ERAP2 protein allotypes show functional diversity in MHC-I antigen presentation in the human population

The Endoplasmic Reticulum AminoPeptidase 2 (ERAP2) gene encodes an aminopeptidase involved in antigenic peptide processing for the MHC-I pathway. Genetic variants in the ERAP2 gene are associated with autoimmune conditions and infectious diseases. The linkage between genetic variants in the ERAP2 gene has given rise to the prevailing assumption that a single ERAP2 allotype with invariant amino acid sequence accounts for all immunological functions of ERAP2. Here, we show by analyzing exon-sequencing data from 160,000 individuals that 15 missense amino acid variants across the ERAP2 gene result in an array of different protein allotypes that are maintained in the European population. These allotypes can be divided into three haplotype groups, defined by the genotypes of two common splice-altering variants. We found novel associations between newly identified protein allotypes and immune-mediated diseases, suggesting that ERAP2 functional variation modifies disease susceptibility at the population level. An MHC class I antigen presentation assay revealed that disease-associated ERAP2 allotypes differ in their capacity to generate antigenic peptides for MHC-I presentation, resulting in differential activation of an antigen-specific T-cell receptor compared to non-disease-associated allotypes. These findings provide strong evidence that ERAP2 function is allotype-dependent and demonstrate that ERAP2 diversity shapes MHC-I antigen presentation and T-cell immunity. Significance statementThe ERAP2 enzyme modulates adaptive immunity and plays a role in autoimmunity, infection, and cancer. The authors discovered that a variety of protein allotypes of ERAP2 are maintained in the human population. Allotypes that increase disease risk for autoimmune and cardiovascular conditions are functionally distinct in their capacity to activate T-cells. The results of this study demonstrate that ERAP2 is a functionally diverse immune modulator that contributes to immune variation and influences susceptibility to immune-mediated diseases.