In order to identify the developmental changes controlling the switch from disease susceptibility to resistance, we performed global gene expression analysis on non-infected and infected intestinal tissues taken from 4-day- and 7-day-old animals. Experiment Overall Design: RNA from intestinal tissues of 4-day- or 7-day-old mice infected or not with invasive (INV+) or non-invasive (INV-) Shigella strains during 2 or 4 hours were hybridized on Murine MOE430A Affymetrix Genechip.