Leptospiral lipopolysaccharide-induced expression of inflammatory cytokines and mononuclear-macrophage infiltration in viscera of mice with Leptospira interrogans infection

Abstract

Objective To understand the role of leptospiral lipopolysaccharide (L-LPS) in inducing human monocytes or mouse mononuclear-macrophages to produce inflammatory cytokines and to analyze the infiltration of peripheral blood-derived mononuclear-macrophages in mice with Leptospira interrogans (L.interrogans) infection. Methods Phenol-water method was used to extract L-LPS from L.interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai. The endotoxic activity of L-LPS was determined by using limulus test. Cytokine antibody array was used to detect the cytokines produced by human THP-1 monocytes or mouse J774A.1 mononuclear-macrophages after treatment with L-LPS or infection with L.interrogans strain Lai. The infiltration of peripheral blood-derived mononuclear-macrophages in lung, liver and kidney tissues, and the cytokines in serum samples collected from L.interrogans strain Lai-infected C3H/HeJ mice were detected by immunohistochemical examination using HRP-labeled peripheral blood-derived mononuclear-macrophage-specific antibody against CD68 and cytokine antibody array, respectively. Results The activity of L-LPS was about 1/5 of that of Escherichia coli LPS (E-LPS) with respect to solidifying limulus amebocyte lysate. Treating THP-1 and J774A.1 cells with L-LPS significantly increased the production of 29 and 9 cytokines (P<0.05 or P<0.01), respectively, including the major proinflammatory cytokines IL-6 and TNF-α and multiple chemokines of mononuclear-macrophages. The results of cytokine detection in the supernatants of L.interrogans-infected cells and the serum samples collected from L.interrogans-infected mice were similar to those in L-LPS-treated cells. A great number of peripheral blood-derived mononuclear-macrophages were presented in the lung, liver and kidney tissues of the infected mice after infection with the L.interrogans strain Lai. Conclusion L-LPS played a critical role in inducing the expression of multiple inflammatory cytokines by mononuclear-macrophages and in promoting the expression of mononuclear-macrophage chemokines. Mononuclear-macrophages were the major inflammatory cells infiltrating the viscera of L.interrogans-infected mice. Key words: Leptospira interrogans; Lipopolysaccharide; Inflammatory cytokine; Mononuclear-macrophage; Infiltration