How do macrophages know what to eat?

[mark]

Just to expand into another grey area that was talked about in the past 
in the idea of danger and non-danger.  Polly Matzinger hypothesis is that 
 dying cells release compounds which would activate dendritic cells in 
the case of danger and wouldn't in the lack of danger. That activation, 
if her model is correct, may play a role in controlling responsivity. 
This idea could be approximated to include bacteria. However, by binding 
bacteria the phagocyte is promoted to engulf it. the other posts have 
talked about how this process is mechanically controlled (opsinization 
with C' and/or AB.  Sialic residues can initiate binding to macs as 
well.  However, phagocytosis and antigen presentation are NOT 
self/nonself discrimination.  All peptides from degraded proteins are 
presented (to one extent or another) self and non-self.