Recent animal studies suggest that indirect T-cell recognition of alloantigen plays an important role in allograft rejection and tolerance. In this study, we generated T cell clones from Lewis (LEW, RT1 1) rat lymph node cells that had been primed in vivo by immunization with immunogenic class II MHC allopeptide RT. 1D u β2, representing residues 20-44 of the polymorphic β chain of RT1. Dβ u (Wistar Furth [WF]). Using reverse transcriptase polymerase chain reaction transcript analysis with specific rat T cell receptor Vβ primers, we show that six out of nine T cell clones specifically proliferated to RT1. D u β2 and expressed Vβ 9. One of these clones, clone 2F4, which specifically proliferated to RT1. D u β2 in a dose-response fashion and produced interferon-γ in response to restimulation by RT1. D u β2, was selected for further studies.