Dendritic cells (DCs) are key regulators of immune responses that activate naive antigen-specific T lymphocytes. In draining lymph nodes, antigen-bearing DCs are reported to be rare and short-lived. How such small numbers of short-lived DCs can activate rare antigen-specific T cells is unclear. Here we show that after immunization of mouse skins by gene gun, the number of antigen-bearing DCs that migrate to draining lymph node is 100-fold higher than previously estimated and that they persist for approximately 2 weeks. The substantial frequency and longevity of DCs in situ ensures ample antigen presentation and stimulation for the rare antigen-specific T cells in draining lymph nodes.