MICB is released at higher levels by purified and activated CD4⁺ T cells. CD3⁺ T cells were isolated by negative selection and further purified to obtain subpopulations of CD4⁺CD3⁺ (CD4) and CD8⁺CD3⁺ (CD8) T cells. CD4⁺ and CD8⁺ T cells were stimulated with SEB in the presence of irradiated autologous PBMCs. (A) Cell culture supernatants were harvested after 3 and 5 days and tested in ELISA for the presence of sMICB. Each symbol represents one donor tested on both cell populations. Dotted line shows the detection limit of the assay. Solid lines indicate the average of all measurements in the respective group. Statistical analysis on all donors with paired Student t test. (B) The same donors were monitored also for cell-surface expression of MICB by anti-CD3 and anti-CD8 staining, followed by flow cytometry. IgG isotype control MFI values were always subtracted. Mean values of MFI are indicated by horizontal bars and were calculated on all donors. Statistical analysis with paired Student t test.