Immunization against experimental rabbit cysticercosis using liposome-associated antigen preparations

Rabbits were vaccinated once, by subcutaneous and intradermal injection, with sonicates of oncospheres (TpO) or conditioned media from in vitro maintained mature metacestodes (TpMcES) of Taenia pisiformis. Extracts were either incorporated into or mixed with unilamellar liposomes (reverse phase evaporative vesicles) or emulsified in Freund's Incomplete Adjuvant (FIA). Control groups received liposomes or FIA without antigen, or antigen preparation without adjuvant. Rabbits were challenged orally two weeks after vaccination with approximately 1500 eggs of T. pisiformis and necropsied eight weeks after challenge. A mean of 155 cysts was recovered from seven control rabbits. A 67% reduction in peritoneal cyst numbers was obtained in TpO-IFA vaccinated rabbits compared to 75% for the TpO-liposome entrapped group. The highest level of protection (86%) was obtained when TpO was mixed with but not entrapped in liposomes. Only 32% and 39% reduction in peritoneal cyst numbers was obtained after immunizing with the TpMcES preparation in liposomes or IFA respectively, however greater than 85% of peritoneal metacestodes were dead (necrotic or calcified) and suggests a different immune response than occurs after vaccination with oncosphere extracts. Specific anti-oncospheral or anti-metacestode ES antibody (IgG) responses at two weeks post vaccination were similar in rabbits immunized with liposome or IFA associated extracts.