A new discussion in immunology

Shahram Mori smori at nmsu.edu
Wed Jan 26 14:07:27 EST 1994


Hello Immunetters,
I came across an article in science Vol 262 pg 844-845 and I wanted to get
your opinion on it.
There has been evidence that indicates the presence of a new protein that
is a costimulator of T-cells.Earlier a protein called B7-1 was involved in
transmiting a signl needed for the T cell activation. However there  is new
evidence that indicates a new protein with 26% identity to B7-1. This protein
was named B7-2. Evidence that B7-1 is not the only stimulatory signal came
with antibody studies against B7-1 which showed that there was still about 30%
activation present.Others lines of evidence indicated that mouse with a
knocked out B7-1 gene also indicated stimulation of Tcells. The evidence
for B7-2 came from studies involving mice with a knocked out B7-1 gene.
The Cd-28 receptor ( to which B7-1 binds ) has a related receptor CTLA-4 which
binds even better than CD-28. When a soluble form of CTLA-4 was given to
these knocked out mice , there was much surprise because the APC's bound
the CTLA-4 just as strongly as the normal mice. This was the first real
evidence of a second Costimulatory signal.
So there are 2 costimulatory signals B7-1 and B7-2. When they tried to
find which plays a more important role by looking at the times that B7-1
and B7-2 appeared on an active APC's surface. They found out that B7-1 did not
pop up until 24-48 hrs after an APC sent its first signal to the T cell.
This sounds strange because T- cells need costimulatory signal within 24
hrs after receiving the first. B7-2 however has mRNA that is present in
unstimulated APC's. This brings up the question as to what is the function
of B7-1 if it's not even produced soon enough to stimulate the T-cell?
Also does the prenesence of an mRNA in ustimulated cells mean that it's
produced first? It's likely but not certain until one looks at
translational regulation and Post-translational modification.

Thanks for responding. I guess posting it is better than e-mailing it so
that other people can read other's ideas
Cheers
Shahram
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