Tamilnadu Board Class 12 Zoology Chapter 8 - Cdn1.byjus
8UNIT - IIIIMMUNOLOGYCHAPTERChapter outline8.1 Basic concepts of immunology8.2 Innate immunity8.3 Acquired immunity8.4 Immune responses8.5 Lymphoid organs8.6 Antigens8.7 Antibodies8.8 Antigen- antibody interactions8.9 Vaccines8.10 Vaccination and immunization8.11 Hypersensitivity8.12 Immunodeficiency diseases8.13 Autoimmune diseases8.14 Tumour immunologyLearning objectives Understands the basicconcepts of immunology. Differentiates betweeninnate immunity andacquired immunity,primary immune responseand secondary immuneresponse, active and passive immunity. Realizes the importance of immunization. Learns to comphrend the concept ofhypersensitivity.Natural forces within us are the true healers ofdisease- HippocratesIn the previous chapter, we have studied indetail the various infections which causediseases in human beings. In this chapter, weshall discuss how our body protects us fromthese infections by the effective mechanism ofthe immune system.8.1 Basic concepts of immunologyImmunology is the study of immunesystem. This system protects an indvidualfrom various infective agents. It refers toall the mechanisms used by the body forprotection from environmental agents thatare foreign to the body.When the immune system does notfunction efficiently in an individual, it leads toinfection causing disease. The overall abilityof body to fight against the disease causingpathogen is called immunity. It is also calleddisease resistance and the lack of immunityis known as susceptibility. Immunity is highlyspecific.Normally many of the responses of theimmune system initiate the destruction andelimination of invading organisms and anytoxic molecules produced by them. Theseimmune reactions are destructive in natureand are made in response only to molecules136TN GOVT XII Zoology chapter 8.indd 13625-02-2019 20:06:07
that are foreign to the host and not to those ofhost itself. This ability to distinguish foreignmolecules from self is another fundamentalfeature of the immune system. However,occasionally, it fails to make its distinctionand reacts destructively against the host'sown molecules; such autoimmune diseasescan be fatal to the organism.Almost all the macromolecules e.g.proteins, polysaccharides, nucleic acids,etc., as long as they are foreign to recipientorganism can induce immune response.Any substance capable of eliciting immuneresponse is called an ANTIGEN (ANTIbodyGENerator). There are two broad classes ofimmunity responses namely, innate immunityand acquired immunity (Fig. (immunization)Passive(antobodytransfer)Fig. 8.1 Immune system8.2 Innate immunityInnate immunity is the naturalphenomenon of resistance to infection whichan individual possesses right from the birth.Table 8.1 Innate immunity- types and mechanismsType of innate immunityMechanism1. Anatomical barriersSkinPrevents the entry of microbes.Its acidic environment (pH 3-5) retards the growth of microbes.Mucus membraneMucus entraps foreign microorganisms and competes with microbesfor attachment.2. Physiological barriersTemperatureNormal body temperature inhibits the growth of pathogens.Fever also inhibits the growth of pathogens.Low pHAcidity of gastric secretions (HCl) kills most ingested microbes.Chemical mediatorsLysozyme acts as antibacterial agent and cleaves the bacterial cell wall.Interferons induce antiviral state in the uninfected cells.Complementary substances produced from leucocytes lyse thepathogenic microbes or facilitate phagocytosis.3. Phagocytic barriersSpecialized cells (Monocytes, neutrophils, tissue macrophages)phagocytose, and digest whole microorganisms.4. Inflammatory barriersTissue damage and infection induce leakage of vascular fluid,containing chemotactic signals like serotonin, histamine andprostaglandins. They influx the phagocytic cells into the affected area.This phenomenon is called diapedesis.137TN GOVT XII Zoology chapter 8.indd 137Immunology25-02-2019 20:06:07
The innate defense mechanisms are non-specificin the sense that they are effective against awide range of potentially infectious agents. It isotherwise known as non-specific immunity ornatural immunity.as cell mediated immune response or cellmediated immunity. This is brought about by Tcells, macrophages and natural killer cells.A number of innate defense mechanisms areoperative non-specifically against a large numberof microorganisms as shown in the Table 8.1 andFig. 8.2.When pathogens are destroyed by theproduction of antibodies, then it is knownas antibody mediated or humoral immunity.This is brought about by B cells with the helpof antigen presenting cells and T helper cells.Antibody production is the characteristicfeature of vertebrates only.Lysozyme in tearsRemoval of ical barrierRapid pH changeFlushing ofurinary tractLow pHof vaginaFig. 8.2 Various anatomical and physiologicalbarriers to microbial attack8.3 Acquired immunityThe immunity that an individual acquiresafter birth is known as acquired immunity.It is the body's resistance to a specific pathogen.The unique features of acquired immunityare antigenic specificity, diversity, recognition ofself and non-self and immunological memory.Components of acquired immunity2. Antibody mediated immunity or humoralimmunityTypes of acquired immunityAcquired immunity may be activeimmunity or passive immunity (Table 8.2).The immunological resistance developedby the organisms through the productionof antibodies in their body is called activeimmunity. Active immunity is acquired throughthe use of a person’s immune responses, whichlead to the development of memory cells.Active immunity results from an infection or animmunization.Passive immunity does not require thebody to produce antibodies to antigens. Theantibodies are introduced from outside into theorganism. Thus, passive immunity is acquiredwithout the activation of a person’s immuneresponse, and therefore there is no memory.The process of productionof blood cells in thebone marrow is calledhaematopoiesis.8.4 Immune responsesAcquired immunity has two components –cell mediated immunity (CMI) and antibodymediated immunity or humoral immunity.The immune responses may be primaryor secondary (Table 8.3).1. Cell mediated immunityPrimary immune responseWhen pathogens are destroyed by cellswithout producing antibodies, then it is knownThe primary immune response occurswhen a pathogen comes in contact with theImmunologyTN GOVT XII Zoology chapter 8.indd 13813825-02-2019 20:06:07
Table 8.2 Differences between active and passive immunitySl.NoActive ImmunityPassive Immunity1Active immunity is produced actively byhost’s immune system.Passive immunity is received passively andthere is no active host participation.2It is produced due to contact with pathogenor by its antigen.It is produced due to antibodies obtainedfrom outside.3It is durable and effective in protection.It is transient and less effective.4Immunological memory is present.No memory.5Booster effect on subsequent dose ispossible.Subsequent dose is less effective.6Immunity is effective only after a shortperiod.Immunity develops immediately.immune system for the first time. Duringthis, the immune system has to learn torecognize the antigen, produce antibodyagainst it and eventually produce memorylymphocytes. The primary immune responseis slow and short-lived.Within hours after recognition of the antigen, anew army of plasma cells are generated. Within2 to 3 days, the antibody concentration in theblood rises steeply to reach much higher levelthan primary response. This is also called as“booster response”.Secondary immune response8.5 Lymphoid organsThe secondary immune response occurswhen a person is exposed to the same antigenagain. During this time, immunological memoryhas been established and the immune systemcan start producing antibodies immediately.Immune system of an organism consists ofseveral structurally and functionally differentorgans and tissues that are widely dispersedin the body. The organs involved in the origin,maturation and proliferation of lymphocytesare called lymphoid organs (Fig. 8.3). Based onTable 8.3 Differences between primary and secondary immune responsesSl.NoPrimary Immune ResponseSecondary Immune Response1It occurs as a result of primary contactwith an antigen.It occurs as a result of second andsubsequent contacts with the sameantigen.2Antibody level reaches peak in 7 to 10days.Antibody level reaches peak in 3 to 5days.3Prolonged period is required to establishimmunity.It establishes immunity in a short time.4There is rapid decline in antibody level.Antibody level remains high for longerperiod.5It appears mainly in the lymph nodesand spleen.It appears mainly in the bone marrow,followed by the spleen and lymph nodes.139TN GOVT XII Zoology chapter 8.indd 139Immunology25-02-2019 20:06:07
Primary lymphoid organsBursa of Fabricius of birds, bone marrowand thymus gland of mammals constitutethe primary lymphoid organs involvedin the production and early selection oflymphocytes. These lymphocytes becomededicated to a particular antigenic specificity.Only when the lymphocytes mature in theprimary lymphoidal organs, they becomeimmunocompetent cells. In mammals, B cellmaturation occurs in the bone marrow andT cells maturation occurs in the thymus.ThymusFig. 8.3 Lymphoid organs in human bodytheir functions, they are classified into primaryor central lymphoid organs and secondaryor peripheral lymphoid organs. The primarylymphoidorgansprovideappropriateenvironment for lymphocytic maturation. Thesecondary lymphoid organs trap antigens andmake it available for mature lymphocytes, whichcan effectively fight against these antigens.The thymus is a flat and bilobed organlocated behind the sternun, above the heart.Each lobe of the thymus contains numerouslobules, separated from each other byconnective tissue called septa. Each lobuleis differentiated into two compartments,the outer compartment or outer cortex, isdensely packed with immature T cells calledthymocytes, whereas the inner compartmentor medulla is sparsely populated withthymocytes. One of its main secretions is thehormone thymosin. It stimulates the T cell tobecome mature and immunocompetent. Bythe early teens, the thymus begins to atrophyand is replaced by adipose tissue (Fig. 8.4).Thus thymus is most active during theneonatal and pre-adolescent periods.7K\URLGJODQG7UDFKHD5LJKW OREH/HIW OREH7K\PXV6HSWDH/REXOH Bursa of Fabricius is a primary lymphoid organof birds. It is attached to the dorsal side of thecloaca. B lymphocytes mature in the bursa andbring about humoral immunity.ImmunologyTN GOVT XII Zoology chapter 8.indd 140%/XQJV HDUWFig. 8.4 Primary lymphoid organ - ThymusA) Location B) Structure14025-02-2019 20:06:07
Bone marrowBone marrow is a lymphoid tissue foundwithin the spongy portion of the bone.Bone marrow contains stem cells known ashaematopoietic cells. These cells have thepotential to multiply through cell divisionand either remain as stem cells or differentiateand mature into different kinds of blood cells.Secondary or peripheral lymphoidorgansIn secondary or peripheral lymphoidorgans, antigen is localized so that it can beeffectively exposed to mature lymphocytes.The best examples are lymph nodes,appendix, Peyer’s patches of gastrointestinaltract, tonsils, adenoids, spleen, MALT(Mucosal-Associated Lymphoid Tissue),GALT (Gut-Associated Lymphoid Tissue),BALT (Bronchial/Tracheal-AssociatedLymphoid Tissue).Peyer’s patches are oval-shapedareas of thickened tissue that areembedded in the mucus-secreting liningof the small intestine of humans andother vertebrate animals. Peyer’s patchescontain a variety of immune cells,including macrophages, dendritic cells,T cells, and B cells.The tonsils (palatine tonsils) area pair of soft tissue masses located atthe back of the throat (pharynx). Thetonsils are part of the lymphatic system,which help to fight infections. They stopinvading germs including bacteria andviruses.Spleen is a secondary lymphoidorgan located in the upper part of theabdominal cavity close to the diaphragm.Spleen contains B and T cells. It bringshumoral and cell mediated immunity.The adenoids are glandslocated in the roof ofthe mouth, behind thesoft palate where thenose connects to thethroat. The adenoids produce antibodiesthat help to fight infections. Typically,the adenoids shrink during adolescenceand may disappear by adulthood.Lymph nodeLymph node is a small bean-shapedstructure and is part of the body’s immunesystem. It is the first one to encounterthe antigen that enters the tissue spaces.Lymph nodes filter and trap substances thattravel through the lymphatic fluid. Theyare packed tightly with white blood cells,namely lymphocytes and macrophages.There are hundreds of lymph nodes foundthroughout the body. They are connectedto one another by lymph vessels. Lymph isa clear, transparent, colourless, mobile andextracellular fluid connective tissue. As thelymph percolates through the lymph node,the particulate antigen brought in by thelymph will be trapped by the phagocytic cells,follicular and interdigitating dendritic cells.Afferent lymphatic vesselSinusesMantle zoneFollicleCortexParacortexMedullarycordsEfferent lymphatic vesselFig. 8.5 Secondary lymphoid organ –Structure of lymph node141TN GOVT XII Zoology chapter 8.indd 141Immunology25-02-2019 20:06:08
Lymph node has three zones (Fig. 8.5).They are the cortex, paracortex and medulla.The outer most layer of the lymph node iscalled cortex, which consists of B-lymphocytes,macrophages, and follicular dendritic cells.The paracortex zone is beneath the cortex,which is richly populated by T lymphocytesand interdigitating dendritic cells. The innermost zone is called the medulla which issparsely populated by lymphocytes, but manyof them are plasma cells, which activelysecrete antibody molecules. As the lymphenters, it slowly percolates through the cortex,paracortex and medulla, giving sufficientchance for the phagocytic cells and dendriticcells to trap the antigen brought by the lymph.The lymph leaving a node carries enrichedantibodies secreted by the medullary plasmacells against the antigens that enter the lymphnode. Sometimes visible swelling of lymphnodes occurs due to active immune responseand increased concentration of lymphocytes.Thus swollen lymph nodes may signal aninfection. There are several groups of lymphnodes. The most frequently enlarged lymphnodes are found in the neck, under the chin, inthe armpits and in the groin.Cells of the immune systemThe immune system is composed of manyinterdependent cells that protect the body frommicrobial infections and the growth of tumourcells. The cellular composition of adult humanblood is given in Table 8.4.Table 8.4 The cellular composition of adulthuman bloodCell typeThe mucosa-associated lymphoidtissue (MALT) is a diffuse system ofsmall concentrations of lymphoid tissuein the alimentary, respiratory and urinogenital tracts. MALT is populated bylymphocytes such as T and B cells, as wellas plasma cells and macrophages, eachof which is well situated to encounterantigens passing through the mucosalepithelium.Gut-associated lymphoid tissue(GALT) is a component of the mucosaassociated lymphoid tissue (MALT)which works in the immune system toprotect the body from invasion in the gut.Bronchus Associated LymphoidTissues (BALT) also a component ofMALT is made of lymphoid tissue(tonsils, lymph nodes, lymph follicles) isfound in the respiratory mucosae fromthe nasal cavities to the lungs.ImmunologyTN GOVT XII Zoology chapter 8.indd 142Red blood cellsNumber ofcells per µl4200,000 6500,000Approximatepercentage-White blood cellsAgranulocytesLymphocytes1500 - 400020-30Monocytes200 - 9502-7Neutrophils2000-700050-70Basophils50-100 00,000-All these cells are derived from pluripotenthaematopoetic stem cells. Each stem cell has thecapacity to produce RBC, WBC and platelets.14225-02-2019 20:06:08
The only cells capable of specifically recognisingand producing an immune response are thelymphocytes. The other types of white blood cellsplay an important role in non specific immuneresponse, antigen presentation and cytokineproduction.LymphocytesAbout 20-30% of the white blood cells arelymphocytes. They have a large nucleus fillingmost of the cell, surrounded by a little cytoplasm.The two main types of lymphocytes are B andT lymphocytes. Both these are produced in thebone marrow. B lymphocytes (B cells) stay in thebone marrow until they are mature. Then theycirculate around the body. Some remain in theblood, while others accumulate in the lymphnodes and spleen. T lymphocytes leave the bonemarrow and mature in the thymus gland. Oncemature, T cells also accumulate in the same areasof the body as B cells. Lymphocytes have receptorproteins on their surface. When receptors on aB cell bind with an antigen, the B cell becomesactivated and divides rapidly to produce plasmacells. The plasma cells produce antibodies. SomeB cells do not produce antibodies but becomememory cells. These cells are responsible forsecondary immune response. T lymphocytes donot produce antibodies. They recognize antigenpresenting cells and destroy them. The twoimportant types of T cells are Helper T cells andKiller T cells. Helper T cells release a chemicalcalled cytokine which activates B cells. Killercells move around the body and destroy cellswhich are damaged or infected (Fig. 8.6).Apart from these cells neutrophils andmonocytes destroy foreign cells by phagocytosis.Monocytes when they mature into large cells,they are called macrophages which performphagocytosis on any foreign organism.Dendritic cells are called so becauseits covered with long, thin membraneextensions that resemble dendrites of nervecells. These cells present the antigen toT-helper cells. Four types of dendritic cellsare known. They are langerhans, interstitialcells, myeloid and lymphoid cellsFig. 8.6 Cells of the immune system143TN GOVT XII Zoology chapter 8.indd 143Immunology25-02-2019 20:06:08
8.6 AntigensThe term antigen (Ag) is used in twosenses, the first to describe a molecule whichgenerates an immune response and the second,a molecule which reacts with antibodies. Ingeneral antigens are large, complex molecularsubstances that can induce a detectable immuneresponse. Thus an antigen is a substance that isspecific to an antibody or a T-cell receptor andis often used as a synonym for immunogen.The histocompatibilityantigens are cell surfaceantigens that induce animmune response leadingto rejection of allografts.An immunogen is a substance capable ofinitiating an immune response. Haptens aresubstance that are non-immunogenic but can reactwith the products of a specific immune response.Substances that can enhance the immuneresponse to an antigen are called adjuvants.Epitope is an antigenic determinant and is theactive part of an antigen. A paratope is the antigen– binding site and is a part of an antibody whichrecognizes and binds to an antigen.Antigenicity is the propertyof a substance (antigen)that allows it to react withthe products of the specificimmune response.Types of antigensOn the basis of origin, antigens areclassified into exogenous antigens andendogenous antigens.The antigens which enter the host from theoutside in the form of microorganisms, pollens,drugs, or pollutants are called exogenousantigens. The antigens which are formed withinthe individual are endogenous antigens. Thebest examples are blood group antigens.ImmunologyTN GOVT XII Zoology chapter 8.indd 1448.7 AntibodiesAntibodies are immunoglobulin (Ig)protein molecules synthesized on exposureto antigen that can combine specifically withthe antigen. Whenever pathogens enter ourbody, the B-lymphocytes produce an armyof proteins called antibodies to fight withthem. Thus, they are secreted in response toan antigen (Ag) by the effect of B cells calledplasma cells. The antibodies are classifiedinto five major categories, based on theirphysiological and biochemical properties.They are IgG (gamma), IgM (mu), IgA(alpha), IgD (delta) and IgE (epsilon).In the 1950s, experiments by Porter andEdelman revealed the basic structure of theimmunoglobulin. An antibody moleculeis Y shaped structure that comprises offour polypeptide chains, two identical lightchains (L) of molecular weight 25,000 Da(approximately 214 amino acids) and twoidentical heavy chains (H) of molecularweight 50,000 Da (approximately 450 aminoacids). The polypeptide chains are linkedtogether by di-sulphide (S-S) bonds. Onelight chain is attached to each heavy chainand two heavy chains are attached to eachother to form a Y shaped (Fig. 8.7) structure.Hence, an antibody is represented by H2 L2.The heavy chains have a flexible hinge regionat their approximate middles.Antigen bindingsiteVariableregionLight chainDisulphidebondHeavy chainConstantregionFig. 8.7 Structure of immunoglobulin14425-02-2019 20:06:08
Each chain (L and H) has two terminals. They areC - terminal (Carboxyl) and amino or N-terminal.Each chain (L and H) has two regions. They havevariable (V) region at one end and a much largerconstant (C) region at the other end. Antibodiesresponding to different antigens have very different(V) regions but their (C) regions are the samein all antibodies. In each arm of the monomerantibody, the (V) regions of the heavy and lightchains combines to form an antigen – binding siteshaped to ‘fit’ a specific antigenic determinant.Consequently each antibody monomer has twosuch antigen – binding regions. The (C) regionsthat forms the stem of the antibody monomerdetermine the antibody class and serve commonfunctions in all antibodies.When antigen and antibody are closelyfitted, the strength of binding is great. Whenthey are apart binding strength is low.The bondsthat hold the antigen to the antibody combiningsite are all non-covalent in nature. Theseinclude hydrogen bonds, electrostatic bonds,Van der Waals forces and hydrophobic bonds.Antibody affinity is the strength of the reactionbetween a single antigenic determinant and asingle combining site on the antibody.The functions of immunoglobulin areagglutination, precipitation, opsonisation,neutralization etc.,The chief application of antigen - antibodyreactions are to determine blood groups fortransfusion, to study serological ascertainmentof exposure to infectious agents, to developimmunoassays for the quantification of varioussubstances, to detect the presence or absenceof protein in serum and to determine thecharacteristics of certain immunodeficiencydiseases.8.8 Antigen andantibody interactionDifferent types of antigen and antibodyreactionsThe reaction betweenan antigen and antibodyis the basis for humoralimmunity or antibodymediated immunity. Thereaction between antigenand antibody occurs inthree stages. During the first stage, the reactioninvolves the formation of antigen - antibodycomplex. The next stage leads to visible eventslike precipitation, agglutination, etc., The finalstage includes destruction of antigen or itsneutralization (Fig. 8.8).Binding force of antigen - antibodyreactionThe binding force between antigen andantibody is due to three factors. They arecloseness between antigen and antibody, noncovalent bonds or intermolecular forces andaffinity of antibody.The reaction between soluble antigenand antibody leads to visible precipitateformation, which is called precipitin reaction.Antibodies that bring about precipitateformation on reacting with antigens are calledas precipitins.Whenever a particulate antigen interactswith its antibody, it would result in clumping oragglutination of the particulate antigen, whichis called agglutination reaction. The antibodyinvolved in bringing about agglutinationreaction is called agglutinin.Opsonisation or enhanced attachmentis the process by which a pathogen is markedof ingestion and destruction by a phagocyte.Opsonisation involves the binding of anopsonin i.e., antibody, to a receptor on thepathogen’s cell membrane. After opsoninbinds to the membrane, phagocytes areattracted to the pathogen. So, opsonisation isa process in which pathogens are coated with145TN GOVT XII Zoology chapter 8.indd 145Immunology25-02-2019 20:06:08
Antigen and Antibody interactionsNeutralisation(Exotoxin, toxoid)Agglutination(Particulate antigen)Precipitation(Soluble antigen)Complement lesBacteriumForeign cellHoleLeads toEnhancesCell rophageFig. 8.8 Antigen and antibody reactiona substance called an opsonin, marking thepathogen out for destruction by the immunesystem. This results in a much more efficientphagocytosis.The neutralization reactions are thereactions of antigen-antibody that involve theelimination of harmful effects of bacterialexotoxins or a virus by specific antibodies.These neutralizing substances i.e., antibodiesare known as antitoxins. This specificantibody is produced by a host cell in responseto a bacterial exotoxin or correspondingtoxoid (inactivated toxin).8. 9 VaccinesA vaccine is a biological preparationthat provides active acquired immunityto a particular disease and resembles thogenicform (vaccine)Live attenuated vaccineNatural live nKilled pathogens(vaccine)ToxinToxoid(vaccine)Fig. 8.9 Types of vaccinesImmunologyTN GOVT XII Zoology chapter 8.indd 14614625-02-2019 20:06:08
disease-causing microorganism and isoften made from weakened or attenuatedor killed forms of the microbes, theirtoxins, or one of its surface proteins.Vaccines “teach” our body how to defenditself when viruses or bacteria, invade it.Vaccines deliver only very little amounts ofinactivated or weakened viruses or bacteria,or parts of them. This allows the immunesystem to recognize the organism withoutactually experiencing the disease. Somevaccines need to be given more than once(i.e., a ‘booster’ vaccination) to make surethe immune system can overcome a realinfection in the future.Vaccine initiates the immunizationprocess. The vaccines are classified as first,second and third generation vaccines.First generation vaccine is furthersubdivided into live attenuated vaccine,killed vaccine and toxoids (Fig. 8.9). Liveattenuated vaccines use the weakened(attenuated), aged, less virulent formof the virus. E.g. Measles, mumps andrubella (MMR) vaccine and the Varicella(chickenpox) vaccine, Killed (inactivated)vaccines are killed or inactivated by heatand other methods. E.g. Salk’s polio vaccine.Toxoid vaccines contain a toxin or chemicalsecreted by the bacteria or virus. They makeus immune to the harmful effects of theinfection, instead of to the infection itself.E.g. DPT vaccine (Diphtheria, Pertussisand Tetanus).Second generation vaccine containsthe pure surface antigen of the pathogen.E.g.Hepatitis-B vaccine. Third generationvaccine contains the purest and the highestpotency vaccines which are synthetic ingeneration. The latest revolution in vaccine isDNA vaccine or recombinant vaccine (ReferChapter- 10 for details).Vaccino therapy is themethod of use of vaccinefor treatment of disease.Dr.EdwardJennerprepared first vaccinefor small pox in 1796. Polio vaccine wasdeveloped by Dr. Jonas Salk (vaccineconsists of inactivated microorganism)and Dr. Albert Sabin (live attenuatedoral polio vaccine). Louis Pasteur (1885)discovered vaccine against rabies, anthraxand cholera. BCG vaccine was developedby Calmette and Guerin againsttuberculosis in France in the year 1908.8. 10 Vaccination andimmunization“Vaccination is the process ofadministrating a vaccine into the body or the actof introducing a vaccine into the body to produceimmunity to a specific disease.” Immunizationis the process of the body building up immunityto a particular disease. Immunization describesthe actual changes in the body after receiving avaccine. Vaccines work by fighting the pathogenand then recording it in their memory systemto ensure that the next time this pathogen entersthe body, it is eliminated far quickly. Once, thebody is able to fight against the disease, it isbelieved to have built the immunity for it, alsoknown as the body being immunized againstthe disease.8.11 Hypersentivity – OveractiveImmune ResponseSome of the individuals are very sensitiveto some particles present in the environment.The exaggerated response of the immune systemto certain antigens present in the environmentis called allergy (allo-altered, erg-reaction).The substances to which such an immuneresponse is produced are called allergens. An147TN GOVT XII Zoology chapter 8.indd 147Immunology25-02-2019 20:06:09
allergen is an antigen that causes an allergicreaction. Allergic reactions begin within fewseconds after the contact with the allergenand last about half an hour. The commonexamples of allergens are mites in dust, pollensand some proteins in insect venom. Hay feverand asthma are some common examples ofallergy. Symptoms of allergic reactions includesneezing, watery eyes, running nose anddifficulty in breathing. Allergy is a form of overactive immune response mediated by IgE andmast cells. It can also be due to the release ofchemicals like histamine and serotonin fromthe mast cells.Anaphylaxis is the classical immediatehypersensitivity reaction. It is a sudden, systematic,severe and immediate hypersensitivity reactionoccurring as a result of rapid generalized mast-celldegranulation.Structure of HIVThe human immunodeficiency virusbelongs to the genus Lentivirus. Whenobserved under the electron microscope,HIV is seen as a spherical virus, 100-120nm in diameter, containing a dense coresurrounded by a lipoprotein envelope.The envelope has glycoprotein (gp)spikes termed gp 41 and gp 120. At thecore, there are two large single strandedRNA. Attached to the RNA are
Active immunity is produced actively by host's immune system. Passive immunity is received passively and there is no active host participation. 2 It is produced due to contact with pathogen or by its antigen. It is produced due to antibodies obtained from outside. 3 It is durable and effective in protection. It is transient and less effective.
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