Chapter 17: Vaccines, Diagnostics, and Immune Disorders

Active Immunization

• Injecting antigen

• Stimulating immune system to actively make antigen-specific antibodies and T cells

• Memory of the antigen is retained

Passive Immunization

• Protective antibodies are administered, no memory is generated

  Examples:

• Injection of immune globulin (antibodies)

• Antitoxins: snake venom, antivenom

• Breastfeeding: IgA in it, provides babies with immunity in the GI tract

Antitoxins

• An antibody that binds to and inactivates microbial exotoxins

• Another form of passive immunization

Requirements of an Effective Vaccine

1. It should not harm the person being vaccinated

2. It should stimulate B cell (antibodies produced) and T cell (cytotoxic T lymphocytes) adaptive immune responses

3. It should result in long term memory

4. It should not require many boosters

5. It should protect against the natural pathogen

4 basic types of vaccines: killed whole cells or inactivated viruses

• Uses microbes inactivated by formalin or phenol

• Its ability to stimulate an immune response (antigenicity) remains

  • Proteins still look similar to the live, natural antigen

• Ex: cholera and rabies

4 basic types of vaccines: live, attenuated (weakened) bacteria or viruses

• in general are most effective

• mutated for growth in host only

• mimic infection, generated stronger immunity

• the act of replicating in a host, even a little, leads to a more robust immune response.

• Ex: MMR (measles, mumps, rubella); intranasal flu vaccine

4 basic types of vaccines: Antigen molecules purified from the pathogen

• not a whole pathogen, pieces of it

• Toxoid vaccines: inactivated microbial toxin, stimulate production of antitoxin antibodies in the person vaccinated

• Subunit vaccines: fragments of a microorganism or toxin

• Conjugated vaccines: link highly immunogenic protein to poorly immunogenic capsule

4 basic types of vaccines: DNA vaccines

• not commercially available

• injecting DNA or RNA encoding the antigen directly into muscle

• mRNA vaccines are commercially available (covid vaccines: mRNA make spike proteins)

Herd immunity

• The concept that an unvaccinated individual is protected from person-to-person transmission of a pathogen because most members of the community were vaccinated against that pathogen, lessening the likelihood that the unvaccinated person will come in contact with an infected person.

• Only possible for diseases that are contagious and transmitted between humans

• estimates ¾ of a population or more must be immunized to reduce disease

• Varies with each pathogen (Measles needs 95% immunized)

Allergen

Foreign antigen that has a similar structure or shape to host

Type 1 Hypersensitivity

• alllergic reactions, mild allergies

• Immediate: anaphylaxis

• Antibody mediated

• Can be mild or localized (Hay fever: rhinitis, pollen in air, watery itchy eyes, sneezing)

• Severe systemic response: Swelling (edema), low BP, cardiovascular collapse, breathing difficulties, suffocation

Type 1 Hypersensitivity Sensitization process

• Initial exposure:

  • allergen elicits IgE production

  • IgE binds to mast cells

• Second exposure:

  • mast cell degranulation

  • histamine, leukotriene, and prostaglandin release

Skin test for type one hypersensitivity

• useful in identifying the antigen to which a patient is allergic

• allergens are delivered locally to the skin to determine if there is an inflammatory reaction

Type 2 versus type 3 hypersensitivity

• both antibody mediated

• Type 2 occurs when antibody binds to antigen on a cell surface

• Type 3 occurs when antibody binds to soluble antigen (floating around in serum, tissue, etc.)

Type 2 Hypersensitivity

• Cell surface antigens, antibody mediated

• ABO blood typing

• Rh incompatibility

• Incompatibility occurs when specific antibodies in serum bind to antigen on foreign RBCs

• Cell lysis: complement activation, induce inflammation

• Hemolytic disease of newborn

Type 3 Hypersensitivity

• soluble antigens, antibody mediated

• immune complex disease: IgG antibody binding to soluble antigen forms an immune complex, immune complexes circulate in bloodstream

• embed in vessel walls (kidneys and joints)

• Bind complement and trigger inflammation

• Polymorphonuclear leukocytes/neutrophils (PMNs): release proteases, reactive oxygen species

• Damage host cells, inflammation

• Ex: rheumatoid arthritis

Type 4 Hypersensitivity

• delayed, cell mediated (t cells), 24-48 hours

• Triggered by antigen specific T cells

• ex: tuberculin skin test

  • BCG vaccine: has tuberculosis antigens

  • Attenuated strain of Mycobacterium bovis: produced cell mediated immunity, memory T cells

  • Second exposure: memory T cells activated, elicit a localized reaction

Self Tolerance

B and T cells learn not to react with self antigens

• T cells: deleted in the thymus

• B cells: undergo apoptosis

Loss of self tolerance

autoimmune disease, results in tissue damage, immune system mistakenly attacks the body's own healthy cells and tissues

Infection can trigger the formation of autoimmune reactions

• M protein of S. pyogenes

• antigenic mimicry

Graves’ disease

• Autoantibodies bind to thyroid-stimulating hormone receptor, causing hyperthyroidism

• increased metabolism, anxiety, diarrhea, bulging eyes

• Type 2 hypersensitivity

Hashimoto’s disease

• Autoantibodies bind and damage the thyroid, causing hypothyroidism

• tired, dry skin, brittle hair, decreased metabolism

Myasthenia gravis

• autoantibodies bind and block the muscle receptors for acetylcholine

• drooping eyelid, profound muscle weakness

• Type 2 hypersensitivity

Diabetes

• Type 1 usually occurs in childhood when T cells attack the islet cells of the pancreas

Rheumatoid arthritis

• Antibodies form immune complexes to connective tissue in joints and cause inflammation

• type 3 hypersensitivity

• 1:100 people