The colonic epithelium responds quicker to microbial exposure than the ileal. (A) Schematic overview of the experimental setup. GF mice were colonized with a normal microbiota. Tip and crypt epithelial fractions were harvested by LCM on days (d) 0, 1, 3, 5 and 7 during the time course of colonization and then used for microarray analysis. (B) Hierarchical clustering of the microarray data.