Bioactivities in Milk & Mammary Gland: Stuck Between Nutrition, Cell Regulation, and Inflammation?

The mammary gland has evolved to efficiently deliver milk to the young.  For many species, milk provides total nutrition for a substantial time after birth.  The milk volume and composition is adjusted to the needs of the young for amount and spectrum of nutrients required for their growth.  To develop the capacity for lactation, the mammary gland undergoes developmental growth and differentiation culminating in the capacity for copious secretion of mature milk.  In so doing, the secretions from each stage of the developing mammary gland contain bioactive materials that reflect the major activity of the gland at that stage.  In addition to its well-known dedication to lactation, the mammary gland plays a critical but less well known role in infant development and well-being by adding growth regulators, immunoglobulins, immune regulator proteins (cytokines), and nonimmune disease defense proteins.  At any stage of development, the mammary gland may be diverted into inflammation in which nonimmune disease defenses are prominent.  The inflammatory response is highly choreographed, with a sequence of expression events that includes a rapid early response and subsequent amplifying or moderating responses.  This results from upregulation and secretion into milk of several cytokines, proteases, other enzymes, nitric oxide, and altered milk protein output characterized by decreased casein and increased lactoferrin synthesis.  Of interest to the Milk Genome project, several agents of the inflammatory response have potential therapeutic value.  Of the many bioactivities in milk or mammary secretions, the multifunctional inflammation marker lactoferrin contributes several,  including regulation of the cell cycle, immune regulation, antitumor activity, and anti-inflammatory activity.   Lactoferrin was recently shown to be expressed from an alternate promoter that produced a truncated protein lacking a secretion signal which was unable to be secreted; it appears to assert cell cycle regulation upon its host cell.  Mammary inflammation, especially if associated with engorgement, may enrich the protective agents in milk for increased protection of an infant whose milk demand has suddenly decreased – an interesting form of maternal/infant communication. 

Floyd Schanbacher and Samar Al-Maalouf; Dept. of Animal Sciences, Ohio Agric. Res. & Dev. Center, Ohio State University, Wooster, OH.