PROTEOMIC INSIGHT INTO IMMUNE PATHWAYS AND BIOMARKER DISCOVERY IN PERIPROSTHETIC JOINT INFECTION

Aim Periprosthetic joint infection (PJI) is a serious complication of total joint arthroplasty with unclear pathophysiology. This study analyzed protein expression in infected synovial fluid to identify key proteins and pathways involved. Method This study was conducted at a single academic institution, where patient samples were prospectively collected from August 2023-September 2024. Synovial fluid was obtained during arthroplasty surgery from 33 patients across three groups: (i) primary TKA (n=9), (ii) aseptic revision (n=10), and (iii) septic revision meeting the 2018 ICM criteria for PJI (n=14). Synovial fluid was sent to SomaLogic for proteomic analysis using the 1500 custom SomaScan assay. Fold-change was calculated by first averaging the expression of each group then using the following equation: (Aseptic or Septic expression)/(TKA expression) and transformed using log 2 . Nonparametric false discovery rate (FDR) p-values were calculated using the Wilcoxon rank-sum test and transformed using -log 10 for volcano plot analysis or Kruskall-Wallis test when all groups were compared. Proteins with ≥2-fold change and P-value≤0.05 were considered significant for further analysis. Results A total of 20 upregulated and 126 downregulated proteins were found in the septic group compared to control TKA, and five upregulated and six downregulated proteins were found in the aseptic group compared to control TKA. Of significantly regulated proteins, three upregulated and five downregulated proteins were shared between aseptic and septic groups suggesting their expression may be a revision-dependent. Further assessment of differential protein expression between groups shows marked upregulation in immune pathways including, immune response and regulatory proteins (fold-change reported septic/aseptic) –VVN2 (12.5, p<0.001), C3 (2.09, p<0.05), HLA-DOB (4.37, p<0.001) and antimicrobial and defense proteins – DEFA4 (5.96, p<0.01), LCN2 (47.03, p<0.001), LTF (2.02, p<0.01), S100A8 (5.33, p<0.001), RNASE3 (4.45, p<0.001), and marked downregulation in immune modulation proteins – LAG3 (-3.91, p<0.001), CD28 (-6.97, p<0.01), CD163 (-7.80, p<0.001), NRP1 (-3.87, p<0.01), IL17-related proteins – IL17RA (-10.64, p<0.001), IL-1RL1 (-2.79, p<0.05), IL-27RA (-4.69. p<0.01) and immune signaling – STAT1 (-5.29, p<0.001) and PRKCA (-4.34, p<0.001) in the septic group only. Conclusions This first comprehensive proteomic analysis of synovial fluid in periprosthetic joint infection reveals distinct protein expression and pathway activation, uncovering underexplored immune responses and informing future diagnostic and pathophysiology studies.