IUBio

First immuno response

Dom Spinella dspinella at chugaibio.com
Fri May 8 12:36:57 EST 1998


> Trond Erik <teva at online.no> writes:

> Sorry if this question has been recently debated...
> 
> I've been wondering about this for a while. It seems like a version of
> the classic hen and egg.
> 
> To be able to battle infections, plasma cells (active B-cells) secrets
> spesific antibodies. But for a B-cell to become active, it has to be
> stimulated by a helper-T-cell. And for a helper-T-cell to be active, it
> needs to be stimulated by an APC. An APC is a former makrofag who has
> ingested antigen/antibody-complexes, therby becoming an APC.
> 
> Let's say we have a child who hasn't been infected before. That is to
> say it hasn't secreted antibodies yet. When the first infection arrives,
> how can it respond? It doesn't have the necesarry secreted antibodies to
> facilitate ingestion by makrofags. And that is the first step in humoral
> immuno response.
> 
> I guess some of my theory above is wrong. Please correct me ;)
> 
> Regards
> Trond Erik Vee Aune

Trond:
The incorrect assumption here is that antigen presentation by APCs
absolutely requires preliminary coating of antigen by antibody
(sometimes called opsonization).  While this does indeed increase the
efficiency with which certain APCs (notably macrophages) uptake antigen,
it is not abolutely required.  In fact, several other cell types
(especially B-cells and dendritic cells) can and do function as APCs and
may be more globally important sources of antigen presentation than
macrophages (particularly the dendritic cells).  All of these cells are
normally quite phagocytic and can uptake and process native (i.e.
unopsonized) antigens.  B-cells can also capture cognate antigens via
cell-surface Ig molecules, and also process and present to T-helper
cells.
Hope that helps.
--Dom Spinella



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