MICB is expressed mostly on the surface of SEB-activated CD8⁺ T cells. PBMCs were CFSE labeled and then stimulated with SEB. Cells were harvested at the indicated times and stained with anti-CD8–, anti-CD3–, and anti-MICB–specific mAbs in a 4-color FACS analysis. Subpopulations of CD8⁺ and CD4⁺ T lymphocytes were identified by gating on CD8⁺CD3⁺ or CD8⁻CD3⁺ cells, respectively, and further analyzed for the expression of MICB. (A) Time-course analysis of MICB expression on CD4⁺ and CD8⁺ T cells. MFI values relative to MICB are reported. One representative donor of 14 is shown. (B) Expression levels of MICB analyzed on SEB-activated CD4⁺ or CD8⁺ T lymphocytes from different donors (n = 14) at day 3. Each donor is represented by a symbol. The dashed line delimits negative donors (MFI values < 2). Mean values of MFI are indicated by horizontal bars and were calculated on positive donors. They were 25 plus or minus 14 on CD8⁺ T cells (ranging from 12 to 69) and 9 plus or minus 6 on CD4⁺ T cells (ranging from 3 to 26). Statistical analysis on all donors with paired Student t test. (C) MICB is preferentially expressed on proliferating cells. Progressive loss of CFSE fluorescence intensity in CD4⁺ or CD8⁺ T lymphocytes is indicated by the R1 region. The MFI relative to MICB and calculated on cells gated in R1 is shown. A representative donor of 14 analyzed is shown at day 3 after SEB stimulation.