Chapter 16
Immunity and Serology
16.1 Immunity to Disease
• Acquired Immunity Can Result by Actively Producing Antibodies to an Antigen
• 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
• There Are Several Types of Vaccine Strategies
• 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
• 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
• 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
• 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)
• Acquired Immunity Can Also Result by Passively Receiving Antibodies to an
Antigen
• 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
• 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)
• The immune system may recognize foreign serum proteins as “nonself”
and mount an allergic reaction
• Immune complexes may form and serum sickness may develop
• Herd Immunity Results from Effective Vaccination Programs
• 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
• Do Vaccines Have Dangerous Side Effects?
• Adverse reactions to vaccines are reported to the Vaccine Adverse Events
Reporting System (VAERS)
• People with egg allergies should not take flu vaccinations
• The risk of contracting a disease is much greater than any risk associated
with vaccines
16.2 Serological Reactions
• Serological Reactions Have Certain Characteristics
• Serological reactions can help diagnose microbial infections
• 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
• 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
• The Schick test is used to determine if a person is immune to diphtheria
•
Precipitation Requires the Formation of a Lattice Between Soluble Antigen and
Antibody
• Precipitation reactions involve antigens and antibodies cross-linked in a
huge lattice
• In fluid, the molecules diffuse until they reach the idea/concentration (the
zone of equivalence)
• In immunodiffusion, antigens and antibodies diffuse through a gel until
they reach the zone of equivalence
• In immunoelectrophoresis, diffusion is combined with electrophoresis
• Agglutination Involves the Clumping of Antigens
• 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
• Hemagglutination is used to:
• determine blood type
• Detect viruses that cause agglutination of red blood cells
• Complement Fixation Can Detect Antibodies to a Variety of Pathogens
• 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
• The radioimmunoassay (RIA) is extremely sensitive, using radioactivitylabeled antigens
• The radioallergosorbent test (RAST) uses radioactive antiglobulin
antibodies
• The enzyme-linked immunosorbent assay (ELISA) is similar to RAST
• It uses an enzyme system instead of radioactivity
• It is often used to detect antibodies against HIV
16.3 Additional Laboratory Tests
• 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
• In the lab, antibodies recognizing one epitope (monoclonal antibodies [mAb]) are
produced using myelomas
• Myeloma cells are fused to an 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)
• Gene Probes Are Single-Stranded DNA segments
• They hunt down complementary DNA fragments 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