Class swith recombination : single step or more steps ?

Daniele Focosi mi at
Wed Nov 6 06:53:31 EST 2002

Can anyone explain me if during class swith recombination in plasma
cells more steps are needed to reach the final isotype or if DNA
deletion occurs in a single step looping out the whole region between
the past and the new Fc segments ? I know different cytokines milieu
can drive class switch to defined classes : what I'm asking is if to
switch from, e.g., IgM to IgA you need sequential deletion (one by
one) of all Fc segments interposed, and so if IgG-producing
intermediate exist. If such intermediates exist, how long does it take
on average to switch from a class to another ? It could be reasonably
to say that all cytokines milieu are required in a defined order and
so it would be a quite rare event ....
Furthermore, I have read that some class switch recombinations can
occur without DNA deletion (e.g. IgE produced without deleting
interposed segments) : do sustained evidences for such affermations
exist or are they just experimental mistakes ?
Many thanks !


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