(A) CD8 T cells were detected in the spleens of B6 wt, PA28-/-, β5i/LMP7+β2i/MECL-1-/- and PA28+β5i/LMP7+β2i/MECL-1-/- mice by staining with anti-CD8α mAb and FACS analysis. Frequencies of CD8 T cells as percentage of total lymphocytes are shown (means plus SEM, n=3). (B) CD4:CD8 T cell ratios in spleen and thymus of B6 wt, PA28-/-, β5i/LMP7+β2i/MECL-1-/- and PA28+β5i/LMP7+β2i/MECL-1-/- mice. Data are representative for two independent experiments (means plus SEM; n=3).