Surface expression of MHC and B7 molecules on tumor lines used in this study.

Expression levels of the MHC class I molecules H-2K^b and H-2D^b are shown by shaded histograms; open histograms show background staining with isotype control mAb. Expression of B7-1 and B7-2 (shaded histograms) was detected using CTLA4-Ig + goat anti–human IgG biotin + SA-PE. Open histograms represent control staining with CTLA4-Ig + SA-PE. In addition to using CTLA4 immunoglobulin, tumors used in each experiment were stained directly with anti-CD80 and anti-CD86 mAbs to confirm B7-1 and B7-2 surface expression, respectively (data not shown).