Transferrins are iron binding transport proteins which can bind two Fe(3+) ions in association with the binding of an anion, usually bicarbonate. Lactotransferrin is a major iron-binding and multifunctional protein found in exocrine fluids such as breast milk and mucosal secretions. Has antimicrobial activity. Antimicrobial properties may include bacteriostasis, which is related to its ability to sequester free iron and thus inhibit microbial growth, as well as direct bactericidal properties leading to the release of lipopolysaccharides from the bacterial outer membrane. May have anabolic, differentiating and anti-apoptotic effects on osteoblasts and may also inhibit osteoclastogenesis, possibly playing a role in the regulation of bone growth. May interfere with the lipopolysaccharide (LPS)-stimulated TLR4 signaling (By similarity). The lactotransferrin transferrin-like domain 1 functions as a serine protease of the peptidase S60 family that cuts arginine rich regions. This function contributes to the antimicrobial activity. Shows a preferential cleavage at -Arg-Ser-Arg-Arg-|- and -Arg-Arg-Ser-Arg-|-, and of Z-Phe-Arg-|-aminomethylcoumarin sites. Monomer. Found in a complex with LTF, CLU, EPPIN and SEMG1 (By similarity). Secreted into most exocrine fluids by various endothelial cells. Stored in the secondary granules of neutrophils (By similarity). Belongs to the transferrin family.