TCRβ Chain That Forms Peptide-Independent Alloreactive TCR Transfers Reduced Reactivity with Irrelevant Peptide/MHC Complex

Abstract

A major feature of the TCR repertoire is strong alloreactivity. Peptides presented by allogeneic MHC are irrelevant for recognition by a subset of alloreactive T cells. To characterize peptide-independent TCRs at the molecular level, we forced the expression of a TCRβ chain isolated from a peptide-independent alloreactive CD8+ T cell line. The alloreactive TCR repertoire in the transgenic mouse was peptide dependent. However, analysis of essential TCR contacts formed during the recognition of self-MHC-restricted Ag showed that fewer contacts with peptide were established by the transgenic TCRβ chain, and that this was compensated by additional contacts formed by endogenous TCRα chains. Thus, reduced interaction with the peptide appears to be a transferable feature of the peptide-independent TCRβ chain. In addition, these findings demonstrate that reactivity to peptides is preferred over the reactivity to MHC during the formation of the TCR repertoire.

Adaptable TCR Avidity Thresholds for Negative Selection

“…T cells from most TCR␤-transgenic mice displayed selectively enhanced responses and/or precursor frequencies specific for the original Ag (4,(33)(34)(35)(36)(37). In contrast, MTB T cells displayed increased reactivity against the original alloantigen (H-2K d devoid of TAP-dependent peptides), as well as the irrelevant (H-2L d ) alloantigen not recognized by the original T cell line (6). Therefore, it appears that the MTB transgene from the original cell line transferred the avidity for MHC molecules rather than peptide specificity.…”

“…BXSB mice were obtained from The Jackson Laboratory. The generation of MTB TCR␤-transgenic mice has previously been described (6). MBP␤ and 2B4␤ TCR␤-transgenic mice were obtained from Drs.…”

“…For generation of CTLs, 25 ϫ 10 6 spleen cells from WT or MTB mice were cultured for 5 days with the same number of irradiated (2500 rad) BALB/c spleen cells. Cytotoxic T cell activity against various targets was measured using the chromium release assay as previously described (6,14).…”

“…Although TCR-transgenic mice were instrumental for studying many aspects of negative selection in the thymus, the need to address the outstanding questions using the polyclonal TCR repertoire of TCR␤-transgenic mice has recently been recognized (4,5). We have recently described a TCR␤-transgenic mouse, designated MTB, that displayed stronger reactivity against alloantigens (6). The stronger reactivity was observed against the original alloantigen recognized by the parental T cells, as well as against an irrelevant alloantigen, suggesting that the transgenic TCR␤ chain displays an increased reactivity to nonpolymorphic portions of MHC molecules.…”

T-cell allorecognition: a case of mistaken identity or déjà vu?

“…29 No.5 As we now know, the MHC molecules on foreign cells are occupied by a diverse number of cell-derived peptides (with current estimates of between 2000 and 10 000 peptides per cell) [25], creating ample possibilities for the TCR to focus on the peptide. Santori et al [26] identified a 'peptideindependent' alloreactive T cell where reduced interaction with the peptide was transferable in TCRb-chain transgenic mice, but the TCRa-chain made compensatory peptide contacts, reaffirming the importance of the peptide ligand in allorecognition. The notion that alloreactive TCRs interact with peptide is also consistent with the important role of self-peptides in thymic positive selection.…”