DC Endocytosis of SVLP Figure 7. SVLP association with clathrin and transferrin. (A) DC were incubated with 2.5 mg/ml SVLP (green) on ice, shifted to 39uC for different times, fixed/permeabilised, and labelled using antibody targeting clathrin (red). Acquisition was by confocal microscopy; high-resolution stacks were prepared using IMARIS, including algorithmic co-localisation analysis for co-localised voxels. Arrows show co-localisation on the merged image. Scale bars: 20 mm (top-left), 5 mm (zooms). (B) DC were incubated with 2.5 mg/ml SVLP (green) and 10 mg/ml transferrin-546 (red) for 20 min on ice, washed and shifted to 39uC with addition of fresh transferrin-546 for different times at 39uC. Acquisition was by confocal microscopy; high- resolution stacks were prepared using IMARIS. Arrows show co-localisation on the merged image. Scale bars: 30 mm (left-panel) and 5 mm (zooms). doi:10.1371/journal.pone.0043248.g007 endocytose antigens. In contrast to more degradative cells, such as macrophages, DC display a lower lysosomal proteolytic activity and show greater control of proteasees process [9,24,25]. Indeed, Delamarre et al related this limited protease activity of DC to their slower in vivo degradation of internalized antigens and retention of antigen in lymphoid organs for extended periods. They remarked that this limited lysosomal proteolytic activity would favour antigen presentation, and help explain the DC ability for efficient accumulation, processing, and dissemination of antigens. Considering these characteristics of DC, we sought to determine how DC would process a complex antigen resembling a small synthetic virus-like particle – SVLP. Many current vaccines act against viruses, and many vaccines are based on virus particles. SVLP have a high immunogenicity in mice, rabbits [17] and pigs PLOS ONE | www.plosone.org 11 August 2012 | Volume 7 | Issue 8 | e43248