Investigating the inflammatory markers involved in Schistosoma haematobium protective immunity and susceptibility to infection

Abstract

Schistosomiasis is a neglected tropical disease that affects more than 200 million people globally. In Zimbabwe, areas have been mapped that contain high S. haematobium morbidity. The effects are mostly felt in rural areas where children have higher infection rates than adults. The immune mechanisms that lead to resistance of the disease are very complex and not yet fully understood. The current control method recommended to reduce morbidity is by mass drug treatment with praziquantel. This thesis reports the work aimed at monitoring the response of protective inflammatory markers in 124 children from an S.haematobium endemic area, aged between 7-13 years old, under praziquantel mass drug treatment. Parasitological data was obtained using the Kato-Katz and urine filtration to diagnose infected and uninfected children by counting and identifying the presence or absence of eggs in their urine and stool samples. The enzyme-linked immunosorbent assay was used to measure the inflammatory markers IgE, IgG4, IgM and IFN-γ in the participant’s serum that have been associated with resistance and susceptibility to infection. The antibodies were measured using the Sh13 antigen which is a potential vaccine candidate. The Amplification Refractory Mutation System Polymerase Chain Reaction was used to genotype the children who had mutations at the IFN-γ +874A/T promoter site to investigate the influence of genotype in production of IFN-γ and susceptibility to infection. At baseline 42% of the children were found to be infected and 58% were uninfected.Post treatment results showed that all the study participants were now uninfected. All the inflammatory markers in this study had no statistically significant difference in their levels between baseline and follow-up. Infected children had higher levels of IgE, IgG4 and IgM compared to uninfected children. The p values of IgE, IgG4, and IgM of infected vs. uninfected analysis were 0.242, 0.0443 and less than 0.0001 respectively. The blocking antibodies associated with susceptibility to infection: IgM and IgG4 levels were higher than the protective antibody IgE levels. IFN-γ levels on the other hand were lower in infected children and higher in uninfected children with a p value of 0.0214. The genotyping results showed that the children had 3 genotypes: AA (21 %), AT (73 %) and TT (6 %). After analysis of variance at p<0.05, it was found that the genotypes produced different levels of IFN-γ and had a p value of 0.0090. The children containing the homozygous AA were higher producers of IFN-γ compared to those containing the AT, and TT genotype, the children with the AT genotype produced the least IFN-γ. The AA and TT genotypes had low infection intensities while the AT genotype children had low, medium and high infection intensities.