ACTIVATED THP-1 CELLS DEPRESS MITOCHONDRIAL RESPIRATION IN HEP G2 CELLS INFECTED WITH INFLUENZA-B VIRUS

Influenza B virus has been aetiologically linked to Reye Syndrome (RS) , but the mechanism(s) by which this pathogen could disrupt liver meta bolism and produce the hepatic mitochondrial injury characteristic of the syndrome are unknown. In this study, two mechanisms by which infec tion of hepatocytes with influenza B virus could disrupt cellular meta bolism were investigated. (1) virus-induced increase in pro-oxidant ir on with subsequent iron-induced lipid peroxidation (LP) and (2) increa sed membrane permeability. Hep G2 cells, a well-differentiated continu ous human liver cell line derived from a hepatoblastoma, were infected with allantoic-fluid derived influenza and Lee/40 virus (AFDV) at a m ultiplicity of infection of 10 for 24 h; productive infection was conf irmed by both haemagglutination of chick erythrocytes and by plaque as say. Infection of Hep G2 cells preloaded with Fe-59-transferrin result ed in increased release of Fe-59 (153 +/- 17% of controls, P<0.03). Ho wever, the iron released did not result in increased LP (assessed by t hiobarituric acid reactive substances; TBARS). To confirm that this la ck of increase in TBARS was not due to insensitivity of the cell line to pro-oxidant iron, cells were exposed to 15 mu M iron ascorbate for 60 min. Production of TBARS was increased (122 +/- 4% of-controls, P<0 .0003). Release of Cr-51 from infected cells was also increased (128 /- 12% of controls, P<0.05); thus the infected cells exhibited a gener alized increase in membrane permeability. However, infection did not d epress mitochondrial respiration (as assessed by the formation of 4,5- dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide-formazan. To de termine if the combination of viral infection and soluble products of activated macrophages would affect mitochondrial respiration, infected hepatocytes were exposed to the supernatant fluid from THP-1 cells wh ich had previously been incubated with lipopolysaccharide at 100 ng ml (-1) for 18 h. This supernate did depress the formation of MTT-f (81 /- 5% of controls, P<0.03). We conclude that influenza B virus does pr oductively infect Hep G2 cells, and does increase hepatocyte membrane permeability. This effect does not impair mitochondrial respiration di rectly. However, infection does act in concert with soluble products o f activated macrophages to depress hepatic mitochondrial respiration. Whether this interaction can be explained by virus-induced permeabilit y changes and/or other effects of infection deserves further investiga tion.