hypersensitivity- stiner Flashcards
what is hypersensitivity?
Exaggerated or aberrant immune response to an antigen resulting in inflammation and tissue damage
what are hypersensitivity diseases?
Disorders that are caused by aberrant immune responses.
another name for Type 1 hypersensitivity is:
allergy, atopy, or immediate hypersensitivity
when does a type 1 hypersensitivity occur?
Occurs within minutes after reexposure to antigen/allergen.
what are the characteristics of a type 1 reaction?
Rapid IgE and mast cell mediated vascular and smooth muscle reaction
give examples of type 1 reactions
hives, hay fever, food allergies, bronchial asthma, anaphylaxis.
what is the first step in a type 1 reaction
Initial exposure to antigen and production of IgE antibodies (Ab) = Sensitization.
1) TH2 cells secrete IL’s
2) TH2 cell CD40L binds to B cell CD40
what is the second step in a type 1 reaction?
Binding of IgE Ab to Fc receptors on mast cells
what are the immediate and late responses of a type 1 hypersensitivity reaction
A) Immediate Effects
—Dilation of blood vessels, increased vascular permeability, smooth muscle contraction (immediate reaction).
B) Late Response
—Inflammation (late phase reaction).
Mast cell degranulation
Immediate Response
- Vasoactive amines (histamine and serotonin) and proteases
- Synthesis and secretion of lipid mediators (prostaglandins and leukotrienes made from arachidonic acid)
what are the 2 lipid mediators in type 1 reactions?
Prostaglandins and Leukotrienes
prostoglandins cause what to occur?
vasoconstriction in the lungs or dilation in vascular smooth muscle
leukotrienes are made by what process? what do they induce?
- Made via the lipoxygenase pathway
- powerful inducer of bronchoconstriction, increased vascular permeability, increased secretion and accumulation of mucus, and inflammatory cell infiltration into airways
what are the most common asthma signs and symptoms
coughing, wheezing and shortness of breath
what are the most common asthma triggers?
Airborne allergens, such as pollen, animal dander, mold, cockroaches and dust mites
during dust mite induced asthma, what enzyme cleaves the occludins in tight junctions?
Der P 1
what are the 2 main treatments for asthma?
1) Inhaled corticosteroids- These medicines are the most effective long-term control medicine
2) Leukotriene modifiers- These medicines help block the chain reaction that increases inflammation in your airways
what Determines the Type of IgE-mediated Allergic Rxn that occur?
the dose and route of entry
type 1 hypersensitivity key points
1) All clinical and pathologic features of immediate hypersensitivity reactions are driven by mediators produced by mast cells.
2) The most severe form of immediate hypersensitivity is anaphylaxis.
what is anaphylaxis
1) Response driven by the systemic release of vasoactive amines and lipid mediators from mast cells
2) Causes life-threatening drop in BP accompanied by severe bronchoconstriction
3) Treated with epinephrine (vasoconstrictor and bronchodilator) and antihistamine
what is type 2 hypersensitivity?
A) antibodies produced by the immune response that bind to antigens on our own cell surfaces
—Primarily IgG and IgM isotypes
B) host Ab binds foreign Ag on cell surfaces
or binds self Ag
C) can activate complement resulting in membrane attack complex formation
—leads to destruction of cells, inflammation, or interfere with normal cellular function
what is Hemolytic Disease of the Newborn (Erythroblastosis fetalis)
Maternal Ab’s target fetal RBC’s for destruction
what is Hemolytic anemia?
Auto-antibodies are produced against self Ag’s on the surface of RBC’s. This triggers the rapid destruction of RBC’s leading to anemia
Grave’s Disease
TSH receptor Ab’s stimulate TSH receptor to over produce thyroid hormone
Myasthenia Gravis
Ach receptor Ab’s bind to and block the Ach receptor
strategies to treat type 2 diseases
Autoimmune hemolytic Anemia -Prednisone or blood transfusion HDNB -Anti-Rh Ab Graves Disease -Radioactive iodine, anti-thyroid drugs, or thyroid removal Myasthenia Gravis -cholinesterase inhibitors and corticosteroids
type 2 summary
Host Ab binds foreign Ag on cell surfaces or binds self Ag
IgG
type 3 hypersensitivity
1) Ag-Ab complexes clump and deposit in blood vessels or tissues attracting an acute inflammatory reaction.
2) An immune complex is a complex consisting of an Ag bound to its specific Ab
examples of type 3 hypersensitivity
Systemic lupus, Arthus reaction, serum sickness, lupus nephritis, and rhematoid arthritis.
What can cause type 3 hypersensitivity?
Can be caused by exogenous or endogenous Ag
what are immune complexes?
aggregations of antigens and IgG and IgM antibodies
where are deposits usually found in type 3?
generally accumulate at sites where antigen is localized or at sites of turbulence (vessel branches) or high pressure (kidney)
Immune complexes trigger inflammation via three mechanisms
- Mast cell activation
- Macrophages release TNF-alpha and IL-1 that induce the inflammatory cascade.
- Cells bearing Fc receptors for IgG (or IgM) and IgE may be crucial for antibody complex mediated hypersensitivity
Arthus reaction (type 3)
1) Triggered in the skin by IgG
2) Immune complexes form
3) Complexes bind Fc receptors on mast cells and other leukocytes
(Can occur as a result of repeated subcutaneous injections of tetanus toxoid)
symptoms of Arthus reaction
Swelling, induration, severe pain, edema, hemorrhage, and occasionally by necrosis (which can lead to gangrene in extreme cases).
Usually occur within a few hours after exposure
Serum sickness is a classic example of what?
transient systemic immune complex-mediated syndrome. (type 3 reaction)
what causes serum sickness?
Caused by an injection of a foreign protein or proteins which leads to an antibody response.
1) Antivenin (serum from horses immunized with snake venoms)
2) Antibiotics
3) Streptokinase (a bacterial enzyme
therapeutic treatments for type 3 hypersensitivity
Arthus Reaction
-Avoidance or anti-inflammatory agents
Serum Sickness
-Drug avoidance, antihistamines, corticosteroids, etc
Lupus
-NSAID’s, corticosteroids, immunosuppressive agents, etc
type 3 summary
Type III Hypersensitivity/Immune-Complex mediated: Ag-Ab complexes clump and aggregate in or near blood vessels attracting an acute inflammatory reaction.
Primarily IgG (possibly IgM or IgE)
Immune complex
Ex. Arthus Rxn, serum sickness, and SLE
type 4 hypersensitivity
mediated by Ag specific T cells which induce macrophage infiltration in a sensitized individual
is type 4 hypersensitivity antibody mediated?
NO
mediated by Ag specific T cells which induce macrophage infiltration in a sensitized individual
Generally, what initiates type 4 reactions?
Small molecules that must become bound to a larger carrier molecule in order to illicit an immune or inflammatory response
Th cells secrete cytokines with activate macrophages
Tuberculin Test (Mantoux PPD test) determines what? which type of sensitivity does it rely on?
determine previous exposure/infection with Mycobacterium tuberculosis
uses type 4 sensitivity
-The response is mediated by TH1 cells and infiltrating macrophages and other inflammatory mediators, causing visible swelling
Contact Dermatitis
- hapten complexed with skin proteins and become internalized by APC’s in the skin
- CD4 or CD8 T cells
- Inflammation occurs as a result of the inflammatory response initiated by T cells
what are the 2 phases of contact hypersensitivity?
sensitization and elicitation
when does Sensitization occur? how long does it take? which cells play a pivotal role?
1) Occurs during first exposure to Ag
2) Takes 10-14 days (delayed response) to develop.
3) Langerhans’ cells in skin
- (APC of the skin) take up Ag and present to T cells.
4) Formation of CD4+ memory T cells specific for the Ag
when does Elicitation occur? which cells produce cytokines?
Upon reexposure to Ag
Develops within 24-48 h.
Involves LC Ag presentation to memory T cells at site of Ag entry.
T cells release IFN-gamma & pro-inflammatory cytokines
what is poison ivy an example of?
contact dermatitis
chronic asthma- type 4 hypersensitivity
1) Mast cell degranulation leads to Th2 (IL-5) and eosinophil influx
2) Eosinophils activate and degranulate
3) Chronic inflammation can cause irreversible damage and death
Granulomatous Inflammation/Crohn’s
Disease
- type 4 reaction
- Type of Inflammatory Bowel Disease (IBD) of the terminal ileum
- Initial presentation may be in oral cavity and pharynx
therapeutic treatments for type 4 hypersensitivity
TB Test injection
-Self limiting
Contact hypersensitivity
-Limit exposure, corticosteroids, antihistamines, etc..
Chronic Asthma
-Corticosteroids, bronchodilators, cromolyn, etc ..
Crohn’s Disease
-Corticosteroids, immunosuppressants, etc..
type 4 hypersensitivity overview
-mediated by Ag specific T cells which induce macrophage infiltration in a sensitized individual.
-DTH response to injected or absorbed Ab
2-3 days
-Ex. TB test, contact dermatitis, chronic asthma, Crohn’s
