Human intrahepatic ILC3 may modulate hepatic stellate cell activation

Background:

Innate lymphoid cells (ILCs) are a new group of RAG-independent lymphocytes which are classically divided into three major groups: Group 1 ILCs, comprising NK cells and IFN-γ producing ILC1, IL-13 producing ILC2 and IL-22 producing ILC3. Recent data obtained in mouse models has suggested that ILCs might be critically involved in the regulation of hepatic fibrogenesis. As however only few reports have tried to elucidate this subject in humans, we here studied the potential role of ILCs in chronic liver disease.

Material and methods:

Human tissue-infiltrating lymphocytes were isolated from non-fibrotic (n = 18) and fibrotic/cirrhotic (n = 14) livers, from ectomized tonsils (n = 5), intestinal biopsies and resectates (n = 14) as well as from peripheral blood (n = 32). Phenotypical and functional characterization of tissue-resident ILCs was performed using multiparameter flow cytometry. Furthermore, liver ILCs were studied on the basis of single cell gene expression analysis utilizing the Chromium™ Single Cell 3' Reagent Kit v2 from 10x Genomics, Inc. In functional experiments, primary human hepatic stellate cells (HSCs, ScienCell™ #5300) were cultured in the presence or absence of recombinant human cytokines or purified ILC3 and then studied for mRNA expression and cytokine secretion.

Results:

As shown before by our group, ILC3 represented the major hepatic non-NK ILC fraction and were significantly increased in cirrhotic livers. Moreover, phenotypic and gene expression analysis revealed significant alterations of liver ILC3 in cirrhotic patients. Analyzing their functional capacity, we found that human intrahepatic ILC3 dispalyed a distinct profile with a low IL-22 expression and an increased production of the ILC2-specific cytokine IL-13. Furthermore, the percentage of these intrahepatic IL-13+ ILC3 was increased in patient with chronic liver disease. Although previously reported to exert direct profibrotic effects, we could show that in primary human HSCs treatment with rhIL-13 did not affect the expression of profibrotic marker genes such as COL1A1, ACTG2 and MMP2. However, rhIL-13 as well as stimulated liver ILC3 promoted a pro-inflammatory phenotype of HSCs, characterized by increased expression of CXCL8, CXCL1, IL33 and IL1B.

Conclusion:

Taken together our findings indicate that human intrahepatic ILC3 represent a so far unrecognized source of IL-13 in the liver and as such might act as a proinflammatory modulator of HSCs.