In order to measure the earliest time point at which the cells entered S-phase, 2×105 CD19 positive B cells were infected with 3000 Green Raji Units (GRUs) of viral supernatants and [3H]-thymidine incorporation was measured immediately after virus infection on day 0 and on day 2, 4, 6, 8, and 14 post infection (p.i.). The gene discussed is CD19; the disease is viral infectious disease.