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Variation in the biochemical forms of transforming growth factor-alpha present in human milk and secreted by human
C L Wagner1, D W Forsythe, W B Pittard
1Department of Pediatrics, Medical University of South Carolina, Charleston 29425, USA.
Objective:
Transforming growth factor-alpha (TGF-alpha), present in human milk, is thought to play a significant role in postnatal gut development. Macrophages, which abound in human milk, are known to secrete various isoforms of TGF-alpha in other areas of the body. It was hypothesized that human milk macrophages (HMM) secrete TGF-alpha, and HMM are a source of TGF-alpha isoforms present in human milk. We sought to measure in vitro HMM TGF-alpha secretion, and to compare the TGF-alpha isoform(s) present in human milk with those secreted by HMM.
Study Design:
Colostrum and mature milk samples, obtained from mothers (n = 48) on postpartum days 3-30, were centrifuged. HMM were isolated, placed in culture for 24 h, and cell-free media collected. The biochemical forms of TGF-alpha in media in human milk supernatant samples were identified by Western blot analysis under reducing conditions. The concentration of the mature (6-kD) TGF-alpha isoform in those samples was quantified using a radioimmunoassay.
Results:
Western blot analysis under reducing conditions identified a single 6-kD TGF-alpha isoform in all human milk supernatant samples tested, but variable (6- and 30- to 46-kD) TGF-alpha isoforms in HMM media. The mean (+/- SE) concentration of the 6-kD TGF-alpha isoform found in human milk supernatants was 706 +/- 88 pg/ml and 17.6 +/- 2.6 pg/ml in HMM media.
Conclusion:
These experiments show that HMM secrete TGF-alpha in biochemical forms both similar to and distinct from that found in human milk supernatant.