Lecture (10)
Dr. Baha, H.AL-Amiedi
Ph.D.Microbiology
• mucosal &Systemic immunity of oral cavity
• mucosal component MALT:
• The mucosal surfaces of the body are secretary in nature and have their own immune system, the mucosa-associated lymphoid tissue, or MALT. The main mucosal surfaces are the gastrointestinal tract (including oral mucosa and the salivary glands), the genitourinary tract, and the respiratory tract. The secretion of the mammary glands (colostrum) is also part of the MALT. This branch of the immune system is stimulated through mucosa-associated lymphoid tissue, which is organized into discrete areas in the gut known as Peyer s patches,
• just below the epithelial cells in the lamina propria. Antigen travels through specialized epithelium (M cells) to the subepithelial lymphoid tissue. The main antibody produced at these sites is secretory IgA, a dimeric immunoglqbu-lin which acquires its secretory component during transport across the epithelium
• Oral immunity:
• Oral health is dependent on the integrity of the oral mucosa, which normally functions as an effective barrier against microorganisms. In addition, the oral mucosa is in continuity with a number of anatomical structures, if the oral defenses break down. amajor area of risk is the junction between the gingival and the tooth and the various forms of periodontal disease.
• There are several factors which may prevent penetration of intact oral mucosa by micro-organisms).
• Protective barrier:
• 1-Saliva
• 2-Keratin
• 3-Granular layer
• 4-Basement membrane
• 5-leucocytes
• 6-Antibody
• Saliva
• Saliva is a very important component of the oral defenses, both by its mechanical washing activity and by means of the antimicrobial factors that it contains. The important antimicrobial activities and components of saliva are summarized in (Tabel.2).
• 1-Mechanical cleaning
• 2-Lysozyme
• 3-peroxidase
• 4-lactoferrin
• 5-lecocytes
• 6-Secratory IgA
• Role of Secretary IgA in oral Gavity:
• Secretary IgA is by far the most important immunoglobulin in saliva. IgA is secreted by salivary gland plasma cells, two molecules of which are combined by means of a J chain (Fig.2), which is also secreted by local plasma cells. The resultant dimeric IgA is then complexes to the secretary component, synthesized by epithelial cells of the salivary acing, and the complete secretary IgA is transported into the duct lumen and thence into the mouth. Secretary IgA is more resistant to proteolysis degradation than other immunoglobulin. It probably functions by combining with micro-organisms and preventing their adherence to host surfaces.
• Gingival crevicular fluid
• Blood components, including leucocytes, are able to reach the oral cavity via the flow of fluid through the junctional epithelium of the gingiva. The flow of this so-called gingival crevicular fluid (GCF) increases greatly with the inflammation accompanying periodontal disease. Experiments using radiolabelled IgG, IgM, IgA and neutrophils have shown that both humoral and cellular components from blood can reach the oral cavity in GCF
• In addition to immunoglobulin, complement components have been detected in GCF, suggesting that both the classical and alternative complement pathways may be activated in the gingival crevice. Other components include enzymes such as lysozyme, proteases and collagenases released by cells of both the host and bacteria. Specific proteases which inactivate IgA have been described.
• The cellular component of GCF comprises mainly neutrophils, with small numbers of macrophages and B- and T-lymphocytes. These cells migrate continuously from the blood through the junctional epithelium into the gingival crevice. Over 80% of neutrophils in the gingival crevice are functional and can phagocytose micro-organisms.
• It is clear, therefore, that the tooth surface is influenced by both local salivary immune mechanisms, mediated largely through secretory IgA, and by systemic immunity involving all the varied immune components present in blood. The way in which these contributing factors interact to provide immunity within the oral cavity is illustrated in Fig.
Immunological techniques
• the study of biological reactions relevant to the pathogenesis of disease, epidemiology, and diagnosis. Serology, the measurement of specific antibodies in serum to diagnose indirectly a specific infection, still has a major rook in clinical microbiology. Some of rhea most commonly used techniques involve the use of tagged, or labeled antibodies, where the label can be a fluorescent dye,
• ELISA):
• An enzyme, or a radioactive isotope. Two of the most commonly used techniques are enzyme-linked immunosorben assay (ELISA), and immunobiotcing (Western blotting). Both techniques involve the ultimate detection of antibody-antigen complexes, where either the antigen or the antibody is being assayed. The third technique, latex agglutination (or a variation called coagglutination) is used as an extremely rapid technique for the detection of antigen or toxin in clinical specimens.
• antibody is covalently labelled with an enzyme. The complex of antigen, first antibody, and second antibody-enzyme conjugate is detected by adding a chromogenk substrate for the enzyme, i.e. the product of the enzyme is coloured, or a different colour from the substrate. The intensity of the colour produced, which is proportional to the amount of antibody bound by the antigen, can be read quantitatively in a purpose-designed microplate spectrophotometer
A converse assay for the detection and quantitation of antigen can be performed by a capture or sandwich ELISA where the capture antibody is bound to the plastic. After capture of the antigen, it can be detected either directly with an enzyme-labelled antibody, or indirectly with a second antibody raised in a different species from the capture antibody. This second antibody can be detected as described above for the antibody-detection ELISA