Receptor binding of lactoferrin by human monocytes.
The binding of iron-saturated 125I-lactoferrin to human monocytes was studied at pH 7.4 and 37 degrees C. Monocytes in suspension bound 125I-lactoferrin by a reversible, saturable and specific binding indicating the presence of a receptor. The dissociation constant (KD) of the binding was estimated at about 4.5 x 10(-9) M and the number of receptors was about 1.6 x 10(6) per monocyte. The affinity of native lactoferrin (20% iron saturated) was only slightly below that of iron-saturated lactoferrin (KD about 7.9 x 10(-9) M). Human transferrin, horse cytochrome c and human immunoglobulin G were without inhibitory effect on the binding of 125I-lactoferrin. The majority of cell-bound 125I-lactoferrin was dissociable. The dissociation rate was not affected by addition of unlabelled lactoferrin to the dissociation medium. The binding of 125I-lactoferrin to adherent mononuclear blood cells showed an about 100-fold lower affinity (KD about 2.5 x 10(-7) M) than to cells in suspension, but the specificity of the binding was the same. These results are compatible with the idea that lactoferrin exerts a biological effect mediated by an interaction with cells of the monocyte/macrophage lineage.
D000328:Adult; D002448:Cell Adhesion; D003574:Cytochrome c Group / Q000494:pharmacology; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007700:Kinetics; D007781:Lactoferrin / Q000097:blood*; D007782:Lactoglobulins / Q000097:blood*; D009000:Monocytes / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014168:Transferrin / Q000494:pharmacology
D003574:Cytochrome c Group; D007074:Immunoglobulin G; D007782:Lactoglobulins; D011956:Receptors, Cell Surface; D014168:Transferrin; C038340:lactoferrin receptors; D007781:Lactoferrin