T-helper 17 cells are associated with pathology in human schistosomiasis

Abstract

Background: Schistosome infections are often clinically silent, but some individuals develop severe pathological reactions. In several disease processes, T-helper 17 (Th17) cells have been linked to tissue injuries, while regulatory T cells (Tregs) are thought to downmodulate inflammatory reactions. We assessed whether bladder pathology in human Schistosoma haematobium infection is related to the balance of Th17 cells and Tregs. We used a murine model of Schistosoma mansoni infection to further investigate whether the peripheral profiles reflected ongoing events in tissues.

Methods: We characterized T-helper cell subsets in the peripheral blood of children residing in a S. haematobium-endemic area and in the peripheral blood, spleen, and hepatic granulomas of S. mansoni-infected high-pathology CBA mice and low-pathology C57BL/6 mice.

Results: S. haematobium-infected children with bladder pathology had a significantly higher percentage of Th17 cells than those without pathology. Moreover, the Th17/Treg ratios were significantly higher in infected children with pathology, compared with infected children without pathology. Percentages of interleukin 17-producing cells were significantly higher in spleen and granulomas of CBA mice, compared with C57BL/6 mice. This difference was also reflected in the peripheral blood.

Conclusions: This is the first study to indicate that Th17 cells may be involved in the pathogenesis of human schistosomiasis.

Figure 1.

Increased RORγt-expressing cells in patients with pathology. A, The gating strategy for determining the frequencies of RORγt⁺, FOXP3⁺, and CD25^high+FOXP3⁺ CD4⁺ T cells. Total lymphocytes were gated on CD3⁺CD4⁺ T cells for analysis of RORγt, FOXP3, or CD25^highFOXP3 expression. Box plots representing percentages of CD4⁺RORγt⁺ (B), CD4⁺FOXP3⁺ (C), and CD4⁺CD25^high+FOXP3⁺ (D) T cells and scatter plots of the ratio of CD4⁺RORγt⁺ to CD4⁺FOXP3⁺ (E) and CD4⁺RORγt⁺ to CD4⁺CD25^high+FOXP3⁺ (F) T cells in the S−P− (n = 10), S+P− (n = 6), and S+P+ (n = 10) groups are shown. Data are expressed as medians and interquartile ranges. P values are based on comparison of groups by the nonparametric Mann–Whitney U test. Only statistically significant P values are shown in the figures. *P < .05, **P < .01. Abbreviations: P, pathology; S, Schistosoma haematobium infection; −, negative; +, positive.

Figure 2.

Increased interleukin 17 (IL-17)–producing cells in patients with pathology. The gating strategy for determining the frequencies of interleukin 17 (IL-17)–, interleukin 22 (IL-22)–, and interleukin 10 (IL-10)–producing CD4⁺ T cells. Total lymphocytes were gated on CD3⁺CD4⁺ T cells for analysis of IL-17, IL-22, and IL-10 expression. Box plots representing median and interquartile ranges of the percentages of CD4⁺IL-17⁺ (B), CD4⁺IL-22⁺ (C), and CD4⁺IL-10⁺ (D) T cells and scatter plots (median and IQR are shown) of the ratio of IL-17⁺ to IL-10⁺ cells (E) in the S−P− (n = 10), S+P− (n = 6), and S+P+ (n = 10) groups are shown. P values are based on comparison of the groups by the nonparametric Mann–Whitney U test. Only statistically significant P values are shown in the figures. **P < .01. Abbreviations: P, pathology; S, Schistosoma haematobium infection; −, negative; +, positive.

Figure 3.

T-helper 1 cell and T-helper 2 cell levels do not differ between the three study groups. A, The gating strategy for determining the frequencies of T-bet or GATA3 expressing CD4⁺ T cells and interferon γ (IFN-γ)– or interleukin 4 (IL-4)–producing CD4⁺ T cells. Total lymphocytes were gated on CD3⁺CD4⁺ T cells for analysis of expression of T-bet, GATA3, IFN-γ, or IL-4. Box plots of percentages of CD4⁺T-bet⁺ (B) and CD4⁺GATA3⁺ (C) T cells, scatter plots of the ratio of CD4⁺T-bet⁺ to CD4⁺GATA3⁺ (D), box plots of CD4⁺INF-γ⁺ (E) and CD4⁺IL-4⁺ (F) T cells, and scatter plots of the ratio of INF-γ⁺CD4⁺ to IL-4⁺CD4⁺ T cells (G) in the S−P− (n = 10), S+P− (n = 6), and S+P+ (n = 10) groups are shown. Data are expressed as median values and interquartile ranges. P values were calculated using the nonparametric Mann–Whitney U test. No statistically significant P values were found. Abbreviations: P, pathology; S, Schistosoma haematobium infection; −, negative; +, positive.

Figure 4.

Increased numbers of granulocytes in patients with pathology. Scatter plots of median and interquartile ranges of total granulocytes (A), neutrophils (B), and eosinophils (C) in the S−P− (n = 10), S+P− (n = 6), and S+P+ (n = 10) groups are shown. P values are based on the Mann–Whitney U test. Only statistically significant P values are shown. *P < .05. Abbreviations: P, pathology; S, Schistosoma haematobium infection; −, negative; +, positive.

Figure 5.

Increased T-helper 17 cells in peripheral blood, spleen, and granulomas from CBA mice. The percentages of interleukin 17 (IL-17)⁺, interferon γ (IFN-γ)⁺, and interleukin 4 (IL-4)⁺ CD4⁺ T cells in peripheral blood mononuclear cells (PBMCs; A) and spleen cells (B) from uninfected and infected CBA and BL/6 mice are shown. C, Percentages of IL-17⁺, IFNγ⁺, and IL-4⁺ CD4⁺ cells in granulomas of infected CBA and BL/6 mice are depicted. For PBMCs and spleen cells, data are expressed as values from individual mice and are representative of 3 independent experiments. For granuloma cells, the average of 2 groups of pooled is shown. Data are shown as mean ± SD. P values were calculated using 1-way analysis of variance. Only statistically significant P values between CBA and BL/6 mice are shown. *P < .05, ***P < .005. Abbreviations: N, naive; I, Schistosoma mansoni infected.

Figure 6.

Foxp3⁺ cells in peripheral blood, spleen, and granulomas from BL/6 mice. Scatter plots of the percentage of Foxp3⁺CD4⁺ in peripheral blood mononuclear cells (PBMCs; A) and spleen cells (B) from uninfected and infected CBA and BL/6 mice, as well as the percentage of Foxp3⁺CD4⁺ granuloma cells (C) in infected CBA and BL/6 mice are shown. For PBMCs and spleen cells, data are expressed as values from individual mice and are representative of 3 independent experiments. For granuloma cells, the average of 2 groups of pooled granuloma cells is shown. Data are shown as mean ± SD. P values were calculated using 1-way analysis of variance. Only statistically significant P values between CBA and BL/6 mice are shown. *P < .05. Abbreviations: N, naive; I, Schistosoma mansoni infected.