Bovine, but not mouse, CD11a substitutes for human CD11a. Wild-type Jn.9 cells, mutant J-β2.7 cells and cells expressing human (J-β2.7/hCD11a), mouse (J-β2.7/mCD11a) or bovine (J-β2.7/bCD11a) CD11a on the cell surface were subjected to Ltx and viability determined via trypan blue exclusion assay (see Experimental procedures). Bovine leukaemia cells (BL3) served as a control. Transfection of human or bovine, but not mouse, CD11a into mutant J-β2.7 restored susceptibility to Ltx equal to that of the wild-type Jn.9. (* significant; NS: not significant when compared with wild-type Jn.9 P < 0.001).