Evaluation of hepatosplanchnic circulation and intestinal oxygenation in dogs with a condition that mimicked septic shock induced by continuous infusion of a low dose of lipopolysaccharide

A comparative review of toll-like receptor 4 expression and functionality in different animal species

Toll-like receptors (TLRs) belong to the pattern recognition receptor (PRR) family, a key component of the innate immune system. TLRs detect invading pathogens and initiate an immediate immune response to them, followed by a long-lasting adaptive immune response. Activation of TLRs leads to the synthesis of pro-inflammatory cytokines and chemokines and the expression of co-stimulatory molecules. TLR4 specifically recognizes bacterial lipopolysaccharide, along with several other components of pathogens and endogenous molecules produced during abnormal situations, such as tissue damage. Evolution across species can lead to substantial diversity in the TLR4’s affinity and specificity to its ligands, the TLR4 gene and cellular expression patterns and tissue distribution. Consequently, TLR4 functions vary across different species. In recent years, the use of synthetic TLR agonists as adjuvants has emerged as a realistic therapeutic goal, notably for the development of vaccines against poorly immunogenic targets. Given that an adjuvanted vaccine must be assessed in pre-clinical animal models before being tested in humans, the extent to which an animal model represents and predicts the human condition is of particular importance. This review focuses on the current knowledge on the critical points of divergence between human and the mammalian species commonly used in vaccine research and development (non-human primate, mouse, rat, rabbit, swine, and dog), in terms of molecular, cellular, and functional properties of TLR4.

Pathophysiologic and immunologic changes in a canine endotoxemia over a period of 24 hours

In this study, the pathophysiologic and immunologic parameters from a 24-hr of canine endotoxemia model by lipopolysaccharide (LPS) infusion were evaluated. For that, twelve healthy beagles received a continuous 24-hr IV infusion of low dose LPS (10 µg/kg/h, from Escherichia coli serotype O111:B4) dissolved in saline. Complete blood counts and serum biochemical analysis as well as histopathologic examination were performed to assess pathophysiologic changes such as neutrophil migration and organ injury. To evaluate immunologic parameters, the concentrations of plasma tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10 were determined, and neutrophil activation was also evaluated based on cell surface expression of CD11b using flow cytometry analysis. As results, systemic signs of endotoxemia including fever, vomiting, and hemorrhagic diarrhea were observed within short time after LPS infusion. Severe leukopenia and increased fluorescent intensity of CD11b on neutrophils were observed at 3 hr while percent positive of CD11b was the maximum at 12 hr during the experiment. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and creatinine phosphokinase (CPK) concentrations increased markedly, and organ damage was confirmed on histopathologic examination. Plasma TNF-α peaked at 3 hr and decreased rapidly, while the concentrations of IL-6 and IL-10 increased gradually until 6 hr and decreased thereafter. Using this canine endotoxemia model, we were able to determine the kinetics of pathophysiologic and immunologic parameters over a period of 24 hr. This study will enhance our understanding of their mechanisms underlying canine sepsis.

Effects of continuous low-dose infusion of lipopolysaccharide on expression of E-selectin and intercellular adhesion molecule-1 messenger RNA and neutrophil accumulation in specific organs in dogs

OBJECTIVE

To determine the effects of continuous low-dose infusion of lipopolysaccharide (LPS) on the expression of E-selectin and intercellular adhesion molecule-1 (ICAM-1) mRNA and neutrophil accumulation in the lungs, liver, spleen, small intestine, and pancreas in dogs.

ANIMALS

11 healthy adult Beagles.

PROCEDURE

Dogs received a continuous infusion of a low dose (10 microg/kg/h, i.v.) of LPS (Escherichia coli 055:B5) or saline (0.9% NaCI) solution (20 mL/kg/h, i.v.) for 8 hours. Activity levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interleukin-6 (1L-6) and the number of WBCs in circulation were examined before and 1, 2, 4, and 8 hours after the onset of LPS infusion. Expression of E-selectin and ICAM-1 mRNA and the number of neutrophils in each tissue were examined.

RESULTS

After the onset of LPS infusion, serum TNF-alpha and IL-1beta activities transiently increased. Thereafter, IL-6 activity increased, and high IL-6 activity was maintained throughout the experiment. In dogs in the LPS group, expression of E-selectin mRNA increased only in the lungs, and expression of ICAM-1 mRNA increased in the lungs and liver; the number of neutrophils in the tissue increased in the lungs and liver.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that expression of E-selectin and ICAM-1 mRNA increased during sepsis, particularly in the lungs and liver, and that this increase was associated with neutrophil accumulation. Hence, inhibiting the activation of endothelial cells in the lung and liver may decrease organ damage caused by accumulated neutrophils and help regulate multiple-organ dysfunction.