Antibody isotype responses to Schistosoma japonicum antigens in subjects from a schistosomiasis area with repeated praziquantel chemotherapy compared with a new endemic zone in Hunan Province, P.R. China

Abstract To demonstrate the dynamics of specific antibody isotypes against schistosome adult worm (AWA) and soluble egg (SEA) antigens, we evaluated (in 1999–2000) 112 subjects infected with Schistosoma japonicum from 2 regions of Hunan Province, China. Fifty-eight subjects were from Area A, a well-known endemic area with repeated chemotherapy. Area B ( n = 54) is a new endemic focus in another part of the same province. Serum samples were collected prior to praziquantel (PZQ) chemotherapy, and at 2 and 12 months post-treatment. IgM, IgA, IgG, IgG 2 , IgG 4 and IgE antibodies to AWA and SEA were measured by quantitative enzyme-linked immunosorbent assay (ELISA). Pre-treatment antibody isotype levels from Area A, except IgA against AWA and SEA, were significantly higher than those from Area B. In response to chemotherapy, most antibody isotype levels fell or remained stable. However, in Area A there was a significant increase in the IgA, IgE and IgG 4 responses to AWA 2 months after PZQ—which fell to approach pre-treatment levels by 12 months. A similar response was seen in Area B with IgE and IgG 4 to AWA. Levels of all AWA-specific IgE and IgG 4 were significantly higher in subjects from Area A compared with Area B at all time-points. AWA-IgE levels demonstrated significant linear correlations with age and number of previous PZQ treatments in Area A only. All SEA-specific isotypes in both areas fell significantly in response to treatment—except IgE, which remained stable in both areas. All SEA-specific isotype levels (except IgA) were significantly higher from Area A at baseline. This significant difference was maintained through 12-months follow-up for IgE, IgG 2 and IgG 4 only. This study suggests that multiple episodes of schistosome infection may be required to generate antibody isotype levels that have been associated with resistance to re-infection in other studies. Further, a surrogate marker of successful chemotherapy (AWA-IgG 4 ) performed less effectively in patients with previous treatment courses.