Phenotypic and Functional Analyses of KIR3DL1+ and KIR3DS1+ NK Cell Subsets Demonstrate Differential Regulation by Bw4 Molecules and Induced KIR3DS1 Expression on Stimulated NK Cells

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Abstract
Recently, the Z27 mAb was shown to recognize the NK cell-activating receptor KIR3DS1, and several genetic studies suggest that the most probable ligands of KIR3DS1 are HLA class I molecules with the Bw4 motif. Despite these findings, the attempts to establish a functional interaction between KIR3DS1 and its potential ligand have been unsuccessful. Here, we study the proliferation and cytotoxicity of KIR3DS1+ NK cells, compared with KIR3DL1+ NK cells, according to the Bw4+ or Bw4− allogeneic environment. Our results show for the first time that KIR3DS1 expression on NK cells can be induced after exposure to stimulator cells (221, K562, EBV-B cell lines, and B cells), polyinosinic-polycytidylic acid, IL-15, or IL-2. Furthermore, whereas KIR3DL1+ NK cell proliferation and cytotoxicity were inhibited in a Bw4+ but not a Bw4− context, KIR3DS1+ NK cell functions were not influenced by the presence of Bw4 on target cells. Nevertheless, despite the absence of demonstrated regulation of KIR3DS1+ NK cell functions by HLA-Bw4 molecules, we found a higher KIR3DS1+ NK cell frequency and higher levels of KIR3DS1 expression in Bw4+ compared with Bw4− individuals. Altogether, these results suggest that KIR3DS1 does not recognize HLA-Bw4 molecules in a physiological context, and they highlight the induced expression of KIR3DS1 observed on stimulated NK cells and the higher frequency of KIR3DS1+ NK cells in Bw4+ individuals. Because a protective KIR3DS1-Bw4 association has been reported in viral infections, our results further the understanding of the role of KIR3DS1+ NK cells in controlling viral infections.

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