How do granulocytes and macrophages detect enemies?

J.R. Pelmont Jean.Pelmont at
Sat Oct 4 10:18:24 EST 1997

John Richard Seavitt <jrseavit at> wrote:

> ..........
> Phagocytes also have proteins on their surface that bind, for example
> bacteria, in specific ways.  This is not the 'specificity' of antigen
> receptor recombination, but rather based on certain differences bewteen
> bacterial cells and mammalian cells.  For example, bacterial cell walls
> have a component called LPS, which phagocytes have receptors for. 
> However, no human cells have LPS, and thus this is a way to distinguish
> the two.  There are some additional blood proteins that have affinity for
> various bacterial products, and for which phagocytes have specific
> receptors. 

Yes, polynuclear neutrophiles, after stimulation by several factors,
migrate toward the site of infection. One type of stimuli is provided by
formylated peptides freed from damaged bacterial cells, recognized by
specific receptors. The migration is a complicated process, involving
sticking to the endothelium wall of the vessels, rolling on the surface
and extruding themselves by diapedesis. Special proteins help this. Once
on the spot, phagocytosis starts, triggerring in turn the synthesis by
leucocytes of various non specific agents aiming at bacteria. Oxidations
produce superoxide and hydrogen peroxide. The latter is used by a
myeloperoxidase, an extraordinary system converting ordinary chloride
ions to ClO- ions. The machinary of this has been the object of a long
research since the last fifteen years. It is called respiratory burst.
It involves a complex biochemical and regulatory system. In some persons
having an hereditary defect, chronic granulomatosis, respiratory burst
is deficient and these people usually die soon from multiple infections.
Just like other hereditary disorders in the complement system, a very
essential line of defense too. Once the enemy has been detected,
respiratory explosion is an important factor in our defenses, but acts
non specifically, contrary to antibodies. Cheers

jean.pelmont at
Fax (33)0 476 51 4336

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