a, Experimental set up for live imaging of LIPSTIC labeling. Cd40−/− B cells and Cd40lg−/Y CD4+ T cells were transduced with G5-CD40 (Tomato reporter) or CD40L-SrtA (GFP reporter), respectively. CD40L-SrtA+ T cells were loaded with AlexaFluor647-SELPETGG, mixed with G5-CD40+ B cells on intercellular adhesion molecule (ICAM)-coated chambers to allow interactions, and immediately imaged. b, Time series showing transfer of AlexaFluor647-SELPETGG (white) from CD40L-SrtA+ T cells (green) to G5-CD40+ B cells (red) upon interaction. Data are representative of two independent experiments.