Binding of any antigen to antibody, the latter one always an immunoglobulin (Ig), occurs through hydrophobic interaction and exclusion of cations from the antigen-antibody interface. On the side of the antigen this surface is termed epitope, whichever its size an impressive structure nevertheless.
On the side of the antibody the surface is a stealth at the N-terminal of the Ig, part of it alongside contributed by heavy (H) chain and part by light (L) chain of Ig. Electrostatic van der Waals forces, and not chemical linkeages hold antigen and antibody together, like a handshake with a potential for an on and off close encounter. John Marrack proposed in the 1930ies that antigen-antibody complexes (synonymous: immune complexes) form a lattice structure (see: Nature Medicine 2004;10:1270). In the framework of the Global Alliance for Vaccines and Immunization (GAVI) (www.who.int/vaccines/GIVS/, with current fears on avian flu pandemic, the vaccine developers test the capacity of their antigens to induce specific antibody formation and efficient immune complex-mediated antigen presentation to follicular dendritic and/or antigen presenting cells. The supplement of Nature Medicine, which goes into depth is: www.nature.com/nm/supplements/. Please visit also:

http://en.wikipedia.org/wiki/Immune_complex

Thanks to nanontechnology, crystallography and proteomics the conviction grows, that it is the fine structure of the partners (not only amino acid sequence but also 3D-configuration, carbohydrate substitution, isoelectric points) which decides on ultimate properties of immune complexes conveyed by the complementarity determining regions (CDR) on the Fab recognition site of the Ig molecule. Influence of some amino acids, like tyrosin, might prevail. Immune complexes are a normal phenomenon serving to remove antigen - however, if they last and remain detectable in peripheral blood or in tissues, they express underlying pathology.

The 7th International Congress on Autoimmunity will be held in Ljubljana, Slovenia, may 5-9, 2010