Background: While tissue engineering offers promise for organ and tissue transplantation, it can also be used to examine transplant and immune biology. Endothelial cells engrafted within 3-dimensional matrices create stable units that produce all of the factors of a functional quiescent endothelium. Perivascular implantation of tissue engineered endothelial cell constructs provides long-term control of vascular repair after injury. This control is established without restoration of the natural luminal:mural endothelium, and most intriguingly, without engendering host allo- and xenogeneic immune responses. We examined how endothelial immunogenicity is controlled by interaction with 3-dimensional matrices.
Materials and methods: Human aortic endothelial cells (HAE) were either grown to confluence on polystyrene tissue culture plates or within 3-dimensional collagen-based matrices. Major histocompatibility complex (MHC) class II, integrin, interferon (IFN)-gamma receptor expression, and signaling were analyzed via confocal microscopy, flow cytometry, reverse transcription polymerase chain reaction (RT-PCR), and microarray. Splenocyte proliferation was assayed by thymidine incorporation.
Results: Despite similar expression levels of IFN-gamma receptors, matrix-embedded HAE elicited far less STAT-1 phosphorylation upon IFN-gamma stimulation, and expressed 2-fold less MHC II than HAE grown to confluence on culture plates (P < .001). This effect correlated with reduced expression of integrin alpha(v) and beta(3) (P < .002), and muted proliferation of porcine splenocytes (P < .001).
Conclusions: Matrix architecture is critical for modulation of endothelial immunogenicity. Embedding HAE within a physiologic 3-dimensional environment affects activity of intracellular signaling pathways, MHC II expression, and subsequent activation of immune cells. These findings might offer novel insights into our understanding of endothelial-mediated diseases and might enhance our ability to leverage the potential for cell-based therapies.