CD8A and hepatitis B virus infection: Upregulation of the co-inhibitory marker 2B4 is associated with a decrease in virus-specific CD8+ cytotoxic T lymphocyte (CTL) function in lymphocytic choriomeningitis virus (LCMV) infection in mouse models, HIV, Hepatitis B and Hepatitis C virus infections in humans, chronic HTLV-1 infection is associated with an expansion of CD8+ effector memory T-cells but which are dysfunctional.