How do macrophages know what to eat?

Marc Buhler mbuhler at STOP_SPAMmail.usyd.edu.au
Thu Feb 12 09:27:04 EST 1998

Axel Boldt wrote:
> Hi,
> I've asked this question here before, I didn't quite understand the
> answers, was advised to read a good immunology book and did just
> that. However, every book I get my fingers on seems to gloss over the
> (from my perspective) most important point about the whole immune
> system.
> Neither B- nor T-cells nor anybody else will take any action unless a
> new antigen has been engulfed, processed and presented by a macrophage
> (let's talk about thymus-dependant antigens only for now); so the most
> central question of all should be: how do macrophages know what to
> engulf? 

If antibodies are stuck to it, the macrophage can use Fc receptors (tail
end of the antibody, as it were) to "know" they should engulf it.  There
is no need for the macrophage to choose between "self" and
"non-self".... most *everything* should be taken in, digested and
presented. It is then up to the repertoire of T-cells (selected in the
thymic education stages of T-cell development) to be able to tell
"non-self" from "self".  So there really isn't a problem for the
macrophage in terms of choice here, as I see it.

>Which soluble proteins, which free viruses, which bacteria?
> How do THEY distinguish self from non-self?  And, given this huge
> evolutionary pressure, why are there not more pathogens who can
> circumvent this macrophage detection mechanism and thereby bypass the
> whole immune defense? Why does everybody talk about the wonders of
> gene rearrangement and somatic mutation which account for the
> specificity of antibody, when the genes that tell macrophages what to
> do are much more important?

You should read up a bit on the recent findings about dendritic cells -
nox *these* guys seem to have a few roles to play in the initiation of
immune response, and perhaps in the long-term memory aspects.

> Thanks for any reply that could help clear this up for me.
> Cheers,
>   Axel

(signed) marc


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