Gel filtration and gel electrophoresis of refolded HLA-A2/EBV peptide monomers (a; c, lanes 3 and 4) and HLA-B27/EBV peptide monomers (b; c, lanes 1 and 2). In both experiments the amount of protein aggregation is low, indicated by small amounts of eluted proteins between 7 and 13 ml. The peaks eluted at 13.7 ml contained the soluble MHC monomer. The gel in (c) shows that both eluted monomers are highly purified (lanes 1 and 3) and that most soluble monomers bind to streptavidin if added (lanes 2 and 4). (d) Antigen-specific T cells could be detected with both tetramers, although HLA-A2 tetramers stained with greater intensity (log 0.8 more) than HLA-B27. A280, absorption at 280 nm; asterisks, protein aggregates; SA, streptavidin.