Neutrophil primary granule proteins HBP and HNP1–3 boost bacterial phagocytosis by human and murine macrophages
Oliver Soehnlein, … , Birgitta Agerberth, Lennart Lindbom
Oliver Soehnlein, … , Birgitta Agerberth, Lennart Lindbom
Published September 11, 2008
Citation Information: J Clin Invest. 2008;118(10):3491-3502. https://doi.org/10.1172/JCI35740.
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Research Article Immunology

Neutrophil primary granule proteins HBP and HNP1–3 boost bacterial phagocytosis by human and murine macrophages

Abstract

In acute inflammation, infiltrating polymorphonuclear leukocytes (also known as PMNs) release preformed granule proteins having multitudinous effects on the surrounding environment. Here we present what we believe to be a novel role for PMN-derived proteins in bacterial phagocytosis by both human and murine macrophages. Exposure of macrophages to PMN secretion markedly enhanced phagocytosis of IgG-opsonized Staphylococcus aureus both in vitro and in murine models in vivo. PMN secretion activated macrophages, resulting in upregulation of the Fcγ receptors CD32 and CD64, which then mediated the enhanced phagocytosis of IgG-opsonized bacteria. The phagocytosis-stimulating activity within the PMN secretion was found to be due to proteins released from PMN primary granules; thorough investigation revealed heparin-binding protein (HBP) and human neutrophil peptides 1–3 (HNP1–3) as the mediators of the macrophage response to PMN secretion. The use of blocking antibodies and knockout mice revealed that HBP acts via β2 integrins, but the receptor for HNP1–3 remained unclear. Mechanistically, HBP and HNP1–3 triggered macrophage release of TNF-α and IFN-γ, which acted in an autocrine loop to enhance expression of CD32 and CD64 and thereby enhance phagocytosis. Thus, we attribute what may be a novel role for PMN granule proteins in regulating the immune response to bacterial infections.

Authors

Oliver Soehnlein, Ylva Kai-Larsen, Robert Frithiof, Ole E. Sorensen, Ellinor Kenne, Karin Scharffetter-Kochanek, Einar E. Eriksson, Heiko Herwald, Birgitta Agerberth, Lennart Lindbom

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Figure 2

PMN-sec enhances activation of macrophages and expression of FcγRs.

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PMN-sec enhances activation of macrophages and expression of FcγRs. ...
(A) Human macrophages were incubated with PMN-sec for either 2 or 24 hours or with medium. In some wells, the PMN-sec was washed off after the 2- or 24-hour incubation period and replaced by medium. Subsequently the phagocytic activity was quantified. For each analysis, 4 independent experiments were performed. *P < 0.05 versus control; **P < 0.05 versus control and the respective 2-hour treatment group. (B and C) Expression of activation markers (B) and phagocytic receptors (C) in macrophages in response to treatment with PMN-sec for 24 hours. Expression is given as percentage change compared with basal expression. All values are isotype corrected. For each analysis, 6–8 independent experiments were performed. (D) Representative images of antibody staining for CD32 and CD64 in macrophages after treatment with PMN-sec or medium. Scale bar: 10 μm. (E) Human macrophages were incubated with PMN-sec or medium for 24 hours. Blocking antibodies toward CD64, CD32, or CD16 were added 30 minutes before incubation with IgG-opsonized S. aureus. The number of phagocytosed bacteria after 1 hour was quantified. For each analysis, 6 independent experiments were performed. †P < 0.05 versus group treated with PMN-sec.