The macrophage inflammatory proteins 1 alpha and 1 beta, two closely related but distinct proteins, were originally co-purified from medium conditioned by a LPS-stimulated murine macrophage cell line. Mature mouse MIP-1 alpha shares approximately 77% and 70% amino acid identity with human MIP-1 alpha and mouse MIP-1 beta, respectively. MIP‑1 proteins are expressed primarily in T cells, B cells, and monocytes after antigen or mitogen stimulation. The MIP-1 proteins are members of the beta (C-C) subfamily of chemokines.
Both MIP-1 alpha and MIP-1 beta are monocyte chemoattractants in vitro. Additionally, the MIP-1 proteins have been reported to have chemoattractant and adhesive effects on lymphocytes, with MIP-1 alpha and MIP-1 beta preferentially attracting CD8+ and CD4+ T cells, respectively. MIP-1 alpha has also been shown to attract B cells as well as eosinophils. MIP-1 proteins have been reported to have multiple effects on hematopoietic precursor cells and MIP-1 alpha has been identified as a stem cell inhibitory factor that can inhibit the proliferation of hematopoietic stem cells in vitro as well as in vivo. In the same assays, MIP-1 beta was reported to be much less active. The functional receptor for MIP-1 alpha has been identified as CCR1 and CCR5.
