Dermatology: Types and Mechanisms of Hypersensitivity Rxns

Question 1

name a type I hypersensitivity rxn

Answer 1

anaphylactic and atopic

Question 2

name mechanism of anaphylactic and atopic HSN RXN

Answer 2

antigen cross links IgE on presensitized most cells and basophils, triggering the release of vasoactive amines like histamine. rx develops rapidly as a result of preformed antibody

Question 3

name examples of anaphylactic HSN RXNs

Answer 3

anaphylaxis, asthma, urticarial drug rxns, local wheal and flare

Question 4

name a type II HSN RXN?

Answer 4

cytotoxic

Question 5

name mechanism of cytotoxic HSN RXN?

Answer 5

IgM and IgG bind to antigen on an “enemy” cell leading to lysis by complement or phgocytosis

Question 6

what complex is formed in type II HSN RXN?

Answer 6

antibody and complement lead to membrane attach complex MAC

Question 7

give examples of cytotoxic HSM RXN

Answer 7

autoimmune hemolytic anemia, erythroblastosis fetalis, Goodpasture’s syndrome rheumatic fever

Question 8

give examples of type III HSN RXN?

Answer 8

immune complexes, serum sickness, arthus reaction

Question 9

name mechanism of immune complex HSN RXN

Answer 9

antigen-antibody complexes activate complement which attracts PMNs, PMNs release lysosomal enzymes

Question 10

which HSN RXN includes many glomerulonephrides and vasculitides

Answer 10

immune complex- type III

Question 11

name examples of immune complexes HSN RXN

Answer 11

polyarteririts nodosa, immune complex glomerulonepritis, SLE, rheumatoid arthritis

Question 12

name mechanism of serum sickness

Answer 12

antibodies to the foreign proteins are produced in 5 days. immune complexes form and are deposited in membranes, where they lead to tissue damage by fixing complement

Question 13

what is serum sickness caused by? what are signs and symptoms.

Answer 13

-most is caused by drugs, not serum

fever, urticaria, arthralgias, proteinuria, and lymphadenopathy occurs 5-10 days after antigen exposure

Question 14

which is most common serum sickness or arthus rxn

Answer 14

serum sickness

Question 15

name mechanism of arthus rxn

Answer 15

a local reaction to antigen by preformed antibodies characterized by vascular necrosis and thrombosis

Question 16

when does arthus rxn occur?

Answer 16

rarely 4-12 hrs after vaccination

Question 17

name example of arthus rxn

Answer 17

hypersensitivity pneumonitis

Question 18

name example of type IV HSN RXN

Answer 18

delayed cell mediated type

Question 19

name mechanism of delayed cell mediated

Answer 19

sensitized T lymphocytes encounter antigen and then release lymphokines (leading to macrophage activation)

Question 20

is type IV HSN RXN transferable by serum

Answer 20

it’s cell mediated therefore it is not transferable by serum

Question 21

give examples of delayed cell-mediated

Answer 21

TB skin tests, transplant rejection, contact dermatitis