Table I.

Alignment of the core region of three α- and six γ-gliadin T cell epitopes, presentation by DQ2.2 homozygous APC, and the IC50 values in both DQ2.5 and DQ2.2 peptide binding assaysa

Gliadin EpitopePeptide-Binding Register, P1-P9Pro in P3DQ2.2 T Cell StimulationIC50 (μM)
123456789DQ2.5DQ2.2
α-IQLQPFPQP E LPY+3.522
α-IIPQP E LPYPQPQLPY+(+)1942
α-IIIPQPQLPYPQP E LPY+(+)860
γ-IPEQPQQSFP E Q Q RP+4.38.8
γ-IIGIIQP E QPAQL++2.58.9
γ-IIIFP Q QP E QPYP Q Q+(+)2850
γ-IVFSQPEQ E FPQPQ++/−b6.42.7
γ-VIP Q QPFP E QP Q Q+71>167
γ-VIIPQP E Q Q FPQ+(+)NDND
Q QP E QPFPQ+(+)NDND
  • a The sequences of deamidated 11–14-mer peptides used in peptide binding assays are aligned according to their peptide binding frames to DQ2.5. The Gln deamidation sites (by TG2) critical for T cell recognition are denoted by bold E, whereas underlined Q indicates other noncritical deamidation sites that nonetheless are targeted by TG2. Both groups of TG2-targeted Gln sites were synthetically converted to Glu in peptides used for peptide binding assays. For T cell recognition with DQ2.2 APC, + indicates equally well presentation by DQ2.2 compared with DQ2.5, (+) indicates presentation by DQ2.2 with lower efficiency compared with DQ2,5, and − indicates no T cell recognition with DQ2.2 APC at all. The radiolabeled HLA class I α 46–60 peptide EPRAPWIEQEGPEYW was used as an indicator peptide in both DQ2.5 and DQ2.2 peptide binding assays.

  • b DQ2.2 T cell stimulation of peptide FSQPEQEFPQPQ was seen with the cross-reactive γVII TCC387.19 (data not shown) but not with the γIV TCC430.1.112 (Fig. 3J).