# Distinct HLA Associations for Antibody Multireactivity With Citrulline‐Containing Type II Collagen Epitopes Versus More Limited Antibody Reactivity With Citrulline‐Containing IgG Epitopes in Rheumatoid Arthritis

## TL;DR

This study explores how different HLA alleles are linked to antibody reactivity patterns in rheumatoid arthritis patients.

## Contribution

The study identifies distinct HLA associations with antibody multireactivity to citrulline-containing collagen versus IgG epitopes in rheumatoid arthritis.

## Key findings

- HLA-DQA1*01:02 is more common in patients with anticitrullinated collagen antibodies and multireactive sera.
- HLA-DRB1*04:01 is more frequent in patients with rheumatoid factor (RF) regardless of citrulline-serine motif.
- Different HLA alleles correlate with distinct antibody reactivity patterns in rheumatoid arthritis.

## Abstract

Anticitrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA) can be promiscuous, with cross‐reactive binding to many antigens containing short motifs, or private with little cross‐reactivity. Also, ACPA reactivity patterns differ among patients with RA, including for motif‐containing epitopes in important self‐antigens like collagen and IgG (bound by RA‐associated rheumatoid factors [RFs]), with limited understanding of the underlying mechanism. The objective of this study was to determine if HLA alleles associate with ACPA reactivity patterns.

For 100 ACPA+RF+ participants with RA, serum IgG binding was quantified by enzyme‐linked immunosorbent assay to 10 citrulline‐containing peptides derived from Type II collagen and IgG1 (nine with motifs), and HLA loci were genotyped. Also, antibody and serum multireactivity were evaluated. HLA alleles present differentially in RA participants with high versus low IgG binding to specific peptides, as well as with multireactivity versus limited reactivity were identified by Fisher's exact test.

Serum IgG multireactivity for citrulline‐glycine motif‐containing collagen peptides was high, at least partially due to promiscuous antibodies. HLA‐DQA1*01:02 was present in more participants with anticitrullinated collagen antibodies and multireactive sera. In contrast, serum multireactivity was low for IgG1‐derived peptides due at least in part to more private antibodies. Shared epitope–containing HLA‐DRB1*04:01 was present more frequently in participants with RA‐associated RFs irrespective of the citrulline‐serine motif and less frequently in participants with anticitrullinated collagen antibodies. Several HLA alleles associated with specific antibody reactivities.

Different HLA alleles may contribute to the different reactivity patterns of promiscuous anticitrullinated collagen antibodies and more private RA‐associated RFs.