Practice #10 Flashcards
What are the 4 hyper sensitivity reactions?
- Allergic reaction (IgE mediated)
- Cytotoxic reaction/ tissue injury (mediated by auto IgG antibodies against self cellular of matrix components)
- Immune complexes deposition (mediated by IgG)
- Cell mediated (delayed response)
What is the time requires for avary hyper sensitivity reaction to occur?
- minutes
- 4-6 hours
- 6-8 hours
- 2-3 days
What is the most severe hypersensitivity reaction?
1
What is the least severe hypersensitivity reaction?
4
What are the criteria for an allergan?
- Small protein (often glycated) or chemical bound to a protein
- Size 5-70kDa
- Usually enzymes (proteases)
5 types of allergic responses according to the site of entry of the allergan?
- Acute urticaria (Nattle rash) by insect sting or latex
- Food allergy by peanut, fish, milk
- Allergic rhinitis by inhaled pollen
- Asthma by inhaled pollen
- Systemic anaphylactic reaction by animal toxin, intravenous drug, ingested peanuts
What is the sequence of events in sensitization to an allergan?
- Phagocytosis by DC and presentation
- Activation of naive Th cells to become Th2 (by IL4)
- Th2 secrete IL4, IL13 to induce class switching of activated B lymphocyes from IgM to IgE
- IgE bind to Fc epsilon RI on mast cells
What is the sequence of events during the second exposure to an alllergan?
- Allergan binds to IgE on mast cells inducing mast cell degranulation, AA derivatives secretion and IL5 secretion
- Phagocytosis by DC and presentation
- Activation of naive Th cells to become Th2
- Th2 cells secrete IL5
- IL5 from mast cells and Th2 will activate eosinophil degranulation
Upon activation of mast cells what is the chronological sequence of events?
- Degranulation and secretion of Histamine, Heparin, Serotonine, Enzymes like Tryptase
- Activation of PLA releasing AA from the membrane and activation of COX, LOX pathways to produce prostaglandins, leukotrienes and PAF
- Signal transduction to activate cytokine gene expression and secretion of IL5
Histamine receptors and their functions
H1R mucosal secretion, vascular permeability, bronchospasm, HR increase, intestinal hypermotility
H2R vasodialation, air way mucous production
H4R itching, chemotaxis of eosinophils, mast cells and DC
H3R found in the brain (systemic His cannot cross the BBB)
Prostaglandins and leukotrienes effects
Bronchospasm
Increased vascular permeability
Inflammation
Intestinal hypermotility
Tryptase activity
Anticoagulant
Bronchospasm
Heparin function
Anticooagulant
What is the treatment for an allergic reaction?
- Adrenalin
- Corticosteroids
- Antihistamines
- Sodium chromo-glycolate (mast cell degranulation inhibitor)
What are the basics of skin allergy test?
Negative control: Glycerol- saline
Positive control: Histamine
Intra dermal injection of different allergans and examination of the diameter around the site of injection
If it is larger then 3mm over the negative control or identical to the positive control the test is positive to the allergan
What are the skin allergy test contra indications?
- Pregnancy
- Beta blocker therapy
- skin infection in the forearm
*If the patient is taking antihistamines or antidepressents the treatment should be stopped 3-5 days before the test
What is anaphylactoid reaction?
Reaction induces by drugs (like NSAID, aspirin, opiods etc), by histamine rich food or by radiographic contrast material that may evoke mast cell/ basophils degranulation or increase in histamine levels.
Food hypersensitivity options
- Immunological
- IgE mediated (allergy)
- Non IgE mediated (celiac disease) - Non immunological (lactose intolerance)
Allogenic serum desensitization therapy is based on…
Exposure of the patient to smaller amounts of the allergan at the time and evoke Treg mediated response and by that induce tolerance
Specific allergan desensitization therapy
Infusion of anti allergan IgG antibodies in order to prevent its binding to IgE on mast cells in the short term and in the long term inhibit production of further IgEs by inhibiting B cells via Fc gamma RIIB
What is the mechanism of non allergic eosinophilic airway inflammation?
pollutants, microbes or other irritants activate innate lymphoid cells ILC2, in turn they secrete IL5 that will evoke eosinophil degranulation
Criteria for eosinophilic asthma
- over 3% eosinophils in the sputum
- over 400/microL eosinophils in the blood
- decreased FEV1
- bronchospasm
- good response to glucocorticoids
- positive prick test
