Binding of exogenous β2m tips the balance of open and closed cell surface HLA class I forms. A) Flow cytometry analysis of DAOY, D283 and D556 medulloblastoma cell lines stained with HC-10 (bold lines) or W6/32 (dashed lines) monoclonal antibody followed by PE-conjugated anti-mouse Ig, or control samples with primary antibody omitted (plain lines). B) Exogenous β2m in the absence or presence of W6/32 (W) or HC-10 (H) monoclonal antibodies was added to DAOY cells. Cell lysates were probed by β2m- or GAPDH-specific antibodies. Bar graph indicates quantitative ratios of β2m to GAPDH. C) The effect of exogenous β2m on levels of open and closed conformers in DAOY cells. Untreated (plain lines) or β2m-treated (bold lines) DAOY cells were stained with antibodies specific for open (HC-10; left) or closed (W6/32; right) MHC class I conformation followed by PE-conjugated anti-mouse Ig, and analyzed by flow cytometry.