Changes

==Function==

==Function==

[[Image:Ab-antigen.jpg|thumb|right|150px|Antibody binds 2 whole antigen molecules - B. Catchpole, RVC 2008]]

[[Image:Ab-antigen.jpg|thumb|right|150px|Antibody binds 2 whole antigen molecules - B. Catchpole, RVC 2008]]

*For an overview of the role of immunoglobulins in the adaptive immune response, see [[:Category:Adaptive Immune System|here]]

Antibodies form part of the adaptive immune response. For further information on the adaptive immune response, see [[:Category:Adaptive Immune System|here]]. All antibody classes bind antigen in a similar manner; the initial trigger for all antibody function is the association of antigen with the antigen-binding sites of the immunoglobulin molecules. However, different classes serve different physiological functions and functional differences between antibody classes are reflected in the structural differences in their '''heavy chain constant regions'''. These heavy chain regions comprise the '''effector domains''' of antibody molecules. In general antibodies have four major effector functions:

* All antibody classes bind antigen in a similar manner:

** The initial trigger for all antibody function is the association of antigen with the antigen-binding sites of the immunoglobulin molecules

* However, different classes serve different physiological functions

* Functional differences between antibody classes are reflected in the structural differences in their '''heavy chain constant regions'''

** These regions comprise the '''effector domains''' of antibody molecules

* Antibodies have four major effector functions:

 

==='''Blockade and agglutination'''===

==='''Blockade and agglutination'''===

* The action of antibody binding to antigen can be protective

This action of antibody binding to antigen is a protective function. Antibody may bind to biologically active sites on toxins, inhibiting their binding sites. In a similar manner, antibody can bind the surface of viruses and prevent them from infecting cells. Antibody molecules are at least divalent, and many are greater than divalent which means that antibody can cross-link antibody forming an antibody '''agglutination'''. The ability to cross-link or agglutinate can be the primary function of the antibody. In order to be pathogenic, many micro-organisms must be able to contact viable host cells. If antibody molecules agglutinate these micro-organisms, any cell contact is prevented and the pathogenic effect is removed or reduced. The main biological function of '''[[Immunoglobulin A|IgA]]''' is to cross-link potentially pathogenic molecules.

* Antibody may bind to biologically active sites on toxins, inhibiting their binding sites

* In a similar manner, antibody can bind the surface of viruses and prevent them from infecting cells

* Antibody molecules are at least divalent, and many are greater than divalent

** This means that antibody can cross-link antibody: '''agglutination'''

*** The ability to cross-link can be the primary function of the antibody

* In order to be pathogenic, many micro-organisms must be able to contact viable host cells

** If antibody molecules agglutinate these micro-organisms, cell contact is prevented

*** The pathogenic effect is removed or reduced

* The main biological function of '''[[Immunoglobulin A|IgA]]''' is to cross-link potentially pathogenic molecules

 

==='''Promotion of phagocytosis'''===

==='''Promotion of phagocytosis'''===

* Phagocytes hace receptors for the Fc portion of antibody

* Phagocytes hace receptors for the Fc portion of antibody