PATHOGENESIS 2
demonstrated
both in vitro and in vivo that iron plays an important role in regulating the
expression of T-lymphocyte cell surface markers, influencing the expansion of
different T-cell subsets and perhaps affecting immune cell functions [17].
The
poor ability of lymphocytes to sequester excess iron in ferritin may also help
to
explain
the immune system abnormalities in iron-overloaded patients [17]. Regarding
polymorphonuclear neutrophils, the impaired phagocytosis activity observed in
iron overload results from the deleterious effect of ferritin-associated iron
[20]. At the same time, the high plasma ferritin content in thalassemic
patients may induce the development of anti-ferritin antibodies, which in turn
leads to the production of circulating immune complexes [17]. Direct evidence
implicating iron overload in immune system abnormalities is provided by the
fact that intensive chelation therapy with desferrioxamine has been shown to
improve some of
these
symptoms [20]. To prevent excessive iron load and its complications, chelation
therapy is applied in parallel to transfusions. The first iron chelator applied
and still used in the majority of thalassemia cases is deferoxamine (DFO) [21].
DFO treatment, however, predisposes to infections by the yersinia family of
bacteria. Yersinia species generally have a low pathogenecity, but at the same
time an unusually high requirement for iron. Bearing receptors for ferioxamine,
the compound produced by the binding of DFO with free iron, they become
increasingly pathogenic in patients with iron overload treated with DFO [21].
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