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The V alpha 14 NKT cell TCR exhibits high-affinity binding to a glycolipid/CD1d complex
Stéphane Sidobre1, Olga V Naidenko, Bee-Cheng Sim
1Division of Developmental Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA.
Abstract:
Most CD1d-dependent NKT cells in mice have a canonical V alpha 14J alpha 18 TCR rearrangement. However, relatively little is known concerning the molecular basis for their reactivity to glycolipid Ags presented by CD1d. Using glycolipid Ags, soluble forms of a V alpha 14 NKT cell-derived TCR, and mutant and wild-type CD1d molecules, we probed the TCR/CD1d interaction by surface plasmon resonance, tetramer equilibrium staining, and tetramer staining decay experiments. By these methods, several CD1d alpha-helical amino acids could be defined that do not greatly alter lipid binding, but that affect the interaction with the TCR. Binding of the V alpha 14(+) TCR to CD1d requires the agonist alpha-galactosylceramide (alpha-GalCer), as opposed to the nonantigenic beta-galactosylceramide, although both Ags bind to CD1d, indicating that the carbohydrate moiety of the CD1d-bound Ag plays a major role in the TCR interaction. The TCR has a relatively high-affinity binding to the alpha-GalCer/CD1d complex, with a particularly slow off rate. These unique properties are consistent with the coreceptor-independent action of the V alpha 14 TCR and may be related to the intense response to alpha-GalCer by NKT cells in vivo.
Insights
The T cell receptor (TCR) on V alpha 14 NKT cells binds glycolipid antigens presented by CD1d molecules. This interaction is crucial for NKT cell recognition and response, particularly with the agonist alpha-galactosylceramide.
Area of Science:
- Immunology
- Molecular Biology
- Cellular Biology
Background:
- Most CD1d-restricted NKT cells in mice possess a V alpha 14J alpha 18 TCR rearrangement.
- The molecular mechanisms underlying NKT cell reactivity to CD1d-presented glycolipid antigens remain largely unelucidated.
Purpose of the Study:
- To investigate the molecular basis of the interaction between the V alpha 14 T cell receptor (TCR) and CD1d-glycolipid complexes.
- To identify key residues on CD1d that mediate TCR recognition of glycolipid antigens.
Main Methods:
- Surface plasmon resonance (SPR) was employed to measure binding kinetics.
- Tetramer equilibrium and decay experiments assessed TCR/CD1d complex stability.
- Mutant and wild-type CD1d molecules were utilized alongside glycolipid antigens and soluble TCR forms.
Main Results:
- Specific CD1d alpha-helical amino acids were identified that modulate TCR interaction without significantly affecting lipid binding.
- The V alpha 14(+) TCR binding to CD1d necessitates the agonist alpha-galactosylceramide (alpha-GalCer), not beta-galactosylceramide, indicating the carbohydrate moiety's critical role.
- The TCR exhibits high-affinity binding to the alpha-GalCer/CD1d complex, characterized by a slow dissociation rate.
Conclusions:
- The carbohydrate portion of the CD1d-bound antigen is a major determinant for V alpha 14 TCR recognition.
- The observed high-affinity binding and slow off-rate of the V alpha 14 TCR to the alpha-GalCer/CD1d complex support its coreceptor-independent function.
- These findings provide insights into the molecular basis of NKT cell activation by alpha-GalCer.