Vß2 natural killer T cell antigen receptor-mediated recognition of CD1d-glycolipid antigen.

ABSTRACT

Natural killer T cell antigen receptors (NKT TCRs) recognize lipid-based antigens (Ags) presented by CD1d. Although the TCR α-chain is invariant, NKT TCR Vß exhibits greater diversity, with one (Vß11) and three (Vß8, Vß7, and Vß2) Vß chains in humans and mice, respectively. With the exception of the Vß2 NKT TCR, NKT TCRs possess canonical tyrosine residues within complementarity determining region (CDR) 2ß that are critical for CD1d binding. Thus, how Vß2 NKT TCR docks with CD1d-Ag was unclear. Despite the absence of the CDR2ß-encoded tyrosine residues, we show that the Vß2 NKT TCR engaged CD1d-Ag in a similar manner and with a comparable affinity and energetic footprint to the manner observed for the Vß8.2 and Vß7 NKT TCRs. Accordingly, the germline-encoded regions of the TCR ß-chain do not exclusively dictate the innate NKT TCR-CD1d-Ag docking mode. Nevertheless, clear fine specificity differences for the CD1d-Ag existed between the Vß2 NKT TCR and the Vß8.2 and Vß7 NKT TCRs, with the Vß2 NKT TCR exhibiting greater sensitivity to modifications to the glycolipid Ag. Furthermore, within the Vß2 NKT TCR-CD1d-αGalCer complex, the CDR2ß loop mediated fewer contacts with CD1d, whereas the CDR1ß and CDR3ß loops contacted CD1d to a much greater extent compared with most Vß11, Vß8.2, and Vß7 NKT TCRs. Accordingly, there is a greater interplay between the germline- and nongermline-encoded loops within the TCR ß-chain of the Vß2 NKT TCR that enables CD1d-Ag ligation.