You are in: eMedicine Specialties > Hematology > Immune System and Disorders NeutrophiliaArticle Last Updated: Jun 29, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Nader D Nader, MD, PhD, Chief, Department of Anesthesiology, Western New York VA Healthcare System, Associate Professor, Departments of Anesthesiology, VA Western New York Healthcare System Nader D Nader is a member of the following medical societies: American Society of Anesthesiologists Coauthor(s): Roberta L Reedy, MS, CRNA, Adjunct Faculty, State University of New York at Buffalo, School of Nursing; Research Coordinator, Certified Registered Nurse Anesthetist, Department of Anesthesia, Veterans Administration Western New York Healthcare System Editors: Koyamangalath Krishnan, MD, FRCP, FACP, Dishner Endowed Chair of Excellence in Medicine, Professor of Medicine and Chief of Hematology-Oncology, Program Director, Hematology-Oncology Fellowship, James H Quillen College of Medicine at East Tennessee State University; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Troy H Guthrie, Jr, MD, Director of Cancer Institute, Baptist Medical Center; Rajalaxmi McKenna, MD, FACP, Consulting Staff, Department of Medicine, Southwest Medical Consultants, SC, Good Samaritan Hospital, Advocate Health Systems; Emmanuel C Besa, MD, Professor, Department of Medicine, Division of Hematologic Malignancies, Kimmel Cancer Center, Thomas Jefferson University Author and Editor Disclosure Synonyms and related keywords: leukocytosis, granulocytosis, neutrophils, host defense INTRODUCTIONSection 2 of 9
  The adequate production and distribution of normally functioning neutrophils is vital to host defense. During an infection, chemotactic agents are generated that attract neutrophils to the site of infection, which, in turn, play a critical role in phagocytosing and killing microorganisms. This article focuses on (1) subcellular structure of neutrophils, (2) developmental stages of mature neutrophils from the progenitor cells, (3) distribution of neutrophils in the body, (4) neutrophil function, and (5) causes of neutrophilia. SUBCELLULAR STRUCTURE OF NEUTROPHILSSection 3 of 9
Mature neutrophils are terminally differentiated cells that are no longer capable of growth or division. Mature neutrophils contain at least 4 types of granules that are specialized lysosomes and serve as microbiocidal mediators designed to destroy the microbial invader. Granules have been classified as, (1) primary or azurophil granules, (2) secondary or specific granules, (3) tertiary or gelatinase granules, and (4) secretory vesicles. Primary or azurophilic granules Azurophilic granules fuse with phagocytic vesicles and deliver their contents. Primary or azurophilic granules contain the enzyme myeloperoxidase and several other proteins and enzymes. Myeloperoxidase, which constitutes approximately 5% of the dry weight of neutrophils, catalyzes the production of hypochlorite from chloride and hydrogen peroxide. Various other components of azurophilic granules include defensins, lysozyme, azurocidin, bacterial permeability–increasing protein (BPI), elastase, cathepsin G, proteinase, and esterase N. Defensins are proteins that defend the body against a variety of bacteria, fungi, and viruses. Lysozyme is an enzyme that degrades bacterial peptidoglycans. Azurocidin demonstrates antibacterial activity and antifungal activity against Candida albicans. BPI has antibacterial activity against some gram-negative bacteria. Secondary or specific granules Secondary or specific granules are released into the extracellular space, as opposed to the primary granule content that is released into phagocytic vesicles. Secondary granules contain apolactoferrin, vitamin B-12–binding protein, plasminogen activator, lysozyme, and collagenase. Apolactoferrin binds to the iron, thereby depriving bacteria of iron essential for cell growth. Collagenase degrades collagen and thus augments movement of neutrophils through collagen. Tertiary or gelatinase granules Tertiary or gelatinase granules contain gelatinase, acetyltransferase, and lysozyme. Tertiary granules are up-regulated to the surface with stimulation, as are specific granules. Secretory vesicles Secretory vesicles contain alkaline phosphatase, cytochrome b558, and N-formyl-1-methionyl-1-leucyl-1-phenylalamine (FMLP) receptors. Secretory vesicles can be up-regulated to the surface even in the absence of extracellular calcium, in contrast to specific and gelatinase granules that need extracellular calcium for release. Neutrophil plasma membrane and cytoplasm The neutrophil plasma membrane contains several membrane channels, adhesive proteins, receptors for various ligands, ion pumps, and ectoenzymes. Neutrophils contain a complex cytoskeleton, which is responsible for chemotaxis, phagocytosis, and exocytosis. Some proteins that make up the cytoskeleton are actin, actin-binding protein, alpha-actinin, gelsolin, profilin, myosin, tubulin, and tropomyosin. Besides many components common to all cells, approximately 45% of the neutrophil cytosolic protein is comprised of migration inhibitory factor–related proteins (MRPs), MRP-8 and MRP-14. Neutrophils contain a large amount of glycogen in the cytoplasm. Glycogen provides neutrophils with a source of energy, especially in areas of low extracellular glucose, as in abscesses. NEUTROPHIL DEVELOPMENTSection 4 of 9
Hematopoietic stem cells are pluripotent cells that are capable of self-replication and differentiation. Committed stem cells capable of developing into myeloblasts are formed from the multipotent hematopoietic stem cell. The first 3 morphologic stages in the development of mature neutrophils are capable of replication. The later stages of neutrophil development only undergo cell differentiation. The representative cells in the first 3 stages are myeloblasts, promyelocytes, and myelocytes. Myeloblast stage The myeloblast cell has a large nucleus, is round or oval, and has a small amount of cytoplasm. No condensation of chromatin is observed, and 2-5 nucleoli are present. No granules are present in the cytoplasm at this stage. Promyelocyte stage The promyelocyte cell is larger than the myeloblast. The nucleus is round or oval, and the nuclear chromatin is diffuse, as in the myeloblast. Nucleoli tend to become less prominent as the cell develops. The azurophilic or primary granules appear at this stage, but the secondary granules are not yet present. The primary granules are budded off the concave surface of the Golgi complex. Myelocyte stage In the myelocyte stage, the secondary granules appear. These granules are smaller than the primary granules and stain heavily for glycoprotein. A pinkish ground-glass background, which is the glycoprotein, is observed when the cell is stained. Secondary granules arise from the convex surface of the Golgi complex. The myelocyte nucleus is eccentric and round or oval. The nuclear chromatin is coarse. The nucleoli are smaller and less prominent in the myelocyte stage when compared to the promyelocyte stage. Primary granule formation is limited to the promyelocyte stage. With each subsequent cell division, the number of primary granules decreases. In mature neutrophils, the ratio of secondary granules to primary granules in humans is approximately 2-3:1. Metamyelocyte stage The next stage, metamyelocyte, is characterized by an indented or horseshoe-shaped nucleus without nucleoli. The nuclear chromatin is dense, with considerable clumping along the nuclear membrane. The cytoplasm is filled with primary, secondary, and tertiary granules. The metamyelocyte stage is not capable of cell division, in contrast to its precursors. Polymorphonuclear stage In the last stage, band neutrophils undergo further condensation of the nuclear chromatin. The nucleus has a sausage shape with uniform diameter throughout its length. The nucleus progressively begins to develop one or more constrictions, and, as the cell develops into the polymorphonuclear stage, the nucleus has 2 or more lobes connected with filamentous strands. In the polymorphonuclear stage, the cytoplasm appears faintly pink due to an abundance of specific granules. NEUTROPHIL FUNCTIONSection 5 of 9
The major role of neutrophils is to protect the body against infectious agents. The interaction of bacteria with antibodies and the complement system results in the formation of various chemotactic agents. The initial response of the neutrophil is to migrate directionally toward the source of irritation. Upon arrival at the site of infection or inflammation, the neutrophils adhere to the vascular endothelium. This adhesive interaction is mediated by adhesion molecules that are present on the neutrophils and the endothelial cells. The major types of adhesion molecules are the selectins, integrins, and immunoglobulin-type molecules. The selectins are the initial mediators of endothelial attachment, followed by the beta-2 integrins. Integrins are proteins on the leukocyte surface that, once activated, anchor the leukocyte to the endothelium. The next step is migration (diapedesis) through the vascular matrix. Following the increasing gradient of chemotaxins, neutrophils migrate toward the source of tissue irritation. During the migration, the presence of chemotactic agents primes the neutrophil for subsequent activation. Various chemoattractants, such as N-formyl peptides (eg, FMLP), C5a, leukotriene B4, and platelet-activating factor (PAF), are released in response to infection. The chemoattractants bind to specific receptors on neutrophils, initiating cellular signal transduction pathways that set in motion ion fluxes, morphological changes, and metabolic activation. These processes are governed by G proteins, protein kinases, and phospholipases. Many chemotactic factor receptors are coupled to G proteins and, when activated, cause phospholipase C activation, which then hydrolyzes phosphatidylinositol bisphosphate into 2 messengers. These messengers are inositol 1,4,5-triphosphate (IP3) and 1,2-diacylglycerol. IP3 binds to specific receptors on intracellular membranes, resulting in the release of intracellular calcium, which is rapidly augmented by an influx of extracellular calcium. This rise in intracellular calcium is thought to be responsible for the release of both specific and azurophil granules. The elevated intracellular calcium is transient and returns to baseline in 1-3 minutes. Neutrophils move along the gradient of chemotactic agents by projecting pseudopodium in front of the cell. This involves alterations in the polymerization state of actin, regulated by several proteins including actin-binding protein, gelsolin, and others, and adenosine triphosphate–dependent contraction of the actin network mediated by myosin. The process of phagocytosis involves the projection of pseudopodia around a foreign particle, which then fuses with the neutrophil through invagination of the cell membrane, forming a phagosome. This process is more efficient if the organism is opsonized by antibodies or complement factors. The contents of the neutrophil storage granules are discharged into this so-called biological prison. Fusion of azurophil and specific granules with the phagosome follows (phagolysosome). Azurophilic granules contain many antibacterial compounds that are responsible for bacterial cell death. Specific granules contain products that, when released, extracellularly activate the complement cascade. Specific granules also contain collagenase, which helps hydrolyze the extracellular matrix, facilitating locomotion of the neutrophil through the tissues. Tertiary granules contain gelatinase, which plays a similar role in locomotion. Bacterial cell death in the phagosome results from oxidative and nonoxidative mechanisms. Oxidative mechanisms can be mediated by myeloperoxidase (MPO) or can be independent from MPO. Following activation, a massive increase in the consumption of oxygen by the neutrophil occurs; this is called the respiratory burst. The respiratory burst results in the production of superoxide (O2-), hydrogen peroxide (H2O2), and glucose oxidation via a hexose monophosphate shunt. NADPH is nicotinamide adenine dinucleotide phosphate, and NADP+ is the oxidized form of NADPH. 2O2 + NADPH (NADPH oxidase) ® 2O2- + NADP+ + H+
Most O2- is rapidly converted to H2O2 either spontaneously or by superoxide dismutase. 2O2-+ 2H+® O2 + H2O2
O2 and H2O2 are not potent microbicides by themselves; rather, they help generate more potent oxidizing agents such as oxidized halogens and oxidizing radicals. MPO in the azurophilic granules is released into the phagosome, which combines with H2O2 and a halide (Cl- or Br-) to form oxidized halogen, which is a potent antimicrobial. Cl- + H2O2 (MPO) ® H2O + OCl-
MPO-independent oxidative mechanisms of bacterial killing involve H2O2, superoxide anion (O2-), hydroxyl (OH) radical, and singlet oxygen (*O2). Oxygen-independent mechanisms play a role in bacterial killing in anaerobic conditions. These include acid, lysozyme, lactoferrin, defensins, BPI, azurocidin, serine proteinases, elastase, cathepsin G, and proteinase 3. Enzymes and oxidative agents are also released into the extracellular environment to kill invading bacteria. This process may result in tissue destruction. NEUTROPHIL KINETICSSection 6 of 9
In humans, neutrophil production takes place in the bone marrow. The life cycle of a neutrophil can be divided into bone marrow, blood, and tissue phases. The myeloblast, promyelocyte, and myelocyte are capable of cell division and differentiation. These forms constitute the mitotic compartment. The more mature forms, ie, metamyelocyte, band, and polymorphonuclear cells, are incapable of cell division but do undergo cell maturation and differentiation. These cells constitute the maturation compartment. The cells from the maturation compartment flow into the blood and are distributed into either the circulating granulocyte pool (CGP) or the marginal granulocyte pool (MGP). The total blood granulocyte pool (TBGP) is the sum of the CGP and the MGP. Cells in these 2 pools are in constant equilibrium. Both pools are approximately equal in size. An estimate of the CGP size can be determined by multiplying the neutrophil count per mm3 of blood by the known circulating blood volume. The MGP consists of cells still within the vascular space, but they are adherent to the walls of small vessels, especially postcapillary venules. Brief exercise or an epinephrine injection can increase the CGP by approximately 50% for a brief period, but the TBGP remains unchanged. This is due to the release of cells from the marginal pool. This demargination involves disruption of the bond between the endothelium and leukocyte adhesion receptors, presumably modulated by cytokines. The response with endotoxin injection is one of initial transient neutropenia followed by a subsequent increase in the TBGP a few hours later. The initial neutropenia is from the shift of the CGP to the MGP. An outpouring of cells from the bone marrow follows, resulting in the increase of TBGP. NEUTROPHIL KINETICS IN PATIENTS WITH NEUTROPHILIASection 7 of 9
Neutrophilia refers to a higher than normal number of neutrophils. Neutrophilia may result from a shift of cells from the marginal to the circulating pool (shift neutrophilia) without an increase in the TBGP or from a true increase in TBGP size (true neutrophilia). Shift neutrophilia is usually transient and may occur in association with vigorous exercise or epinephrine injection and usually lasts 20-30 minutes. It also is seen in seizures and paroxysmal tachycardia. No increase in nonsegmented forms occurs because no change occurs in the inflow of neutrophils from the marrow. True neutrophilia occurs in most cases of neutrophilia related to infections. The TBGP may be increased 5-6 times normal. During early infection, the neutrophil count may actually decrease briefly due to margination of cells from the blood. This is followed rapidly by egress of cells from the marrow, resulting in an increase in the TBGP and blood neutrophilia. If the demand of cells is high, a shift to the left in the differential count may occur. A left shift is characterized by the appearance of more immature neutrophil forms in the blood. During established infection, the neutrophil count remains elevated, with equal numbers in the marginal and the circulating pool. During the recovery phase, the flow of cells from the marrow decreases, with a resultant decrease in neutrophilia. CAUSES OF NEUTROPHILIASection 8 of 9
Acute infections Neutrophilia can occur from acute infections caused by cocci (eg, staphylococci, pneumococci, streptococci, meningococci, gonococci); bacilli (eg, Escherichia coli, Pseudomonas aeruginosa, Actinomyces species); certain fungi (eg, Coccidioides immitis); spirochetes; viruses (eg, rabies, poliomyelitis, herpes zoster, small pox, varicella); rickettsia; and parasites (eg, liver fluke). This is seen with furuncles, abscesses, tonsillitis, appendicitis, otitis media, osteomyelitis, cholecystitis, salpingitis, meningitis, diphtheria, plague, and peritonitis. In acute infections, leukocyte counts typically are 15-25 X 109/L. Infections such as typhoid fever, parathyroid fever, mumps, measles, and tuberculosis usually are not associated with leukocytosis. Noninfectious inflammation In noninfectious conditions, such as burns, postoperative state, acute myocardial infarction, acute attacks of gout, acute glomerulonephritis, rheumatic fever, collagen vascular diseases, and hypersensitivity reactions, neutrophilia can occur. Neutrophilia in severe burns is accompanied by a shift to the left and the presence of degenerative forms, including toxic granulation and Dohle bodies. Postoperatively, neutrophilia occurs for 12-36 hours as a result of tissue injury–related increases in adrenocortical hormones. Leukocytosis also can occur in intestinal obstruction and strangulated hernia. Neutrophil activation during cardiopulmonary bypass (CPB) may occur because of the release of complement chemotactic products or the local release of IL-8. The expression of beta-2 integrins on the surface of neutrophils is increased in response to IL-8 and to certain components of complement during CPB. Both IL-8 and the complement system are activated during CPB. Patients with acute myocardial infarction experience a transient but significant rise in serum IL-8 concentration within 24 hours after the onset of symptoms. An upregulation of mRNA for IL-8 occurs in the inflammatory infiltrate near the border between necrotic and viable myocardium. Thus, IL-8 is likely involved in the pathogenesis of myocardial injury following CABG surgery. Metabolic Neutrophilia commonly occurs in diabetic ketoacidosis, preeclampsia, and uremia, especially with uremic pericarditis. Poisoning Neutrophilia can result from poisoning with lead, mercury, digitalis, camphor, antipyrine, phenacetin, quinidine, pyrogallol, turpentine, arsphenamine, and insect venoms. In patients with lead colic, leukocyte counts as high as 20 X 109/L may be seen. Acute hemorrhage Acute hemorrhage, especially into body spaces such as the peritoneal cavity, pleural cavity, joint cavity, and intracranial (eg, extradural, subdural, or subarachnoid space) cavity is associated with leukocytosis and neutrophilia. This probably is related to the release of adrenal corticosteroids and/or epinephrine secondary to pain. Local inflammation due to pressure necrosis and generation of chemotactic factors from lysis of leukocytes also contributes. During the first 1-3 hours, neutrophilia occurs because of a shift from the marginal pool to the circulating pool. After 3-6 hours, neutrophils are released from the marrow. Acute hemolysis leukocytosis occurs following transfusion of mismatched blood or during acute hemolytic disease. Malignant neoplasms Neutrophilia can occur in association with rapidly growing neoplasms when the tumor outgrows its blood supply. This is thought to be due to tumor necrosis factor-alpha. Some tumor types produce neutrophilic growth factors (eg, G-CSF production by squamous cell cancers of the head and neck). Physiologic neutrophilia Strenuous exercise and epinephrine injection can cause transient neutrophilia. Physiologic neutrophilia also is seen in pregnancy, labor, and in newborns. Other causes Chronic myelocytic leukemia, polycythemia vera, myelofibrosis, and myeloid metaplasia result in neutrophilia. Neutrophilia can occur in association with convulsions and paroxysmal tachycardia. Acute or chronic administration of corticosteroids causes neutrophilia. Neutrophilia is seen in association with Cushing disease. Neutrophilia may be present without an identifiable cause; in this case, it is known as chronic idiopathic neutrophilia. Hereditary neutrophilia has been described. REFERENCESSection 9 of 9
Article Last Updated: Jun 29, 2006 |
