FIGURE 4.

Detection of peptide-empty A2 conformers by means of the 64-3-7 epitope tag. HeLa cells expressing 64-3-7 epitope-tagged A2 molecules were stained with either (A) mAb BB7.2, which is specific for folded A2 conformers, or (B) mAb 64-3-7, which has been shown for several other MHC alleles to be specific for peptide-empty, or “open” MHC conformers. Addition of specific peptide TAX (thick black line) increased levels of BB7.2 and decreased reactivity with 64-3-7. Nonspecific peptide MCMV (gray dotted line) had no effect. No peptide (thin black line) and secondary-only controls (filled histogram) are also shown. The inset in B shows peptide dose-dependent changes in the ratio of open to folded MHC conformers for cells fed TAX peptide (thick black line), MCMV negative control peptide (dotted gray line), or no peptide (thin black line).