha acts as a chemoattractant to a variety of cells including monocytes, T cells, B cells and eosinophils.
The two human MIP-1 alpha genes arise by duplication/mutation. They code for MIP-1 alpha isoforms CCL3/LD78a and CCL3L1/LD78b, which share 94% amino acid sequence homology. Whereas the human CCL3/LD78a is a single-copy gene, the human CCL3L1/LD78b gene copy number varies within the population. Human CCL3L1/LD78b binds and signals through chemokine receptors CCR1, CCR5. When compared to CCL3/LD78a, CCL3L1/LD78b has higher binding affinity to CCR5, which also functions as a coreceptor for HIV-1 entry. The copy number of CCL3L1 is one of several genetic determinants of HIV-1 susceptibility.