Transforming growth factor-β levels in maternal milk and expression in postnatal rat duodenum and ileum

After birth, the gastrointestinal tract of the neonate is exposed to food and bacterial and environmental antigens. Maternal milk components may play a role in regulation of mucosal immune activity to luminal antigens. In this study we determine the ontogeny of transforming growth factor (TGF)- β1-producing cells in the rat pup small intestine and assess maternal milk concentrations of TGF-β. Intestinal tissue samples of duodenum and ileum were collected, processed, and stained for TGF-β1, and in situ hybridization for TGF-β1 mRNA was also performed on the duodenum. TGF-β levels in milk were assayed by ELISA. TGF-β2 levels in milk were high at d 6, and declined thereafter at d 10 and 19. TGF-β1 was not detected. In contrast, the cell number and intensity of staining of TGF-β1 peptide in the small intestine was low in 3- and 10-d-old rats and increased markedly by 19 d of life. In the duodenum mRNA levels mirrored this trend. TGF-β1 expression in the lamina propria was absent before d 19, and increased progressively over time. Maternal milk TGF-β2 levels are high in early milk and decrease during the weaning period. In contrast, endogenous TGF-β production in the small intestine increases during the weaning period.