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Fig. 1. Schematic representation of CD1a and modes by which T cell receptors interact with the CD1a-lipid complex.
(A) The structural feature of CD1a. The heavy chain consists of three domains (α1, α2, α3) with a short cytoplasmic tail, and it is non-covalently associated with a light chain (β2m). The α1 and α2 domains form the lipid antigen-binding groove, which bears two pockets, A′ and F′. (B) TCRs recognize CD1a-lipid complexes by three modes: head-group recognition (upper), absence of interference (middle) and interference (bottom). 1) Some TCRs interact with a specific head-group of lipids protruding out of the CD1a and form a ternary lipid-CD1a-TCR complex. 2) Some headless lipids are completely buried within antigen binding groove and allow TCRs the opportunity to directly bind to the A roof of CD1a. In this case, TCRs do not need interact with antigens, but CD1a itself. 3) Bulky head-groups of some lipids can interfere TCR:CD1a interaction, thereby controlling the activation of CD1a-autoreactive T cells. β2m, β2-microglobulin.
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