Interactions of lactoferrin with monocytic and mucosal cells; its role in iron uptake and absorption

Lactoferrin is a non-haem iron binding glycoprotein present in virtually all mammalian body fluids, especially milk, as well as being secreted from the secondary granules of activated neutrophils. It is structurally similar to the plasma non transport protein transferrin, and shares with it the ability to bind reversibly two ferric ions per molecule of the protein. This work is undertaken to investigate the possible role of lactoferrin in non transport and the mechanism of iron transfer involved. The transfer of iron to the cells by transferrin occurs by a mechanism involving binding to a specific receptor followed by endocytosis, during which iron is retained by the cell and the receptor is recycled. Assuming that lactoferrin could deliver its non utilising a similar pathway, this work has been focussed to study the interactions of lactofeixin with a promonocytic cell line, U937. Binding studies have shown that both lactoferrin and transferrin could bind to these cells. There are however some fundamental differences in the binding pattern. The total binding of lactoferrin to the cells was about ten times greater than total binding of transferrin but most of the lactoferrin binding was non-specific. In contrast most of transferrin binding occurred via a specific receptor. Nevertheless the number of specific binding sites on the cell is similar for both proteins (Lf, 3.0 x 10.