Hypersensitivity Flashcards
How can identifying the antigen specificity of a T cell receptor help in determining if a T cell proliferation is neoplastic?
If they all have the same TCR then the proliferation is clonal and likely neoplastic
So if we can use the TCR to identify a T cell neoplasm, what can be use to identify a B cell neoplasm?
immunoglobulins - if it’s all the same antibody, likely neoplastic
What mediates a type 1 HSR?
It’s a rapid immunologic reaciton occuring within minutes of exposure, mediated by IgE-dependent activation of mast cells
What leukocytes in particular are recruited in type 1 HSR?
eosinophils
What does “atopy” refer to?
the predisposition to develop localized immediate hypersensitibity reactions - genetic
Atopic individuals tend to have higher levels of what Ig in the serum?
IgE (and more IL-4 producing TH2 cells)
The immediate reaction in Type 1 HSR is characterized by what?
vasodilation, congestion, and edema
The late phase reaction in Type 1 HSR occurs when? Is characterized by what?
2-24 hours after the immediate reaction. characterized by an inflammatory infiltrate rich in eosinophils, neutrophils and T cells
What are some examples of LOCALIZED allergic reactins?
- allergic rhinitis
- some forms of bronchial asthma
- utricaria (hives) - but can also be systemic
- allergic gastroenteritis (food allergy)
What’s the tratment for localized allergic reactions?
avoid the allergen, antihistamines, corticosteroids, leukotriene modifiers, immunotherapy
What is systemic anaphylaxis typically characterized by?
a life threatening systemic allergic reaction with bascular shock, widespread edema and difficulty breathing due to massive mast cell activation
What are some common inciting agents for the systemic anaphylaxis reacitons?
beta lactam antibiotics like penicillin, cephalosporins, radiocontrast agents, foods like peanuts and seafood, insect toxin like bee stings and latex
What’s the treatment for anaphylaxis?
intramuscular epinephrine
Describe desensitization therapy for bee sting allergies?
Repeated injection of very small amounts of th evenom to cause the immune system to develop increasingly greater amounts of IgG antibodies that can bind to the venom before they bind to mast cells
What mediates a type 2 HSR?
ANTIBODIES! They bind to the antigen and cause complement activation and phagocytosis - inflammation, etc.
WHat are some examples of type 2 HSR?
autoimmune hemolytic anemia pemphigus vulgaris goodpasture syndrome myasthenia gravis grave's disease insulin-resistant diabetes pernicious anemia thromobcytopenic purpura
Describe goodpasture syndrome.
Antibodies attack a noncollagenous protein in the basement membranes of the kidney glomeruli and lung albeoli, so you get complement and Fc receptor-mediated inflammation leading to nephritis and lung hemorrhage
What mediates a type 3 HSR?
antigen-antibody complexes that get stuck in blood vessels and elicit inflammation
What are two areas in the body that are particulatly sensitive to type 3 HSR?
blood vessels and any organ where blood is filtered to form other fluids - like kidney sand synovium (so arthritis, vasculitis, and glomerulonephritis)
Levels of what complement protein can be used to monitor type 3 HSR disease activity?
C3 - low levels indicate active disease because the classical pathway is in hyperdrive due to the ICs and you get depletion of C3
What are some examples of diseases cause dy type 2 HSRs?
systemic lupus erythematosus poststreptococcal flomerulonephritis polyarteritis nodosa (hepatitive B!) reactive arthritis (from bacterial infections) serum sickness
What mediates a type 4 HSR?
T cells!
What are the two mechanisms of T-cell mediated hypersensitivity?
- delayed-type hypersensitivity
2. T-cell mediated cytotoxicity
Describe a delayed-type hypersensitivity reaction?
upon repeat exposure to the antigen, CD4+ T cells respond to antigen by secreting cytokines that stimulate inflammation and activate phagoytes, leading to tissue injury - this is the TB test!
Describe a T-cell mediated cytotoxicity reaction.
The CD8+ T cells directly kill the tissue cells - like type 1 diabetes and graft rejection
Describe the mechanism of granuloma formation.
It’s a type 4 HSR…
An antigen presenting cell presents the antigen to a CD4+ T cell
THe T cell then secretes cytokines to bring monocytes out of circulation into the tissue
The macrophages join together to form histiocytes and giant cells, in essence blocking off the invader
When do granulomas form?
When there’s a persistent or nondegradable antigen like TB or fungi - also foriegn bodies
What are some examples of type 4 HSR diseases?
Type 1 diabetes mellitus (against pancreatic islet cells) multiple sclerosis (attacks myelin) rheumatoid arthritis crohn disease peripheral neuropathy/guillain-barre? contact dermatitis
