IgG vs IgM

Mike Preston preston at warren.med.harvard.edu
Mon Oct 16 16:21:23 EST 1995

When one is comparing, for example, the protective efficacy of an IgG
monoclonal antibody to that of an IgM with the same variable regions
(isotype switched) against a bacterial infection in vivo, what is the
correct comparison with regard to antibody concentration to use?  Since
IgM is approximately 5 times the molecular size of IgG do you need to
administer the antibodies on an equimolar basis ie. approximately 5 X as
much IgM on a microgram basis.  Or can the comparison be made using the
same amount of IgG and IgM by weight (to keep this simple let's assume
that IgG and the IgM monomer have the same molecular size).   One could
argue that you need to make the comparison with the same munber of
molecules and use an equimolar basis.  On the other hand you could argue
that IgM is just 5 immunoglobulin molecules tethered together and has an
advantage of increased avidity, increased complement activity etc.
I' making no assumptions about what effector functions might play a
protective  role in vivo.
 What are the arguments either way (or one way)
 Mike P.

Michael Preston
Channing Laboratory
preston at warren.med.harvard.edu

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