Innate-Like Control of Human iNKT Cell Autoreactivity via the Hypervariable CDR3b Loop

• Published in: PLoS biology 2010-06, Vol.8 (6)
• Main Authors: Matulis, Gediminas, Sanderson, Joseph P, Lissin, Nikolai M, Asparuhova, Maria B, Bommineni, Gopal R, Schuemperli, Daniel, Schmidt, Richard R, Villiger, Peter M, Jakobsen, Bent K, Gadola, Stephan D
• Format: Article
• Language: English
• ISSN: 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.1000402

T-cell receptor variability gives rise to a functional hierarchy of human invariant Natural Killer T-cells through a powerful effect on CD1d binding affinity, which is independent of CD1d ligands. Invariant Natural Killer T cells (iNKT) are a versatile lymphocyte subset with important roles in both host defense and immunological tolerance. They express a highly conserved TCR which mediates recognition of the non-polymorphic, lipid-binding molecule CD1d. The structure of human iNKT TCRs is unique in that only one of the six complementarity determining region (CDR) loops, CDR3b, is hypervariable. The role of this loop for iNKT biology has been controversial, and it is unresolved whether it contributes to iNKT TCR:CD1d binding or antigen selectivity. On the one hand, the CDR3b loop is dispensable for iNKT TCR binding to CD1d molecules presenting the xenobiotic alpha-galactosylceramide ligand KRN7000, which elicits a strong functional response from mouse and human iNKT cells. However, a role for CDR3b in the recognition of CD1d molecules presenting less potent ligands, such as self-lipids, is suggested by the clonal distribution of iNKT autoreactivity. We demonstrate that the human iNKT repertoire comprises subsets of greatly differing TCR affinity to CD1d, and that these differences relate to their autoreactive functions. These functionally different iNKT subsets segregate in their ability to bind CD1d-tetramers loaded with the partial agonist a-linked glycolipid antigen OCH and structurally different endogenous b-glycosylceramides. Using surface plasmon resonance with recombinant iNKT TCRs and different ligand-CD1d complexes, we demonstrate that the CDR3b sequence strongly impacts on the iNKT TCR affinity to CD1d, independent of the loaded CD1d ligand. Collectively our data reveal a crucial role for CDR3b for the function of human iNKT cells by tuning the overall affinity of the iNKT TCR to CD1d. This mechanism is relatively independent of the bound CD1d ligand and thus forms the basis of an inherent, CDR3b dependent functional hierarchy of human iNKT cells. Our immune system uses randomly modified T-cell receptors (TCRs) to adapt its discriminative capacity to rapidly changing pathogens. The T-cell receptor (TCR) has six flexible, variable peptide loops that make contact with antigens presented to them on the surface of other cells. Invariant Natural Killer T-cells (iNKT) are regulatory T-cells with a unique type of TCR (iNKT-TCR) that recognizes lipid anti