Acquired Immunity Can Result by Actively Producing Antibodies to an Antigen

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 radioactivity-labeled 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