*Purpose: Microvascular inflammation (MVI) is a feature of antibody mediated rejection. MVI can be seen with or without activation of other effectors of antibody injury such as the complement system. How Endothelial Cell (EC) injury patterns differ across EC beds (glomerular,peritubular) and in respect to complement activation remains unclear. We hypothesized that ScRNA-seq will allow us to study EC activation states to identify drivers of injury thereby allowing for precise therapeutic targeting.

*Methods: We leveraged our surveillance and indication biopsy program to identify 2 patients with MVI (g+ptc >1) without c4d deposition (Group 1) or with c4d deposition (Group 2). 3 living donor pre-perfusion biopsies served as normal controls. ScRNA-seq was performed on a 10X chromium platform and processed per KPMP protocols. Cell-type-specific markers were used for cell clustering. Enrichment analysis for biological pathways was performed with Enrichr tool using NCI 2016 pathway interaction database.

*Results:

Differentially expressed genes (DEG) between Glomerular Endothelial Cells (GEC) and Peritubular endothelial Cells (PTECs) in controls vs. both MVI groups revealed enrichment of genes associated with IL6 signaling pathway.

DEG between MVI groups revealed enrichment of genes associated with VEGF/VEGFR and CD40/CD40L signaling in GECs. Activation of genes associated with MAPK, CXCR2 and TNF receptor signaling was found among PTECs.

*Conclusions: scRNA-seq analysis reveals evidence of endothelial IL6 pathway activation in biopsies with MVI independent of c4d status, suggesting a common pathway being activated across both phenotypes. There were however differences in EC activation states by capillary beds across both groups.

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