The molecules of IgG required to activate the classic complement pathway is:
A. Half the molecules of IgM required
B. Same as the molecules of IgM required
C. Double the molecules of IgM required
D. Quadruple the molecules of IgM required
This is a tough question. I realize now that I don't know too many details in immunology :toosad: But, to activate the classic pathway of the compliment you need the interaction between the antigen and the epitopes which will result in binding of the complement C1 to Fc portion, right? So, if IgM is a pentimer, does it need 5 molecules of C1 to activate the compliment? I don't know. But I think one would be enough. That's why I choose B) Same as the molecules of IgM required.
C ... Double that of IgM ... ( googled for it .. And also IgG4 has no role in activating compliment .. Only the other three can activate the classical compliment pathway )
@ Teona :Yeah .. There is no explanation anywhere ... ( may be that is why they say IgM is a potent activator of compliment .. If I find any explanation , I'll let you know Teona! )
Logically,It should be but that's what he said & that's how I annotated it in my FA. these are from master Goljan
Just know that IgG to IgM is 2:1
IgM is a better activator of Classic PW than IgG
IgM starts in acute state while IgG is chronic cases
IgM drives the PW upto production of C1-C9 while IgG stops at C3
@blade..............goljan mentioned it for antigen pal, not for complement.........regarding binding, IgM, a pentamer and is divalent, thus can bind 10 antigens/epitopes, and only 5 complements.........
the answer here is not related to the binding sites or affinity.............they can't be quantified:...........just remember that when every single IgM molecule can activate the complement, >2 IgG molecules are required for the same effect...................so best answer here would be DD..........>2...................this gives the concept that IgM is the most potent activator of complement, but how potent??-cannot be quantified..............2 or less than 2 molecules of IgG can't activate with same potency is a fact seen experimentally.....................
Hey,I don't get your point.you said Goljan mentioned binding to antigens and not complement?I don't get it?it binds antigens to activate the complements right?maybe you should listen to him again.
What's your source for the quadruple IgG pls?
As I said before,it's even more logical for pentagonal IgG not even bi/quadruple IgG
Some sources may not be available but we've got to share things we know..........
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
USMLE Forums
402.5K posts
115K members
Since 2009
A forum community dedicated to the United States Medical Licensing Examination. Come join the discussion about schools, exams, news, prep, reviews, accessories, classifieds, and more!