Intracellular Retention and Subsequent Release of Bovine Milk Lactoferrin Taken Up by Human Enterocyte-Like Cell Lines, Caco-2, C2BBe1 and HT-29

Lactoferrin (LF) is an iron-binding glycoprotein contained in milk and other exocrine fluids, and is believed to have multiple biological functions. We investigated the intracellular dynamics of LF taken up by three lines of human enterocytes and the subsequent release of internalized LF by using two-site ELISA and confocal microscopy. LF taken up by Caco-2 cells was kept partially intact within the cells and subsequently released to the medium as degraded fragments of 30-50 kDa. The retention and subsequent release of LF by Caco-2 cells were much more abundant than those of ovalbumin, ovomucoid and lysozyme. Such results characteristic of LF were also similarly observed in C2BBe1 and HT29 cells more markedly. LF was detected as punctate signals and partially colocalized with the lactoferrin receptor, intelectin-1, in the respective cytoplasm and nuclei of Caco-2 and C2BBe1 cells. In contrast, LF within the HT-29 cells was detected as much smaller punctate signals scattered in the cytoplasm.