Role of Th17 Cytokines in the Liver's Immune Response during Fatal Yellow Fever: Triggering Cell Damage Mechanisms

Abstract

Yellow fever (YF) is an infectious and acute viral haemorrhagic disease that triggers a cascade of host immune responses. We investigated the Th17 cytokine profile in the liver tissue of patients with fatal YF. Liver tissue samples were collected from 26 deceased patients, including 21 YF-positive and 5 flavivirus-negative patients, with preserved hepatic parenchyma architecture, who died of other causes. Histopathological and immunohistochemical analysis were performed on the liver samples to evaluate the Th17 profiles (ROR-γ, STAT3, IL-6, TGF-β, IL-17A, and IL-23). Substantial differences were found in the expression levels of these markers between the patients with fatal YF and controls. A predominant expression of Th17 cytokine markers was observed in the midzonal region of the YF cases, the most affected area in the liver acinus, compared with the controls. Histopathological changes in the hepatic parenchyma revealed cellular damage characterised mainly by the presence of inflammatory cell infiltrates, Councilman bodies (apoptotic cells), micro/macrovesicular steatosis, and lytic and coagulative necrosis. Hence, Th17 cytokines play a pivotal role in the immunopathogenesis of YF and contribute markedly to triggering cell damage in patients with fatal disease outcomes.

Keywords: Th17 profile; cell damage; liver immune response; yellow fever.

Figure 1

Histopathological analysis in the zones Z3, Z2, and Z1 and PT in the hepatic parenchyma of patients with fatal YF and normal controls. (A) Macrovesicular steatosis (yellow arrow), Councilman bodies (black arrow), coagulative necrosis (circle). (B) Macrovesicular steatosis (yellow arrow), microvesicular steatosis (green arrow), intense haemorrhagic necrosis (circle). (C) Mild coagulative necrosis and steatosis (circle). (D) Presence of inflammatory infiltrates in the PT (circle). (E–H) Preservation of the hepatic parenchyma (Z3, Z2, Z1, and PT) in the control cases (circles). Magnification: 400× (scale bar, 20 µm). Z3: Pericentral zone; Z2: Midzonal zone; Z1: Periportal zone; PT: Portal tract. (Patient 03).

Figure 2

Positive immunohistochemistry staining for IL-6, TGF-β, and ROR-γ in the zones Z3, Z2, and Z1 and PT in the liver parenchyma of patients with fatal YF and normal controls. (A) Immunolabeling for IL-6 (circle) in Kupffer cells (A-Z3), hepatocytes (A-Z2,A-Z1), and the inflammatory infiltrate (A-PT). (B) Immunolabeling for TGF-β (circle) in hepatocytes (B-Z3,B-Z2,B-Z1) and in the inflammatory infiltrate (B-PT). (C) Immunolabeling for ROR-γ (circle) in hepatocytes (C-Z3,C-Z2,C-Z1) and T cells (C-PT). Absence of labelling for IL-6 and preservation of the liver parenchyma (A-NC), slight labelling for TGF-β and ROR-γ in Z2, and preservation of the liver parenchyma (B-NC,C-NC). Magnification: 400× (scale bar, 20 µm). Z3: Pericentral zone; Z2: Midzonal zone; Z1: Periportal zone; PT: Portal tract. (Patient 03).

Figure 3

STAT3, IL-17A, and IL-23 positive immunohistochemistry staining in zones Z3, Z2, and Z1 and PT in the liver parenchyma of patients with fatal YF and normal controls. (A) Immunolabeling for STAT3 in hepatocytes (circle) (A-Z3,A-Z2,A-Z1) and in the inflammatory infiltrate (A-PT). (B) Immunolabeling for IL-17A in hepatocytes (circle) (B-Z3,B-Z2,B-Z1), and in the inflammatory infiltrate (B-PT). (C) Immunolabeling for IL-23 in hepatocytes (circle) (C-Z3,C-Z2,C-Z1) and inflammatory infiltrate in (C-PT). Light marking for STAT3 in Z2 and preservation of the hepatic parenchyma (Circle) (A-NC), absence of marking for IL-17A and IL-23, and preservation of the hepatic parenchyma (circle) (B-NC,C-NC). Magnification: 400× (scale bar, 20 µm). Z3: Pericentral zone; Z2: Midzonal zone; Z1: Periportal zone; PT: Portal tract. (Patient 03).

Figure 4

Quantitative analysis for IL-6 (A), TGF-β (B), ROR-γ (C), STAT3 (D), IL-17A (E), and IL-23 (F) in zones Z3, Z2, and Z1 of acini and PT in the liver parenchyma of 21 patients with fatal YF compared to the 05 normal controls. Z3: Pericentral zone; Z2: Midzonal zone; Z1: Periportal zone; PT: Portal tract. Tukey test *** p < 0.0001; ANOVA *** p < 0.0001.