The levels of CD4+ and NK cells of Group A (i.e., patients whose disease progressed to severe hepatitis) were lower than in the same patients on Day 2 (baseline) of admission (P < 0.01), which were lower than Group B baseline levels (P < 0.01), and the latter was lower than in the healthy control group (P < 0.01). This evidence concerns the gene CD4 and hepatitis A virus infection.