PDCD1 and hepatitis B virus infection: Immunological assays of chronic hepatitis B virus-infected patients have associated high concentrations of PD-1-expressing cytotoxic T lymphocytes with a reduction in acute flares of hepatitis B, while lower number of PD-1-expressing lymphocytes had a higher number of acute flares.82 Furthermore, PD-1-expressing lymphocytes were also shown to be functional and secrete IFN-γ, challenging an assumption that these cells are ‘exhausted’.82 Excess cytokine release by blocking PD-1/PD-L1 may result in destruction of hepatocytes, allowing escape of infectious, previously latent virus.83