Pathway Human Homo sapiens

Immunoglobulin maturation

R-HSA-9938026 in Reactome release 97: under Adaptive Immune System, with 357 genes placed in it by the mapping files and 1 child pathway in the hierarchy.

The same number in the other species

Reactome writes the mouse and rat events it infers from a human pathway under the human number with the species token. A door opens only where that species' own list in this release holds the id: R-MMU-9938026 (mouse), R-RNO-9938026 (rat). Whether the event was inferred from this one is what the record says.

The record
The genes
Parents and children

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01The record

Reactome's own record of this pathway

What this tells you

The pathway list, the hierarchy and the genes on this page are read from the files Reactome publishes for Reactome release 97, built into this site on 2026-09-09: the pathway list, the hierarchy relationship file and the two gene mapping files. The record card is the one live read, Reactome's own record of this pathway.

Reactome's download page describes the mapping files: Mapping files link the source database identifier to the lowest level pathway diagram or subset of the pathway, all levels of the pathway hierarchy or database identifier to all reactions. [R13] The gene list here is the all-levels mapping of NCBI Gene ids, filled from the all-levels mapping of Ensembl ids where the NCBI file has no row for a gene; each row names which file it came from by the shape of its source id. Each row carries the evidence codes the file writes for it, as written and unranked, and both where the file writes both; no page of Reactome's documentation the survey read defines the codes, so this page does not expand them. A gene id the identity files do not name is kept as the source's own id with no door rather than turned into a symbol.

On citing what a search finds, Reactome says: It should be remembered that while we strive to contain the most current and accurate data, Reactome should not be used in citations where other primary sources of information are available. [R12] The record card prints the literature Reactome attaches to a curated pathway for that reason. The data are public domain: All data in the Reactome database and files derived from that data are licensed under the Creative Commons Public Domain Dedication (CC0). User may copy, modify, and distribute these data, even for commercial purposes, without asking for permission. Attribution is encouraged but not required. [R10] The pathway illustrations are licensed apart, under CC BY 4.0, and none is shown here.

A gene on this list is one Reactome places in this pathway in this release, and that is all the row says: it does not say the gene is expressed in a tissue or associated with a disease, which are the other two explorers' questions, read from other sources. Reactome's papers of record are [R01] [R02].

[R01] Ragueneau E, Gong C, Sinquin P, Sevilla C, Beavers D, Grentner A, et al. (2026). The Reactome Knowledgebase 2026. Nucleic Acids Research 54:D673-D681. PMID 41251150, doi 10.1093/nar/gkaf1223.
[R02] Milacic M, Beavers D, Conley P, Gong C, Gillespie M, Griss J, et al. (2024). The Reactome Pathway Knowledgebase 2024. Nucleic Acids Research 52:D672-D678. PMID 37941124, doi 10.1093/nar/gkad1025.
[R10] Reactome, reactome.org. License Agreement. https://reactome.org/license, read 2026-09-09.
[R12] Reactome, reactome.org. Citing us. https://reactome.org/cite, read 2026-09-09.
[R13] Reactome, reactome.org. Download. https://reactome.org/download-data, read 2026-09-09.

Stable id: R-HSA-9938026.1
Class: Pathway
Species: Homo sapiens (human)
Inferred: no: a curated human pathway
Disease pathway: no
Released: 2026-06-17
Events inside: 1, counted from the record

In humans, three loci encode immunoglobulin chains: the IGH locus encodes the heavy chain, the IGK locus encodes the kappa light chain, and the IGL locus encodes the lambda light chain. In the germline, the three loci each contain many alternative gene segments that are capable of producing the variable region of the immunoglobulin (reviewed in Pennell et al. 2023). The heavy chain locus (IGH) also contains nine alternative C-terminal segments capable of producing the constant regions of the nine classes of immunoglobulins: IgM, IgD, IgG3, IgG1, IgA1, IgG2, IgG4, IgE, and IgA2 (listed in order of their occurrence on the chromosome, Xu et al. 2012).

In the B cell lineage in the bone marrow, the three immunoglobulin loci are recombined to produce specific variable regions that can recognize specific antigens (reviewed in Christie et al. 2022). A specific heavy chain is produced by recombination among about 57 variable (V) segments, 23 diversity (D) segments, and 6 joining (J) segments, a process called VDJ recombination (reviewed in Mikocziova et al. 2021). The light chains are produced by recombination between 41 (IGK) or 34 (IGL) V segments and 5 J segments, a process called VJ recombination (reviewed in Mikocziova et al. 2021). The term V(D)J recombination refers to recombination at all of the three loci. V(D)J recombination is initiated by DNA cleavage catalyzed by the RAG1:RAG2 recombinase complex at sites flanking the V, D (if present), and J segments followed by repair of double-strand breaks (reviewed in Schatz and Ji 2011, Yu 2022, Christie et al. 2022).

The initial class of the recombined heavy chain is usually IgM, as the M-type C-terminal segment is the most upstream in the array of C-terminal segments at the IGH locus. In germinal centers (reviewed in Victora and Nussenzweig 2022), a process called class switch recombination (CSR) occurs in which the region encoding the variable domain is recombinationally joined to a gene segment encoding the C-terminal constant domain (reviewed in Xu et al. 2012, Matthews et al. 2014, Liu et al. 2024). Activation-induced cytosine deaminase (AICDA, also called AID) deaminates cytidine residues at the Cmu site upstream of the M-type segment and at specific sites, switch regions, flanking the downstream C-terminal segments (reviewed in Matthews et al. 2014, Yu 2022). DNA repair enzymes act on the resulting G:U mismatches to create and resolve double-strand breaks. This produces recombination events that eliminate the M-type segment and in some cases additional segments to generate one of the eight other class types.

Reading this pathway's record from Reactome (the pathway record).Still reading. A first read of a pathway can take a while; this page waits up to 35 seconds for it, and its scripts then bring in the panel, or a line saying what did not arrive.

02The genes

Genes Reactome places in this human pathway

The mapping files place 357 genes in this human pathway; showing 301 to 357, in pages of 100, sorted by symbol for reading. The order carries no ranking.

Genes Reactome places in this human pathway, page 4 of 4
Gene	Authority id	Mapping file id	Evidence codes
GeneSUPT5H	AuthorityHGNC:11469	Mapping file id6829 NCBI file	EvidenceIEA
GeneSUPT6H	AuthorityHGNC:11470	Mapping file id6830 NCBI file	EvidenceIEA
GeneTAF1	AuthorityHGNC:11535	Mapping file id6872 NCBI file	EvidenceIEA
GeneTAF10	AuthorityHGNC:11543	Mapping file id6881 NCBI file	EvidenceIEA
GeneTAF11	AuthorityHGNC:11544	Mapping file id6882 NCBI file	EvidenceIEA
GeneTAF12	AuthorityHGNC:11545	Mapping file id6883 NCBI file	EvidenceIEA
GeneTAF13	AuthorityHGNC:11546	Mapping file id6884 NCBI file	EvidenceIEA
GeneTAF15	AuthorityHGNC:11547	Mapping file id8148 NCBI file	EvidenceIEA
GeneTAF1L	AuthorityHGNC:18056	Mapping file id138474 NCBI file	EvidenceIEA
GeneTAF2	AuthorityHGNC:11536	Mapping file id6873 NCBI file	EvidenceIEA
GeneTAF3	AuthorityHGNC:17303	Mapping file id83860 NCBI file	EvidenceIEA
GeneTAF4	AuthorityHGNC:11537	Mapping file id6874 NCBI file	EvidenceIEA
GeneTAF4B	AuthorityHGNC:11538	Mapping file id6875 NCBI file	EvidenceIEA
GeneTAF5	AuthorityHGNC:11539	Mapping file id6877 NCBI file	EvidenceIEA
GeneTAF6	AuthorityHGNC:11540	Mapping file id6878 NCBI file	EvidenceIEA
GeneTAF7	AuthorityHGNC:11541	Mapping file id6879 NCBI file	EvidenceIEA
GeneTAF7L	AuthorityHGNC:11548	Mapping file id54457 NCBI file	EvidenceIEA
GeneTAF8	AuthorityHGNC:17300	Mapping file id129685 NCBI file	EvidenceIEA
GeneTAF9	AuthorityHGNC:11542	Mapping file id6880 NCBI file	EvidenceIEA
GeneTAF9B	AuthorityHGNC:17306	Mapping file id51616 NCBI file	EvidenceIEA
GeneTBP	AuthorityHGNC:11588	Mapping file id6908 NCBI file	EvidenceIEA
GeneTCEA1	AuthorityHGNC:11612	Mapping file id6917 NCBI file	EvidenceIEA
GeneTCF3	AuthorityHGNC:11633	Mapping file id6929 NCBI file	EvidenceIEA
GeneTNFRSF13C	AuthorityHGNC:17755	Mapping file id115650 NCBI file	EvidenceIEA
GeneTNFSF13B	AuthorityHGNC:11929	Mapping file id10673 NCBI file	EvidenceIEA
GeneTP53	AuthorityHGNC:11998	Mapping file idENSG00000141510 Ensembl file	EvidenceTAS
GeneTRAV19	AuthorityHGNC:12115	Mapping file idENSG00000211799 Ensembl file	EvidenceIEA
GeneTRAV29DV5	AuthorityHGNC:12127	Mapping file idENSG00000211810 Ensembl file	EvidenceIEA
GeneTRAV8-4	AuthorityHGNC:12149	Mapping file idENSG00000211790 Ensembl file	EvidenceIEA
GeneTRBV12-3	AuthorityHGNC:12185	Mapping file idENSG00000274752 Ensembl file	EvidenceIEA
GeneTRBV7-9	AuthorityHGNC:12243	Mapping file idENSG00000278030 Ensembl file	EvidenceIEA
GeneTUBA1A	AuthorityHGNC:20766	Mapping file id7846 NCBI file	EvidenceTAS
GeneTUBA1B	AuthorityHGNC:18809	Mapping file id10376 NCBI file	EvidenceTAS
GeneTUBA1C	AuthorityHGNC:20768	Mapping file id84790 NCBI file	EvidenceTAS
GeneTUBA3C	AuthorityHGNC:12408	Mapping file id7278 NCBI file	EvidenceTAS
GeneTUBA3D	AuthorityHGNC:24071	Mapping file id113457 NCBI file	EvidenceTAS
GeneTUBA3E	AuthorityHGNC:20765	Mapping file id112714 NCBI file	EvidenceTAS
GeneTUBA4A	AuthorityHGNC:12407	Mapping file id7277 NCBI file	EvidenceTAS
GeneTUBA4B	AuthorityHGNC:18637	Mapping file id80086 NCBI file	EvidenceTAS
GeneTUBA8	AuthorityHGNC:12410	Mapping file id51807 NCBI file	EvidenceTAS
GeneTUBAL3	AuthorityHGNC:23534	Mapping file id79861 NCBI file	EvidenceTAS
GeneTUBB1	AuthorityHGNC:16257	Mapping file id81027 NCBI file	EvidenceTAS
GeneTUBB2A	AuthorityHGNC:12412	Mapping file id7280 NCBI file	EvidenceTAS
GeneTUBB2B	AuthorityHGNC:30829	Mapping file id347733 NCBI file	EvidenceTAS
GeneTUBB3	AuthorityHGNC:20772	Mapping file id10381 NCBI file	EvidenceTAS
GeneTUBB4A	AuthorityHGNC:20774	Mapping file id10382 NCBI file	EvidenceTAS
GeneTUBB4B	AuthorityHGNC:20771	Mapping file id10383 NCBI file	EvidenceTAS
GeneTUBB6	AuthorityHGNC:20776	Mapping file id84617 NCBI file	EvidenceTAS
GeneTUBB8	AuthorityHGNC:20773	Mapping file id347688 NCBI file	EvidenceTAS
GeneTUBB8B	AuthorityHGNC:24983	Mapping file id260334 NCBI file	EvidenceTAS
GeneUBA52	AuthorityHGNC:12458	Mapping file id7311 NCBI file	EvidenceIEA, TAS
GeneUBB	AuthorityHGNC:12463	Mapping file id7314 NCBI file	EvidenceIEA, TAS
GeneUBC	AuthorityHGNC:12468	Mapping file id7316 NCBI file	EvidenceIEA, TAS
GeneUNG	AuthorityHGNC:12572	Mapping file id7374 NCBI file	EvidenceTAS
GeneVCAM1	AuthorityHGNC:12663	Mapping file id7412 NCBI file	EvidenceIEA
GeneWDR5	AuthorityHGNC:12757	Mapping file id11091 NCBI file	EvidenceIEA
GeneZBTB17	AuthorityHGNC:12936	Mapping file id7709 NCBI file	EvidenceTAS

Evidence codes on this page: IEA, TAS, as the mapping file writes them; a row carrying two was written twice by the file, once under each. The mapping file id says which file placed the gene: an NCBI Gene id from NCBI2Reactome_All_Levels.txt, an Ensembl gene id from Ensembl2Reactome_All_Levels.txt. The two files can disagree about a code, so a row's codes are the one file's view. Measured by this site's build over this release on 2026-09-09: of the 138,908 human pathway-gene pairs both files place, 207 (0.149 per cent, over 47 genes) carry TAS in the Ensembl file where the NCBI rows carry IEA alone.

Reactome mapping files, the human rows for this pathway · Reactome release 97 · read 2026-09-09 · Reactome downloads"NCBI2Reactome_All_Levels.txt" and "Ensembl2Reactome_All_Levels.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.

03The hierarchy

Parents and children in this release's hierarchy

Parents

Adaptive Immune SystemR-HSA-12802181,149 genes

Children

Affinity selection of immunoglobulinsR-HSA-9938027357 genes

Reactome's hierarchy is a graph rather than a tree: a pathway can sit under more than one parent, and the gene counts are each pathway's own placements at every level under it, so a parent's count is not the sum of its children's.

Reactome, the human pathway list and hierarchy relationship file · Reactome release 97 · read 2026-09-09 · Reactome downloads"ReactomePathways.txt" and "ReactomePathwaysRelation.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.