MABF2224-25UL Sigma-AldrichAnti-NKR-P1G (KLRB1) Antibody, clone 8A10

Natural killer gene complex-encoded immunomodulatory C-type lectin-like receptors include members of the NKRP1 and C-type lectin-like 2 (CLEC2) gene families, which constitute genetically linked receptor-ligand pairs and are thought to allow for NK cell-mediated immunosurveillance of stressed or infected tissues. The mouse C-type lectin-like receptor Nkrp1g was previously shown to form several receptor-ligand pairs with the CLEC2 proteins Clr-d, Clr-f, and Clr-g, respectively. However, the physiological expression of Nkrp1g and its CLEC2 ligands as well as their functional relevance remained poorly understood. Recently, we demonstrated a gut-restricted expression of Clr-f on intestinal epithelial cells that is spatially matched by Nkrp1g on subsets of intraepithelial lymphocytes. In this study, we investigated expression and ligand interaction of Nkrp1g in the splenic compartment, and found an exclusive expression on a small subset of NK cells that upregulates Nkrp1g after cytokine exposure. Whereas transcripts of Clr-d and Clr-f are virtually absent from the spleen, Clr-g transcripts were abundantly detected throughout different leukocyte populations and hematopoietic cell lines. However, a newly generated anti-Clr-g mAb detected only residual Clr-g surface expression on splenic monocytes, whereas many hematopoietic cell lines brightly display Clr-g. Clr-g surface expression was strongly upregulated on splenic CD8α+ conventional dendritic cells (DCs) and plasmacytoid DCs upon TLR-mediated activation and detectable by Nkrp1g, which dampens NK cell effector functions upon Clr-g engagement. Hence, different to the intestinal tract, in the spleen, Nkrp1g is selectively expressed by a subset of NK cells, thereby potentially allowing for an inhibitory engagement with Clr-g-expressing activated DCs during immune responses.

The integrity of the intestinal epithelium is constantly surveyed by a peculiar subset of innate-like T lymphocytes embedded in the epithelial cell layer, hence called intestinal intraepithelial lymphocytes (IELs). IELs are thought to act as "first-line" sentinels sensing the state of adjacent epithelial cells via both T-cell receptors and auxiliary receptors. Auxiliary receptors modulating IEL activity include C-type lectin-like receptors encoded in the natural killer gene complex such as NKG2D. Here, we report that the CTLR Nkrp1g is expressed by a subpopulation of mouse CD103(+) IELs allowing immunosensing of the intestinal epithelium through ligation of the genetically coupled CTLR Clr-f that is almost exclusively expressed on differentiated intestinal epithelial cells (IECs). Most of these Nkrp1g-expressing IELs exhibit a γδTCR(bright)Nkg2a(-) phenotype and are intimately associated with the intestinal epithelium. As Clr-f expression strongly inhibits effector functions of Nkrp1g-expressing cells and is upregulated upon poly(I:C) challenge, Clr-f molecules may quench reactivity of these IELs towards the epithelial barrier that is constantly provoked by microbial and antigenic stimuli. Altogether, we here newly characterize a genetically linked C-type lectin-like receptor/ligand pair with a highly restricted tissue expression that apparently evolved to allow for a dedicated immunosurveillance of the mouse intestinal epithelium.