Complementarity Determining Regions (CDR-IMGT)
The Complementarity Determining Regions (CDR) and the Framework Regions (FR) are parts of the variable regions of the Immunoglobulin and T cell Receptor chains. The IMGT unique numbering for V-REGION  has allowed to redefine the limits of the Complementarity Determining Regions and Framework Regions, designated as CDR-IMGT and FR-IMGT, respectively in IMGT. The IMGT unique numbering for V-DOMAIN provides a standardized numbering for the CDR3-IMGT and FR4-IMGT of rearranged V-J-REGION and V-D-J-REGION (IMGT Scientific chart).
The lengths of the FR-IMGT and CDR-IMGT are in themselves crucial information which characterize variable regions belonging to a group, a subgroup and/or a gene [2-5]. Tables of the FR-IMGT and CDR-IMGT lengths are available in the IMGT Repertoire.
Amino acids (and codons) belonging to CDR-IMGT of same length and located at the same position in different sequences can be compared without requiring sequence alignments.
Correspondence between V numberings, and more particularly Correspondence between numberings for the CDR-IMGT lengths (horizontal display) (IMGT Scientific chart) allows to compare CDR-IMGT with previous data.
 Lefranc, M.-P., The Immunologist, 7, 132-136 (1999) LIGM:217.
 Lefranc, M.-P. et al., Nucleic Acids Res., 27, 209-212 (1999) PMID: 9847182, LIGM:209.
 Scaviner, D. et al., Exp. Clin. Immunogenet., 16, 234-240 (1999) PMID: 10575277, LIGM:218
 Lefranc, M.-P. and Lefranc, G., The Immunoglobulin FactsBook, Academic Press, 458 pages (2001) ISBN: 012441351X.
 Lefranc, M.-P. and Lefranc, G., The T cell receptor FactsBook, Academic Press, 398 pages (2001) ISBN: 0124413528.