microRNA as a new immune-regulatory agent in breast milk

We profiled miRNA expression in human breast milk and detected high expression levels of immune-related miRNAs in the first 6 months of lactation. Furthermore, these miRNA molecules are stable even in very acidic conditions, indicating that breast milk allows dietary intake of miRNAs by infants.Our findings provide new insight into how breast milk can modulate the development of the infant's immune system. This study suggests the transfer of genetic material as miRNA from human to human occurs by means other than through sexual reproduction.The mammary glands of mammals are specialized organs whose function is to produce milk, the primary source of nutrition for newborns. Breastfeeding is recognized as one of the most valuable contributors to infant health [1]. Human breast milk protects infants not only against infections but also against chronic diseases. Furthermore, human breast milk contains certain growth factors that help the infant intestine to develop, become able to absorb milk and prepare for food intake. When maternal breast milk is unavailable, the alternative is infant formula. Compared with infants fed on formula, infants fed on breast milk have a lower incidence of digestive problems and are more likely to be protected against gastrointestinal and respiratory infections. Despite the fact that breastfeeding is known to be the best method for nourishing infants, how exactly breastfeeding works to provide the best nutrition and protect infants against disease is not fully understood.Many immune-related substances are present in human breast milk, and their effects upon the recipient infants are widely recognized [2,3]. For instance, human breast milk contains large quantities of secretory (s)IgA. These antibodies can bind to pathogens and prevent their attachment to an infant's cells. Furthermore, human breast milk contains measurable levels of leukocytes. In addition to these immunologic components, breast milk contains several nonspecific factors, suc