Immunity to tapeworms: acquired resistance to Hymenolepis citelli in the mouse.

The dynamics of secondary infections with Hymenolepis citelli in mice are described. A primary infection of one and six cysticercoids for 21 days sensitized CFLP male mice against homologous challenge infections. Acquired resistance was manifested mainly as stunting/destrobilation of secondary worms. The severity of stunting depended on the intensity of the primary infection. Secondary worms were not expelled more rapidly than primary worms but the protective response retards growth early in challenge infections. Sensitization of mice for seven days with six or 24 cysticercoids did not confer a measurable protective response, whereas priming by the same regime for 21 days induced a significant protective response. Acquired resistance to challenge waned with time in the absence of the primary worms. The growth and survival of a six-cysticercoid primary infection was enhanced by the administration of the immunosuppressant drug cortisone acetate. Worms from cortisone-treated mice were heavier than those from untreated controls. Acquired resistance to homologous challenge was also partially ablated in cortisone-treated mice. It is suggested that rejection of primary infections and stunting/destrobilation of secondary worms may be immunologically mediated.