Follicular lymphoma and DLBCL cells induce defective immune synapse formation in previously healthy T cells via direct contact interaction. (A) Healthy T cells were cocultured in direct contact for 24 hours with either healthy allogeneic B cells or allogeneic FL or transformed DLBCL (t-FL) and subsequently used in conjugation assays with sAg-pulsed third-party allogeneic healthy donor B cells (APCs, blue). Conjugates were selected at random for imaging and were scored for polarization of F-actin (red) at the immune synapse. Note the prevention of the synapse defect when cell adhesion was blocked by pretreatment of FL or DLBCL cells with anti–ICAM-1 monoclonal antibody before primary coculture with healthy T cells but not with isotype control antibody treatment (IgG). Data are the mean ± SD from 9 independent experiments with at least 50 conjugates analyzed per experiment. The confocal images shown are CD8⁺ T cells. (B) Healthy T cells cocultured for 48 hours with either healthy allogeneic B cells or allogeneic FL or DLBCL cells in transwell culture plates and subsequently used in conjugation assays with ± sAg-pulsed third-party allogeneic healthy donor B cells (APCs). Conjugates were selected at random for imaging and were scored for accumulation of F-actin at the immune synapse. Data are the mean ± SD from 9 independent experiments with 50 conjugates analyzed per experiment.