Lactoferrin regulates important aspects of the ocular immune response. Receptors for lactoferrin are found on myeloblasts, monocytes, macrophages, lymphocytes and epithelial cells. These interactions are complex and, while observed, are not fully elucidated. Generally speaking, lactoferrin is released in inflammation and acts to curtail excessive inflammatory responses both directly, through antigen binding and iron uptake, and indirectly, by stimulating negative feedback signalling pathways within other cells. The capacity for exogenous lactoferrin to act as a local anti-inflammatory agent has been demonstrated in-vivo for gastrointestinal epithelia and cutaneous tissue.
Lactoferrin’s modes of action include iron sequestration, membrane disruption and digestion of bacterial proteins. The first of these to be identified was iron scavenging. Because iron is an essential co-factor, required for the growth of many invasive bacteria, when lactoferrin binds free iron in tears, it interrupts pathogenic bacterial proliferation. Lactoferrin also is able to disrupt bacterial cell membranes. The interaction of the positively charged amino acids at the terminus of lactoferrin and the negatively charged bacterial membrane increases their permeability. This may kill the bacteria or at least increase their susceptibility to other antimicrobials in the tear film.
Low tear lactoferrin directly indicates a compromised ocular immune system and may represent an elevated risk factor for ocular surgery and/or infection.