TRANSFERRIN REDUCES THE PRODUCTION OF SOLUBLE TRANSFERRIN RECEPTOR

The effect of homologous diferric transferrin from which contaminating transferrin receptor had been removed by monoclonal antibody affinity chromatography on soluble transferrin receptor concentrations was stu died in K562 cells and HL60 cells in culture. Diferric transferrin in K562 cells caused a dose-dependent decrease in cellular receptor expre ssion, a dose-dependent increase in cellular ferritin content, and a r eduction in soluble receptor concentration which was of greater propor tional magnitude than the reduction in cell receptor content. In HL60 cells, while there was a dose-dependent Increase in cellular ferritin, cellular receptor content was relatively unaffected, while there was a consistent reduction in soluble receptor concentration. In both cell s, the inhibitory effect of diferric transferrin on soluble receptor c oncentration was evident as early as 3 hr into the incubation. Apotran sferrin, by contrast, did not reduce soluble receptor concentration. W hile elemental iron was capable of producing similar changes in cellul ar receptor and ferritin content, It had no inhibitory effect on propo rtional soluble receptor content. Studies employing other proteins, in cluding human and bovine serum albumin, human lactoferrin, and rat fer ritin, had no inhibitory effect on soluble receptors concentration, th us confirming the specificity of the findings. Control studies exclude d an assay artifact as the explanation for the current findings. Prior contrary reports appear completely explained by the combination of so luble transferrin receptor contaminating the transferrin employed for study and a systematic difference in the assays employed between free and transferrin-bound receptor.