Vascular endothelial cells (ECs) are an initial barrier between allografts and the host immune system and play an important role in initiating allograft rejection. Increasing evidence suggests that the mitochondria are a major source of danger associated molecular patterns that activate innate immune signaling pathways. We hypothesize that mitochondria released from allograft injury are critical mediators of EC activation that can lead to graft rejection through the priming of alloreactive T cells.

Methods: Purity of human mitochondria purified from HeLa cells by differential centrifugation and anti-TOMM22 magnetic beads was determined by western blot and flow cytometry (FACS). Human vascular ECs were cultured with purified mitochondria and assessed by FACS for markers of activation. The interaction of fluorescently-labeled mitochondria and ECs was observed by confocal microscopy. Activated ECs were co-cultured with allogeneic T cells and T cell activation was determined by FACS analysis of intracellular cytokine production and proliferation.

Results: Mitochondria-stimulated ECs demonstrated a 1.7-fold increase in E-selectin surface expression after 4 hrs, and a 2.0-fold increase in ICAM-1 and VCAM-1 expression by 12 hrs. Confocal microscopy demonstrated dramatic uptake of fluorescently-labeled mitochondria by ECs that increased from 4 to 12 hrs post incubation. Activated ECs induced T cell proliferation (CD4 10.4±3.5%, CD8 28.2±7.2%) and CD8+ memory cells demonstrated intracellular dual cytokine production as response (TNF-alpha and IFN-gamma) in response to allogeneic EC stimulation.

Conclusion: These results demonstrate that mitochondria are internalized by human ECs and mitigate their activation, which can lead to alloreactive T cell activation and may promote graft rejection. EC activation by extracellular mitochondria released in the setting of tissue injury may be a critical pathway linking innate and adaptive immunity during initial alloimmune responses.

CITATION INFORMATION: Feng F, Xu H, Lin L, Kirk A, Brennan T. Vascular Endothelial Cell Activation by Mitochondria Links Innate and Adaptive Immune Responses to Allograft Injury. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress