Research has shown that after infection with viruses, including HCV, human immunodeficiency virus (HIV), mouse cytomegalovirus (MCMV), chronic hepatitis B (CHB), and lymphocytic choriomeningitis virus (LCMV), the expression levels of KLRG1 on virus-specific CD8+ T-cells [92, 93] and NK cells [14, 19, 94] are elevated, and KLRG1 function increases after receiving repeated and sustained antigenic stimulation. The gene discussed is KLRG1; the disease is chronic hepatitis B virus infection.