LAG-1 is CC chemokine that signals through the CCR5 receptor. LAG-1 is identical to MIP-1β (ACT II isotype) except for two amino acid substitutions; arginine for histidine at position 22 and serine for glycine at position 47 of the mature protein. LAG-1 chemoattracts monocytes, and exhibits activity as an HIV-suppressive factor.