Axel Boldt wrote:
>> Marc Buhler <mbuhler at STOP_SPAMmail.usyd.edu.au> said:
>> Axel> Neither B- nor T-cells nor anybody else will take any action unless a
> Axel> new antigen has been engulfed, processed and presented by a macrophage
> Axel> (let's talk about thymus-dependant antigens only for now); so the most
> Axel> central question of all should be: how do macrophages know what to
> Axel> engulf?
>> Marc> If antibodies are stuck to it, the macrophage can use Fc receptors (tail
> Marc> end of the antibody, as it were) to "know" they should engulf
> Marc> it.
>> At this point, we don't have antibodies. Before the B-cell can produce
> antibodies, it has to be stimulated by a Th cell, which has to find
> something on a macrophage surface. So the macrophage must know what to
> eat without the help of antibodies.
>> Marc> is no need for the macrophage to choose between "self" and
> Marc> "non-self".... most *everything* should be taken in, digested and
> Marc> presented.
>> That would be a possibility of course, but wouldn't that mean that
> macrophages chew on the good stuff all day and destroy valuable
> proteins and cells along the way?
>> Axel
If you've read the post in this thread from Ian York, you will see some
good comments on this subject. I agree with him - cells are damaged and
die and as bits are available to be engulfed, so they are. It's a bit
of a paradox in immunological dogma that the "non-self" pathway of
immune recognition also has to contend with "self" presented in that
way. But *HOW* could the phagocytic cell pcik things apart?? Well - as
Ian and Mark have said, they can't. Hence the t-cell deletion and t-cell
/ b-cell regulation in the development of a "self-deleted" repertoire.
(signed) marc
