The differential effects of low dose and high dose concanavalin A on cytokine profile and their importance in liver injury

Objective: Intravenous injection of concanavalin A (ConA) can cause mice to suffer from acute liver failure in a dose dependent manner and little is known about the difference between the high dose and the low dose of ConA regarding the immune response they initiate. The aim of this study was to analyze whether differential effects exist between the low dose and high dose of concanavalin A on the intrahepatic immune system and their importance in the development of liver injury. Materials and methods: A high dose of Con A (15 mu g/g) was injected intravenously to induce murine hepatitis. A low dose of ConA (3 mu g/g) was injected intravenously 12h before the injection of the high dose of Con A (15 mu g/g). Liver injury was evaluated by serum transaminase assay and H&E staining. Serum cytokine concentrations were determined by enzyme-linked immunosorbent assay (ELISA), intrahepatic cytokine and Fas mRNA levels by reverse transcriptase polymerase chain reaction. Intracellular cytokine expression and FasL expression were analyzed by flow cytometry and Fas protein expression in hepatocytes by Western-blotting. Intrahepatic apoptosis was evaluated by terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL). Results: Low dose ConA injection induced a distinct cytokine expression profile, characterized by a preferentially elevated serum IL-6 at the early stage of stimulation, whereas high dose ConA injection provoked significant elevation of various cytokines involved in ConA-induced hepatitis. Pretreatment with a low, nonhepatoxic dose of ConA (3 mu g/g) significantly decreased production of proinflammatory cytokines induced by the high dose ConA (15 mu g/g). Furthermore, low dose ConA pretreatment could significantly decrease the serum levels of transaminases and liver necrosis induced by high dose of ConA. The intrahepatic Fas expression was also apparently reduced, accompanied by a decrease in hepatocyte apoptosis. Conclusion: Low dose ConA stimulation induced a different cytokine profile from high dose ConA stimulation resulting in differential importance in the development of liver injury.