type 1 hypersensitivity Flashcards
define shock
failure to maintain an adequate cardiac output
what are the main types of shock?
hypovolaemic
obstructive
cardiogenic
distributive
what is the role of IgG?
block pathogen binding, activate complement and opsonise antigen for phagocytes
what is the role of IgM?
block pathogen binding and activate the complement (early stages of immunity.
what is the role of IgA?
blocks pathogen binding (neutralisation).
what is the role of IgE?
activates mast cells
what is the role of IgD?
not secreted and function is unknown
in what ways can mast cells and basophils be activated?
- Cross-linking of surface IgE by antigen
- Via complement proteins C3a and C5a
- Via nerves: axon reflex of sensory nerves, substance P (released from primary afferent neurons).
- Direct contact with the pathogen through innate receptors (PAMP), toll like receptors.
what is atopy?
inherited predisposition to make IgE to common environmental antigens
what mediators do mast cells release?
histamine, cytokines, leukotrienes
what does histamine do?
increase in permeability of post-capillary venules, vasodilation of arterioles, itch and contraction of smooth muscle
what do leukotrienes do?
increase in permeability of post-capillary venules as well as chemotaxis
what are the 2 clinical manifestations of type 1 hypersensitivity?
- Local = asthma, atopic eczema, urticaria (epidermal and dermal oedema), angioedema (subcutaneous and mucosal oedema).
- Systemic = anaphylactic shock - Patient does not have to be atopic.
what are the clinical manifestations of anaphylactic shock?
• Drop in blood pressure - Leak of fluid into interstitial space and dilation of great veins
• Urticaria , raised itchy red rash and sore red itchy eyes.
o Sudden onset of nasal soreness, secretions, sneezing.
• Angioedema: face, lips, hands, feet, pharynx, larynx.
• Bronchoconstriction
o Tries to stop more antigen from entering system.
• Nausea and vomiting, abdominal bloating, diarrhoea
• Headache, confusion, loss of consciousness.
• Feeling of impending doom
define urticaria
hives
what is a raised itchy red rash?
inflammation in dermis
define angiodema?
swelling in subcutaneous tissues
define bronchoconstriction
wheeze, respiratory obstruction
why does bronchoconstriction occur in anaphylactic shock?
tries to stop more antigen from entering the system
give examples of antigens that trigger anaphylaxis
- Drugs = beta lactams (penicillin), monobactams, aspirin, NSAIDS, insulins.
- Latex
- Peanuts
- Bee stings
what are acute treatments for anaphylaxis?
- Intramuscular adrenaline 500 micrograms
- Oxygen high flow
- Antihistamines
- Glucocorticosteroidd (200mg hydrocortisone)
what is anaphylactoid shock? how is it similar and different to anaphylactic shock?
• Anaphylactoid shock (non-allergic) = same symptoms but IgE not involved.
o Mast cells and basophils are activated by another mechanism
how does desensitisation work?
arthropod venoms, drugs, peanuts etc… are administered sublingually/subcutaneously under medical supervision. This induces replacement of IgE response with IgA/IgG or stops.
