Both MIP-1 alpha and MIP-1 beta 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 alpha and MIP-1 beta exert similar effects on monocytes their effect on lymphocytes differ; with MIP-1 alpha selectively attracting CD8+ lymphocytes and MIP-1 beta selectively attracting CD4+ lymphocytes. Additionally, MIP-1 alpha and MIP-1 beta have also been shown to be potent chemoattractants for B cells, eosinophils and dendritic cells. Both human and murine MIP-1 alpha and MIP-1 beta are active on human and murine hematopoietic cells. Recombinant murine MIP-1 beta is a 7.8kD protein containing 69aa, including the four highly conserved cysteine residues present in CC chemokines.