The number of CD4+ T cells declined to ~200 cells/μl at 3 weeks after inoculation, and remained at zero level throughout the infection in MM376 and MM340, whereas in MM273, the number of CD4+ T cells recovered to ~300 cells/μl from 12 to 20 wpi, but after 46 wpi, it maintained a zero level (Figure 1B). This evidence concerns the gene CD4 and infection.