Novel trends in neutrophil structure, function and development

doi:10.1016/S0167-5699(99)01500-5

Immunology Today

Volume 20, Issue 12, 1 December 1999, Pages 535-537

Immunology Today

https://doi.org/10.1016/S0167-5699(99)01500-5 Get rights and content

Abstract

Neutrophils are the most abundant leukocytes in blood, being the first line of defense against infection. A recent workshop* discussed the different levels at which neutrophil availability for combating infections is regulated: proliferation and maturation of precursor cells in bone marrow, apoptosis, diapedesis and activation of bactericidal systems.

Section snippets

The role of chemokines in myeloid development and PMN activation

An emerging family of cytokines, called chemokines, is being implicated in the production and mobilization of PMNs. Over 50 chemokines and 14 chemokine receptors have been identified. Many of the chemokine receptors bind more than one chemokine and some chemokines bind more than one receptor. Mice deficient in CXCR2 [interleukin 8 receptor (IL-8R)], CCR2 or CCR1 [macrophage inflammatory protein 1α (MIP-1α) receptor)] have been used to demonstrate the different roles of these receptors in

Development of PMN granules

CCAAT enhancer-binding proteins (C/EBP) play a central role in PMN development, by inducing transcription of granule protein coding genes, either by direct binding to the promoters of the corresponding genes or by activating transcription of the granulocyte colony-stimulating factor receptor (G-CSFR). Myelopoiesis in C/EBPα-knockout mice fails to proceed beyond the myeloblast stage; whereas transfection of C/EBPα in U937 promonocytic cells induces PMN differentiation and synthesis of PMN

Clearance of apoptotic PMNs

Many of the daily produced neutrophils undergo apoptosis before leaving the bone marrow. Apoptotic neutrophils can be removed by macrophages (in which case, neutrophils are anonymously degraded) or by dendritic cells (leading to antigen presentation and autoimmunity). Anti-apoptotic signals generated by growth factors and cytokines, and through integrin-mediated signalling, affect neutrophil survival after they leave the bone marrow, during diapedesis and at the site of bacterial intrusion.

Regulation of PMN adhesion

PMN rolling and arrest on endothelium is mediated through successive interactions of selectins and β₂-integrins that can withstand hydrodynamic stress. PMNs adhere to endothelial cell borders at points where the Weibel-Palade bodies fuse with the plasma membrane, increasing surface expression of P-selectin³. When intercellular adhesion molecule 1 (ICAM-1) is highly expressed on activated endothelial cells, PMN adhesion proceeds via direct β₂-integrin–ICAM-1 recognition. Rolling PMNs usually

SNARE proteins in phagocytosis and exocytosis

Using chimeric constructs of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein VAMP-3 (vesicle-associated membrane protein 3) tagged with green fluorescent protein, S. Grinstein (Toronto) demonstrated that endosomes bearing VAMP-3 first fuse with the plasma membrane where phagocytosis is being initiated and are subsequently internalized. VAMP-2 behaved similarly to VAMP-3. Microinjection of tetanus toxin cleaved VAMPs and partially inhibited phagocytosis,

Regulation of phagocytosis

During phagocytosis of antibody-coated red cells (EIgG) by PMNs, phosphorylation of ERK2 occurs through phospholipase D (PLD) activation, which generates diglycerides, leading to translocation of PKCδ and Raf-1 from the cytosol to the plasma membrane. Raf-1 activates MEK, leading to phosphorylation of ERK2 and, subsequently, to phosphorylation of myosin light chain kinase. This activates myosin, allowing generation of pseudopods, which are required for phagocytosis. Phagocytosis is terminated

Bactericidal/permeability-increasing protein (BPI)

BPI shows a 45% identity with lipopolysaccharide-binding protein (LBP), both of which are thought to arise from gene duplication. LBP is generated in liver cells and binds lipopolysaccharide (LPS) from the surface of Gram-negative bacteria. The LBP–LPS complexes are then presented via CD14 receptors to monocytes and T cells, thereby initiating an inflammatory response. BPI is made only in PMNs and stored in azurophilic granules. BPI binds LPS and is cytotoxic towards Gram-negative bacteria,

NADPH oxidase: molecular constituents and clinical disorders

Phagocytic cells contain an NADPH-dependent oxidase that transfers electrons from NADPH to O₂ to form O₂⁻. The oxidase contains a membrane-bound flavocytochrome b composed of an α (p22^phox) and β (gp91^phox) subunit. Three cytosolic proteins, p40^phox, p47^phox and p67^phox, and a GTP-binding protein p21rac are required for activation of electron transport. The cytosolic phox proteins are associated with the cytoskeleton through an actin-binding protein, coronin, promoting p47^phox phosphorylation

Gene therapy of PMN disorders

Gene therapy is being employed to correct the functional defect in O₂⁻ generation in both the autosomal and X-linked forms of CGD (Ref. 11). MFGS-p47^phox and MFGS-gp91^phox retrovirus vectors were employed for ex vivo transduction of G-CSF-mobilized, peripheral blood CD34⁺ cells to correct p47^phox- and X-linked-deficient forms of CGD. Under optimal conditions, about 70% of CD34⁺ cells were transduced in two patients, resulting in a peak of 0.1–0.2% functionally corrected blood PMNs, with lower

Concluding remarks

PMNs are short-lived non-mitotic cells generated in large numbers in the bone marrow through a highly controlled process of myelopoiesis, where C/EBPα plays a central role. One of the major decisions leading to PMN generation is made by stem cells committed to the myeloid lineage; genes coding for granule proteins are turned on to synthesize the granule constituents that will endow the PMN with its battery of microbicidal proteins.

The high heterogeneity of PMN granules is due to the continued

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^*: The Juan March Workshop on ‘Neutrophil Development and Function’ was held at Madrid, Spain, on 26–28 April 1999.

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TrendsNovel trends in neutrophil structure, function and development

Abstract

Section snippets

The role of chemokines in myeloid development and PMN activation

Development of PMN granules

Clearance of apoptotic PMNs

Regulation of PMN adhesion

SNARE proteins in phagocytosis and exocytosis

Regulation of phagocytosis

Bactericidal/permeability-increasing protein (BPI)

NADPH oxidase: molecular constituents and clinical disorders

Gene therapy of PMN disorders

Concluding remarks

Blood

Blood

Blood

J. Leukocyte Biol.

Curr. Opin. Hematol.

Trends
Novel trends in neutrophil structure, function and development