Both MIP-1 α and MIP-1 β are structurally and functionally related CC chemokines. They participate in the host response to invading bacterial, viral, parasite and fungal pathogens by regulating the trafficking and activation state of selected subgroups of inflammatory cells e.g. macrophages, lymphocytes and NK cells. While both MIP-1 α and MIP-1 β exert similar effects on monocytes their effect on lymphocytes differ; with MIP-1 α selectively attracting CD8 lymphocytes and MIP-1 β selectively attracting CD4 lymphocytes. Additionally, MIP-1 α and MIP-1 β have also been shown to be potent chemoattractants for B cells, eosinophils and dendritic cells. Both human and murine MIP-1 α and MIP-1 β are active on human and murine hematopoietic cells. Recombinant murine MIP-1 α is a 7.8 kDa protein containing 69 amino acid residues, including the four highly conserved cysteine residues present in CC chemokines.