Effect of Iron on Antigen Presenting Cells: Implications For Transfusion Dependent Hemoglobinopathies.

Ibrahim Mustafa, Duncheng Wang and Mark D. Scott

Canadian Blood Services and the Centre for Blood Research and the Department of Pathology and Laboratory Medicine at the University of British Columbia, Vancouver, BC, Canada

Background: The thalassemias and Sickle Cell Disease (SCD) are characterized by destabilized hemoglobin that can lead to a potentially life-threatening anemia. This anemia arises due to iron-driven destruction of the RBC. Removal of oxidatively damaged RBC in vivo occurs primarily via erythrophagocytosis by the mononuclear phagocytic system (MPS). This clearance mechanism may result in negative immune consequences such as the observed increased risk of bacterial infections in these patients. Methods: To determine the functional consequences of iron and iron chelators on the MPS, the effects of ferric iron (Fe3+; ferric ammonium citrate, FAC) on dendritic cells (DC) antigen presentation [tetanus toxoid (TT Ag)] and the proliferation of peripheral blood mononuclear cells (PBMC) were examined. The iron chelators tested included Desferal (DFO) and Deferiprone (L1). PBMC were labelled with the fluorescent dye 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) to measure cell proliferation. In addition, the effects of iron +/- iron chelators on the expression of CD83, CD80, CD86 and HLA-DR on mature DC were examined. Results: Importantly, iron significantly inhibited antigen presentation and PBMC proliferation. Treatment of DC cells with 200 µM FAC for 24 hours resulted in a ~70% reduction in PBMC proliferation in response to the TT Ag following 14 days culture. However, inclusion of iron chelators (e.g., 200 µM DFO or L1) restored near normal proliferation. Similarly, CD83 an important co-stimulatory molecule expressed on DC cells was also negatively affected by FAC in a dose (0-200 µM) dependent manner. Following 24 hours treatment with 200 µM FAC, a ~30% reduction in the mean fluorescence of CD83 was observed via flow cytometric assay. Treatment with DFO or L1 overcame the effects of iron on CD83 expression. There were no significant effects of iron on CD80 or CD86. Conclusions: As shown, iron has significant immunosuppressive effects on antigen presentation and lymphocyte proliferation. Iron chelators can effectively bind and remove free and complexed iron and reverse iron-mediated immunosuppression. These data suggest that iron chelation may provide a mechanism to diminish the risk of recurrent bacterial infections in patients with unstable hemoglobins or with iron-overload (hemochromatosis or secondary iron overload).

Note: This abstract was published on conference proceedings, of Canadian Society for Transfusion Medicine 2010 held at Vancouver