CCR4 is a GPCR that is activated by chemokines TARC (thymus and activation regulated chemokine) and MDC (macrophage-derived chemokine) (Olsen and Ley, 2001). NK cells, Th2 cells, cutaneous memory T cells, macrophages and platelets express CCR4 and respond to TARC and MDC (Andrew et al., 2001; Inngjerdingen et al., 2000; Gear et al., 2001; Soler et al., 2003). CCR4-null mice display reduced airway hyperresponsiveness to fungal spores, lipopolysaccharide-induced endotoxic shock, and cardiac allograft rejection (Chvatchko et al., 2000; Schuh et al., 2002; Huser et al., 2005). In addition, antibody -mediated antagonism of MDC inhibits development of insulitis and diabetes in NOD mice (Kim et al., 2002). Chemicon's CCR4 membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of agonists and antagonists at CCR4. The cell line exhibits a calcium response with EC50 of 3.31nM for TARC. The membrane preparations exhibit EC50 of 5.76 nM for TARC in a GTPγS binding assay.