B cell–mediated Th-cell suppression involves induction of T-cell apoptosis. (A) Annexin binding of PKH-26–labeled Th cells cultured alone or with ^lgB25⁺ cells + cCD3/IL-2 after different incubation times between 24 and 96 hours, 1 representative experiment of 4 independent experiments shown. (B) Annexin staining of T cells cultured alone or with ^lgB25⁺ or ^smB25⁻ cells at different time points. Mean plus or minus SEM of 6 independent experiments shown. (C) Immunofluorescence microscopy after 24-hour incubation time; 40× magnification. Sixteen adjacent areas in a 4 × 4 array were imaged and stitched together. Images were acquired with respective filters for CD4-APC, CD19-FITC, and annexin-PE; overlay colors: green indicates B cells; blue, T cells; purple, Ax-positive T cells; and yellow, Ax-positive B cells. One representative area with T+ ^lgB25⁺ and T+ ^smB25⁻ is shown.