Markedly increased IL-18 liver expression in adult-onset Still's disease-related hepatitis

OBJECTIVES First, to investigate the prevalence of liver involvement in adult-onset Still's disease (AOSD) Italian patients; secondly, to measure serum IL-18 concentration and correlate its level to other inflammatory markers and disease activity; and thirdly to characterize the expression level and the cellular source of IL-18 in the liver of a patient with AOSD with hepatitis. METHODS The clinical charts of 41 consecutive Italian AOSD patients were evaluated with special attention to liver involvement. Serum levels of IL-18 were measured in 21 patients. Finally, the case of a 33-year-old woman with hepatitis where a liver biopsy was obtained and sections stained with antibodies against IL-18 and CD68 is described in detail. RESULTS Of the 41 AOSD patients, 32 and 39% displayed increased AST level or ALT level, respectively, generally normalizing with steroid treatment, while 41% had evidence of hepatosplenomegaly. Circulating IL-18 levels were significantly higher in those with active disease compared with 85 controls. A correlation was observed between IL-18 serum level and disease activity, serum ferritin level and neutrophil count. IL-18 concentration was markedly increased in the patient with active hepatitis. Intense IL-18 expression was detected within the liver parenchyma and double staining with IL-18 and CD68 clearly showed colocalization of the cytokine with the macrophage marker. CONCLUSION Macrophage-derived IL-18 might play a central role in the pathogenesis of AOSD. IL-18 serum level is higher in patients with active AOSD and its local, rather than systemic, expression may be responsible for tissue damage in some target organs, such as liver.