The immunological response of the rat to infection with Taenia taeniaeformis. VII. Immunization by oral and parenteral administration of antigens

Abstract

Rats immunized with in vitro products and saline-soluble antigens derived from Taenia taeniaeformis were found to be significantly protected against challenge infection. Oral and intraperitoneal administration of antigen solutions alone were effective in stimulating resistance. Adjuvants, however, were required for successful immunization when the antigens were injected intramuscularly. Bordetella pertussis and aluminium hydroxide were able to improve markedly the protective effects of antigens given parenterally by either route, but Freund's complete adjuvant (FCA) was not effective as an adjuvant in this system. Reaginic antibodies to parasite antigens were detected in the sera of rats immunized with parasite antigens and B. pertussis or Al(OH)₃, but none were detected in those given antigens incorporated in FCA. The possible role of reaginic antibodies in immunity to T. taeniaeformis is discussed.

A single dose of antigen given orally produced significant protection. Increasing the number of daily doses of antigen administered orally enhanced the degree of protection to a limited but significant extent. There did not appear, however, to be any advantage to giving large doses (> 1 mg protein) of antigen, or extending the immunizing schedule over several weeks. Reaginic antibodies were not detected in the sera of rats immunized orally, but these animals were resistant to both oral and intravenous challenge infection with parasites. These observations are discussed in relation to the phenomena of immune exclusion of antigen by the gut, and gastrointestinally induced systemic tolerance with respect to IgE production.

Sera from rats immunized by all routes were found to be ineffective in conferring resistance upon recipients when given at the dose of 1 ml/rat. Furthermore, sera from donors vaccinated intramuscularly with saline soluble antigens and B. pertussis increased the susceptibility of recipient rats to infection with T. taeniaeformis. This is in sharp contrast to our previous experience in which we have shown that sera from rats with an active infection are highly effective in passive transfer. Possible reasons for these observations are discussed. The requirements for adequately controlled immunization procedures to assess the contributory effects of adjuvant type and the route of antigen inoculation in immunizing against taeniid infections are emphasized in the discussion.