Lactoferrin: an alternative view of its role in human biological fluids

Antimicrobial compounds in tears

The tear film coats the cornea and conjunctiva and serves several important functions. It provides lubrication, prevents drying of the ocular surface epithelia, helps provide a smooth surface for refracting light, supplies oxygen and is an important component of the innate defense system of the eye providing protection against a range of potential pathogens. This review describes both classic antimicrobial compounds found in tears such as lysozyme and some more recently identified such as members of the cationic antimicrobial peptide family and surfactant protein-D as well as potential new candidate molecules that may contribute to antimicrobial protection. As is readily evident from the literature review herein, tears, like all mucosal fluids, contain a plethora of molecules with known antimicrobial effects. That all of these are active in vivo is debatable as many are present in low concentrations, may be influenced by other tear components such as the ionic environment, and antimicrobial action may be only one of several activities ascribed to the molecule. However, there are many studies showing synergistic/additive interactions between several of the tear antimicrobials and it is highly likely that cooperativity between molecules is the primary way tears are able to afford significant antimicrobial protection to the ocular surface in vivo. In addition to effects on pathogen growth and survival some tear components prevent epithelial cell invasion and promote the epithelial expression of innate defense molecules. Given the protective role of tears a number of scenarios can be envisaged that may affect the amount and/or activity of tear antimicrobials and hence compromise tear immunity. Two such situations, dry eye disease and contact lens wear, are discussed here.

miR-214 promotes tumorigenesis by targeting lactotransferrin in nasopharyngeal carcinoma

LTF (lactotransferrin, or lactoferrin) plays important role in innate immunity, and its anti-tumor function has also been reported in multiple cancers. We previously reported that LTF is significantly down-regulated in nasopharyngeal carcinoma (NPC) and acts as a tumor suppressor by suppressing AKT signaling. However, the exact mechanism of the down-regulation of LTF in NPC has not been revealed. In the current study, we screened and identified LTF is a bona fide target of miR-214 in NPC cells. miR-214 mimics significantly suppressed LTF mRNA and protein expression levels in NPC cells. miR-214 not only can promote NPC cell proliferation and invasion abilities in vitro, but also can accelerate tumor formation and lung metastasis in a mouse xenograft model. The pro-tumor function of miR-214 was depended on LTF suppression since LTF re-expression can reverse it. miR-214 can also activate AKT signaling by suppressing LTF expression. Furthermore, miR-214 expression level was up-regulated in NPC especially in metastasis-prone NPC tumor tissues compared with normal nasopharyngeal epithelial tissues, while the LTF expression level was negatively correlated with miR-214, suggesting that miR-214 targeting is partly responsible for LTF down-regulation in NPC specimens.

Molecular biology of lactoferrin and its role in modulating immunity and viral pathogenesis

Lactoferrin (Lf), also known as lactotransferrin, is a globular glycoprotein belonging to the transferrin family that is widely expressed in several fluids such as milk, tears, gastric fluid and saliva. Apart from its ability to bind and regulate iron levels in body secretions, Lf possesses antimicrobial activity and is specifically a component of the innate immune system. The antibacterial activity of Lf occurs by depriving the environment of iron essential for bacterial growth. In the case of antiviral activity, Lf may act as a competitor for the cell membrane receptors commonly used by viruses to enter cells. This review summarizes the roles of Lf under normal physiology, with a special emphasis on viruses. The authors also discuss in great detail the interactions between Lf and Kaposi’s sarcoma-associated herpesvirus, as well as possible future directions of research that may progress toward designing modern-day therapeutics to counter viral infections.