Lactoferrin secretion into milk: Comparison between ruminant, murine, and human milk

Abstract

Lactoferrin is an iron-binding protein found in external secretions such as tears, saliva, and milk and the secondary granules of granulocytes. As part of the innate nonspecific immune system it seems to play a wide variety of roles in infection and inflammation. The functions of milk lactoferrin have been postulated to include iron transfer to the neonate, iron scavenging from the neonatal gut, stimulation of intestinal growth, and defense against infection. The concentration of lactoferrin in milk varies widely from one species to another. It is highest in human milk (2 g/L, 25 × 10-6M), moderate in murine milk (.28 mg/L, 3.5 × 10-6M), and very low in ruminant milk (-.01 mg/L in bovine milk,.12 × 10-6M). Unlike other milk proteins, lactoferrin has been found at high levels in the prepartum secretions of the cow and human and at very high levels in postweaning mammary secretions from the cow, sheep, guinea pig, mouse, and human. It is also elevated in mastitic mammary glands. Data accumulated over the past three decades suggest that the protein may play an important role in defending the mammary gland against infection, particularly during periods of milk stasis.