P095 Reciprocal relationship of skeletal muscle function and peripheral blood lymphocytes in juvenile idiopathic arthritis: an observational pilot study

Background/Aims Chronic inflammation in ageing is associated with loss of skeletal muscle mass and function, known as sarcopenia. Sarcopenia is associated with multimorbidity. Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease that presents before age sixteen that carries enhanced risk of sarcopenia. The SARC-F survey is a validated screening tool for sarcopenia. The aim of this was to investigate the utility of SARC-F in identifying sarcopenia in JIA and to explore the relationship between musculoskeletal (MSK) function and peripheral lymphocyte profile in young adults with JIA. Methods Participants with JIA completed the SARC-F survey and self-reported exercise habits through online questionnaires. Peripheral blood samples were collected, and peripheral blood mononuclear cells (PBMCs) were isolated. SARC-F scores were used as a measure of MSK function to identify two groups: MSK function impaired (MFI); and MSK function not impaired (MFNI). Participants were also subdivided based on self-reported frequency of moderate exercise. PBMCs were stained and T, B and NK cell subsets were immunophenotyped using flow cytometry. Frequencies of subsets were compared between the MFI and MFNI groups and based on moderate exercise activity. Statistical analyses were performed using the Mann-Whitney U test with significant values considered as p < 0.05. Results Of the 18 participants in total, five belonged to the MFI group and 13 to the MFNI group. Median age was 24 years in both groups; 80.00% and 38.46% were female in the MFI group and MFNI groups, respectively. The MFI group had fewer CD45RA+CD27+ naïve CD4+ T cells (26.60% v. 45.30%, p = 0.0264) and greater CD45RA-CD27- effector memory CD4+ T cells (11.90% v. 7.00%, p = 0.0350). There were no differences between the CD8+ T cells phenotypes. The MFI group also had fewer CD56-CD16+ NK cells compared to the MFNI group (2.60% v. 4.28%, p = 0.0194). 13 participants reported moderate exercise activity, and five others did not. The moderate exercise group had increased total CD4+ T cells (54.06% v. 37.30%, p = 0.0140), however showed no differences between CD4+ T cell subpopulations. There was no difference in the total CD8+ T cells. However, the moderate exercise group had 3-fold fewer CD45RA+CD27- EMRA CD8+ T cells (3.17% v. 10.40%, p = 0.0350). There were no significant differences between the frequencies of B cell subpopulations. Conclusion A significant limitation of the study is the confounding effect of drug treatments on peripheral lymphocytes. Allowing for this, the study findings, such as 3-fold lower frequency of CD8+ TEMRA T cells, suggest a potential reciprocal relationship between MSK function on the peripheral immune profile suggestive of immunosenescence in JIA with impaired muscle function. Moreover, SARC-F has the potential to screen for sarcopenia in JIA. The complex relationship between skeletal muscle function, sarcopenia and the immune system in JIA warrants further investigation. Disclosure Z.D. Ladan: None. A. Ahmad: None. S. Oruganti: None. S. Sayegh: Grants/research support; SS received funding support for this work from the MRC grant. N. Zhang: None. C. Hadjicharalambous: None. J. Glanville: None. M. Castelino: None. C. Fisher: None. M. Leandro: None. A. Akbar: None. V.R. Reddy: Grants/research support; VR received funding support for this work from MRC-CARP Fellowship, Versus Arthritis, and the Division of Medicine Fellowship. D. Sen: Grants/research support; DS received funding support for this work from the MRC grant.