Follow-up of antibody avidity in BALB/c mice infected with Toxocara canis.

In human Toxocara canis infection, an association has been shown between high IgG avidity in the chronic phase and low IgG avidity in recently acquired toxocarosis. The evolution of the antibody response in terms of avidity has been carried out through a T. canis infection in BALB/c mice. Infection with T. canis embryonated eggs (EE) was carried out with single doses (SD) of 6, 12, 50, 100, 200 or 1000 EE/mouse and with multiple doses (MD) of 200 and 1000 EE. Specific antibodies against T. canis (IgM+G, IgG, IgG1 and IgM) were detected by ELISA and Western Blot (WB) techniques in the presence and absence of urea. With the ELISA method, an increase in the avidity index (AI) of around 50% was detected from days 40-80 p.i. to the end of the study, with all the doses studied. The WB method showed the presence of high avidity antibodies bound to 100 kDa and 75 kDa T. canis proteins in all the cases when the IgM+G and the IgG1 antibodies were investigated. Antibodies of variable avidity were observed in those sera that recognized the group of low molecular weight proteins, between 37 kDa and 25 kDa.