Hypersensitivity & Immunity Flashcards
Causes of hypersensitivity
Autoimmunity
Reaction to environmental antigens
Reactions Against Microbes
How does Reactions Against Microbes causes hypersensitivity?
Cross-Reactivity: Occasionally, antibodies or T-cells that react to a microbe also mistakenly attack similar-looking tissues in the body. For instance, in rheumatic heart disease, the immune response to a strep infection also damages heart tissue.
Collateral Damage: Sometimes, the immune system’s response to clear an infection damages the body’s own tissues. For example, in viral hepatitis, immune cells attack liver cells infected by the virus, causing liver damage.
Excessive Immune Response: Sometimes, the immune response to a microbial infection (like bacteria or viruses) is too strong, or the microbe remains in the body for a long time, leading to persistent inflammation.
Immune Complexes: If antibodies (proteins that help fight infections) bind to microbial antigens (foreign substances), they form complexes that can deposit in tissues and cause inflammation. This is seen in diseases like poststreptococcal glomerulonephritis, where the kidneys get inflamed after a strep infection.
T-Cell Responses: Persistent infections can cause T-cells (a type of immune cell) to create severe inflammation, leading to tissue damage. An example is tuberculosis, where T-cells form granulomas (clusters of immune cells) in the lungs.
List the types of hypersensitivity rxns?
What are their other names?
Type 1,2,3,4
Explain type 1 hypersensitivity
Immediate (Type I) Hypersensitivity (Allergy)
Key Players: TH2 cells, IgE antibodies, mast cells, and other white blood cells (leukocytes).
Mechanism:
TH2 cells stimulate the production of IgE antibodies.
IgE antibodies attach to mast cells.
When an allergen (like pollen) binds to IgE on mast cells, these cells release chemicals (mediators).
Mediators cause blood vessels to expand and smooth muscles to contract, leading to symptoms like itching, swelling, and difficulty breathing.
Cytokines released by mast cells attract more inflammatory cells, worsening the reaction.
Example: Think of mast cells as loaded cannons. The IgE antibodies are like the trigger, and the allergen pulls the trigger, causing the cannon (mast cell) to fire its contents (mediators) and cause an allergic reaction.
Explain type 2
Antibody-Mediated Disorders (Type II Hypersensitivity)
Key Players: IgG and IgM antibodies.
Mechanism:
IgG and IgM antibodies bind to antigens on cell surfaces or in tissues.
This binding can lead to cell damage by:
Promoting phagocytosis (engulfing and digesting) of the cells.
Causing cell lysis (breaking down cells).
The antibodies also induce inflammation by activating other immune components.
In some cases, antibodies can alter cell functions without causing direct cell damage, leading to diseases.
Example: Imagine the antibodies as markers that label cells for destruction. The immune system then targets and destroys these marked cells, leading to tissue damage.
Explain type 3
Immune Complex–Mediated Disorders (Type III Hypersensitivity)
Key Players: IgG and IgM antibodies, antigen-antibody complexes, neutrophils, and monocytes.
Mechanism:
IgG and IgM antibodies bind to antigens in the bloodstream, forming complexes.
These antigen-antibody complexes deposit in blood vessel walls and tissues.
The deposition triggers inflammation as immune cells like neutrophils and monocytes are recruited to the site.
These cells release enzymes and toxic substances that damage tissues.
Example: Picture the antigen-antibody complexes as clumps of debris. When they settle in the tissue, they attract immune cells that try to clean up but end up causing more damage.
Explain type 4
T Cell–Mediated (Type IV) Hypersensitivity
Key Players: T lymphocytes (TH1 and TH17 subsets), cytokines, neutrophils, macrophages, CD8+ cytotoxic T lymphocytes (CTLs).
Mechanism:
TH1 and TH17 T cells produce cytokines that cause inflammation.
These cytokines activate neutrophils and macrophages, leading to tissue damage.
CD8+ CTLs can directly kill host cells that they recognize as infected or abnormal.
Example: Think of T cells as soldiers that call for reinforcements. The cytokines they release attract more immune cells to the site, which then cause inflammation and tissue damage
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