Knowledge in Immune system
IgD - IMMUNOGLOBULIN
IgD resembles IgG structurally. It is present inconcentration of about 3 mg per 100 ml of serum and is mostly intravascular. It has a half life of about three days. IgD and IgM occur on the surface of unstimulated B lymphocytes and serve as recognition receptors forantigens. Combination of cell membrane-bound IgD or IgM with the corresponding antigen leads to specific stimulation of the B cell either activation and cloning to produce antibody, or suppression.
Yamini Chandru
IgE - IMMUNOGLOBULIN
This immunoglobulin was discovered in 1966by Ishizaka during the investigation of atopic reagin antibodies. It is an 8 S molecule (MW about 190,000), with a half life of about two days. It resembles IgG structurally. It exhibits unique properties such as heat lability (inactivated at 56 °C in one hour) and affinityfor the surface of tissue cells. (particularly mast cells) of the same species (homocytotropism) It mediates the Prausnitz-Kustner reaction It is susceptible to mercaptoethanol. It does not pass the placental barrier or fix complement. It is mostly extravascular in distribution Normal serum contains only traces (a few nanograms per ml) but greatly elevated levels are seen in atopic (type 1 allergic) conditions such as asthma,hay fever and eczema. Children living in insanitary conditions, with a high load of intestinal parasites, havehigh serum levels of IgE.IgE is chiefly produced in the lining of the respiratory and intestinal tract. IgE deficiency has been associated with IgA deficiency in individuals with impaired immunity who present undue susceptibility to infection.IgE is responsible for the anaphylactic type ofhypersensitivity. The physiological role of IgE appears to be protection against pathogens by mast cell degranulation and release of inflammatory mediators. It is also believed to have a special role in defenceagainst helminthic infections.In general, IgG protects the body fluids, IgA thebody surfaces and IgM the bloodstream, while IgE mediates reaginic hypersensitivity. IgD is a recognition molecule on the surface of B lymphocytes.
ABNORMAL IMMUNOGLOBULIN
Apart from antibodies, other structurally similar proteins are seen in serum in many pathological processes, and sometimes even in healthy persons. The earliest description of an abnormal immunoglobulin was the discovery by Bence Jones (1847) of the protein thatbears his name. The Bence Jones protein is typically found in multiple myeloma. It can be identified in urine by its characteristic property of coagulation when heated to 50 °C but redissolving at 70 °C(Bence Jonesproteins are the light chains of immunoglobulins and so may occur as the kappa or lambda forms. But in anyone patient, the chain is either kappa or lambda only and never both, being uniform in all other respects.This is because myeloma is a plasma cell dyscrasia in which there is unchecked proliferation of one clone of plasma cells, resulting in excessive production of the particular immunoglobulin synthesised by theclone. Such immunoglobulins are, therefore, called Monotonal)Multiple myeloma may affect plasma cellssynthesising IgG, IgA, IgD or Ige. Similar involvementof IgM producing cells is known as Waldenstrom macroglobulinemia In this condition, there is excessive production of the respective myeloma proteins M proteins) and of their light Chains (Bence Jones proteins). A different disorder is found in 'heavy chaindisease', which is a lymphoid neoplasia characterised by the overproduction of the Fc parts of the immunoglobulin heavy chains.Cryoglobulinemia is a condition in which a gelor precipitate is formed on cooling the serum,which dissolves on warming. It may not always be associated with disease but is often found in myelomas macroglobulinemias and autoimmune conditions such as systemic lupus erythematosus. Most cryoglobulinsconsist of IgG, IgM or their mixed precipitates.Because of the monoclonal nature of Bence Jones and other M proteins, they have been valuable models for the understanding of immunoglobulin structureand function.
IMMUNOGLOBULIN SPECIFICITY
The immunoglobulin specificity of the greatestbiological importance is idiotypic specificity pertaining to the nature of the antigen binding sites (paratopes).The specific antigenic determinants on the paratope are called idiotopes. The sun total of idiotopes on an Ig molecule constitutes its idiotype. By immunisation with Fab fragments, anti-idiotypic antibodies can be produced. These resemble the epitopes of the original antigen. Used as a vaccine, theseshow protection against the original antigen (pathogen or tumour) in experimental animals. Sequential anti- idiotypic antibody formation is the basis of Jerne's network hypothesis of immune regulation.Immunoglobulins exhibit other geneticallydetermined specificities based on their antigenic structure. The antigenic specificities which distinguish between the different classes and subclasses of immunoglobulins present in all normal individuals of a given species are termed isotypic specificities. Antigenicspecificities which distinguish immunoglobulins of the same class, between different groups of individuals inthe same species, are called allotypic specificities. Immunoglobulin allotypes have been studied in detail in the rabbit and guinea pig by using type-specific immunesera. Such deliberate immunisation is not possible in human beings, but anti isotype-specific antibodies may develop following blood transfusion or passage of maternalIgG into the fetus. Anti Allotypic antibodies are also found in sera containing rheumatoid arthritis factor'Two allotypic systems are known in humans: the Gm system (for gamma marker) and the InV system (abbreviation of patient's name). Gm is associated with the Fc portion of the IgG heavy chain. More than 25 Gm types have been identified so far. The InV system is associated with the kappa light chain and so has been renamed Km. Three Km allotypes have been identified.Genetic markers associated with IgA are called 'Am. To date, in the human system no allotypic markers have been found for lambda light chains or u, dor e heavy chains.
GENERAL FEATURES OF ANTIGEN ANTIBODY REACTIONS
Antigen-antibody reactions have the following general characteristics:1. The reaction is specific, an antigen combining only with its homologous antibody and vice versa The specificity, however, is not absolute and cross reactions' may occur due to antigenic similarity or relatedness.2. Entire molecules and not fragments react. When an antigenic determinant present in a large molecule or on a 'carrier' particle reacts with its antibody, whole molecules or particles are agglutinated.3. There is no denaturation of the antigen or theantibody during the reaction.4. The combination occurs at the surface. Therefore, it is the surface antigens that are immunologically relevant. Antibodies to the surface antigens of infectious agents are generally protective.5. The combination is firm but reversible. The firmness of the union is influenced by the affinity and avidity of the reaction. Affinity refers to the intensity of attraction between the antigen and antibody molecules. It is a function of the closeness of fit between an epitope and the antigen combining region of its antibody. Avidity is the strength of the bond after the formation of the antigen-antibody complexes. It reflects the overall combining propertyof the various antibody molecules in an antiserum,possessing different affinity constants with the multiple epitopes of the antigen.6. Both antigens and antibodies participate in the formation of agglutination or precipitates.7. Antigens and antibodies can combine in varying proportions, unlike chemicals with fixed valencies. Both antigens and antibodies are multivalent. Antibodies are generally bivalent, though IgM molecules may have five or ten combining sites.Antigens may have valencies up to hundreds.
MEASUREMENT OF ANTIGEN AND ANTIBODY
Many methods are available for the measurement of antigens and antibodies participating in the primary, secondary or tertiary reactions. Measurement may bein terms of mass (for example, mg nitrogen) or more commonly as units or titre. The antibody titre of a serum is the highest dilution of the serum that shows an observable reaction with the antigen in the particular test. The titre of a serum is influenced by the nature and quantity of the antigen and the type and conditionsof the test. Antigens may also be titrated against sera.Two important parameters of serological tests are sensitivity and specificity. Sensitivity refers to the ability of the test to detect even very minute quantities of antigen or antibody. When a test is highly sensitive, false negative results will be absent or minimal. Specificity refers to the ability of the test to detect reactions between homologous antigens andantibodies only, and with no other. In a highlyspecific test, false positive reactions are absent or minimal.In general, sensitivity and specificity of a test arein inverse proportion.Originally, reagents for serological tests wereprepared by individual laboratories, leading to batch variation, and lack of reproducibility and comparability.The commercial availability of readymade standardised test kits has simplified test procedures, improved quality and greatly enlarged their scope and use.
IMMUNODIFFUSION
Immunodiffusion (Precipitation in gel): There are several advantages in allowing precipitation to occur in a gel rather than in a liquid medium. The reaction is visible as a distinct band of precipitation, which is stable and can be stained for preservation, if necessary.As each antigen-antibody reaction gives rise to a line of precipitation, the number of different antigens in the reacting mixture can be readily observed.Immunodiffusion also indicates identity, cross-reaction and non identity between different antigens. Immunodiffusion is usually performed in a soft (1%) agar or agarose gel. Different modifications of the testare available:1. Single diffusion in one dimension (Oudin procedure): The antibody is incorporated in agar gel in a test tube and the antigen solution is layered over it. The antigen diffuses downward through the agar gel, forming a lineof precipitation that appears to move downwards. This is due to the precipitation formed at the advancing frontof the antigen, and is dissolved as the concentration of antigen at the site increases due to diffusion. The number of bands indicates the number of differentantigens present.2. Double Diffusion in one dimension (Oakley-Fulthorpe procedure): Here, the antibody is incorporated in gel, above which is placed a column of plain agar.The antigen is layered on top of this. The antigen and antibody move towards each other through the intervening column of plain agar and form a band of precipitate where they meet at optimum proportion.3. Single diffusion in two dimensions (Radialimmunodiffusion): Here the antiserum isincorporated in agar gel poured on a flat surface (slide or Petri dish). The antigen is added to the wells cut on the surface of the gel. It diffuses radially from the well and forms ring-shaped bands of precipitation (halos) concentrically around the well. The diameter of the halo gives an estimate of theconcentration of the antigen. This method has been employed for the estimation of the immunoglobulin classes in sera and for screening sera for antibodies to influenza viruses, among others.4. Double diffusion in two dimensions (Ouchterlony procedure): This is the immunodiffusion method most widely employed and helps to compare differentantigens and antisera directly. Agar gel is poured on a slide and wells are cut using a template. The antiserum is placed in the central well and different antigens in the surrounding wells. If two adjacent antigens are identical, the lines of precipitate formed by them will fuse. If they are unrelated, the lines will cross each other. Cross-reaction or partial identityis indicated by spur formation (Fig. 13.3). A special variety of double diffusion in two dimensions is the Elek test for toxigenicity in diphtheria bacilli. When diphtheria bacilli are streaked at right angles to a filter paper strip carrying the antitoxin implanted on a plate of suitable medium, arrowhead-shaped linesof precipitation appear on incubation, if the bacillus is toxigenic.5. Immunoelectrophoresis: The resolving power of immunodiffusion was greatly enhanced when Grabar and Williams devised the technique of immunoelectrophoresis. This involves the electrophoretic separation of a composite antigen (such as serum) into its constituent proteins, followed by immunodiffusion against its antiserum,resulting in separate precipitin lines, indicatingreaction between each individual protein with its antibody. This enables identification and approximate quantitation of the various proteins present in the serum. The technique is performed on agar or agarose gel on a slide, with an antigen well and an antibody trough cut on it. The test serum is placedin the antigen well and electrophoresed for about an hour. Antibody against human serum is then placed in the trough and diffusion allowed to proceed for 18-24 hours. The resulting precipitin lines can be photographed and the slides dried, stained and preserved for record. Over 30 different proteins can be identified by this method in human serum. This is useful for testing for normal and abnormal proteins in serum and urine.
OPSONISATION
The name 'opsonin' was originally given by Wright (1903) to a heat labile substance present in fresh normal sera, which facilitated phagocytosis. This factor was subsequently identified as a complement.A heat stable serum factor with similar activity was called "bacteriotropin'. This appears to be a specific antibody. The term opsonin is now generally used to refer to both these factors.Wright used the 'opsonic index' to study the progress of resistance during the course of diseases. The opsonic index was defined as the ratio of the phagocytic activityof the patient's blood for a given bacterium, to the phagocytic activity of blood from a normal individual.It was measured by incubating fresh citrated blood with the bacterial suspension at 37 °C for 15 minutes and estimating the average number of phagocytosed bacteria per polymorphonuclear leukocytes (phagocytic index) from stained blood films.
RADIOIMMUNOESSAY
Besides fluorescent dyes, many other distinctive Labels also can be conjugated to antigens and antibodies.The most commonly used labels are radioisotopes and enzymes. A variety of tests have been devised for themeasurement of antigens and antibodies using such labeled reactant. The term binder-ligand-assay has been used for these reactions. The substance (antigen) whose concentration is to be determined is termed the analyte or ligand. The binding protein (ordinarily, the antibody) which binds to the land is called the binderThe first reaction of this type was radioimmunoassay (RIA) described by Benson and Yalow in 1939 RIA (108 ) quantities. RIA and its modifications have permits the measurement of analytes up to picogramversatile applications in various areas of biology and medicine, including the quantitation of hormones drugs, tumour markers, IgE and viral ang The importance of RIA was acknowledged when the Nobel Prize was awarded to Yallow for its discoveryin 1977.RIA is a competitive binding assay in which fined amounts of antibody and radiolabeled antigen in the presence of unlabeled antigen. The labeled and unlabeled antigens compete for the limited binding sites on the antibody. This competition is determined by the level of the unlabeled test) antigen presentthe reacting system. After the reaction, the antigen separated into free and bound fractions and the radioactive counts measured. The concentration the test antigen can be calculated from the ratio of thebound and total antigen labels, using a standard dose response curveFor any reacting system, the standard dose response or calibration curve has to be prepared first. This is done by running the reaction with fixed amount of antibodyand labeled antigen, and carving known amounts of unlabeled antigen. The ratio of bound: total labels (8:T ratio) plotted against the analyte concentrations give the standard calibration curve. The concentration of antigen in the test sample is computed from theBT ratio of the test by interpolation from thecalibration curve.
IMMUNOPRECIPITATION
The immunoprecipitation technique has the advantage of allowing the isolation of the antigen of interest for further analysis. It also provides a sensitive assay for the presence of aparticular antigen in a given cell or tissue type. An extract produced by disruption of cells or tissues is mixed with an antibody against the antigen of interest in order to form an antigen-antibody complex that will precipitate. However, if the antigen concentration is low (often the case in cell and tissue extracts), the assembly of antigen-antibody complexes into precipitates can take hours, even days, and it is difficult to isolate the small amount of immuno precipitate that forms. Fortunately, there are a number of ways to avoid these limitations. One is to attach the antibody to a solid support,such as a synthetic bead, which allows the antigen-antibody complex to be collected by centrifugation. Another is to adda secondary antibody specific for the primary antibody to bind the antigen-antibody complexes. If the secondary antibody is attached to a bead, the immune complexes can be collected by centrifugation. A particularly ingenious version of this procedure involves the coupling of the secondary antibody to magnetic beads. After the secondary antibody binds to the primary antibody, immunoprecipitates are collected by placing a magnet against the side of the tubeWhen used in conjunction with biosynthetic radioisotope labeling, immunoprecipitation can also be used to determine whether a particular antigen is actually synthesized by a caltor tissue. Radiolabeling of proteins synthesized by cells of interest can be done by growing the cells in cell-culture medium containing one or more radiolabeled amino acids.Generally, the amino acids used for this application are those most resistant to metabolic modification, such as leucine.cysteine, or methionine. After growth in the radioactive medium, the cells are lysed and subjected to a primary antibody specific for the antigen of interest. The Ag-Ab complexis collected by immunoprecipitation, washed free of union corporated radiolabeled amino acid and other impurities, and then analyzed. The complex can be counted in a scintillation counter to obtain a quantitative determination of the amount of the protein synthesized. Further analysis often involves disruption of the complex, usually by use of SDS and heat, so that the identity of the immunoprecipitated antigencan be confirmed by checking that its molecular weight is that expected for the antigen of interest. This is done by separation of the disrupted complex by SDS-PAGE and subsequent autoradiography to determine the position of the radiolabeled antigen on the gel.
How to Develop a Healthy Immune System
Take a look at some of the steps that will help you develop a healthier immune system:1. Stay HydratedSome common effects of dehydration include headaches, loss of strength, and exhaustion. Make sure you hydrate so that your organs and body systems continue to function properly.2. Eat Foods Rich in Fiber and ProteinKeep track of the foods you’re consuming. Choose oats and other foods high in fiber for better digestion and incorporate fruits high in vitamins and nutrients.3. Get Enough SleepSleep deprivation can lead to a host of conditions like high blood pressure, diabetes, and other serious conditions. See to it that you get at least seven hours of sleep at night. 4. Engage in Fitness ActivitiesExercise isn’t just for people wanting to shed extra pounds. Overall, exercise helps improve heart health and blood circulation. It also helps reduce stress levels which can also be a cause of other ailments.5. Take ShowersWant to relieve the pain of sore muscles after a workout? A cold shower will do the trick. Do you have a blocked nose and want to clear your nasal passages? In that case, a hot shower will help.Adjusting water temperatures is easy with a water heater. Read the Titan SCR2 N-120 Electric Tankless Water Heater Review form this website to find out if this is the right water heater for your home.
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