bryan fisk (bryan_fisk at gyn.mda.uth.tmc.edu) wrote:
: >So once again I ask, How do T cells distinguish foreign antigens from
: >idiotypes presented by B cells? Why should the former activate and the
: >latter not?
: For peptides from the idiotypic region to be presented by MHC class I or
: II molecules it must a) possess the proper binding MHC binding motif and
: b) have a sufficiently high binding affinity and/or be present in high
: enough concentration to effectively compete with other self-peptides.
: Thus, it would appear doubtful that every B-cell would effectively
: present idiotypic peptides. Also, B-cells which present peptides via
: class II but not class I may have an advantage in recieving added T-cell
: help (possible means of autoimmunity?). Finally, it seems of very low
: probability that a single, non-proliferating, naive B-cell will
: encounter a cognate T-cell in the periphery.
The problem I have with this answer is:
1) At least some B cells present their idiotypes (I confess, I don't know
the fraction)
2) Many of these B cells that do present their idiotypes will become
activated in the course of their lifetimes
3) If an activated B cell can activate a naive T cell, an autoreactive T
cell that cross-reacts on that B cell idiotype could do a lot of damage.
As rare as you think such a situation may be, it only takes one encounter
of an autoreactive T cell with a B cell presenting a cross-reacting
idiotype during the entire lifetime of the animal to do (possibly)
significant and potentially lethal damage.
Ephraim Fuchs
