Lactoferrin binding to human peripheral blood cells has been investigated. Purified human lactoferrin (LF) was radiolabeled with 125I, and its binding to platelets, neutrophils, adherent mononuclear cells (ADMC), null cells, rosetting cells (E+), and nonrosetting cells (E-) was assessed. Significant levels of binding, suggestive of a specific receptor mechanism, were observed with ADMC and E- cells. Neutrophils exhibited some LF binding, but this appeared to be largely nonspecific. A complete dose-response curve of cells in suspension could not be obtained because of cell aggregation beyond a LF concentration of about 250 μg/ml. An attempt to overcome this problem was made by using ADMC coated in plastic vials; this procedure yielded a figure of 2.0 x 108 LF receptors per ADMC and a mean binding affinity of 3.75 x 105 liter/mol. The binding to cells was calcium dependent but was not influenced by metabolic inhibitors (sodium azide, sodium fluoride, ouabain, or N-ethylmaleimide) or by incubation at 4°C. The addition of mannose (20 mg/ml) to the 125I LF prior to incubation with cells resulted in a reduction of LF binding of 1 order of magnitude. There was no steric hindrance of LF binding by monomeric IgG, aggregated IgG, transferrin, anti-Ia antiserum, or normal human serum depleted of LF. A subpopulation of ADMC with LF receptors (LRF+) was demonstrated after enrichment of LFR+ cells by rosetting with LF-coated red cells; this subpopulation of ADMC exhibited a 60-fold increase in LF binding. Metabolic stimulation of ADMC by incubation with E. coli endotoxin resulted in a 48-fold increase in LF binding. The apparently very high number of LF receptors per cell is probably an artefact caused by the fact that LF usually exists as a polymer; it is hypothesized that the LF receptor may have a unique structure capable of interacting with many LF polymers.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Immunology|
|State||Published - Jan 1 1981|
ASJC Scopus subject areas
- Immunology and Allergy