(K) Ex vivo BHEL proliferation after 3d of co-culture with control or NEF-expressing CD4OT-II cells. BHEL cells were labelled with the cell proliferation dye eFluor670 and co-cultured with NGFR-enriched CD4OT-II cells expressing NEF in the presence or absence of HEL-OVA Ag. T cell-dependent B cell proliferation was assessed by quantification of the dilution of eFluor670 using flow cytometry. 