Evidence that the B5 molecule on sheep lymphocytes is a homologue of mouse Ly 6 and human CD59.

When analysed by SDS-PAGE, the B5 molecule immunoprecipitated from sheep thymocytes, T cells and B cells migrated as multiple bands within a size range of 11,000-17,000 MW. After digestion with endoglycosidase-F, the precipitate from all cell types yielded a 6000 MW band. T-cell lysates gave an additional band at 6300 MW. All forms of the B5 molecule were anchored to the cell membrane via phosphatidylinositol. These results strengthen earlier evidence that the B5 molecule is a sheep homologue of the mouse Ly 6 antigen. The additional protein unit found on T cells may be of functional importance since the B5 molecule is known to be involved in an activation pathway of T cells but not of thymocytes or B cells.