Activation and proliferation of HEL specific B cells exposed to HEL-VLPs. (A) Naïve B-cells from SW-HEL mice were co-cultured for one day with splenic DCs and CD4+ T-cells from either non-immunized (naive) or GagPol immunized (Ad-Hgp) mice in the presence of HEL-VLPs or control VLPs lacking HEL. Cells were stained with Alexa488-conjugated HEL and antibodies to B220 and anti-CD69. The CD69 expression pattern of HEL+B220+ cells is shown. The experiment was performed three times with similar results, data of one representative experiment are shown. (B) Naïve B-cells from SW-HEL mice were labelled with CFSE and adoptively transferred into non-immunized or GagPol-immunized mice. Two hours later, half of the acceptor mice were injected i.v. with HEL-VLPs. Three days later, spleen and LN cells were stained with Alexa647-conjugated HEL-and anti-B220 antibodies. The CFSE fluorescence intensity of HEL+B220+ cells is shown. Two independent experiments with three to four mice were performed. Representative data are shown.