Blood purification in two patients with clinically amyopathic dermatomyositis associated with interstitial lung disease with anti-melanoma differentiation-associated gene-5 antibody (MDA-5)

The central helicase domain holds the major conformational epitopes of melanoma differentiation-associated gene 5 autoantibodies

OBJECTIVE

Autoantibodies against MDA5 (melanoma differentiation-associated protein 5) serve as a biomarker for DM (dermatomyositis) and indicate a risk factor for interstitial lung disease (ILD). MDA5 is a protein responsible for sensing RNA virus infection and activating signalling pathways against it. However, little is known about the antigen epitopes on MDA5 autoantibodies. We aimed to determine the interaction of the MDA5 autoantibody-antigen epitope.

METHODS

Cell-based assays (CBAs), immunoprecipitation-immunoblot assays, and various immunoblotting techniques were used in the study.

RESULTS

We demonstrated that DM patient autoantibodies recognize MDA5 epitopes in a native conformation-dependent manner. Furthermore, we identified the central helicase domain （3Hel） formed by Hel1, Hel2i, Hel2, and pincer as the major epitopes. As proof of principle, the purified 3Hel efficiently absorbed MDA5 autoantibodies from patient sera through immunoprecipitation-immunoblot assay.

CONCLUSION

Our study uncovered the nature of the antigen epitopes on MDA5 and can provide guidance for diagnosis and a targeted therapeutic approach development.

Therapeutic plasma exchange for clinically amyopathic dermatomyositis (CADM) associated with rapidly progressive interstitial pneumonia

BACKGROUND

Patients with clinically amyopathic dermatomyositis (CADM) with anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 Ab) frequently develop rapidly progressive interstitial pneumonia (RPIP), often with fatal outcomes. Therapeutic plasma exchange (TPE) has been reported as effective against CADM-RPIP refractory to conventional immunosuppressive therapy. However, the detailed mechanisms by which TPE improves disease activity of CADM-RPIP remain unclear.

AIM

To elucidate the clinical and demographic characteristics of patients with anti-MDA5 Ab-positive CADM-RPIP treated with TPE and to analyze changes in laboratory findings before, during, and after TPE.

MATERIALS & METHODS

Patients hospitalized for CADM-RPIP and treated with TPE in 2017 and 2018 were analyzed retrospectively.

RESULTS

Three patients were successfully treated with TPE, with good tolerance. Anti-MDA5 Ab titers decreased significantly over the course of TPE.

CONCLUSION

We emphasize that TPE could represent an effective treatment option for CADM-RPIP refractory to traditional therapy. Removal of anti-MDA5 Ab and other pathogenic factors may facilitate favorable outcomes.