The detection and occurrence of circulating antigens of Trichinella spiralis during worm development

Four enzyme-based immunoassays were compared in detecting circulating antigens (CA) of Trichinella spiralis, i.e. microfluorescence, dissociated enhanced lanthanide fluoroimmunoassay (DELFIA), enhanced chemiluminescence and enzyme-linked immunosorbent assay (ELISA). Parameters which could affect the sensitivity and specificity of the assays were evaluated. Different combinations of polyclonal antibody (PA) and five monoclonal antibodies (mAbs) against the excretory/secretory antigens of the nematode were tested to produce an optimal antigen-detecting system. DELFIA and a "sandwich" consisting of PA as capturing antibody and mAb 7C2C5 as detecting antibody, yielded the most stable and sensitive results; and 1 ng CA/ml could be detected. The assay did not cross-react with heterologous antigens of Angiostrongylus cantonensis, Ascaris suum, Cysticercus cellulosae, Fasciolopsis buski, Gnathostoma hispidum and Trichuris suis. Fluctuating levels of CA were observed in the serum of experimentally infected mice at various periods post-infection. As early as days 4 and 6, a significant amount of CA was detected. The level reached a peak at day 10, then declined and another peak was observed at day 18. The monitoring of the corresponding antibody response by ELISA showed that IgM was first detected at day 10, reaching a peak at day 16. A marked increase in IgG1 was noted from day 16 and its level was significantly higher than that of IgG2.