The source of antigen in an adult tapeworm

Hopkins C. A. and Barr I. F. 1982. The source of antigen in an adult tapeworm. International Journal for Parasitology12: 327–333. Although a primary infection of Hymenolepis diminuta is not rejected for 9–15 days by a mouse, it has been shown that a primary infection terminated chemically after only 3 days induces as good protection against challenge. This demonstrated that a scolex and 1–2 mm of neck tissue (all that is formed by day 3 post infection) are an adequate source of ‘protective’ antigen. Irradiated (350 Gy) cysticercoids which survive but show little growth immunize as effectively as normal cysticercoids which indicates actively growing neck tissue is not essential and hence the scolex alone is a sufficient source of ‘protective’ antigens. In the rat irradiated cysticercoids were found to establish, double their length over 3–6 days and then slowly shrink, but 14% of the worms were still present 49 days p.i. Although a primary infection of normal worms in a rat markedly depresses growth of a secondary infection administered 7 days after the chemical expulsion of the primary, irradiated scoleces induced no measurable protection. These results are discussed in relation to the source of antigen and the fundamental difference in the protective response of mice (an abnormal host) and rats (a normal host) to the tapeworm H. diminuta in the small intestine.