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99 Cards in this Set

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Define hypersensitivity:
Excessive or aberrant immune responses following antigen challenge
Type I:
IgE
Type II:
IgG/IgM
Type III:
Immune complexes
Type IV:
Cells
What is Type I Hypersensitivity called?
Immediate
What are the pathologic immune mechanisms of Type I?
-Th2 cells
-IgE antibody
-Mast cells
-Eosinophils
What are the mechanisms of tissue injury and disease in Type I?
1. Mast-cell mediators
2. Cytokine mediated inflammation
What are 3 examples of Type I?
-Allergic rhinitis
-Asthma
-Systemic anaphylaxis
What tissue does Type I allergy target?
Vascular endothelium and smooth muscle
What is atopy?
The propensity of some individuals to developing an allergy
What is rhinitis?
Hay fever
What is a common side effect of immediate hypersensitivity?
Late phase reaction of inflammation
What determines Atopy?
Genes
What are some allergens that trigger allergy?
-Pollen
-Foods
-Insect venom
-Animal dander
-Drugs
What is the first step in develping a Type I reaction?
Allergen exposure
What is the initial response to allergen exposure?
Bcell activation and Th2 cell activation via Il-4; Class switching to IgE
What does IgE do once it is secreted by Bcells in a Type I reaction?
Binds to Mast cells
What is the mast cell receptor for IgE?
Fc-epsilon-R1
When is the real reaction seen in Type I hypersensitivity?
Upon REPEAT exposure to the allergen
What happens when repeat exposure to allergen occurs?
Now the IgE that has coated mast cells get crosslinked by the allergen; this activates the mast cell and it degranulates.
What do mast cells release when they degranulate?
-Vasoactive amines
-Lipid mediators
When does immediate hypersensitivity reaction occur?
Minutes after repeat exposure to the allergen
When does the cytokine-stimulated late phase reaction occur?
6-24 hours after the repeat exposure.
What does a late phase reaction consist of?
Recruitment of more eosinophils and PMNs - inflammation.
What are some drugs that can cause immediate hypersensitivity?
-Opiates
-Vancomycin
-Penicillin
What are three important molecules that cause Bcell production to switch to IgE?
IL-4
IL-13
CD40/CD40L costimulation
So the two general steps of Type I reactions are:
1. Sensitization of mast cells
2. Activation and degranulation
What are 2 main types of mast cell mediators?
1. Preformed
2. Synthesized
What are the preformed mediators in mast cells?
Vasoactive amines (histamine)
Proteases (chymase)
What are the synthesized mast cell mediators of allergy?
-Eicosanoids
-Cytokines
When are the vasoactive amines and eicosanoids released?
Immediately - within minutes of mast cell degranulation
When are the cytokines released?
In the later phase.
Why does it take longer for the cytokine release?
Because it requires transcriptional activation of cytokine genes.
3 cytokines that are released by mast cells:
1. IL4
2. TNF
3. Chemokines
And what is the effect of IL4, TNF, and chemokines released in the late phase reaction of Type I hypersensitivity?
Recruitment of leukocytes, so inflammation.
Going back to early phase; What is the main vasoactive amine released by mast cells?
Histamine
What are the 2 effects of histamine?
1. Vascular dilation
2. Smooth muscle contraction
What does the protease chymase result in?
Tissue damage
What are the 2 secreted lipid mediators (eicosanoids) from mast cells?
-Prostaglandins
-Leukotrienes
What is the effect of prostaglandins?
Vascular dilation
What is the effect of leukotrienes?
Smooth muscle contraction
What are 3 allergens that cause Systemic Anaphylaxis?
-Drugs
-Serums
-Food
What are the routes of entry for systemic anaphylaxis allergens?
Oral and IV
What are 5 responses seen in systemic anaphylaxis?
-Edema
-Increased vascular permeability
-Tracheal occlusion
-Circulatory collapse
-Death
What is another name for Acute urticaria?
Wheal and flare
What are 3 allergens that cause acute urticaria?
-Insect bites
-Allergy testing
-Venom
What is the route of entry for the allergens that cause urticaria?
Subcutaneous
What is the response to acute urticaria?
A local increase in bloodflow and vascular permeability
What is another name for allergic rhinitis?
Hay fever
What causes hay fever?
Pollen
Route of entry for pollen
Inhalation
What is the response to hay fever?
Edema and irritation of the nasal mucosa
What are 3 allergens that cause asthma?
-Pet dander
-Pollen
-Dust mites
What is the route of entry for allergens that cause asthma?
Inhalation
What are the 3 responses to asthma inducing allergens?
-Bronchial constriction
-Increased mucus production
-Airway inflammation
What is the therapy for systemic anphylaxis?
Epinephrine
What are 2 treatments for asthma?
-Corticosteroids
-PDE inhibitors
What are 4 treatments for most allergic diseases?
-Densitization
-Anti-IgE antibody
-Antihistamines
-Cromolyn
What does cromolyn do?
Inhibits mast cell degranulation
What is Type II hypersensitivity mediated by? Type III?
Type II: antibody
Type III: immune complex
How does opsonization and phagocytosis work?
1. Ab binds and coats antigen
2. Fc region binds FcR on phagocyte
3. Activates lysozyme, ROS, NO production for better killing
What are the antibodies in Type II and III hypersenstivity often directed against?
Self antigens - like in the ECM or in the bloodstream circulation
What types of disorders result from auto-antibody induced hypersensitivity?
Chronic disorders
Why do auto-antibodies develop in the first place?
Because of a breakdown in tolerance
What is the isotype of antibodies in type II hsn?
Igm or IgG
Where do the IgM or IgG antibodies deposit in Type II hsn?
In tissue expressing the antigen
What is the nature of the disorder then in type II Hsn?
Local
What is an example of an antigen that causes type II hsn?
Drugs that bind to cell surfaces or the ECM.
What are 4 treatments for Ab-mediated HSN diseases?
1. Corticosteroids to limit inflammation and damge
2. Plasmapheresis
3. Blocking CD40/CD40L contact
4. Splenectomy for AIHA
What are 3 diseases that are Type III HSN?
1. SLE
2. Polyarteritis nodosa
3. Post-streptococcal glomerulonephritis
What is the Antibody specificity in Systemic lupus?
Anti-DNA, Anti-nucleoproteins, and others
What are the clinicopathologic manifestations of SLE?
-Nephritis
-Arthritis
-Vasculitis
What is the antibody specificity in Polyarteritis nodosa?
Anti-Hepatitis B virus surface antigen
What is the clinicopathologic manifestation of polyarteritis nodosa?
Vasculitis
What is the antibody specificity in post-strep glomerulonephritis?
Anti-streptococcal cell wall antigen
What is the clinicopathologic manifestation of Post-strep glomerulonephritis?
Nephritis
What is the mechanism of all 3 diseases?
Complement and Fc-receptor mediated inflammation
What causes serum sickness?
The result of injecting a large dose of antigen like Penicillin or antibiotics
What is the reaction that occurs in serum sickness?
-IgG/antigen complexes stimulate classical complement cascade
-C3a activates mast cells
What is the treatment for serum sickness?
-Corticosteroids to blunt inflammation
-Self limiting - as the antigen gets cleared.
What is the other name for Type IV HSN?
Delayed type hypersensivitity
What are all Type IV HSN's mediated by?
Tcells
What is the classic example of DTH?
The PPD skin test for TB
How is the TB skin test done?
-Inject Mycobacterial protein subcutaneously
-Local APCs process/present it
-Th1 response results in inflammation, visible lesion
What do we call DTH that is not on purpose?
Contact hypersensitivity
What are 3 antigens that stimulate contact hypersensitivity?
-Haptens
-Small metal ions
-Topical drugs
What are the consequences of contact hypersensitivity?
-Local epidermal reaction
-Erythema, cell infiltrate, intraepidermal abcesses
What is a hapten?
A small chemical which only becomes antigenic after its coupled to a protein carrier
What is the classic time duration for presentation of poison ivy?
2 days after exposure
What is Pentadecacatechol?
The chemical in poison ivy leaves that stimulates a T-cell response.
When a person first brushes against poison ivy, what happens?
The pentadecacatechol oil gets on the skin cells, and a self protein haptenates them.
What happens to the haptenated poison ivy oil?
They are taken up by Langerhan's dendritic cells, processed, and presented on MHCII to T cells
What type of Tcells respond to poison ivy haptenated complexes?
Th1
But what do we know about the types of immunity elicited in poison ivy infections?
Both Th1 and CTLs respond
How do CTLs get stimulated by poison ivy?
The pentadecacatechol is membrane permeant so becomes intracellular and presented on MHC I as well!
What are the forms of treatment for poison ivy contact dermatitis?
-Corticosteroids
-Benadryl
What is benadryl? what is it for?
Antihistamine - it blocks the products released by mast cells.
What are 4 other types of Tcell-mediated HSN that are not contact dermatitis?
1. IDDM (type I diabetes)
2. Rheumatoid arthritis
3. Exper. Allergic Encephalomyelitis
4. Inflammatory bowel disease