Fine specificity and MHC restriction of trinitrophenyl-specific CTL

In this study, the fine specificity and MHC restriction of a CTL response s pecific to the trinitrophenyl (TNP) hapten was analyzed. Based on the struc ture of peptide/K-b complexes and ternary TCR/Ag/MHC complexes, four TNP pe ptides, two octamers, and two nonamers were chosen for eliciting anti-TNP C TL responses. Hapten was conjugated at position 4 in the octamers and at po sition 5 in the nonamers, positions which should allow engagement of the ha pten by TCRs, potent CTL activity for each of the TNP peptides was obtained that was highly hapten-specific; however, there were considerable differen ces in the extent of cross-reactivity with other TNP peptides, with the oct amers generating more cross-reactive CTL than the nonamers. MHC restriction analysis suggested that anti-hapten responses were less dependent on MHC r ecognition than anti-peptide responses. This was evidenced by the relative ease of detecting cross-reactivity to haptenated peptides presented by allo -MHC and by the relative insensitivity of anti-hapten vs anti-peptide CTL t o mutations in the K-b molecule at potential TCR interaction sites. One pot ential explanation for this insensitivity to MHC mutation was the finding t hat the anti-hapten response appeared to be of higher avidity, since a > 10 0-fold difference in the amount of Ag required to sensitize target cells wa s found between these two types of Ags.