IG, TR and IgSF, MHC and MhcSF: what do we learn from the IMGT Colliers de Perles?

The immunoglobulin superfamily (IgSF) comprises the immunoglobulins (IG), T cell receptors (TR) and proteins that have the common feature of having at least one Ig-like domain. The major histocompatibility complex (MHC) superfamily (MhcSF) comprises, in addition to the MHC, proteins which share the common feature of having Mhc-like domains. IMGT, the international ImMunoGeneTics information system (http://imgt.cines.fr) has set up a unique numbering system and standardized 2D graphical representations, or IMGT Colliers de Perles, which take into account the structural features of the Ig-like and Mhc-like domains. In this article, we review the IMGT Scientific chart rules for the description of the IgSF (V and C types) and of the MhcSF (G type) domains. These rules are based on the IMGT-ONTOLOGY axioms and concepts and are applicable for the sequence and structure analysis, whatever the species, the IgSF or MhcSF protein, or the chain type. These IMGT Colliers de Perles are particularly useful for antibody engineering, sequence-structure analysis, visualization and comparison of positions for mutations, polymorphisms and contact analysis.