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A functional defect in hereditary haemochromatosis monocytes and monocyte-derived macrophages
E Moura1, A F Verheul, J J Marx
1University Hospital Utrecht, The Netherlands.
Background:
Hereditary haemochromatosis (HH) is a disease of the metabolism of iron characterized by increased iron absorption and heavy parenchymal iron deposition, but with the presence of little iron in the mononuclear phagocytic system (MPS).
Methods:
To investigate the role of the MPS, the phagocytic ability of HH monocytes (MNs) and in vitro monocyte-derived macrophages (MDMs) was studied. HH patients with different degrees of iron accumulation were chosen.
Results:
We observed that HH patients' MNs and MDMs have a significantly decreased ability to phagocytose rabbit red blood cells (RRBCs) and that HH MNs possess a significantly decreased capacity to phagocytose Staphylococcus aureus (S. aureus). The decrease in the ability to phagocytose S. aureus, however, was kinetic in nature, explaining the absence of increased prevalence of bacterial infections among HH patients. Both RRBCs and S. aureus were preopsonized with heat-inactivated serum. No alteration in the complement-dependent phagocytosis of Cryptococcus neoformans was demonstrated when normal human serum was used. The phagocytosis defect was observed in 100% of HH patients and was independent of the magnitude of iron overload, age or liver damage, and affected the antibody-mediated uptake of bacteria and (R)RBCs.