Lactoferrin in human milk: its role in iron absorption and protection against enteric infection in the newborn infant.

The existence of lactoferrin was first reported by S0rensen and S0rensen,' who observed a red protein fraction in human milk. The protein was first isolated by Groves2 from bovine and by Johansson3 from human milk, and subsequent studies showed that this protein (which has been variously called red milk protein, ekkrinosiderophilin, and lactotransferrin) is strikingly similar in many respects to the serum iron-binding protein transferrin. Human milk is unusually rich in lactoferrin, the normal concentration ranging from abo4t 7 mg/ml in colostrum to not less than 1 mg/ml in mature milk.4 Although bovine colostrum also contains up to 5 mg/ml lactoferrin, levels drop very rapidly as lactation proceeds, so that mature bovine milk normally contains only 20-200 jig/ml lactoferrin.5 Lactoferrin is now known to be present also in various other exocrine secretions (vaginal, nasal, bronchial, and intestinal), in pancreatic juice, and in the secondary granules of neutrophils.68 Although there has been a great deal written about the structure, iron-binding properties, and in vitro biological activities of lactoferrin, no in vivo biological function has as yet been unequivocally established for it. The possible role ofmilk lactoferrin in iron absorption and in the control of the intestinal microflora of the newborn is discussed, as is the ability of lactoferrin to remain undegraded in the gastrointestinal tract of the infant.