Dendritic cells are crucial to the activation as well as suppression of the immune response. Previous repots have illustrated chat APC interacting with antigen-specific T suppressor cells become tolerogenic, inducing T helper anergy. To characterize the molecular changes occurring in tolerogenic APC, the mRNA profile of KG-1 dendritic cells exposed to allospecific T helper and T suppressor cells were analyzed. This study now provides evidence that immature dendritic cells stimulated by T suppressor cells differentiate into mature dendritic cells with a distinct phenotype. The identification of Ts induced pathways of dendritic cell differentiation is critical to the development of new therapeutic strategies. (C) American Society for Histocompatibility and Immunogenetics, 2001. Published by Elsevier Science Inc.