|Year : 2006 | Volume
| Issue : 1 | Page : 3-8
Neutrophils in health and disease: An overview
SM Rashmi1, DK Alka2, SN Ramakant2
1 Dept. of Oral Pathology, Pravara Inst. of Medical Science, Loni, India
2 Dept. of Oral Pathology, K.L.E.S Institute of Dental Sciences, Belgaum, India
S M Rashmi
Dept of Oral pathology, Pravara Institute Of Medical Sciences, Loni, Tal Rahata, Dist Ahmednagar State Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Neutrophils are granulocytes, which form an essential component of the cellular innate system involved in killing bacteria and fungi. They play critical role in host defence by phagocytizing and digesting microorganisms and inappropriate activation of neutrophils may result in damage to normal host tissues. The structure, functions of neutrophils, mechanism of controlling periodontal bacteria, and neutrophilic abnormalities with oral manifestations are discussed in this article.
Keywords: Microphages, barr bodies, granules, ′Organulocytic′ migratory rate, nitroblue tetrazolium reduction test (NBT), Leukocyte alkaline phosphatase activity, risk markers, neutrophilic abnormalities.
|How to cite this article:|
Rashmi S M, Alka D K, Ramakant S N. Neutrophils in health and disease: An overview. J Oral Maxillofac Pathol 2006;10:3-8
|How to cite this URL:|
Rashmi S M, Alka D K, Ramakant S N. Neutrophils in health and disease: An overview. J Oral Maxillofac Pathol [serial online] 2006 [cited 2022 Sep 26];10:3-8. Available from: https://www.jomfp.in/text.asp?2006/10/1/3/37740
| Introduction|| |
Neutrophils are so named because of their neutral staining with Wright stain. They are also known as PMNs or polys or microphages (when neutrophils leave the blood, they always retain their small size). They are round cells approximately 12-14 pm in diameter. The multilobed nucleus contributes to the extreme elasticity of the cell, which is important for the cell to make rapid transit from the blood through tight gaps in the endothelium. In 1904, Arneth introduced a method for classification of neutrophilic granulocytes (six types) according to the number of nuclear lobes (40-50% being with trilobed nucleus).
In the resting uninfected host, the production and elimination of neutrophils are balanced, resulting in fairly constant concentration of neutrophils in peripheral blood. When infection occurs, chemotactic agents are generated, that result in migration of neutrophils to the site of the infection and activation of neutrophil defensive function .
| Life History|| |
Neutrophils are abundant in the circulation, present at a concentration of 2x109 to 7x109 per litre and equal numbers are marginated on vessel walls or sequestrated in closed capillaries. The half-life in the blood is 6-7 hours and in the tissue it is not exactly known and is estimated to range from 1-4 days. The blood and bone marrow form an abundant pool of cells and neutrophils are recruited and called to the sites of infection and inflammation as and when required on stimulation by a cytokine. In the bone marrow, the myeloid precursor cells mature to segmented neutrophils in about 9 days.
Neutrophils are activated by numerous stimuli; some of the most described molecules involved include the complement component C5a, LTB4, FMLP, and interleukin-8 (IL-8). As many as 25-50 particles (bacteria) can be engulfed by a single cell. After emigration to the tissues, they never return to the bloodstream. They are probably disposed of internally by cells of the reticuloendothelial system; however, there are several routes of external neutrophil loss. Emigration through gingiva into the saliva and excretion in urine is common. Neutrophils occur in the secretions of the uterus during the second half of the menstrual cycle.
Since the mature neutrophil has limited capacity to regenerate expended lysosomal and specific enzymes, which are rapidly depleted by phygocytic activity, the neutrophil is thus incapable of continuous function and degenerates after a single burst of activity. Dead leukocytes release a granulocyte-inducing factor, which causes mobilization of reserve cells in the marrow and also stimulate new granulocyte formation. Because PMNs are not concerned with their own survival, they are free to use delivery modes, which can be suicidal. Cytosolic and granule components can be delivered by apoptotic process (programmed death) .
| Subcellular structure of neutrophils|| |
Immunoelectron microscopy and subcellular fractionation are the two techniques commonly used to understand the functions of neutrophils better.
Four well-defined types of granules have been defined in neutrophils, which are azurophilic (Primary) granules, specific (Secondary) granules, (Tertiary) gelatinase granules, and secretory vesicles.
Under the electron microscope, the granules are seen to consist of a finely granular matrix bounded by a typical membrane. The granules have been shown to be quite heterogeneous with some rounded forms, some in the shape of grain of rice or small dumbles and their number has been shown to vary from 500-1500/granulocyte. Granules contain large amount of protein and traces of lipids and nucleic acids. These granules are essential for post phagocytic fraction of PMN leucocytes. Their constituents are essential in inflammation and are determinants of intraleukocytic antimicrobial events.
Among the azurophilic contents are myeloperoxidase, defensins, lysozyme, azurocidin, etc, that have antibacterial function. These granules fuse with phagocytes vesicles, resulting in the delivery of their contents to the ingested organism. The greenish coloration to pus is imparted by myeloperoxidase.
Specific granules are three times more common in the cytoplasm. Release of specific granule contents like collagenase, apolactoferrin, lysozyme, histaminase, etc, may modify the inflammatory process.
Collagenase and elastase break down fibrous structures in the extracellular matrix, facilitating progress of the neutrophil through the tissues.
| Sex is indicated by leukocytes|| |
Only one X chromosome is essential for the normal activity of the cell; the other in the normal XX female remains unextended and thus is visible as a chromatin body.
The sex chromatin (Barr) body of neutrophil of female is a small mass, usually adjacent to the nuclear membrane that stains deeply with haematoxyiln, cresyl violet, fuchsin gallocyanin, Feulgen, and thionine and is about 0.7-1.2 µm in diameter. It takes the form of a drumstick projecting from one of the nuclear lobes. These bodies are present in 80-90% of the somatic cells of the normal female subjects. Confirmation of the X-chromosome in the drumstick has been provided by in situ hybridization.
In humans, the structures having an appearance similar to "drumstick" can be seen in the normal state but only in small percentage of cells. These have been assigned a variety of names like sessile nodules, tennis rackets, golf clubs, large or small nuclear lobes etc. Identifying them is often difficult 
| Leucocytes in the dentogingival area and saliva|| |
Leukocytes found in clinically healthy gingival sulci are predominantly neutrophils. In healthy human gingival sulci, they are found to be 91.2% to 91.5% and mononuclear cells are only 8.5 to 8.8%.
It is interesting to note that the main portal of entry of leukocytes into the oral cavity is the gingival sulcus. The majority of these cells is viable and has been found to have phagocytic and killing capacity. Therefore they constitute a major protective mechanism against extension of plaque into the gingival sulcus.
pH changes in the periodontal environment could alter the balance between the host and bacteria, even though pH is one of the many factors, the PMNs are exposed to. Studies on pH changes are useful for giving insight into the determinants of PMN activation at diseased periodontal sites.
In addition to desquamated epithelial cells, the saliva contains all forms of leukocytes, the majority being PMNs. The number of leukocytes varies from person to person and at different times of the day. Living PMNs in saliva are sometimes referred to as 'Orogranulocytes'. The rate of their migration into the oral cavity is termed the 'Organulocytic' migratory rate. Skougoard in 1994 proposed that the rate of migration is correlated with the severity of gingival inflammation and is hence a reliable index for assessing gingivitis .
| Neutrophil interface with microorganisms|| |
Half the leukocytes infiltrating the junctional epithelium and 90% of the leukocytes isolated from the crevicular fluid are neutrophils. While PMNs predominate the sulcus and the junctional epithelium, lymphocytes and monocytes/macrophages predominate within the subadjacent connective tissue (Page, Schroeder, 1976).
The concentration of neutrophils in the periodontal tissues exceeds the concentration in blood. In minimally inflamed gingiva, 2.5 x 107PMN/cm3 infiltrate the connective tissue and 1.7 x 108 PMN/cm3 are found at the junctional epithelium (blood levels normally range from 1 x 106 to 4 x 106 PMN /cm3).
Rather than a homogeneous bacteria neutrophil mixture in the gingival crevice, the PMNs form a "leukocyte wall" interposed between the periodontal plaque mass and the junctional and sulcular epithelium.
The leukocyte wall may function both as a secretory and as a digestive organ and crevicular neutrophils exhibit both partial degranulation and ingested bacteria.
| Control of periodontal bacteria by neutrophils|| |
Initially, the periodontopathic microorganisms encounter plasma factors viz; complement within extracellular fluids or crevicular fluids. The result of this encounter is the initiation of inflammation as evidenced by the recovery of complement product from the crevice. If the complement is not successful in controlling the pathogen, the host defense turns to neutrophil (Miller, 1984)
Neutrophils within the gingival crevice provide the first cellular host mechanisms to control periodontal bacteria. If PMNs are unsuccessful, monocytes are recruited which infiltrate the connective tissue, develop into tissue macrophages, and digest the antigen in association with the major histocompatibility complex (MHC) encoded class II molecules to lymphocytes.
Perhaps to avoid systemic infection, chronic periodontal inflammation, may produce localized specific immune responses and a cytokine orchestrated amputation of connective tissue, which we call "periodontal diseases".
Thus the neurophils are important because they control periodontal micro-ecology prior to the involvement of chronic inflammatory cells.
The ability of neutrophils to destroy microorganisms with intracellular enzymes can be evaluated by the nitroblue tetrazolium reduction test (NBT). Normal neutrophils contain enzymes that convert colorless NBT to dark blue granules within the cell. When dark blue granules are not seen, neutrophils will not destroy bacteria.
Studies that evaluate the other aspects of neutrophil function include the following:
a) The steroid challenge, which assesses neutrophil reserves in the bone marrow.
b) The epinephrine challenge, which assesses neutrophil reserves in the marginal pool.
c) The endotoxin challenge, which measures the ability of neutrophils to migrate to the peripheral tissues.
[Table - 1]
| Oral manifestations associated with decrease in circulating neutrophils and neutrophil dysfunction|| |
The oral manifestations associated with a decrease in the number of circulating neutrophils are well documented and include mucous membrane infection, gingivitis, and periodontitis. Conditions such as agranulocytosis, congenital or cyclic neutropenia, and leukaemia result in severe breakdown of oral tissues .
Agranulocytosis is a serious disease involving white blood cells. The white blood cell count is often below 2000 cells per cubic millimeter with an almost complete absence of granulocytes or PMNs
Neutropenia, like anemia is not a disease but sign of an underlying disorder; it has a wide range of underlying causes. Decreased production of neutrophils is associated with deficiencies of vitamin B12 and folic acid. Certain infections decrease the number of neutrophils in the circulating blood because of increased migration of neutrophils into the tissue, sequestration of neutrophils or direct toxic effect of the microorganism and its toxins on the bone marrow. Infections with viruses particularly Hepatitis A, Human Immuno deficiency virus (HIV 1) and Epstein- Barr virus, are associated with neutropenia and overwhelming bacterial infection, particularly septicemia can be accompanied by neutropenia because the cells are used at rapid rate to overcome the infection. Oral ulcer, advanced periodontal disease, periocoronitis, and pulpal infections in patients with severe neutropenia should be considered potentially life threatening because they may lead to bacteremia and septicemia.
With few exceptions, the oral status of patients with normal neutrophil numbers but decreased neutrophil function is infrequently reported. The concentration of neutrophils in the periodontal tissue exceeds the concentration in the blood. The most susceptible tissues to pathologic changes in the oral cavity studied in conditions of neutrophil dysfunction are the tissues of the periodontium.
Because accumulation of PMNs in the connective tissue, junctional epithelium and gingival crevice or periodontal pocket of the periodontium is a characteristic morphologic feature of chronic periodontal disease at all stages. It is not surprising that a decrease in neutrophil function might result in more severe periodontal breakdown.
[Table - 2]
| Neutrophilic abnormalities with oral manifestations|| |
Though individuals with chronic granulomatous disease (CGD) exhibit greater incidence of oral ulceration and gingivitis but they are not strongly associated with severe periodontitis. Inspite of recurrent systemic infections, the absence of periodontal disease is indeed surprising. Two reasons could be sited for this. One reason is importance of OZ dependent mechanisms and the other reason could be the routine intake of antibiotic prophylaxis by these patients, which may suppress the periodontopathic pathogens. The cutaneous and periodontal changes appear together before the age of 4 years. Primary teeth are usually lost by 5 to 6 years of age. The permanent teeth then erupt normally but, these are also lost by 15 years. Patients are usually edentulous. About one half of patients with Down syndrome (DS) suffer from chemotactic defects in PMN. As such, the PMNs are not quantitatively decreased in number in DS patients. The PMN defect in DS is a qualitative one, in which the cells fail to exert their normal bactericidal function. Different stages in the bactericidal activity may be affected and neutrophil adhesiveness may be reduced.
Leukocyte alkaline phosphatase activity (LAP) of the various granulocytic enzymes present in the neutrophil has been studied extensively as a diagnostic tool, as neutrophils are freely accessible body cells. LAP activity has been reported to be altered in pregnancy, mylofbrosis, polycythaemia vera, leukaemoid reaction, Cushing's syndrome, hypophosphataemeia, familial myeloproliferative disease in various neoplasms like lymphomas, melanomas, endometrial carcinoma, and chronic myeloid leukemia.
Till date there is no explanation for the alteration of LAP activity. The suggested hypotheses for this alteration are,
1) production of abnormal alkaline phosphatase
2) decreased production of blood cells or
3) alteration in cellular enzymes and complement system induced by chromosomal aberration and viral oncogenesis .
| Pulpal Inflammation|| |
The most common form of leukocyte found in pulpal inflammation is the neutrophil, although eosinophils and basophils are occasionally detected. It is important to know that although neutrophils are not normally present in intact healthy pulps, with injury and cell death, they rapidly migrate into the areas from nearby capillaries and venules. They are the major cell type in micro abscess formation and very effective at destroying and phagocytizing bacteria or dead cells. Unfortunately their participation often injures adjacent cells and may contribute to the development of wider zones of inflammation .
| Periapical lesions|| |
The inflammatory response associated with periapical lesions is similar to an inflammatory response any where in the body .
| Wound Healing|| |
A number of functions other than defence against bacteria have been attributed to neutrophils in healing wounds. These include (a) Cell lysis (b) Phagocytosis of cells, debris, exudate, foreign particles, immune complexes, and erythrocytes. (c) Fibrinolysis by phagocytosis and extracellular lysis (d) Assisting in epithelial cell migration (e) Release of cytokines that regulate fibroblast growth factor (f) Release of proteolytic enzymes such as elastase, which can destroy the fibronectin coating of fibroblasts that enable them to differentiate and migrate and (g) An influence on blood flow and albumin extravasation in granulation tissue.
In a relatively bacteria-free wound, macrophages phagocytose the free neutrophil granules and effete neutrophils. However, when the wounds are exposed to bacteria, neutrophils are an essential part of the normal healing process.
| Implants|| |
The soft tissue surrounding osseointergrated dental implants share both anatomical and functional similarities with the gingiva around natural teeth. The neutrophil granulocyte is the primary defender against bacterial invasion, but it has also been implicated as an effector cell in several inflammatory tissue destructive diseases including periodontitis. Neutrophil derived enzymes in the crevicular fluid have been used as risk markers for tissue destruction in periodontal disease and may also prove useful as a sensitive marker of destructive process around implants.
Elastase has also been shown to correlate with bone reduction around implants. Elastase, a serine protease derived from the primary granule of the neutrophil is released extracellularly during phagocytosis and may therefore serve as a marker of neutrophil activity .
| Conclusion|| |
Patients with neutrophil dysfunction or well-defined abnormalities of neutrophils such as Hyperimmunoglobunemia E-recurrent infection (Job's syndrome), chronic granulomatous disease (CGD), Chediak-Higashi syndrome (CHS), and neutrophil specific granule deficiency regardless of age are more susceptible to gingival disease and to ulceration of the oral mucosa.
| References|| |
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[Table - 1], [Table - 2]
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