Allergy and Immunology Flashcards
First Aid and NEJM Knowledge+
Differentiate epidermal vs intradermal tests for allergen skin testing
Both are used to test for presence of allergen-specific IgE antibody
Epidermal skin test- some antigen extract put on skin then punctured into epidermis to see if IgE mediated response
-adequate for most things
Intradermal test of injected antigen into dermis for drug reactions
-use for venom and penicillin testing
Both should include histamine and saline controls, look for wheal and flare reaction 15-20 minutes after injection
What is RAST testing used for?
(a) What allergies can it not test for
RAST test = test serology for antigen-specific IgE (basically to see if there is an allergy)
Use when skin testing unavailable or not possible (ex: pt just took benadryl or would cause anaphylaxis)
-more for environmental and food allergens
However RAST alone is not adequate for venom (bee sting) or drug allergy (need intradermal skin test)
Candida and PPD purified antigens injected into skin- what is this a test of?
Both test for cell-mediated immunity
Lack of response to injection indicates inadequate cell-mediated immunity or anergy
Buzzword: otherwise healthy pt p/w recurrent neisseria meningitis
Recurrent neisserial infections c/w terminal complement deficiency (C5-C9 which makes the MAC complex)
What can be used as a screening test for the classic complement pathway?
CH50 can be used as a screening test for the classic complement pathway (triggered by immune complexes)
B/c all elements C1-C9 are needed to make normal CH50
Mnemonic for hypersensitivity type I-IV reactions
‘ACID’
Type I- anaphylactic
Type II- cytotoxic (antibodies directed at self cells)
type III- immune complex mediated
type IV- delayed hypersensitivity (T- cell mediated)
Describe the mechanism of type I hypersensitivity reaction
Type I = anaphylactic
Antigen exposure causes cross-linking of IgE on mast cells or basophils => release of histamine, leukotrienes, PGEs, and tryptase => symptoms
Give clinical examples of type II hypersensitivity
ACID- anaphylactic, cytotoxic (Ab mediated), immune complex, delayed hypersensitivity (T-cell)
Examples of antibody mediated hypersensitivity reaction:
- drug-induced (ex: PCN) autoimmune hemolytic anemia
- autoimmune thyroiditis
- Goodpasture’s syndrome
- ABO incompatibility
Describe the mechanism of type II hypersensitivity reaction
IgM or IgG antibodies produced that attack self- cell surface or tissue antigens
These IgM/G antibodies destroy cells by
- opsonization (coating for phagocytosis)
- complement-mediated lysis
- antibody-dependent cellular toxicity
Describe the mechanism of type III hypersensitivity reaction
‘ACID’: anaphylaxis, cytotoxic (auto-immunity), immune complex, delayed (T-cell)
Exposure to antigen in genetically predisposed individuals cause antigen-antibody complex formation, these immune complexes activate complement and neutrophil invasion => tissue inflammation
Prototypical type III hypersensitivity rxn
Serum sickness- where exposure to certain drugs (most frequently beta-lactam abx) causes symptoms 10-14 days after exposure due to immune complex deposition (causing inflammation and neutrophil invasion) into tissues
=>
rash pruritus arthralgia fever lymphadenopathy malaise hypotension
Most common type of type IV hypersensitivity rxn
Allergic contact dermatitis such as poison ivy (diagnosed by skin patch testing)
Describe the mechanism of type IV hypersensitivity reaction
Antigen (ex: poison ivy) directly activates already sensitized T cells (usually CD4+ cells)
CD4 activation => tissue inflammation 48-96 hrs after exposure
Best diagnostic test for allergic contact dermaitits
Allergen patch test- substance covered by adhesive x48 hrs- then watch for erythema, edema, vesiculation
Which to test for the following deficiencies
(a) Humoral immunity deficiency
(b) NK cell deficiency
(a) Test CD19 for B cell immunity
(b) Test CD16 and CD56 for natural killer cell immunity
19 y/oM w/ asthma- taking ICS BID and albuterol as needed
Persistent wheeze and cough day and night 2x per week
Next step in management?
Is on meds for mild persistent (ICS and SABA PRN) but now meets criteria for moderate persistent (given more than 2 nights a month) =>
Increase to medium dose ICS
Add LABA
Use of methacholine challenge in diagnosing asthma
Methacoline challenge alone is not diagnostic for asthma- negative test rules out asthma (sensitive) but not very specific (positive test can be from other things)
So sensitive but not specific
Numeric datapoint useful in helping when to use systemic corticosteroids in asthma exacerbation
Consider systemic ‘roids when PEF (peak expiratory flow) remains under 80% of personal best after albuterol
Which asthma related med, when used as mono therapy, is associated w/ asthma-related deaths
LABA (salmeterolol, formoterol) mono therapy associated w/ asthma-related death => hence why always used in combo w/ ICS
ex: symbicort = budesonde (ICS) + formoterol (LABA)
Distinguish mild persistent and moderate persistent asthma
Mild persistent: more than 2 days per week but less than 1 time/day or more than 2 nights per month
PEF is still 80 or above
While moderate persistent is daily symptoms or more than one night per week, PEF 60-80%