Intestinal immunity to tapeworms : The rejection of Hymenolepis citelli by mice and rats

The work described in this thesis was undertaken to provide evidence that Hymenolepis citelli is rejected by an immunologically-mediated mechanism and that acquired immunity to homologous challenge infections is present in the absence of the primary infection. The growth and survival of the parasite was characterised in CFLP mice: it was shown that over 80% of H. citelli worms became established and grew, thereafter survival depended on the intensity of the primary infection. Immunity to homologous challenge infections was unequivocally demonstrated in the absence of the primary worms in mice. Immunity was manifested mainly as stunting/destrobilation of secondary worms; the severity of stunting was related to the intensity and duration of the primary infections. The effectiveness of the protective response waned with time in the absence of continuing antigenic stimulation. Rejection was completely suppressed in cortisone-treated mice and furthermore, growth of worms was much enhanced. The in vivo interactions between H. citelli, H. diminuta and H. microstoma were investigated: cross-protection exists between the species. An interaction between Nematospiroides dubius and H. citelli was also studied; the survival of H. citelli was enhanced, but its growth depressed in concurrent primary infections with the nematode. Immunity against a homologous challenge infection with H. citelli was not ablated by a concurrent N. dubius infection. The rat was also used as a model for studying immunity to H. citelli. Growth and survival of worms in primary infections of varying intensities were described in CFHB rats. Acquired immunity to challenge infections was demonstrated; the effectiveness of the protective response was related to the intensity of both the primary and secondary infections. Immunity diminished with time in the absence of the primary worms. Cross-protective responses between H. citelli and H. diminuta were also demonstrated. The proliferation of IgA, IgM and IgG1-positive immunocytes in the intestinal lamina propria of uninfected, primary and secondary infected mice was studied: there was no evidence for the involvement of plasma cells in the response to H. citelli and H. diminuta, although with H. microstoma infections there was some evidence for the involvement of IgA and IgM immunocytes. The occurrence of immunog1obu1ins on worm surfaces was also investigated. The results presented in the thesis are discussed in relation to current concepts of immunity to tapeworms. Future lines of research are suggested