DNAM-1 augments CD8 T cell division in response to superantigen. (A and B) FACS analysis of CFSE dilution 72 h after (A) WT or (B) DNAM-1^−/− T cells were co-cultured with A20 cells or A20 cells expressing mCD155 in the presence of the indicated concentrations of SEB. The percentage of undivided CD8 T cells is indicated. (left) Two control panels show the CFSE content of T cells incubated with unpulsed APCs. (C) Percentage of dividing CD8 T cells stimulated by A20 or A20-mCD155 at graded concentrations of SEB. (D) Proliferation of WT or DNAM-1^−/− T cells stimulated by A20 or A20-mCD155 in the presence of graded concentrations of SEB measured by [³H]thymidine incorporation. Results are means ± SEM. **, P < 0.01. (E) Expression of MHC class II and mCD155 on control and CD155-transfected A20 B cell lymphoma.