Genes in two major histocompatibility complex class I regions control selection, phenotype, and function of a rat Ly-49 natural killer cell subset

We have generated a monoclonal antibody (STOK2) which reacts with an inhibitory MHC receptor on a subset of alloreactive NK cells in the rat. This receptor, termed the STOK2 antigen (Ag), belongs to the Ly-49 family of lectin-like molecules and displays specificity for the classical MHC class I molecule RT1-A1c of PVG rats. Here, we have investigated the influence of the MHC on the selection, phenotype and function of the STOK2+ NK subset in a panel of MHC congenic and intra-MHC recombinant strains. STOK2 receptor density was influenced by the presence of its classical MHC I ligand RT1-A1c, as evidenced by a reduction of STOK2 Ag on the surface of NK cells from RT1-A1c+, as compared with RT1-A1c-, strains. In addition, a role for nonclassical MHC I RT1-C/E/M alleles in the selection of the STOK2 Ag was demonstrated. The relative number of STOK2+ NK cells was fivefold higher in rats expressing the RT1-C/E/M(av1) as compared with those expressing the RT1-C/E/M(u) class Ib haplotype. The STOK2 ligand RT1-A1c inhibited cytotoxicity of STOK2+ NK cells regardless of effector cell MHC haplotype. Allospecificity of STOK2+ NK cells varied markedly with effector cell MHC, however, and suggested that inhibitory MHC I receptors apart from STOK2 were variably co-expressed by these cells. These data provide evidence for the MHC-dependent regulation of the allospecific repertoire within a subset of potentially autoreactive Ly-49+ rat NK cells.

Recruitment of pleckstrin and phosphoinositide 3-kinase gamma into the cell membranes, and their association with G beta gamma after activation of NK cells with chemokines

The role of phosphoinositide 3 kinases (PI 3-K) in chemokine-induced NK cell chemotaxis was investigated. Pretreatment of NK cells with wortmannin inhibits the in vitro chemotaxis of NK cells induced by lymphotactin, monocyte-chemoattractant protein-1, RANTES, IFN-inducible protein-10, or stromal-derived factor-1 alpha. Introduction of inhibitory Abs to PI 3-K gamma but not to PI 3-K alpha into streptolysin O-permeabilized NK cells also inhibits chemokine-induced NK cell chemotaxis. Biochemical analysis showed that within 2-3 min of activating NK cells, pleckstrin is recruited into NK cell membranes, whereas PI 3-K gamma associates with these membranes 5 min after stimulation with RANTES. Recruited PI 3-K gamma generates phosphatidylinositol 3,4,5 trisphosphate, an activity that is inhibited upon pretreatment of NK cells with wortmannin. Further analysis showed that a ternary complex containing the beta gamma dimer of G protein, pleckstrin, and PI 3-K gamma is formed in NK cell membranes after activation with RANTES. The recruitment of pleckstrin and PI 3-K gamma into NK cell membranes is only partially inhibited by pertussis toxin, suggesting that the majority of these molecules form a complex with pertussis toxin-insensitive G proteins. Our results may have application for the migration of NK cells toward the sites of inflammation.

Recruitment of Pleckstrin and Phosphoinositide 3-Kinase γ into the Cell Membranes, and Their Association with Gβγ After Activation of NK Cells with Chemokines

The role of phosphoinositide 3 kinases (PI 3-K) in chemokine-induced NK cell chemotaxis was investigated. Pretreatment of NK cells with wortmannin inhibits the in vitro chemotaxis of NK cells induced by lymphotactin, monocyte-chemoattractant protein-1, RANTES, IFN-inducible protein-10, or stromal-derived factor-1α. Introduction of inhibitory Abs to PI 3-Kγ but not to PI 3-Kα into streptolysin O-permeabilized NK cells also inhibits chemokine-induced NK cell chemotaxis. Biochemical analysis showed that within 2–3 min of activating NK cells, pleckstrin is recruited into NK cell membranes, whereas PI 3-Kγ associates with these membranes 5 min after stimulation with RANTES. Recruited PI 3-Kγ generates phosphatidylinositol 3,4,5 trisphosphate, an activity that is inhibited upon pretreatment of NK cells with wortmannin. Further analysis showed that a ternary complex containing the βγ dimer of G protein, pleckstrin, and PI 3-Kγ is formed in NK cell membranes after activation with RANTES. The recruitment of pleckstrin and PI 3-Kγ into NK cell membranes is only partially inhibited by pertussis toxin, suggesting that the majority of these molecules form a complex with pertussis toxin-insensitive G proteins. Our results may have application for the migration of NK cells toward the sites of inflammation.

RT1-U: identification of a novel, active, class Ib alloantigen of the rat MHC

In common with other mammalian species, the laboratory rat (Rattus norvegicus) expresses MHC class I molecules that have been categorized as either classical (class Ia) or nonclassical (class Ib). This distinction separates the class Ia molecules that play a conventional role in peptide Ag presentation to CD8 T cells from the others, whose function is unconventional or undefined. The class Ia molecules are encoded by the RT1-A region of the rat MHC, while the RT1-C/E/M region encodes up to 60 other class I genes or gene fragments, a number of which are known to be expressed (or to be expressible). Here we report upon novel MHC class Ib genes of the rat that we have expression cloned using new monoclonal alloantibodies and which we term RT1-U. The products detected by these Abs were readily identifiable by two-dimensional analysis of immunoprecipitates and were shown to be distinct from the class Ia products. Cellular studies of these molecules indicate that they function efficiently as targets for cytotoxic killing by appropriately raised polyclonal alloreactive CTL populations. The sequences of these class Ib genes group together in phylogenetic analysis, suggesting a unique locus or family. The combined serological, CTL, and sequence data all indicate that these products are genetically polymorphic.

RT1-U: Identification of a Novel, Active, Class Ib Alloantigen of the Rat MHC

In common with other mammalian species, the laboratory rat (Rattus norvegicus) expresses MHC class I molecules that have been categorized as either classical (class Ia) or nonclassical (class Ib). This distinction separates the class Ia molecules that play a conventional role in peptide Ag presentation to CD8 T cells from the others, whose function is unconventional or undefined. The class Ia molecules are encoded by the RT1-A region of the rat MHC, while the RT1-C/E/M region encodes up to 60 other class I genes or gene fragments, a number of which are known to be expressed (or to be expressible). Here we report upon novel MHC class Ib genes of the rat that we have expression cloned using new monoclonal alloantibodies and which we term RT1-U. The products detected by these Abs were readily identifiable by two-dimensional analysis of immunoprecipitates and were shown to be distinct from the class Ia products. Cellular studies of these molecules indicate that they function efficiently as targets for cytotoxic killing by appropriately raised polyclonal alloreactive CTL populations. The sequences of these class Ib genes group together in phylogenetic analysis, suggesting a unique locus or family. The combined serological, CTL, and sequence data all indicate that these products are genetically polymorphic.

MIP-3alpha, MIP-3beta and fractalkine induce the locomotion and the mobilization of intracellular calcium, and activate the heterotrimeric G proteins in human natural killer cells

We demonstrate here that the CC chemokines macrophage inflammatory protein-3alpha (MIP-3alpha), macrophage inflammatory protein-3beta (MIP-3beta) and the CX3C chemokine fractalkine induce the chemotaxis of interleukin-2 (IL-2)-activated natural killer (IANK) cells. In addition, these chemokines enhance the binding of [gamma-35S]guanine triphosphate ([gamma-35S]GTP) to IANK cell membranes, suggesting that receptors for these chemokines are G protein-coupled. Our results show that MIP-3alpha receptors are coupled to Go, Gq and Gz, MIP-3beta receptors are coupled to Gi, Gq and Gs, whereas fractalkine receptors are coupled to Gi, and Gz. All three chemokines induced a robust calcium response flux in IANK cells. Cross-desensitization experiments show that MIP-3alpha, MIP-3beta or fractalkine use receptors not shared by each other or by the CC chemokine regulated on activation, normal, T-cell expressed, and secreted (RANTES), the CXC chemokines stromal-derived factor-1alpha (SDF-1alpha) and interferon-inducible protein-10 (IP-10), or the C chemokine lymphotactin.

Role of classical (RT1.A) and nonclassical (RT1.C) MHC class I regions in natural killer cell-mediated bone marrow allograft rejection in rats

BACKGROUND

We have studied the role of the different MHC (RT1) subregions in acute natural killer (NK) cell-mediated bone marrow allograft rejection in lethally irradiated, bone marrow cell (BMC) reconstituted rats.

METHODS

We employed a series of MHC congenic and intra-MHC recombinant rat strains so that effects of mismatches in defined RT1 subregions could be studied systematically. BMC allograft survival was measured as 125IUdR uptake in the spleen between day 5 and day 7 after irradiation and BMC reconstitution.

RESULTS

We found that in certain RT1 haplotype combinations, nonclassical RT1.C disparities by themselves could determine graft rejection (i.e., in the u/av1 recombinant haplotypes), whereas in another combination (between the av1 and c haplotypes) a mismatch for an isolated classical RT1.A region was decisive for engraftment. Thus, PVG.R1 BMC failed to proliferate in PVG rats, differing in the RT1.A region only, whereas in PVG.1U rats rejection could be determined by isolated differences in the RT1.C region (LEW.1WR1). Also, RT1 homozygous rats (RT1.U) rejected semi-allogeneic F1 hybrid BMC. The acute rejection of BMC was mediated by NK cells, as athymic nude rats, lacking alloreactive T cells but with normal alloreactive NK cells, showed the same patterns of rejection as did normal rats. Nude rats also rejected allogeneic lymphocytes, a previously documented NK-mediated phenomenon, with identical requirements of MHC disparity.

CONCLUSIONS

This investigation shows that rat effector NK cells are radioresistant, independent of the thymus, and capable of recognizing and rejecting MHC mismatched transplanted BMC on the basis of mismatches in both classical and nonclassical class I regions in vivo. The studies underline the importance also of NK cells in determining BMC allograft survival.

Identification of an Inhibitory MHC Receptor on Alloreactive Rat Natural Killer Cells

Studies of allogeneic lymphocyte cytotoxicity have shown that the rat NK allorecognition repertoire is controlled by genetic elements in both the MHC (RT1) and the NK gene complex (NKC). DA rats, possessing NK cells that are unable to lyse allogeneic lymphoblasts, were immunized with alloreactive NK cells from MHC-matched PVG.1AV1 rats, and two mAb, STOK1 and STOK2, were generated. STOK1 and STOK2 stained identical subsets of NKR-P1+ T and NK cells from certain strains of rats. Relative numbers varied markedly in a panel of MHC congenic strains, however, implicating a role for self MHC genes in their development. Both STOK1 and STOK2 immunoprecipitated a 110-kDa disulfide-linked homodimeric molecule, with extensive N-linked glycosylations, encoded by a gene that mapped to the NKC. NK cells expressing this glycoprotein displayed an increased ability to lyse allogeneic lymphoblasts, while syngeneic targets were spared. However, blockade of the STOK2 Ag with F(ab′)2 of STOK2 permitted the NK lysis of syngeneic targets, but did not affect NK allorecognition. These results indicate that mAb STOK1 and STOK2 identify an NKC-encoded MHC receptor in the rat that acts as a negative regulator of cytotoxicity.

Identification of an inhibitory MHC receptor on alloreactive rat natural killer cells

Studies of allogeneic lymphocyte cytotoxicity have shown that the rat NK allorecognition repertoire is controlled by genetic elements in both the MHC (RT1) and the NK gene complex (NKC). DA rats, possessing NK cells that are unable to lyse allogeneic lymphoblasts, were immunized with alloreactive NK cells from MHC-matched PVG.1AV1 rats, and two mAb, STOK1 and STOK2, were generated. STOK1 and STOK2 stained identical subsets of NKR-P1+ T and NK cells from certain strains of rats. Relative numbers varied markedly in a panel of MHC congenic strains, however, implicating a role for self MHC genes in their development. Both STOK1 and STOK2 immunoprecipitated a 110-kDa disulfide-linked homodimeric molecule, with extensive N-linked glycosylations, encoded by a gene that mapped to the NKC. NK cells expressing this glycoprotein displayed an increased ability to lyse allogeneic lymphoblasts, while syngeneic targets were spared. However, blockade of the STOK2 Ag with F(ab')2 of STOK2 permitted the NK lysis of syngeneic targets, but did not affect NK allorecognition. These results indicate that mAb STOK1 and STOK2 identify an NKC-encoded MHC receptor in the rat that acts as a negative regulator of cytotoxicity.

Functional coupling of NKR-P1 receptors to various heterotrimeric G proteins in rat interleukin-2-activated natural killer cells

NKR-P1 molecules constitute a family of type II membrane receptors in natural killer (NK) cells that preferentially activate NK cell killing and release of interferon-gamma from these cells. Here, we demonstrate that anti-NKR-P1 enhances GTP binding in rat interleukin-2-activated NK cell membranes; GTP binding to Gi3alpha, Gsalpha, Gq,11alpha, and Gzalpha increased noticeably in these cell membranes after treatment with anti-NKR-P1. Western blot analysis of membrane proteins prepared from interleukin-2-activated NK cells reveals the presence of Gi1,2alpha, Gi3alpha, Goalpha, Gsalpha, Gq, 11alpha, Gzalpha, and G12alpha, but not G13alpha. However, only alphai3, alphas, alphaq,11, and alphaz, but not alphai1,2, alphao, alpha12, or alpha13 subunits when immunoprecipitated with the appropriate anti-G protein antibodies, are associated with NKR-P1 when immunoblotted with anti-NKR-P1. Reciprocally, NKR-P1 immunoprecipitated with anti-NKR-P1 is associated with alphai3, alphas, alphaq,11, and alphaz immunoblotted with anti-G proteins. These results are the first to demonstrate the physical and functional coupling of NKR-P1 to the heterotrimeric G proteins in NK cells.

Sequential development of intraepithelial gamma delta and alpha beta T lymphocytes expressing CD8 alpha beta in neonatal rat intestine: requirement for the thymus

Previous studies in congenitally athymic nude rats have suggested that the thymus is important for the development of intestinal T cells. Here we have examined the effect of the nude mutation on intraepithelial lymphocyte (IEL) development from the perinatal period. By immunohistochemistry it was shown that CD3(-)CD8 alpha alpha + putative IEL precursors colonized the epithelium of both normal and athymic neonatal rats. Mature T cells, however, did not develop in athymic neonates. In normal rats, gamma delta T cells were present at birth and alpha beta T cells appeared within 8 days of postnatal life. At this age, the composition and relative number of intraepithelial T cells were similar to that in normal adult rats, with the exception that most neonatal T-cell receptor-gamma delta + and -alpha beta + IEL expressed CD8 beta. By contrast, extrathymic T-cell maturation in the gut of congenitally athymic rats occurred slowly, as CD3+ IEL did not appear until 4-6 months of age. These intraepithelial T cells displayed variable phenotypes and appeared to be induced by environmental antigens as they were not found in isolator-kept old nudes. In conclusion, the present results indicate that the major colonization of the gut epithelium with gamma delta and alpha beta T cells expressing CD8 alpha beta takes place perinatally and requires the presence of the thymus. The developmental relationship between these neonatal T cells and more immature CD3- CD8 alpha alpha +/- IEL remains elusive.

Regional phenotypic specialization of intraepithelial lymphocytes in the rat intestine does not depend on microbial colonization

Recent studies in mice and humans have provided evidence for regional specialization of gut intraepithelial lymphocytes (IEL). Here the authors report striking regional variability in the composition of IEL in rat small and large intestine. Two-colour immunofluorescence in situ analysis showed that the distribution of the CD3+ and CD3- IEL subpopulations varied, the proportion of T cells (CD3+) being higher in the ileum than in the jejunum and smallest in the colon. These differences were explained by variable numbers of the T-cell receptor (TCR)alpha/beta + (both CD8+ and CD4+) but not the TCR gamma/delta + subset. Moreover, the various IEL subpopulations showed distinct intraepithelial distribution patterns with CD4+ and CD8 alpha beta + T cells situated near the lamina propria, while CD3- IEL were located preferentially towards the adluminal part of the epithelium. Regional phenotypic variation did not depend on intestinal colonization because analogous results were obtained in germ-free rats. Conventionalization nevertheless caused a marked relative increase of small intestinal TCR alpha/beta + but not TCR gamma/delta + IEL. This increase was more sustained in the jejunum than ileum and eventually reduced the phenotypic IEL differences between the two sites. By contrast, microbial colonization of the colon induced only a transient increase of intraepithelial TCR alpha/beta + cells with no permanent phenotypic alterations. Both CD3+ and CD3- IEL contained subpopulations that expressed NKR-P1 independent of intestinal colonization. These results demonstrate phenotypic specialization of IEL at different levels of the gut and suggest that the indigenous flora is not essential to this end.

Interferon-inducible protein-10 and lymphotactin induce the chemotaxis and mobilization of intracellular calcium in natural killer cells through pertussis toxin-sensitive and -insensitive heterotrimeric G-proteins

We show here that interferon-inducible protein-10 (IP-10), an ELR lacking CXC chemokine, and the C chemokine lymphotactin (Ltn) induce the chemotaxis and calcium mobilization in IL2-activated NK (IANK) and CC chemokine-activated NK (CHAK) cells. Cross-desensitization experiments show that IP-10 or Ltn use receptors not shared by other C, CC, or CXC chemokines. The chemotaxis induced by either IP-10 or Ltn for both cell types is inhibited upon pretreatment of these cells with pertussis toxin (PT). Also, Ltn-induced [Ca2+]i in IANK but not in CHAK cells is inhibited upon pretreatment with PT, whereas IP-10-induced [Ca2+]i in IANK and CHAK cells is inhibited upon pretreatment with this toxin. These results suggest important roles for PT-sensitive and -insensitive G-proteins in IP-10-induced and Ltn-induced chemotaxis and calcium fluxes in activated NK cells. This was further implicated after streptolysin O permeabilization of CHAK and IANK cells and after introduction of inhibitory antibodies to the PT-sensitive Gi and Go or the PT-insensitive Gq. Our results suggest that IP-10 and Ltn receptors are coupled to Gi, Go, and Gq in IANK cells and to Gi and Gq in CHAK cells, with a possible low coupling of IP-10, but not of Ltn, receptors to Go in these cells. Together, these results show that IP-10 and Ltn-dependent chemotaxis and calcium mobilization may differentiate at the level of receptor coupling to the heterotrimeric G-proteins.

Cloning, functional activities and in vivo tissue distribution of rat NKR-P1+ TCR alpha beta + cells

We have successfully cloned nine NKR-P1+ TCR alpha beta + cells from PVG rat spleens, utilizing murine macrophage inflammatory protein-1 alpha (MIP-1 alpha) and IL-2. These clones are either double negative (DN, CD4-CD8-), which included clones 3.31, 3.71, 4.19, 4.59 and 4.65, or single positive (SP, CD4+CD8-), which included clones 1.64, 3.8, 3.76 and 3.78. No CD8+ clone was recovered. All nine clones are restricted in terms of their expression of the V beta antigens, since they express V beta 8.2 but not V beta 8.5, V beta 10 or V beta 16. These clones are agranular and they fall to generate NK or LAK activity upon incubation with IL-2, IL-12 or their combination. On the basis of their production of intracellular cytokines they can be divided into three categories: (I) SP clones (1.64, 3.8, 3.76 and 3.78) do not produce IL-2 or IL-4, but produce IFN-gamma and IL-12, and they vary in their production of IL-1, RANTES or tumor necrosis factor (TNF)-alpha; (II) DN clones 4.59 and 4.65 produce IL-1 alpha and IFN-gamma only, and fall to produce other cytokines; and (III) DN clones 3.31, 3.71 and 4.19 produce IL-1 alpha, IL-1 beta, IL-2, IL-12, IFN-gamma, RANTES and TNF-alpha. From all the clones examined only DN clones 3.31 and to a lesser degree 4.19 produce IL-4. In vivo tissue localization of clones 3.8, 3.31 and 4.59 shows that these cells distribute into the liver and bone marrow 24 h post i.v. administration. Their accumulation in the liver and bone marrow along with their ability to secrete various cytokines suggest that these cells may influence the generation, differentiation or apoptosis of immune or hematopoietic cells.

Selective activation of cAMP-dependent protein kinase type I inhibits rat natural killer cell cytotoxicity

The present study examines the expression and involvement of cAMP-dependent protein kinase (PKA) isozymes in cAMP-induced inhibition of natural killer (NK) cell-mediated cytotoxicity. Rat interleukin-2-activated NK cells express the PKA alpha-isoforms RIalpha, RIIalpha, and Calpha and contain both PKA type I and type II. Prostaglandin E2, forskolin, and cAMP analogs all inhibit NK cell lysis of major histocompatibility complex class I mismatched allogeneic lymphocytes as well as of standard tumor target cells. Specific involvement of PKA in the cAMP-induced inhibition of NK cell cytotoxicity is demonstrated by the ability of a cAMP antagonist, (Rp)-8-Br-adenosine 3',5'-cyclic monophosphorothioate, to reverse the inhibitory effect of complementary cAMP agonist (Sp)-8-Br-adenosine 3',5'-cyclic monophosphorothioate. Furthermore, the use of cAMP analog pairs selective for either PKA isozyme (PKA type I or PKA type II), shows a preferential involvement of the PKA type I isozyme, indicating that PKA type I is necessary and sufficient to completely abolish killer activatory signaling leading to NK cell cytotoxicity. Finally, combined treatment with phorbol ester and ionomycin maintains NK cell cytotoxicity and eliminates the cAMP-mediated inhibition, demonstrating that protein kinase C and Ca2+-dependent events stimulate the cytolytic activity of NK cells at a site distal to the site of cAMP/PKA action.

Positive and negative MHC class I recognition by rat NK cells

The prompt rejection of transplanted allogeneic lymphocytes by rat NK cells in non-sensitized recipients (allogeneic lymphocyte cytotoxicity or ALC) is determined by MHC genes as well as by genes located in the NK complex. The same genetic control is found when NK alloreactivity is measured by an in vitro assay, and we have employed this assay to delineate the specificity of NK cells for the MHC. The MHC of the rat, RT1, contains class I genes situated on either side of the class II/class III region. The majority of these class I genes are located in the RT1.C region and expressed class I products usually behave as non-classical (class Ib) molecules. They do not serve as restriction elements for the vast majority of conventional alpha/beta T-cells, in contrast to those class I molecules encoded by one or more loci in the classical (class Ia) region, RT1.A. However, NK cells appear to recognize the products of either class I region. Immunogenetic studies suggest that NK cells are inhibited by RT1. A molecules, whereas RT1.C region molecules may have a dual role in regulating NK cytolytic activity, i.e. they either inhibit or activate natural killing. Based on these premises, a model is proposed in which identification of a target as self or non-self depends on different receptors for class I in single NK cells, interpreting coincident positive and negative signals from the various target class I molecules. The putative role of peptides presented by class I, the biological implications, and the evolution of the NK receptors and their ligands are discussed.

Major histocompatibility complex class I-independent killing of xenogeneic targets by rat allospecific natural killer cells

Major histocompatibility complex class I molecules can inhibit mouse as well as human natural killer (NK) cell cytotoxicity. In contrast, antigens encoded in the RT1.C region of the rat MHC gene complex have been suggested to trigger, rather than inhibit, rat NK cells. In an attempt to analyze rat NK cell specificity, with respect to the cross-species difference that may exist in NK cell-mediated cytotoxicity, we investigated the ability of interleukin 2-activated, allospecific rat NK cells to recognize MHC class I-positive and -deficient target cells of mouse and human origins. Recognition of xenogeneic target cells by rat allospecific NK cells was found to be MHC class I independent; target cell MHC class I was not required for killing, and expression of different sets of mouse and human MHC class I molecules did not influence the cytotoxic response. These results indicate that rat NK cells can recognize xenogeneic nontransformed cells by mechanisms not related to target cell MHC class I expression, and that mouse and human MHC class I molecules, at least among those tested in this study, are unable to confer inhibition of rat NK cells.

Preferential involvement of Go and Gz proteins in mediating rat natural killer cell lysis of allogeneic and tumor target cells

IL-2-activated NK cells from PVG rats potently lyse target cells expressing allo-MHC class I determinants. Here, we investigated the role that G proteins play in mediating this activity. Pretreatment of NK cells with pertussis toxin (PT) or cholera toxin (CT) inhibited NK cell killing of tumor (YAC-1 or P815), and allogeneic target cells. ADP ribosylation assay revealed that PT ADP ribosylates a 39-kDa G protein, whereas CT ADP ribosylates a 45 to 47-kDa G protein in PVG NK cell membranes. Membranes prepared from intoxicated NK cells with either PT or CT lost their ability to incorporate [32P]NAD. These membranes possess Gi, Go, Gs, and Gz as demonstrated by immunoblot analysis. However, Gq was not clearly detected by this method. IL-2-activated NK cells were permeabilized with streptolysin O. Permeabilized cells incorporated Abs to Gi, Go, Gz, Gs, and Gq as determined by flow cytometric analysis. When Abs to Go or Gz, but not to Gi, Gs, or Gq, were incorporated inside permeabilized NK cells, a significant reduction in the lysis of tumor or allo-MHC target cells was observed, suggesting that Go and Gz play important roles in transducing the signals necessary to lyse target cells. Our results show for the first time a role for G proteins in mediating NK cell killing of allo-MHC-encoded target cells, and provide evidence for Gz protein involvement in NK cell recognition of target cells. The effect of Gz is novel and has not been previously described in any other system or cell type.

Preferential involvement of Go and Gz proteins in mediating rat natural killer cell lysis of allogeneic and tumor target cells

IL-2-activated NK cells from PVG rats potently lyse target cells expressing allo-MHC class I determinants. Here, we investigated the role that G proteins play in mediating this activity. Pretreatment of NK cells with pertussis toxin (PT) or cholera toxin (CT) inhibited NK cell killing of tumor (YAC-1 or P815), and allogeneic target cells. ADP ribosylation assay revealed that PT ADP ribosylates a 39-kDa G protein, whereas CT ADP ribosylates a 45 to 47-kDa G protein in PVG NK cell membranes. Membranes prepared from intoxicated NK cells with either PT or CT lost their ability to incorporate [32P]NAD. These membranes possess Gi, Go, Gs, and Gz as demonstrated by immunoblot analysis. However, Gq was not clearly detected by this method. IL-2-activated NK cells were permeabilized with streptolysin O. Permeabilized cells incorporated Abs to Gi, Go, Gz, Gs, and Gq as determined by flow cytometric analysis. When Abs to Go or Gz, but not to Gi, Gs, or Gq, were incorporated inside permeabilized NK cells, a significant reduction in the lysis of tumor or allo-MHC target cells was observed, suggesting that Go and Gz play important roles in transducing the signals necessary to lyse target cells. Our results show for the first time a role for G proteins in mediating NK cell killing of allo-MHC-encoded target cells, and provide evidence for Gz protein involvement in NK cell recognition of target cells. The effect of Gz is novel and has not been previously described in any other system or cell type.

Microbial colonization influences composition and T-cell receptor V beta repertoire of intraepithelial lymphocytes in rat intestine

Studies in mice have shown that the composition of intestinal intraepithelial lymphocytes (IEL) may be markedly altered by gut microbial colonization. Such modulation was studied in a rat model by the use of germ-free and conventionalized animals from which IEL from the small intestine were isolated and analysed by flow cytometry. Conventionalization caused expansion as well as phenotypic alterations of T-cell receptor (TCR) alpha/beta + IEL in that the proportions of CD4+ and CD8 alpha beta + TCR alpha/beta + cells were increased, while the double negative (CD4- CD8-) fraction was reduced. microbial colonization also influenced the TCR V beta repertoire of CD8+ IEL in that the proportions of V beta 8.2+ and V beta 10+ cells were increased, whereas V beta 8.5+ and V beta 16+ cells were relatively decreased. Moreover, conventionalization influenced the levels of TCR cell surface expression in the same V beta subsets. Three-colour flow-cytometric analysis demonstrated that skewing of the V beta repertoire was most pronounced in the CD8 alpha alpha + subset, although the numerical increase of IEL mainly included the CD8 alpha beta + subset. In contrast to IEL, the TCR V beta repertoire in mesenteric lymph nodes was unchanged after intestinal colonization. These results confirm that TCR alpha/beta + IEL subpopulations respond dynamically to the microbial gut flora and suggest that their V beta repertoire can be shaped by luminal microbial antigens.

Genes in two MHC class I regions control recognition of a single rat NK cell allodeterminant

We have previously presented evidence suggesting that the non-classical class I region of the rat MHC, RT1.C, encodes polymorphic molecules which induce the cytolytic activity of alloreactive NK cells. Those studies used target cells from a panel of MHC congenic rat strains possessing recombined portions of the RT1a, RT1l and RT1u MHC haplotypes. We have now examined in addition a set of rat strains bearing MHC haplotypes recombinant between RT1av1 and RT1c, and a more complex picture of the MHC control of rat NK alloreactivity has emerged. The expression of a major NK allodeterminant [the allogeneic lymphocyte cytotoxicity (ALC) determinant 2 or ALC-2, defined operationally using cold-target inhibition assays], appears to be under the control of both the RT1.C and the classical class I RT1.A region. Similarly, the alloreactive repertoires of NK cells from these recombinant strains are influenced by elements encoded within these two MHC class I regions. We present a model in which the classical class I autoantigen RT1.Ac exhibits dominant inhibition of NK cytotoxicity specific for the stimulatory determinant ALC-2 shared by the nonclassical class I molecules RT1.Cav1, RT1.Ca and RT1.Cc, and also prevents the deletion of NK cells of this specificity during their development.

Alloreactive natural killer cells in the rat: complex genetics of major histocompatibility complex control

A major role for the nonclassical major histocompatibility complex (MHC) class I region, i.e. RT1.C, in controlling rat natural killer (NK) cell alloreactivity has recently been established, and several findings suggested the existence of NK-triggering alloantigens coded for by this region. Here, we have extended our studies on the MHC control of NK cell cytotoxicity against concanavalin A-activated T cell blasts by comparing semi-syngeneic and fully allogeneic combinations, and we show the following: (a) The self MHC exerted a strong influence on the NK allorecognition repertoire. (b) When anti-F1 hybrid cytolytic activities of parental strain NK cells were measured, both recessively and non-recessively inherited susceptibility patterns emerged. (c) In most combinations parental strain cells were lysed by F1 hybrid NK cells, thus resembling the hybrid resistance phenomenon described in mice. The cytotoxicity was lower in strain combinations where NK susceptibility was inherited non-recessively, i.e. when parent anti-F1 reactivity was detected, than in recessive combinations. (d) LEW.1LM1 (RT1lm1) target cells, with a deletion in the RT1.C region that includes expressed class I genes, were more sensitive to lysis by MHC matched NK cells (PVG.1L(LEW), RT1l) than were parental LEW (RT1l) cells. The effect of the deletion was the opposite when MHC allogeneic (RT1c, RT1u) as well as semi-syngeneic (RT1l/c) NK cells were employed, i.e. sensitivity was decreased. We conclude that certain MHC-encoded antigens, depending on the haplotype combination of effector and target cells, may either trigger or inhibit rat NK cell cytotoxicity. Furthermore, the potential role of peptides bound to MHC class I molecules recognized by NK cells is discussed.