Our observation of resistance to C. parvum intestinal infection in conditional intestinal epithelial Ifnar1−/− neonatal mice, but not in vitro infection in cultured cells lacking Ifnar1, suggests that type I IFN signaling may modulate intestinal anti-Cryptosporidium defense induced by determinants from other cell types during infection in vivo. This evidence concerns the gene IFNAR1 and digestive system infectious disorder.