Immune - 15a Flashcards
(46 cards)
Hypersensitivity Reactions - define it and describe the four types
Refers to an EXCESSIVE immune response.
Four Types:
I, II, III - ANTIBODY-mediated
IV - CELL-mediated
What is Type I Hypersensitivity commonly known as?
An allergy
Type I hypersensitivity involves reactions mediated by IgE antibodies.
What mediates Type I Hypersensitivity reactions?
IgE antibodies produced by plasma cells
These antibodies bind to mast cells, causing degranulation and histamine release.
What are the two types of Type I Hypersensitivity reactions?
- Systemic (e.g., anaphylaxis)
- Localised (e.g., hay fever, eczema, irritant contact dermatitis)
Type I hypersensitivity can manifest in various forms.
What is the onset time for Type I Hypersensitivity reactions?
Immediate/rapid (within minutes of exposure)
This quick response is a characteristic feature of Type I hypersensitivity.
What is Type II Hypersensitivity associated with?
Rhesus incompatibility
This condition is seen in hemolytic disease of the newborn and blood transfusion reactions.
What type of antibodies are involved in Type II Hypersensitivity?
IgG antibodies
These antibodies bind to antigens on the cell surface to activate the complement system.
What is the onset time for Type II Hypersensitivity reactions?
Rapid onset
Like Type I hypersensitivity, Type II also features a quick response.
Which antibody is known to cross the placenta in Type II Hypersensitivity?
IgG
This property allows IgG antibodies to affect the fetus in cases like Rhesus incompatibility.
What is Type III Hypersensitivity associated with?
Glomerulonephritis, rheumatoid arthritis, systemic lupus erythematosus
These conditions involve immune complex deposition and trigger immune responses.
What causes immune complex deposition in the glomeruli?
Higher blood pressure (four times higher than systemic circulation)
This increased pressure facilitates the deposition of antibody-antigen complexes.
What mediates Type III Hypersensitivity?
IgG, IgM, IgA
These antibodies form complexes that activate the complement system and lead to inflammation.
What is the onset time for Type III Hypersensitivity?
Four to eight hours
This refers to the time it takes for the immune response to manifest after exposure.
What are the main characteristics of Type IV Hypersensitivity?
Cell-mediated, delayed type hypersensitivity
Unlike Type III, this hypersensitivity does not involve antibodies.
What conditions are associated with Type IV Hypersensitivity?
Skin graft rejection, allergen contact dermatitis, multiple sclerosis
These conditions involve an over-reaction of T-lymphocytes to antigens.
What is the role of cytotoxic T-cells in Type IV Hypersensitivity?
Activated cytotoxic T-cells release cytokines that can damage normal tissues
This process contributes to the symptoms observed in conditions like multiple sclerosis.
What is the typical time frame for the reaction in Type IV Hypersensitivity?
48 to 72 hours
This delayed response distinguishes it from other hypersensitivity types.
What happens during the demyelination process in multiple sclerosis?
Breakdown of myelin sheath
This results from the overreaction of cytotoxic T-cells against the antigen.
What is the initial response to an allergen exposure?
Sensitisation, a slow response as not many cells have the correct specificity to respond to the antigen.
This occurs because the immune system has not yet been activated by the allergen.
What type of antibodies are produced specifically for an allergen?
IgE
This production occurs through the process of B-cell activation into plasma cells.
What happens during subsequent exposure to the same allergen?
An exaggerated immune response occurs with readily available antibodies.
This means the body has developed a full immune response.
What role does IgE play in allergic reactions?
IgE cross-links mast cells and the allergen.
This interaction leads to the activation of mast cells and subsequent allergic symptoms.
What are some mild symptoms of an allergic reaction?
Runny nose and streaming eyes.
These symptoms can vary in severity.
What is anaphylaxis?
A severe and potentially fatal allergic reaction characterized by swelling of airway mucosa.
It is a rapid response that can occur within minutes of allergen exposure.
