In article <9411081312.AA15640 at xtal220.harvard.edu> collins%xtal220 at HARVARD.HARVARD.EDU writes:
>>Okay, I think we all agree and understand that the mechanisms for presenting
>self or foreign peptides are interrelated and that macrophages are no
>different in that respect than any other APC. The question has strayed from
>that point I think. The question is: How do macrophages recognize a body to
>be phagocytosed? While I agree that other systems can make it easy for the
>macrophage (ie recognition by antibodies), this requires that the immune
>system have previous knowledge of the foreign particle. Certainly it is true
>that there will be cross-reactive antibodies around, but this is like the old
>arguement about the chicken and the egg. To anthropomorphize a bit, don't y
>believe that there must be a mechanism for the macrophage to make up its own
>mind?
First, thanks for clarifying the discussion. If I've been
carefully answering a question nobody asked, I apologize . . .
Phagocytosis is outside my field, so if there is a phagocytosis
expert listening in please jump right in. My understanding is that there
is a continous background uptake of just about anything - especially
particulate material - but that this background can be cranked up under a
number of circumstances: the rate and efficiency of the phagocytosis can
go up in inflammatory states, and different substances can be
phagocytosed more efficiently. Some of these have intrinsic qualities -
mebranes etc that make them more attractive. Complement and antibody
also enhance this. Since complement can be activated by the alternative
system, there isn't necessarily the chicken and egg scenario with this.
I also picture, though, a positve feedback mechanism. The background
phagocytosis inefficiently triggers a low level of T cell response, which
turns on the various factors (upregulation of phagocytosis, inflammation,
perhaps antibody expression, etc) and this enhances the
uptake/presentation, etc.
Obviously I need to review phagocytosis.
Ian
--
Ian York (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-4328 Fax (617)-632-2627
