Injured bile ducts resulting from PBC lead to the upregulation of CX3CL1 expression in BECs, followed by the chemoattraction of CX3CR1-expressing mononuclear cells, including CD4 (+) and CD8 (+) T cells, their adhesion to BECs, and the accumulation of biliary intraepithelial lymphocytes. The gene discussed is CD4; the disease is primary biliary cholangitis.