Supportive cellular elements for hepatic T cell differentiation: T cells expressing intermediate levels of the T cell receptor are cytotoxic against syngeneic hepatoma, and are lost after hepatocyte damage

Role of NK, NKT cells and macrophages in liver transplantation

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

Biology of autoreactive extrathymic T cells and B-1 cells of the innate immune system

Cumulative evidence has shown that extrathymic T cells can be autoreactive and that B-1 cells may produce autoantibodies. These T and B-1 cells, which form part of the innate immune system, tend to be activated simultaneously when conventional T and B cells are in a suppressive state, for example, when thymic atrophy occurs by stress or involution with aging. In other words, autoreactive T cells and autoantibody-producing B cells are different from thymus-derived T cells and bone marrow-derived B cells. Activated extrathymic T cells and B-1 cells are often observed in numerous autoimmune diseases, aging, malarial infection and chronic graft-versus-host disease. It is thought that the autoreactivity of extrathymic T cells and B-1 cells may be important for the elimination of "abnormal self" tissues or cells. However, over-activation of innate lymphocytes may be related to the onset of disease or self-tissue destruction. However, it must be emphasized that the autoreactivity of innate lymphocytes is not generated by failure of the thymic pathway of T-cell differentiation or the conventional pathway of B-2 cells.

Antitumor immunity produced by the liver Kupffer cells, NK cells, NKT cells, and CD8 CD122 T cells

Mouse and human livers contain innate immune leukocytes, NK cells, NKT cells, and macrophage-lineage Kupffer cells. Various bacterial components, including Toll-like receptor (TLR) ligands and an NKT cell ligand (α-galactocylceramide), activate liver Kupffer cells, which produce IL-1, IL-6, IL-12, and TNF. IL-12 activates hepatic NK cells and NKT cells to produce IFN-γ, which further activates hepatic T cells, in turn activating phagocytosis and cytokine production by Kupffer cells in a positive feedback loop. These immunological events are essentially evoked to protect the host from bacterial and viral infections; however, these events also contribute to antitumor and antimetastatic immunity in the liver by activated liver NK cells and NKT cells. Bystander CD8⁺CD122⁺ T cells, and tumor-specific memory CD8⁺T cells, are also induced in the liver by α-galactocylceramide. Furthermore, adoptive transfer experiments have revealed that activated liver lymphocytes may migrate to other organs to inhibit tumor growth, such as the lungs and kidneys. The immunological mechanism underlying the development of hepatocellular carcinoma in cirrhotic livers in hepatitis C patients and liver innate immunity as a double-edged sword (hepatocyte injury/regeneration, septic shock, autoimmune disease, etc.) are also discussed.

Coincidence of autoantibody production with the activation of natural killer T cells in α-galactosylceramide-mediated hepatic injury

Natural killer T (NKT) cells are known to be specifically activated by α-galactosylceramide (α-GalCer) via their interaction with CD1d. At that time, NKT cells mediate autoreactivity and eventually induce hepatic injury. As these immune responses resemble acute autoimmune hepatitis, it was examined whether autoantibody production and the activation of autoantibody-producing B-1 cells were accompanied by this phenomenon. Autoantibodies against Hep-2 cells and double-stranded DNA were detected in sera as early as day 3 (showing a peak at day 14) when mice were treated with α-GalCer. On day 3, B220(low) cells appeared in the liver. These B220(low) cells were CD5(-) (i.e. B-1b cells) and CD69(+) (an activation marker). Primarily, such B220(low) cells were present in the peritoneal cavity, but the proportion of B220(low) cells increased with the administration of α-GalCer even at this site. In parallel with the appearance of B220(low) cells in the liver, hepatic lymphocytes acquired the potential to produce autoantibodies in in vitro cell culture in the presence of lipopolysaccharide. These results suggested that hepatic injury induced by α-GalCer administration resembled acute autoimmune hepatitis and that the major effector lymphocytes were NKT cells with autoreactivity and autoantibody-producing B-1 cells.

Immunosuppression in the livers of mice with obstructive jaundice participates in their susceptibility to bacterial infection and tumor metastasis

Although patients with obstructive jaundice are susceptible to bacterial infections and cancers, the mechanisms remain to be elucidated. In the present study, liver mononuclear cells (MNCs) of bile duct-ligated (BDL) mice were immunologically assessed. Liver natural killer T cells were greatly decreased within 24 h after BDL. Upon injection of Escherichia coli (E. coli; 10 colony-forming units) at 7 days after the procedure, all BDL mice had died, but no sham mice died. Consistently, an overgrowth of E. coli was seen in the livers of BDL mice. Although the serum IL-12 and IL-18 levels after E. coli challenge in BDL mice were higher than those in sham mice, the IFN-gamma level was greatly suppressed. However, exogenous IFN-gamma injection significantly increased BDL mouse survival after E. coli challenge. Furthermore, liver MNC of BDL mice exhibited a lower cytotoxic activity against tumors, and BDL mice intravenously injected with liver metastatic EL-4 cells showed markedly increased EL-4 metastases. The total bile acids, as well as the bile acid fractions, increased in the sera and liver. IFN-gamma production by liver MNC from normal mice stimulated with LPS in vitro was inhibited by the addition of bile acids, whereas, conversely, the production of IL-12 and IL-18 increased. In conclusion, liver natural killer T cells were diminished in BDL mice, and the function of liver MNC (IFN-gamma production) was also impaired presumably due to increased bile acids. This may partly explain the increased susceptibility of BDL mice to bacterial infections and tumor metastasis.

Co-appearance of autoantibody-producing B220(low) B cells with NKT cells in the course of hepatic injury

Severe hepatic injury is induced by Concanavalin A (Con A) administration in mice, the major effector cells being CD4(+) T cells, NKT cells and macrophages. Since autologous lymphocyte subsets are associated with tissue damage, Con A-induced hepatic injury is considered to be autoimmune hepatitis. However, it has remained to be investigated how autoantibodies and B-1 cells are responsible for this phenomenon. In this study, it was demonstrated that autoantibodies which were detected using Hep-2 cells in immunofluorescence tests and using double-strand (ds) DNA in the ELISA method, appeared after Con A administration (a peak at day 14). Moreover, autoantibody-producing B220(low) cells (i.e., B-1 cells) also appeared at this time. Purified B220(low) cells were found to have a potential to produce autoantibodies. These results suggest that Con A-induced hepatic injury indeed includes the mechanism of autoimmune hepatitis.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Activation of mouse natural killer T cells accelerates liver regeneration after partial hepatectomy

BACKGROUND & AIMS

Activation of natural killer T cells with the synthetic ligand alpha-galactosylceramide (alpha-GalCer) induced hepatotoxicity through the tumor necrosis factor (TNF) and Fas-ligand-mediated pathway in aged mice. The aim of this study was to elucidate how alpha-GalCer-activated natural killer T cells function in hepatocyte proliferation and liver regeneration in partially hepatectomized (PHx) mice.

METHODS

Mice were injected with alpha-GalCer at 36 hours after 70% PHx. Hepatocyte mitosis was evaluated by either mitotic figures or proliferating cell nuclear antigen staining. The role of TNF and Fas-ligand in hepatocyte mitosis also was assessed.

RESULTS

In PHx mice injected with alpha-GalCer, hepatocyte mitosis was greatly enhanced at 44 hours after surgery and the increase was more obvious in aged mice than in young mice. The expression of both TNF receptor 1 and Fas-ligand in liver natural killer T cells tended to increase after alpha-GalCer injection in PHx mice. Treatment of mice with anti-NK1.1 Ab 3 days before and just after hepatectomy greatly inhibited the effect of alpha-GalCer on hepatocyte mitosis and liver regeneration. Furthermore, pretreatment of PHx mice with either anti-TNF Ab or anti-FasL Ab 1 hour before alpha-GalCer injection mostly abrogated the increase in hepatocyte proliferation. alpha-GalCer injection did not accelerate hepatocyte proliferation in Fas-mutated lpr mice after PHx. CD1d-/- mice without alpha-GalCer injection showed decreased hepatocyte mitosis after PHx.

CONCLUSIONS

Activated natural killer T cells help hepatocyte proliferation and liver regeneration after PHx via the TNF and Fas/Fas-ligand-mediated pathway.

Numbers and activities of CD56+ T cells and natural killer cells in cirrhotic livers with hepatitis C

AIM: To study the numbers and anti-tumor activities of CD56⁺ T cells and natural killer (NK) cells in cirrhotic liver with hepatitis C (HC).

METHODS: Hepatic mononuclear cells (MNC) were isolated from liver specimens obtained from the patients (n = 16) with HC-induced cirrhosis by liver biopsy. In addition, the numbers of CD56⁺ T cells and natural killer cells were determined by flow cytometry. Liver MNC and peripheral blood mononuclear cells (PBMC) were co-cultured with the interleukin-2 (IL-2), respectively, and the production of interferon-g (IFN-g) and the antitumor activity were measured.

RESULTS: The percentages of CD56⁺ T cells among hepatic MNC in health individuals, HC and HC-induced cirrhosis patients were 20.4% ± 6.2%, 11.2% ± 3.1% and 5.0% ± 1.6%, respectively; the proportions of NK cells among liver MNC in the three groups were 31.1% ± 9.7%, 31.6% ± 8.3% and 18.3% ± 5.4%, respectively; the productions of IFN-g in the three groups were 7.4 ± 2.4, 3.2 ± 1.8 and 1.9 ± 0.5 mg/L, respectively; the anti-tumor activities hepatic MNC in the three groups were 61.1% ± 17.1%, 59.2% ± 14.6%, and 26.7% ± 8.5%, respectively. For the above four groups of parameters, the changes in HC-induced cirrhosis patients was the most significant (P < 0.05).

CONCLUSION: The numbers and anti-tumor activities of CD56⁺T cells and NK cells are decreased in cirrhotic livers with HC.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

Decrease of CD56(+)T cells and natural killer cells in cirrhotic livers with hepatitis C may be involved in their susceptibility to hepatocellular carcinoma

CD56(+)T cells and CD56(+)natural killer (NK) cells are abundant in the human liver. The aim of this study was the further characterization of these cells in the liver with or without hepatitis C virus (HCV) infection. Liver mononuclear cells (MNC) were isolated from liver specimens obtained from the patients during abdominal surgery. In addition to a flow cytometric analysis, liver MNC and PBMC were cultured with the immobilized anti-CD3 Ab, IL-2, or a combination of IL-2 and IL-12 and their IFN-gamma production and the antitumor cytotoxicity were assessed. The liver MNC of HCV (-) patients contained 20% CD56(+)T cells whereas the same proportions decreased to 11% in chronic hepatitis livers and to 5% in cirrhotic livers. The proportion of NK cells also decreased in the cirrhotic livers. On the other hand, the populations of these cells in PBMC did not significantly differ among patient groups. The IFN-gamma production and the cytotoxicity against K562 cells, Raji cells, and a hepatocellular carcinoma, HuH-7 cells, greatly decreased in the cirrhotic liver MNC. In contrast, the cytotoxicity in PBMC did not significantly differ among the patient groups and was lower than that in the liver MNC of HCV (-) patients. CD56(+)T cells and NK cells but not regular T cells purified from liver MNC cultured with cytokines showed potent cytotoxicities against HuH-7 cells. These results suggest that a decreased number of CD56(+)T cells and NK cells in cirrhotic livers may be related to their susceptibility to hepatocellular carcinoma.

Disparate effect of beige mutation on cytotoxic function between natural killer and natural killer T cells

Beige mice lack natural killer (NK) cytotoxicity, although NK cells are normally present. In recent studies, NK T cells have been newly identified. We therefore examined the number and function of NK T cells in beige mice. The number of NK T cells was at a normal level in the liver of beige mice. NK cytotoxicity was decreased in the liver of these mice, whereas NK T cytotoxicity was intact. When immunochemical staining for perforin was conducted, the majority of NK cells and the minority of NK T cells in beige mice carried a giant granule, containing perforin, in the cytoplasm. In the case of control B6 mice, the majority of NK cells and the minority of NK T cells had multiple, dispersed granules containing perforin. These results suggest that NK T cytotoxicity is unaffected by the beige mutation, owing to their cytotoxicity being mediated without the secretion system of perforin.

Resistance of extrathymic T cells to stress and the role of endogenous glucocorticoids in stress associated immunosuppression

When mice were exposed to restraint stress for 12 or 24 h, severe lymphopenia was induced in all immune system organs, including the liver and the thymus. However, in adrenalectomized mice, this response was completely absent. Phenotypic characterization revealed that interleukin (IL)-2Rbeta+CD3int cells (i.e. extrathymic T cells) with CD4+ phenotype and the NK1.1+ subset of CD3int cells (i.e. NKT cells) in the liver as well as the mature conventional T cells in the thymus were resistant to such stress. In adrenalectomized mice, there was no significant change in the distribution of lymphocyte subsets in all tested organs before stress. Interestingly, the number of lymphocytes in the liver and spleen and the proportion of NKT cells in the liver rather increased after stress in these adrenalectomized mice. Therefore, endogenous steroid hormones were indicated to be important in the induction of immunosuppressive states after stress. Among stress associated cytokines, the secretion of tumour necrosis factor (TNF)-alpha was completely suppressed while that of IL-6 was partially suppressed in adrenalectomized mice. These results suggest that endogenous steroid hormones are important for the induction of the stress associated immunosuppression and that NKT cells are resistant to stress, namely, resistant to exposure to endogenous steroid hormones.

Quick recovery in the generation of self-reactive CD4low natural killer (NK) T cells by an alternative intrathymic pathway when restored from acute thymic atrophy

The thymus comprises the mainstream of T cell differentiation which produces conventional T cells and an alternative pathway which produces primordial T cells with intermediate density of T cell receptor (TCR)-CD3 complex on the surface (i.e. intermediate TCR cells or TCRint cells). We induced acute thymic atrophy in mice by an administration of hydrocortisone (10 mg) or irradiation (6.5 Gy). It was demonstrated that CD3intCD4lowNK1.1+ T cells were immediately generated by an alternative intrathymic pathway without passing through the double-positive CD4+8+ stage, when restored from thymic atrophy (days 3-14). These CD3intCD4lowNK1.1+ T cells mediated self-reactivity and appeared even in the periphery. mRNA of an invariant chain of TCR Valpha14Jalpha281 gene product was detected in these CD4low T cells, but not remaining CD4high T cells. The mainstream of T cell differentiation in the thymus was not restored up to day 14 and there was no leakage of self-reactive clones into the population generated through the mainstream. These results reveal that an alternative intrathymic pathway is associated with the generation of self-reactive T cells, in an early restoration phase after thymic atrophy.

Activation of mouse liver natural killer cells and NK1.1(+) T cells by bacterial superantigen-primed Kupffer cells

Although bacterial superantigens have been well characterized as potent stimulators of T cells, their role in natural killer (NK)-type cells remains largely unknown. In the present study, we examined the effect of bacterial superantigens on mouse liver NK cells and NK1.1 Ag(+) (NK1(+)) T cells. C57BL/6 mice were intravenously injected with staphylococcal enterotoxin B (SEB) or streptococcal pyrogenic exotoxin A (SPE-A), and mononuclear cells (MNC) of various organs were obtained from mice 4 hours after being injected with superantigen. MNC were cultured for 48 hours, and interferon gamma (IFN-gamma) levels of supernatants were measured. The antitumor cytotoxicities of the liver and spleen MNC were also evaluated 24 hours after the mice were injected with superantigen. Liver MNC produced more IFN-gamma than did splenocytes, and peripheral blood and lung MNC did not produce any detectable IFN-gamma. In addition, liver MNC acquired a potent antitumor cytotoxicity by the SEB injection, and both NK cells and NK1(+)T cells but not cluster of differentiation (CD)8(+) T cells were responsible for the cytotoxicity as demonstrated by either in vivo or in vitro cell depletion experiments, and the NK-type cells were partly responsible for the increased serum IFN-gamma. Activation of liver NK-type cells was also supported by the fact that liver NK cells proportionally increased and NK1(+) T cells augmented their CD11a expressions after SEB injection. The pretreatment of mice with anti-IFN-gamma Ab and/or with anti-interleukin-12 (IL-12) Ab diminished the SEB-induced cytotoxicity of liver MNC. Furthermore, the in vivo depletion of Kupffer cells decreased the SEB-induced cytotoxicity of liver MNC. Consistent with these results, liver MNC stimulated with superantigens in the presence of Kupffer cells in vitro produced a greater amount of IFN-gamma than did the liver MNC without Kupffer cells or splenocytes. Our results suggest that bacterial superantigen-primed Kupffer cells produce IL-12 and other monokines, while also nonspecifically activating both NK cells and NK1(+) T cells to produce IFN-gamma.

Administration of glucocorticoids markedly increases the numbers of granulocytes and extrathymic T cells in the bone marrow

Glucocorticoids, steroid hormones, are widely used as an anti-inflammatory drug. However, clinicians have sometimes encountered adverse drug reactions such as ulcers and tissue damage. In this study, we investigated how such adverse reactions of glucocorticoids are evoked, using an experimental mice model. When hydrocortisone (0.5 or 1.0 mg/day/mouse) was administered daily for 2 weeks, severe leukocytopenia was induced in all immune system organs. However, granulocytes (Gr-1(+)Mac-1(+)) were increased in number in the bone marrow and peripheral blood. This seemed to be due to an elevated level of myelopoiesis in the bone marrow. As well as increasing in number, granulocytes were functionally activated as estimated by the Ca2+ influx and superoxide production. The proportion of primordial T cells (CD3(int)IL-2Rbeta+) in the thymus and the number of primordial T cells in the bone marrow also increased. Mice administered hydrocortisone became susceptible to stress. Thus, these mice showed gastric ulcers when they were exposed to restraint stress for 12 h. These results suggest that activated granulocytes and primordial T cells might provide a mechanism involved in steroid ulcers and tissue damage, possibly through the superoxide production of granulocytes and the autoreactivity of primordial T cells.

Expansion of Extrathymic T Cells as Well as Granulocytes in the Liver and Other Organs of Granulocyte-Colony Stimulating Factor Transgenic Mice: Why They Lost the Ability of Hybrid Resistance

When we attempted to characterize the immunological state in G-CSF transgenic mice, a large number of not only granulocytes but also lymphoid cells expanded in various immune organs. Such lymphoid cells were present at unusual sites of these organs, e.g., the parenchymal space in the liver. We then determined the phenotype of these lymphoid cells by immunofluorescence tests. It was demonstrated that CD3intIL-2Rβ+ cells (i.e., extrathymic T cells), including the NK1.1+ subset of CD3int cells (i.e., NKT cells), increased in the liver and all other tested organs. These T cells as well as NK cells mediated NK and NK-like cytotoxicity, especially at youth. However, they were not able to mediate such cytotoxicity in the presence of granulocytes. This result might be associated with deficiency in the hybrid resistance previously ascribed to these mice. In other words, G-CSF transgenic mice had a large number of extrathymic T cells (including NKT cells) and NK cells that mediate hybrid resistance, but their function was suppressed by activated granulocytes. Indeed, these granulocytes showed an elevated level of Ca2+ influx upon stimulation. The present results suggest that, in parallel with overactivation of granulocytes, extrathymic T cells and NK cells are concomitantly activated in number but that their function is suppressed in G-CSF transgenic mice.

Protective effect of NK1.1(+) T cells as well as NK cells against intraperitoneal tumors in mice

Peritoneal resident cells of mice normally contain small populations of NK cells and NK1.1(+) alphabetaT cells. These populations increased after either 3LL or EL4 tumor inoculations into the peritoneal cavity. In vivo depletion of NK cell alone by anti-asialo GM1 (ASGM1) Ab significantly decreased survival time of tumor-injected mice, while depletion of both NK cells and NK1.1(+) T cells by anti-NK 1.1 Ab greatly shortened mouse survival time. NK1. 1(+) T cells in peritoneal cavity consist of a larger proportion of double-negative T cells and smaller populations of CD4(+) T cells and Vbeta8(+) T cells compared with liver NK1.1(+) T cells and normally lack Vbeta2(+) T cells. Tumor inoculation induced rapid IL-12 and IFN-gamma mRNA in tumor-infiltrating mononuclear cells (TIM). Although anti-NK1 Ab pretreatment in vivo abrogated IFN-gamma mRNA expression and IFN-gamma production of TIM, NK cell depletion alone by anti-ASGM1 Ab pretreatment retained IFN-gamma mRNA expression and partly inhibited IFN-gamma production of TIM. Peritoneal NK cells as well as NK1.1(+) T cells but not NK1.1(-) T cells of 3LL cell- or EL4 cell-injected mice showed cytotoxicities against the same tumor cells. Further, either anti-IL-12 Ab or anti-IFN-gamma Ab ip injection significantly shortened EL4 cell-inoculated mouse survival time. Our findings suggest that peritoneal macrophages activated by tumors produce IL-12 which activates NK cells and NK1.1(+) T cells to produce IFN-gamma and both NK cells and NK1.1(+) T cells are important in suppressing the growth of the intraperitoneal tumors.

Development of intraepithelial T lymphocytes in the intestine of irradiated SCID mice by adult liver hematopoietic stem cells from normal mice

BACKGROUND/AIMS

We recently reported the adult mouse liver to contain c-kit+ stem cells that can give rise to multilineage leukocytes. This study was designed to determine whether or not adult mouse liver stem cells can generate intraepithelial T cells in the intestine as well as to examine the possibility that adult liver c-kit+ stem cells originate from the fetal liver.

METHODS

Adult liver mononuclear cells, bone marrow (BM) cells, liver c-kit+ cells or bone BM c-kit+ cells of BALB/c mice were i.v. transferred into 4 Gy irradiated CB17/-SCID mice. In other experiments, fetal liver cells from Ly5.1 C57BL/6 mice and T cell depleted adult BM cells from Ly5.2 C57BL/6 mice were simultaneously transferred into irradiated C57BL/6 SCID mice (Ly5.2). At 1 to 8 weeks after cell transfer, the SCID mice were examined.

RESULTS

Not only BM cells and BM c-kit+ cells but also liver mononuclear cells and liver c-kit+ cells reconstituted gamma delta T cells, CD4+ CD8+ double-positive T cells and CD8 alpha+beta- T cells of intestinal intraepithelial lymphocytes of SCID mice. Injection of a mixture of fetal liver cells from Ly5.1 C57BL/6 mice and adult BM cells from Ly5.2 C57BL/6 mice into Ly5.2 C57BL/6 SCID mice induced both Ly5.1 and Ly5.2 T cells, while also generating c-kit+ cells of both Ly5.1 and Ly5.2 origins in the liver.

CONCLUSIONS

Adult mouse liver stem cells were able to generate intestinal intraepithelial T cells of the SCID mice, and it is thus suggested that some adult liver stem cells may indeed be derived from the fetal liver.

Mechanisms involved in graft-versus-host disease induced by the disparity of minor histocompatibility M1s antigens

In this study we investigated which type of T cells: high T-cell receptor (TCRhigh, cells of thymic origin) or intermediate TCR (TCRint, cells of extrathymic origin), expanded in the liver and other organs, resulting in the induction of graft-versus-host disease (GVHD) with minor lymphocyte stimulating (M1s) disparity. When 6.5 Gy-irradiated BALB/c (H-2d M1s-1b2a) mice were injected with interleukin-2 receptor beta-chain(-) (IL-2Rbeta(-)) CD3high cells purified from the spleen of B10.D2 (H-2d M1s-1b2b) mice, IL-2Rbeta(+)CD3high cells expanded in the liver and other organs of recipient mice. The majority of these cells were found to be IL-2Ralpha(-)Mel-14(-)CD4(+)Vbeta3(+) in GVHD mice. The CDR3 region in their TCR-alphabeta (i.e. N-Dbeta-N) was polyclonal, although there were skewed usages of Vbeta3 and Jbeta2.4. The majority of cells were confirmed to be of donor origin by the individual discrimination method, namely, they originated from isolated IL-2Rbeta(-)CD3high cells. Interestingly, these T cells lacked cytotoxicity against both a natural killer (NK)-sensitive target and thymocytes with M1s disparity and nondisparity. Another important finding was that activated granulocytes expanded at generalized sites in GVHD mice. The present results raise the possibility that M1s disparity is mainly recognized by TCRhigh cells with unique properties but that direct effector cells that induce GVHD might not be such T cells but rather accompanied granulocytes.

Intermediate TCR cells can induce graft-versus-host disease after allogeneic bone marrow transplantation

Mice fall victim to GVHD when subjected to immunosuppressive treatment and injected with allogeneic bone marrow cells. A major population of cells associated with GVHD is known to be T cells. However, whether such T cells are of thymic or extrathymic origin is obscure. We applied two immunosuppressive conditions, 9 and 6.5 Gy irradiation, to C3H/He mice (H-2k). Bone marrow cells for injection were obtained from C57BL/6 (B6) mice (H-2b). The 9-Gy mice were reconstituted by lymphocytes of donor origin and showed GVHD, whereas 6.5-Gy mice were reconstituted by lymphocytes of recipient origin and showed mild GVHD. The liver was the organ where the reconstitution of lymphocytes occurred efficiently, and a major lymphocyte subset was intermediate (int) CD3 cells (i.e., CD3int cells) in both mice. CD3int cells had the properties of extrathymic T cells, showing the phenotype of NK1.1 + CD3int using invariant V alpha 14 chain. In 6.5-Gy mice, allogeneic cells were rejected by extrathymic T cells of recipient origin. The stored CD3int cells from the liver of 9-Gy mice evoked similar GVHD when transferred into 6.5-Gy irradiated C3H/He mice. These results suggest that CD3int cells of extrathymic origin are a major population for the induction of GVHD under immunosuppressive conditions.

Antimetastatic effect of NK1+ T cells on experimental haematogenous tumour metastases in the liver and lungs of mice

Depletion of both natural killer 1.1+ (NK1+) intermediate alpha beta T-cell receptor (int T) cells and NK cells by in vivo treatment with anti-NK1 antibody greatly increased hepatic metastases of intravenously injected EL4 cells as well as pulmonary metastases of 3LL cells in C57BL/6 mice. However, depletion of NK cells alone by anti-asialo GM1 (AGM1) antibody treatment did not increase the metastases in either organ. Interleukin-12 (IL-12) administration into mice induced strong cytotoxicities of NK cell-depleted liver and lung mononuclear cells (MNC) comparable to those without NK-cell depletion and inhibited metastases in either organ. In contrast, in both NK cell- and NK1+ int T-cell-depleted mice, IL-12 could not induce cytotoxic activity of liver and lung MNC and metastases in both organs increased with or without IL-12 treatment. These results confirmed the fact that NK+ int T cells are more potent antitumour effectors than NK cells against experimental haematogenous tumour metastases.

Numerical and functional characteristics of lymphocyte subsets in centenarians

The immune system in the aged is a very interesting subject for study. In this study, analysis was extended to extrathymic T cells as well as NK cells and "conventional" T cells (i.e., thymus-derived T cells) in terms of their constitution and function in both healthy and unhealthy centenarians. Middle-aged persons were used as controls. Healthy and unhealthy centenarians showed lower levels in the proportion and absolute number of lymphocytes. The major change in the constitution of lymphocyte subsets was increased levels in the proportion of NK cells (CD56+/CD57+) and extrathymic T cells (CD3+CD57+). Inversely, conventional T cells decreased in proportion and function (i.e., proliferative response to mitogen). Although NK cells increased in centenarians, NK activity by whole lymphocytes and the purified NK fraction decreased. The difference between healthy and unhealthy centenarians was small in all parameters, the only difference being a lower level of expression of CD56 antigens on CD57+ T cells in unhealthy centenarians. These results indicate that there is a major shift in lymphocyte population from conventional T cells to NK cells and extrathymic T cells with aging. Concerning the age-associated increases in CD56+ T and CD57+ T cells, these cells correspond to NK1+ T cells in mice.

Autologous killing by a population of intermediate T-cell receptor cells and its NK1.1+ and NK1.1- subsets, using Fas ligand/Fas molecules

Self-reactive clones, estimated by anti-V beta monoclonal antibodies (mAb) in conjunction with the Mls system, are confined to a population of intermediate (int) T-cell receptor (TCR) (or CD3) cells (i.e. TCRint cells), but are not found among TCRhigh cells. The next questions to be answered are whether autologous killing is confined to TCRint cells and how such killing is mediated. In this study, 51Cr-labelled thymocytes of syngeneic or allogeneic origin were used as target cells (4-hr assay). When liver and splenic mononuclear cells (MNC) obtained from B6 mice were used as effector cells, prominent autologous killing was seen in liver MNC, but not splenic MNC. Such killing was not seen when thymocytes from B6-lpr/lpr mice (i.e. Fas-) were used as target cells, nor when liver MNC from MRL-gld/gld mice (i.e. Fas ligand-) were used as effector cells (target thymocytes of MRL(-)+/+ mice). Cell separation experiments using a cell sorter revealed that autologous killing was mediated for the most part by CD3int cells, while allogeneic killing was mediated entirely by natural killer (NK) cells, TCRint cells and TCRhigh cells. Among CD3int cells, the NK1.1+ subset (i.e. NK1.1+ T cells) manifested a higher level of autologous killing than did the NK1.1- subset. Consistent with the results of a functional assay, it was found by reverse-transcription-polymerase chain reaction (RT-PCR) assay that CD3int cells among liver MNC showed the expression of Fas ligand mRNA, while thymocytes expressed Fas mRNA. When class I major histocompatibility complex (MHC)- thymocytes (from beta 2-microglobulin-deficient mice) were used as target cells, NK cells, but not CD3int cells, showed potent cytotoxicity. These results suggest that autologous killing is a major function of TCRint cells with self-reactivity, and that such killing is mediated by means of Fas ligand/Fas molecules.

Absolute dependence of T cell receptor(hi) cell generation and relative dependence of T cell receptor(int) cell generation on the thymus

Recent evidence indicates that conventional T cells are generated by the mainstream of T cell differentiation in the thymus and acquire a high density of T cell receptor expression (i.e. TCRhi). In contrast, primordial T cells (or NK1.1+ T cells) are generated by the extrathymic pathways or an alternative intrathymic pathway and express an intermediate density of TCR (i.e. TCRint). To obtain further evidence, it was examined how thymus grafting influenced the distribution of T cell populations in athymic nude mice. When BALB/c nu/nu mice were engrafted with thymocyte-depleted BALB/c+/+ fetal thymi, two changes emerged after grafting: nude mice generated TCRhi cells de novo in the periphery as well as in the grafted thymi, and the absolute number of interleukin-2 receptor beta chain+ TCRint cells increased prominently in number in the periphery. Among thymic hormones tested, the administration of thymosin alpha induced a slight expansion of CD3int cells in nude mice. To examine a possible interaction of TCRint cells with TCRhi cells in the periphery, B6 nu/nu mice (Ly5.2+) were injected with TCRhi cells purified from the spleen of B6 Ly5.1 congenic mice. In this case, TCRint (Ly5.2+) cells expanded well in all tested organs of nude mice. These results suggest that the generation of TCRhi cells is absolutely dependent on the thymus and that TCRint cells expand under the influence of the thymus (humoral) and due to interaction with thymus-derived conventional T cells.

c-kit+ stem cells and thymocyte precursors in the livers of adult mice

Livers of the adult mice contain c-kit+ stem cells that can reconstitute thymocytes, multiple lineage cells, and bone marrow (BM) stem cells. Transfer of 1 x 10(7) hepatic mononuclear cells (MNC) and 5 x 10(4) hepatic c-kit+ cells of BALB/c mice induced DP thymocytes within a week in four Gy-irradiated CB17/-SCID mice, but 2 wk were required for BM cells or BM c-kit+ cells to produce DP thymocytes. Moreover, B cell-depleted BM cells or liver MNC of SCID mice that had been rescued by hepatic MNC of BALB/c mice again reconstituted thymus and B cells of other irradiated SCID mice. CD3- IL-2R beta- populations of both BM cells and hepatic MNC of C57BL/6 (B6) mice could generate T cells with intermediate TCR (mostly NK1.1-) in the liver of irradiated B6 SCID mice before thymic reconstitution (extrathymic T cells). Furthermore, transfer of liver c-kit+ cells of B6-Ly 5.1 mice into irradiated B6 SCID (Ly5.2) mice revealed that liver c-kit+ cells can reconstitute myeloid and erythroid lineage cells. These results strongly suggest that the liver contains pluripotent stem cells and serves an important hematopoietic organ even into adulthood.