Genetic susceptibility and resistance to

Schistosomiasis • By:1. Bashir Alsiddiq2. Amal Badawi

Human Schistosomiasis• Is parasitic disease which caused by Schistosoma

species mainly include: 1- Schistosoma haematobium 2- Schistosoma mansoni 3- Schistosoma japonicum

• Approximately 300 million people are exposed to Schistosoma in 74 countries worldwide with a concentration in Asia, Africa, and South America Each year 280,000 people die of this disease.

Immunology• The following agent used by human to protect

against Schistosomisis (Antibodies, Complement, Eosinophils and Cytokines)

• The immunity is mainly drive by Th2 response.• The most important mechanisms against

Schistosoma is ADCC (Antibody dependant cell mediated cytotoxicity).

Immunopathology• Cercarial dermatitis is due to hypersensitivity

reactions.• Katayama syndrome is due to immune

complex formation.• Chronic Schistosomiasis is due to granuloma

formation whish is followed by Fibrosis and then severe complications.

Factors involved in Schistosomiasis

• Schistosomiasis is a multifactorial disease involving number of factors include:

1. environmental.2. Behavioral.3. Parasitic.4. vector.5. host factors (Genetic factor and Immunity)

Genetic susceptibility• We can classify into:1. Genetic susceptibility to Schistosomiasis

infection.2. Genetic susceptibility to Schistosomiasis

complications.

Genetic susceptibility and resistance to Schistosomiasis

infection

gene polymorphism orLinkage.

The effect

5q31-q33 1- D5S636 and CSF1R2- D5S393 and D5S410

Role in resistance to schistosomiasis.

IL-13 IL13-1055T/T protect against schistosomiasis .

STAT-6 rs324013C/T Associated with highest level of infection

FCER1A rs2251746 and rs2427837

Affinity of receptors to IgE

RAD50 1- Polymorphism2- LD between RAD-50 and Il-13 locus.

Associated with IgE level.

• In 1991, Dessein et al. performed segregation analysis, the first step to determine the mode of inheritance of a given trait from family data, on 20 Brazilian pedigrees (269 individuals), issued from an endemic area of S.m., in the aim to investigate whether a major gene controls human susceptibility/resistance to infection by Schistosoma.

• The deleterious allele occurs with a frequency of 0.16 (A). This frequency correlates:

• 3% of AA predisposed to high infections• 27% of Aa with an intermediate level of

infection• 70% of aa the population resistant.

• To localize the major gene involved in the control of infection by Schistosoma, referred as SM1, the authors also carried out a genome-wide study on 142 Brazilian subjects belonging to 11 informative families pedigrees.

• In a primary map (246 markers; interval of 15cM between adjacent markers).Dessein et al, 1999

• SM-1 region:Contains several candidate genes involved in the

regulation of the immune response to Schistomiasis:A. The genes encoding for the interleukins 4 (IL-4), IL-5,

IL-9, and IL-13.(Th2 response).B. The region also contains the gene encoding for the

IL12p40 subunit common to the proinflammatory cytokines IL12 and IL23.

C. the Interferon Regulatory Factor 1 (IRF1), which encodes a transcriptional activator of interferonα and β.

D. the Colony-Stimulating Factor 1 Receptor (CSF1R) gene

Linkage analysis

• two adjacent markers on chromosome 5q31-33, D5S393 and D5S410, provided lod scores greater than 1.9, indicating a suggestive linkage.

• Significant evidence of linkage was obtained with 2 proximal markers: D5S636 and the Colony Stimulating Factor-1 Receptor (CSF1R), provided lod scores = 5.45

• This result was confirmed later in an independent study done in a Senegalese population living in an endemic area for S.m.

• Marquet et al 1999, found that four additional markers in three other regions provided interesting lod-score values above 0.83:

A. 1p22.2 with D1S216 (Zmax=+0.91) which contain candidate gene= The IL12 receptorβ2 chain gene is located close to the 1p22.2 region ,and plays an important role in the regulation of the Th1-type immune response.

B.21q22- qter with D21S1259 (Zmax=+1.09) which contain candidate gene= The interferon-beta receptor (IFN-βR) and interferon-alpha receptor (IFN-αR) genes.

C. the two adjacent markers D7S483 (Zmax=+0.91) and D7S550 (Zmax=+1.02,) in the 7q36 region. which contain candidate gene= the beta T cell receptor (TCRβ) gene maps closed to the 7q36 region

IL13• The study was performed in two Dogon villages in

Mali, where Schistosoma haematobium is endemic.

• Associations were tested using family-based association tests and logistical regression analysis.

• The alleles IL13-1055C (p 0.05) rs1800925 and IL13-591A (p 0.01) rs2069743 and IL13-1258 are shown, by family-based association test, to be preferentially transmitted to children with the 10% highest infections.

• The result shows IL13-1055 C/C, C/T and T/T genotypes, age, gender, and village of residency, applied to the whole study population, showed that subjects bearing the IL13-1055T/T genotype were on average much less infected than individuals with other genotypes.

• So IL13-1055T/T gene protect against schistosomiasis .(Bourema Kouriba et al, 2005)

IL4 and IL5

• There is polymorphism in the IL4 promoter (IL4-590C/T) and also there is another polymorphism in IL5 promoter (IL5-202G/A).

• Need further study to show the association of these polymorphism with Schistosomiais.

STAT 6• Another study carried By logistic regression

analysis, they found an association between (SNP) in the STAT6 gene (rs324013) and infection levels (P=0.04).They confirmed this association in analyses restricted to subjects under 20 years age and living in Boul.

• They found rs324013C/T associated with highest infection level than other alleles.

• Also they detected an additive effect of the rs324013 significant association between rs324013C/T and the highest infection levels and rs1800925 polymorphisms (P=0.005).(Isnard A et al, 2008).

FCER1A• In a genome-wide association study (GWAS),

SNPs for association with serum IgE levels from the population-based study.

• Functional variants in the gene encoding the alpha chain of the high affinity receptor for IgE (FCER1A) on chromosome 1q23 (A/C rs2251746 and C/G rs2427837) Alleles were strongly associated with efficacy IgE.

• Polymorphisms within the RAD50 gene (rs2706347) on chromosome 5q31 were consistently associated with IgE levels.

• Also there is disequilibrium (LD) block which encompasses the entire RAD50 gene and extends into the promoter region of the IL13, whereas rs20541 showed low levels of LD with RAD50 variants.(Stephan Weidinger et al, 2008)

Genetic Susceptibility And Resistance to

schistosomiasis complications

The gene The origin The effect

SM2 IFNGR1 Locus in 6q23-q24

Increase susceptibility to hepatic fibrosis.

SM1 IL13-1055T/T genotype in 5q31-q33

Reduce the egg load in the genital tissue but increase susceptibility to asthma.

HLA class II HLA-DRB1*0901 & HLA-DQB1*0303

Associated with susceptibility to hepatic fibrosis.

HLA-DRB1*1501 & HLA-DQB1*0601

associated with resistance to hepatosplenic disease.

GST-M1 & GST-T1polymorphism

increased risk for bladder cancer.

SM2

•In Sudan, 2-10% of infected subjects with S.mansoni die from periportal hepatic fibrosis in endemic region of the Schistosomiasis.•Severe hepatic fibrosis occurs more frequent in certain families and absent in others despite the fact that all families had been living for years in the same conditions of infection (Mohammed Ali et al 1999).

SM2• Linkage analysis done for four candidate regions : 1. Chromosome region 5q31-q33.2. HLA TNF region 6p21.3. Chromosome region 12q15.4. Chromosome region 6q22-q23.

SM2

• shows that this major locus maps to 6q22-q23 and its closely linked (multipoint LOD score 3.12) to INFGR1 gene encoding receptor of antifibrogenic cytokine IFNɣ.

• This result suggests that polymorphism within the IFNGR1 gene could determine severity of hepatic disease due to S.mansoni ,

Cont…..

and that IFNGR1 gene is strong candidate for the control of abnormal fibrosis observed in other disease such as tuberculosis (Pierre-Audigier et al., 1997; Roesler et al., 1999) • So SM2 in 6q22-q23 influencing disease progression with a possible involvement in the regulation of IFN-gamma.

• This results will stimulate new strategies in drug and vaccine development (Alain J. Dessein et al 1999)

IFNGR1

• Two polymorphisms located in the third intron of the IFN-gamma gene are associated with periportal fibrosis (PPF).

• These two polymorphisms are not in linkage disequilibrium ( p 0.246).

• The IFN-gamma +2109 A/G polymorphism is associated with a higher risk for developing PPF.s

• whereas the IFN-gamma +3810 G/A polymorphism is associated with less PPF.

IFNGR1

• These results are consistent with the results of previous studies. Indeed, PPF is controlled by a major locus located on chromosome 6q22-q23, closely linked to the gene encoding the alpha-chain of the IFN-gamma receptor, and low IFN-gamma producers have been shown to have an increased risk of severe PPF. (Chevillard et al, 2003).

HLA class II• In endemic area of S.japonicum in China, there are

associations between host genetic factors and the onset of liver fibrosis.

• Two HLA-DRB1 alleles, HLA-DRB1*0901 (P=0.012) and *1302 (P=0.039), and two HLA-DQB1 alleles, HLA-DQB1*0303 (P=0.012) and *0609 (P=0.037), were found to be significantly associated with susceptibility to fibrosis.

• These associated DRB1 and DQB1 alleles are in very strong linkage disequilibrium, with DRB1*0901-DQB1*0303 and DRB1*1302-DQB1*0609 found as common haplotypes in this population.

HLA class II

• The alleles HLA-DRB1*1501 (P=0.025) and HLA-DQB1*0601 (P=0.022) were found to be

associated with resistance to hepatosplenic disease.

• The alleles DQB1*0303 and DRB1*0901 did not increase susceptibility in the presence of DQB1*0601, indicating that DQB1*0601 is dominant over DQB1*0303 and DRB1*0901. (Mcmanus DP et al, 2001)

HLA class II

• HLA-DRB1*1101-DQA1*0501-DQB1*0301 (Pc<0.02) and HLA-DRB1*1501-DRB5*0101 (Pc<0.02) haplotypes are associated with protection and susceptibility to grade I fibrosis, respectively,

• HLA-DPA1*0103 -DPB1*0201 haplotype (Pc<0.02) is associated with protection from both grade II and III severe fibrosis. There was no association between HLA-B DNA haplotypes and the disease (Hirayama et al, 1999).

HLA class II

• These findings indicate that the HLA-class II molecules play a role in preventing or promoting fibrotic liver change after deposition with Schistosome eggs.

• Moreover, a tendency was observed within the HLA class II genes for the HLA-DR-DQ alleles to be associated with protection against early changes in liver fibrosis, whereas HLA-DP alleles were associated with protection from the late phase of fibrosis or severe hepatosplenic schistosomiasis.

IL13 polymorphism

• There is hypothesis that will need confirmation. Helminth infections have long been suspected to have selected for alleles that predispose to asthma and atopy.

• This slective effect has no relation with resistance to urinary tract disease because they did not find an association between urinary tract disease and either of the IL13-1055 alleles.

IL13 polymorphism

• This associated with the presence of S.haematobium eggs in the lower genital tract

• These effects of S. Haematobium eggs on female reproductive capacity may select for IL13 genotypes that reduce egg load in genital tissues but aggravate the risk of asthma. (Bourema Kouriba et al, 2005)

GST-M1 and GST-T1 polymorphism

• This study done in 30 Egyptian patients with S.haematobium with bladder cancer (15), and without bladder cancer (15), as well as 15 normal individuals as a control.

• The results proved that GST serum level was significantly deceased in S.haematobium patients with bladder cancer as compared to the other groups.

• The PCR results for the GST-M1 & GST-T1 genotyping showed 4 categories, (M1+ve/T1+ve, M1+ve/T1-ve, M1-ve/T1+ve, M1-ve/T1/-ve).

GST-M1 and GST-T1 polymorphism

• There was a significant decrease in enzyme levels in patients with GST-M1-ve/T1-ve as compared to the other categories.

• there was a significant increased risk for bladder cancer development in patients with combined gene deletion (OR = 40) which represented mainly in S. haematobium patients with bladder cancer (53.3% = M1-ve/TI-ve).

• (al nouby ka et al, 2008)

Conclusion

• Schistosomiasis is multifactorial disease in which host genetic factors play a crucial role in the pathology of the disease.

• The major gene that involved in susceptibility and resistance to schistosomiasis mapped in 5q31-q33 that called SM1.

• The major gene that involved in susceptibility to hepatic fibrosis in Sudan, mapped in 6q22-q24 that called SM2.

• This results stimulate a new strategies in drug and vaccine development.

THANK YOU