The VP2 proteins of HBoV1-4 were expressed in insect cells using a baculovirus expression system. The generation of HBoV VLPs was verified by ultracentrifuge-purification and electron microscopy (EM). Typical parvovirus-like particles of 22-24 nm in size, similar to the particles of infectious parvovirus virions, were visualized under EM (data not shown). The purified VLPs of HBoV1, 2, 3 and 4 were also reactive to murine antisera specific for the VP2 protein of the respective HBoV species in Western blot assays ( Figure 1B ).