Cloning and characterization of a novel activating Ly49 closely related to Ly49A

The majority of the known Ly49 family members have been isolated from either C57BL/6 (B6) or BALB/c mice. Interestingly, the anti-Ly49 Ab reactivities observed in 129/J mice are different from those of B6 mice. Furthermore, immunoprecipitation of 129/J NK cell lysates with YE1/32 and YE1/48, Abs specific for the inhibitory Ly49A in B6, resulted in detection of the activation-associated DAP12 molecule. These results indicated a need for a more detailed study of this strain. Therefore, a cloning strategy was devised to isolate Ly49 cDNAs from 129/J mice. An immunoreceptor tyrosine-based inhibitory motif-containing, Ly49D-related clone was discovered that we have named Ly49O, and one immunoreceptor tyrosine-based inhibitory motif-lacking, Ly49A-related clone was discovered that we have named Ly49P. No anti-Ly49 mAb reacted with Ly49O, whereas the molecule encoded by the Ly49P cDNA was found to react with YE1/32 and YE1/48. Ly49P was found to associate with mouse DAP12, and Ab-mediated cross-linking of Ly49P resulted in mouse DAP12 phosphorylation and Ca2+ mobilization, indicating that Ly49P is a competent activation receptor. Ly49P, therefore, represents a novel member of the Ly49 activating receptor subfamily.

Cloning and Characterization of a Novel Activating Ly49 Closely Related to Ly49A

The majority of the known Ly49 family members have been isolated from either C57BL/6 (B6) or BALB/c mice. Interestingly, the anti-Ly49 Ab reactivities observed in 129/J mice are different from those of B6 mice. Furthermore, immunoprecipitation of 129/J NK cell lysates with YE1/32 and YE1/48, Abs specific for the inhibitory Ly49A in B6, resulted in detection of the activation-associated DAP12 molecule. These results indicated a need for a more detailed study of this strain. Therefore, a cloning strategy was devised to isolate Ly49 cDNAs from 129/J mice. An immunoreceptor tyrosine-based inhibitory motif-containing, Ly49D-related clone was discovered that we have named Ly49O, and one immunoreceptor tyrosine-based inhibitory motif-lacking, Ly49A-related clone was discovered that we have named Ly49P. No anti-Ly49 mAb reacted with Ly49O, whereas the molecule encoded by the Ly49P cDNA was found to react with YE1/32 and YE1/48. Ly49P was found to associate with mouse DAP12, and Ab-mediated cross-linking of Ly49P resulted in mouse DAP12 phosphorylation and Ca2+ mobilization, indicating that Ly49P is a competent activation receptor. Ly49P, therefore, represents a novel member of the Ly49 activating receptor subfamily.

Ly-49 receptor expression and functional analysis in multiple mouse strains

We present data on the strain distribution and functional characteristics of the Ly-49 receptors A, C/I, D, and G2 on DX5+ natural killer (NK) cells. We have examined tyrosine phosphorylation of the Ly-49 molecules, regulation of NK cytotoxic functions, and in vivo marrow rejection capability. The flow cytometry results demonstrate a diverse and complex pattern of expression of the Ly-49 receptors in the 11 strains examined. The vast majority of NK cells express Ly-49s, although some NK1.1+ CD3+ cells also express these receptors. The results of our functional analysis indicate that H-2Dd was able to inhibit the function of Ly-49G2+ NK cells, not only in B6 mice, but also by NK cells derived from several haplotypes. The examination of Ly-49 receptor tyrosine phosphorylation, which is a biochemical measure of inhibitory function, was consistently observed in the 11 mouse strains examined. In contrast, analysis of Ly-49D function suggests its expression appears to be more restricted and that H-2Dd is an activating ligand for this receptor. In addition, the in vivo examination of both inhibitory (Ly-49G2) and activating (Ly-49D) receptors demonstrated regulatory roles of these class I binding receptors in marrow transplantation.

Tolerance and alloreactivity of the Ly49D subset of murine NK cells

Class I-specific stimulatory and inhibitory receptors expressed by NK cell subsets contribute to the alloreactive potential of the self-tolerant murine NK cell repertoire. In this report, we have studied potential mechanisms of tolerance to the function of the positive signaling Ly49D receptor in mice that express one of its ligands, H2-Dd. Our results demonstrate that H2-Dd-expressing mice possess a large Ly49D+ subset of NK cells that is functionally capable of rejecting bone marrow cell (BMC) allografts in vivo and lysing allogeneic Con A lymphoblasts in vitro. Also, we show that the Ly49D receptor is responsible for the ability of H2b/d F1 hybrid mice to reject H2d/d parental BMC (hybrid resistance). Thus, deletion or anergy of Ly49D+ cells in H2-Dd+ hosts cannot explain self tolerance. Our functional studies revealed that coexpression of the Dd-specific Ly49A or Ly49G2 inhibitory receptors by Ly49D+ cells resulted in tolerance to Dd+ targets, while coexpression of Kb-specific inhibitory receptors Ly49C/I resulted in tolerance to Kb+ targets. Only in H2d/d cells did Ly49C/I dominantly inhibit Ly49D-Dd stimulation. This correlated with an increased mean fluorescence intensity of Ly49C expression, as well as an increased percentage of Ly49C+ cells in the Ly49D+A/G2- compartment. Therefore, we conclude that self tolerance of the Ly49D subset can be achieved through coexpression of a sufficient level of self-specific inhibitory receptors.

Tolerance and Alloreactivity of the Ly49D Subset of Murine NK Cells

Class I-specific stimulatory and inhibitory receptors expressed by NK cell subsets contribute to the alloreactive potential of the self-tolerant murine NK cell repertoire. In this report, we have studied potential mechanisms of tolerance to the function of the positive signaling Ly49D receptor in mice that express one of its ligands, H2-Dd. Our results demonstrate that H2-Dd-expressing mice possess a large Ly49D+ subset of NK cells that is functionally capable of rejecting bone marrow cell (BMC) allografts in vivo and lysing allogeneic Con A lymphoblasts in vitro. Also, we show that the Ly49D receptor is responsible for the ability of H2b/d F1 hybrid mice to reject H2d/d parental BMC (hybrid resistance). Thus, deletion or anergy of Ly49D+ cells in H2-Dd+ hosts cannot explain self tolerance. Our functional studies revealed that coexpression of the Dd-specific Ly49A or Ly49G2 inhibitory receptors by Ly49D+ cells resulted in tolerance to Dd+ targets, while coexpression of Kb-specific inhibitory receptors Ly49C/I resulted in tolerance to Kb+ targets. Only in H2d/d cells did Ly49C/I dominantly inhibit Ly49D-Dd stimulation. This correlated with an increased mean fluorescence intensity of Ly49C expression, as well as an increased percentage of Ly49C+ cells in the Ly49D+A/G2− compartment. Therefore, we conclude that self tolerance of the Ly49D subset can be achieved through coexpression of a sufficient level of self-specific inhibitory receptors.

Induction of DAP12 phosphorylation, calcium mobilization, and cytokine secretion by Ly49H

The ability of several Ly49 family members to inhibit natural killer (NK) cell functions through recruitment of SHP-1 phosphatase has been reported. In contrast, the mechanisms underlying the activating signal generated by Ly49D are poorly understood. A homodimeric phosphoprotein (pp16) that physically and functionally associates with Ly49D has been described. In this study, a rabbit anti-mouse pp16 antiserum was generated and used to demonstrate that pp16 corresponds to the recently described DAP12 molecule. In addition, we show that a second Ly49 family member that lacks an immunoreceptor tyrosine-based inhibitory motif and contains a charged residue in the transmembrane domain, Ly49H, also associates with DAP12. Furthermore, we show that engagement of the Ly49H/DAP12 complex results in phosphorylation of DAP12, intracellular calcium mobilization, and tumor necrosis factor secretion in transfected cells. These results thus provide evidence that Ly49H is an activating receptor that associates with DAP12, previously described as a pp16 component of the Ly49D receptor complex.

The natural killer gene complex genetic locus Chok encodes Ly-49D, a target recognition receptor that activates natural killing

Previously, we established that natural killer (NK) cells from C57BL/6 (B6), but not BALB/c, mice lysed Chinese hamster ovary (CHO) cells, and we mapped the locus that determines this differential CHO-killing capacity to the NK gene complex on chromosome 6. The localization of Chok in the NK gene complex suggested that it may encode either an activating or an inhibitory receptor. Here, results from a lectin-facilitated lysis assay predicted that Chok is an activating B6 NK receptor. Therefore, we immunized BALB/c mice with NK cells from BALB.B6-Cmv1(r) congenic mice and generated a mAb, designated 4E4, that blocked B6-mediated CHO lysis. mAb 4E4 also redirected lysis of Daudi targets, indicating its reactivity with an activating NK cell receptor. Furthermore, only the 4E4(+) B6 NK cell subset mediated CHO killing, and this lysis was abrogated by preincubation with mAb 4E4. Flow cytometric analysis indicated that mAb 4E4 specifically reacts with Ly-49D but not Ly-49A, B, C, E, G, H, or I transfectants. Finally, gene transfer of Ly-49DB6 into BALB/c NK cells conferred cytotoxic capacity against CHO cells, thus establishing that the Ly-49D receptor is sufficient to activate NK cells to lyse this target. Hence, Ly-49D is the Chok gene product and is a mouse NK cell receptor capable of directly triggering natural killing.

Role of a STAT binding site in the regulation of the human perforin promoter

The pore-forming protein perforin is preferentially expressed in NK and cytotoxic T cells. To investigate the molecular regulation of human perforin gene transcription, the activity of the human perforin promoter was analyzed in human NK and T cell lines using various promoter fragments linked to a luciferase reporter gene. A core promoter was identified within 55 bp upstream of the transcription start site. This promoter region contains a guanine/cytosine box and has basal activity in YT, Kit225-k6, and Jurkat cells. A strong enhancer activity was identified between positions -1136 and -1076, a region that includes a STAT-like element. This enhancer region was active in YT cells, which have constitutive perforin expression and activated STAT3 protein, but not in Kit225-k6 or Jurkat cells, which do not have constitutive perforin expression. Mutation of the STAT binding site resulted in a dramatic down-regulation of promoter activity. Electrophoretic mobility shift assays, using a probe containing the STAT element of the perforin promoter, indicated that this element can bind STAT3 from YT cells. Moreover, the STAT element was shown to bind STAT5a/b induced by IL-2 as well as STAT1alpha induced by IL-6 in human NK cells. Together, these results suggest that STAT proteins play a key role in perforin gene transcription and provide a model by which cytokines can regulate perforin gene expression.

Role of a STAT Binding Site in the Regulation of the Human Perforin Promoter

The pore-forming protein perforin is preferentially expressed in NK and cytotoxic T cells. To investigate the molecular regulation of human perforin gene transcription, the activity of the human perforin promoter was analyzed in human NK and T cell lines using various promoter fragments linked to a luciferase reporter gene. A core promoter was identified within 55 bp upstream of the transcription start site. This promoter region contains a guanine/cytosine box and has basal activity in YT, Kit225-k6, and Jurkat cells. A strong enhancer activity was identified between positions −1136 and −1076, a region that includes a STAT-like element. This enhancer region was active in YT cells, which have constitutive perforin expression and activated STAT3 protein, but not in Kit225-k6 or Jurkat cells, which do not have constitutive perforin expression. Mutation of the STAT binding site resulted in a dramatic down-regulation of promoter activity. Electrophoretic mobility shift assays, using a probe containing the STAT element of the perforin promoter, indicated that this element can bind STAT3 from YT cells. Moreover, the STAT element was shown to bind STAT5a/b induced by IL-2 as well as STAT1α induced by IL-6 in human NK cells. Together, these results suggest that STAT proteins play a key role in perforin gene transcription and provide a model by which cytokines can regulate perforin gene expression.

Positive Recognition of MHC Class I Molecules by the Ly49D Receptor of Murine NK Cells

Members of the murine Ly49 family of receptors have been shown to inhibit and activate NK cell function. Subsets of Ly49-expressing NK cells mediate the rejection of bone marrow cell allografts and the lysis of allogeneic lymphoblasts. In this report we have studied Ly49-mediated positive and negative signaling in an in vitro cytotoxicity assay using sorted NK cell subsets as effectors and a panel of 51Cr-labeled Con A lymphoblasts as targets in the presence or the absence of Abs to Ly49 and/or class I molecules. Our results demonstrate that the activating receptor Ly49D delivers stimulatory signals for target cell lysis upon interacting with H2-Dd, Dr, and Dsp2, but not H2b or H2k class I Ags. On the other hand, the inhibitory receptor Ly49G2 delivers negative signals for target cell lysis upon interacting with Dd, Dr, and H2k, but not H2b or Dsp2, class I Ags. Furthermore, Ly49-mediated negative signaling dominates Ly49D-mediated positive signaling. Thus, lysis of class I MHC-bearing targets by NK cells is not merely the consequence of the absence of an Ly49-mediated negative signal, but also requires positive recognition of class I molecules by certain Ly49 receptors. Activation of NK cells by nonself class I molecules was not predicted by the missing self hypothesis.

Positive recognition of MHC class I molecules by the Ly49D receptor of murine NK cells

Members of the murine Ly49 family of receptors have been shown to inhibit and activate NK cell function. Subsets of Ly49-expressing NK cells mediate the rejection of bone marrow cell allografts and the lysis of allogeneic lymphoblasts. In this report we have studied Ly49-mediated positive and negative signaling in an in vitro cytotoxicity assay using sorted NK cell subsets as effectors and a panel of 51Cr-labeled Con A lymphoblasts as targets in the presence or the absence of Abs to Ly49 and/or class I molecules. Our results demonstrate that the activating receptor Ly49D delivers stimulatory signals for target cell lysis upon interacting with H2-Dd, Dr, and Dsp2, but not H2b or H2k class I Ags. On the other hand, the inhibitory receptor Ly49G2 delivers negative signals for target cell lysis upon interacting with Dd, Dr, and H2k, but not H2b or Dsp2, class I Ags. Furthermore, Ly49-mediated negative signaling dominates Ly49D-mediated positive signaling. Thus, lysis of class I MHC-bearing targets by NK cells is not merely the consequence of the absence of an Ly49-mediated negative signal, but also requires positive recognition of class I molecules by certain Ly49 receptors. Activation of NK cells by nonself class I molecules was not predicted by the missing self hypothesis.

Mouse Ly-49D recognizes H-2Dd and activates natural killer cell cytotoxicity

Although activation of natural killer (NK) cytotoxicity is generally inhibited by target major histocompatibility complex (MHC) class I expression, subtle features of NK allorecognition suggest that NK cells possess receptors that are activated by target MHC I. The mouse Ly-49D receptor has been shown to activate NK cytotoxicity, although recognition of MHC class I has not been demonstrated previously. To define Ly-49D-ligand interactions, we transfected the mouse Ly-49D receptor into the rat NK line, RNK-16 (RNK.mLy-49D). As expected, anti- Ly-49D monoclonal antibody 12A8 specifically stimulated redirected lysis of the Fc receptor- bearing rat target YB2/0 by RNK.mLy-49D transfectants. RNK.mLy-49D effectors were tested against YB2/0 targets transfected with the mouse MHC I alleles H-2Dd, Db, Kk, or Kb. RNK.mLy-49D cells lysed YB2/0.Dd targets more efficiently than untransfected YB2/0 or YB2/0 transfected with Db, Kk, or Kb. This augmented lysis of H-2Dd targets was specifically inhibited by F(ab')2 anti-Ly-49D (12A8) and F(ab')2 anti-H-2Dd (34-5-8S). RNK.mLy-49D effectors were also able to specifically lyse Concanavalin A blasts isolated from H-2(d) mice (BALB/c, B10.D2, and DBA/2) but not from H-2(b) or H-2(k) mice. These experiments show that the activating receptor Ly-49D specifically interacts with the MHC I antigen, H-2Dd, demonstrating the existence of alloactivating receptors on murine NK cells.

The Role of LY49 NK Cell Subsets in the Regulation of Murine Cytomegalovirus Infections

The distributions and functions of NK cell subsets, as defined by the expression of Ly49 NK cell receptors, were examined in murine CMV (MCMV)-infected mice. MCMV induced a reduction in NK1.1+ cell number in the spleen and an increase in the peritoneal exudate cells. Within the splenic NK1.1+ population, proportional increases in Ly49A+ and Ly49G2+ cells but decreases in Ly49C+ and Ly49D+ cells were observed 3 days post-MCMV infection, but within the peritoneal NK1.1+ cell populations there were proportional decreases in Ly49A+ cells and increases in Ly49C+, Ly49D+, and Ly49G2+ cells. Lymphocytic choriomeningitis virus did not elicit a comparable NK cell subset distribution. Lymphokine-activated killer cells were sorted into different Ly49 NK cell subsets and adoptively transferred into C57BL/6 suckling mice. Regulation of MCMV synthesis in these suckling mice was shown to be an IFN-γ-dependent, perforin- and Cmv-1-independent process, and each NK cell subset mediated anti-viral activity. In adult C57BL/6 mice, the control of MCMV in the spleen is mediated by a perforin-dependent mechanism, regulated in part by the Cmv-1 gene, which maps closely to the Ly49 family. In vivo depletions of either one or two of the Ly49 subsets in adult mice did not affect the ability of the residual NK cells to regulate MCMV synthesis. These data provide evidence of NK cell subset distribution and function in MCMV infection, but no individual subset was required for the Cmv-1-like regulation of MCMV synthesis.

The role of LY49 NK cell subsets in the regulation of murine cytomegalovirus infections

The distributions and functions of NK cell subsets, as defined by the expression of Ly49 NK cell receptors, were examined in murine CMV (MCMV)-infected mice. MCMV induced a reduction in NK1.1+ cell number in the spleen and an increase in the peritoneal exudate cells. Within the splenic NK1.1+ population, proportional increases in Ly49A+ and Ly49G2+ cells but decreases in Ly49C+ and Ly49D+ cells were observed 3 days post-MCMV infection, but within the peritoneal NK1.1+ cell populations there were proportional decreases in Ly49A+ cells and increases in Ly49C+, Ly49D+, and Ly49G2+ cells. Lymphocytic choriomeningitis virus did not elicit a comparable NK cell subset distribution. Lymphokine-activated killer cells were sorted into different Ly49 NK cell subsets and adoptively transferred into C57BL/6 suckling mice. Regulation of MCMV synthesis in these suckling mice was shown to be an IFN-gamma-dependent, perforin- and Cmv-1-independent process, and each NK cell subset mediated anti-viral activity. In adult C57BL/6 mice, the control of MCMV in the spleen is mediated by a perforin-dependent mechanism, regulated in part by the Cmv-1 gene, which maps closely to the Ly49 family. In vivo depletions of either one or two of the Ly49 subsets in adult mice did not affect the ability of the residual NK cells to regulate MCMV synthesis. These data provide evidence of NK cell subset distribution and function in MCMV infection, but no individual subset was required for the Cmv-1-like regulation of MCMV synthesis.

IL-13 production by NK cells: IL-13-producing NK and T cells are present in vivo in the absence of IFN-gamma

In this study, we demonstrate that human NK cells, human NK clones, the human NK cell line (NK3.3), and a population of murine NK cells can produce the type 2 cytokine IL-13 in response to IL-2 or phorbol myristate acetate plus ionomycin. IL-2 rapidly induced new IL-13 mRNA and protein synthesis in the NK3.3 cell line. Six of 12 human NK clones tested produced IL-13 protein in response to IL-2 or phorbol myristate acetate and ionomycin. Intracellular analysis revealed that approximately 2% of human peripheral NK cells produced IL-13 protein in response to IL-2. Isolated NK cells from SCID and RAG-2 knockout (-/-) mice that lack T and B cells as well as normal mice also can produce IL-13 mRNA and protein in response to IL-2. We hypothesized that in the absence of IFN-gamma, IL-13-producing NK cells may predominate in vivo. Utilizing IFN-gamma knockout (-/-) mice as a model system, IL-2-activated liver NK and T cells expressed 10-fold more IL-13 and IL-5 mRNA and protein than normal controls following IL-2 treatment in vitro. These results suggest that in the absence of IFN-gamma, an IL-13- and IL-5-producing NK and T cells predominate in vivo. The existence of this cell type has important implications in innate immunity given that the balance between IFN-gamma and IL-13/IL-5-producing NK cells may influence the early development of a cell-mediated or humoral immune response.

IL-13 Production by NK Cells: IL-13-Producing NK and T Cells Are Present In Vivo in the Absence of IFN-γ

In this study, we demonstrate that human NK cells, human NK clones, the human NK cell line (NK3.3), and a population of murine NK cells can produce the type 2 cytokine IL-13 in response to IL-2 or phorbol myristate acetate plus ionomycin. IL-2 rapidly induced new IL-13 mRNA and protein synthesis in the NK3.3 cell line. Six of 12 human NK clones tested produced IL-13 protein in response to IL-2 or phorbol myristate acetate and ionomycin. Intracellular analysis revealed that ∼2% of human peripheral NK cells produced IL-13 protein in response to IL-2. Isolated NK cells from SCID and RAG-2 knockout (−/−) mice that lack T and B cells as well as normal mice also can produce IL-13 mRNA and protein in response to IL-2. We hypothesized that in the absence of IFN-γ, IL-13-producing NK cells may predominate in vivo. Utilizing IFN-γ knockout (−/−) mice as a model system, IL-2-activated liver NK and T cells expressed 10-fold more IL-13 and IL-5 mRNA and protein than normal controls following IL-2 treatment in vitro. These results suggest that in the absence of IFN-γ, an IL-13- and IL-5-producing NK and T cells predominate in vivo. The existence of this cell type has important implications in innate immunity given that the balance between IFN-γ and IL-13/IL-5-producing NK cells may influence the early development of a cell-mediated or humoral immune response.

DAP12-mediated signal transduction in natural killer cells. A dominant role for the Syk protein-tyrosine kinase

The murine Ly49 family contains nine genes in two subgroups: the inhibitory receptors (Ly49A, B, C, E, F, G2, and I) and the noninhibitory receptors (Ly49D and H). Unlike their inhibitory counterparts, Ly49D and H do not contain immunoreceptor tyrosine-based inhibitory motifs but associate with a recently described co-receptor, DAP12, to transmit positive signals to natural killer (NK) cells. DAP12 is also expressed in myeloid cells, but the receptors coupled to it there are unknown. Here we document the signaling pathways of the Ly49D/DAP12 complex in NK cells. We show that ligation of Ly49D results in 1) tyrosine phosphorylation of several substrates, including phospholipase Cgamma1, Cbl, and p44/p42 mitogen-activated protein kinase, and 2) calcium mobilization. Moreover, we demonstrate that although human DAP12 reportedly binds the SH2 domains of both Syk and Zap-70, ligation of Ly49D leads to activation of Syk but not Zap-70. Consistent with this observation, Ly49D/DAP12-mediated calcium mobilization is blocked by dominant negative Syk but not by catalytically inactive Zap-70. These data demonstrate the dependence of DAP12-coupled receptors on Syk and suggest that the outcome of Ly49D/DAP12 engagement will be regulated by Cbl and culminate in the activation of transcription factors.

Recruitment of hepatic NK cells by IL-12 is dependent on IFN-gamma and VCAM-1 and is rapidly down-regulated by a mechanism involving T cells and expression of Fas

NK cells have been shown to be important antitumor or antiviral effector cells in the liver. In the present study we have examined the factors that regulate the initial recruitment and subsequent fate of hepatic NK and T cells in mice treated with IL-12 or IL-2. Daily administration of IL-12 caused a rapid initial increase in NK cells followed by a subsequent decrease that coincided with an accumulation of T cells. The recruitment of hepatic NK cells by IL-12, but not the subsequent T cell infiltrate, was abrogated in IFN-gamma(-/-) mice. In contrast, daily administration of IL-2 caused a sustained increase in liver-associated NK cells that was not diminished in IFN-gamma(-/-) mice. The IL-12-induced recruitment in both hepatic NK and T cells was abrogated by in vivo treatment with anti-VCAM-1 mAbs, while treatment with anti-ICAM-1 Abs decreased only the recruitment of T cells in the IL-12-treated mice. The rapid loss of newly recruited hepatic NK cells in IL-12-treated mice did not occur in SCID mice or in B.MRL-Fas(lpr) (Fas-) and B6Smn.C3H-Fasl(gld) (FasL-) mutant mice, suggesting that T cells can actively eliminate hepatic NK cells through a Fas-dependent mechanism. These findings also imply that during the endogenous innate immune response to infectious agents or tumors or in the host response induced by cytokine therapies, the biologic effects of NK cells may be limited by T cell-mediated effects.

Recruitment of Hepatic NK Cells by IL-12 Is Dependent on IFN-γ and VCAM-1 and Is Rapidly Down-Regulated by a Mechanism Involving T Cells and Expression of Fas

NK cells have been shown to be important antitumor or antiviral effector cells in the liver. In the present study we have examined the factors that regulate the initial recruitment and subsequent fate of hepatic NK and T cells in mice treated with IL-12 or IL-2. Daily administration of IL-12 caused a rapid initial increase in NK cells followed by a subsequent decrease that coincided with an accumulation of T cells. The recruitment of hepatic NK cells by IL-12, but not the subsequent T cell infiltrate, was abrogated in IFN-γ−/− mice. In contrast, daily administration of IL-2 caused a sustained increase in liver-associated NK cells that was not diminished in IFN-γ−/− mice. The IL-12-induced recruitment in both hepatic NK and T cells was abrogated by in vivo treatment with anti-VCAM-1 mAbs, while treatment with anti-ICAM-1 Abs decreased only the recruitment of T cells in the IL-12-treated mice. The rapid loss of newly recruited hepatic NK cells in IL-12-treated mice did not occur in SCID mice or in B.MRL-Faslpr (Fas−) and B6Smn.C3H-Faslgld (FasL−) mutant mice, suggesting that T cells can actively eliminate hepatic NK cells through a Fas-dependent mechanism. These findings also imply that during the endogenous innate immune response to infectious agents or tumors or in the host response induced by cytokine therapies, the biologic effects of NK cells may be limited by T cell-mediated effects.

Phenotypic and functional characterization of a panel of cytotoxic murine NK cell clones that are heterogeneous in their enhancement of Ig secretion in vitro

NK cells not only function as cytotoxic effector cells, but also have immunoregulatory roles including the enhancement of Ig secretion. To have a stable and uniform population of NK cells to study their role in Ig secretion, we generated murine NK clones. Thus, culture of splenocytes from mice that were homozygous for a mutation in the p53 tumor suppressor gene (p53-KO) with IL-2 and poly(IC) resulted in a long-term NK line, from which four stable clones were derived. This approach also yielded a long-term NK line from splenocytes of normal C57BL/6 mice. Identification of the clones as members of the NK lineage was based on large granular morphology, expression of NK-TR and absence of TCR gene rearrangement. Flow cytometry revealed that all clones expressed IL-2R alpha and beta, chains and B220, but no CD3, NK1.1, DX5 or Ly-49. RT-PCR analysis showed heterogeneity in NK1.1 gene expression, and demonstrated expression of perforin and several granzymes in all clones. Three out of four clones lysed YAC-1, but not P815 target cells, corresponding to a pattern of NK specificity. All NK clones enhanced Ig secretion in an in vitro model for T cell-independent type 2 antigens, albeit to varying degrees. We found no correlation between the degree of helper activity of the NK clones and the level of their cytotoxic activity on YAC-1 targets. Thus, we established murine NK clones, and show that they mediate both cytotoxicity and enhancement of Ig secretion.

Characterization of cytokine differential induction of STAT complexes in primary human T and NK cells

Cytokines, IL-2, IL-4, IL-6, IL-7, IL-12, and IL-15 are key regulators of human peripheral blood T and NK cell activation and differentiation but the precise mechanisms that give rise to their differential activities within these cells are not clear. Recent studies reveal that a family of transcription factors, signal transducers and activators of transcription (STATs) directly mediate many cytokine signals. We analyzed the activation of STATs in primary human T and NK cells by a variety of specific cytokines. We demonstrate that IL-12 induces STAT4 only in freshly isolated primary NK cells, but not in primary T cells, consistent with the lack of the IL-12 receptor in resting T cells. In contrast, IL-4 induces different C epsilon GAS DNA-protein binding complexes in both T and NK cells. Moreover, IL-4 costimulation with IL-2 or IL-12 does not alter their own preferential GAS-like DNA binding patterns when C epsilon-, Fc gamma RI-, and SIE GAS motif containing oligonucleotide probes are compared, suggesting that induction of GAS-like DNA-protein binding complexes by IL-2, IL-4, and IL-12 is highly selective and represents one important factor in determining specific gene activation. In addition, IL-6 and IL-2 synergistically induce homo- and heterodimerized STAT1 alpha and STAT3 in both NK and T cells, consistent with their reported synergism in modulating perforin gene expression. We further demonstrated that IL-2, -7, and -15 induce multiple STAT proteins, including STAT5a, STAT5b, STAT1 alpha, STAT3, and another unidentified Fc gamma RI GAS DNA-binding protein. Finally, we observed that activated STAT5a and STAT5b proteins form distinct Fc gamma RI GAS binding patterns in T and NK cells, suggesting that they might have different roles in gene regulation. Our data provide evidence that the differential responses in gene expression and cell activation seen in primary NK and T cells on direct stimulation with different cytokines may be a direct result of distinct activation of STAT transcription factors.

Differential regulation of the Janus kinase-STAT pathway and biologic function of IL-13 in primary human NK and T cells: a comparative study with IL-4

IL-13, a cytokine similar to IL-4, is a regulator of human B cell and monocyte functions. Biologic effects of IL-13 on primary human NK and T cells have not been well defined. We demonstrate that, in primary NK cells, IL-13, but not IL-4, may induce low levels of IFN-gamma secretion. When NK cells were costimulated with IL-13 and IL-2, IL-13 generally resulted in two types of reactivity: IL-13 synergized with IL-2 to stimulate IFN-gamma production or it modestly inhibited IL-2-mediated IFN-gamma production. In both types of donors, the effect of IL-13 on IL-2-induced IFN-gamma production was in marked contrast to the strong inhibition seen with IL-4 in NK cells. Additionally, IL-13 suppresses IL-2-induced NK cytolytic and proliferative activities although less efficiently than IL-4. In T cells, IL-13 inhibits anti-CD3 mAb/IL-2- or PHA-mediated IFN-gamma production and enhances cytolytic potential. Furthermore, we demonstrate that IL-13, like IL-4, induces distinct STAT6-DNA binding complexes and tyrosine phosphorylation of STAT6 and Janus kinase 3 (JAK3) in NK and T cells. We observed that Abs directed against unique domains of STAT6 have differential effects on complexes in T cells but not in NK cells, suggesting different STAT6 isoforms. These findings show that IL-13 and IL-4 have the ability to regulate NK and T cell activation and that IL-13 is a potent regulator of STAT6 and JAK3 in these cell types.

Differential Regulation of the Janus Kinase-STAT Pathway and Biologic Function of IL-13 in Primary Human NK and T Cells: A Comparative Study with IL-4

IL-13, a cytokine similar to IL-4, is a regulator of human B cell and monocyte functions. Biologic effects of IL-13 on primary human NK and T cells have not been well defined. We demonstrate that, in primary NK cells, IL-13, but not IL-4, may induce low levels of IFN-γ secretion. When NK cells were costimulated with IL-13 and IL-2, IL-13 generally resulted in two types of reactivity: IL-13 synergized with IL-2 to stimulate IFN-γ production or it modestly inhibited IL-2-mediated IFN-γ production. In both types of donors, the effect of IL-13 on IL-2-induced IFN-γ production was in marked contrast to the strong inhibition seen with IL-4 in NK cells. Additionally, IL-13 suppresses IL-2-induced NK cytolytic and proliferative activities although less efficiently than IL-4. In T cells, IL-13 inhibits anti-CD3 mAb/IL-2- or PHA-mediated IFN-γ production and enhances cytolytic potential. Furthermore, we demonstrate that IL-13, like IL-4, induces distinct STAT6-DNA binding complexes and tyrosine phosphorylation of STAT6 and Janus kinase 3 (JAK3) in NK and T cells. We observed that Abs directed against unique domains of STAT6 have differential effects on complexes in T cells but not in NK cells, suggesting different STAT6 isoforms. These findings show that IL-13 and IL-4 have the ability to regulate NK and T cell activation and that IL-13 is a potent regulator of STAT6 and JAK3 in these cell types.

Characterization of an associated 16-kDa tyrosine phosphoprotein required for Ly-49D signal transduction

Ly-49D is an activating receptor on NK cells that does not become tyrosine phosphorylated upon activation. This report demonstrates that immunoprecipitation of Ly-49D, following pervanadate treatment or specific Ab cross-linking, coprecipitates a 16-kDa tyrosine-phosphorylated protein (pp16). Immunoblotting experiments and data from TCR-zeta/Fc epsilonRIgamma double knockout mice confirm that pp16 is not TCR-zeta, TCR-eta, or Fc epsilonRIgamma. Association of pp16 with Ly-49D involves a transmembrane arginine since mutation to leucine (Ly-49D[R54L]) abolishes association with pp16 in transfected P815 cells. In addition, Ly-49D(R54L) transfectants fail to mediate Ca2+ mobilization following Ab cross-linking. Therefore, signaling through Ly49D on NK cells depends on association with a distinct tyrosine phosphoprotein (pp16) in a manner analogous to that of TCR and FcR. Expression of this novel signaling peptide in both the NK and myeloid lineages indicates that pp16 is likely involved in the signal transduction cascade of additional receptor families.

Cutting Edge: Characterization of an Associated 16-kDa Tyrosine Phosphoprotein Required for Ly-49D Signal Transduction

Ly-49D is an activating receptor on NK cells that does not become tyrosine phosphorylated upon activation. This report demonstrates that immunoprecipitation of Ly-49D, following pervanadate treatment or specific Ab cross-linking, coprecipitates a 16-kDa tyrosine-phosphorylated protein (pp16). Immunoblotting experiments and data from TCR-ζ/FcεRIγ double knockout mice confirm that pp16 is not TCR-ζ, TCR-η, or FcεRIγ. Association of pp16 with Ly-49D involves a transmembrane arginine since mutation to leucine (Ly-49DR54L) abolishes association with pp16 in transfected P815 cells. In addition, Ly-49DR54L transfectants fail to mediate Ca2+ mobilization following Ab cross-linking. Therefore, signaling through Ly-49D on NK cells depends on association with a distinct tyrosine phosphoprotein (pp16) in a manner analogous to that of TCR and FcR. Expression of this novel signaling peptide in both the NK and myeloid lineages indicates that pp16 is likely involved in the signal transduction cascade of additional receptor families.