Murine MHC class I and CD1d molecules physically associate.(A and B) Lysates from BMDCs (A) or mock-treated and acid-stripped KT4-CD1d1, KT4-CD1d1TD, or KT4-control cells (B) were co-immunoprecipitated with the 1H6 mAb or an isotype control mAb and immunoblotted with an anti-MHC class I mAb. Presence of a MHC class I–specific band in the lane loaded with lysate co-immunoprecipitated with the CD1d-specific mAb 1H6, but not in the lane loaded with lysates treated with an isotype control mAb, shows the association of MHC class I and CD1d molecules. The graphs below (B) indicate relative band intensities. (C) Mock- or acid-treated KT4-CD1d1 cells were lysed to prepare membrane and cytosolic fractions; the association of MHC class I and CD1d was analyzed in both fractions. (D) Confocal microscopy shows co-localization of CD1d (green) and MHC class I (red). (E) KT4-CD1d1, KT4-CD1d1TD and KT4-control cells were mock-infected or infected with a control VV or VV-TAP1 for 4 h. Cells were lysed and co-immunoprecipitated with the 1H6 mAb and immunoblotted with an anti-MHC class I mAb.