Defensins: Endogenous Antibiotic Peptides in Human Mammary Epithelia

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Abstract 411 Human Milk Poster Symposium, Sunday, 5/2

Although the anti-infective property of milk has been attributed to factors such as immunoglobulins, cellular components and cytokines, the entirety of milk's antibacterial activity has not yet been elucidated. Of particular interest is a class of heat-stable endogenous antibiotic peptides shown to be present in several tissues, called defensins. Defensins are a family of small, cationic, disulfide-linked peptides with a molecular weight of 3-4 kDa, containing about 20-40 amino acids. Two classes of defensins exist in humans: α-defensins and β-defensins. β-defensins are found mainly in epithelial tissues, and to date, two β-defensin isoforms have been identified: human β-defensin-1 (hBD-1) and human β-defensin-2 (hBD-2). hBD-1 is expressed in kidney, pancreas, airway epithelia and female urogenital tissues, while hBD-2 is expressed in several organs including skin, lung and kidney. It is thought that these tissues, which are constantly bombarded with bacteria, secrete defensins onto their surface, fighting and preventing bacterial invasion. Our hypothesis is that mammary gland epithelium produces and secretes β-defensins into breast milk, thereby potentiating the anti-infective property of milk and/or protecting the mammary gland from infection. To test this hypothesis, we have developed an RT-PCR assay to detect hBD-1 mRNA expression in human mammary gland. Our data reveal that hBD-1 mRNA is expressed in a human mammary epithelial cell line (MCF-12A). Restriction digests and uni-directional sequencing were used to confirm these results. Identifying that the mammary cell line expresses hBD-1 mRNA enabled us to assay mammary tissue for transcript expression. Our results indicate that mammary glandular tissue from nine non-lactating women expresses hBD-1 mRNA. Moreover, using milk cells as a surrogate for lactating epithelium, we showed that epithelial cells harvested from milk of lactating women also express the hBD-1 transcript. Our findings suggest a biological role of β-defensins in human milk.

This work is supported by a Pediatric Consultants Seed grant (Hospital for Sick Children), a Research Institute Seed Grant (Hospital for Sick Children) and by an MRC grant (MT13747).

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(Spon by: Philip Sherman)

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Tunzi, C., Harper, P., Bar-Oz, B. et al. Defensins: Endogenous Antibiotic Peptides in Human Mammary Epithelia. Pediatr Res 45, 71 (1999) doi:10.1203/00006450-199904020-00428

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