P165 Molecular and cellular biomarkers that discriminate juvenile idiopathic arthritis from septic arthritis

Career situation of first and presenting author Student for a master or a PhD. Introduction Juvenile idiopathic arthritis (JIA) and septic arthritis (SA) are the most frequent cause of arthritis among children under the age of 16 years. JIA is an inflammatory disorder with articular inflammation that persists for more than 6 weeks, while SA is caused by bacterial infection in children joints. Although these diseases have different physiopathological basis and involve different treatments and prognoses, they share clinical similarities. Objectives To date, there are no markers sufficiently reliable to discriminate between these two forms of arthritis at the onset of the disease. Our goal is to identify diagnostic biomarkers capable of discriminating between JIA and SA. To that end, we focused on microRNAs (miRNAs) and myeloid cell subsets, both playing a major role in the immune system. Methods We analyzed serum and synovial fluid (SF) samples from JIA or SA patients using a miRNAs Whole Transcriptome Assay associated with a next-generation sequencing detection technology to measure the expression level of 2083 miRNAs in a pilot study (oligoarticular JIA (oJIA): n=5; SA: n=3) and validated using RT-qPCR in a replicative study (oJIA: n=9; SA: n=9). In parallel, we performed a phenotypic characterization of peripheral blood (PB) and SF myeloid subpopulations using a flow cytometer (oJIA: n=9; SA: n=8). Results Principal component analysis and hierarchical clustering characterizations did not show significant differences between serum miRNAs of oJIA and SA patients. However, we observed a distinct miRNA profile signature in SF between the two diseases with 16 upregulated miRNAs and 5 down-regulated that perfectly discriminates oJIA and SA (p Conclusions In this study, we propose for the first time a SF-based miRNA signature as well as 5 myeloid cell subsets that discriminate between oJIA and SA and might be used as potential diagnosis markers in juvenile arthritis. Moreover, these markers give an insight into the mecanisms that are differentially altered between inflammatory and infectious arthritis. Disclosure of Interest None declared.