Transforming growth factor-beta2 (TGF-beta2) levels in rat milk are high in early lactation, whereas endogenous TGF-beta1 expression in the neonatal gut increases toward midweaning. Three types of transmembrane TGF-beta receptors have been identified in mammals. The receptor III (or betaglycan) binds and presents TGF-beta1 or beta2 to receptor II. Receptor I then interacts with receptor II, forming a signaling receptor complex, and propagates the signal. To determine whether TGF-beta receptor expression in the gut is also developmentally regulated, the present study assessed ontogeny of TGF-beta receptor expression in the postnatal rat small intestine. Jejunum and ileum tissues from rat pups at d 3, 10, 14, 21, and 28 of age were collected. Cryostat sections were stained with antibodies against TGF-bea receptors I, II, and III, and various cell markers by immunofluorescence. In both regions, receptor I staining was seen on apical and basolateral membranes of the villus and crypt epithelium at all ages, and staining on the apical membrane increased with age; receptor II was predominantly expressed in the crypt, and staining on the villi appeared after d 10; receptor III was distributed throughout the mucosa at early ages but diminished from the epithelium postweaning by d 28. T cells, B cells, and dendritic cells in the lamina propria expressed TGF-beta receptor III but lacked expression of receptor I and II. The pattern of TGF-beta receptor expression changes with age in a manner that may reflect the change in ligand from TGF-beta2 (milk-derived) to TGF-beta1 (endogenously produced).
