14 Hypersensitivity and Autoimmunity I Flashcards
What are the two ways in which the immune system can go wrong?
exaggerated responses (hypersensitivity) and autoimmune responses
what are the four mechanisms of immunopathology?
Type I. Anaphylactic/atopic
Type II. Cytotoxic injury
Type III. Immune-complex mechanism
Type IV. Delayed hypersensitivity
What is the mechanism of Type I hypersensitivity?
First, IgE binding to mast cells and basophils results in release of histamine, which causes vasodilation and leakage, an increase in mucus, eosinophil infiltration, and vascular collapse. Later, synthesis and release of prostaglandins and leukotrienes results in prolongation of symptoms.
T/F: Type II hypersensitivity may involve either cytotoxic or noncytotoxic mechanisms.
T
How does cell death occur in Type II cytotoxic hypersensitivity?
The target cells are opsonized by antibodies, and undergoes various cytotoxic processes, such as attack by killer T-cells and myeloid cells, complement mediated lysis, and immune adherence to and destruction by phagocytes of spleen
T/F: hemolysis of donor RBCs of an incompatible blood type is an example of type III hypersensitivity.
F; type II
What are non-cytotoxic type II reactions?
antibodies to structural proteins (eg Pemphigous and pemphigoid diseases)
review slide 12 for examples of immunohistochemistry staining of blistering diseases.
.
antibodies to cell receptors in Type II reactions can activate or deactivate a cellular function. Name an example for each.
Thyrotoxicosis (Graves disease): Ab activates TSH receptor
Myasthenia gravis - Ab inactivates ACh receptors
what are the symptoms of Graves disease?
heat intolerance, weight loss, hyperreflexia, and exopthalmia/proptosis
what are the symptoms of myasthenia gravis?
muscle weakness
What is the mechanism of Type III hypersensitivity?
1) Antibodies form against foreign or self antigens in the circulation
2) Complement activation leads to increased vascular permeability and increased activity of PMNS. Increased PMN activity leads to greater tissue infiltrate and phagocytosis and local destruction of blood vessels and connective tissue.
What are the signs and symptoms of systemic immune complex diseases?
fever, urticaria, arthralgias, proteinuria and hematuria, lymphadenopathy
T/F: hypersensitivity reactions are all mediated by antibodies.
F; I-III are, but IV is t cell mediated
what are the two types of Type IV hypersensitivity reactions?
delayed hypersensitivity and cell-mediated cytotoxicity
What is the mechanism of a type IV delayed hypersensitivity reaction?
Sensitized T lymphocytes direct the reaction, but recruit additional cells (especially macrophages) to act as major effector cells.
What type of cells mediate type IV cell-mediated cytotoxicity reactions?
CD8 t cells
TB skin test reaction is an example of what?
delayed hypersensitivity
what is the time course of a delayed hypersensitivity reaction?
local erythema and induration appear after 8-12 hours. Reaction peaks after 2-7 days and slowly subsides.
what is the time course of a granulomatous reaction?
Require weeks to months to develop and may resolve slowly or persist indefinitely.
Transplant rejection is most like what type of hypersensitivity reaction?
Type IV
T/F: in Graft vs. Host disease, the host attacks a transplanted tissue.
F; that is the definition of rejection. In GvHD, the graft immune cells attack the host
Acute rejection is what type of hypersensitivity reaction?
Type IV
Hyper acute rejection is what type of hypersensitivity reaction?
Type II
What is hyper acute rejection?
occurs when host Abs attack vascular endothelium, resulting in antigen-Ab complexes and destruction of the vessels
what is is called when anti-donor antibodies cause necrotizing vasculitis?
Acute humoral rejection
What is goodpastures?
a condition in which patients make antibodies to type IV collagen in the lungs and kidneys, resulting in glomerulonephritis and pulmonary hemorrhages
what type of hypersensitivity reaction is goodpastures?
Type II
what type of hypersensitivity reaction is serum sickness?
Type III
what are the symptoms of serum sickness?
high fever, rash, joint pain, and lymphadenopathy
what causes serum sickness?
usually presents 1 wk after innoculation with anti-venom or drug treatment (eg streptokinase)
