Elegant intravital imaging in mouse models has visualized CD8 T cells patrolling the extensive, narrow-lumenal, sinusoidal vasculature and surveying hepatocytes (through fenestra in the endothelium) for infection with HBV or malaria sporozoites (Guidotti et al., 2015; Fernandez-Ruiz et al., 2016). The gene discussed is CD8A; the disease is infection.