How do macrophages know what to eat?

[Axel Boldt]

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