4 Hypersensitivity & Allergies Flashcards
Define anaphylaxis.
A severe, immediate, and system-wide harmful immune response to a non-pathogenic antigen
it was the first identified hypersensitivity reaction
Define hypersensitivity reaction.
an immediate or delayed immune response to innocuous antigen resulting in damage to healthy tissue
How many types of hypersensitivity reactions are there?
four
Which types of hypersensitivity reactions are humorally mediated?
Types I, II, and III
Type IV hypersensitivity reactions are ______ mediated.
cell-mediated
What specific antibody mediates Type I hypersensitivities?
IgE
What hypersensitivity is typically mediated by IgG?
Type III (forms antibody aggregates in vessels)
What specific part of humoral immunity mediates the Type II hypersensitivity?
IgG antibodies targeting non-self antigens on the surface via complement proteins (i.e. graft rejection)
Delayed type reaction describes what kind of hypersensitivity?
Type IV
Antigens (or allergens) that cause a Type I hypersensitivity have what characteristic(s)?
They’re either proteins or glycoproteins and are often times enzymatically active
What do enzymatically active proteins do to the body at the mucosal membrane?
The proteases will typically bind to pattern recognition receptors (PRRs) and activate B cells to produce IgE targeted for that protein
A systemic reaction to a Type I hypersensitivity presents as what?
anaphylactic shock
A type I reaction will result in what cellular response?
Degranulation of mast cells as well as eosinophils and basophils
In a Type I reaction, the antigens are presented on MHC Class II and presented to what T cell?
CD4 Th2 cells, which then use interleukins to activate granulocytes
What interleukins are used to activate mast cells during a Type I reaction?
Primarily IL-9 but also IL-4, IL-5, and IL-13
What interleukin is overly expressed to cause eosinophilia?
IL-5
Name four enzymes used by mast cells to repair connective tissue.
Tryptase, Chymase, Cathepsin G, and Carboxypeptidase
What do mast cells use histamine and heparin for?
Poison parasites, increase vascular permeability and contract smooth muscle
What effect do mast cells have on the airway when they respond to an allergen?
Decrease airway diameter (smooth muscle contraction via histamine/heparin) and increase mucus secretion
Name two enzymes used by eosinophils.
Peroxidase (to kill parasites/mammalian cells, and trigger histamine release from mast cells) and Collagenase (to remodel connective tissue)
What are three toxic proteins produced and released by eosinophils?
Major basic protein, cationic protein, and an eosinophil-derived neurotoxin
Why is eosinophilia bad?
It’s the concentration of eosinophils which degranulate their highly toxic contents and promote more inflammation
What is the hygiene hypothesis?
In developed countries children aren’t exposed to as many antigens which cause their immune system to be poorly educated, leading to allergy and autoimmune disorders
What are the two phases of allergic responses?
Early response which involves smooth muscle contraction, vasodilation, and fluid/mucus secretion; and Late response which involves leukocyte migration and activation
What is hyposensitization?
When you have repeated exposures to escalating dosages of allergens to reduce Type I reactions
What other therapies can be used to relieve Type I reactions?
Antihistamines, Leukotriene antagonist, Corticosteroids, Immunotherapeutics - all of these treat the symptoms, not the cause
A mast cell expressing a lot of IgG4 will do what?
It’ll be less likely to degranulate because unlike IgE, IgG4 is an inhibitor of degranulation
What is the effector cell in a Type II reaction?
CD8 T cells
What forms in a Type III hypersensitivity reaction?
An aggregate of antibodies and antigens that get stuck in either the vasculature or the tissue
What does the aggregate do in a Type III reaction?
The aggregate will recruit C3b complement proteins which then promote inflammation
Is it an innate or adaptive inflammatory response in a Type III reaction?
Innate immune response
What cell does most of the damage to tissue in a Type III reaction?
neutrophils
Rheumatoid arthritis is an example of what type of hypersensitivity?
Type III
What cells mediate Type IV reactions?
CD4 T cells
Molecules causing Type IV reactions function as ________.
adjuvants
