The Role of NK Cells in Pig-to-Human Xenotransplantation

Figure 3

Receptors and ligands involved in pig endothelial cells lysis by human NK cells. There is a tight balance between activating and inhibitory signals that control NK cytotoxicity. The activating NK receptors NKG2D and NKp44 bind to their pig ligands: pULBP-1 and an unidentified molecule, respectively, and trigger lytic granule release (shown by red arrows and yellow circles). A role of CD2 and variant CD28 in facilitating NK cytotoxicity has been described in NK subpopulations, potentially by interacting with porcine CD58 and CD86, respectively. The inhibitory NK receptors, KIR, ILT2, and CD94/NKG2A, poorly recognize porcine MHC-I molecule (SLA-I) including the pig ortholog for HLA-E leading to a lack of inhibitory signals (in dotted blue) and NK cell activation.