Relationships between IgG, IgM, IgE and resistance to reinfection during the early phase of infection with Clonorchis sinensis in rats

An enzyme linked immunosorbent assay (ELISA) was used to study the correlation between the levels of IgG, IgM and IgE immunoglobulin isotypes and resistance to reinfection in rats during the first month of infection with Clonorchis sinensis. Rats were infected with Clonorchis sinensis (primary infection), and then treated with praziquantel on the 1st, 3rd, 7th, 14th and 28th day post infection (p.i.). To measure resistance, rats were re-infected with C. sinensis (secondary infection), 2 weeks after the treatment and worms were recovered 4 weeks later. During the primary infection, significantly increased levels of IgG isotype were observed on days 14 and 28 p.i. (P < 0.001) and IgM levels were significantly increased on 3rd and 28th day (P < 0.001). During the secondary infection, significantly increased levels of IgG isotype were found from 3rd to 28th day and IgE isotype on 7th and 14th day (P < 0.01) while significant levels of IgM were found on the 3rd and 28th day (P < 0.05). Furthermore, significant differences of worm numbers between infected and control group was found on the 14th and 28th day (P < 0.001). An inverse correlation betwee the IgG levels and the resistance to re-infection was also observed (r = -0.948, P = 0.004), indicating that the resistance to reinfection is highly associated with the levels of IgG during the early phase of infection, and then with the IgM and IgE.