CELLULAR AND SUBCELLULAR-LOCALIZATION OF THE BACTERICIDAL PERMEABILITY-INCREASING PROTEIN OF NEUTROPHILS

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  • 1 February 1987
    • journal article
    • research article
    • Vol. 69  (2) , 652-659
Abstract
Human and rabbit polymorphonuclear leukocytes contain a bactericidial/permeability-increasing protein (BPl), a potent cytotoxin active specifically against gram-negative bacteria. To identify the cell population(s) producing BPl, we have examined mature and immature human blood cells for BPl by immunofluorescence of intact cells and radioimmunoassay and bioassay of cell extracts. By immunofluorescence and radioimmunoassay of cells from peripheral blood, BPl was detected only in neutrophils; immunofluorescent staining was punctate, indicative of the granule localization of BPl. Nearly all (>90%) BPl was recovered during the subcellular fractionation of neutrophils (N2 cavitation and discontinuous Percoll gradient) in fractions containing primary granules. Little BPl was released from intact cells during degranulation (cytochalasin B and f-Met-Leu-Phe) or could be extracted from isolated granules with salt or weak acid, which suggests that most granule-associated BPl is membrane bound. Double staining of bone marrow smears for BPl and lactoferrin revealed BPl only in neutrophil precursors including (pro)myelocytelike cells lacking lactoferrin, a marker of neutrophil secondary granules. Of several human cell lines tested, only the promyelocytelike HL-60 (and to a lesser extent, KG-1) cells contained BPl. BPl was present in a more mature subpopulation (<25%) of untreated HL-60 cells, recognized by surface marker analysis (rosetting with IgG-sensitized sheep RBC, the absence of proliferation-associated cell surface antigen). Induction of neutrophilic or monocytic differentiation caused, respectively, a small (approximately 50%) rise or fall in the BPl content. These findings indicate that BPl is a specific product of the neutrophil lineage and, hence, of the specialized cytotoxic apparatus of the neutrophil that plays an essential role in host defense v gram-negative bacteria.

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