The expression of the measles virus H protein alone can down regulate surface expression of SLAM and CD46. Human 1A2 B cells were infected with vaccinia virus recombinants that expressed Edmonston F (Ed F), Edmonston H (Ed H), or Montefiore H (Wt H) proteins. FACS analyses of SLAM surface expression (A) and CD46 surface expression (B) were performed. Black line, 1A2 cells infected with wild-type vaccinia virus (VV) incubated with an FITC-conjugated goat anti-mouse secondary antibody; gray line, 1A2 cells infected with wild-type vaccinia virus stained with a mouse anti-SLAM antibody (A) or mouse anti-CD46 antibody (B) and detected with an FITC-conjugated goat anti-mouse antibody; solid peak, 1A2 cells infected with the indicated vaccinia virus recombinants, stained with a mouse anti-SLAM antibody (A) or mouse anti-CD46 antibody (B), and detected with an FITC-conjugated goat anti-mouse secondary antibody. Infected 1A2 cells were stained for surface expression of the F and H proteins (black line) with a rabbit polyclonal antibody specific for the F protein and a monoclonal antibody directed against measles virus H proteins (C). The dashed lines represent wild-type vaccinia virus-infected cells probed for expression of the F and H proteins.