Chemokines play important roles in inflammation and critical for the recruitment of effector immune cells to sites of infection. Chemokines activate leukocytes by binding to G protein coupled receptors. The ever-growing chemokine receptor subtypes can be divided into 2 major groups, CXCR and CCR, based on the 2 major classes of chemokines. One of the CCR receptors, CCR1, is expressed on neutrophils, monocytes, lymphocytes, and eosinophils and binds the leukocyte chemoattractant and hemopoiesis regulator macrophage-inflammatory protein (MIP-1 ), eotaxin, as well as several other related chemokines. Mice lacking the chemokine receptor CCR1 have defects in neutrophil trafficking and proliferation.