Supplementary Material for: Cytomegalovirus-Infected Primary Endothelial Cells Trigger NKG2C+ Natural Killer Cells

Among innate cells, natural killer (NK) cells play a crucial role in the defense against cytomegalovirus (CMV). In some individuals, CMV infection induces the expansion of NKG2C<sup>+</sup> NK cells that persist after control of the infection. We have previously shown that KIR2DL<sup>+</sup> NK cells, in contrast to NKG2C<sup>+</sup> NK cells, contribute to controlling CMV infection using a CMV-infected monocyte-derived dendritic cell (MDDC) model. However, the nature of CMV-infected cells contributing to the expansion of the NKG2C<sup>+</sup> NK cell subset remains unclear. To gain more insight into this question, we investigated the contribution of NKG2C<sup>+</sup> NK cell activation by CMV-infected primary human aortic endothelial cells (EC) isolated from kidney transplant donors, which constitutively express the human leukocyte antigen (HLA)-E molecule. Here, we show that, although classic HLA class I expression was drastically downregulated, nonclassic HLA-E expression was maintained in CMV-infected EC. By comparing HLA expression patterns in CMV-infected EC, fibroblasts and MDDC, we demonstrate a cell-dependent modulation of HLA-E expression by CMV infection. NKG2C<sup>+</sup> NK cell degranulation was significantly triggered by CMV-infected EC regardless of the nature of the HLA-E allele product. EC, predominantly present in vessels, may constitute a privileged site for CMV infection that drives a ‘memory' NKG2C<sup>+</sup> NK cell subset.