RSAD2 and infection: To explore the role of viperin in this process we analyzed the viral particles generated in the presence and absence of viperin by quantitating cytoplasmic non-enveloped particles (capsids and tegumented capsids) and enveloped particles (double-layered particles formed by tegumentation and secondary envelopment in the secretory pathway) in control and viperin knockdown cells by electron microscopy, late in infection to allow accumulation of quantifiable virions (Figure 3A).