Polyinosine-polycytidylic Acid Aggravates The Liver Injury Induced By Trichloroethylene Sensitization

Background: Trichloroethylene is a common organic solvent. Workers who are exposed to TCE for a period of time may suffer from ODMLT accompanied with severe liver injury. It is shown by the clinical observation that the patients are often attacked by headache and fever which is the representative symptoms of the systemic viral infection at the early stage of the disease. In addition, studies indicate that the antibody titer to virus in patients is significantly enhanced and the reactivations of herpesvirus and cytomegalovirus are also identified, which prove the fact that viral infection and ODMLT are closely associated. Previous studies find that TCE-sensitized mice may develop immune liver injury, which is mediated by complement activation. Meanwhile, some basic investigations reveal that the virus mimic poly(I:C) can stimulate Toll-like receptor 3 and promote complement activation through the alternative pathway by enhancing factor B expression. In this study, we explore the possibility that if i.p. injection of poly(I:C) is capable to aggravate the liver injury induced by TCE sensitization by facilitating complement activation. Besides, we want to shed light on the potential mechanism association between ODMLT and viral infection.Objective: We used TCE sensitization animal model as the fundamental and adopted i.p. injection of poly(I:C) as a simulation to the systemic viral infection of ODMLT patients. We observed whether this treatment exacerbated the liver injury induced by TCE sensitization. In addition, we detected whether the hepatic local complement system was activated excessively to explore if this part of the innate immune system participated in this potential amplification of the immune damage.Methods: 6-8 week female BALB/c mice were divided into solvent control, poly(I:C) control, TCE treatment group and cotreatment group. Mice in the cotreatment group were given i.p. injection of 50μg poly(I:C) 3 hours before the last TCE challenge. The cutaneous response was assessed 48 hours after the last challenge, by which mice were categorized into sensitized and non-sensitized group. Next, mice were sacrificed and serum and liver were harvested. The liver function parameters ALT and AST were determined by biochemical analyzer. The serum level of C3 was detected by turbidimetric inhibition immunoassay. The histological damage of liver was observed by HE stain. The local complement activation and cytokines deposition were examined by immunohistochemistry. The transcriptions of C3, complement regulatory proteins and factor B were studied by Real-time RT-PCR. The expression of complement regulatory proteins and factor B were studies by Western Blotting.Results: 1. Cutaneous hypersensitive response assessment: No dermatitis was observed in solvent control and poly(I:C) control. The sensitization rate was 40.0% in the TCE treatment group, while it was 33.3% in the cotreatment group. The difference did not reach statistical significance.2. The appraisal of liver gross appearance and the organ coefficient: No apparent damage was observed in two control groups. Likewise, no injury was detected in the non-sensitized group. The TCE sensitized liver was swelling. The ratio between liver and body weight was significantly higher than that of the solvent control(P<0.05). The sensitized liver in the cotreatment group was yellowish and fragile. The ratio was also higher than that of the solvent control(P<0.05).3. The histological study of the liver injury: No apparent histological damage was observed in two control groups and the non-sensitized group. Hepatocytes swelling the infiltration of leukocytes were occasionally detected in the TCE sensitized liver. Massive hepatocytes swelling with regular ballooning degeneration and leukocytes infiltration was observed in the sensitized liver from the cotreatment group.4. The elevation of ALT and AST serum level: there was no significant difference between the levels of ALT and AST in poly(I:C) control and solvent control. Likewise, compared with the solvent control, the levels in the non-sensitized group were not higher. However, the levels in TCE sensitization group is slightly higher than those in solvent control(P<0.05). Furthermore, the levels in the sensitized mice from the cotreatment group were profoundly higher than those in solvent control and the TCE-sensitized group.5. The assessment the hepatic cytokines depositions: No depositions of TNF-α, IL-1β and IL-6 were detected in solvent control, poly(I:C) control and non-sensitized group. These three cytokines were also discovered in livers of TCE-sensitized and cotreatment-sensitized group with identical amount, of which the level of TNF-α was higher than the other two proteins.6. The comparison of serum C3 level: There was no significant difference between the level of serum complement 3 in the solvent control and the level in the poly(I:C) group and the TCE-sensitized group. The level in the cotreatment-sensitized group was markedly lower than it in the solvent control and the TCE-sensitized group(P<0.05).7. The comparison of hepatic C3 transcriptional level: Compared with the hepatic C3 transcriptional level in solvent control, the levels in, TCE-sensitized group and cotreatment-sensitized group were not up-regulated or down-regulated.8. The assessment of the hepatic local complement activation level: No complement activation was identified in solvent, poly(I:C) and non-sensitized group. Only modest depositions of C3 fragments and MAC were observed in the TCE sensitized liver. However intense staining of these proteins were found in the sensitized mice from the cotreatment group.9. The comparison of the transcriptions of complement regulatory proteins: Compared with the solvent control, the expressions of the four proteins(CD55, CD59, CD46 and Crry) in poly(I:C) control and cotreatment-sensitized were not altered. However the amounts of CD59, CD46 and Crry in TCE-sensitized group were significantly decreased(P<0.05).10. The comparison of the expression of complement factor B: Compared with the solvent control, the expressions of factor B in poly(I:C) control and TCE-sensitized group were not altered. Whereas the expression in cotreatment sensitization group was significantly elevated(P<0.05).Conclusions: 1. i.p. injection of poly(I:C) before challenge significantly aggravates the liver injury induced by TCE sensitization;2. The increased production of C3 fragments in TCE-sensitized group is likely to be caused by downregulation of complement regulatory proteins;3. The cotreatment possibly facilitates the complement activation by enhancing factor B expression;4. The cotreatment markedly promotes the local complement activation and consumes the circulated complement C3, leading the decline of serum C3 level.