Date Published: July 10, 2019
Publisher: Public Library of Science
Author(s): Christine Yee, Nathan M. Main, Alexandra Terry, Igor Stevanovski, Annette Maczurek, Alison J. Morgan, Sarah Calabro, Alison J. Potter, Tina L. Iemma, David G. Bowen, Golo Ahlenstiel, Fiona J. Warner, Geoffrey W. McCaughan, Susan V. McLennan, Nicholas A. Shackel, Partha Mukhopadhyay.
Chronic inflammation is the driver of liver injury and results in progressive fibrosis and eventual cirrhosis with consequences including both liver failure and liver cancer. We have previously described increased expression of the highly multifunctional glycoprotein CD147 in liver injury. This work describes a novel role of CD147 in liver inflammation and the importance of leukocyte aggregates in determining the extent of liver injury.
Non-diseased, progressive injury, and cirrhotic liver from humans and mice were examined using a mAb targeting CD147. Inflammatory cell subsets were assessed by multiparameter flow cytometry.
In liver injury, we observe abundant, intrahepatic leukocyte clusters defined as ≥5 adjacent CD45+ cells which we have termed “leukocyte aggregates”. We have shown that these leukocyte aggregates have a significant effect in determining the extent of liver injury. If CD147 is blocked in vivo, these leukocyte aggregates diminish in size and number, together with a marked significant reduction in liver injury including fibrosis. This is accompanied by no change in overall intrahepatic leukocyte numbers. Further, blocking of aggregation formation occurs prior to an appreciable increase in inflammatory markers or fibrosis. Additionally, there were no observed, “off-target” or unpredicted effects in targeting CD147.
CD147 mediates leukocyte aggregation which is associated with the development of liver injury. This is not a secondary effect, but a cause of injury as aggregate formation proceeds other markers of injury. Leukocyte aggregation has been previously described in inflammation dating back over many decades. Here we demonstrate that leukocyte aggregates determine the extent of liver injury.
The classical hallmark of liver injury is the deposition of abnormal/fibrotic extracellular matrix (ECM) and the eventual development of cirrhosis, which is mediated by the activated hepatic stellate cell (HSC). Chronic inflammation drives ongoing HSC activation and fibrosis . Chronic liver inflammation can be regarded as commencing with an initial innate immune response and progressing with an ongoing insult, into a chronic injury with both sustained innate and adaptive immune components [2–6]. T-cell responses are clearly pivotal to the development of chronic immune-mediated hepatic injury and it has now been shown that B-cells are essential for the development of intrahepatic fibrosis leading to cirrhosis [7–11].
This study has demonstrated that with progressive inflammation-associated tissue injury, immune cells aggregate and directly contribute to the severity of the injury. Our novel discovery is that with liver injury, CD147 is principally upregulated on the surface of leukocytes and mediates cell-cell aggregation that determines the extent of liver injury. We have also shown that if CD147 is blocked with a mAb, then the numbers of infiltrating CD45+ cells in the liver remain unchanged but leukocytes are no longer found in aggregates. Importantly, we have already reported that there is a significant reduction in liver injury seen with anti-CD147 mAb . Further, CD147-mediated leukocyte aggregation appears to cause (or significantly exacerbate) injury as aggregate formation proceeds the development of significant fibrosis . Therefore, this is not just a reduction in aggregation and inflammatory markers (AST/ALT) but also a reduction in resultant fibrosis.