Immunity

Immunity

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  1 UNIT: IV IMMUNITY DEFINITIONS: 1) ACTIVEIMMUNITY: specific resistance to disease acquired by individual as a result of their own reaction to pathogenic microorganisms or to the products of such organisms. 2) ALLERGY: a type of antigen antibody reaction marked by an exaggerated physiological response to a substance in sensitive individuals. 3) ANAPHYLATOXIN: a complement derived peptide, c5a that causes the release of histamine from mast cells. 4) ANAPHYLAXIS: hypersensitivity following the parenteral injection of an antigen. 5) ANTIBODY: serum proteins produced by an animal in response to the antigen. 6) ANTISERUM: blood serum that contains antibodies. 7) ANTITOXIN: an antobody capable of uniting with and neutralizing a specific toxin. 8) AUTOIMMUNE DISEASE: a condition in which the body develops an immunological reaction against it on tissues. 9) HUMORAL IMMUNITY: immunity arising from the formation of specific antobodies that circulates in blood stream in response to the introduction of an antigen. 10) HYPERSENSITIVITY: an immune response that damages the body’s own tissues. 11) IMMUNE SERUM: blood serum that that contains one or more specific 12) IMMUNITY: a natural or acquired resistance to a specific disease. 13) IMMMUNIZATION: any process that develops resistance to a specific disease in a host. 14) IMMUNOGLOBULIN: any of the serum proteins such as gamma globulin, which possess antibody activity. 15) IMMUNOLOGY: the study of immunity to disease. 16) IMMUNOPROPHYLAXIS: the prevention of disease by the administration of vaccines or hyper immune sera. 17) SERODIAGNOSIS: diagnosis by observing the reaction of blood serum. 18) SEROLOGY: the branch of medical science which deals with the study of serum. 19) TOXIN: a poisonous substance such as a bacterial toxin elaborated by an organism. 20) TOXIN- antitoxin: a mixture of toxin and anti- toxin content slightly more toxin than anti- toxin. 21) TOXOID: a toxin that has been treated to destroy its toxic properties without affecting its antigenic properties. 22) VACCINATION: inoculation with biological preparation to produce immunity. 23) VACCINES: preparations of live attenuated or dead organisms which when introduced in to the body produce artificially active immunity. IMMUNITY • The term immunity refers to the resistance exhibited by the host towards infection caused by microorganisms and their products (toxins). • This is based on the property of self and non self recognition. That means immunity is carried out by the process of recognition and disposal of non self or materials that enter the body. • Immune response is the reaction of the body against any foreign antigen. • But protection against infection disease is only a part of it. INSIDE: A. IMMUNITY- DEFINIIONS AND TYPES OF IMMMUNITY B. IMMUNIZATION SHEDULE, IMMUNOPROPHYLAXIS C. HYPERSENSITIVITY AND AUTOIMMUNITY D. PRINCIPLES AND USES OF SEROLOGICAL TESTS
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  2 DEFINITION OF IMMUNITY Immunityis defined as the resistance offered by the host to toxic molecules, microorganisms and foreign cells. TYPES OF IMMUNITY • Immunity against infectious disease is 2 types: 1. Innate or Native immunity 2. Adaptive or Acquired immunity Immunity against infectious diseases Innate or Native immunity a. Non-specific B. Specific i. Species immunity i. Species immunity ii. Racial immunity ii. Racial immunity iii. Individual immunity iii. Individual immunity Adaptive or Artificial immunity a. Active immunity b. Passive immunity i. Natural i. Natural ii. Artificial ii. Artificial Innate or Native immunity a. Non-specific b. Specific i. Species immunity i. Species immunity ii. Racial immunity ii. Racial immunity iii. Individual immunity iii. Individual immunity Adaptive or Artificial immunity a. Active immunity b. Passive immunity i. Natural i. Natural ii. Artificial ii. Artificial INNATE IMMUNITY • First line of defense against infections • Not affected by prior contact with infectious microorganisms or by immunization. • Specific (resistance to particular pathogen) • Non-specific (general degree of resistance to infections) Species immunity • Example: Resistance to plant pathogens and large number of animal pathogens like rinderpest and distemper. • Mechanism- unclear but may be due to physiological and biochemical differences between the tissues of different host species • Determines whether or not a pathogen can multiply in them Total or relative refractoriness to a pathogen, shown by all members of the species. Racial immunity • High degree of resistance of Algerian sheep to anthrax. • In USA, people of African origin more susceptible than Causcasians to tuberculosis
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  3 . • Geneticresistance to Plasmodium falciparum malaria – some parts of Africa and Mediterranean coast • Hereditary abnormality ‘Sickling’ confers immunity – survival advantage in malarial environment. Within a species, different races may show differences in susceptibility to infection. Genetic in origin, by selection and inbreeding, races possess high degrees of resistance or susceptibility to various pathogens. Individual immunity • Genetic basis evident from studies on incidence of infectious disease in twins. • Ex: Homozygous twins exhibit similar degrees of resistance or susceptibility to lepromatous leprosy and tuberculosis. Mechanisms of innate immunity a. Epithelial surfaces: -Intact skin and mucosal membrane – mechanical barrier, bactericidal activity (due to high salt concentration in drying sweat, sebaceous secretions and long chain fatty acids and soaps). -Salmonella kept over glass slide ans skin at intervals. -Frequent mycotic and pyogenic infections seen in persons who immerse their hands in soap water for longer periods. - Mucosa of nose- Architecture prevents the inhaled particles entering the passage, also by mucus lining the epithelium and are swept back to the pharynx which tend to be swallowed or coughed out. Mechanisms of innate immunity a. Epithelial surfaces: (CONTINUED) -Mouth (saliva); Stomach (gastric digestive juices); Conjunctiva: flushing action of lacrimal secretion. -Tears contains lysozyme, an antibacterial agent (Fleming), also present in all tissue fluids except in CSF; -Flushing action of urine eliminates bacteria from urethra. -Spermine and zinc present in sperm has antibacterial activity. -Acidity of adult vagina due to glycogen fermentation in epithelial cells by resident acid uric lactobacilli makes it inhospitable for many infections b.Antibacterial substances in the blood & tissues: - Betalysin (thermos table) – active against anthrax and related bacilli - Basic polypeptides like Leukins and Plakins from Leukocytes and Platelets - Acidic substances like Lactic acid in tissues - Lactoperoxidase in milk - Interferon (Protection against viral infections) Mechanisms of innate immunity - Microbial antagonism: Skin and Mucus membrane has resident commensal bacterial flora which prevent colonization by pathogens. Germ free animal (Gnotobiotic animals are susceptible to all types of infections) C. Cellular factors: Phagocytes – Metchnikoff- Phagocytosis – Microphages (Polymorphonuclear leukocytes) & Macrophages (Histiocytes- wandering ameboid cells in the tissues). - Encapsulated Streptococcus pneumoniae are not phagocytosed in the presence of opsonins. - Brucella, Salmonella typhi and Lepra bacilli resist intracellular digestion and may actively multiply inside the phagocytic cells. -NK cells activated by interferons – non-specific defense against viral infections and tumors d. Inflammation e. Fever: Theraputic indication of fever was instituted in treponema pallidum infection causing Syphilis. f. Acute phase proteins: Enhance host resistance, prevent tissue injury and promote repair of inflammatory lesions. CRP, alpha-1 acid glycoprotein, serum amyloid P component, mannose binding protein, hs-crp etc. g. Toll-like receptors: Cell associated receptors in Innate immunity ADAPTIVE IMMUNITY • Also known as Acquired immunity • Antigenic specificity • Diversity • Immunological memory • Self/non-self recognition: Self-tolerance. Failure of self tolerance results in autoimmunity Types of Adaptive immunity • Active immunity • Passive immunity
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  4 Active immunity: • Functioningimmune system – B lymphocytes – Antibody production – Production of immunologically active cells. • Sets only after latent period, often there is a negative phase where measurable immunity may be lower than it was before the antigenic stimulus. Because antigen binds to specific antibody and lower its level in circulation. • Once developed, it is long-lasting, second immune response is rapid. • Bothe CMI and humoral immunity developed; Immunological memory is present. • Active immunity more effective and confers protection than passive immunization. Resistance developed by individual as a result of antigenic stimulus. Also called adaptive immunity Natural active immunity • Clinical or inapparent infection by microbe. • Patient recovered from attack of Measles develops natural active immunity. • Large proportion to poliomyelitis due to childhood infection. • Immunity is lifelong as in Chicken pox & Measles. • Influenza or common cold; short-lived, can recur. • Premunition immunity: In Syphilis, re-infection lasts only as long the original infection remains active. Once disease is cured patient is prone for spirochete infection. • But in Chancroid, caused by Hemophilus ducreyi, no effective immunity produced, re- infection common Artificial active immunity • Resistance induced by vaccines • Bacterial vaccines: Live (BCG for TB), Killed (Cholera vaccine), Subunit (Typhoid Vi antigen), Bacterial products (Tetanus toxoid). • Viral vaccines: Live (Oral polio vaccine - Sabin), Killed (Injectable polio vaccine-Salk), Subunit (Hepatitis vaccine) Artificial active immunity • Live vaccines – initiate infection without causing disease or injury. Immunity lasts for several years, but booster dose necessary. Can be administered orally or parenterally. • Killed vaccines – Less immunogenic than live vaccines. Protection lasts only for a short period. Atleast 3 doses required 1. Primary dose, 2. booster dose. Ideal route: Parenteral. May be given orally, but not effective. • Humoral antibody response following parenteral immunisation can be improved by adding ‘adjuvants’ like Aluminium phosphate. Passive immunity: • No active role from host’ immune system. No need antigenic stimulus. Preformed antibodies are administered. • No latent period. Immediately after administration, renders active protection. • No negative phase. No secondary IR. • Immunity is transient, lasting days to weeks, only till the passively transmitted antibodies are metabolised and eliminated. • Factor of Immune elimination limits the usefulness of repeated passive immunisation. • Less effective, acts immediately so it provides ‘instant immunity’ Resistance transmitted passively to a recipient in readymade form. Types of Passive immunity • Natural passive immunity • Artificial passive immunity
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  5 • Combined immunization Naturalpassive immunity • Resistance passively transferred from mother to baby. • Maternal antibodies are transmitted to baby by placenta. • Human colostrum- rich in IgA, resistant to intestinal digestion, gives protection to the neonates. • Human fetus, by 20th week starts producing IgM but still inadequate at birth. • By 3 months of age- infant acquires some immunological independence, though maternal antibodies give passive protection. • Active immunisation of mothers during pregnancy can improve the quality of passive immunity in infants. Artificial passive immunity • Resistance transferred to a recipient by administration of antibodies. • Hyperimmune serum of humans or animals • Convalescent sera and pooled human gamma globulin. • Equine hyperimmune sera such as anti- tetanic serum (ATS) prepared from hyperimmunised horses was extensively employed but now stopped due to hypersensitivity reactions and immune elimination. Artificial passive immunity • Human hyperimmune globulin such as Tetanus Immune Globulin (TIG) free from those complications and provides more lasting protection. • Animal preparations (antisera) like anti-gas gangrene, anti-venom & anti-botulinum preparations are used due to non-availability of human preparations. • Convalescent sera (Acute phase serum and serum obtained from patients recovering from infectious diseases) contains high level of specific antibody. • Pooled human gamma globulin (from healthy adults) contains antibodies against common pathogens prevalent in the region. • Convalescent sera and pooled immune globulin is used for passive immunization against some viral hepatitis A infections. • Human gamma globulin is used in treatment of patients with immunodeficiencies. • Indications: • For immediate and temporary protection in a non- immune host faced with threat of infection. • To suppress active immunity if it is injurious, for ex: rh immune globulin during delivery to prevent IR to Rhesus factor in Rh negative women with Rh positive babies. Active immunity Passive immunity a. Produced actively by the host’s immune system a. Received passively. No active host participation b. Induced by infection or by immunogen b. Readymade antibody transferred c. Durable effective protection c. Transient, less effective d. Immunity effective only after lag period d. Immediate immunity e. Immunological memory present e. No immunological memory f. Booster effect on subsequent dose f. Subsequent dose less effective g. Negative phase may occur g. No negative phase h. Not applicable in the immunodeficient h. Applicable in the immunodeficient IMMUNOPROPHYLAXIS Immunoprophylaxis is the prevention of disease by the administration of vaccines or hyper immune sera or it may be defined as the
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  6 prevention of diseaseby the production of active or passive immunity. Immunization according to who definition is the process where by a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine.immunization is of three types: Protection against infectious diseases by (immunization) acquired by the individual either passively or actively: I- Passive acquired immunity II- Ii- active acquired immunity I- PASSIVE ACQUIRED IMMUNITY Readymade ab transferred to individual giving rapid protection and short lasting immunity: A-naturally acquired passive immunity occurs when antibody are transferred from mother to fetus (igg ) or in colostrum (ig a). b- Artificially acquired passive immunity Short-term immunization by injection of antibodies, for examples: - injection of antitoxic serum for treatment of diphtheria or tetanus. - Injection of gamma globulin that are not produced by recipient's cells, to hypogammaglobulin children. II- ACTIVE ACQUIRED IMMUNITY Individual actively produces his own ab. Immunity develop slowly and long lasting due to development of immunological memory: A-natural active acquired immunity the person becomes immune as a result of previous exposure to a live pathogen B-artificially active acquired immunity a vaccine stimulates a primary response against the antigen without causing symptoms of the disease. TYPES OF IMMUNIZATION 1. Active immunisation Vaccines are preparation of live attenuated or dead organisms which when introduced in to the body produce artificially active immunity. Types of vaccine I. Live attenuated vaccines: there are the suspensions of living organisms with reduced virulence but are able to produce antibodies. A single dose include long lasting immunity and the immunity can be reinforced by subsequent booster dose. Example: bcg vaccine, oral typhoid vaccine, opv, measles vaccine, mumps vaccine, rubella vaccine, varicella vaccine. II. Inactivated or killed vaccine: in such vaccines the organism is killed by heat, formalin, phenol, alcohol or uv radiations.usually three dose of vaccines are given.generally 2nd dose is given 6th weeks after first dose and 3rd dose after 6th month of 2nd dose. Example: pertussis vaccine, plague vaccine, cholera vaccine, killed polio vaccine, hepatitis a vaccine III. Toxoids: toxoids are modified toxins that have lost toxigenicity but retain antigenecity.toxoids are usually prepared by inactivating exotoxins with formalin or heat. Examples: diphtheria toxoid vaccine, tetanus toxoid vaccine. 2. Passive immunization: it involves injection of exogenous antibody present in human or animal serum to provide immediate protection to an infection.the immunity so produced is for a limited period and short lasting till the antobodies are eliminated from the body. Three types of preparations are available for passive immunizations: 1) Pooled immunoglobulin: it is prepared from pooled normal human serum containing high levels of appropriate antobody.human normal immunoglobulin is used in short term prophylaxis against hepatitis a and measles in contacts or travelers who intend to visit countries where such disease are more prevalent. 2) Specific immunoglobulin or specific human immunoglobulin: it is prepared from the serum
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  7 of patients whoare recovering from infection or from person who have been actively immunized against a specific infection. Specific immunoglobulin are available against tetanus as human tetanus imunoglobulin,hepatitis b as human immunoglobulin,rabies human rabies immunoglobulin (hrig) 3) Homologous and hetrologous sera: antibacterial, antiviral antibodies in human serum are injected to provide temporary protection against infection. 2. Combined passive and active immunization: in some disease, passive immunization is undertaken in conjution with inactivated vaccine products in order to provide both immediate passive immunity which is tempory and slowly developing active immunity which lasts for longer periods of time. Both the preparations should be injected at different sites in a body. VACCINE SERUM Vaccine is a mixture of live orr dead germs or viruses of a particular disease. Serum is a clear, hay colored liquid which is obtained after the clotting of blood cells. Vaccine is injected to raise resistance of the body against that disease Not applicable with serum Vaccine generally contains antigens Serum contains antibodies Vaccine is used to fight against disease Serum is used in diagnostic tests and blood typing The content of vaccine is specific Serum is a mixture of many different substances 2. HYPERSENSITIVITY Hypersensitivity is an exaggerated immune response that results in tissue damage and is manifested in the individual on a second or subsequent contact with an antigen. Hypersensitivity reactions can be classified as either immediate or delayed. There are six types: i.ii.iii.iv.v.vi IMMEDIATE HS DELAYED HS Reaction appears immediately within minutes and recedes rapidly usually in one hour. Appears slowly within 24- 72 hours and lasts longer for days Antibody mediated reaction Cell mediated reaction Passive transfer possible by serum or their extracts. Transfer possible only with lymphoid cells Desensitization is easy but short lived Difficult but long lasting Wheal and flare with maximum diameter in 6 hour. Erythema and induration with maximum diameter in 24 to 48 hours. TYPE-I: HYPERSENSITIVITY: ANAPHYLACTIC REACTION The term anaphylaxis is used when the manifestations of allergic reaction are severe. It is ige mediated hypersensitivity reaction that occurs quickly when a large shocking dose of antigen is introduced after one or more small sensitizing doses. Features of anaphylaxis: 1. Reaction occurs immediately in few second to few minutes after administration of shocking dose. 2. Ige produced has affinity for skin cells and is probably synthesized in man only. 3. The manifestations occurs due to constriction of smooth muscle and increased vascular permeability. 4. Duration is short. 5. It is not a heritable disease. Manifestation of anaphylaxis:
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  8 Manifestations of anaphylaxisdepend on species of animals, amount of shocking dose, site of injection and portal of entry of antigen. The manifestations may be local or systemic. Localized anaphylaxis: it include cutaneous and mucosa anaphylaxis. Systemic anaphylaxis: it is rare in man and occasionally observed in hypersensitivity individuals by insect stings, injection of foreign serum or drugs antibiotics etc... ATOPY it is a type i hypersensitivity reaction that occurs spontaneously in response to substances that are usually present i our environment in everyday life.about 1% population is prone to such environmental antigen such as pollen, animal dander, wheat husk, certain foods etc. The most common manifestations are fever and asthma. Features of Atopy: Atopy shows familial distribution Reactions occurs at the site of entry of ag. Atopy is ige mediated hypersensitivity reaction. 2. TYPE-II: CYTOTOXIC REACTION It is mediated by antibodies – igg, igm that are directed towards antigens present on the surface of cell or other tissue components and ultimately resulting in damage of cell. The antibody is produced against an antigen that can be microbial product absorbed on to a cell or drug. Both igg and igm are produced in type ii reaction. The ab attaches to ag via fab region followed by complement fixation via fc region causing damage to cell as a result of ag-ab reaction. Examples: isoimmune reactions, autoimmune reaction, drug reactions etc… 3. TYPE-III: IMMUNE COMPLEX REACTION It involves formation of immune complex. Normally these complexes are phagocytosed effectively by monocytes and macrophages. In the presence of excess amounts of some soluble antigens, the antigen antibody complexes may not be effectively removed. And it leads to inflammatory response in the body. 4. TYPE:IV: DELAYED REACTION It involves delayed, cell mediated immune response. A major factor in the type IV reaction is the time required for t cells to antigen to migrate and accumulate near the antigens. 5. TYPE:V:STIMULATORY TYPE REACTION It is a modification of type ii hs reaction in which an interaction of abs with ags occur on surface of cell that cause proliferation and differentiation of cell instead of killing. Such antibodies produced in this reaction are non- complement fixing and the ag-ab complex enhances the functional activity of affected cell. The classical example of this type of hypersensitivity reaction is graves’ disease in which thyroid hormone are produced in excess amount. 6. TYPE-VI: ANTIBODY DEPENDENT CELL MEDIATED CYTOTOXICITY ADCC REACTION It is mediated through natural killer cells. Target cells coated with low concentration of abs are killed by NK cells through an extracellular non- phagocytic mechanism. AUTOIMMUNITY AN autoimmune disorder is a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue or any of a large group of disease characterized by abnormal functioning of the immune system that causes your immune system to produce antibodies against your own
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  9 tissue. There aremore than 80 different types of autoimmune disorders 1. Addison’s disease 2. Celiac disease 3. Dermatomyositis 4. Graves’ disease 5. Chronic thyroiditis 6. Multiple sclerosis 7. Myasthenia gravis 8. Pernicious anemia 9. Reactive arthritis 11. Rheumatoid arthritis 12. Sjögren syndrome 13. Systemic lupus erythematosus 14. Type 1 diabetes. PRINCIPLES AND USES OF SEROLOGICAL TESTS  Serum is the liquid portion of blood that contains many different components, especially the immunoglobulins or antobodies.  Serology is the study of serum.  It is the science that studies antigen antibody or immunological reactions of the body using a serum specimen.  Serological reactions are simple, rapid and specific. The test results are reliable and responsible.  Serological tests to detect the antibodies against the infecting microorganisms provide a useful means of indirect diagnosis. PRINCIPLES OF SERODIAGNOSTIC TESTS 1) PRECIPITATION When a soluble antigen combines with its corresponding ab in presence of electrolyte at a suitable temperature, the ag-tb complex forms an insoluble precipitate a reaction called precipitation. 2) FLOCCLATION It is the aggregation of inert particles like latex, charcoal, and cholesterol emulsion coated with an antigen as a result of immunological reaction. This flocculation technique is best applied in vdrl test for the diagnosis of syphilis. 3) AGGLUTINATION When an immune complex is formed by cross linking cells or particles with specific antibodies, it is called an agglutination reaction.aggllutination reaction usually forms visible aggregates or clumps. Such clumps are called agglutinates which can be seen through unaided eyes. Direct agglutination reactions are very useful in the diagnosis of certain disease. Example: blood grouping, Widal test. 4) NEUTRALIZATION REACTION In neutralization toxin produced by the pathogen is used as the reagent which is neutralized by the antibody produced by the patient or present in his serum. It os applied in the antistreptolysin o test for the diagnosis of a streptococcus pyogenes infection. 5) COMPLEMENT FIXATION When complement binds to an antigen antibody complex it becomes fixed and used up. A known antigen is mixed with test serum lacking complement. When immune complexes form complement is added. If immune complexes are present they will fix and consume complement. Afterwards sensitized indicator cells usually sheep red blood cells are added to the mixture. Lysis of the indicator cells occur if immune complexes do not form. Absence of Lysis shows that specific antibodies are present in the test serum Complement fixation is used for diagnosis of syphilis.
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  10 6) IMMUNOFLUORESCENE TESTS Theseasaays use the same principle as Ela, and like eia they can be constructed to detect either viral antibody or antigen in the patient specimen. However instead of the enzyme aubstratre detector system of eia fluorescein labelled anti human antibody is used to detect a positive reaction which apperas as apple green fluoresecene under a light microscope. 7) WESTERN LOT OR LINE IMMUNOASAAYS Specific viral proteins are transferred on blotting paper either from a gel or produced by recombination or peptide synthesis. Further steps are similar to those of eia. The viral antigen band on the blotting paper develops colour if specific antibody to that particular antigen is present in the serum. 8) ANTIBODY AVIDITY ASSAYS: The host antibody response matures over several weeks’ post-acute infection. Therefore antibody detected > 3 months after acute infection binds strongly to antigen used in laboratory assays, as a corollary the antibody in the first 3 months has weak binding and can be easily dissociated from the antigen antibody complexes. SEROLOGICAL TEST USES2. TEST USES COMPLEMEN T FIXATION TEST (CFT) Respiratory viruses- measures total antibody, to diagnose recent infection acute and convalescent serum samples are required to show rise in titer. ENZYME LINKED IMMUNOSORBENT ASSAYS – EIA OR ELISA Igg/ igm antibody- rubella, measles, mumps, hiv, hepatitis a, etc. IMMUNOFLUROR ESCENCE- IF Ige /igm antibody- ebv, vzv antigen- rsv, influenza and other respiratory viruses in respiratory sectetions. LATEX AND GEL PARTICLE AGGLUTINATION Antibody- rubella, toxoplsama Antigen- rotavirus Norovirus WESTERN BLOT – WB AND LINE ASSAYS -LIA Used to confirm hiv and hcv screen positive specimens IgG AVIDITY ASSAYS To confirm recent cmv, rubella and toxoplasma infections