Type 1 Hypersensitivity and Anaphylactic Shock Flashcards
What is meant by ‘atopy’?
This is the predisposition to make IgE to common environmental antigens
What are the cells of the innate immune system?
Neutrophils, monocytes (macrophages on activation), eosinophils and mast cells
What are the cells of the adaptive immune system?
B and T lymphocytes
What is clonal deletion?
Where lymphocytes in the thymus (T cells) or bone marrow (B cells) are maturing, and they are tested for autoimmune response, if they cause a reaction to self-antigens then they are destroyed
What is clonal expansion?
In a clonal expansion of lymphocytes, all progeny share the same antigen specificity in order to elicit a greater binding and thus immune response to the foreign antigen
What are the differences between T and B lymphocytes?
B lymphocytes are produced in the bone marrow and not the thymus gland, and can bind to antigens directly via their antibody receptors whereas T cells have to bind to antigens presented by APCs
What molecule acts as an antigen receptor on B cells?
Antibodies act as the antigen receptor on B cells
Where do B lymphocytes mature?
Bone marrow
Where do T cells mature?
Thymus gland
How do T cells recognise antigens?
They only recognise antigens once they are presented by APCs as their own receptor secretion is very little
How do innate immune cells bind to foreign antigens?
They can bind antibodies to their cell surface via the Fc receptor and use the antibody specificity to facilitate binding.
Which type of antibody can pass across the placenta?
IgG
What is the action of IgG antibodies presented by innate immune cells?
This can block pathogen binding, active complement and activate opsonisation to prepare the antigens/pathogens for phagocytosis
What is the action of IgM antibodies presented by innate immune cells?
Block pathogen binding and activate complement
What is the action of IgA antibodies presented by innate immune cells?
This antibody blocks pathogen binding and is present in many secretions such as tears and digestive juices
What is the action of IgE antibodies presented by innate immune cells?
Binding to this antibody activates mast cells
How may mast cells and/or basophils be activated?
> Via cross-linking of surface IgE on their surface antigens
Complement activation by C3a and C5a
Substance P or directly from nerves
Direct contact with pathogen
Which complement factors can activate mast cells and basophils?
C3a and C5a
What is the action of histamine produced as result of type 1 hypersensitivity?
> Increases permeability of the post-capillary venues
Vasodilates arterioles
Causes contraction of some smooth muscle e.g. bronchial
Increases itch
What is the action of leukotrienes that are produced as result of type 1 hypersensitivity?
> Increase permeability of post-capillary venules
> Facilitates chemotaxis (increases inflammation)
What is the action of prostaglandin produced as result of type 1 hypersensitivity?
> Arteriolar dilatation
Pain
Fever production
What is the pathophysiology behind type 1 hypersensitivity?
This type of hypersensitivity involves mast cell activation which leads to the release of mediators such as histamine, leukotrienes and prostaglandins.
What is anaphylactic shock?
Where there is systemic manifestation of allergic reaction that leads to systemic vasodilation and therefore shock due to insufficient cardiac output
What causes the drop in blood pressure in anaphylactic shock?
Due to the increased permeability of the post-capillary venues as result of histamine and leukotriene release in allergic response, there is leakage of fluid into the interstitial space
What is urtricaria?
This is also known as his and is is a raised, itchy red rash that is caused by inflammation of the skin dermis
What is angiodema?
This is swelling in the subcutaneous tissue
What may trigger anaphylaxis?
Certain antibiotics (beta lactams), aspirin, NSAIDS, anaesthetics, latex, foods, bee stings (arthropod venom) and exercise perhaps
What drugs may trigger anaphylactic reaction?
Beta lactams, monobactams (antibiotics), aspirin, NSAIDS and anaesthetics
How is anaphylactic shock treated?
Adrenaline given (to increase sympathetic tone and cause vasoconstriction to increase blood pressure and venous return to the heart), oxygen is given (in case there is airway obstruction), antihistamine, fluid IV and hydrocortisone (cortisol analogue which will increase water retention to increase blood volume and thus BP)
