Background: The idiopathic inflammatory myopathies (IIM) are characterized by inflammation of proximal skeletal muscles and skin. Anti-Jo-1 antibody is found most in about 30% of patients with IIM and often associated with interstitial lung disease and severe prognosis. B cells are likely to play an important role in pathogenesis in anti-Jo-1 antibody-positive IIM, however there are few reports about detailed immunophenotyping of B cell in anti-Jo-1 antibody-positive IIM.

Objectives: The aim of this study was to understand immunological phenotyping profiles of peripheral B cells from the patients with anti-Jo-1 antibody-positive IIM by spectral flowcytometry.

Methods: Enriched B cells from peripheral blood mononuclear cells from 7 patients with treatment-naive IIM, 6 patients with inactive IIM, 4 patients with active and treated IIM and 8 age- and sex-matched healthy donors were analyzed on spectral flowcytometry with a 24-marker panel. The dimensionality reduction and clustering analysis were applied to pre-gated CD19+ B cells. All 17 IIM patients were positive for anti-Jo-1 antibody.

Results: Analyzing the composition of CD27-IgD+ naïve B cells and CD27+ memory B cells, the CD27+IgD- switched memory cells and the CD27+IgD+ unswitched memory B cells were significantly decreased in the active IIM patients compared to healthy controls (median: 3.4% vs 11.9%, p=0.01 and 1.3% vs 10.3%, p=0.006, respectively). When examining the expression of CD73, a key enzyme that converts ATP to adenosine, both MFI of CD73 on B cells and the frequency of CD73+ B cells were significantly lower from the patients with active IIM compared to healthy controls (median: 727 vs 1517, p=0.003 and 60.4% vs 79.0%, p=0.01, respectively), which was found both in CD27-IgD+ and CD27-IgD- B cells. Next, comparing the distribution of 10 clusters obtained by cluster analysis using FlowSOM, we found that the CD73- naïve B cell cluster was significantly increased in the patients with treatment-naïve IIM compared to healthy controls (median: 12.9% vs 4.5%, p=0.02). Overall, CD73-IgM+ naïve B cells were significantly increased in IIM patients with high disease activity compared to healthy controls (median: 19.2% vs 8.2% of naïve B cells, p=0.01).

Conclusion: The expression of CD73 was significantly lower on peripheral B cells from the patients with IIM compared to healthy controls. This may lead to hyperactivation of B cells through ATP/adenosine pathway in pathogenesis of anti-Jo-1 antibody-positive IIM.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: None declared.