Decreased Tim-3 expression is associated with functional abnormalities of monocytes in decompensated cirrhosis without overt bacterial infection

Background & Aims

Patients with advanced cirrhosis usually exhibit altered monocyte function. However, the molecular mechanisms underlying the functional changes of monocytes are poorly understood.

Methods

We investigated the role of T-cell immunoglobulin domain and mucin domain-containing molecule-3 (Tim-3) in regulating monocyte function in 94 patients with decompensated liver cirrhosis (DC-LC) (decompensation was defined by ascites, hepatic encephalopathy or upper gastrointestinal bleeding), 58 with compensated liver cirrhosis (C-LC) and 52 healthy controls (HC) by characterizing the frequency of Tim-3⁺ monocytes, their phagocytosis capacity, HLA-DR expression, cytokine secretion and MAP kinase activation induced by lipopolysaccharide (LPS).

Results

Tim-3 expression on CD14⁺ monocytes in DC-LC group were significantly lower than that in C-LC and HC and were associated with increased levels of plasma endotoxin, enhanced cytokine production, decreased phagocytic capacity, and reduced HLA-DR expression. Tim-3 expression on monocytes and monocyte function did not differ between C-LC and HC group. Tim-3⁺CD14⁺ cells had more potent phagocytic capacity, higher levels of HLA-DR, CD86, CD80, CD163, and CD206 expression, but lower levels of CD1a and CD83, related to that of Tim-3⁻CD14⁺ monocytes. In addition, Tim-3⁺CD14⁺ cells produced less TNF-α but higher levels of IL-10 in response to LPS. Treatment with anti-Tim-3 antibody significantly reduced phagocytic capacity, but enhanced LPS-stimulated TNF-α, IL-6, and IL-10 secretion. Furthermore, blocking Tim-3 signaling increased p38 MAP kinase phosphorylation in monocytes upon LPS stimulation.

Conclusions

Downregulation of Tim-3 expression was associated with endotoxemia and functional alterations of monocytes in patients with decompensated cirrhosis.

Introduction

Epidemiological studies have demonstrated that cirrhotic patients, especially those with hepatic decompensated function, have increased risk to develop sepsis and septic shock [1], [2], [3]. Indeed, these patients are commonly infected with Gram negative bacilli [4]. The patients with increased susceptibility to infection harbor various immune abnormalities, particularly altered monocyte function [5], [6]. Stimulation of monocytes from non-infected patients with advanced cirrhosis by lipopolysaccharides (LPS) increases the levels of tumor necrosis factor alpha (TNF-α) and such hypersensitivity to LPS is believed to exacerbate detrimental effects of bacterial infections in cirrhotic patients by inducing systemic complications and progression of the liver injury [7], [8]. On the other hand, downregulated HLA-DR expression on monocytes are commonly detected in cirrhotic patients and are associated with immune suppression in several diseases, such as septic shock [9], pancreatitis [10] and on burn victims [11], and poor outcome [9]. Collectively, these findings suggest dysfunctional monocytes may be crucial for the progression of hepatic cirrhosis. However, the molecular mechanisms underlying monocyte dysfunction have not been fully understood.

T-cell immunoglobulin and mucin domain-containing molecule-3 (Tim-3), an immunoregulatory molecule, is expressed on various immune cells, including monocytes [12], [13], [14]. Tim-3 can negatively regulate adaptive immune response to tumor [15], autoimmune diseases [16] and chronic viral diseases [17], [18], [19]. However, little is known about the role of Tim-3 in regulating monocytic function during the process of cirrhosis. This study is aimed at examining the functional status of monocytes in non-infected cirrhotic patients with hepatic decompensation and exploring the potential contribution of the Tim-3 pathway to the distinct functional state of monocytes in these patients.