Figure 4

A, Increase of infected cells by prolonged period of culturing before MCMV infection. Brain slices from 21-day-old BALB/c mice (a to f) were cultured for 0 days (a and b), 7 days (c and d), or 14 days (e and f) before infection with mutant MCMV (RM461). The brain slices were cultured in serum-containing medium (a, c, and e) or serum-free medium (b, d, and f). The infected slices were incubated for 3 days, then fixed and stained with X-Gal. The number of X-Gal-positive cells increased when the culture period before infection was longer. The number of virus-infected cells stained with X-Gal was significantly higher in brain slices cultured in serum-containing medium than in those cultured in serum-free medium. B, Comparison of the susceptibility of brain slices cultured in serum-containing medium with those cultured in serum-free medium. Brain slices from 21-day-old mice were cultured for the indicated periods before infection as described in A. Infection ratios were calculated as described in Figure 1B. The infection ratios of brain slices cultured in serum-containing medium were significantly higher than those of brain slices cultured in serum-free medium. Data are expressed as the mean ± sd of at least three independent experiments. ★ p < 0.05 compared with brain slices cultured in serum-free medium.