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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This page reads the pathway's record from its source while you read the rest; with scripts off the card stays at its loading line. Reload with scripts on to see it, or open the source's own page from the link in the card.

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 101 to 200, in pages of 100, sorted by symbol for reading. The order carries no ranking.

Genes Reactome places in this human pathway, page 2 of 4
Gene	Authority id	Mapping file id	Evidence codes
GeneGTF2F1	AuthorityHGNC:4652	Mapping file id2962 NCBI file	EvidenceIEA
GeneGTF2F2	AuthorityHGNC:4653	Mapping file id2963 NCBI file	EvidenceIEA
GeneHLA-DMA	AuthorityHGNC:4934	Mapping file id3108 NCBI file	EvidenceTAS
GeneHLA-DMB	AuthorityHGNC:4935	Mapping file id3109 NCBI file	EvidenceTAS
GeneHLA-DOA	AuthorityHGNC:4936	Mapping file id3111 NCBI file	EvidenceTAS
GeneHLA-DOB	AuthorityHGNC:4937	Mapping file id3112 NCBI file	EvidenceTAS
GeneHLA-DPA1	AuthorityHGNC:4938	Mapping file id3113 NCBI file	EvidenceIEA, TAS
GeneHLA-DPB1	AuthorityHGNC:4940	Mapping file id3115 NCBI file	EvidenceIEA, TAS
GeneHLA-DQA1	AuthorityHGNC:4942	Mapping file id3117 NCBI file	EvidenceIEA, TAS
GeneHLA-DQA2	AuthorityHGNC:4943	Mapping file id3118 NCBI file	EvidenceIEA, TAS
GeneHLA-DQB1	AuthorityHGNC:4944	Mapping file id3119 NCBI file	EvidenceIEA, TAS
GeneHLA-DQB2	AuthorityHGNC:4945	Mapping file id3120 NCBI file	EvidenceIEA, TAS
GeneHLA-DRA	AuthorityHGNC:4947	Mapping file id3122 NCBI file	EvidenceIEA, TAS
GeneHLA-DRB1	AuthorityHGNC:4948	Mapping file id3123 NCBI file	EvidenceIEA, TAS
GeneHLA-DRB3	AuthorityHGNC:4951	Mapping file id3125 NCBI file	EvidenceIEA, TAS
GeneHLA-DRB4	AuthorityHGNC:4952	Mapping file id3126 NCBI file	EvidenceIEA, TAS
GeneHLA-DRB5	AuthorityHGNC:4953	Mapping file id3127 NCBI file	EvidenceIEA, TAS
GeneHOXC4	AuthorityHGNC:5126	Mapping file id3221 NCBI file	EvidenceIEA
GeneICAM1	AuthorityHGNC:5344	Mapping file id3383 NCBI file	EvidenceIEA
GeneICAM2	AuthorityHGNC:5345	Mapping file id3384 NCBI file	EvidenceIEA
GeneICOS	AuthorityHGNC:5351	Mapping file id29851 NCBI file	EvidenceIEA
GeneICOSLG	AuthorityHGNC:17087	Mapping file id23308 NCBI file	EvidenceIEA
GeneIFI30	AuthorityHGNC:5398	Mapping file id10437 NCBI file	EvidenceTAS
GeneIGH	AuthorityHGNC:5477	Mapping file id3492 NCBI file	EvidenceIEA
GeneIGHD	AuthorityHGNC:5480	Mapping file idENSG00000211898 Ensembl file	EvidenceIEA
GeneIGHG1	AuthorityHGNC:5525	Mapping file idENSG00000211896 Ensembl file	EvidenceIEA
GeneIGHG2	AuthorityHGNC:5526	Mapping file idENSG00000211893 Ensembl file	EvidenceIEA
GeneIGHG4	AuthorityHGNC:5528	Mapping file idENSG00000211892 Ensembl file	EvidenceIEA
GeneIGHM	AuthorityHGNC:5541	Mapping file idENSG00000211899 Ensembl file	EvidenceIEA
GeneIGHV1-2	AuthorityHGNC:5550	Mapping file idENSG00000211934 Ensembl file	EvidenceIEA
GeneIGHV1-46	AuthorityHGNC:5554	Mapping file idENSG00000211962 Ensembl file	EvidenceIEA
GeneIGHV1-69	AuthorityHGNC:5558	Mapping file idENSG00000211973 Ensembl file	EvidenceIEA
GeneIGHV2-5	AuthorityHGNC:5576	Mapping file idENSG00000211937 Ensembl file	EvidenceIEA
GeneIGHV2-70	AuthorityHGNC:5577	Mapping file idENSG00000274576 Ensembl file	EvidenceIEA
GeneIGHV3-11	AuthorityHGNC:5580	Mapping file idENSG00000211941 Ensembl file	EvidenceIEA
GeneIGHV3-13	AuthorityHGNC:5581	Mapping file idENSG00000211942 Ensembl file	EvidenceIEA
GeneIGHV3-23	AuthorityHGNC:5588	Mapping file idENSG00000211949 Ensembl file	EvidenceIEA
GeneIGHV3-30	AuthorityHGNC:5591	Mapping file idENSG00000270550 Ensembl file	EvidenceIEA
GeneIGHV3-33	AuthorityHGNC:5596	Mapping file idENSG00000211955 Ensembl file	EvidenceIEA
GeneIGHV3-48	AuthorityHGNC:5606	Mapping file idENSG00000211964 Ensembl file	EvidenceIEA
GeneIGHV3-53	AuthorityHGNC:5610	Mapping file idENSG00000211967 Ensembl file	EvidenceIEA
GeneIGHV3-7	AuthorityHGNC:5620	Mapping file idENSG00000211938 Ensembl file	EvidenceIEA
GeneIGHV4-34	AuthorityHGNC:5650	Mapping file idENSG00000211956 Ensembl file	EvidenceIEA
GeneIGHV4-39	AuthorityHGNC:5651	Mapping file idENSG00000211959 Ensembl file	EvidenceIEA
GeneIGHV4-59	AuthorityHGNC:5654	Mapping file idENSG00000224373 Ensembl file	EvidenceIEA
GeneIGK	AuthorityHGNC:5715	Mapping file id50802 NCBI file	EvidenceIEA
GeneIGKV1-12	AuthorityHGNC:5730	Mapping file idENSG00000243290 Ensembl file	EvidenceIEA
GeneIGKV1-16	AuthorityHGNC:5732	Mapping file idENSG00000240864 Ensembl file	EvidenceIEA
GeneIGKV1-17	AuthorityHGNC:5733	Mapping file idENSG00000240382 Ensembl file	EvidenceIEA
GeneIGKV1-33	AuthorityHGNC:5737	Mapping file idENSG00000242076 Ensembl file	EvidenceIEA
GeneIGKV1-39	AuthorityHGNC:5740	Mapping file idENSG00000242371 Ensembl file	EvidenceIEA
GeneIGKV1-5	AuthorityHGNC:5741	Mapping file idENSG00000243466 Ensembl file	EvidenceIEA
GeneIGKV1D-12	AuthorityHGNC:5746	Mapping file idENSG00000278857 Ensembl file	EvidenceIEA
GeneIGKV1D-16	AuthorityHGNC:5748	Mapping file idENSG00000241244 Ensembl file	EvidenceIEA
GeneIGKV1D-33	AuthorityHGNC:5753	Mapping file idENSG00000239975 Ensembl file	EvidenceIEA
GeneIGKV1D-39	AuthorityHGNC:5756	Mapping file idENSG00000251546 Ensembl file	EvidenceIEA
GeneIGKV2-28	AuthorityHGNC:5783	Mapping file idENSG00000244116 Ensembl file	EvidenceIEA
GeneIGKV2-30	AuthorityHGNC:5785	Mapping file idENSG00000243238 Ensembl file	EvidenceIEA
GeneIGKV2D-28	AuthorityHGNC:5799	Mapping file idENSG00000242534 Ensembl file	EvidenceIEA
GeneIGKV2D-30	AuthorityHGNC:5801	Mapping file idENSG00000239571 Ensembl file	EvidenceIEA
GeneIGKV2D-40	AuthorityHGNC:5804	Mapping file idENSG00000251039 Ensembl file	EvidenceIEA
GeneIGKV3-11	AuthorityHGNC:5815	Mapping file idENSG00000241351 Ensembl file	EvidenceIEA
GeneIGKV3-15	AuthorityHGNC:5816	Mapping file idENSG00000244437 Ensembl file	EvidenceIEA
GeneIGKV3-20	AuthorityHGNC:5817	Mapping file idENSG00000239951 Ensembl file	EvidenceIEA
GeneIGKV3D-20	AuthorityHGNC:5825	Mapping file idENSG00000211625 Ensembl file	EvidenceIEA
GeneIGKV4-1	AuthorityHGNC:5834	Mapping file idENSG00000211598 Ensembl file	EvidenceIEA
GeneIGKV5-2	AuthorityHGNC:5835	Mapping file idENSG00000211599 Ensembl file	EvidenceIEA
GeneIGL	AuthorityHGNC:5853	Mapping file id3535 NCBI file	EvidenceIEA
GeneIGLC2	AuthorityHGNC:5856	Mapping file idENSG00000211677 Ensembl file	EvidenceIEA
GeneIGLC3	AuthorityHGNC:5857	Mapping file idENSG00000211679 Ensembl file	EvidenceIEA
GeneIGLV1-40	AuthorityHGNC:5877	Mapping file idENSG00000211653 Ensembl file	EvidenceIEA
GeneIGLV1-44	AuthorityHGNC:5879	Mapping file idENSG00000211651 Ensembl file	EvidenceIEA
GeneIGLV1-47	AuthorityHGNC:5880	Mapping file idENSG00000211648 Ensembl file	EvidenceIEA
GeneIGLV1-51	AuthorityHGNC:5882	Mapping file idENSG00000211644 Ensembl file	EvidenceIEA
GeneIGLV2-11	AuthorityHGNC:5887	Mapping file idENSG00000211668 Ensembl file	EvidenceIEA
GeneIGLV2-14	AuthorityHGNC:5888	Mapping file idENSG00000211666 Ensembl file	EvidenceIEA
GeneIGLV2-23	AuthorityHGNC:5890	Mapping file idENSG00000211660 Ensembl file	EvidenceIEA
GeneIGLV2-8	AuthorityHGNC:5895	Mapping file idENSG00000278196 Ensembl file	EvidenceIEA
GeneIGLV3-1	AuthorityHGNC:5896	Mapping file idENSG00000211673 Ensembl file	EvidenceIEA
GeneIGLV3-19	AuthorityHGNC:5903	Mapping file idENSG00000211663 Ensembl file	EvidenceIEA
GeneIGLV3-21	AuthorityHGNC:5905	Mapping file idENSG00000211662 Ensembl file	EvidenceIEA
GeneIGLV3-25	AuthorityHGNC:5908	Mapping file idENSG00000211659 Ensembl file	EvidenceIEA
GeneIGLV3-27	AuthorityHGNC:5910	Mapping file idENSG00000211658 Ensembl file	EvidenceIEA
GeneIGLV6-57	AuthorityHGNC:5927	Mapping file idENSG00000211640 Ensembl file	EvidenceIEA
GeneIGLV7-43	AuthorityHGNC:5929	Mapping file idENSG00000211652 Ensembl file	EvidenceIEA
GeneIL21	AuthorityHGNC:6005	Mapping file id59067 NCBI file	EvidenceIEA
GeneIL4	AuthorityHGNC:6014	Mapping file id3565 NCBI file	EvidenceIEA
GeneIRF4	AuthorityHGNC:6119	Mapping file id3662 NCBI file	EvidenceIEA
GeneIRF8	AuthorityHGNC:5358	Mapping file id3394 NCBI file	EvidenceIEA
GeneITGA4	AuthorityHGNC:6140	Mapping file id3676 NCBI file	EvidenceIEA
GeneITGAL	AuthorityHGNC:6148	Mapping file id3683 NCBI file	EvidenceIEA
GeneITGB1	AuthorityHGNC:6153	Mapping file id3688 NCBI file	EvidenceIEA
GeneITGB2	AuthorityHGNC:6155	Mapping file id3689 NCBI file	EvidenceIEA
GeneIWS1	AuthorityHGNC:25467	Mapping file id55677 NCBI file	EvidenceIEA
GeneJUND	AuthorityHGNC:6206	Mapping file id3727 NCBI file	EvidenceIEA, TAS
GeneKDM6A	AuthorityHGNC:12637	Mapping file id7403 NCBI file	EvidenceIEA
GeneKIF11	AuthorityHGNC:6388	Mapping file id3832 NCBI file	EvidenceTAS
GeneKIF15	AuthorityHGNC:17273	Mapping file id56992 NCBI file	EvidenceTAS
GeneKIF18A	AuthorityHGNC:29441	Mapping file id81930 NCBI file	EvidenceTAS
GeneKIF20A	AuthorityHGNC:9787	Mapping file id10112 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.