Background: Juvenile Dermatomyositis (JDM) is a paediatric autoimmune disorder, characterised by proximal muscle weakness and associated skin disease. T helper cell imbalances in JDM have previously been identified in peripheral blood, however, their contribution to JDM pathology is undefined.

Objectives: We aim to identify whether Th1 and Th17 cell dysregulation is present in JDM, and whether this is associated with clinical disease activity.

Methods: Flow cytometric analysis was carried out in two cohorts of JDM patients and healthy controls. Cohort 1 consisted of treatment-naïve patients (n = 38), on-treatment patients (n = 24) and healthy controls (n = 39). Cohort 2 consisted of treatment-naïve patients (n = 17), on-treatment patients (n = 27) and healthy controls (n = 34). JDM patients were recruited from the UK JDM Cohort and Biomarker Study (JDCBS), and healthy controls from the Centre for Adolescent Rheumatology at UCL, UCLH and GOSH. Clinically active disease and remission were defined using the Almeida et al amended PRINTO criteria (2015). In cohort 1, expression of IFNγ and IL-17 in CD4+ T cells from peripheral blood mononuclear cells (PBMC) was assessed by flow cytometry, following PMA/Ionomycin/Brefeldin A stimulation. Expression of chemokine receptors, CXCR3 and CCR6, was assessed by flow cytometry in unstimulated PBMCs. Cohort 2 was used for validation of intracellular cytokine staining (ICS) following PMA/Ionomycin/Brefeldin A stimulation. In a subset of cohort 2, Cytometric Bead Array was used to measure IFNγ and IL-17 secretion following αCD3/αCD28 stimulation of negatively selected CD4+ T cells for 36 hours (treatment-naïve, n = 3; on-treatment, n = 5; healthy control, n = 11). Across both cohorts, Kruskal-Wallis test with Dunn’s multiple comparison are reported.

Results: We identified a significant decrease in the frequency of Th1 (CD3+CD4+IFNγ+) cells in cohort 1 treatment-naïve patients (p<0.0001) compared to healthy controls. We also identified a significant decrease in frequency of Th17 (CD3+CD4+IL-17+) cells in treatment-naïve patients (p<0.0001) compared to healthy controls. Evaluation of chemokine receptor expression highlighted a significant decrease in CXCR3+CCR6- CD4+ T cells in treatment-naïve patients (p=0.0035) compared to healthy controls. Furthermore, a significant increase in the frequency of CXCR3-CCR6- CD4+ T cells in treatment-naïve (p=0.0006) and on-treatment (p=0.0275) JDM was observed compared to healthy controls. Cohort 2 confirmed a significant decrease in the frequency of Th1 cells (p<0.0001) and Th17 cells (p=0.0317) in treatment-naïve patients compared to healthy control subjects. The consistent decrease in Th1 cell frequency in JDM patients was further validated by Cytometric Bead Array which showed a significant decrease in IFNγ secretion from CD4+ T cells in on-treatment JDM patients with active disease (p=0.0076), compared to healthy controls. Further analysis stratified cohort 2 based on clinical outcomes (treatment-naïve, n = 15; on-treatment active disease, n = 12; on-treatment in remission, n = 6; healthy control, n = 34). These analyses identified a significant increase in Th1 cell frequency assessed by ICS in on-treatment JDM patients in remission compared to treatment-naïve patients with active disease (p=0.0143), suggesting that a deficit of Th1 cells is associated with more severe clinical disease and recovery of this population is achieved in remission of JDM.

Conclusions: Our findings show reduced Th1 cell frequencies and impaired IFNγ secretion in treatment-naïve JDM patients with active disease, compared to healthy controls. Subsequently, our findings indicate that recovery of the Th1 population frequency is seen in remission of JDM, suggesting that Th1 restoration may reflect, and potentially contribute to clinical improvement in JDM.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: Nia Evans: None declared, Lucy Marshall: None declared, Aris Eleftherios Syntakas: None declared, Beth Jebson: None declared, Vicky Alexiou: None declared, Melissa Kartawinata: None declared, Coziana Ciurtin: None declared, Anna Radziszewska: None declared, Hannah Peckham: None declared, Claire Deakin: None declared, Elizabeth Rosser: None declared, Meredyth Wilkinson: None declared, Lucy Wedderburn Previous speaker fees from Pfizer paid to UCL, Consultancy with Pfizer and Cabaletta paid to UCL, Research grant from Pfizer.