Detection and characterisation of transforming growth factor-beta in porcine colostrum

Porcine colostrum and milk collected at different stages of lactation were assessed for transforming growth factor-beta (TGF-beta) activity using an epithelial cell bio-assay. A high level of TGF-beta activity was recorded in all colostrum samples after transient acidification treatment, ranging between 126 and 260 ng/ml for samples collected at the time of parturition and 73 ng/ml for the sample collected 12 h after parturition. Without transient acidification treatment TGF-beta activity was detected only in 2 samples collected at the time of parturition (12 ng/ml) and 12 h after parturition (9 ng/ml), respectively. TGF-beta activity was undetectable in milk collected 5 days after parturition. These results suggest that TGF-beta exists mainly in latent form in porcine colostrum and the concentration declines rapidly as lactation proceeds. After enrichment with cation exchange chromatography a low level of TGF-beta activity was detected in porcine milk. Further separation by size exclusion chromatography revealed two molecular mass forms of TGF-beta in both colostrum and milk samples, a major peak of about 80 kD and a minor peak of about 25 kD representing latent and active forms of TGF-beta, respectively. A further experiment showed that the latent form of TGF-beta in colostrum can be activated at pH 3.5 or less. It is speculated that TGF-beta found in the colostrum may play a physiological role in regulating postnatal adaptation of the gastro-intestinal tract in newborns.