Divergent functions of CD4+ T lymphocytes in acute liver inflammation and injury after ischemia-reperfusion

Hepatic ischemia-reperfusion results in an acute inflammatory response culminating in the recruitment of activated neutrophils that directly injure hepatocytes. Recent evidence suggests that CD4(+) lymphocytes may regulate this neutrophil-dependent injury, but the mechanisms by which this occurs remain to be elucidated. In the present study, we sought to determine the type of CD4(+) lymphocytes recruited to the liver after ischemia-reperfusion and the manner in which these cells regulated neutrophil recruitment and tissue injury. Wild-type and CD4 knockout (CD4(-/-)) mice were subjected to hepatic ischemia-reperfusion. CD4(+) lymphocytes were recruited in the liver within 1 h of reperfusion and remained for at least 4 h. These cells were comprised of conventional (alpha beta TCR-expressing), unconventional (alpha beta TCR-expressing), and natural killer T cells. CD4(-/-) mice were then used to determine the functional role of CD4(+) lymphocytes in hepatic ischemia-reperfusion injury. Compared with wild-type mice, CD4(-/-) mice had significantly greater liver injury, yet far less neutrophil accumulation. Adoptive transfer of CD4(+) lymphocytes to CD4(-/-) mice recapitulated the wild-type response. In wild-type mice, neutralization of interleukin (IL)-17, a cytokine released by activated CD4(+) lymphocytes, significantly reduced neutrophil recruitment in association with suppression of MIP-2 expression. Finally, oxidative burst activity of liver-recruited neutrophils was higher in CD4(-/-) mice compared with those from wild-type mice. These data suggest that CD4(+) lymphocytes are rapidly recruited to the liver after ischemia-reperfusion and facilitate subsequent neutrophil recruitment via an IL-17-dependent mechanism. However, these cells also appear to attenuate neutrophil activation. Thus the data suggest that CD4(+) lymphocytes have dual, opposing roles in the hepatic inflammatory response to ischemia-reperfusion.