Characterization of the ovalbumin-specific TCR transgenic line OT-I: MHC elements for positive and negative selection

The present report provides the first extensive characterization of the OT- I TCR transgenic line, which produces MHC class I-restricted, ovalbumin-spe cific, CD8(+) T cells (OT-I cells). These cells an shown to be positively s elected in vivo in H-2(b) C57BL/6 mice and in bm5 mice, which express the K -bm5 mutant molecule. In contrast, OT-I cells were not selected by mutant K -b molecules in bm1,bm3, bm8, bm10, bm11 or bm23 mice. Interestingly, howev er, when positive selection was examined in vitro in foetal thymic organ cu lture (FTOC), bm1 and bm8 were still poorly selective, but the bm3 haplotyp e now selected as efficiently as B6. The ability to select in vitro correla ted with the capacity to present the ovalbumin (OVA) peptide to OT-I cells, as measured by induction of an OVA-specific proliferative response. These results suggest that a lower affinity TCR:MMC interaction may be necessary for positive selection in FTOC compared with selection in situ.