Examination of murine antibody response to secondary hydatidosis using ELISA and immunoelectrophoresis

Antibody responses in mice with up to 64 weeks of secondary Echinococcus granulosus hydatidosis were examined by ELISA using hydatid protoscolex antigen (Px), Antigen 5 (Ag5) and Antigen B (AgB), and by immunoelectrophoresis (IEP) using sheep hydatid cyst fluid (SHCF). Anti-Px IgG antibodies, evident from 3-5 days post infection (p.i.), increased steadily until 16 weeks and maintained a high level afterwards. Anti-Ag5 IgG antibodies were negligible up to two weeks, but they showed a small increase around 2-3 weeks which was followed by a big increase around 16 weeks p.i. The high level of anti-Ag5 IgG antibodies persisted to the end of experiment. The level of anti-AgB IgG antibodies remained relatively low throughout infection. Anti-Px IgM antibodies appeared in the early period of infection, but became insignificant as the infection proceeded. Specific IgM antibodies to Ag5 and AgB showed two waves of increase, one between 3 days to 4 weeks p.i. and the other between 16 weeks to 46 weeks p.i. The level of IgA antibodies to Ag5 and AgB was low and only a moderate amount of anti-Px IgA antibodies was detected. Generally, a higher level of serum antibodies are associated with a larger number of mature cysts. Serum samples from 5 of 8 mice harbouring hydatid cysts formed 1-3 bands with SHCF in IEP, including Arc 5, but a precipitation are with AgB was not observed. Analysis of hydatid cyst fluid from the infected mice (MHCF) in IEP also failed to demonstrate AgB. Despite the high levels of antihydatid antibodies generated in the infected mice, protoscoleces appeared to be unhindered in their growth to mature cysts.