Some Features of Bone Marrow Macrophages in Patients with Homozygous β-Thalassaemia

Authors

  • S. N. Wickramasinghe,

    Corresponding author
    1. Department of Haematology and MRC Experimental Haematology Unit, St Mary's Hospital Medical School, University of London, and Division of Experimental Pathology, The Mathilda and Terence Kennedy Institute of Rheumatology, London
      Dr S. N. Wickramasinghe, Department of Haematology, St Mary's Hospital Medical School, London, W.2.
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  • Madeleine Hughes

    1. Department of Haematology and MRC Experimental Haematology Unit, St Mary's Hospital Medical School, University of London, and Division of Experimental Pathology, The Mathilda and Terence Kennedy Institute of Rheumatology, London
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Dr S. N. Wickramasinghe, Department of Haematology, St Mary's Hospital Medical School, London, W.2.

Summary

The bone marrow macrophages of patients with homozygous β-thalassaemia were frequently situated adjacent to collagen fibres and sometimes formed intrasinusoidal cytoplasmic protrusions. They also appeared to phagocytose processes of erythroblast cytoplasm (at times containing precipitated α-chains) which projected into them from neighbouring erythroblasts. The cytoplasm of the macrophages included large numbers of heavily-iron-loaded secondary lysosomes of various sizes and shapes in addition to phagocytosed erythroblasts, erythrocytes and extruded erythroblast nuclei. Numerous ferritin molecules were found in the cytoplasmic matrix but there were hardly any in the mitochondria, endoplasmic reticulum or golgi saccules. A small number of ferritin molecules were present within the nucleus. Electron microscope autoradiographs of marrow fragments which had been incubated with [3H]leucine for 1 h revealed the presence of newly-synthesized protein molecules in all types of secondary lysosomes. Light microscope autoradiographs showed that the [3H]thymidine labelling index of the bone marrow macrophages was less than 1% and suggested that only a very small proportion of these cells were actively preparing for division.

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