Regulation of allotype expression in heterozygous rabbits. II. Concomitant suppression of b4 and b6 allotypes in the same cell.

Cells from heterozygous b4b6 rabbits were treated at 4 degrees with anti-b4 or anti-b6 antibodies and then warmed at 37 degrees. A disappearance of both b4 and b6 allotypes (concomitant modulation) ensued. When cells which had undergone extensive comodulation were cultured overnight we noted that those cells were unable to re-express either allotype at pre-modulation levels. This suppression was likely linked to the initial events which culminated in comodulation. Those cells were not further suppressible when suppressive antibodies were added to the cultures whereas cell cultures which had undergone little or no previous modulation or comodulation were readily suppressed for both allotypes after anti-allotype antibodies had been added to the cultures overnight (concomitant suppression). This indicated that in vitro suppression of allotype may depend on cell surface allotype being present at a sufficiently high density. We present data which show that events at the cell surface may play a role in the regulation of cell surface allotype expression and propose that concomitant suppression may have bearing on cellular mechanisms which control allotype expression and also allotype suppression.