Dissection of Cross-Reactivities Using a Panel of H-2Ld Alloreactive T Cell Hybridomas

In order to explore the role which class I structure plays in alloreactivity, we have generated Ld-reactive T cell hybridomas by fusion of a dm2 anti-BALB/cJ MLR with the BW5147 cell line and examined their stimulation by the following class I molecules (α1/α2/ α3): Lq, Dq, dm1, LPd/Ld/Dd, Lq/Dq/Ld, and Q10/Q10/Ld. We found that their specificities differed in their patterns of cross-reactions and were reasonably representative of those present in the bulk population of MLR-generated CTLs. Ld/Ld/Dd and Q10/Q10/Ld stimulated the majority of the hybridomas, Lq and dm1 were recognized by over half of the panel, and Lq/Dq/Ld stimulated only modestly, while Dq was not recognized by any hybridoma. Correlation of these observed reactivities with class I structure suggests that putative TCR contact residues may play a significant role in recognition when compared to the polymorphic amino acid residues which control pocket specificity and peptide binding. Specifically, Lq and Dq possess very similar or identical pockets, in contrast to those of dm1 and Q10. However, Q10 has identical TCR contact residues to Ld, both on the α1 and α2 α helices, unlike Dq which is mismatched on both helices. Lq and dm1 are mismatched compared to Ld on only one helix. Thus, a molecular rationale for the cross-reactions observed in this study involves the direct participation of residues of class I molecules in allorecognition.