Release of iron from phagocytosed Escherichia coli and uptake by neutrophil
lactoferrin
AL Molloy and CC Winterbourn
Department of Pathology, School of Medicine, Christchurch Hospital, New
Zealand.
Escherichia coli were labeled with 59Fe and then either treated with
myeloperoxidase, H2O2, and chloride or opsonized and mixed with human
neutrophils. The myeloperoxidase system at pH 7.4 caused release of most of
the bacterial 59Fe. A similar result has been obtained by Rosen and
Klebanoff (J Biol Chem 257:13731, 1982) but at pH 5. Iron release at pH 7.4
did not require the presence of a chelator, and the majority passed through
a 10,000 relative molecular mass cut-off ultrafiltration membrane. When
iron-poor lactoferrin was present during incubation with myeloperoxidase,
88% of the released 59Fe was precipitated with anti- lactoferrin antiserum,
indicating that it was lactoferrin-bound. When the bacteria were mixed with
neutrophils in a 10:1 ratio, approximately 50% were phagocytosed. About 40%
of the 59Fe was released from the ingested bacteria over a 40-minute
period. Initially, most remained associated with the neutrophil phagosomes,
but with time, there was gradual transfer of some of the iron to the
medium. Using anti- lactoferrin antiserum, 50% to 60% of phagosomal iron
and 64% to 71% of iron in the medium was shown to be bound to lactoferrin.
Thus, iron is released from phagocytosed E coli. Most becomes bound to
lactoferrin, and some of this is released into the surroundings of the
neutrophils. This suggests that neutrophil lactoferrin may function to trap
iron from ingested microorganisms, enabling its removal from sites of
inflammation. This may prevent iron from catalyzing undesirable oxidative
reactions, as well as making it unavailable for growth of microorganisms
that survive the killing process.
Volume 75,
Issue 4,
pp. 984-989,
02/15/1990
Copyright © 1990 by The American Society of Hematology
