Abstract
The NKR-P1 receptors were identified as prototypical natural killer (NK) cell surface antigens and later shown to be conserved from rodents to humans on NK cells and subsets of T cells. C-type lectin-like in nature, they were originally shown to be capable of activating NK cell function and to recognize ligands on tumor cells. However, certain family members have subsequently been shown to be capable of inhibiting NK cell activity, and to recognize proteins encoded by a family of genetically linked C-type lectin-related ligands. Some of these ligands are expressed by normal, healthy cells, and modulated during transformation, infection, and cellular stress, while other ligands are upregulated during the immune response and during pathological circumstances. Here, we discuss historical and recent developments in NKR-P1 biology that demonstrate this NK receptor–ligand system to be far more complex and diverse than originally anticipated.
Highlights
Natural killer (NK) cells are innate lymphocytes that recognize and respond to a variety of different pathological target cells via cytotoxicity and secretion of type I helper cytokines, most notably IFN-γ
Target cell recognition is mediated by a variety of receptors on NK cells that detect specific cognate ligands, which in turn are differentially expressed on pathological versus normal cells [1]
Healthy cells broadly express a number of inhibitory ligands, which are frequently lost during pathological transformation, infection, or cell stress; this has been termed “missing-self ” recognition [1, 2]
Summary
Natural killer (NK) cells are innate lymphocytes that recognize and respond to a variety of different pathological target cells via cytotoxicity and secretion of type I helper cytokines, most notably IFN-γ. Many NK cell receptors are encoded by genes linked to the NK gene complex (NKC), located on chromosome 6 in mice, chromosome 4 in rats, and chromosome 12 in humans [5,6,7] (Figure 1). There are numerous other NK cell receptors encoded in various regions in the genome, including the SAP/SLAM family of receptors found on mouse and human chromosome 1 [13, 14], the natural cytotoxicity receptors (NCR1, 2, 3) [15, 16], and others Within these regions, most NK cell receptors can be broadly classified into two structurally divergent categories: immunoglobulinlike receptors (e.g., KIR, NCR) and C-type lectin-like receptors (e.g., KLR, Ly49). This review will outline the historical and recent discoveries surrounding the NKR-P1:Clr systems in rodents and humans, and provide an update on their nomenclature, as well as known expression, structure, and function
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