Multiple Cytokines Regulate the NK Gene Complex-Encoded Receptor Repertoire of Mature NK Cells and T Cells

Abstract

Mature NK cells comprise a highly diverse population of lymphocytes that express different permutations of receptors to facilitate recognition of diseased cells and perhaps pathogens themselves. Many of these receptors, such as those belonging to the NKRP1, NKG2, and Ly49 families are encoded in the NK gene complex (NKC). It is generally thought that these NKC-encoded receptors are acquired by a poorly understood stochastic mechanism, which operates exclusively during NK cell development, and that following maturation the repertoire is fixed. However, we report a series of observations that demonstrates that the mature NK cell repertoire in mice can in fact be radically remodeled by multiple cytokines. Thus, both IL-2 and IL-15 selectively induce the de novo expression of Ly49E on the majority of mature NK cells. By contrast, IL-4 not only blocks this IL-2-induced acquisition of Ly49E, but reduces the proportion of mature NK cells that expresses pre-existing Ly49 receptors and abrogates the expression of NKG2 receptors while leaving the expression of several NKRP1 receptors unaltered. IL-21 also abrogates NKG2 expression on mature NK cells and selectively down-regulates Ly49F. IL-4 and IL-21 additionally cause dramatic and selective alterations in the NKC-encoded receptor repertoire of IL-2-activated T cells but these are quite different to the changes induced on NK cells. Collectively these findings reveal an unexpected aspect of NKC receptor expression that has important implications for our understanding of the function of these receptors and of the genetic mechanisms that control their expression.

DifferentialLy49eExpression Pathways in Resting versus TCR-Activated Intraepithelial γδ T Cells

“…As bone marrow NK precursors acquire Ly49E expression in vitro in the absence of stromal cells (37), which is at variance with other Ly49 members (38,39), it can be hypothesized that Ly49E expression, regardless of the cell type by which it is expressed, is differently regulated compared with the other Ly49 members. This hypothesis adds to the list of unique characteristics of Ly49E within the Ly49 family: Ly49E 1) contains both inhibitory and activating motifs in its cytoplasmic and transmembrane region, 2) is highly conserved between different mouse strains, 3) is the only Ly49 member expressed by fetal and neonatal NK cells and by fetal thymic DETC precursors and adult skin DETCs, 4) is triggered by the non-MHC class I protein uPA, and finally 5) as we showed in the current study for intraepithelial gd T cells and as was already shown for NK cells (19), can be upregulated in several innate lymphocytic subpopulations. Combined with our previous observation that Ly49E exerts inhibitory functions through the stress-induced uPA in Ly49E pos IL-2-activated NK cell lines (20), we hypothesize that Ly49E upregulation might be a general feature of several lymphocytic populations to temper their immune response after initial activation and hence to prevent autoimmunity.…”

“…It was shown initially by semiquantitative PCR that de novo Ly49E-expressing, IL-2-activated NK cells contain both Ly49e Pro1 and Pro2 transcripts (19). To study Ly49e promoter activities in de novo Ly49E-expressing TCR-activated DETCs and iIELs, we therefore designed qPCR primers for the specific detection of Pro1 versus Pro2 transcripts (referred to as Ly49E Pro1 and Ly49E Pro2) (Fig.…”

“…Similarly, a low percentage of peripheral adult NK cells bears Ly49E, in contrast to their fetal thymic precursors (16)(17)(18). However, Ly49E expression can be reinduced on a large proportion of peripheral adult NK cells upon IL-2 or IL-15 culture (19). Importantly, the immune response of IL-2-cultured, Ly49E high NK cell lines is tempered by urokinase plasminogen activator (uPA) through Ly49E (20).…”

“…Studies of Ly49 promoter elements have revealed three distinct sites of transcript initiation, as follows: Pro1, Pro2, and Pro3 (21). The frequency of transcription from forward versus reverse Ly49 Pro1 promoter elements during NK cell maturation correlates with ultimate Ly49 expression frequencies in mature resting NK cells (22), in which either the conventional Pro2 (Ly49a, Ly49c, Ly49e, and Ly49d) or the unconventional Pro3 promoter (Ly49g and Ly49j) initiates Ly49 transcription (19,23,24). Controversial data exist with regard to the role of LTab-LTbR signaling and its downstream signaling molecules NF-kB p50/p52 in Pro1 activity and Ly49 receptor acquisition during NK cell maturation (25)(26)(27)(28).…”

Ly49B Is Expressed on Multiple Subpopulations of Myeloid Cells

“…The LNK line (11) was provided by Dr. S. Anderson (National Cancer Institute, Frederick, MD). Ly49-transfected YB2/0 and RNK cells were generated as described previously (12).…”