CsCl VLPs+Lewis b Fig. 3 Binding of NoV VLPs to synthetic ABH histo-blood group antigens. Sucrose-purified VLPs (Sucrose VLPs, purified according to procedure B in Fig. 1a) , heat-denatured NoV VLPs (60°C, 1 h) (Heattreated VLPs) and CsCl-purified VLPs (CsCl VLPs) were tested for binding to H type 3 and Lewis b carbohydrates at the indicated concentrations. The pH value in the binding assay was 7.4 respectively) were homogenous and intact, and approximately 38 nm in size. However, CsCl-purified VLPs appeared heterogeneous in size, with a few broken particles, although comparable to the morphology seen by others [7] . CsCl purification is known to introduce several impurities at the end of the process and cause aggregation of the VLPs during storage [5] . The poorest morphology was seen after concentration of the VLPs by dialysis against PEG, which resulted in aggregation. In addition, residual PEG, which leaks through the dialysis membrane, might interfere with further applications of the VLPs [19] .