Fig. 4.

Direct interaction between live B cells and dendritic cells is required for antigen transfer. (a) Contribution of apoptotic B cells to antigen transfer is trivial. Apoptosis of antigen pulsed B-LCLs was induced by hyperthermia. Primary DCs were co-cultured for 18 hr with viable (1 ×10⁶ cells) B cells pulsed with non-specific Ab (dotted curve) or aIg (black solid curve) or with apoptotic B cells (3 ×10⁵ cells; number of apoptotic cells within viable population) pulsed with aIg (dark gray curve). Levels of antigen were assessed for the CD19⁻:CD14⁻:CD11c⁺ gated population. (b) Antigen transfer from apoptotic B cells was significantly less compared to viable cells. MFI values for transferred antigen (AF488) are given for 4 independent experiments (* p= 0.001; n=4; thin bars represent value range). (c) Antigen transfer is abrogated upon separation of B cells from dendritic cells. Primary DCs were co-cultured in the absence of transwell (No TW) with B cells pulsed with non-specific Ab (dotted curve) or in the absence (black curve) or presence (8 um TW) (dark gray line) of transwell with B cells pulsed with aIg.