Lactotransferrin is a member of the transferrin family that transfer iron to the cells and control the level of free iron in the blood and external secretions. Lactotransferrin is a secreted protein and contains two transferrin-like domains. Lactotransferrin can be cleaved into the following four chains: Kaliocin-1, Lactoferroxin-A, Lactoferroxin-B, and Lactoferroxin-C. Lactoferroxin A, Lactoferroxin B, and Lactoferroxin C have opioid antagonist activity. Lactoferroxin A shows preference for mu-receptors, while Lactoferroxin B and Lactoferroxin C have somewhat higher degrees of preference for kappa-receptors than for mu-receptors. LTF has antimicrobial activity (bacteriocide, fungicide) and is part of the innate defense, mainly at mucoses.