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.

Use of liposomes for protective immunisation in sheep against Echis carinatus snake venom.

Nigerian Echis carinatus venom incorporated into sphingomyelin-cholesterol liposomes stabilized with osmium tetroxide produced a rapid, sustained and protective immune response when injected i.v. into sheep. The response was similar to that reported earlier in mice. The implications of the findings are discussed in relation to the production of cheaper and more effective antivenoms. The possible use of immunostimulants for increasing the protective effect of antisera raised using this method are also considered.

Liposomal immunisation against snake venoms.

A method is described which produces a high, permanent antibody response following a single injection of venom. Animals (mice, rabbits, sheep) were given intravenous, subcutaneous or orally administered Nigerian Echis carinatus (carpet viper) venom which had been incorporated into sphingomyelin-cholesterol liposomes whose membranes had been stabilized by cross-linking adjacent molecules of sphingomyelin using osmium tetroxide. Before use the preparations were thoroughly dialysed to remove any unbound osmium tetroxide. Antibody levels were estimated using enzyme immunoassay. Venom treated in this way and administered i.v. or s.c. produced a powerful, sustained and protective antibody response lasting for the lifetime of a mouse. We also report the development of significant antibody responses after oral administration of liposome-entrapped but not free venom.

Liposomes of controllable size in the range of 40 to 180 nm by defined dialysis of lipid/detergent mixed micelles.

Liposomes, in the size range of 40--180 nm, are formed when lipid and additives are solubilized with detergent, yielding defined mixed micelles, and the detergent is subsequently removed by controlled dialysis. Their most important properties are that they are indeed unilamellar with usefully large encapsulated volumes and are homogeneous in size. Liposomes have been formed from both natural and synthetic phospholipids with cholesterol and charged molecules added. This relatively simple technique may be particularly useful for encapsulating drugs, enzymes and other macromolecules and in studies of reconstitution of membrane proteins.