Effects of multiple treatments and reinfections on the Levels of schistosome specific antibody isotypes in Occupationally exposed individuals in western Kenya

Abstract

Previous studies have demonstrated that treatment of schistosome infection in people from endemic areas results in significant alterations of their parasite specific humoral responses. However, these responses have not been fully characracterised. This longitudinal study was carried out to investigate the effects of multiple treatments and reinfe"c-' tions on the levels of schistosome specific antibody isotypes in chronically exposed sand harvesters and newly exposed car washers in Kisumu District in western Kenya. ELISA was used to detect specific levels of IgE, IgG1 IgG2, IgG3 IgG4 and IgM isotypes against Schistosoma mansoni soluble worm antigenic preparation (SWAP) before treatment, 6 months post treatments, and up to 3 years post treatments. Infection intensities were determined by modified Kato/Katz thick smear technique and expressed as egg per gram (EPG) of feaces. Results showed that IgG4 responses significantly positively correlated with the intensity of the infection in car washers (r =0.6066, P< 0.0001) and sand harvesters (r =0.4557, P< 0.0001) at baseline, and IgG1 responses significantly positively correlated with the intensity of infection in chronically exposed sand harvesters (r =0.3960, P<O.OOOl).At 6 months post treatments, IgE and IgG2 responses showed significant mean increase in sand harvesters. At :3 years post treatments, IgE, IgG1 and IgG4 responses against SWAP showed an increasing tendency-with a significant increase in the levels of IgE responses from pre-treatment levels in both groups. IgG1 levels also increased significantly from pre-treatment levels in car washers at the same time. IgG3 responses against SWAP showed a declining trend in both groups with a significant decline in both groups from pre-treatment levels 3 years post multiple treatments. IgG2 and IgM responses also showed a declining tendency in both groups at last follow up 3 years post multiple treatments. From these results, it is clear that multiple episodes of treatments influenced the isotype responses towards protective immunity development with a significant elevation of potentially protective IgE responses in both groups at last follow up coupled with a significant increase in the levels of protective IgG1 in car washers and the response elevatation levels in sand harvesters. These results suggest that it is possible to define vaccine capabilities that have responses associated with resistance to schistosomiasis infection. However, further research into the precise roles of the blocking antibody isotypes in human schistosomiasis in relation to expression of immunity is also necessary.