Immunology Flashcards
What are appropriate immune responses?
Occur to foreign harmful agents such as viruses, bacteria, fungi, parasites
- Required to eliminate pathogens
- May be concomitant tissue damage as a side effects, but as long as pathogen is eliminated quickly, it will minimal and repaired easily
- Involves antigen recognition by cells of the immune system and antibody production
What can appropriate immune tolerance occur to?
- Self
- Food
- Pollens
- Other plant proteins
- Animal proteins
- Commensal bacteria
What causes appropriate immune tolerance?
- Antigen recognition and regulatory T cells and regulatory antibody (IgG4) production
What are hypersensitivity reactions?
- Occur when immune responses are mounted against
- Harmless foreign antigens (allergy, contact, hypersensitivity)
- Autoantigens (autoimmune diseases)
- Alloantigens (serum sickness, transfusion reactions, graft rejection)
How are hypersensitivity reactions classified?
Type I: Immediate hypersensitivity
Type II: Antibody-dependent cytotoxicity
Type III: Immune complex mediated
Type IV: Delayed cell mediated
Give examples of type I hypersensitivity reactions
- Anaphylaxis
- Asthma
- Rhinitis (seasonal, perennial)
- Food allergy
What happens during Type I immediate hypersensitivity?
Primary antigen exposure:
- The immune system is sensitised to the specific antigen
- IgE antibody production
- IgE binds to Mast cells & Basophils
Secondary antigen exposure:
- More IgE antibodies are produced
- Antigen cross-links IgE on mast cells/basophils
- Degranulation
What is the clinical presentation of Type II Antibody-dependent hypersensitivity in organ-specific autoimmune diseases?
1) Myasthenia gravis- antibodies act on Ach receptors in muscle
2) Glomerulonephritis- antibodies act of glomerular basement membrane
3) Pemphigus vulgaris- act on epithelial cell cement proteins
4) Pernicious anaemia- intrinsic factor blocking antibodies
What is the clinical presentation of Type II antibody-dependent hypersensitivity in Autoimmune cytopenias?
Antibody destruction of blood cells leads to cell shortage
- Haemolytic anaemia (RBC)
Thrombocytopenia (platelets
Neutropenia (neutrophila)
How is type II antibody-dependent hypersensitivity tested for?
Test for specific antibodies
- Immunofluorescence
- ELISA
What is involved in Type III immune complex mediated hypersensitivity?
- Formation of antigen-antibody complexes in the blood
- Deposition of complexes in a tissue
- Complement and cell recruitment/activation
- Activation of other cascade e.g. clotting
- Tissue damage (vasculitis) such as systemic lupus erythematosus (SLE) and vasculitides
Give examples of Type IV delayed hypersensitivity responses
Th1 mediated: - Chronic graft injection - GVHD - Coeliac disease - Contact hypersensitivity Th2 mediated - Asthma - Rhinitis - Eczema
What are the three main varieties of type IV delayed hypersensitivity responses and the mechanisms?
Th1, Cytotoxic, Th2
Transient/persistent antigen is processed and presented by APC, which causes T cell activation of macrophages and CTLs
- Th1 mediated reactions involve the release of IFN-gamma and IL-2 from Th1 cells.
IFN-gamma leads to macrophage activation and pro-inflammatory TNF-alpha release
IL-2 activates cytotoxic T lymphocyte activation which leads to cell destruction
- Much of tissue damage is dependent upon TNF
What are the signs of inflammation?
- Redness
- Heat
- Swelling
- Pain
What are the features of inflammation?
- Vasodilation, increased blood flow
- Increased vascular permeability
- Inflammatory mediators and cytokines
- Inflammatory cells and tissue damage
What causes increased vascular permeability in inflammation?
C3a
C5a
Histamine
Leukotrienes
What cytokines are involved in inflammation?
IL-1 Il-6 IL-2 TNF IFN-gamma
What chemokines are involved in inflammation?
IL-8/CXCL8
IP-10/CXCL10
What des the inflammatory cell infiltrate involve?
- Cell trafficking: chemotaxis
- Neutrophils, macrophages, lymphocytes, mast cells
- Cell activation
What are the genetic risk factors of allergy?
Polygenic
- 50-100 genes linked to asthma/atopy
- Genes of IL-4 gene cluster (chromosome 5) linked to raised IgE, asthma, atopy
- Genes on chromosome 11q (IgE receptor) linked to atopy and asthma
- Genes linked to structural cells links to eczema (filaggrin) and asthma (IL-33, ORMDL3)
What are the environmental risk factors of allergy?
1) Age- increases from infancy, peaks in teens and reduces in adulthood
2) Gender- asthma more common in males in childhood, females in adults
3) Family size- more common in small families
4) Infections- early life infections protect
6) Animals- early exposure protects
7) Diet- breast feeding, anti-oxidants, fatty acids protect
What are the types of inflammation in allergy?
1) Anaphylaxis, urticaria, angioedema
- Type I hypersensitivity (IgE mediated)
2) Idiopathic/chronic urticaria
- Type II hypersensitivity (IgG mediated)
3) Asthma, rhinitis, eczema
- Mixed inflammation
- Type I hypersensitivity (IgE mediated)
- Type IV hypersensitivity (chronic inflammation)
What des expression of allergic disease require?
- Development of sensitisation to allergens to sensitise instead of tolerance (primary response- usually in early life)
- Exposure to produce disease (memory response- any time after sensitisation)
What happens during subsequent exposure in atopic airway disease?
- Subsequent exposure to the allergen causes memory T cells to rapidly differentiate to Th2 cells leading to IgE secretion from plasma cells
- IgE then binds to IgE receptors on mast cells, cross-linking the receptors causing mast cell degranulation and release of inflammatory mediators
- Th2 also releases IL-5 which causes eosinophils to release inflammatory mediators
What happens during primary sensitisation in atopic airway disease?
- Antigen is inhaled
- Allergen in picked up in airway lumen. It is processed and presented in naive T cells by dendritic cells
- Naive T cell differentiates to form either Th1, Th2 or T-reg cell.
- T-reg cells secrete IL-10, Th1 secreted IFN-gamma. Both inhibit differentiation of naive T cells into Th2 cells
- Th2 cells then secrete IL-4 and IL13, which stimulate the proliferation and differentiation of B cells into plasma cells, which in turn synthesise and release IgE
What are eosinophils?
- 2-5% of blood leukocytes
- Present in blood but most reside in tissues
- Recruited during allergic inflammation
- Generated from bone marrow
- Polymorphous nucleus- 2 lobes
- Contains large granules with toxic proteins
- Can lead to tissue damage
What are mast cells?
- Tissue resident cells
- IgE receptors on the cell surface
- Crosslinking of IgEs leads to degranulation and mediator release.
- Mediators may be preformed (histamine, cytokines and toxic proteins) or newly synthesised (leukotrienes and prostaglandins)
What are neutrophils?
- Important in virus induced asthma, severe asthma and atopic eczema
- 55-70% of blood leukocytes
- Nucleus contains several loves
- Granules contain digestive enzymes
- Synthesise oxidant radicals, cytokines and leukotrienes
What causes acute inflammation of the airways in asthma?
- Mast cell activation and degranulation
- The pre- stored mediator involved is histamine
- The newly synthesised mediators involved are prostaglandins and leukotrienes
- Results in acute airway narrowing
What causes chronic inflammation of the airways in asthma?
- Cellular infiltrate of Th2 lymphocytes and eosinophils
- Smooth muscle hypertrophy
- Mucous plugging
- Epithelial shedding
- Sub-epithelial fibrosis
What are the clinical features of asthma?
- Reversible generalised airway obstruction: chronic episodic wheeze
- Bronchial hyper-responsiveness: bronchial irritability
- Cough
- Mucous production
- Breathlessness
- Chest tightness
- Response to treatment
- Spontaneous variation
- Reduced and variable peak flow
What is allergic rhinitis?
May be
Seasonal: hay fever- grass, tree pollens
Perennial- House dust mites or animal proteins
What are the symptoms of allergic rhinitis?
- Sneezing
- Rhinorrhoea
- Itchy nose, eyes
- Nasal blockage, sinusitis, loss of smell/taste
What is allergic eczema?
- Chronic itchy skin rash
- Flexures of arms and legs
- House dust mite sensitisation and dry cracked skin
- Complicated by bacterial and viral infections (herpes simplex)
- 50% clears by 7 years
- 90% by adulthood
What food allergies are seen in infants and children/adults?
Infancy- 3 years: Egg, cows milk
Children/adults- Peanut, shell fish, nuts, fruits, cereals, soya
What are the mild and severe symptoms of food allergies?
Mild: Itchy lips, mouth, angioedema, urticaria Severe: Nausea, abdominal pain, diarrhoea Anaphylaxis
What is anaphylaxis?
- Severe generalised allergic reaction
- Uncommon, potentially fatal
- Generalised degranulation of IgE sensitised mast cells
What are the symptoms of anaphylaxis?
- Itchiness around the mouth, pharynx, lips
- Swelling of the lips, throat and other parts of the body
- Wheeze, chest tightness, dyspnoea
- Faintness, collapse
- Diarrhoea and vomiting
- Death if severe and untreated
What systems are affected in anaphylaxis?
- Cardiovascular: vasodilation, cardiovascular collapse
- Respiratory: bronchospasm, laryngeal oedema
- Skin: vasodilation, erythema, urticaria, angioedema
- GI: vomiting, diarrhoea
How are allergies investigated and diagnosed?
- Careful history essential
- Skin prick testing
- RAST (blood specific IgE)
- Total IgE
- Lung function (asthma)
How is anaphylaxis treated?
Epipen and anaphylaxis kit
- Includes antihistamine, steroid and adrenaline
How is allergic rhinitis treated?
- Antihistamines: sneezing, itching rhinorrhoea
- Nasal steroid spray: nasal blockage
- Cromoglycate: children, eyes
How is eczema treated?
- Emollients
- Topical steroid cream
If severe: anti- IgE, anti-IL4/13, anti IL-5 mAb
What are the steps in asthma treatment?
Step 1: Use short acting Beta-2 agonist drugs as required by inhalation
- Salbutamol
Step 2: Inhaled steroid low-moderate dose
- Beclomethasone/Budenesonide
- Fluticasone
Step 3: add further therapy
- Add long acting beta-2 agonist, leukotriene antagonist
- High dose inhaled steroids
Step 4: Add courses of oral steroids
- Prednisolone
- Anti-IgE, anti-IL4/13, anti-IL-5 mAbs
What is immunotherapy used for?
Effective for single antigen hypersensitivies: venom allergy, pollens, house dust mite, antigen used is purified
- Subcutaneous immunotherapy (SCIT): 3 years needed, weekly/monthly clinic visits
- Sublingual immunotherapy (SLIT): 2-3 years, can be taken at home
What is autoimmunity?
Adaptive immune responses with specificity for self ‘antigens’ (autoantigens)
What are the mechanisms of autoimmunity?
- Adaptive immune reactions against self use the same mechanisms as immune reactions against pathogens
- Autoimmune diseases involve breaking T-cell tolerance
- Because self tissue is always present, autoimmune disease are chronic conditions
- Effector mechanisms resemble those of hypersensitivity reactions, types II, III and IV
Give examples of major autoimmune diseases
- Rheumatoid arthritis
- Type I diabetes
- Multiple sclerosis
- Systemic lupus erythematosus (SLE)
- Autoimmune thyroid disease
What gender are autoimmune diseases more common in?
Women
Give examples of organ-specific autoimmune diseases and their targets
Graves disease- Thyroid Hashimoto's thyroiditis- Thyroid Type I diabetes- Pancreas Goodpasture's syndrome- Kidney Pernicious anaemia- Stomach Primary biliary cirrhosis- Liver, bile Myasthenia gravis- Muscles Dermatomyositis- Skin/Muscles Vasculitis- Blood vessels Rheumatoid arthritis- Joints SLE- Multiple targets