THE NATURE OF THE IMMUNE STATE PRODUCED BY INACTIVATED VACCINIA VIRUS IN RABBITS

Boulter, E. A. (Microbiological Research Establishment, Porton Down, Salisbury, Wiltshire, England), H. T. Zwartouw, D. H. J. Titmuss and H. B. Maber. The nature of the immune state produced by inactivated vaccinia virus in rabbits. Amer J Epidem 94: 612–620, 1971.—The immune state evoked in rabbits by inactivated vaccinia virus differs from that produced by live virus. The latter induces a neutralizing antibody response, resistance to intradermal inoculation of live virus and immunity to an otherwise lethal infection with rabbitpox; this immunity is passively transferable with serum from immunized animals. Inactivated virus also evokes neutralizing antibody and protection against fatal rabbitpox, but not resistance to intradermal challenge with live virus. Furthermore, protection against fatal rabbitpox is neither correlated with antibody level nor passively transferable with serum. These anomalies appear to be due to a previously unrecognized antigenic difference between intracellular and naturally released extracellular forms of the virus. Inactivated vaccines, which usually are prepared from intracellular virus extracted from infected cells or tissues, produce antibody that neutralizes intracellular but not extracellular virus. As the latter form of the virus is mainly responsible for the spread of infection in vivo, such antibody cannot prevent the progression of a lethal infection such as rabbitpox. The strong active immunity engendered by inactivated intracellular virus may represent a cellular type of immunity.