The software GenePix Pro 7 was used to obtain the median foreground and background intensity for each spot. The raw intensity of the spot was defined as the ratio of the foreground to background median intensity. There are 324 ''blank'' spots on each protein chip, and the raw intensity distribution of these spots has a mean value of approximately 1. Assuming that the raw intensity distributions of ''blank'' spots are the same across all microarrays, we can standardize the protein signals such that