IgG-subclass antibody responses and the natural history of hepatic cystic echinococcosis in asymptomatic patients

Given that cystic echinococcosis (CE) is a serious clinical problem in endemic countries, there is still relatively little information available on the natural history of the human disease. The aim of the present study was to correlate serological status with pathology, in ultrasound-characterised, asymptomatic cases of human CE. Serum concentrations of IgG reacting with antigen B from cyst fluid and of similarly specific IgG(1), IgG(2), IgG(3) and IgG(4) were determined by ELISA and further investigated by immunoblotting. CE cases with simple cysts (Type I), or cysts with clear laminations and daughter cysts (Types II and III) exhibited elevated IgG(4) seropositivity, whereas concentrations of specific IgG(1) and IgG(4) declined in CE cases characterised by cyst infiltration or calcifications (Types IV and V). The responses of each specific IgG subclass were used, in association with an ultrasound classification, to try to develop an immunoserological natural-history profile of CE in asymptomatic patients. Specific IgG(4) antibody responses were particularly associated with the evolutive phase of CE (Types I, II and III), whereas the IgG(1), IgG(2) and IgG(3) responses tended to be associated with the involutive phase (Types IV and V). These results indicated that an IgG(4) antibody response was associated with (or was a marker for) cystic development, growth and disease progression, whereas the IgG(1), IgG(2) and IgG(3) responses occurred predominantly when cysts became infiltrated or were destroyed by the host. The findings support the view that evolutive and subsequent involutive phases occur in untreated CE.