Graft-infiltrating dendritic cells (DC) and alloreactive T lymphocytes play a critical role in renal allograft rejection. Renal proximal tubular epithelial cells (TEC) are considered as active players in the attraction of leukocytes during renal inflammatory responses. Macrophage inflammatory protein (MIP)-3alpha/CCL20 is a major chemokine expressed by epithelial cells that attracts immature DC. In the present study, we present evidence that also the transplanted kidney can be a major source of MIP-3alpha/CCL20. Renal transplant recipients with rejection showed significantly increased excretion of urinary MIP-3alpha/CCL20 that correlated with transplant function. The tubular staining for MIP-3alpha/CCL20 in renal biopsies of patients with rejection as well as in vitro studies with primary human TEC indicated that TEC might be responsible for the increased urinary MIP-3alpha/CCL20. Furthermore, MIP-3alpha/CCL20 produced by activated TEC was highly potent in the attraction of CD1a+CD34+-derived DC precursors. These data suggest a role for MIP-3alpha/CCL20 in amplification of the immune response during renal allograft rejection by attraction of CCR6+ inflammatory cells, which may include DC, to the site of inflammation.