High mobility group box-1 (HMGB-1) and its receptors in the pathogenesis of malaria-associated acute lung injury/acute respiratory distress syndrome in a mouse model

Abstract

The DNA-binding protein high mobility group box-1 (HMGB-1) mediates proinflammatory cytokines that contribute to acute lung injury (ALI). Although ALI is a frequent complication of malaria infection, the contribution of HMGB-1 and its receptors to the pathogenesis of malaria-associated ALI/acute respiratory distress syndrome (MA-ALI/ARDS) has not been investigated in a mouse model. Here, the malaria-infected mice were divided into two groups according to lung injury score: the ALI/ARDS and non-ALI/ARDS groups. The expression of HMGB-1 and its receptors (RAGE, TLR-2 and TLR-4) in lung tissues was investigated by using immunohistochemical staining and real-time polymerase chain reaction (PCR). Additionally, HMGB-1 and proinflammatory cytokine (TNF-α, IFN-γ, IL-1 and IL-6) levels in plasma and lung tissues were quantified by using enzyme-linked immunosorbent assays. Cellular expression of both HMGB-1 and its receptors (RAGE, TLR-2 and TLR-4) was significantly increased in the lung tissues of the ALI/ARDS group compared with those in the non-ALI/ARDS and control groups. The levels of HMGB-1, TNF-α, IFN-γ, IL-1 and IL-6 were significantly increased in both plasma and lung tissues of the ALI/ARDS group compared with those in the non-ALI/ARDS and control groups, which were similar to the results obtained by real-time PCR. Increased mRNA expression of RAGE, TLR-2 and TLR-4 was found in the lung tissues of the ALI/ARDS group. Furthermore, the plasma HMGB-1 level was positively correlated with TLR-4 mRNA expression in the ALI/ARDS group. HMGB-1 levels were significantly increased in plasma and lung tissues of MA-ALI/ARDS mice and were related to the upregulated expression of HMGB-1 and proinflammatory cytokines. In conclusion, this study demonstrates that HMGB-1 is an important mediator of MA-ALI/ARDS pathogenesis and may represent a target for therapeutic malaria interventions with ALI/ARDS.

Keywords: Acute lung injury; Acute respiratory distress syndrome; HMGB-1; Malaria.

Figure 1

Histopathological changes in H&E-stained lung tissues in the control (A), malaria-infected without ALI/ARDS (B) and malaria-infected with ALI/ARDS (C and D) groups. Malaria-infected mice with ALI/ARDS showing alveolar oedema, thickening of alveolar septa and infiltration of leukocytes. Type I alveolar epithelial cell (Type I), Type II alveolar epithelial cell (Type II), alveolar macrophage (M), alveolar sac (S), capillary (C) and alveolar fibrin (F). All images were taken at 400× magnification. Bar = 20 μm.

Figure 2

Immunoperoxidase staining for HMGB-1 in lung tissues of the control (A), malaria-infected without ALI/ARDS (B) and malaria-infected with ALI/ARDS (C) groups. Type I alveolar epithelial cells (Type I), Type II alveolar epithelial cells (Type II), alveolar macrophages (M), and alveolar sacs (S). All images are 400× magnification. Bar = 20 μm.

Figure 3

Immunoperoxidase staining for RAGE in lung tissues of the control (A), malaria-infected without ALI/ARDS (B) and malaria-infected with ALI/ARDS (C) groups. Type I alveolar epithelial cells (Type I), Type II alveolar epithelial cells (Type II), alveolar macrophages (M), and alveolar sacs (S). All images are 400× magnification. Bar = 20 μm.

Figure 4

Immunoperoxidase staining for TLR-2 in lung tissues of the control (A), malaria-infected without ALI/ARDS (B) and malaria-infected with ALI/ARDS (C) groups. Type I alveolar epithelial cells (Type I), Type II alveolar epithelial cells (Type II), alveolar macrophages (M), and alveolar sacs (S). All images are 400× magnification. Bar = 20 μm.

Figure 5

Immunoperoxidase staining for TLR-4 in lung tissues of the control (A), malaria-infected without ALI/ARDS (B) and malaria-infected with ALI/ARDS (C) groups. Type I alveolar epithelial cells (Type I), Type II alveolar epithelial cells (Type II), alveolar macrophages (M), and alveolar sacs (S). All images are 400× magnification. Bar = 20 μm.

Figure 6

Levels of HMGB-1 and proinflammatory cytokines in the plasma and lung tissue of the control mice (n = 10), malaria-infected mice without ALI/ARDS (n = 17) and malaria-infected mice with ALI/ARDS (n = 11). The levels of HMGB-1 (A), IFN-γ (B), IL-1 (C), IL-6 (D), and TNF-α (E) were measured in plasma by ELISA. The levels of HMGB-1 (F), IFN-γ (G), IL-1 (H), IL-6 (I), and TNF-α (J) were measured in lung tissue by ELISA. ^ap < 0.001 compared with the control group. ^bp < 0.001 compared with the non-ALI/ARDS group. The data are presented as the mean ± SEM.

Figure 7

Schematic representation of HMGB-1 and its receptors in the pathogenesis of MA/ALIARDS.