FIG. 1.

Downregulation of CD46 from the surface of CHO cells expressing CD46 isoforms and chimeric CD46-CD4 proteins after contact with persistently infected U937-p cells. Schematic representations of the CD46 isoforms and CD46-CD4 chimeric molecules are shown for stably (A) and transiently (B) expressing cells. Molecules a and b are naturally expressed CD46 isoforms. Recombinant c is missing CCP domain 2 (cross-hatched thin line), which is important for the interaction with MV H. STP domains B and C, the transmembrane domain, and the cytoplasmic domains CYT1 and CYT2 of CD46 were replaced by corresponding domains of CD4 in recombinants d to l. Surface expression of the CD46 forms was detected with antibody 13/42, directed against the first CD46 domain (cross-hatched dark line), in the case of stable transfectants or with a polyclonal serum against CD46 in the case of the transient transfectants. The percentages of downregulation (n = 3) were calculated from the differences in the mean fluorescence intensities of cells contacted at 37°C and kept at 4°C and are given in the corresponding lower panels for stable expression (A, lanes 1 to 8) and transient expression (B, lanes 1 to 5).