The Virus Particles-Elementary Bodies

Abstract

Before the availability of tissue culture systems, vaccinia virus was routinely propagated in chicken embryos, notably on the chorioallantoic membrane (Joklik, 1962 c), or it was obtained from calf lymph, the usual source of human vaccine material. Procedures were introduced by Craigie and his colleagues (Craigie, 1932) for laboratory production of EBs on a larger scale, to give yields up to 100 mg or more of virus particles. For this purpose, shaved areas of rabbit skin are inoculated by scarification, allowing the virus to proliferate and spread throughout the epidermis. Within a few days, the entire epidermal surface becomes a mass of dead cells filled with EBs, which can be collected readily by scraping the surface. The Rockefeller Institute group, using a combination of Craigie’s and Ledingham’s (1931) partial purification methods, developed a scheme for obtaining pure EBs (Smadel and Hoagland, 1942). Briefly, rabbit epidermal pulp was suspended in distilled water, and the larger debris was removed by centrifugation at low g forces. Then, the virus was sedimented at higher speeds in an angle rotor of a centrifuge which had just been invented and developed by Pickels. The homogeneity of EB preparations was established using electrophoretic analysis and sedimentation in an analytical ultracentrifuge. In both instruments, the virus particles formed a characteristic single boundary pattern, and examination in the electron microscope revealed the presence of isolated EBs free of contamination (Smadel and Hoagland, 1942). In more recent times, we and others have also employed the rabbit skin in conjunction with modern purification schemes for producing large quantities of pure rabbitpox virus and can attest to the usefulness of this procedure (Zwartouvw, 1964; P. Gold and S. Dales, unpublished).