Pathway Human Homo sapiens

Antigen Presentation: Folding, assembly and peptide loading of class I MHC

R-HSA-983170 in Reactome release 97: under Class I MHC mediated antigen processing & presentation, with 30 genes placed in it by the mapping files and 0 child pathways 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-983170 (mouse), R-RNO-983170 (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-983170.5
Class: Pathway
Species: Homo sapiens (human)
Inferred: no: a curated human pathway
Disease pathway: no
Released: 2011-06-14
Last updated: 2022-04-07
Events inside: 16, counted from the record

Unlike other glycoproteins, correct folding of MHC class I molecules is not sufficient to trigger their exit from the ER, they exit only after peptide loading. Described here is the process of antigen presentation which consists of the folding, assembly, and peptide loading of MHC class I molecules. The newly synthesized MHC class I Heavy Chain (HC) is initially folded with the help of several chaperones (calnexin, BiP, ERp57) and then binds with Beta-2-microglobulin (B2M). This MHC:B2M heterodimer enters the peptide loading complex (PLC), a multiprotein complex that includes calreticulin, endoplasmic reticulum resident protein 57 (ERp57), transporter associated with antigen processing (TAP) and tapasin. Peptides generated from Ub-proteolysis are transported into the ER through TAP. These peptides are further trimmed by ER-associated aminopeptidase (ERAP) and loaded on to MHC class I molecules. Stable MHC class I trimers with high-affinity peptide are transported from the ER to the cell surface by the Golgi apparatus.

Literature Reactome attaches

The known unknowns of antigen processing and presentationNat Rev Immunol, 2008, vol. 8, p. 607-18PubMed 18641646
Post-proteasomal antigen processing for major histocompatibility complex class I presentationNat Immunol, 2004, vol. 5, p. 670-7PubMed 15224092
Molecular mechanisms of MHC class I-antigen processing: redox considerationsAntioxid Redox Signal, 2009, vol. 11, p. 907-36PubMed 19178136
Assembly and export of MHC class I peptide ligandsCurr Opin Immunol, 2003, vol. 15, p. 75-81PubMed 12495737
The quality control of MHC class I peptide loadingCurr Opin Cell Biol, 2008, vol. 20, p. 624-31PubMed 18926908

Reactome's record lists 14 orthologous events, R-MMU-983170 (Mus musculus), R-RNO-983170 (Rattus norvegicus) among the species this site serves, and 12 in species this site opens no page for.

Reactome ContentService, this pathway's record · Reactome v97 · read 2026-09-30 ET · Reactome pathway browser"Antigen Presentation: Folding, assembly and peptide loading of class I MHC". Reactome, release 97, https://reactome.org/PathwayBrowser/#/R-HSA-983170 with StableID: R-HSA-983170.5 (accessed 2026-09-30 ET). Reactome version 97 (CC0).

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 30 genes in this human pathway; showing 1 to 30, in pages of 100, sorted by symbol for reading. The order carries no ranking. 1 of the rows shown carries an id the identity file does not name, kept as the source wrote it.

Genes Reactome places in this human pathway, page 1 of 1
Gene	Authority id	Mapping file id	Evidence codes
GeneATG14	AuthorityHGNC:19962	Mapping file id22863 NCBI file	EvidenceTAS
GeneB2M	AuthorityHGNC:914	Mapping file id567 NCBI file	EvidenceTAS
GeneBCAP31	AuthorityHGNC:16695	Mapping file id10134 NCBI file	EvidenceTAS
GeneBECN1	AuthorityHGNC:1034	Mapping file id8678 NCBI file	EvidenceTAS
GeneCALR	AuthorityHGNC:1455	Mapping file id811 NCBI file	EvidenceTAS
GeneCANX	AuthorityHGNC:1473	Mapping file id821 NCBI file	EvidenceIEA, TAS
GeneERAP1	AuthorityHGNC:18173	Mapping file id51752 NCBI file	EvidenceTAS
GeneERAP2	AuthorityHGNC:29499	Mapping file id64167 NCBI file	EvidenceTAS
GeneHLA-A	AuthorityHGNC:4931	Mapping file id3105 NCBI file	EvidenceIEA, TAS
GeneHLA-B	AuthorityHGNC:4932	Mapping file id3106 NCBI file	EvidenceIEA, TAS
GeneHLA-C	AuthorityHGNC:4933	Mapping file id3107 NCBI file	EvidenceIEA, TAS
GeneHLA-E	AuthorityHGNC:4962	Mapping file id3133 NCBI file	EvidenceIEA, TAS
GeneHLA-F	AuthorityHGNC:4963	Mapping file id3134 NCBI file	EvidenceIEA, TAS
GeneHLA-G	AuthorityHGNC:4964	Mapping file id3135 NCBI file	EvidenceIEA, TAS
GeneHSPA5	AuthorityHGNC:5238	Mapping file id3309 NCBI file	EvidenceIEA, TAS
GenePDIA3	AuthorityHGNC:4606	Mapping file id2923 NCBI file	EvidenceIEA, TAS
GenePIK3C3	AuthorityHGNC:8974	Mapping file id5289 NCBI file	EvidenceTAS
GenePIK3R4	AuthorityHGNC:8982	Mapping file id30849 NCBI file	EvidenceTAS
GeneSAR1B	AuthorityHGNC:10535	Mapping file id51128 NCBI file	EvidenceTAS
GeneSEC13	AuthorityHGNC:10697	Mapping file id6396 NCBI file	EvidenceTAS
GeneSEC23A	AuthorityHGNC:10701	Mapping file id10484 NCBI file	EvidenceTAS
GeneSEC24A	AuthorityHGNC:10703	Mapping file id10802 NCBI file	EvidenceTAS
GeneSEC24B	AuthorityHGNC:10704	Mapping file id10427 NCBI file	EvidenceTAS
GeneSEC24C	AuthorityHGNC:10705	Mapping file id9632 NCBI file	EvidenceTAS
GeneSEC24D	AuthorityHGNC:10706	Mapping file id9871 NCBI file	EvidenceTAS
GeneSEC31A	AuthorityHGNC:17052	Mapping file id22872 NCBI file	EvidenceTAS
GeneTAP1	AuthorityHGNC:43	Mapping file id6890 NCBI file	EvidenceTAS
GeneTAP2	AuthorityHGNC:44	Mapping file id6891 NCBI file	EvidenceTAS
GeneTAPBP	AuthorityHGNC:11566	Mapping file id6892 NCBI file	EvidenceTAS
Geneno symbol in the identity file	Authoritynone	Mapping file id43740577 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

Class I MHC mediated antigen processing & presentationR-HSA-983169376 genes

Children

None: no pathway of this release's list names this one as a parent.

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.