Immune Attack On Tissues: Hypersensitivity, Allergy And Transplant Rejection

Question 0

Type 1 hypersensitivity definition

Answer 0

Atopic allergy 
Immediate
Anaphylaxis 
Antibody mediated
Damage to self tissue triggered bŷ an adaptive immune response to non infectious agents

Question 1

Immunity, allergy and autoimmunity: self or foreign

Answer 1

Material recognised->material damaged-> result
Foreign-> foreign-> immunity
Foreign-> self-> allergy
Self-> self-> autoimmunity

Question 2

Type 1 hypersensitivy mechanism, immediate

Answer 2

Often harmless antigen reacts with specific IgE antibodies located on mast cells and basophils.

• > rapid release of preformed chemicals from mast cell
• > histamine-> vasoactive and inflammatory
• > Leukotrienes and prostaglandins-> vasodilation, smooth muscle spasm, vasopermeability, excessive epithelial secretion

Question 3

Type 1 hypersensitivy mechanism, late

Answer 3

Chronic response
Antigen is presented to Th2 cells
-> produce IL-4
-> stimulates B cells to produce IgE ->IgE binds mast cells->IgE-mast cell complex -> if exposed to antigen again-> reaction
Also produce IL-5-> stimulates eosinophils
Chronic tissue damage as a result of cytokines and eosinophil products

Question 4

Anaphylaxis

Answer 4

Systemic
Common allergens-> drugs, serums, venoms, peanuts
Route of entry-> intravenous or oral absorption
Responses-> edema, increased vasuclar permeability, tracheal occlusion, circulatory collapse, death
Acute widespread effects due to antigen reaching the blood stream

Question 5

Acute urticaria

Answer 5

Wheal and flare
Allergens-> insect bites! allergy testing
Route of entry-> subcutaneous
Response-> local increase in blood flow and vascular permeability

Question 6

Allergic rhinitis

Answer 6

Allergens-> pollens, dust mite faeces
Route of entry-> inhalation
Responses-> edema of nasal mucosa, irritation of nasal mucosa

Question 7

Asthma

Answer 7

Allergens-> danders (cat), pollens, dust mite faeces
Route of entry-> inhalation
Responses-> bronchial constriction! increased mucous production! airway inflammation
Inflammatory mediators increase mucous production-> acute response
Cytokines and eosinophils-> chronic response

Question 8

Food allergy

Answer 8

Allergen->foods
Route of entry-> oral
Response-> d and v, pruritis, urticaria (hives), anaphylaxis

Question 9

Skin prick test

Answer 9

Tests for sensitivity to specific allergens by intra dermal exposure
-> induces a wheel and flare reaction if allergic
Immediate-> redness and inflammation 15-60mins
Immediate + late-> redness and inflammation, appearance of IgE and T cells at 4-12 hours, disappear after 48
Delayed-> no redness till 12-48 hrs after appearance of Th1 cells
Eczematous test-> redness at 15-60mins, IgE and Th2 at 12-48 hrs-> broken skin

Question 10

Type II hypersensitivity definition

Answer 10

Circulating antibodies attaching to specific body antigens leading to death of the cells and tissues bearing the specific antigen

Question 11

Type II hypersensitivity mechanism

Answer 11

IgG, IgA or IgM antibodies bind to cell surface antigens
Results in antibody coated cells
Induces damage either by:
Lysis via activation of the complement system, cells can’t be phagocytosed so neutrophils secrete lysosomes
Or by killer cells directed against antibody covered cells
May also be phagocytosed by macrophages
Requires at least two IgG bound to target.

Question 12

Examples of type II hypersensitivity

Answer 12

-Immune haemolytic anaemia:
Allergic haemolytic anaemia
Autoimmune haemolytic anaemia 
Blood transfusion reactions
Haemolytic disease of new born 
Drug induced-> IgG specific for drugs that bind to the surface of RBC allergy. 
-autoimmune thrombocytopenia 
-pemphigold (skin)
-goodpastures disease 
-myasthenia gravis
-Graves' disease

Question 13

Type III hypersensitivity, definition

Answer 13

A normal response becomes excessive
Deposition of soluble circulating antigen-antibody complexes in vessel walls or other tissues
Characterised by vasculitis-> firbinoid necrosis of small blood vessel walls
Low blood complement
Small complexes excredted

Question 14

Type III hypersensitivity, mechanism

Answer 14

Several soluble antigens and antibodies cross link to form a lattice-> immune complex
Immune complex becomes lodged in tissues when too much is produced and can’t be removed fast enough
-> activate complement-> attract neutrophils
Neutrophils and factors attracted by platelets initiate the damage-> tissue inflammation and necrosis

Question 15

Type III hypersensitivity examples

Answer 15

Allergic alveolitis
Production of antibodies in response to inhaled fungal spores
Immune complexes form in alveoli walls leading inflammation and fibrosis
Results in breathlessness due to poor gas exchange

Question 16

Type IV hypersensitivity definition

Answer 16

Cell mediated, no antibodies involved

Caused by sensitised T lymphocytes

Question 17

Type IV hypersensitivity, mechanism

Answer 17

Sensitised T lymphocytes contact with a specific antigen
-> release cytokines
-> IL-2-> activates Tc cells
-> IFN-Y activates macrophages-> granuloma formation
Large numbers of lymphocytes and macrophages

Question 18

Type 3 hypersensitivity, examples

Answer 18

Reactions stimulated by Microorganisms-> TB and leprosy, also some fungi-> candidiasis 
Contact dermatitis-> react with carrier protein in the skin 
Acute graft rejection
Autoimmune:
Thyroiditis 
Adrenal it's
Gastritis
Type diabetes

Question 19

Transplant rejection, definition

Answer 19

Transplanted tissue destroyed by the immune system
Cell mediated hypersensitivity
Blood group and HLA antigens must match

Question 20

Acute graft rejection, mechanism

Answer 20

Major stimulus is differences between HLA proteins of donor and recipient that are recognised by T cells of the recipient
T cells react against HLA particularly type 2
Graft becomes infiltrated with lymphocytes-> t cells and macrophages
Recognition can be->
Direct-> by recognition of HLA proteins on antigen presenting cells of donor origin in lymph
Indirect-> recognition of peptides derived from donor proteins presented by recipients APCs