Immune attack on tissues

What is tissue damage in immunology

Hypersensitivity

What is an allergy

A disorder in which the immune system is overly sensitive to a foreign substance

What is tissue damage in immunology

Hypersensitivity

What is an allergy

A disorder in which the immune system is overly sensitive to a foreign substance

What is autoimmunity?

When body attacks its own cells

What is type 1 hypersensitivity?

-Antigen binds to IgE found on mast cells or basophils

-triggers release of histamine

-occurs in allergies

What is type II hypersensitivity?

IgG or IgM attack antigens on body's own cells

triggers activation of complement ,NK cells and macrophages

Type III hypersensitivity

soluble antigen forms complex with IgG/IgM and accumulate in tissues causing damage

Type I II and III hypersensitivity are

Antibody mediated

Type IV hypersensitivity reaction

T-cell mediated disorders

T H1 activate macrophages to clear foreign material

Leads to Tissue damage

What are the 4 hypersensitivity reactions

Normal immune reactions but activated inappropriately or excessively

Another rename for type 1 hypersensitivity

Atopic allergy

3 components of atopic allergy

Mast cells

Allergens

IgE

What do mast cells usually do

Generate rapid inflammatory response

What happens in atopic allergy

IgE get cross linked

Because it's bound to an allergen

Activated mast cell to degranulate

To release inflammatory mediators

And cause smooth muscle contraction and oedema

What does degranulate mean

Release of contents of granules

From mast cells

Like inflammatory mediators

Mechanism of tissue damage 1

Antigen up by APC

Presented on MHC 2 (not a virus)

Interact with CD4 T helper 2 cell

Produce cytokines (IL4)

Helps B cell change surface IgM to Class switch to produce IgE

Specific to the allergen

Bind to mast cell Receptor

Allergen returns binds to surface IgE on mast cell

releases hisramines

Performed and newly performed mediators

Inflammation

What is first exposure to allergen

Sensitisation

Is presented by MHC 2

What do Th2 cells do?

stimulate humoral (antibody) response

What interleukins are released by TH2 (EEM)

IL4 - class switch to IgE

IL5 - stimulate eosinophils

IL 10 - mast cell activation

What is second exposure to same allergen called

Elicitation

What happens in the elicitation phase

IgE bind to allergen

Cross linked

Mast cell produce pre formed and newly formed mediators

Inflammation

What are in preformed granules (made and released quickly )

Histamine

Heparin

Tryptase

What are in newly generated granules

Arachidonic acid

Leukotrienes

Prostaglandins

Cytokines

How can you get systemic anaphylaxis

IV entry of allergen

Causes oedema tracheal occlusion

Death

How to get urticaria (wheal and flare)

Subcutaneous entry - under the skin

Local increase in blood flow and permeability

trigger a reaction that causes high levels of histamine and other chemicals to be released in the skin, leading to swelling and itchiness

What causes allergic rhinitis

Inhalation of allergen

Oedema of nasal mucosa

What causes asthma?

Inhalation of allergen into lungs

Bronchial constriction and increased airway inflammation

What causes food allergy reaction

Oral entry

Vomiting

Diarrhoea

Urticaria

Anaphylaxis

What is pruritus?

severe itching

What is urticaria (hives)?

How to determine what a person is allergic to

Introduce 0.2 micro litres of allergen intradermally - wait 20 mins and see where inflammation is because of mast cell IgE cross link

What is type II hypersensitivity

Can be a foreign or self tissue leading to reaction

involved IgG IgM

What is a type III hypersensitivity reaction?

immune complex reaction - found in systemic lupus and rheumatoid arthritis

Immune complexes not cleared and triggers huge systemic response

What is extrinsic allergic alveolitis

Caused by organic allergens (Bird poo , mouldy hay , wood dust)

Immune complexes deposit

Lead to fibrosis

Difficulty breathing (can present similar to asthma)

What is a type IV hypersensitivity reaction?

Type IV (D) reactions or cell-mediated delayed hypersensitivity requires sensitized lymphocytes to start the inflammatory reactions. Type IV reactions are seen in contact dermatitis .

What is Type IV reaction mediated by

T H1 cell and macrophages

Takes 2-4 days for reaction

Examples of Type 1 hypersensitivity

Allergic rhinits

asthma

eczema

food allergies

acute urticaria

Type 2 hypersensitivty

Blood transfusion reactions

Allergic hemolytic anemia

Pemphigoid

Type 3 hypersensitivity

Dermititis

Allergic alveolotis

systempic lupus

rhematoid arthritis

Type 4 hypersensitivity

Contact dermatitis

TB

Type 1 diabetes

Gastritis