Thymic and tonsillar DC precursors express mRNA for pT. Thymic DC precursors, CD4 ISP, mature CD4 SP thymocytes, and tonsillar DC precursors were analyzed for expression of mRNA for HPRT, pT, and RAG-1. pT mRNA expression was also determined for thymic DC precursors cultured for 2 and 7 days with IL-3.