Human peripheral dendritic cells form characteristic cell aggregates (clusters) with autologous T cells. We investigated the surface markers and function of the T cells that formed these clusters. The T cells that formed clusters were mainly CD4 positive, while CD8 positive cells were few. Moreover, the T cells that formed clusters were mostly 2H4 positive. However, some were 4B4 positive. These data showed that the T cells that formed clusters were mainly CD4 positive-2H4 positive cells. The function of the T cells that formed clusters was also investigated. These T cells significantly inhibited PWM-induced immunoglobulin production from autologous lymphocytes compared with non-clustered T cells. Or data indicated that the T cells that formed clusters were mainly suppressor-inducer T cells.