Chemokine function in vivo depends on the presentation by structures of the extracellular matrix or on endothelial surfaces. CCL5 contains two clusters of basic amino acid residues ((44)RKNR(47) and (55)KKWVR(59)) implicated in presentation of the protein. While (44)RKNR(47) has been shown to moderate CCL5 binding to glycosaminoglycans (GAGs), no direct role for the basic residues in the so called 50s loop ((55)KKWVR(59)) as a presentation structure has been published to date. In ex vivo studies both regions were found to be necessary for direct tissue binding suggesting a role for (55)KKWVR(59). In vitroT lymphocyte and monocyte induced firm adhesion under flow, as well as leukocyte recruitment to the peritoneal cavity in vivo was reduced in the 50s mutant. The binding of the 50s mutant to endothelial cells was significantly reduced as compared to the wild type protein demonstrated by ELISA. The 50s mutant had little impact on GAG binding in vitro. These data suggest that functional CCL5 presentation is mediated through both the 40s as well as the 50s loop with differential functions of the two loops of clusters of basic residues.