CD5L is a pleiotropic player in liver fibrosis controlling damage, fibrosis and immune cell content.

Background: Chronic hepatic inflammation leads to liver fibrosis, which may progress to cirrhosis, a condition with high morbidity. Our aim was to assess the as yet unknown role of innate immunity protein CD5L in liver fibrosis.

Methods: CD5L was measured by ELISA in plasma samples from cirrhotic (n = 63) and hepatitis (n = 39) patients, and healthy controls (n = 7), by immunohistochemistry in cirrhotic tissue (n = 12), and by quantitative RT-PCR in mouse liver cell subsets isolated by cell sorting. Recombinant CD5L (rCD5L) was administered into a murine model of CCl-induced fibrosis, and damage, fibrosis and hepatic immune cell infiltration, including the LyC6 (pro-fibrotic)-LyC6 (pro-resolutive) monocyte ratio were determined. Moreover, rCD5L was added into primary human hepatic stellate cells to study transforming growth factor β (TGFβ) activation responses.

Findings: Cirrhotic patients showed elevated plasma CD5L concentrations as compared to patients with hepatitis and healthy controls (Mann-Whitney test p < 0·0001). Moreover, plasma CD5L correlated with disease progression, FIB4 fibrosis score (r:0·25, p < 0·0001) and tissue expression (r = 0·649; p = 0·022). Accordingly, CCl-induced damage increased CD5L levels in total liver, particularly in hepatocytes and macrophages. rCD5L administration attenuated CCl-induced injury and fibrosis as determined by reduced serum transaminase and collagen content. Moreover, rCD5L inhibited immune cell infiltration and promoted a phenotypic shift in monocytes from LyC6 to LyC6. Interestingly, rCD5L also had a direct effect on primary human hepatic stellate cells promoting SMAD7 expression, thus repressing TGFβ signalling.

Interpretation: Our study identifies CD5L as a key pleiotropic inhibitor of chronic liver injury. FUND: Fundació Marató TV3, AGAUR and the ISCIII-EDRF.