Why is Coombs a Type2 but immunofluorescence a Type3 hypersensitivity?

[cameraGEEK]

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From first aid, page 210:
Why is Coombs a Type 2 but immunofluorescence a Type 3 hypersensitivity? Both involve an antibody on an antibody attached to a protein... seems like if one is a complex, the other one should be considered a complex as well?

 

[gravitywave]

Type III is not merely complexes, it's circulating complexes. Type II is completely or mostly tissue-specific: Goodpastures, Graves Dz, autoimmune hemolysis. Type III is free complexes going all over the place and recruiting neutrophils to the scene wherever they land: SLE, strep glomerulonephritis, serum sickness.

IF isn't Type III specific, BTW. it's a diagnostic tool used to see where the complexes are showing up. You could use IF to diagnose type II or III, depending.

 

[turkeyjerky]

Type III is not merely complexes, it's circulating complexes. Type II is completely or mostly tissue-specific: Goodpastures, Graves Dz, autoimmune hemolysis. Type III is free complexes going all over the place and recruiting neutrophils to the scene wherever they land: SLE, strep glomerulonephritis, serum sickness.

IF isn't Type III specific, BTW. it's a diagnostic tool used to see where the complexes are showing up. You could use IF to diagnose type II or III, depending.

One issue w/ your post: the deposited immune complexes in PSGN are actually formed in situ, not circulating.

 

[gravitywave]

One issue w/ your post: the deposited immune complexes in PSGN are actually formed in situ, not circulating.

meh. the available evidence suggests that it's not that clear-cut, and for the purposes of this discussion (and for the Step) I wanted to keep things simple. Arthus reaction is the archtype for the mechanism, and PSGN is under that umbrella in all the basic path texts.

edit: meant serum sickness as the archetype for Type III, not Arthus. mah B.

 

[stepvictory]

From first aid, page 210:
Why is Coombs a Type 2 but immunofluorescence a Type 3 hypersensitivity? Both involve an antibody on an antibody attached to a protein... seems like if one is a complex, the other one should be considered a complex as well?

Type 2 hypersensitivity - caused by antibodies IgG or IgM formed to fix antigens .leads to cytokine activation and membrane attack complex. cytokines recruits neutrophils leading to tissue damage.
the antigen may be mimic our own tissue Eg rheumatic fever
or antigen may be due to autoimmunity(our own tissue) Eg Myasthenia gravis

type 2 hypersensitivity diagnosed by Coombs test to detect the antibodies.

Type 3 hypersensitivity - caused by immune complexes . which circulate and deposit in diff tissues.once they deposit.the immune complex (antigen antibody complex) activate complement which attracts lot of neutrophils and cause damage.
immune complex may deposit in various tissues causing damage
deposit in veins - vasculitis - polyarteritis nodosa
deposit in lung- farmer's lung
deposit in kidney-PSGN

diagnosed by -immunofluorescent staining which detects immune complexes in the tissue