Salivary lactoferrin is recognized by the human herpesvirus-8

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.

Adenoviruses use lactoferrin as a bridge for CAR-independent binding to and infection of epithelial cells

Most adenoviruses bind to the coxsackie- and adenovirus receptor (CAR). Surprisingly, CAR is not expressed apically on polarized cells and is thus not easily available to viruses. Consequently, alternative mechanisms for entry of coxsackievirus and adenovirus into cells have been suggested. We have found that tear fluid promotes adenovirus infection, and we have identified human lactoferrin (HLf) as the tear fluid component responsible for this effect. HLf alone was found to promote binding of adenovirus to epithelial cells in a dose-dependent manner and also infection of epithelial cells by adenovirus. HLf was also found to promote gene delivery from an adenovirus-based vector. The mechanism takes place at the binding stage and functions independently of CAR. Thus, we have identified a novel binding mechanism whereby adenovirus hijacks HLf, a component of the innate immune system, and uses it as a bridge for attachment to host cells.