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IMGT/LIGM-DB^1^ is the first and the largest IMGT^®^ database^2^ in which are managed, analysed and annotated more than 136,000 immunoglobulin (IG) and T cell receptor (TR) nucleotide sequences from human and 235 other vertebrate species (April 2009). The expert annotation of these sequences and the added standardized knowledge are based on IMGT-ONTOLOGY, the first ontology developed in the field of immunogenetics and immunoinformatics.^3^ The annotation of immunogenetic sequences requires important expertise, owing to the unusual structure (non-classical exon/intron structure) of the IG and TR genes and characteristic chain synthesis owing to DNA V-J and V-D-J rearrangements. The way to annotate these sequences depends on the molecular type (gDNA, mRNA, cDNA or protein) and the configuration type (germline or rearranged), and if sequences from the concerned species are present or not in the IMGT reference directory sets. IMGT/V-QUEST^5^ and internal tools (IMGT/Automat, IMGT/LIGMotif, IMGT/BLAST and IMGT/DomainGapAlign) were developed. The first step in annotation allows to identify the chain type (for instance IG-Heavy) and to assign standardized keywords (IDENTIFICATION axiom). The second step is the classification of IG and TR genes and alleles (CLASSIFICATION axiom). The third step is the description (DESCRIPTION axiom) of the V, D, J and C genes and alleles with specific standardized labels. There are more than 590 IMGT standardized labels from which 64 have been entered in Sequence Ontology (SO). The delimitation of the FR-IMGT and CDR-IMGT lengths and the positions of conserved amino acids based on the IMGT unique numbering (NUMEROTATION axiom) allow to bridge the gap between sequences and 3D structures.^6^ The complete annotation of immunogenetic germline (V, D, J) and C sequences is followed by the update of the IMGT Repertoire (IMGT Gene tables, Alignments of alleles, Protein displays, Colliers de Perles, etc.), IMGT® gene database (IMGT/GENE-DB) and IMGT reference directory sets of the IMGT® tools (IMGT/V-QUEST, IMGT/JunctionAnalysis and IMGT/DomainGapAlign).

The cDNA sequences of immunoglobulins (IG) and T cell receptors (TR) represent more than one half of the sequences in the IMGT^®^ nucleotide database IMGT/LIGM-DB^1^ and 75% of them are from human and mouse. A few cDNA are germline but the great majority results from a V-D-J or V-J gene rearrangement, spliced to a C gene. The IG and TR genes have been studied extensively in IMGT^®^ ("http://www.imgt.org":http://www.imgt.org) ^2^, which allowed to set up their nomenclature and the corresponding germline reference sequences. These standardized reference directory sets (one for each group of each locus) and the IMGT-ONTOLOGY axioms and derived concepts^3^ are the key elements indispensable to perform the annotation of IG and TR cDNA sequences. A Java program, IMGT/Automat^4^, was developed by IMGT^®^, to automatically annotate the IG and TR cDNA sequences and to produce a totally automatic and complete annotation. More than 9,000 human and mouse cDNA have already been successfully automatically annotated. The quality of the cDNA automatic annotation is equivalent to the quality of the annotation achieved by a human expert. The IMGT^®^ strategy is currently the only way, in the field of immunogenetics, to guarantee the annotation quality and the management of an always increasing number of IG and TR cDNA nucleotide sequences.

The immunoglobulin (IG) and T cell receptor (TR) major loci span about 6 Megabases (Mb) of the human genome on chromosomes 2, 7, 14 and 22, and 9 Mb in mouse on chromosomes 6, 12, 13, 14 and 16. There are seven major loci: three IG loci (IGH, IGK, IGL) and four TR loci (TRA, TRB, TRG, TRD), with a distinct repartition of the variable (V), diversity (D), joining (J) and constant (C) genes. The human genome comprises a total number of 608-665 IG and TR genes (371-422 IG and 237-243 TR), depending on the haplotypes, per haploid genome ^1, 2^ of which 531-588 genes are located in the major loci (distributed in 369-418 V, 32 D, 105-109 J and 25-29 C genes). There are also 77 orphons (68 IG and 9 TR) including two processed IG genes, outside the major loci. The number of functional IG and TR genes is 308-356 (136-171 IG and 172-185 TR) per haploid genome. The mouse genome comprises an approximate number of 876 IG and TR genes (624 IG and 252 TR). All these genomic data are available in the IMGT® gene database, IMGT/GENE-DB ^3^. The major contribution of IMGT/GENE-DB has been to establish, for the first time, a standardized nomenclature of the IG and TR genes and alleles of humans and other vertebrates. In April 2009, IMGT/GENE-DB manages 1999 genes and 3026 alleles. [1] Lefranc M.-P. and Lefranc G., The Immunoglobulin FactsBook, Academic Press, London, 458 pages (2001).[2] Lefranc M.-P. and Lefranc G., The T cell receptor FactsBook, Academic Press, London, 398 pages (2001).[3] Giudicelli V. et al. Nucleic Acids Res., 33, D256-261 (2005).