Haplotype-Specific Expression Analysis of MHC Class II Genes in Healthy Individuals and Rheumatoid Arthritis Patients.

Miranda Houtman,Vivianne Malmström,Lars Rönnblom,Espen Hesselberg,Lars Klareskog,Leonid Padyukov

doi:10.3389/fimmu.2021.707217

Abstract

HLA-DRB1 alleles have been associated with several autoimmune diseases. For anti-citrullinated protein antibody positive rheumatoid arthritis (RA), HLA-DRB1 shared epitope (SE) alleles are the major genetic risk factors. In order to study the genetic regulation of major histocompatibility complex (MHC) Class II gene expression in immune cells, we investigated transcriptomic profiles of a variety of immune cells from healthy individuals carrying different HLA-DRB1 alleles. Sequencing libraries from peripheral blood mononuclear cells, CD4+ T cells, CD8+ T cells, and CD14+ monocytes of 32 genetically pre-selected healthy female individuals were generated, sequenced and reads were aligned to the standard reference. For the MHC region, reads were mapped to available MHC reference haplotypes and AltHapAlignR was used to estimate gene expression. Using this method, HLA-DRB and HLA-DQ were found to be differentially expressed in different immune cells of healthy individuals as well as in whole blood samples of RA patients carrying HLA-DRB1 SE-positive versus SE-negative alleles. In contrast, no genes outside the MHC region were differentially expressed between individuals carrying HLA-DRB1 SE-positive and SE-negative alleles, thus HLA-DRB1 SE alleles have a strong cis effect on gene expression. Altogether, our findings suggest that immune effects associated with different allelic forms of HLA-DR and HLA-DQ may be associated not only with differences in the structure of these proteins, but also with differences in their expression levels.

Highlights

Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting approximately 0.5-1% of the population worldwide [1]
We identified five major histocompatibility complex (MHC) Class II genes (HLA-DRB4, HLA-DQA2, HLA-DRB1, HLADQA1, and HLA-DQB1) that were differentially expressed to a great degree in peripheral blood mononuclear cells (PBMCs) of HLA-DRB1 shared epitope (SE)-positive versus SE-negative individuals (Figure 2A and Table S1)
The major finding of our study is the identification of relatively high differences in gene expression levels for several MHC Class II genes in immune cells of healthy individuals depending on MHC haplotypes, which are known as genetic risk factors for autoimmune diseases

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting approximately 0.5-1% of the population worldwide [1]. The exact cause of RA remains unknown, a set of so-named shared epitope (SE) alleles, HLA-DRB1*01 (*01:01 and *01:02), *04 (*04:01, *04:04, *04:05, and *04:08), and *10 (*10:01), have been associated with RA [2] and with anti-. Haplotype-Specific Expression of HLA Genes citrullinated protein antibody (ACPA)-positive RA [3]. These alleles share a sequence encoding five amino acids in position 7074 of the antigen-binding groove of the HLA-DR beta chain. It has been suggested that citrullinated antigens may bind preferentially to HLA-DRB1 SE sequences leading to the activation of autoreactive T-cells [5]. HLA-DRB1 is expressed in cells with all HLA-DRB1 haplotypes, whereas expression of the paralogs is haplotype-specific (Figure 1)

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