Long-term IgG anti-gp350/220 antibodies are generated in mice immunized with EBVgp350/220-F VLPs, UV-EBV and soluble recombinant gp350/220 ED. Groups of five mice were immunized intraperitoneally with either EBVgp350/220-F VLPs (green line), UV-EBV (red line) or soluble recombinant gp350/220 ED (purple line). Each immunogen contained equivalent amounts of gp350/220. TNE served as vehicle control (blue line). All immunizations were performed in the absence of adjuvant. Anti-gp350/220 IgG titers were determined over time up to day 228. Booster immunizations were performed on days 43, 172, 183 and 218 as indicated on the time line (bottom). Primary and booster vaccinations contained equivalent immunogen. Specific anti-gp350/220 ED titers were determined by ELISA (Methods). X-axis shows the day on which serum was obtained for ELISA. Y-axis displays anti-gp350/220 antibody titer on a log scale. Vertical lines indicate the average titer produced by groups of five mice at the time of serum collection and associated error bars indicate the standard deviation.