Properidin-- leading to membrane attack complex
there was a post earlier.. but cant find it...so am posting here
earlier a question was put up about what was the primary mechanism of cleaving an RBC in an immune reaction such as an ABO mismatch
the two choices that produced most arguments were between
1--- properidin cleaving of C3
2--- membrane attack complex
earlier had put forward a point that 1---- leads to 2.. but cudnt explain it in decent words
didnt understand the concept too well either.. but knew something like that existed...
anyways.. hv found an article now that will explain it...
am putting up the link and the excerpt from it
(what it basically says is MAC to form.. needs C5 to be activated...
C5 is activated by "activated" C3b/a
Properidin activates this C3--> C3b/a
and hence is the PRIMARY CAUSE in the cleaving of RBC)
The alternate pathway may be initiated by immunologic (e.g. IgA or IgE) or non-immunologic (e.g. LPS) means. The cascade begins with C3. A small amount of C3b is always found in circulation as a result of spontaneous cleavage of C3 but the concentrations are generally kept very low (see below). However, when C3b binds covalently to sugars on a cell surface, it can become protected. Then Factor B binds to C3b. In the presence of Factor D, bound Factor B is cleaved to Ba and Bb; Bb contains the active site for a C3 convertase. Next. properdin binds to C3bBb to stabilize the C3bBb convertase on cell surface leading to cleavage of C3. Finally, a C3bBb3b complex forms and this is a C5 convertase, cleaving C5 to C5a/b. Once formed, C5b initiates formation of the membrane attack complex as described above
hope this helps clear the air... and also helps us to actually answer questions on the exam!!
all the best to everyone
Last edited by mbbs2010; 02-14-2012 at 06:53 AM.
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