STAT4 and primary biliary cholangitis: Understanding the molecular mechanisms of STAT4 in immune responses and immune-mediated diseases would allow the development of novel therapeutic options for human diseases such as chronic hepatitis B (CHB), hepatocellular carcinoma (HCC), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), psoriasis, inflammatory bowel diseases (IBDs), Behçet's disease (BD), Sjögren's syndrome (SS), systemic sclerosis (SSc), primary biliary cirrhosis (PBC), and other diseases.