15 Hypersensitivity Flashcards
What is Hypersensitivity?
Exaggerated immune response that causes damage to the individual
What is immediate hypersensitivity?
an exaggerated immune response mediated by an antibody or antigen-antibody complexes that manifests within minutes - hours after exposure to an antigen
What is the Type I immediate hypersensitivity?
IgE-mediated hypersensitivity
What is the Type II immediate hypersensitivity?
IgG or IgM-mediated hypersensitivity
What is the Type III immediate hypersensitivity?
Immune complex-mediated hypersensitivity
What is delayed-type hypersensitivity (DTH)?
a type-sensitive response that is mediated by T helper cells that release various cytokines/chemokines
When does DTH response take place?
generally 2-3 days after T helper cells interact with an antigen
What is the Type IV DTH hypersensitivity?
cell-mediated hypersensitivity (T cells)
What are the four types of hypersensitivity reactions?
Type I: Allergy and Atopy
Type II: Antibody-mediated hypersensitivity
Type III: Immune complex-mediated hypersensitivity
Type IV: Delayed-type hypersensitivity
What is an allergy?
An allergy is a type I hypersensitivity reaction
What is responsible for type I hypersensitivity?
IgE antibodies interact with a multivalent antigen, so, IgE antibodies
How do allergies come to be?
IgE antibodies cross-link Fcε receptors on the surfaces of innate immune cells, and granule contents are released, like histamine, heparin, proteases, leukotrienes, prostaglandins, and chemokines. Mediators act up on surrounding tissues and cells which causes the symptoms of allergies. (Note: Abs are not harmful by themselves, it’s the linking of the Fcε receptors via IgE antibodies which is why they are the cause of allergies)
What are allergens?
Specific type of antigen that induces a type I hypersensitivity reaction. Examples: nuts, milk, dust mites, penicillin, birch trees
Atopy
Abnormality in people that causes a predisposition to generate IgE Abs against common environmental antigens. Normally, IgE response is against parasitic infection.
Where are mast cells located?
Tissue
Where are basophils located?
They are in circulation throughout the immune system and are recruited into inflammatory sites
What helps Abs when fighting against immune reactions?
Granule contents (histamine, heparin, proteases) and mediators around the affected tissues/cells that cause symptoms
What is the high-affinity IgE receptor? What does it do?
FcERI, responsible for most allergy symptoms; found on basophil/mast cells
What is the low-affinity IgE receptor? What does it do?
FcERII, regulates production of IgE by B cells
True or False: Innate immune cells produce molecules responsible for Type I hypersensitivity symptoms
TRUE.
What are the steps of response from Type I hypersensitivities?
Early response: within minutes of allergen exposure, mediated by mast cell granule contents
Late response: hours later from recruited inflammatory cell types (ex. neutrophils)
Third phase: 3rd day after exposure, peaks at 4th day post-exposure. Massive eosinophil infiltration
What is systemic anaphylaxis? What is it caused by? What cures it?
Shock-like, often fatal state with a within-minutes onset. Caused by venom (bee, ants), drugs (insulin, penicillin), or food (seafood, nuts). Cure: epinephrine
What is anaphylaxis?
Serious allergic reaction with rapid onset that may cause death
What are some examples of localized hypersensitivity reactions (atopy scenarios)?
Hay fever, asthma, eczema, and food allergies
True or False: Type I hypersensitivity is environmental-only, not genetics-based
FALSE: allergy-linked genes include proteins (MHC, cytokines/chemokines), Airway remodeling genes, and transcription factors that regulate epigenetic modifications
What can be done about allergies?
Hyposensitization (repeated low-dose exposures), dosing of antihistamines/ihalation corticosteroids, exposure to pathogens early in life to increase T-cell balance
What is an example of Type II hypersensitivity?
Transfusion reactions
Is IgG or IgM-mediated hypersensitivity a type I or type II reaction?
Type II
What are Blood group Ag?
Carbohydrates
True or False: Adults possess antibodies to the blood type they do NOT have
TRUE! This is why if a transfusion of a diff. blood type is given, the antibodies will attach to the donor blood cells to degrade them, which can build to toxic levels of degraded RBC components
What is an example of a disease caused by Type II reactions?
Hemolytic disease in newbornes
What is another name for Type III hypersensitivity?
Immune complex-mediated hypersensitivity
How can immune complexes damage tissues?
- May trigger release of inflammatory/vasoactive mediators which recruit neutrophils
- symptoms that follow include fever/rashes/protein in the urine
- if the Ags don’t go away, complexes aren’t cleared, like in autoimmune complexes
What are some examples of Type III hypersensitivity reactions?
Multiple sclerosis, autoimmune diseases, and malaria
What is another name for Type IV hypersensitivity?
Delayed type hypersensitivity
True or false: DTH is Ab mediated
FALSE: DTH is purely cell-mediated and initiated by t cells
What is required from Type IV hypersensitivity? What characterizes it?
Delayed-type hypersensitivity (DTH) requires a delay for the reaction to develop. Characterized by macrophage recruitment at the inflammation site
What is the most common example of DTH?
Poison ivy contact dermatitis
What does the initiation of a type IV DTH response involve?
Sensitization by an antigen, or the sensitization phase. Initial exposure triggers T-cell response production (Often CD4+TH1), takes 1-2 weeks to settle in
What does the second exposure to a sensitizing Ag for DTH do?
Induces production of TH1 inflammatory cytokines that help recruit/activate macrophages, leading to granuloma formation. AKA the effector phase
How can a DTH reaction be detected? When is this used commonly?
Skin test: inject small amount of Ag under skin and wait to see if a red, firm lesion develops in 48-72 hrs for a positive result. Commonly used in the US for tuberculosis (TB) exposure
What antibodies/lymphocytes are induced by which reactions?
I - IgE
II - IgM, IgG
III - IgG
IV - TH1 cells
