In support of this hypothesis, which cannot be tested in humans because of the limitations of collecting liver biopsies in acutely infected patients, are the observations that (1) CD4+ T cell depletion in chimpanzees prior to infection precludes effective T cell priming and causes persistent infection with minimal immunopathology (Asabe et al., 2009), and (2) detection of CD8+ T cells in the liver of HBV-infected chimpanzees coincides with the hepatic detection of CD4+ T cells (Guidotti et al., 1999). The gene discussed is CD4; the disease is infection.