Most potent stimulator of naive T cell is:

Dendritic cells (sometimes called interdigitating dendritic cells) are the most impoant antigen-presenting cells for initiating T-cell responses against protein antigens. The following contribute to this: First, these cells are located at the right place to capture antigens--under epithelia, the common site of entry of microbes and foreign antigens, and in the interstitia of all tissues, where antigens may be produced. Second, dendritic cells express many receptors for capturing and responding to microbes (and other antigens), including TLRs and lectins. third, dendritic cells express high levels of MHC and other molecules needed for presenting antigens to and activating T cells.