The effect of iron and iron-binding proteins on murine and human lymphocytes

Djeha, Abdelhakim (1990) The effect of iron and iron-binding proteins on murine and human lymphocytes. PhD thesis, University of Glasgow.

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Abstract

It is well documented that iron deficiency affects the function of lymphocytes because this essential element is required by these cells. However, the way that lymphocytes respond to high levels of iron is not fully understood. Reports of an increased incidence of infection and neoplasia among iron-overloaded patients might indicate that excess iron causes depression of specific immune responses in these patients. The broad objective of these study was therefore to investigate how lymphocytes react to different degrees of extracellular iron availability. Iron uptake by proliferating mouse lymphocytes from transferrin (Tf) saturated to different degrees with iron showed a gradual increase at saturations below complete saturation of the protein. The uptake rose sharply when non-Tf bound iron was present in the medium and the ratio of iron uptake to iron available increased. The proliferative capacity of these cells assayed alongside iron uptake was low at low Tf saturations and an increased rate of transformation was associated with increased percentage of saturation of Tf with iron. When saturation exceeded the binding capacity of the protein, proliferation decreased and at high levels of iron it was reduced below control level. Ferric nitrilotriacetate (FeNTA) was found to donate very large amounts of iron to cells compared to Tf but did not promote proliferation and when present in high amounts caused inhibition. In contrast ferric pyridoxal isonicotinoyl hydrazone (FePIH) which donated iron to cells at a slightly higher rate than Tf was found to support proliferation as efficiently as Tf. A study has been made of intracellular events in the iron metabolism of proliferating mouse lymphocytes to clarify the relationship between iron uptake and intracellular iron metabolism in these cells cultured with different iron carriers and to relate this to their ability to promote proliferation. This involved iron chelation, immunoprecipitation and ultrafiltration. In cells cultured with FeNTA, iron was found predominantly in an insoluble non-Ferritin (Ft) macromolecular form, while in the cells cultured with FeTf or FePIH the largest proportion of iron was found in the intermediate molecular weight fraction, which probably represents iron being used to form enzymes. The cells showed no marked increase in synthesis of Ft irrespective of the form of iron present. Mouse lymph node cells were also found to contain endogenous Tf. Synthesis of Tf was found in in vivo-stimulated lymphocytes, and macrophages were found to be the most active cells in synthesising this protein. Comparable studies of the effect of different iron carriers on cellular proliferation were performed with human lymphocytes and a related cell line, the T-lymphoblastoid CCRF-CEM line. Generally human lymphocytes gave similar results to mouse cells except with FePIH which was found to be less effective than with mouse cells. In addition, the presence of non-Tf bound iron in the form of FeNTA, but not FePIH, caused a decrease in CD4/CD8 ratio, due mainly to depression of the proportion of CD4+ cells. However unlike normal cells CCRF-CEM cells did not show any difference in their proliferative activity at different saturations of Tf and were able to achieve good proliferation when high levels of non-Tf bound iron in the form of FeNTA or FePIH was present in the culture medium. These cells were also found to have the ability to make their own Tf. Unlike Tf, Lf, the other member of the Tf family did not have any effect on proliferation of stimulated human lymphocytes whether added in the (apo) or loaded from. However, in the presence of excess non-Tf bound iron, apoLf increased the ability of these cells to proliferate. Therefore the main conclusion of this study is that the presence of concentrations of iron above the level that saturates all transferrin present in the medium inhibits proliferation of lymphocytes, and preferentially affects the helper subsets. It seems likely that some mechanism for uptake of unbound iron into these cells may exist resulting in toxic consequences.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Jeremy H Brock
Keywords: Immunology
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-72874
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: http://theses.gla.ac.uk/id/eprint/72874

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