Figure 4. Reverse transcription polymerase chain reaction analysis of SMAD2 and SMAD3 in human corneal epithelial cells infected with HSV-1. A: Agarose gel pattern of RT–PCR products. The band intensities of SMAD3, not SMAD2, decreased during the period of post-infection. GAPDH was used as an internal control. B: The level of mRNA was expressed as the ratio of IOD of specific PCR products over the GAPDH gene IOD. The mean values of three independent experiments are shown. Single asterisks indicate significant differences (p<0.05).