Immune profiling links autoimmune hepatitis to human herpes virus 6 and relaxin receptor antigens

Autoimmune hepatitis (AIH) is a severe, chronic disease where IgG elevation and autoantibody profile are defining features. However, linking autoantibodies to AIH pathogenesis remains elusive. We employed Phage Immunoprecipitation-Sequencing (PhIP-seq) and uncovered a novel humoral signature specific to AIH. Embedded within this signature were antibodies against the known AIH autoantigen SLA/LP and novel reactivities to disco interacting protein 2 homolog A (DIP2A), and the relaxin family peptide receptor 1 (RXFP1). Fine mapping of the DIP2A epitope revealed preferential enrichment for a nearly-identical 9-amino acid sequence derived from the U27 protein of human herpes virus 6 (HHV-6). Pre-incubation with the HHV-6 epitope blocked DIP2A binding, consistent with cross-reactivity. AIH patients positive for anti-DIP2A had higher titers of HHV6 IgG, suggestive of reactivation. AIH patients had antibodies against the anti-fibrotic receptor, RXFP1, which inhibited relaxin-2 signaling in an IgG-dependent manner. These data provide evidence for a novel serological profile in AIH, linking HHV-6 reactivation anti-RXFP1 antibodies to disease pathogenesis. 

Methods
DNA libraries were barcoded and amplified, gel purified, and subjected to Next-Generation Sequencing on an Illumina NextSeq or NovaSeq Instruments (Illumina, San Diego, CA). Sequencing reads from raw fastq files were aligned to the reference library using RAPSearch2, and RPK was calculated. This data is uploaded here.