In the present study, we evaluated circulating and intra-hepatic IL34 in HBV related liver diseases. Serum IL34 from HBVHCC patients was significantly higher than that of CHB, HBVcirrhosis and HCs. IL34 and AFP were correlated with the incidence of HBVHCC. Furthermore, serum IL34 was decreased following antitumor TACE treatment in HBVHCC. Intrahepatic IL34 from these groups was consistent with serum IL34. Intrahepatic IL34 was associated with high HBVDNA, HBeAg−, low tumor differentiation and small tumor size of HBV-HCC patients. Intrahepatic CD68+ TAMs were increased in HBVHCC compared to that from CHB and HBVcirrhosis. Intrahepatic CD68+ TAMs were associated with high HBVDNA, high tumor differentiation, big tumor size, abnormal AFP and more tumor number.
Chronic HBV infection is a major risk factor for HCC globally, which is supported by the findings, showing a close correlation among chronic viral hepatitis, liver cirrhosis after hepatitis, primary liver cancer (29). It is well documented there is close association between HBV infection, as well as, the level of HBsAg, and the incidence of HCC (30, 31). Based on the APSAL guideline, it is considered that CHB, liver cirrhosis, HCC are reflecting the different stages of the liver diseases. Up to date, two major therapeutic strategies are applied for CHB, i.e. direct acting antiviral drugs and immune modulatory agents (32). However, there is no effective treatment to cure HBV infection, resulting in certain CHB patients progress to cirrhosis and HCC (1). Therefore, early detection, diagnosis and treatment are the key points in reducing the incidence of HBVHCC.
In our current study, serum IL34 from HBVHCC patients was significantly higher than that of CHB, HBVcirrhosis, and HCs, suggesting that IL34 may contribute to tumorigenesis of HCC, enhancing progression from CHB patients to cirrhosis and finally HCC. Furthermore, intra-hepatic IL34 was consistent with the result of serum. Our results are in line with previous studies documenting high IL34 in pathological conditions (22, 23, 33). IL34 is overexpressed in the inflamed synovium of patients with rheumatoid arthritis, where it perhaps acting synergistic with TNF and IL1β, induces osteoclastogenesis and contributes to tissue inflammation and bone erosion (34).
The development of tumor is closely related to the microenvironment, including tumor cells, monocytes/macrophages, cytokines and neovasculization. TAMs are mixed phenotype, expressing M1 or M2 markers (13), and may be influenced by different microenvironments in different regions and/or in different individuals. CD68, regardless the status of their polarization in many studies, has been widely used as a marker in marking TAMs which is infiltrating in solid tumors (35). In our current study, intrahepatic CD68+ TAMs were increased gradually with the order from CHB, HBVcirrhosis to HBVHCC patients. Our current observation invites speculation that the increased infiltrating CD68+ TAMs may be M1 dominant, contributing to antitumor activity, which will be determined in our future experiments.
It was reported that IL34 was upregulated in hepatitis C virus infection and inhibited the production of IFNγ(19), and IL34 may also be associated with inflammatory activity and liver fibrosis in CHB (28). Moreover, baseline serum IL34 levels seem to serve as a prognostic factor for progression in such patients. In our current study, there was only IL34 significantly decreased in postantitumor treatment compared to that of pre-treatment of HBVHCC in serum. Serum IL34 was significantly correlated with the incidence of HBVHCC. This further suggests that IL34 could be used as a predictor for HBVHCC, which will be further determined in vitro and in vivo.
IL34 induces differentiation of leukemia cells into monocytelike, macrophagelike cells and mature macrophages through the JAK/STAT and PI3K/Akt signaling pathways (36), suggesting IL34 enhances differentiation of other cancers(15, 21). This is consistent with our current finding that IL34 was correlated with the differentiation and tumor size of HBVHCC. In addition, intrahepatic IL34 was associated with HBVDNA, HBeAg, tumor differentiation and tumor size of HBVHCC patients. Our data may provide an explanation for the possible role of IL34 in the development of HBVHCC, i.e. IL34 also regulates HBVHCC differentiation, which would have potential clinical relevance regarding IL34 as a therapeutic target for malignancy. IL-34 is able to inhibit HBV replication in vivo and in vitro (37). Such finding is in line with our current clinical study, showing that IL-34 is beneficially to the HCC patients for potential therapeutic target.
We acknowledge that there are limitations in the current study. There is no kinetics of intrahepatic or circulating IL34 during the development and management of HCC, and no correlation between IL34 and prognosis is detected. These two interesting points will be determined in our future study. We also acknowledge that the sample size in the current study is relatively small, which may not perfectly reflect the real cases. However the current experiment is just a proof of concept. We will explore the underlying mechanism with large sample size and multiple center studies in future.
In summary, the current study improves our understanding of the role of IL34 in HBV related liver disease. Increased IL34 may contribute to the transformation of the tumor, which is a potential predictor of HBVHCC. The underlying mechanism of IL34 in HBVHCC is being currently investigated.