Immunostimulatory complexes containing Eimeria tenella antigens and low toxicity plant saponins induce antibody response and provide protection from challenge in broiler chickens

Immunostimulating complexes (ISCOMs) are unique multimolecular structures formed by encapsulating antigens, lipids and triterpene saponins and are one of the most successful antigen delivery systems for microbial antigens. In the current study, both the route of administration and the antigen concentration of ISCOMs, containing Eimeria tenella antigens and saponins from native plants, were evaluated in their ability to stimulate humoral immunity and to protect chickens against a challenge infection with E. tenella. Broiler chickens were immunized with ISCOM preparations containing E. tenella antigens and the purified saponins Gg6, Ah6 and Gp7 isolated from Glycyrrhiza glabra, Aesculus hippocastanum and Gipsophila paniculata, respectively. The effects of the route of administration, dose of antigen and type of saponin used for construction of ISCOMs were evaluated for ability to stimulate serum IgG and IgM and to protect chickens against a homologous challenge. A single intranasal immunization was the most effective route for administering ISCOMs although the in ovo route was also quite effective. Dose titration experiments demonstrated efficacy after single immunization with various ISCOM doses but maximum effects were observed when ISCOMs contain 5–10 μg antigen. Immunization of birds by any of the three routes with E. tenella antigens alone or antigens mixed with alum hydroxide adjuvant resulted in lower serum antibody and reduced protection to challenge relative to immunization with ISCOMs. Overall the results of this study confirm that significant immunostimulation and protection to challenge are achieved by immunization of chickens with ISCOMs containing purified saponins and native E. tenella antigens and suggest that ISCOMs may be successfully used to develop a safe and effective vaccine for prevention of avian coccidiosis.