The bactericidal/permeability-increasing protein (BPI) is membrane-associated in azurophil granules of human neutrophils, and relocation occurs upon cellular activation

Authors

  • Jero Calafat,

    1. Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
    2. The Netherlands, Current affiliation: Department of Dermatology/Allergology, University Hospital Utrecht, Utrecht
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  • Hans Janssen,

    1. Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
    2. The Netherlands, Current affiliation: Department of Dermatology/Allergology, University Hospital Utrecht, Utrecht
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  • Edward F. Knol,

    1. Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam
    2. The Netherlands, Current affiliation: Department of Dermatology/Allergology, University Hospital Utrecht, Utrecht
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  • Johan Malm,

    1. The Netherlands, Current affiliation: Department of Dermatology/Allergology, University Hospital Utrecht, Utrecht
    2. The Netherlands Department of Clinical Chemistry University Hospital, Malmö, Sweden
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  • Arne Egesten

    Corresponding author
    1. The Netherlands, Current affiliation: Department of Dermatology/Allergology, University Hospital Utrecht, Utrecht
    2. Medical Microbiology, Lund University, Malmö University Hospital, Malmö, Sweden
      Department of Medical Microbiology, Malmö University Hospital, SE-205 02 Malmö, Sweden, e-mail: Arne.Egesten@medforsk.mas.lu.se
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Department of Medical Microbiology, Malmö University Hospital, SE-205 02 Malmö, Sweden, e-mail: Arne.Egesten@medforsk.mas.lu.se

Abstract

Neutrophilic granulocytes contain the 55 kDa bactericidal/permeability-increasing protein (BPI). BPI binds to lipopolysaccharides (LPS), and exerts bacteriostatic and bactericidal effects against a wide variety of Gram-negative bacterial species. We have investigated the subcellular location of BPI in immature and mature neutrophils using cryotechnique for immunoelectron microscopy. BPI was found to colocate with myeloperoxidase (MPO), a marker for azurophil granules, and it also showed the same pattern of distribution as CD63, a transmembrane-anchored protein. This suggests that BPI is membrane-associated in the azurophil granules in neutrophils. Its presence in azurophil granules was further confirmed by the finding of BPI in the azurophil granules of neutrophil promyelocytes of the bone marrow. Induction of selective release of azurophilic granules by the Na-ionophore monensin resulted in fusion of endosomes with azurophil granules, leading to the formation of large vacuoles containing MPO, CD63, and BPI. After phagocytosis of serum-treated zymosan (STZ), BPI was detected in phagosomes, both in association with membranes as well as in the lumen, suggesting the release of BPI into activated compartments. The results show that BPI is present in azurophil granules, is probably primarily membrane-associated, and is relocated after activation, following the same route as MPO and CD63.

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