Regarding your question about the lack of deletion of certain Vb subsets:
Although I haven't done these experiments myself, I looked into doing them
in some of our transgenic mice that are on the C57BL/6 background. What I
found was that the evidence for an increase in certain TCR Vb subsets after
injection of superantigen came from studies primarily done in BALB/c mice.
I have read one paper (Immunity 2:185-194, 1995) where they used both
C57BL/6 mice and BALB/c mice. They saw no expansion in CD4+ Vb8+ T cells on
day 4 after injection of SEB into B6 or (B6 X 129)F2 mice. I think these
changes may be dependent on the strain of mice that you use. Some
superantigens preferentially bind to I-E, and B6 mice do not express I-E.
I hope this helps,
Charles Sentman