Increased nucleolar sizes and numbers were also observed (Fig. 3F and G), suggesting that IMPDH2 is the key molecule that is involved in the cell proliferation and nucleolar hypertrophy of primary B cells with or without an EBV infection, whereas MYC is not required to induce IMPDH2 in the case of activation by CD40L and IL-4. This evidence concerns the gene CD40LG and Epstein-Barr virus infection.