The Natural Killer Gene Complex (NKC) encodes for numerous C-type lectin-like receptors (CTLR) variably expressed on lymphocytes and myeloid cells. Well-known representatives of NKC-encoded CTLR are NKG2D, CD69, and Ly49 molecules. However, the NKC also contains a considerable number of genes which are barely characterized. Recently, we described the CLEC2A gene encoding for a new member of the human CLEC2 family of NKC-encoded CTLR. CLEC2A, in contrast to other human CLEC2 family members such as CD69/CLEC2C and AICL/CLEC2B, is virtually not expressed by peripheral leukocytes, but its expression appears restricted to skin. We now report that CLEC2A encodes for a non-disulfide-linked, homodimeric surface CTLR which is expressed on freshly isolated skin cells. Addressing a potential immune-associated function, we find that CLEC2A stimulates cytotoxicity and cytokine release of human NK cells. However, we failed to ascertain CLEC2A engagement by known activating NK receptors. Instead, we identified a hitherto undescribed NKC-encoded CTLR (NKp65) that specifically interacts with CLEC2A and activates NK cytotoxicity. In summary, we define CLEC2A as a skin-specific and NK cell-stimulating CTLR engaging NKp65, a novel activating CTLR which may allow for dedicated immunosurveillance of human skin.

This work was supported by funds (SFB 685/A1) of the German Research Foundation (DFG).