Immunopathology - SRS,LM and whoever else wants a piece I reckon, this one is big. Flashcards
What cells mediate Type I reactions?
TH2 cells, by cytokines
What causes B cells to class switch to IgE?
IL-4
Type II hypersensitivity reactions are mediated by?
Antibodies - IgG and IgM, cause injury to cells directly
Type III reactions are mediated by what?
Immune complexes, IgG and IgM antibodies bind antigens and the antigen antibody complexes deposit in tissues and induce inflammation.
What mediates Type IV reactions?
Sensitized T-Lymphocytes (TH17 and TH1 cells along with CTLs)
What is the immune mechanism for Type I reactions?
Production of IgE antibody → immediate release of vasoactive amines and other mediators from mast cells; later recruitment of inflammatory cells
What is the immune mechanism for Antibody-mediated (type II) hypersensitivity?
Production of IgG, IgM → binds to antigen on target cell or tissue → phagocytosis or lysis of target cell by activated complement or Fc receptors; recruitment of leukocytes
What is the immune mechanism for Immune complex-mediated (type III) hypersensitivity?
Deposition of antigen-antibody complexes → complement activation → recruitment of leukocytes by complement products and Fc receptors → release of enzymes and other toxic molecules
What is the immune mechanism for Cell-mediated (type IV) hypersensitivity?
Activated T lymphocytes →
(1) release of cytokines → inflammation and macrophage activation;
(2) T cell-mediated cytotoxicity
What type of reaction is described by these lesions?
Phagocytosis and lysis of cells; inflammation; in some diseases, functional derangements without cell or tissue injury.
Type II
What type of lesion is described by the following lesions?
Vascular dilation, edema, smooth muscle contraction, mucus production, tissue injury, inflammation.
Type I
What type of reaction is described by the following lesions?
Inflammation, necrotizing vasculitis (fibrinoid necrosis)
Type III
What type of lesion is described by the following lesions?
Perivascular cellular infiltrates; edema; granuloma formation; cell destruction
Type IV
Name 2 examples of Type II reactions we need to be aware of.
- Autoimmune hemolytic anemia/thrombocytopenia;
- Goodpasture syndrome
Name three examples of type III reactions we covered.
- Systemic lupus erythematosus;
- some forms of glomerulonephritis;
- serum sickness;
- Arthus reaction (in situ dermal injection of antigen).
What are 6 examples of type IV sensitivity reactions?
- Contact dermatitis;
- multiple sclerosis;
- type 1 diabetes;
- tuberculosis;
- rheumatoid arthritis;
- inflammatory bowel disease
A 69 year old woman was stung on her right hand by a wasp. She had been stung several times in the past, most recently two weeks before this sting.
Within 5 minutes she felt faint. She then developed a headache, chest tightness and became unconscious.
She was gasping for air and appeared grey. She regained consciousness in 2 minutes but lost it when she tried to stand. Intramuscular adrenaline and intravenous antihistamines corrected her problem.
•Labs: serum IgE elevated, antibodies to wasp venom elevated, but anti-bee venom normal.
What is the long term treatment modality for this?
Desensitization over 12 weeks followed by monthly maintenance for 3 years.
What are the three changes seen in the immediate or initial reaction to a type I hypersensitivity?
- dilated leaky vessels –> edema
- contraction of smooth muscle
- increased mucus production
Describe the mechanism of the immediate phase reaction.
TH2 activation –> IgE class switch in B cells –> IgE –> release of mediators from mast cells
Describe the late phase reaction mechanism for type I rxns.
Late phase reaction = TH2, epithelial and mast cells secrete IL-5 and eotaxin →eosinophils → enzyme,major basic protein and cationic protein release → tissue destruction
To what receptors on mast cells does IgE bind?
FceRI
What are the common cutaneous manifestations of anaphylaxis?
Urticaria and angioedema
Flushing
Pruritus without rash
What are the common respiratory manifestations of anaphylaxis?
Dyspnea
Wheeze
upper airway angioedema
Rhinitis
What are some common abdominal manifestations of anaphylaxsis?
Nausea
vomiting
diarrhea
Cramping pain
























