Treatment of DC with the glycyl-tRNA synthetase inhibitor ethanolamine inhibits Th-1 responses induced by DC loaded with overlapping class I and II MHC binding peptides only when glycine residues are present in the class I/II sequence overlap region. (A) Addition of ethanolamine reduced CD8⁺ production by more than 70% when DC were loaded with the glycine-containing B8-166/DR3-162 peptide pair. CD8⁺ production induced by the non–glycine-containing peptide pair A2-443/DR3-440 was unaffected; y-axis: percentage of CD3⁺CD8⁺ cells. (B) Addition of ethanolamine reduced CD8⁺CD25⁺ production by more than 80% when DC were loaded with the glycine-containing B8-166/DR3-162 peptide pair. CD8⁺CD25⁺ production induced by the nonglycine-containing peptide pair A2-443/DR3-440 was largely unaffected; y-axis: percentage of CD8⁺CD25⁺ cells. For panels A and B, 1 representative experiment of 3 independent experiments is shown.