Beta-defensin expression in human mammary gland epithelia

Milk of mammalian species contains a wide spectrum of anti-infectious factors, some of which are heat stable. Focusing on recently discovered heat-stable antibacterial peptides called defensins, which are expressed in epithelial tissues such as airway, skin, and kidney, we hypothesized that mammary gland epithelia produce and secrete defensins onto the epithelial surface and into milk. Using a reverse-transcription PCR assay, we identified the human beta-defensin-1 (hBD-1) gene transcript in a human mammary gland epithelial cell line, MCF-12A, and in mammary glandular tissue of nine nonlactating women. Epithelial cells harvested from milk of lactating women also expressed hBD-1 mRNA. Presence of hBD-1 peptide in mammary epithelia was confirmed by immunostaining with an hBD-1 antibody. In contrast, expression of human beta-defensin-2 was not apparent both at mRNA and protein levels. Our findings suggest a biologic role of hBD-1 in the human mammary gland.