Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: lein on 23/07/2004 16:02:34

Title: phagocytosis
Post by: lein on 23/07/2004 16:02:34
Is opsonization which will help the phagocytosis, possible with IgA?

Cause in biologybooks there are only discriptions that IgG captures a bacterial cel (with their fab fragments). I know that IgG is more common in our body, so there's a bigger chance that there are antibodies specific to a bacteria that are IgG's.
Title: Re: phagocytosis
Post by: chris on 04/08/2004 09:52:13
Opsonisation is the process by which foreign material - such as a bacterium - is "flagged" by special proteins, known as opsonins, which improve the efficiency of their removal (phagocytosis) by acting as a beacon to attract white blood cells (phagocytes) to the site of infection.

The 2 chief opsonins are IgG class antibodies, and a protein called C3b which is produced by another branch of the immune system known as the complement pathway.

IgG antibodies recognise bacterial epitopes by their 'fab' portion, and C3b is 'sticky' and locks on to bacterial surfaces. C3b is produced by enzymes called C3 convertases which are activated by antibody (IgG or IgM) binding (the so called classical complement pathway) or by the physical presence of micro-organisms (the alternative complement pathway).

IgA is primarily a mucosal antibody - it is secreted to protect exposed membrane surfaces like the eyes, mouth, GI tract and genitals. At these sites phagocytosis does not play a major role - preventing entry is more important. So many IgA's will block surface receptors preventing viruses from locking on to target cells, or bacteria from gaining a foothold.


"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: phagocytosis
Post by: lein on 06/08/2004 09:31:27

But what if there is not enough (IgA) to prevent virusses/ bacteria anymore. I was thinking about a product which has got specific IgA/IgG against bacteria which causes serious problems in the GI tract. This product you have to drink/eat so it has to pass the gastric juice. It's known that IgA could pass that part and IgG will mostly denature.
That's why I asked myself if IgA also could opsonize bacteria to enhance the phagocytosis.
I now know that it is possible against Bordetella pertussis infection. But this is reached by vaccination and that's not an option in this case.

Title: Re: phagocytosis
Post by: chris on 10/08/2004 09:10:24
You could use IgA to neutralise gut pathogens, but it would be a terrifically expensive exercise. Targeted immunoglobulins (usually of the IgG class) are used to provide at-risk individuals with so called 'passive immunity' under certain circumtances, but the immunoglobulins are all human in origin and hence in very short supply.

Examples of where this is used currently include Zoster immunoglobulin (Zig) to protect non-immune pregnant women who have been exposed to chicken pox, Hepatitis B immunoglobulins which are used under certain circumstances to protect neonates born to Hep B positive mothers, and anti-rabies immunoglobulin.

I think there are probably better ways to protect yourself from infection, although you may know different ?


"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx