IgG subclasses in human hydatid disease: prominence of the IgG4 response

To assess the participation of the four subclasses of IgG in the humoral response to Echinococcus granulosus infection, we determined total and parasite-specific IgG1, IgG2, IgG3 and IgG4 in sera from 46 patients with hydatid disease using an enzyme-linked immunosorbent assay (ELISA). Parasite-specific IgG subclass antibodies were quantitatively measured by means of standard curves obtained by affinity chromatography. Sera from 35 healthy individuals served as controls. The total component of IgG1, IgG2, and IgG3 showed a slight increase in patients with hydatidosis in comparison to normal control subjects with no significant differences. For the IgG4 subclass, however, a marked elevation was found in the patients group (p = 0.001 by analysis of variance). IgG1 and IgG4 subclasses showed a high anti-echinococcus antibody response, whereas there was a low parasite-specific IgG2 and IgG3 response. Indeed IgG-specific antibodies were found to belong mainly to IgG1 (63%) and to IgG4 (30%) and to a lesser extent to IgG2 (5%) and IgG3 (2%). The percentage of the total serum IgG4 antibodies that were specific for hydatid antigen reached a mean level of 18%, significantly higher than that of any of the other three IgG subclasses (p < 0.001 by Student's t test). Thus, the continuous antigenic stimulation of hydatidosis may result in an enhanced IgG4 subclass response.