Hepatic Natural Killer Cells Research Articles

Reaction of fumonisin with glucose prevents promotion of hepatocarcinogenesis in female F344/N rats while maintaining normal hepatic sphinganine/sphingosine ratios.

The reaction of the primary amine of fumonisin B(1) (FB(1)) with glucose was hypothesized to detoxify this mycotoxin. Eighty 10-day-old female F344/N rats were injected intraperitoneally with diethylnitrosamine (DEN; 15 mg/kg of body weight). At 4 weeks of age, the weaned rats were randomly assigned to one of four treatment groups with 20 rats each. At 9 weeks of age, four rats from each treatment group were killed. At 12 weeks, another five rats from each group were killed. At 20 weeks of age, the remaining rats were killed. In comparison with the rats fed basal diet or FB(1)-glucose (containing 25 ppm of FB(1)), rats fed 8 ppm (residual amount of free FB(1) in the FB(1)-glucose mixture) or 25 ppm of FB(1) had greater alanine aminotransferase activity at 9 and 20 weeks of age (P < 0.001), greater endogenous hepatic prostaglandin E(2) production at 20 weeks of age (P < 0.05), and significantly lower plasma cholesterol at 20 weeks of age (P < 0.01). Placental glutathione S-transferase (PGST)-positive and gamma-glutamyltransferase (GGT)-positive altered hepatic foci (AHF) occurred only in rats fed 25 ppm of FB(1) at 20 weeks of age. Hepatic natural killer (NK) cell activities were similar among the four groups, but the percentage of total liver-associated mononuclear cells exhibiting the NKR-P1(bright) marker was significantly greater in rats fed FB(1)-glucose, FB(1) (8 ppm) and FB(1) (25 ppm) than in control rats at 9 weeks of age, and FB(1)-glucose-treated rats had significantly lower NKR-P1(bright) cells as a percentage of total liver-associated mononuclear cells than rats fed 25 ppm of FB(1) at 20 weeks of age (P < 0.05). PGST- or GGT-positive AHF were not detected in any treatment group at 9 or 12 weeks of age. At 20 weeks of age, half of the rats fed 25 ppm of FB(1) had PGST- and GGT-positive AHF. The sphinganine (Sa) concentration and the Sa/sphingosine (So) ratio were significantly greater in the rats fed 25 ppm of FB(1) diet as compared with the control groups at, respectively, 12 or 20 weeks of age. Therefore, modifying FB(1) with glucose seems to prevent FB(1)-induced hepatotoxicity and promotion of hepatocarcinogenesis. The Sa/So ratio was not the most sensitive biomarker of FB(1) toxicity.

Rat Hepatic Natural Killer Cells (Pit Cells) Express mRNA and Protein Similar to in Vitro Interleukin-2 Activated Spleen Natural Killer Cells

Pit cells are liver-specific natural killer (NK) cells that can be divided into high- (HD) and low-density (LD) subpopulations. The characteristics of pit cells were further investigated in this report. LD and HD pit cells express the specific NK-activation markers gp42, CD25, and ANK44 antigen. LD cells and IL-2-activated NK cells have a high mRNA expression of perforin, granzymes, interferon-γ, and tumor necrosis factor-α. LD pit cells, unlike spleen NK cells, have a weak response to IL-2 with regard to proliferation, cytotoxicity, and production of NK-related molecules. The characteristics of HD cells are intermediate between LD and spleen NK cells. These results show that pit cells, especially LD cells, possess characteristics similar to IL-2-activated NK cells. This is the first evidence on a molecular level that pit cells could be considered in vivo activated NK cells.

Participation of CD45, NKR-P1A and ANK61 antigen in rat hepatic NK cell (pit cell)mediated target cell cytotoxicity.

AIM:Several triggering receptors have been described to be involved in natural killer (NK) cell-mediated target cytotoxicity. In these studies, NK cells deriv ed from blood or spleen were used. Pit cells are liver-specific NK cells that possess a higher level of natural cytotoxicity and a different morphology when compared to blood NK cells. The aim of this study was to characterize the role of the NK triggering molecules NKR P1A, ANK61 antigen, and CD45 in pit cell medi ated killing of target cells.METHODS:( 51) Crrelease and DNA fragmentation were used to quantify target cell lysis and apoptosis, respectively.RESULTS:Flow cytometric analysis showed that pit cells expressed CD45, NK R P1A, and ANK61 antigen. Treatment of pit cells with monoclonal antibody (mAb)to CD45 (ANK74) not only inhibited CC531s or YAC 1 target lysis but also apopt osis induced by pit cells. The mAbs to NKR P1A (3.2.3) and ANK61 antigen (ANK61 )had no effect on pit cell mediated CC531s or YAC 1 target cytolysis or apopto sis, while they did increase the Fcgamma receptor positive (FcgammaR(+)) P815 cytolysi s and apoptosis. This enhanced cytotoxicity could be inhibited by 3,4 dichloroi socoumarin, an inhibitor of granzymes.CONCLUSION:These results indicate that CD45 participates in pit cell med iated CC531s and YAC-1 target cytolysis and apoptosis. NKR-P1A and ANK61 antigen on pit cells function as activation structures against Fc gammaR( +) P 815 cells, which was mediated by the perforin/granzyme pathway.

Liposome‐encapsulated OK‐432 specifically and sustainedly induces hepatic natural killer cells and intermediate T cell receptor cells

OK-432 is a biological response modifier used in Japan to augment host immunity and is known to increase the host antitumour response. By using liposomes, which are vesicles made from phospholipids that have a structure resembling the cell membrane, we encapsulated OK-432. Encapsulated OK-432 was injected into the tail veins of mice, and its effect was compared with that of unencapsulated OK-432 given intravenously. In mice that received either form of OK-432, both the number of natural killer (NK) and intermediate T cell receptor (intTCR) cells (intrahepatic T cells generated by extrathymic differentiation) increased markedly in the liver, with the peak level occurring 3 days after administration. Both forms of OK-432 also increased cytotoxic activity against Yac-1 cells. The increase in numbers of cells and in cytotoxic activity in the liver persisted for longer in mice that received encapsulated OK-432 than in animals that received unencapsulated OK-432. Because it has been shown that both NK and intTCR cells play an important role in tumour immunity, an increase in the number of such cells can be considered likely to have an increased antitumour effect. Encapsulated OK-432 elicited liver-specific augmentation of cytotoxic activity and the effect was more persistent than that produced by OK-432 given in the conventional form; therefore, it may be useful for the treatment of tumours, particularly those arising in the liver.

Involvement of LFA-1 in hepatic NK cell (pit cell)-mediated cytolysis and apoptosis of colon carcinoma cells

Backgroundl Aims: Previous studies have shown that hepatic natural killer (NK) cells, also called pit cells, have a higher cytotoxicity against certain tumor cells and have a higher expression of the cell adhesion molecule CD11a as compared with blood NK cells. We further investigated the involvement of the adhesion molecules, reported to be involved in target cell killing by blood NK cells, in pit cell-mediated colon carcinoma cell killing. Methods: 51Cr-release and DNA fragmentation were used to quantify target cell lysis and apoptosis, respectively. Adhesion of pit cells to CC531s monolayers was quantitated. Results: Flow cytometric analysis showed that pit cells expressed CD2, CD11a, CD18 and CD54. CC531s cells expressed only CD54. Treatment of freshly isolated pit cells with monoclonal antibodies (mAbs) to CD11a and CD18 inhibited not only the pit cell-mediated CC531s cytolysis but also the pit cell-induced apoptosis of CC531s cells. The combination of mAbs to CD11a, CD18 and CD54 further increased the inhibition of pit cell-mediated CC531s cytolysis and apoptosis. Anti-CD2 mAb did not affect these processes. The binding of pit cells to CC531s cells was also inhibited by anti-CD11a, and CD18 mAbs, but not by anti-CD2 mAb. Anti-CD54 mAb reduced the target cell killing and the binding only slightly. Conclusions: These results indicate that CD11a/CD18 (LFA-1) present on pit cells plays an important role in pit cell-mediated target cell adhesion, lysis and apoptosis. This finding might explain why pit cells, which have a higher expression of LFA-1 as compared to blood NK cells, are more cytotoxic against tumor cells as compared to blood NK cells.

Pit cells (Hepatic natural killer cells) of the rat induce apoptosis in colon carcinoma cells by the perforin/granzyme pathway.

The high mortality of colon cancer is to a large extent caused by the frequent occurrence of liver metastasis. This is remarkable, because the liver harbors two distinct cell populations that can eliminate invading cancer cells, namely hepatic natural killer (NK) cells and Kupffer cells. These hepatic NK cells, known as pit cells, are the most cytotoxic cells of the naturally occurring NK cells. However, the mechanism by which pit cells eliminate tumor cells is largely unknown. Because we recently found an indication that apoptosis is involved, we tried to assess the role of this mode of cell death using an in vitro system with isolated pure pit cells (>90%) and CC531s cells, a rat colon carcinoma (CC) cell line. Pit cells induced apoptosis in CC531s cells as shown by quantitative DNA fragmentation, agarose gel electrophoresis, and different modes of microscopy. When extracellular Ca2+ was chelated by ethylene glycol-bis(beta-aminoethyl ether)-N,N,-tetraacetic acid (EGTA) during coincubation or when the pit cells were preincubated with the granzyme inhibitor 3,4-dichloroisocoumarin (DCI), the induction of apoptosis was abolished. These results show that pit cells use the Ca2+-dependent perforin/granzyme pathway to induce apoptosis in the CC531s cells, and not the alternative Ca2+-independent Fas pathway. To further exclude the possibility of the involvement of the Fas pathway, we treated CC531s cells with recombinant Fas ligand. This treatment did not result in the induction of apoptosis, indicating that CC531s cells are resistant to Fas-mediated apoptosis. We conclude therefore that pit cells induce apoptosis in CC cells in vitro by the perforin/granzyme pathway.

Liver-associated natural killer activity in cirrhotic rats.

An impaired host defense mechanism is well known in patients with liver cirrhosis (LC). Using a sinusoidal lavage method, lymphocytes were obtained from LC rats that were administered thioacetamide, and natural killer (NK) activity was measured by 51Cr-release assay. The NK cell count was measured by flow cytometric analysis using monoclonal antibody (Mab) 3.2.3 and/or CD 3-8+ as markers for NK cells, and by immunohistochemical staining using Mab 3.2.3. Furthermore, interferon (IFN) alpha was administered to LC rats and the subsequent changes in hepatic NK activity and NK cell count were observed. In the large granular lymphocyte (LGL)-rich fraction (Fr.1, LGLs: 60-90%), the NK activity was significantly lower in the LC rats (40.0 +/- 3.8%) compared to that in the control rats (48.4 +/- 4.3%) (P < 0.005). In addition, the number of NK cells in the liver tissues of the LC rats was significantly lower compared to that in the liver tissues of the control rats by morphometric analysis (P < 0.05). For LC rats, NK activity of the Fr.1 24 hr after IFN alpha administration (5 x 10(4) IU/100 g body weight) increased significantly (P < 0.005). Hepatic NK activity and NK cell count were reduced in the LC rats, and recovered following IFN alpha administration. The results obtained in this study may give clues to better understanding the impaired host defense mechanism in LC patients.

The role of adhesion molecules in the recruitment of hepatic natural killer cells (pit cells) in rat liver.

Previous studies showed that blood large granular lymphocytes (LGL), which possess natural killer (NK) activity, develop within rat liver sinusoids into high-density (HD) and subsequently into low-density (LD) pit cells which show an increasing level and spectrum of tumor cytotoxicity. In this study, we investigated the role of adhesion molecules, such as CD2, CD11a, CD18, and CD54 in the recruitment of pit cells to the liver. Immunostaining for electron microscopy, and two color flow cytometry showed that most pit cells expressed CD2, CD11a, CD18, and CD54. After intravenous injections into rats with anti-CD2, anti-CD11a, and anti-CD18 antibodies, the number of pit cells per square millimeter in frozen sections of liver tissue decreased. Treatment of rats with zymosan increased the number of pit cells fivefold, whereas subsequent treatment with anti-adhesion-molecule antibodies resulted in approximately 60% lower number of pit cells. Anti-CD54, supposed to block CD54 expression on sinusoidal endothelial cells, also decreased the number of pit cells. The number of blood LGL was, however, not affected by these antibodies. These results indicate that blocking of CD2, CD11a, CD18, and CD54 antigens on blood LGL and/or liver endothelium decreased the number of pit cells in the liver. These adhesion molecules therefore play an important role in the recruitment of pit cells in the liver.

The role of adhesion molecules in the recruitment of hepatic natural killer cells (pit cells) in rat liver

Previous studies showed that blood large granular lymphocytes (LGL), which possess natural killer (NK) activity, develop within rat liver sinusoids into high-density (HD) and subsequently into low-density (LD) pit cells which show an increasing level and spectrum of tumor cytotoxicity. In this study, we investigated the role of adhesion molecules, such as CD2, CD11a, CD18, and CD54 in the recruitment of pit cells to the liver. Immunostaining for electron microscopy, and two color flow cytometry showed that most pit cells expressed CD2, CD11a, CD18, and CD54. After intravenous injections into rats with anti-CD2, anti-CD11a, and anti-CD18 antibodies, the number of pit cells per square millimeter in frozen sections of liver tissue decreased. Treatment of rats with zymosan increased the number of pit cells fivefold, whereas subsequent treatment with anti-adhesion-molecule antibodies resulted in approximately 60% lower number of pit cells. Anti-CD54, supposed to block CD54 expression on sinusoidal endothelial cells, also decreased the number of pit cells. The number of blood LGL was, however, not affected by these antibodies. These results indicate that blocking of CD2, CD11a, CD18, and CD54 antigens on blood LGL and/or liver endothelium decreased the number of pit cells in the liver. These adhesion molecules therefore play an important role in the recruitment of pit cells in the liver. (Hepatology 1996 Dec;24(6):1475-80)

Kinetics of organ-associated natural killer cells and intermediate CD3 cells during pulmonary and hepatic granulomatous inflammation induced by mycobacterial cord factor.

We investigated here the kinetics of natural killer (NK) cells and extrathymic T cells, which include intermediate CD3 cells and gamma delta T cells, in the cord factor-induced granulomatous inflammation of the lungs and liver. In Balb/c mice, pulmonary inflammation elevated the proportion of NK cells and that of extrathymic T cells to mononuclear cells in the lungs. C3H/He mice exhibited shorter-term inflammation of the lungs than Balb/c mice and accordingly showed a smaller increase in the proportions of pulmonary NK cells and intermediate CD3 cells. In the liver of Balb/c mice, hepatic NK cells increased as well with the granulomatous changes, while intermediate CD3 cells exhibited a transient decrease before they increased. The present study has demonstrated that granulomatous inflammation is accompanied by the increase of lung-associated NK cells and extrathymic T cells and that there exists a difference between these two mouse strains in the induction of these lymphocyte subsets by cord factor.

A high level of prostaglandin E2 (PGE2) in the portal vein suppresses liver-associated immunity and promotes liver metastases.

Prostaglandin E2 (PGE2) is generally accepted to be an immunosuppressant produced by cancer cells and their surrounding macrophages. Although several investigators have reported detecting high concentrations of PGE2 in the portal veins of patients with colorectal cancer, the relationship between these high concentrations of PGE2 in the portal vein and liver-associated immunity remains unclear. In this study, we attempted to determine if the portal administration of PGE2 suppresses the immune function of the liver in a rat model. Donryu rats were administered PGE2 via the portal vein for 7 days, following which the cytotoxic activity of hepatic sinusoidal lymphocytes (HSL) against natural killer (NK)-sensitive YAC-1 and rat syngeneic AH60C tumor cells was assessed. Purified HSL are spontaneously cytolytic; however, the continuous administration of PGE2 dramatically suppressed the cytotoxic activity of HSLs in a dose-dependent fashion. Flow cytometric analysis showed that the large granular lymphocyte (LGL) fraction, hepatic natural killer (pit) cells, and CD4-8+ killer/suppressor T cells were mainly reduced in number in the HSLs following PGE2 infusion. In this rat AH60C metastasis model, the continuous administration of PGE2 increased the number and size of metastatic tumor nodules in the liver, suggesting that high concentrations of PGE2 in the portal vein suppress liver-associated immunity and promote the formation of hepatic metastasis.

The role of Kupffer cells in the differentiation process of hepatic natural killer cells

Pit cells, or hepatic natural killer (NK) cells, present in rat liver sinusoids, represent an organ-associated NK cell population, with a higher level of activation and a different morphology when compared with peripheral blood NK cells. These cells are the result of an influx of peripheral blood NK cells in the liver microenvironment, followed by an activation or differentiation process toward the highly activated phenotype. In this work we investigated the role of Kupffer cells in this differentiation process of NK cells in the liver sinusoids. In vivo elimination of Kupffer cells with the macrophage cytotoxic drug dichloromethylene diphosphonate induced a decrease in number of hepatic NK cells that paralleled that of Kupffer cells. This effect was further investigated in vitro. Kupffer cell-conditioned medium appeared to enhance the viability, tumor-cytotoxic activity, and adherence of hepatic NK cells to liver endothelial cells in vitro. We conclude therefore that Kupffer cells, present in the microenvironment of the liver sinusoids, play an essential role in the differentiation process of peripheral blood NK cells to the highly activated hepatic NK cell population.

The role of Kupffer cells in the differentiation process of hepatic natural killer cells

Pit cells, or hepatic natural killer (NK) cells, present in rat liver sinusoids, represent an organ-associated NK cell population, with a higher level of activation and a different morphology when compared with peripheral blood NK cells. These cells are the result of an influx of peripheral blood NK cells in the liver microenvironment, followed by an activation or differentiation process toward the highly activated phenotype. In this work we investigated the role of Kupffer cells in this differentiation process of NK cells in the liver sinusoids. In vivo elimination of Kupffer cells with the macrophage cytotoxic drug dichloromethylene diphosphonate induced a decrease in number of hepatic NK cells that paralleled that of Kupffer cells. This effect was further investigated in vitro. Kupffer cell-conditioned medium appeared to enhance the viability, tumor-cytotoxic activity, and adherence of hepatic NK cells to liver endothelial cells in vitro. We conclude therefore that Kupffer cells, present in the microenvironment of the liver sinusoids, play an essential role in the differentiation process of peripheral blood NK cells to the highly activated hepatic NK cell population.

The number and distribution of hepatic natural killer cells (pit cells) in normal rat liver: an immunohistochemical study

Pit cells are a unique population of cells in sinusoids and peripheral blood, which can be considered natural killer (NK) cells with large granular lymphocyte (LGL) morphology. The aim of this study was to investigate the use of the monoclonal antibody (MAb) 3.2.3 as a specific marker of rat pit cells to detect their number and distribution in the liver. The number of 3.2.3-positive cells was comparable to the number of LGL in liver low-density (LD) and high-density (HD) pit cell fractions and in blood lymphocytes ( P > .05). Immunoelectron microscopy showed that nearly all LGL in hepatic LD and HD and in blood fractions were 3.2.3 positive. Using MAb 3.2.3 immunoperoxidase staining, the mean number of pit cells in liver frozen sections was determined to be 13.7 ± 1.1/mm 2. The number of pit cells was similar in the different liver lobes ( P > .05). Reduced nicotinamideadenine dinucleotide (NADH) oxidase histochemical staining, to visualize a portal to central vein gradient, combined with immunostaining was used to analyze the lobular distribution of pit cells. We found that 61.3% (17.1/mm 2) of pit cells were in the periportal area and 38.7% (10.8/mm 2) in the central area. We conclude that MAb 3.2.3 can be used as a specific marker of rat pit cells and therefore can be used to quantify rat pit cell number in various experimental models.

The number and distribution of hepatic natural killer cells (pit cells) in normal rat liver: An immunohistochemical study

Pit cells are a unique population of cells in sinusoids and peripheral blood, which can be considered natural killer (NK) cells with large granular lymphocyte (LGL) morphology. The aim of this study was to investigate the use of the monoclonal antibody (MAb) 3.2.3 as a specific marker of rat pit cells to detect their number and distribution in the liver. The number of 3.2.3-positive cells was comparable to the number of LGL in liver low-density (LD) and high-density (HD) pit cell fractions and in blood lymphocytes (P &gt; 0.05). Immunoelectron microscopy showed that nearly all LGL in hepatic LD and HD and in blood fractions were 3.2.3 positive. Using MAb 3.2.3 immunoperoxidase staining, the mean number of pit cells in liver frozen sections was determined to be 13.7 ± 1.1/mm2. The number of pit cells was similar in the different liver lobes (P &gt; 0.05). Reduced nicotinamide-adenine dinucleotide (NADH) oxidase histochemical staining, to visualize a portal to central vein gradient, combined with immunostaining was used to analyze the lobular distribution of pit cells. We found that 61.3% (17.1/mm2) of pit cells were in the periportal area and 38.7% (10.8/mm2) in the central area. We conclude that MAb 3.2.3 can be used as a specific marker of rat pit cells and therefore can be used to quantify rat pit cell number in various experimental models.

Determinants of differential liver-colonizing potential of variants of the MCA-38 murine colon cancer cell line.

We investigated factors that might contribute to the differing liver tumor colonizing potentials of MCA-38 colonic cancer cell line variants injected into the ileocolic veins of C57Bl/6J mice. Non-colonizing (MCA-38 CD) cells were sensitive to lysis by hepatic natural killer (NK) cells in vitro (51Cr-release assay) and cells with high liver-colonizing potential (MCA-38 LD) were resistant. Following abrogation of NK activity by treatment with anti-asialoGM1, liver-colonizing ability to LD cells but not CD cells was enhanced. MCA-38 CD cells were, however, capable of initial liver colonization after ileocolic vein injection. Differing patterns of membrane sialylation may have contributed to the contrasting hepatic tumorigenicities of LD and CD cells; beta-galactoside alpha 2,6-sialyltransferase mRNA levels and activity were approximately four-fold higher in LD than CD cells and qualitative and quantitative differences existed between their ganglioside profiles. In the MCA-38 model outlined, tumor cell susceptibility or resistance to NK lysis was a relatively unimportant determinant of liver-colonizing potential.

Effect of irradiation on hepatic natural killer cells

The rat liver contains a population of natural killer cells consisting of two morphologically and functionally different subsets, a low-density and a high-density fraction. In this work we describe the influence of low-dose radiation on hepatic natural killer activity. The effect on the cytotoxicity against YAC-1 lymphoma and CC531 colon adenocarcinoma tumor cells was measured in chromium-51 assays, and morphological changes were analyzed by means of electron microscopy. The low-density natural killer fraction showed increased cytotoxicity against YAC-1 which was associated with an increased binding of natural killer cells to the YAC-1 tumor cells shortly after irradiation. These phenomena were paralleled by an increased number of multivesicular bodies and cytoplasmic granules with an electron-lucent halo. In contrast, the other hepatic natural killer cell fraction, the high-density natural killer cells, did not show increased cytotoxicity, binding or morphological alterations. The radiation-stimulated lysis of YAC-1 cells was also observed when in vivo irradiated cells were isolated and tested immediately for in vitro lysis of YAC-1 cells. Sixteen hours after in vitro or in vivo irradiation, the cytotoxicity of hepatic natural killer cells against YAC-1 was no longer enhanced. The cytolysis of and binding of hepatic natural killer cells to CC531 colon adenocarcinoma cells was not stimulated by in vitro irradiation. From these experiments, we conclude that low-dose radiation stimulates the cytotoxicity of hepatic low-density natural killer cells against YAC-1 lymphoma cells immediately after irradiation as the result of enhanced binding of the cells to the tumor cells, in addition to the synthesis of new cytotoxic granules.

Effect of irradiation on hepatic natural killer cells

The rat liver contains a population of natural killer cells consisting of two morphologically and functionally different subsets, a low-density and a high-density fraction. In this work we describe the influence of low-dose radiation on hepatic natural killer activity. The effect on the cytotoxicity against YAC-1 lymphoma and CC531 colon adenocarcinoma tumor cells was measured in chromium-51 assays, and morphological changes were analyzed by means of electron microscopy. The low-density natural killer fraction showed increased cytotoxicity against YAC-1 which was associated with an increased binding of natural killer cells to the YAC-1 tumor cells shortly after irradiation. These phenomena were paralleled by an increased number of multivesicular bodies and cytoplasmic granules with an electron-lucent halo. In contrast, the other hepatic natural killer cell fraction, the high-density natural killer cells, did not show increased cytotoxicity, binding or morphological alterations. The radiation-stimulated lysis of YAC-1 cells was also observed when in vivo irradiated cells were isolated and tested immediately for in vitro lysis of YAC-1 cells. Sixteen hours after in vitro or in vivo irradiation, the cytotoxicity of hepatic natural killer cells against YAC-1 was no longer enhanced. The cytolysis of and binding of hepatic natural killer cells to CC531 colon adenocarcinoma cells was not stimulated by in vitro irradiation. From these experiments, we conclude that low-dose radiation stimulates the cytotoxicity of hepatic low-density natural killer cells against YAC-1 lymphoma cells immediately after irradiation as the result of enhanced binding of the cells to the tumor cells, in addition to the synthesis of new cytotoxic granules. (HEPATOLOGY 1994;19:1453–1458.)

Heterogeneity of hepatic natural killer cells after administration of biological response modifier (BRM)

Heterogeneity of hepatic natural killer cells after administration of biological response modifier (BRM)

Origin and differentiation of hepatic natural killer cells (pit cells).

Liver sinusoids contain a population of large granular lymphocytes or natural killer cells, originally termed pit cells. After isolation and purification, these cells were separated into a low-density and a high-density fraction. The liver low-density fraction differs significantly in morphology and function from cells of the blood, whereas the liver high-density fraction shows intermediate properties. In this study we demonstrate that this morphological and functional heterogeneity is based on subsequent steps of differentiation of the large granular lymphocytes within the liver. When cell proliferation was suppressed by sublethal total body irradiation, the life span of the hepatic large granular lymphocytes could be determined: high-density and low-density populations were totally depleted within 1 and 2 wk after irradiation, respectively. By using intravenous asialo-GM1 anti-serum to deplete animals of asialo-GM1-positive cells, we found that the depletion of the asialo-GM1-positive cells preceded the depletion of asialo-GM1-negative hepatic low-density large granular lymphocytes by approximately 1 wk. Direct evidence that the asialo-GM1-positive high-density large granular lymphocytes are precursors of the low-density large granular lymphocytes was given by adoptive transfer experiments with fluorescent-labeled high-density cells. Three days after their injection, labeled large granular lymphocytes were found in the hepatic low-density fraction of the recipient rat, and these cells had developed morphological characteristics of low-density large granular lymphocytes. It is concluded therefore that marginating blood large granular lymphocytes differentiate through high-density large granular lymphocytes into the typical liver specific low-density large granular lymphocytes or pit cells.