Immunity and Serology

Chapter 20

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• Immunity is a condition under which an individual is protected from the disease

• Two general types of immunity• Innate Immunity• Acquired Immunity

• Types of Acquired Immunity• ACTIVE IMMUNITY

• Naturally Acquired Active Immunity• Artificially Acquired Active Immunity

• PASSIVE IMMUNITY• Naturally Acquired Passive Immunity• Artificially Acquired Passive Immunity

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• Naturally acquired active immunity develops from exposure to an infectious agent• Active immunity occurs when the body’s immune

system responds to antigens by producing antibodies and lymphocytes

• Naturally acquired active immunity follows illness or pathogen exposure

• Artificially acquired active immunity occurs through vaccination• Vaccines contain treated or altered microbes,

toxins, or parts of microbes• a primary immune response occurs• memory cells are formed• the person does not usually become ill

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• Live, attenuated vaccines contain weakened microbes that multiply at only low levels, inducing a strong immune response

• Organisms can revert to a virulent form and cause disease

• A single-dose vaccine can combine vaccines for different diseases

• Vaccines using attenuated bacteria are difficult and not widely used

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• Inactivated vaccines contain killed pathogens, which induce a weaker immune response• Booster shots are required to maintain immunity

• They are safer than attenuated vaccines because they cannot cause disease

• Toxoid vaccines contain inactivated toxins (toxoids)• Since the product is inactivated, booster shots are

required• Prepared by incubating toxins with a chemical

*to avoid multiple injections, vaccines are combined into single-dose vaccine

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• Subunit vaccines contain only those parts of the antigens that stimulate a strong immune response• Recombinant DNA technology can be used to

create recombinant subunit vaccines

• Subunits cannot cause disease

• Conjugate vaccines are created by attaching bacterial capsule polysaccharides to a toxoid• They elicit a strong immune response

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• DNA vaccines depend on the ability of some cells to:• take up and translate foreign DNA • display the resulting proteins, inducing a strong immune

response• Naked DNA vaccines contain engineered plasmids that

contain a gene from a pathogen• They are not infective or replicative, so cannot cause

disease

• Recombinant vector vaccines involve DNA incorporated into an attenuated pathogen• The pathogen:

• takes the DNA into the cells (viral vector) or • incorporates the DNA and present antigens (bacterial vector)

*Adjuvants : increase efficacy of a vaccine or toxoid by increasing availability of the antigen in the lymphatic system. = stimulate phagocytic activity, IL 1 activation, sustained immune response

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Childhood and Adolescent Immunization Schedule - 2006

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• Passive Immunity develops when antibodies enter the body from outside source

• Two Types: NATURAL OR ARTIFICIAL

• Naturally acquired passive immunity (congenital immunity) occurs when antibodies pass from mother to fetus• Maternal IgG antibodies remain in the child 3-6

months after birth

• Maternal antibodies also pass to the newborn through:

• first milk (colostrum) • breast milk

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• Artificially acquired passive immunity involves injection of antibody-rich serum into a body• The serum can be used to:

• prevent disease (prophylactic) • treat disease (therapeutic serum)

• Antiserum: hyperimmune serum or convalescent serum

• The immune system may recognize foreign serum proteins as “nonself” and mount an allergic reaction• Immune complexes may form and serum sickness

may develop

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• In herd immunity, the majority of a population are immune

• Unvaccinated individuals are unlikely to contact an infected individual

• Herd immunity is affected by:• population density • the strength of a

person’s immune system

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• People with egg allergies should not take flu vaccinations

• The risk of contracting a disease is much greater than any risk associated with vaccines

• Thimerosal

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• Serology: branch of immunology that studies serological reactions

• Serological reactions can help diagnose microbial infections

• Ag-Ab reactions are studied under laboratory conditions

• Uses patient’s serum

• Function: confirmatory test, detect organism in tissue, aid MD in following course of disease and determine immune states

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• Titration is the dilution of antigen or antibody solution to the most favorable concentration

• The titer is the most dilute concentration of serum antibody that reacts to its antigen• A rise in the titer ratio (antibody:serum) indicates disease

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• Neutralization Involves Antigen-Antibody Reactions• Neutralization is used to identify toxins and

antitoxins, viruses and viral antibodies

• If a specific agent is suspected, to determine if the toxin has been neutralized, a sample can be:

• mixed with an antitoxin • injected into a lab animal• Example: detection of botulinum toxin in food

• The Schick test is used to determine if a person is immune to diphtheria (intradermal test)

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• Precipitation reactions involve antigens and antibodies cross-linked in a huge lattice

• In fluid, the molecules diffuse until they reach the ideal concentration (the zone of equivalence)

• In immunodiffusion, antigens and antibodies diffuse through a gel until they reach the zone of equivalence• Oudin tube technique• Ouchterlony plate

technique

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• In immunoelectrophoresis, diffusion is combined with electrophoresis

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• Agglutination – antibodies interact with antigens on a surface of a particular object and cause object to clump together.

• A visible reaction requires less antibody or antigen if they are clumped together

• In passive agglutination:• antigens are adsorbed

onto a surface• antibodies are added• agglutination is observed

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• Hemagglutination is used to:• determine blood type • Detect viruses that cause agglutination of red blood

cells• Flocculation : precipitation and agglutination; Ag exists

in a non-cellular particulate form that reacts with antibodies to yield large, visible aggregates.

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• Complement Fixation Can Detect Antibodies to a Variety of Pathogens

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• Labeling Methods Are Used to Detect Antigen-Antibody Binding• A fluorescent

antibody technique can detect antigen-antibody binding by labeling antibodies with a fluorescent marker

• Can be direct or indirect (FTA-ABS)

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• The radioimmunoassay (RIA) is extremely sensitive, using radioactivity-labeled antigens; based on the competition between radioactive labeled Ag and unlabeled Ag for the reactive sites on Ab molecule

• The radioallergosorbent test (RAST) uses radioactive antiglobulin antibodies

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• The enzyme-linked immunosorbent assay (ELISA) is similar to RAST • It uses an enzyme

system instead of radioactivity (horseradish peroxidase)

• It is often used to detect antibodies against HIV

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• Monoclonal Antibodies Are Becoming a “Magic Bullet” in Biomedicine

• Polyclonal antibodies occur because there are multiple epitopes on a pathogen• They activate

different B cell populations

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• In the lab, antibodies recognizing one epitope (monoclonal antibodies [mAb]) are produced using myelomas

• Myeloma cells are fused to and activated B cell to form a hybridoma

• A hybridoma producing the desired mAb can be cloned

• MAbs can be used in:• disease prevention• immunomodulation

(controlling overactive inflammatory responses)

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• Gene Probes Are Single-Stranded DNA segments

• They hunt down complementary DNA fragment and emit a signal

• The polymerase chain reaction (PCR) is used to increase the amount of DNA to be searched

• Gene probes and PCR are use in:

• HIV and HPV detection

• water-quality tests