FIG. 2.

The relative protective effect elicited by pcDNA3-pp89 immunization, as measured by replication in the spleen, increases with increasing viral challenge dose. Naive BALB/c mice were immunized three times in 10 days by i.d. injections of 50 μg of either pcDNA3 or pcDNA3-pp89 as described in Materials and Methods. Two weeks after the last immunization, mice were i.p. challenged with one of four serial dilutions of salivary gland-derived MCMV corresponding to 21 × 10³, 47 × 10³, 95 × 10³, and 127 × 10³ PFU in 0.5 ml of PBS per mouse. Six days postchallenge, spleens were removed and the viral titers were determined. Spleen titer values presented are the means of the log₁₀ PFU per spleen for four mice with the standard deviation (SD) indicated by error bars. Values above each challenge dose indicate the fold reductions of the nonlogarithmic mean titers (i.e., PFU per organ) of pcDNA3-pp89-immunized mice relative to the corresponding pcDNA3-immunized controls.