Anti-Mi2 autoantibodies target the PHD fingers of SP140L and TIF1γ, while anti-TIF1γ autoantibodies primarily recognize epitopes outside the PHD region of TIF1γ

Iago Pinal-Fernandez; Jon Musai; Maria Casal-Dominguez; Katherine Pak; Mariana Kaplan; Blake M Warner; Lisa G Rider; Rohit Aggarwal; Chester V Oddis; Siamak Moghadam-Kia; Gloria Garrabou; Albert Selva-O'Callaghan; Jose C Milisenda; John A Chiorini; Andrew L Mammen; Peter D Burbelo

doi:10.1101/2025.03.04.25323364

Anti-Mi2 autoantibodies target the PHD fingers of SP140L and TIF1γ, while anti-TIF1γ autoantibodies primarily recognize epitopes outside the PHD region of TIF1γ

medRxiv [Preprint]. 2025 Mar 5:2025.03.04.25323364. doi: 10.1101/2025.03.04.25323364.

Authors

Iago Pinal-Fernandez^{1

2}, Jon Musai¹, Maria Casal-Dominguez^{1

2}, Katherine Pak¹, Mariana Kaplan³, Blake M Warner⁴, Lisa G Rider⁵, Rohit Aggarwal⁶, Chester V Oddis⁶, Siamak Moghadam-Kia⁶, Gloria Garrabou^{7

8

9}, Albert Selva-O'Callaghan^{10

11}, Jose C Milisenda^{7

8

9}, John A Chiorini¹², Andrew L Mammen^{1

2}, Peter D Burbelo¹²

Affiliations

¹ Muscle Disease Section, National Institute of Arthritis and Musculoskeletal and Skin Disease, National Institutes of Health, Bethesda, MD, USA.
² Johns Hopkins University School of Medicine, Baltimore, MD, USA.
³ Systemic Autoimmunity Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA.
⁴ Salivary Disorders Unit, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA.
⁵ Environmental Autoimmunity Group, Clinical Research Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Bethesda, MD, USA.
⁶ Division of Rheumatology, University of Pittsburgh, Pittsburgh, PA.
⁷ Muscle Research Unit, Internal Medicine Service, Hospital Clinic, Barcelona, Spain.
⁸ Barcelona University, Barcelona, Spain.
⁹ CIBERER and IDIBAPS, Barcelona, Spain.
¹⁰ Systemic Autoimmune Disease Unit, Vall d'Hebron Institute of Research, Barcelona, Spain.
¹¹ Autonomous University of Barcelona, Barcelona, Spain.
¹² Adeno-Associated Virus Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA.

Abstract

Objectives: Plant homeodomain (PHD) fingers are present in many chromatin-binding proteins. We recently discovered that anti-Mi2 autoantibodies recognize PHD fingers in Mi2 and AIRE. The purpose of this study was to characterize anti-Mi2 autoantibody recognition of PHD fingers in SP140L and TIF1γ as well as to explore recognition of TIF1γ by both anti-TIF1γ and anti-Mi2 autoantibodies.

Methods: Luciferase immunoprecipitation system (LIPS) assays were performed to detect autoantibodies against full-length and protein fragments of SP140L and TIF1γ in serum samples from myositis patients, disease controls, and healthy controls.

Results: Anti-Mi2 autoantibodies recognized SP140L. When a 49 amino acid fragment of the PHD finger of SP140L was used as the target, the specificity for selectively detecting anti-Mi2 autoantibodies increased. Additionally, anti-Mi2 autoantibodies weakly bound TIF1γ compared to anti-TIF1γ autoantibodies. Excluding the TIF1γ PHD finger from the TIF1γ target autoantigen eliminated cross-reactivity with anti-Mi2 autoantibodies, confirming that anti-Mi2 autoantibodies specifically target the PHD finger of TIF1γ. Switching two amino acids in the TIF1γ PHD finger to resemble those in AIRE markedly enhanced anti-Mi2 autoantibody immunoreactivity. Anti-TIF1γ autoantibodies primarily recognized the N-terminal fragment outside of the PHD finger, indicating this region contains the immunodominant epitopes.

Conclusions: Anti-Mi2 autoantibodies recognize the PHD fingers of SP140L and TIF1γ. TIF1γ is recognized by two different myositis-specific autoantibodies: anti-Mi2 autoantibodies bind the C-terminal PHD domain and anti-TIF1γ autoantibodies predominantly bind the N-terminal region. Removing the PHD finger from the anti-TIF1γ target autoantigen can improve the specificity of anti-TIF1γ autoantibody assays by reducing cross-reactivity with anti-Mi2 autoantibodies.

Keywords: Myositis; PHD; anti-Mi2; anti-TIF1 γ; autoantibodies; dermatomyositis; zinc finger domain.

Publication types

Preprint