(433) Fibrin Clot Characteristics and Inflammatory Signature in Pediatric Thromboinflammation

Introduction: Thromboinflammation describes the interplay between pathologic immune activation and thrombi formation resulting in organ injuries and death in diseases such as hemophagocytic lymphohistiocytosis (HLH), coronavirus disease 2019 (COVID), and multisystem inflammatory disease (MISC). We previously showed that adults with severe COVID had pathologic fibrin clots compared to non-COVID sepsis. We also showed pediatric HLH had a distinct inflammatory profile of interferon-gamma (IFN-g) signaling pathways and CD8+ T Cells activation. We hypothesize that children with HLH, COVID & MISC have fibrin clot characteristics (FCC) types that are distinct to the disease-specific inflammatory profiles.

Methods: Plasmas from pediatric critically ill HLH (n=6), COVID (n=6), MISC (n-6) & healthy controls (n=6) were analyzed for ex vivo FCC such as fibrin polymerization potential and fluid flow-through assays. We measured 135 inflammatory plasma proteins by Multiplex Assays. We conducted an unbiased clustering analysis of plasma analytes and FCC by scaling them with standardized scores across groups and clustering them using Euclidean distance.

Results: Peak fibrin clot formation potential was significantly increased in COVID (27%; p=0.02) and decreased in HLH (33%; p=0.05) compared to controls. Resistance to fluid flow-through fibrin clot was increased in HLH, COVID & MISC (100, 78 & 142%; respectively; p< 0.05) compared to controls. 13/135 analytes correlated with FCC. Notably, IFN-g & soluble tumor necrosis factor-receptor (sTNFR) positively correlated with maximum fibrin clot formation potential (R=0.76 & 0.65, respectively; p< 0.05 Pearson’s). IL-1b & Heat Shock Protein (HSP) negatively correlated with fluid flow-through (R=0.97 & 0.80, respectively; p< 0.05). We observed distinct disease-specific thromboinflammatory patterns among HLH, COVID & MISC on unbiased clustered analysis.

Conclusions: Aberrant ex vivo FCC were found in pediatric HLH, COVID & MISC. HLH FCC had a distinct pattern in where the fibrin clot was more resistance to fluid flow-through despite a lower maximum fibrin clot formation potential. IFN-g, a signature inflammatory pathway for HLH, along with IL-1b, sTNFR & HSP seem to drive aberrant FCC. A distinct disease-specific thromboinflammatory signature might exist among HLH, COVID & MISC.