Fun. I - Type I Hypersensitivity

Hypersensitivity

An exaggerated response by the immune system to an antigen that poses little or no threat

A response to self-antigen is considered ____.

autoimmunity

Type I Hypersensitivity Reaction

IgE mediated reaction that causes degranulation of sensitized mast cells/basophils: Releases Histamine

Atopy

A hypersensitivity or allergic state

____ stimulate Type I Hypersensitivity Reactions.

Allergens

Allergens usually have what 3 characteristics?

(1) Internal enzymatic activity

(2) PAMPs/PAMP-Like Structures

(3) Enter host through mucosal tissue

All Hypersensitivity Reactions consist of what 2 phases?

(1) Sensitization Phase: Primary immune response to antigen "primes" mast cells

(2) Effector Stage: Secondary immune response to same antigen

Type I Sensitization Phase

- Allergen-Specific IgE is produced after the first exposure to an antigen

- IgE binds mast cells and basophils

IgE binds to ____.

Fc(epsilon) Receptors on mast cells

Type I Effector Phase

Mast Cell Degranulation induces inflammation, smooth muscle contraction, and vascular dilation

What are the 2 parts to the Type I Hypersensitivity Effector Phase?

Immediate

- Mediated by release of pre-formed molecules in Mast Cells

Late

- Released Chemokines/Cytokines recruit Eosinophils, Basophils, and Lymphocytes to the site

____ play a principal role in allergies.

Eosinophils

Eosinophils

Release Major Basic Protein (MBP) which stimulates continual degranulation of Mast Cells

Histamine drives the ____ phase of Type I Hypersensitivity Reactions.

immediate

____ drive the Late Effector Response of Type I Hypersensitivity Reactions.

Eosinophils

____ and ____, released by Eosinophils, drives the Late Effector Response.

MBP/ECP

ECP

Eosinophil Cationic Protein

What does release of Prostaglandins and Leukotrienes by Mast Cells/Eosinophils cause?

- Tissue Edema

- Smooth Muscle Contraction

- Eosinophil and Th2 Activation

Causes the continual inflammation of an Allergic Reaction

Type I Hypersensitivity GI Effects

- Increased Secretion

- Increased Peristalsis

Type I Hypersensitivity Airway Effects

- Bronchoconstriction

- Mucus Secretion

Type I Hypersensitivity Blood Vessel Effects

- Increased Blood Flow

- Increased Permeability

Systemic Anaphylaxis

Release of IgE leads to mass mast cell/basophil activation

- Bronchoconstriction

- Vasodilation: Low BP

- Tachycardia

- Swelling

Wheal-and-Flare

Rash/Hives that appear due to release of serum into tissues (swelling) and dilation of blood vessels (redness)

Wheal-and-Flare is characteristic of ____.

Type I Hypersensitivity

Purpose of IgE-mediated Immune Responses

Protect against Parasites