Monoclonal antibody to a triggering structure expressed on rat natural killer cells and adherent lymphokine-activated killer cells

Production of recombinant soluble dimeric C-type lectin-like receptors of rat natural killer cells

Working at the border between innate and adaptive immunity, natural killer (NK) cells play a key role in the immune system by protecting healthy cells and by eliminating malignantly transformed, stressed or virally infected cells. NK cell recognition of a target cell is mediated by a receptor “zipper” consisting of various activating and inhibitory receptors, including C-type lectin-like receptors. Among this major group of receptors, two of the largest rodent receptor families are the NKR-P1 and the Clr receptor families. Although these families have been shown to encode receptor-ligand pairs involved in MHC-independent self-nonself discrimination and are a target for immune evasion by tumour cells and viruses, structural mechanisms of their mutual recognition remain less well characterized. Therefore, we developed a non-viral eukaryotic expression system based on transient transfection of suspension-adapted human embryonic kidney 293 cells to produce soluble native disulphide dimers of NK cell C-type lectin-like receptor ectodomains. The expression system was optimized using green fluorescent protein and secreted alkaline phosphatase, easily quantifiable markers of recombinant protein production. We describe an application of this approach to the recombinant protein production and characterization of native rat NKR-P1B and Clr-11 proteins suitable for further structural and functional studies.

Oligomeric Architecture of Mouse Activating Nkrp1 Receptors on Living Cells

Mouse activating Nkrp1 proteins are commonly described as type II transmembrane receptors with disulfide-linked homodimeric structure. Their function and the manner in which Nkrp1 proteins of mouse strain (C57BL/6) oligomerize are still poorly understood. To assess the oligomerization state of Nkrp1 proteins, mouse activating EGFP-Nkrp1s were expressed in mammalian lymphoid cells and their oligomerization evaluated by Förster resonance energy transfer (FRET). Alternatively, Nkrp1s oligomers were detected by Western blotting to specify the ratio between monomeric and dimeric forms. We also performed structural characterization of recombinant ectodomains of activating Nkrp1 receptors. Nkrp1 isoforms c1, c2 and f were expressed prevalently as homodimers, whereas the Nkrp1a displays larger proportion of monomers on the cell surface. Cysteine-to-serine mutants revealed the importance of all stalk cysteines for protein dimerization in living cells with a major influence of cysteine at position 74 in two Nkrp1 protein isoforms. Our results represent a new insight into the oligomerization of Nkrp1 receptors on lymphoid cells, which will help to determine their function.

Role of Tumor Necrosis Factor-α and Natural Killer Cells in Uterine Artery Function and Pregnancy Outcome in the Stroke-Prone Spontaneously Hypertensive Rat

Women with chronic hypertension are at increased risk of maternal and fetal morbidity and mortality. We have previously characterized the stroke-prone spontaneously hypertensive rat (SHRSP) as a model of deficient uterine artery function and adverse pregnancy outcome compared with the control Wistar-Kyoto. The activation of the immune system plays a role in hypertension and adverse pregnancy outcome. Therefore, we investigated the role of tumor necrosis factor-α in the SHRSP phenotype in an intervention study using etanercept (0.8 mg/kg SC) at gestational days 0, 6, 12, and 18 in pregnant SHRSP compared with vehicle-treated controls (n=6). Etanercept treatment significantly lowered systolic blood pressure after gestational day 12 and increased litter size in SHRSP. At gestational day 18, etanercept improved the function of uterine arteries from pregnant SHRSP normalizing the contractile response and increasing endothelium-dependent relaxation, resulting in increased pregnancy-dependent diastolic blood flow in the uterine arteries. We identified that the source of excess tumor necrosis factor-α in the SHRSP was a pregnancy-dependent increase in peripheral and placental CD3^- CD161⁺ natural killer cells. Etanercept treatment also had effects on placental CD161⁺ cells by reducing the expression of CD161 receptor, which was associated with a decrease in cytotoxic granzyme B expression. Etanercept treatment improves maternal blood pressure, pregnancy outcome, and uterine artery function in SHRSP by antagonizing signaling from excess tumor necrosis factor-α production and the reduction of granzyme B expression in CD161⁺ natural killer cells in SHRSP.

Stress impairs the efficacy of immune stimulation by CpG-C: Potential neuroendocrine mediating mechanisms and significance to tumor metastasis and the perioperative period

We recently reported that immune stimulation can be compromised if animals are simultaneously subjected to stressful conditions. To test the generalizability of these findings, and to elucidate neuroendocrine mediating mechanisms, we herein employed CpG-C, a novel TLR-9 immune-stimulating agent. Animals were subjected to ongoing stress (20-h of wet cage exposure) during CpG-C treatment, and antagonists to glucocorticoids, β-adrenoceptor, COX2, or opioids were employed (RU486, nadolol, etodolac, naltrexone). In F344 rats, marginating-pulmonary NK cell numbers and cytotoxicity were studied, and the NK-sensitive MADB106 experimental metastasis model was used. In Balb/C mice, experimental hepatic metastases of the CT-26 colon tumor were studied; and in C57BL/6J mice, survival rates following excision of B16 melanoma was assessed - both mouse tumor models involved surgical stress. The findings indicated that simultaneous blockade of glucocorticoid and β-adrenergic receptors improved CpG-C efficacy against MADB106 metastasis. In mice bearing B16 melanoma, long-term survival rate was improved by CpG-C only when employed simultaneously with blockers of glucocorticoids, catecholamines, and prostaglandins. Prolonged stress impaired CpG-C efficacy in potentiating NK activity, and in resisting MADB106 metastasis in both sexes, as also supported by in vitro studies. This latter effect was not blocked by any of the antagonists or by adrenalectomy. In the CT26 model, prolonged stress only partially reduced the efficacy of CpG-C. Overall, our findings indicate that ongoing behavioral stress and surgery can jeopardize immune-stimulatory interventions and abolish their beneficial metastasis-reducing impacts. These findings have implications for the clinical setting, which often involve psychological and physiological stress responses during immune-stimulation.

Functional Heterogeneity and Antimycobacterial Effects of Mouse Mucosal-Associated Invariant T Cells Specific for Riboflavin Metabolites

Mucosal-associated invariant T (MAIT) cells have a semi-invariant TCR Vα-chain, and their optimal development is dependent upon commensal flora and expression of the nonpolymorphic MHC class I-like molecule MR1. MAIT cells are activated in an MR1-restricted manner by diverse strains of bacteria and yeast, suggesting a widely shared Ag. Recently, human and mouse MR1 were found to bind bacterial riboflavin metabolites (ribityllumazine [RL] Ags) capable of activating MAIT cells. In this study, we used MR1/RL tetramers to study MR1 dependency, subset heterogeneity, and protective effector functions important for tuberculosis immunity. Although tetramer(+) cells were detected in both MR1(+/+) and MR1(-/-) TCR Vα19i-transgenic (Tg) mice, MR1 expression resulted in significantly increased tetramer(+) cells coexpressing TCR Vβ6/8, NK1.1, CD44, and CD69 that displayed more robust in vitro responses to IL-12 plus IL-18 and RL Ag, indicating that MR1 is necessary for the optimal development of the classic murine MAIT cell memory/effector subset. In addition, tetramer(+) MAIT cells expressing CD4, CD8, or neither developing in MR1(+/+) Vα19i-Tg mice had disparate cytokine profiles in response to RL Ag. Therefore, murine MAIT cells are considerably more heterogeneous than previously thought. Most notably, after mycobacterial pulmonary infection, heterogeneous subsets of tetramer(+) Vα19i-Tg MAIT cells expressing CXCR3 and α4β1 were recruited into the lungs and afforded early protection. In addition, Vα19iCα(-/-)MR(+/+) mice were significantly better protected than were Vα19iCα(-/-)MR1(-/-), wild-type, and MR1(-/-) non-Tg mice. Overall, we demonstrate considerable functional diversity of MAIT cell responses, as well as that MR1-restricted MAIT cells are important for tuberculosis protective immunity.

Nkrp1 family, from lectins to protein interacting molecules

The C-type lectin-like receptors include the Nkrp1 protein family that regulates the activity of natural killer (NK) cells. Rat Nkrp1a was reported to bind monosaccharide moieties in a Ca²⁺-dependent manner in preference order of GalNac > GlcNAc >> Fuc >> Gal > Man. These findings established for rat Nkrp1a have been extrapolated to all additional Nkrp1 receptors and have been supported by numerous studies over the past two decades. However, since 1996 there has been controversy and another article showed lack of interactions with saccharides in 1999. Nevertheless, several high affinity saccharide ligands were synthesized in order to utilize their potential in antitumor therapy. Subsequently, protein ligands were introduced as specific binders for Nkrp1 proteins and three dimensional models of receptor/protein ligand interaction were derived from crystallographic data. Finally, for at least some members of the NK cell C-type lectin-like proteins, the “sweet story” was impaired by two reports in recent years. It has been shown that the rat Nkrp1a and CD69 do not bind saccharide ligands such as GlcNAc, GalNAc, chitotetraose and saccharide derivatives (GlcNAc-PAMAM) do not directly and specifically influence cytotoxic activity of NK cells as it was previously described.

Complexity and Diversity of the NKR-P1:Clr (Klrb1:Clec2) Recognition Systems

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.

In vivo suppression of NK cell cytotoxicity by stress and surgery: glucocorticoids have a minor role compared to catecholamines and prostaglandins

Most in vitro and ex-vivo studies indicate a profound suppression of NK cell cytotoxicity (NKCC) by glucocorticoids; while catecholamines and prostaglandins were reported both to suppress and to enhance NKCC. However, methodological considerations hinder our ability to deduce from these findings to the impact of endogenous release of these factors on in vivo levels of NKCC and their implications to NK-dependent resistance to pathologies in living humans or animals. Here we used an in vivo approach that sensitively and specifically reflects NKCC in living F344 rats, based on lung clearance of NK-sensitive tumor cells (MADB106), and based on comparing effects between NK-intact and NK-depleted rats. To study the role of corticosterone, epinephrine, and prostaglandins, we administered these factors to rats, or antagonized their endogenous release following different stress paradigms or surgery. The results indicated that endogenous or exogenous elevated corticosterone levels can suppress in vivo NKCC levels, but only under some conditions, and mostly secondarily to the NK-suppressing impact of epinephrine. Specifically, corticosterone-induced NKCC suppression occurred (i) only under prolonged, but not short exposure to stress, and mainly in males; (ii) was smaller than the prominent impact of epinephrine; (iii) was mostly ascribed to corticosterone-induced potentiation of the effects of epinephrine or/and prostaglandins; and (iv) was completely abolished through antagonizing epinephrine or/and prostaglandins. Overall, these findings markedly limit the significance of stress/surgery-induced corticosterone release in the in vivo suppression of NKCC, and highlight the blockade of epinephrine or/and prostaglandins as effective and clinically feasible approaches to overcome such immuno-suppressive effects.

Stress and skin leukocyte trafficking as a dual-stage process

Stress responses are known to modulate leukocyte trafficking. In the skin, stress was reported both to enhance and reduce skin immunity, and the chronicity of stress exposure was suggested as a key determining factor. We here propose a dual-stage hypothesis, suggesting that stress, of any duration, reduces skin immunity during its course, while its cessation is potentially followed by a period of enhanced skin immunity. To start testing this hypothesis, rats were subcutaneously implanted with sterile surgical sponges for four-hours, during or after exposure to one of several acute stress paradigms, or to a chronic stress paradigm. Our findings, in both males and females, indicate that numbers of sponge-infiltrating leukocytes, and their specific subsets, were reduced during acute or chronic stress, and increased after stress cessation. Studying potential mediating mechanisms of the reduction in leukocyte numbers during acute stress, we found that neither adrenalectomy nor the administration of beta-adrenergic or glucocorticoid antagonists prevented this reduction. Additionally, administration of corticosterone or epinephrine to adrenalectomized rats did not impact skin leukocyte numbers, whereas, in the blood, these treatments did affect numbers of leukocytes and their specific subsets, as was also reported previously. Overall, our findings support the proposed dual-stage hypothesis, which can be evolutionally rationalized and accounts for most of the apparent inconsistencies in the literature regarding stress and skin immunity. Other aspects of the hypothesis should be tested, also using additional methodologies, and its predictions may bear clinical significance in treatment of skin disorders related to hyper- or hypo-immune function.

Fish oil attenuates surgery-induced immunosuppression, limits post-operative metastatic dissemination and increases long-term recurrence-free survival in rodents inoculated with cancer cells

BACKGROUND & AIMS

Omega-3 fatty acids (ω-3FA) attenuate postoperative immunosuppression vis-à-vis infection. Since immune-surveillance targets metastasizing cancer cells, we assessed the effect of ω-3FA consumption on 1) early post-operative Natural Killer cell (NK) cytotoxicity and metastases and 2) long-term recurrence-free survival, in two rodent models of surgery-promoted metastases.

METHODS

C57BL/6J mice were fed standard, ω-3FA-enriched, or ω-6FA-enriched chow, beginning one week before subcutaneous footpad implantation of syngeneic melanoma cells. When tumors reached the volume of 110 μl, the tumor-bearing footpad was amputated, and long-term recurrence-free survival was assessed. Also, F344 rats were fed ω-3FA or ω-6FA for a month before undergoing or not undergoing laparotomy, and were intravenously inoculated with radio-labeled syngeneic adenocarcinoma cells. Marginating-pulmonary (MP)-leukocytes were harvested, and lung tumor retention (LTR) of metastases was assessed.

RESULTS

ω-3FA consumption did not affect the growth of footpad tumors, but significantly enhanced post-amputation recurrence-free survival in mice. Surgery had a deleterious effect on NK cell activity and LTR whereas ω-3FA had large beneficial effects in non-operated rats and an even greater impact in operated rats.

CONCLUSIONS

ω-3FA feeding attenuates or even overcomes postoperative NK cell suppression, increases resistance to experimental and spontaneous metastasis, and enhances recurrence-free survival following excision of metastasizing primary tumors. These findings warrant clinical studies of ω-3FA-based nutrition in patients undergoing resection of a primary tumor.

Induction of lectin-like transcript 1 (LLT1) protein cell surface expression by pathogens and interferon-γ contributes to modulate immune responses

CD161 is a C-type lectin-like receptor expressed on human natural killer (NK) cells and subsets of T cells. CD161 has been described as an inhibitory receptor that regulates NK cell-mediated cytotoxicity and IFN-γ production. Its role on T cells has remained unclear. Studies have shown that triggering of CD161 enhances NK T cell proliferation and T cell-IFN-γ production while inhibiting TNF-α production by CD8(+) T cells. Lectin-like transcript 1 (LLT1), the ligand of CD161, was found to be expressed on Toll-like receptor (TLR)-activated plasmacytoid and monocyte-derived dendritic cells (DC) and on activated B cells. Using newly developed anti-LLT1 mAbs, we show that LLT1 is not expressed on the surface of circulating B and T lymphocytes, NK cells, monocytes, and dendritic cells but that LLT1 is up-regulated upon activation. Not only TLR-stimulated dendritic cells and B cells but also T cell receptor-activated T cells and activated NK cells up-regulate LLT1. Interestingly, IFN-γ increases LLT1 expression level on antigen-presenting cells. LLT1 is also induced on B cells upon viral infection such as Epstein-Barr virus or HIV infection and in inflamed tonsils. Finally, expression of LLT1 on B cells inhibits NK cell function but costimulates T cell proliferation or IFN-γ production, and coengagement of CD161 with CD3 increases IL-17 secretion. Altogether, our results point toward a role for LLT1/CD161 in modulating immune responses to pathogens.

Kinetics of lymphocyte reconstitution after allogeneic bone marrow transplantation: markers of graft-versus-host disease

GVHD causes extensive morbidity and mortality in patients who receive alloHCT. Predictive and reliable markers for GVHD are currently lacking but required to improve the safety and accessibility of alloHCT. We present an experimental rat model of myeloablative total body irradiation and fully mismatched major and minor histoincompatible, T cell-depleted BMT, followed by delayed infusion of donor lymphocytes. This treatment, in contrast to marrow transplantation alone, resulted in severe aGVHD and 100% lethality within 2-6 weeks. We investigated the reconstitution kinetics and phenotypes of donor leukocyte subpopulations as well as the histopathology of selected organs that may correlate with GVHD, with the goal to find potential disease-related markers. We observed histological changes mainly confined to the skin, with degenerative changes in the basal layer. LNs and spleen showed deranged architecture with markedly increased accumulation of lymphocytes, whereas the gut, liver, and lungs appeared normal. Of the lymphocyte markers tested, donor-derived CD62L(+) T cells were markedly decreased in animals suffering from GVHD. Furthermore, we observed peripheral depletion of CD4(+)CD25(hi)FoxP3(+) T(reg), which was in contrast to controls. The relative frequency of these lymphocyte subpopulations in blood may therefore serve as accessible cellular markers of aGVHD. We propose that the animal model presented is instructive for the identification of clinically relevant markers of GVHD, which could improve disease diagnosis and management in alloHCT.

Novel method for isolating untouched rat natural killer cells with higher purity compared with positive selection and fluorescence-activated cell sorting

Natural killer (NK) cells are important effectors of both innate and adaptive immune responses. Although human and mouse NK cells are extensively characterized, much less is known about the rat cells, partly because of the current lack of reliable isolation techniques. We aimed to develop a method for isolating highly pure 'untouched' rat NK cells by negative selection from splenocytes. Thereafter, we characterized them phenotypically and functionally in comparison with those isolated by positive selection targeting the NKR-P1 receptor. Our novel method isolated highly pure untouched NK cells reproducibly with 97 ± 0.7% (n = 7), 96.6 ± 0.8% (n = 3) and 88.3 ± 1.5% (n = 9) in LEWIS, Fischer and athymic nude rats, respectively. The positively selected NK cells were less homogeneous and exhibited undesired method-related activation profiles. Resting negatively selected NK cells were less proliferative and less robust compared with positively selected NK cells. Although resting positively selected NK cells were more cytotoxic, interleukin-2 (IL-2) activation increased the cytotoxicity of negatively selected cells three-fold. The negatively selected NK cells responded to cross-linking of the NKR-P1 receptor by calcium mobilization from intracellular stores. However, combined IL-2 and IL-12 activation resulted in significantly more interferon-γ release from positively selected NK cells. This new NK-cell isolation method will allow a deeper insight into rat NK-cell phenotypes and the roles of their receptors in the biology of these cells.

Listeria monocytogenes infection affects a subset of Ly49-expressing NK cells in the rat

NK cells are protective against certain bacterial and viral infections, and their production of IFN-γ is important for the early innate immune defence against L. monocytogenes. We have previously shown that depletion of NK cells in rats leads to increased bacterial burden upon L. monocytogenes infection, and that a subset of NK cells encompassing the majority of Ly49 receptors (Ly49s3⁺ NK cells) contributed to this effect. In this study, we have further investigated how the Ly49s3⁺ NK cell subset is affected by L. monocytogenes infection. We observed an increased percentage of Ly49s3⁺ NK cells in the spleen and a reduction in the bone marrow within the first 48 hrs of L. monocytogenes infection. Concomitantly, we observed increased expression levels of the inflammatory chemokine receptors CCR5 and CXCR3 by Ly49s3⁺ bone marrow NK cells, as compared to Ly49s3⁻ NK cells, suggesting involvement of Ly49s3⁺ NK cells in the early phase of infection. However, NK cell production of IFN-γ was independent of Ly49 receptor expression. Furthermore, we observed increased expression levels of MHC class I molecules on both macrophages and NK cells during the first 48 hrs of infection, paralleled by a reduction in the surface expression of Ly49s3 on NK cells. In conclusion, L. monocytogenes infection modulates the tissue distribution of Ly49s3⁺ NK cells, and induces increased MHC class I expression and hence reduced surface expression of Ly49 receptors on NK cells. These changes indicate that L. monocytogenes infection may have multiple effects on NK cells in vivo, and suggests the involvement of Ly49-expressing NK cells in the immune responses towards L. monocytogenes.

Partial NK cell tolerance induced by radioresistant host cells in rats transplanted with MHC-mismatched bone marrow

We have studied the effect of radioresistant host cells in inducing tolerance and adaptation of the MHC recognition repertoire of donor-derived NK cells in stem cell allotransplanted (allo-SCT) rats. Sub-lethally irradiated PVG.1AV1 rats (RT1(av1)) were transplanted with bone marrow from fully MHC-mismatched allotype-marked PVG.7B (RT1(c)) rats; MHC-identical PVG (RT1(c)) controls were transplanted in parallel. In the PVG.7B → PVG.1AV1 allogeneic chimeras, NK cells were donor derived and showed partial tolerance toward host cells. Allogeneic chimeras failed to efficiently reject PVG.1AV1 cells by an NK-mediated mechanism in vivo (allogeneic lymphocyte cytotoxicity), and IL-2-cultured NK cells derived from these chimeras showed diminished cytolytic activity against PVG.1AV1 cells in vitro. There were corresponding changes in the phenotype and function of the highly alloreactive Ly49i2(+) NK cells, which are specifically inhibited by a donor MHC class I ligand, RT1-A1(c). The ligand-negative host MHC haplotype apparently induced expression of a second uncharacterized inhibitory MHC receptor responsible for the partial tolerance toward host-derived cells, along with a modest increase in Ly49i2 receptor levels. The host MHC haplotype did not induce a general hyporesponsiveness in Ly49i2(+) NK cells, which showed normal activation responses in a panel of MHC congenic strains. The data suggest that the MHC constitution of radiation-resistant host cells can have permanent, albeit not fully tolerogenic, effects on the development of a functional NK repertoire following allo-SCT.

The marginating-pulmonary immune compartment in rats: characteristics of continuous inflammation and activated NK cells

A significant role has been indicated for cellular immunity in controlling circulating cancer cells, but most autologous tumor cells seem resistant, in vitro, to natural killer cell (NKC) and cytotoxic T lymphocytes cytotoxicity. Addressing this apparent contradiction, we recently identified a unique leukocyte population, marginating-pulmonary (MP)-leukocytes, which exhibit potent natural killer (NK) cytotoxicity. Here, we characterize the MP-compartment in naive and immunostimulated rats, and assessed its cytotoxicity against "NK-resistant" tumors cells. Animals were treated with poly I-C (3x0.2 mg/kg) or saline, and circulating-leukocytes and MP-leukocytes were collected and analyzed in terms of cellular composition, cellular activation markers, and NK cytotoxicity of leukocytes and purified NKCs. Compared with circulating-leukocytes, MP-leukocytes showed greater proportion of granulocytes, monocytes, NKCs, and large NKCs; higher expression of activation and adhesion markers (CD25, CD11a, CD11b, and NKR-P1, IFN-gamma); and elevated NK cytotoxicity of leukocytes and purified NKCs against several syngeneic and xenogeneic NK-resistant target cells (from both F344 and BDX inbred rats). In immunostimulated animals (treated with poly I-C), but not in naive animals, purified NKCs from the MP-compartment showed markedly superior cytotoxicity, suggesting that poly I-C immunostimulation uniquely affect MP-NKCs, and that in naive animals other MP-leukocytes support NK cytotoxicity. Overall, the results suggest that the MP-compartment is characterized by a continuous activated inflammatory microenvironment uniquely affected by immunostimulation. If similarly potent MP-NKCs exist in patients, then circulating autologous tumor cells that are considered "NK-resistant" could actually be controlled by MP-NKCs. Innate immunity may assume greater role in controlling malignant spread, especially after immunostimulation.

Modified electrophoretic and digestion conditions allow a simplified mass spectrometric evaluation of disulfide bonds

Proper formation of disulfide bonds in proteins is a prerequisite to their stability and function. Information on disulfide pattern may therefore serve as an indication of the proper folding of recombinant proteins, and can also be used in protein homology modeling for the purpose of structure refinement. Protein handling and digestion at basic pH leads to disulfide bond scrambling. That is why the samples are usually treated and digested at low pH where no scrambling occurs. Unfortunately, the specific proteases used in protein research are active at high pH values. Here, we present a complete sample handling protocol, which allows processing of disulfide containing proteins at basic pH. We modified the standard SDS gel electrophoresis and protein digestion conditions by the addition of an oxidative agent, cystamine. This modification prevented disulfide scrambling, which we otherwise observed in the samples handled according to the general protocol. Lysozyme from hen egg was used as a model protein for the development of the method. We then applied our protocol to human leukocyte antigen CD69, for which the disulfide bonding is known, but only for its monomeric form. In addition, the disulfide arrangement was then 'de novo' identified in the recombinant murine leukocyte receptor NKR-P1A and in the larger glycosylated proteins beta-N-acetylhexosaminidases from Aspergillus oryzae and Penicillium oxalicum.

Natural killer cell-based immunotherapy in cancer: current insights and future prospects

As our understanding of the molecular mechanisms governing natural killer (NK) cell activity increases, their potential in cancer immunotherapy is growing increasingly prominent. This review analyses the currently available preclinical and clinical data regarding NK cell-based immunotherapeutic approaches in cancer starting from a historical background and an overview of molecular mechanisms taking part in NK cell responses. The status of NK cells in cancer patients, currently investigated clinical applications such as in vivo modulation of NK cell activity, ex vivo purification/expansion and adoptive transfer as well as future possibilities such as genetic modifications are discussed in detail.

Metastatic-promoting effects of LPS: sexual dimorphism and mediation by catecholamines and prostaglandins

Inflammation is implicated in several medical conditions that are sexually dimorphic, including depression, cardiovascular diseases, autoimmunity, and presumably cancer progression. Here we studied the effects of the proinflammatory agent, LPS, on MADB106 lung tumor retention (LTR), and sought to elucidate underlying mechanisms and sexual dimorphism. F344 male and female rats were administered with LPS (0.001-1mg/kg i.v.) simultaneously with tumor cell inoculation, and treated with a beta-blocker (nadolol, 0.2-0.3mg/kg s.c.), a COX inhibitor (indomethacin, 4mg/kg s.c.) or both drugs. To study the role of NK cells, numbers and cytotoxicity of marginating-pulmonary NK cells were studied, and selective in vivo NK-depletion was employed. Serum levels of corticosterone, IL-6, and TNF-alpha were also assessed. The findings indicated that LPS increased LTR in both sexes, but 10-fold higher doses were needed in females to reach the increase evident in males. Additionally, nadolol and indomethacin reduced the effects of LPS, more so in males. In vivo NK-depletion and ex vivo NK activity studies suggested that LPS affected LTR through both NK-independent and NK-dependent mechanisms, the latter mediated through prostaglandin release in males. Corticosterone, IL-6, and TNF-alpha responses to LPS were sexually dimorphic, but were not associated with LPS or drugs' impacts on LTR. Overall, our findings demonstrate sexual dimorphism in LPS-induced elevated susceptibility to MADB106 experimental metastasis, and in potential humoral underlying mechanisms. Further studies are needed to elucidate additional immunological and non-immunological mediators of these dimorphisms, as well as to assess their involvement in other sexually dimorphic pathologies that are associated with inflammation.

CpG-C oligodeoxynucleotides limit the deleterious effects of beta-adrenoceptor stimulation on NK cytotoxicity and metastatic dissemination

Suppression of natural killer (NK) cell activity is common after stress, has been reported to predict malignant recurrence in cancer patients, and was shown to underlie metastatic dissemination in animal models. We have previously reported that catecholamines play a major role in NK cell suppression, particularly in the context of physiologic stress and surgery. In the current study using Fisher 344 rats, we examined the prophylactic use of different regimens of type-C CpG oligodeoxynucleotides (CpG-C ODN) on NK activity and metastatic dissemination in the context of pharmacologic stress (using metaproterenol for beta-adrenoceptor stimulation). Our results indicated that the beneficial effects of CpG-C ODN were more profound under pharmacologic stress than under baseline conditions. A bolus of CpG-C ODN (330 microg/kg, intraperitoneally) 24 hours before metaproterenol-challenge was most effective at reducing lung tumor retention of an experimental syngeneic mammary adenocarcinoma (MADB106), although having no observable side effects. Depletion of NK cells revealed their key role in improving baseline levels of resistance to metastatic dissemination after CpG-C ODN administration. When NK cell cytotoxicity was assessed in the circulation and the marginating-pulmonary immune compartments, we found that CpG-C ODN protected individual NK cells from metaproterenol-induced suppression in both compartments. Moreover, in the critical marginating-pulmonary compartment, CpG-C ODN also elevated baseline cytotoxicity per NK cell against MADB106 tumor cells, and increased NK cell numbers in nonstressed rats. Overall, prophylactic CpG-C ODN treatment can improve immunocompetence and potentially reduce metastatic dissemination, especially in clinical settings characterized by enhanced sympathetic stress responses.

NK cells and their receptors

Despite early reports that natural killer (NK) cells are non-specific or have non-major histocompatibility complex (MHC)- restricted killing, it is now clear that NK cells express a panoply of receptors with defined specificity for ligands expressed on their cellular targets. The roles of these receptors in terms of physiological NK cell effector functions, such as cytotoxicity and cytokine production, are beginning to be unravelled. Inasmuch as NK cells accumulate in the uterus, an appreciation of NK cell receptor specificities and their physiological functions should provide valuable clues to the role of NK cells in the uterus and during pregnancy.

Natural killer cells in peripheral blood and lung tissue are associated with chronic rejection after lung transplantation

BACKGROUND

Natural killer (NK) cells have the capacity to recognize and respond to alloantigen, yet their role in lung transplant rejection is not well defined. The aim of this study was to correlate NK cell numbers and immunophenotype in peripheral blood and tissue with graft function after lung transplantation.

METHODS

NK cell subsets were immunophenotyped in peripheral blood (n = 41). Lung tissue was stained for NK cells via CD16 and morphologic assessment (n = 30).

RESULTS

Peripheral blood NK cells were activated in patients with chronic rejection, but the overall number of cells was lower in these patients when compared with stable patients. Furthermore, there was significantly more CD16(+) NK cells in the lung compartment of patients with bronchiolitis obliterans syndrome compared with stable patients (p = 0.001).

CONCLUSIONS

In patients with chronic rejection, peripheral blood NK cells are activated but their numbers decrease, while the number of NK cells in the lungs increases. This suggests NK cells systemically activate and migrate to the lung during the progression of chronic rejection after lung transplantation.

Natural killer cells and lung transplantation, roles in rejection, infection, and tolerance

Despite improvements in surgical technique, organ preservation, immunosuppression, and management of infection, the long term survival following lung transplantation remains low, mainly due to immune mediated complications such as acute and chronic rejection. Almost all immunosuppressive agents used in the prophylaxis and treatment of rejection following lung transplantation are targets of T cell maturation, function or proliferation, which in theory should cause sufficient disruption of the adaptive immune system to prevent graft rejection. However the five year survival rate of only 50% suggests this is not the case. More recent evidence suggests that NK cells may play a significant role in immune processes following lung transplantation. This article reviews the literature on the potential function of NK cells in rejection, infection, malignancy and tolerance following lung transplantation.

Celecoxib inhibits growth of tumors in a syngeneic rat liver metastases model for colorectal cancer

Introduction

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of colorectal cancer in cyclooxygenase-2 (COX-2) overexpressing colorectal cancers. The present study was designed to evaluate the inhibitory effects of the COX-2 inhibitor celecoxib on the growth of colorectal cancer liver metastases in a syngeneic rat model, CC531.

Materials and methods

The effects of celecoxib on cell viability in vitro were evaluated by treatment of CC531 tumor cell cultures with celecoxib. In vivo, Wag/Rij rats were inoculated with CC531 tumor cells at two sites in the liver and treated with celecoxib starting one week before, or directly after tumor inoculation. Control rats were inoculated without treatment. Three weeks after tumor inoculation rats were sacrificed. Tumor size, immune cell infiltration, caspase-3 activity, PGE₂ and celecoxib levels were determined.

Results

CC531 tumors did not show COX-2 expression. Tumor growth was significantly inhibited by celecoxib treatment in a dose dependent manner. Immune cell infiltration was decreased after celecoxib treatment, indicating that the immune system was not involved in preventing tumor growth. Tumor caspase-3 levels were only significantly increased if treatment was started before tumor inoculation. Celecoxib serum concentration starting at 0.84 μg/ml significantly inhibited the outgrowth of CC531 liver tumors. In contrast, in vitro concentrations of celecoxib of at least 12 μg/ml were needed to affect tumor cell viability.

Conclusion

These results suggest that the inhibitory effects of celecoxib on tumor growth are not by direct cytotoxicity, but by creating an unfavorable environment for tumor growth.

Immunotoxicity of nivalenol after subchronic dietary exposure to rats

Immunobiological effects of nivalenol (NIV), a trichothecene mycotoxin produced by Fusarium nivale, were examined in male F344 rats after 90-day dietary exposure at doses of 0, 0.4, 1.5, and 6.9 mg/kg body weight/day (0, 6.25, 25 and 100 ppm, respectively) in a subchronic toxicity study. With regards to the serum immunoglobulin levels, a slight increase of IgM was observed only at 6.9 mg/kg (26% increase), while levels of IgG and IgA did not fluctuate at any dose. Flow cytometric analysis of splenic cells revealed a dose-dependent decrease of T lymphocyte/B lymphocyte (CD3(+)/B220(+)) ratio from 1.5mg/kg and an elevated CD4(+)helper/CD8(+)cytotoxic T lymphocyte ratio at 6.9 mg/kg. Furthermore, increases of natural killer (NK) activity of splenic lymphocytes against YAC-1 target cells were observed at all doses, while the magnitude of changes was similar between 1.5 and 6.9 mg/kg. At 6.9 mg/kg, the reduction of the ratio of NKR-P1A(+) splenic cells, which is an indicator of NK cells in the spleen, was apparent. As with other previous studies of NIV, decreased body weight was observed from 1.5 mg/kg during the experiment in the present study. In summary, NIV affected immune function in rats after 90-day dietary exposure, the effects being apparent from 0.4 mg/kg judging from the increase of NK activity, although nutritional suppression might have influenced the immunological changes appeared from 1.5mg/kg.

A review of large granular lymphocytic leukemia in Fischer 344 rats as an initial step toward evaluating the implication of the endpoint to human cancer risk assessment

Large granular lymphocyte leukemia (LGLL) is a common fatal disease in aging F344 rats. The current understanding of rat LGLL and a search for mechanistic data/correlations to human leukemia were examined with the goal of improving evaluation of the LGLL endpoint in cancer bioassays as it relates to human cancer risk assessments. The exact cell of origin of the F344 rat LGLL is not fully resolved, although natural killer (NK) cell characteristics were demonstrated in most, if not all cases. Similarities between rat LGLL and a rare human NK-LGLL exist, invalidating claims of no human counterpart, although the underlying etiopathogenesis may be different. There is insufficient data to establish a mode of action of chemical-induced rat LGLL. Evaluation of the National Toxicology Program database revealed only 34 substances (out of over 500 studied) that were possibly associated with increased incidences of LGLL. Of these, only five produced definitive LGLL effects in both sexes; the remaining 29 produced single sex responses and/or only "equivocal" associations with LGLL. Trends of increasing background/variability in LGLL incidence and its modulation by extraneous factors (e.g., corn oil gavage) are key confounders in interpretation. Given that LGLL is a common tumor in control F344 rats, interpretations of bioassays can be improved by increasing the statistical stringency (e.g., p<0.01 over traditional p<0.05), as an indicator of possible carcinogenic effects, but that alone would be insufficient evidence for declaring treatment-related increases. Thus, it was concluded that the evaluation of possible chemically related increases in rat LGLL utilize a "weight-of-evidence" approach.

Cytomegalovirus evasion of innate immunity by subversion of the NKR-P1B:Clr-b missing-self axis

Cytomegaloviruses are known to encode several gene products that function to subvert MHC-dependent immune recognition. Here we characterize a rat cytomegalovirus (RCMV) C-type lectin-like (RCTL) gene product with homology to the Clr ligands for the NKR-P1 receptors. RCMV infection rapidly extinguished host Clr-b expression, thereby sensitizing infected cells to killing by natural killer (NK) cells. However, the RCTL protein functioned as a decoy ligand to protect infected cells from NK killing via direct interaction with the NKR-P1B inhibitory receptor. In vivo, an RCTL mutant virus displayed diminished virulence in an NK-dependent and strain-specific manner, suggesting that host NKR-P1 polymorphisms have evolved to avert the viral decoy mechanism while maintaining Clr-b recognition to preserve self tolerance. These findings reveal a unique strategy adopted by cytomegaloviruses to evade MHC-independent self-nonself discrimination. The existence of lectin-like genes in several poxviruses suggests that this may represent a common theme for viral evasion of innate immunity.

Prophylactic IL-12 treatment reduces postoperative metastasis: mediation by increased numbers but not cytotoxicity of NK cells

Despite a promising potential, interleukin-12 immunotherapy has yielded limited clinical success while causing perilous toxicities. Here we study a context in which IL-12 may prove clinically beneficial--the removal of the primary tumor, when cell-mediated immunity (CMI) may eradicate minimal residual disease (MRD), but is inhibited by postoperative immunosuppression, potentially leading to enhanced malignant progression. F344 rats were preoperatively treated with IL-12 and inoculated postoperatively with syngeneic MADB106 tumor cells. An optimal regimen of eight-day sustained exposure to IL-12 was developed (1 microg/rat/day), which caused mild side effects, increased baseline resistance to experimental MADB106 metastasis, and abolished the promotion of metastasis by laparotomy and other immunosuppressive paradigms. Depletion of NK cells indicated their major role in controlling MADB106 metastasis in naïve and IL-12 treated rats. Studying NK cytotoxicity, we found that IL-12 did not potentiate activity per NK cell, nor protected it from suppression by surgery. However, IL-12 increased the numbers of NK cells in the circulation and marginating pulmonary pool of naïve and operated rats, and correspondingly increased total NK activity in these compartments. Therefore, this study indicates anti-tumor effects of IL-12 based on increased numbers of strategically located NK cells, and advocates a prophylactic approach against the potential metastasis-promoting effects of surgery.

Amelioration of operation-induced suppression of marginating pulmonary NK activity using poly IC: a potential approach to reduce postoperative metastasis

BACKGROUND AND OBJECTIVES

Pulmonary metastasis is a major cause of death in cases of operable cancer, and evidence suggests that postoperative immunosuppression contributes to this complication. In this study, we aimed to circumvent this risk and identify immunocytes critical in preventing pulmonary metastases.

METHODS

F344 rats were treated with either vehicle or repeated low doses of poly I-C (0.2 mg/kg i.p., days 5, 3, and 1 preoperatively), a Th1-cytokine-inducing agent, then subjected or not to laparotomy. Using a non-immunogenic syngeneic mammary adenocarcinoma line (MADB106) we studied: (a) NK cytotoxicity (NKC) in marginating-pulmonary (MP) and in circulating leukocytes; (b) resistance to experimental lung metastasis; and (c) in vitro susceptibility of NKC to corticosterone and prostaglandin-E(2), substances thought to mediate postoperative immunosuppression.

RESULTS

MP but not circulating leukocytes showed significant NKC against MADB106 cells. Surgery suppressed this MP-NKC per NK cell and promoted MADB106 metastasis, and poly I-C treatment completely abolished both effects. Poly I-C quadrupled the numbers of MP-NK cells without causing apparent side effects, and protected MP-NKC from in vitro suppression by corticosterone and prostaglandin-E(2).

CONCLUSIONS

MP-NK cells are unique in their ability to kill this apparently immunoresistant tumor. Low doses of synthetic ds-RNA (poly I-C), and potentially Th1 cytokines, can expand this MP-NK population and protect it from immunosuppression. The novelty of such a prophylactic approach is targeting the immediate postoperative period, which is characterized by high vulnerability to residual disease, and protecting critical anti-metastatic immunity against postoperative suppression. Testing such a potentially innocuous intervention in oncology patients preparing for surgery may reduce metastatic recurrence.

Autologous control of a highly malignant syngeneic CRNK-16 leukemia in the rat: a role for NK cells

It is unclear whether autologous immunity could be recruited to restrict the progression of leukemia. Patients harboring leukemia commonly display suppressed cell mediated immunity, which may contribute to their inability to control the disease. Immune response against leukemia is evident in allogeneic HLA-mismatched bone marrow transplantation, implicating the involvement of NK cells. This graft-versus-leukemia (GVL) activity suggests that, if not suppressed, an autologous NK cell response could potentially control acute leukemia that had down-regulated HLA expression. In the current study we assessed the role of non-suppressed autologous NK cells in controlling a syngeneic highly malignant leukemia, the CRNK-16 line, that constitute a major cause of natural death in aged F344 rats. A minuscule dose of 60 CRNK-16 leukemia cells per rat was sufficient to induce 50% mortality rates, and animals that survived this challenge did not show improved survival upon a second challenge. The CRNK-16 line was found to exhibit low levels of MHC-I, and selective in vivo depletion of NK cells nullified in vitro NK activity against the CRNK-16 line and reduced survival rates from this leukemia. In vivo activation of NK cells, employing low doses of poly I-C or IL-12, increased in vitro NK activity against the leukemia and dramatically improved survival rates when treatment was initiated before, but not after leukemia inoculation. These results indicate the ability of competent autologous NK cells to restrict highly malignant non-immunogenic leukemia. Thereby, this model presents an opportunity to study specific in vivo NK-leukemia interactions.

NKR-P1 biology: from prototype to missing self

Natural killer (NK) cells represent lymphocytes of the innate immune system capable of recognizing and destroying a broad array of target cells, including tumors, virus-infected cells, antibodycoated cells, foreign transplants, and "stressed" cells. NK cells eliminate their targets through two main effector mechanisms, cytokine secretion and cell-mediated cytotoxicity, which in turn depend on detection of target cells through a complex integration of stimulatory and inhibitory receptor-ligand interactions. The NKR-P1 molecules were the first family of NK cell receptors identified, yet they have remained enigmatic in their contribution to self-nonself discrimination until recently. Here, we outline a brief history of the NKR-P1 receptor family, then examine recent data providing insight into their genetic regulation, signaling function, cognate ligands, and gene organization and diversity.

Microglial activation and neuronal apoptosis in Bornavirus infected neonatal Lewis rats

Lewis rats neonatally infected with Borna disease virus have a behavioral syndrome characterized by hyperactivity, movement disorders, and abnormal social interactions. Virus is widely distributed in brain; however, neuropathology is focused in dentate gyrus, cerebellum, and neocortex where granule cells, Purkinje cells and pyramidal cells are lost through apoptosis. Although a transient immune response is present, its distribution does not correlate with sites of damage. Neuropathology is instead colocalized with microglial proliferation and expression of MHC class I and class II, ICAM, CD4 and CD8 molecules. Targeted pathogenesis in this system appears to be linked to microglial activation and susceptibility of specific neuronal populations to apoptosis rather than viral tropism or virus-specific immune responses.

The Novel Inhibitory NKR-P1C Receptor and Ly49s3 Identify Two Complementary, Functionally Distinct NK Cell Subsets in Rats

The proximal region of the NK gene complex encodes the NKR-P1 family of killer cell lectin-like receptors which in mice bind members of the genetically linked C-type lectin-related family, while the distal region encodes Ly49 receptors for polymorphic MHC class I molecules. Although certain members of the NKR-P1 family are expressed by all NK cells, we have identified a novel inhibitory rat NKR-P1 molecule termed NKR-P1C that is selectively expressed by a Ly49-negative NK subset with unique functional characteristics. NKR-P1C(+) NK cells efficiently lyse certain tumor target cells, secrete cytokines upon stimulation, and functionally recognize a nonpolymorphic ligand on Con A-activated lymphoblasts. However, they specifically fail to kill MHC-mismatched lymphoblast target cells. The NKR-P1C(+) NK cell subset also appears earlier during development and shows a tissue distribution distinct from its complementary Ly49s3(+) subset, which expresses a wide range of Ly49 receptors. These data suggest the existence of two major, functionally distinct populations of rat NK cells possessing very different killer cell lectin-like receptor repertoires.

CD161 (Human NKR-P1A) Signaling in NK Cells Involves the Activation of Acid Sphingomyelinase

NK and NKT cells play a major role in both innate immunity and in influencing the development of adaptive immune responses. CD161 (human NKR-P1A), a protein encoded in the NK gene complex, is a major phenotypic marker of both these cell types and is thought to be involved in the regulation of NK and NKT cell function. However, the mechanisms of action and signaling pathways of CD161 are poorly understood. To identify molecules able to interact with the cytoplasmic tail of human CD161 (NKR-P1A), we have conducted a yeast two-hybrid screen and identified acid sphingomyelinase as a novel intracellular signaling pathway linked to CD161. mAb-mediated cross-linking of CD161, in both transfectants and primary human NK cells, triggers the activation of acid, but not neutral sphingomyelinase. The sphingomyelinases represent the catabolic pathway for N-acyl-sphingosine (ceramide) generation, an emerging second messenger with key roles in the induction of apoptosis, proliferation, and differentiation. These data therefore define a novel signal transduction pathway for the CD161 (NKR-P1A) receptor and provide fresh insights into NK and NKT cell biology.

Comparative genomics of natural killer cell receptor gene clusters

Many receptors on natural killer (NK) cells recognize major histocompatibility complex class I molecules in order to monitor unhealthy tissues, such as cells infected with viruses, and some tumors. Genes encoding families of NK receptors and related sequences are organized into two main clusters in humans: the natural killer complex on Chromosome 12p13.1, which encodes C-type lectin molecules, and the leukocyte receptor complex on Chromosome 19q13.4, which encodes immunoglobulin superfamily molecules. The composition of these gene clusters differs markedly between closely related species, providing evidence for rapid, lineage-specific expansions or contractions of sets of loci. The choice of NK receptor genes is polarized in the two species most studied, mouse and human. In mouse, the C-type lectin-related Ly49 gene family predominates. Conversely, the single Ly49 sequence is a pseudogene in humans, and the immunoglobulin superfamily KIR gene family is extensive. These different gene sets encode proteins that are comparable in function and genetic diversity, even though they have undergone species-specific expansions. Understanding the biological significance of this curious situation may be aided by studying which NK receptor genes are used in other vertebrates, especially in relation to species-specific differences in genes for major histocompatibility complex class I molecules.

Chronic allograft nephropathy in athymic nude rats after adoptive transfer of primed T lymphocytes

The impact of presensitized T lymphocytes on the development of chronic allograft nephropathy (CAN) was investigated in nude athymic LEW.RNU recipients of F344 renal allografts. The recipients (n = 8) were reconstituted with 5 x 10(7) T lymphocytes primed against donor skin grafts to induce graft rejection. LEW.RNU (n = 8) and euthymic LEW recipients (n = 6) which underwent no further intervention after transplantation served as control groups. Adoptive transfer of primed T cells induced CAN in LEW.RNU rats. Their kidney function decreased progressively. After 90 days a moderate glomerulopathy, tubular atrophy and interstitial fibrosis were observed, vascular changes were only mild or absent. Cellular infiltrates were predominated by CD4+ T cells and ED1+ macrophages. Deposition of tenascin and laminin was enhanced. Grafts of euthymic recipients displayed only mild signs of CAN according to the Banff criteria. These data implicate an important role for the cellular immune response in the development of CAN.

Mutational Analysis of the Human 2B4 (CD244)/CD48 Interaction: Lys68 and Glu70 in the V Domain of 2B4 Are Critical for CD48 Binding and Functional Activation of NK Cells

Interaction between receptors and ligands plays a critical role in the generation of immune responses. The 2B4 (CD244), a member of the CD2 subset of the Ig superfamily, is the high affinity ligand for CD48. It is expressed on NK cells, T cells, monocytes, and basophils. Recent data indicate that 2B4/CD48 interactions regulate NK and T lymphocyte functions. In human NK cells, 2B4/CD48 interaction induces activation signals, whereas in murine NK cells it sends inhibitory signals. To determine the structural basis for 2B4/CD48 interaction, selected amino acid residues in the V domain of the human 2B4 (h2B4) were mutated to alanine by site-directed mutagenesis. Following transient expression of these mutants in B16F10 melanoma cells, their interaction with soluble CD48-Fc fusion protein was assessed by flow cytometry. We identified amino acid residues in the extracellular domain of h2B4 that are involved in interacting with CD48. Binding of CD48-Fc fusion protein to RNK-16 cells stably transfected with wild-type and a double-mutant Lys(68)Ala-Glu(70)Ala h2B4 further demonstrated that Lys(68) and Glu(70) in the V domain of h2B4 are essential for 2B4/CD48 interaction. Functional analysis indicated that Lys(68) and Glu(70) in the extracellular domain of h2B4 play a key role in the activation of human NK cells through 2B4/CD48 interaction.

Requirement of homotypic NK-cell interactions through 2B4(CD244)/CD48 in the generation of NK effector functions

2B4 belongs to the CD2 subset of the IgG family of receptors. Members in this family have been shown to function as coreceptors via homophilic or heterophilic interactions. Both 2B4 and CD2 bind to CD48, another member of this family. Because all 3 molecules are expressed on natural killer (NK) cells, it raises a possibility that the binding of 2B4 and CD2 to CD48 among NK cells may have functional consequences. Using specific monoclonal antibodies and gene-deficient NK cells, we found that 2B4/CD48, but not CD2/CD48, interaction is essential for IL-2-driven expansion and activation of murine NK cells. In the absence of 2B4/CD48 interaction, NK cytotoxicity and IFN-gamma secretion on tumor target exposure is severely impaired. Impaired activation of NK cells in 2B4-deficient mice was also demonstrated by poor NK-mediated clearance of syngeneic tumor cells in these mice. Functional impairment of NK cells in the absence of 2B4/CD48 interactions was accompanied by defective calcium signaling, suggesting that the early signaling pathway of NK receptors is inhibited. Finally, homotypic interactions among NK cells through 2B4/CD48 was visualized by specific localization of GFP-tagged 2B4 onto NK-NK conjugation sites. Thus, these data identify a novel mechanism whereby NK effector function is regulated via homotypic 2B4/CD48 interactions.

Functional requirements for signaling through the stimulatory and inhibitory mouse NKR-P1 (CD161) NK cell receptors

The NK cell receptor protein 1 (NKR-P1) (CD161) molecules represent a family of type II transmembrane C-type lectin-like receptors expressed predominantly by NK cells. Despite sharing a common NK1.1 epitope, the mouse NKR-P1B and NKR-P1C receptors possess opposing functions in NK cell signaling. Engagement of NKR-P1C stimulates cytotoxicity of target cells, Ca2+ flux, phosphatidylinositol turnover, kinase activity, and cytokine production. In contrast, NKR-P1B engagement inhibits NK cell cytotoxicity. Nonetheless, it remains unclear how different signaling outcomes are mediated at the molecular level. Here, we demonstrate that both NKR-P1B and NKR-P1C associate with the tyrosine kinase, p56(lck). The interaction is mediated through the di-cysteine CxCP motif in the cytoplasmic domains of NKR-P1B/C. Disrupting this motif leads to abrogation of both stimulatory and inhibitory NKR-P1 signals. In addition, mutation of the consensus ITIM (LxYxxL) in NKR-P1B abolishes both its Src homology 2-containing protein tyrosine phosphatase-1 recruitment and inhibitory function. Strikingly, engagement of NKR-P1C on NK cells obtained from Lck-deficient mice failed to induce NK cytotoxicity. These results reveal a role for Lck in the initiation of NKR-P1 signals, and demonstrate a requirement for the ITIM in NKR-P1-mediated inhibition.

Marginating pulmonary-NK activity and resistance to experimental tumor metastasis: suppression by surgery and the prophylactic use of a beta-adrenergic antagonist and a prostaglandin synthesis inhibitor

Surgery is imperative for cancer treatment, but was suggested to suppress immunity and facilitate metastasis. Here we study the involvement of catecholamines and prostaglandins (PG) in such outcomes, and the role played by marginating-pulmonary (MP)-NK cells in controlling MADB106 metastasis. Non-operated and laparotomized F344 rats were injected postoperatively with a PG synthesis inhibitor (indomethacin, 4 mg/kg i.p.), a beta-blocker (nadolol, 0.6 mg/kg s.c.), both drugs, or vehicle. Rats were then inoculated intravenously with non-immunogenic syngeneic MADB106 cells, and 24 h later lung tumor retention was assessed, or 3 weeks later lung metastases were counted. Additionally, 12 h after surgery we harvested MP-NK cells and circulating-NK cells and compared their numbers and cytotoxicity against MADB106 cells and standard YAC-1 target cells. Surgery significantly increased MADB106 metastasis. Nadolol and indomethacin reduced this effect by approximately 50% when used alone, and significantly more (75%) when used together. Only MP-leukocytes exhibited NK cytotoxicity against MADB106 cells. Surgery markedly suppressed it, and nadolol and indomethacin additively restored it. Similar effects were observed assessing MP-NK and circulating-NK cytotoxicity against YAC-1 target cells. Alterations in the numbers of NK cells were partly associated with alterations in total MP-NK activity, but not with circulating-NK activity. Last, administrating nai ve rats with physiologically relevant doses of a beta-adrenergic agonist (metaproterenol), and/or with PGE2, additively and independently of each other promoted MADB106 metastasis, simulating the effects of surgery. These findings point at potential prophylactic measures in cancer patients undergoing surgery, and suggest a role for MP-NK cells in resisting metastasis of apparently insensitive tumors.

The r131 gene of rat cytomegalovirus encodes a proinflammatory CC chemokine homolog which is essential for the production of infectious virus in the salivary glands

Rat cytomegalovirus (RCMV) possesses two adjacent genes, r131 and r129, which have the potential to encode CC chemokine homologs. Interestingly, the amino acid sequences encoded by both genes show similarity to the sequence of the murine CMV (MCMV) MCK-2 protein, which is encoded by the m131/129 gene. In order to study the significance of the r131 gene in the pathogenesis of RCMV infection, we generated two different virus strains in which the r131 open reading frame is disrupted. Replication of these null mutant strains, designated RCMVdeltar131a and RCMVdeltar131b, was evaluated in vitro and in vivo. Both strains were found to replicate with a similar efficiency as wild-type (WT) RCMV in vitro. However, in contrast to WT virus, neither RCMVdeltar131a nor RCMVdeltar131b established a high-titer infection in the salivary glands of immunocompromised rats. Furthermore, in a local, rat footpad infection model, both recombinant viruses induced a significantly lower amount of paw swelling than did WT RCMV. Also, a higher number of infiltrating macrophages was observed in paws infected with WT RCMV than in those infected with the recombinants. Taken together, these results suggest that r131 (i) promotes inflammation at initial sites of inoculation and, subsequently, efficient virus dissemination to or infection of the salivary glands and (ii) might be involved in the persistence of virus infection, at least in the spleen. In addition, our data indicate that r131 represents the functional homolog of the MCMV m131/129 gene.