bluestar
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what are the activators of classic pathway and those of alternative pathway?
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| mash
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classic pathway--Ag-Ab complexes activate C1--
C1---->C2 & C4---->C2b,4b(C3 convertase)----->C3----->C2b,4b,3b(C5 convertase)----->C5------->C5b+C6 and C7------>C5bC6C7+C8 and C9---->C5bC6C7C8C9(MAC)
alternative pathway --microbial surface substances activate C3 and B(bacterial LPS, fungal cell wall and viral env)
---->C3and B----->C3bBb(C3 convertase)----->C3----->C3bBb3b(C5 convertase)---->C5----->same as above
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| mdwannabe
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classic... gotta have C3B and 2 IGg's or 1 IgM and the LPS from bacteria, for Ig to attach to.
alternative... only C3B is necesary, and bacterial membrane.
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| bluestar
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very good. just want to emphasize that in classic pathway, Ab has to be either IgM or IgG and not anything else, and in alternative pathway, we need endotoxin or fungal cell wall or viral envelope. Also according to Goljan, IgM can activates from C1 to C9 while IgG can't go beyond C3. (I don't quite understand this part, does that mean IgG can't active complement all the way by itself and would need IgM's help to accomplish classic pathway eventually? )
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| mash
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IgM is the most potent activator of complement so, it goes frm C1-9 forming MAC in the bld itself ...it has a valence of 10
whereas IgG (valence=2)binds to Ag on cell surface(thru Fab) and to Fc receptor on macrophages... C3b is reqd fr complement activation which binds to C3b receptors on macrophages and then these macrophages phagocytose these cells.
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