Association of <i>Schistosoma mansoni</i>-Specific IgG and IgE Antibody Production and Clinical Schistosomiasis Status in a Rural Area of Minas Gerais, Brazil

<div><p>Background</p><p>Studies in murine models and human populations have indicated that the collagen-rich granulomatous response against parasite eggs trapped in the liver is associated with the development of severe hepatosplenic schistosomiasis, characterized by periportal fibrosis and portal hypertension. The role of the humoral response in parasite susceptibility has been well established, but its participation in disease severity remains poorly understood. In this work, we evaluated the relationship between parasite-reactive IgE and IgG levels and schistosomiasis morbidity in infected patients with similar parasite burdens.</p><p>Methodology/Principal Findings</p><p>Ninety-seven <i>Schistosoma mansoni</i>-infected individuals were subjected to clinical examination and abdominal ultrasound analysis. IgG reactivity and IgE concentration against <i>Schistosoma mansoni</i> soluble egg antigens (SEA) and adult worm antigen preparation (SWAP) were evaluated by ELISA assay. Multivariable linear regression models were used to evaluate the relationship between parasite-reactive antibodies and the co-variables investigated. The study population showed low parasite burden (median 30 eggs/g feces), constant re-infection, and signs of fibrosis was detected in more than 30% of individuals. Most infected individuals showed IgG reactivity, and the median concentrations of IgE anti-SEA and anti-SWAP antibodies were 1,870 and 1,375 ng/mL, respectively. There was no association between parasite burden and antibody response or any parameter of disease severity. However, IgG anti-SWAP level was positively associated with morbidity parameters, such as spleen size and thickness of portal vein at the entrance and secondary branch. In contrast, the data also revealed independent inverse correlations between concentration of parasite-reactive IgE and gallbladder wall thickness, a marker of fibrosis in schistosomiasis.</p><p>Conclusions/Significance</p><p>The data indicate that IgG anti-SWAP is positively associated with severe schistosomiasis, independently of parasite burden, while high production of parasite-specific IgE is associated with mild disease in the human population. Antibody profiles are good correlates for schistosomiasis severity and could be tested as biomarkers of disease severity.</p></div

Anti-SEA and anti-SWAP IgE models for schistosomiasis patients, Minas Gerais.

<p>β, coefficient estimates; SE, standard error.</p

Association between level of anti-SWAP IgG and schistosomiasis-related morbidity.

<p>(A) Parasite-reactive IgG levels were associated with longitudinal spleen size, categorized as <120 or ≥120 mm, as analyzed by Mann-Whitney test. Correlation analyses were performed on the absorbance of anti-SWAP IgG levels by ELISA and the following morbidity parameters: longitudinal spleen size (B), diameter of the portal vein (C), thickness of the portal vein at its entrance into the <i>porta hepatis</i> (D) and its bifurcation inside the liver (E), and the thickness of gallbladder wall (F) determined by ultrasound evaluation. Spearman correlation coefficients and p-values are shown for each graph.</p

Association between parasite-reactive IgE and schistosomiasis-related morbidity.

<p>Correlation analyses were performed on the concentration of anti-SEA IgE (A) or anti-SWAP IgE (B) and the thickness of the gallbladder determined by ultrasound evaluation. Spearman correlation coefficients and p-values are shown for each graph.</p

Association between parasite-reactive antibody production and host age (A) and schistosomiasis treatment (B).

<p>Demographic and social information were obtained from the questionnaire, and antibody levels were estimated by ELISA. There was an inverse correlation between host age and IgG anti-SEA levels, as shown by Spearman analysis (A). The concentration of parasite-specific IgE was significantly lower (Mann-Whitney test) in individuals that had received previous Schistosoma treatment and were re-infected (B). Antibody levels showed no association with other demographic and social factors evaluated.</p

Parasite-reactive antibody in plasma of the evaluated individuals and its association with parasite burden.

<p>(A) Level of IgG anti-SEA and anti-SWAP antigens estimated by ELISA assay in plasma samples from <i>Schistosoma</i>-infected and uninfected controls. (B) Concentration of total IgE and parasite-reactive, SEA and SWAP, IgE in plasma samples of <i>Schistosoma</i>-infected individuals indirectly estimated by ELISA assay in samples before and after been submitted to antigen-specific adsorption. Correlation analyses between parasite burden, estimated by the number of eggs of <i>S. mansoni</i> eliminated in the host feces and production of IgG anti-SEA antigens (C) and IgE anti-SEA antigens (D). Spearman correlation coefficients and p-values, are shown for each graph.</p

Comparison of absorbances between cohort's participants, positive and negative controls, using three different antigens.

<p>A: <i>L. amazonensis.</i> B: <i>L.infantum.</i> C, rK39. Healthy = 22 negative controls; Cohort = 136 inhabitant of endemic area; VL = 8 positive controls (patients with visceral leishmaniasis). Differences statistically significant were sign (p<0.05, p<0.001, Kruskall Wallis and Dunn's test).</p

Positive tests for <i>Leishmania infantum</i> infection among the 136 cohort participants at baseline and 24 months of follow-up. General Carneiro, Minas Gerais.

(1)<p>among those positive at baseline.</p>(2)<p>among those negative at baseline.</p

PCR and hybridization products to identify <i>L. donovani</i> complex in blood samples.

<p>A: PCR products obtained with primers specific for the <i>L. donovani</i> complex (Piarroux, 1993); molecular size markers (lane 1), positive control (lane 2-kDNA extracted from cultured <i>L.infantum</i>), VL patient (lane 3), asymptomatic (lanes 4;7;9), health individuals (lane 5–6); negative control (lane 8- no DNA). B: PCR products obtained with primers for genus <i>Leishmania</i> (<i>Degrave et al 1994</i>); molecular size markers (lane 1), VL patient (lane 2), positive control (lane 3-kDNA extracted from cultured <i>L. chagasi</i>); healthy individual (lane 4), asymptomatic (lanes 5–7, 9–10), negative control (lanes 8 and 11- no DNA). C: Dot-blots obtained using specific probe for the <i>L. donovani</i> complex, hybridized with PCR products.</p

Validity of serological tests in comparison with molecular test to identify <i>L. infantum</i> infection of 136 participants of a cohort study, General Carneiro, Minas Gerais.

<p>Molecular techniques were used as reference test. Criteria: Positive results = positive in PCR with generic primer and specific primer for <i>L.donovani</i> complex and positive in hybridization. Negative results = negative in all molecular techniques.</p><p>TP = True Positive; FP = False positive; FN = False Negative; TN = True Negative; LR+ = Likelihood test positive; LR− = Likelihood test negative.</p