The proliferation and life-span of rat large granular lymphocytes: effects of cytokines

Two complementary rat NK cell subsets, Ly49s3+ and NKR-P1B+, differ in phenotypic characteristics and responsiveness to cytokines

Two major subsets of rat NK cells can be distinguished based on their expression of the Ly49s3 or the NKR-P1B lectin-like receptor. Ly49s3(+) NK cells, but not NKR-P1B(+) NK cells, express a wide range of Ly49 receptors. Here, we have examined differences between these two subsets in their expression of certain NK cell-associated molecules as well as their responses to cytokines. A microarray analysis suggested several differentially expressed genes, including preferential expression of NKG2A/C receptors by NKR-P1B(+) NK cells. This was confirmed by staining with tetramers of RT.BM1, the putative ligand of CD94/NKG2, indicating that Ly49 and CD94/NKG2 receptors separate into distinct NK cell compartments. Further, expression of CD25 by Ly49s3(+) NK cells was associated with more rapid proliferation in response to IL-2 as compared with NKR-P1B(+) NK cells. Thus, certain inflammatory situations may preferentially expand the Ly49s3(+) NK cells. Moreover, freshly isolated Ly49s3(+) and NKR-P1B(+) NK cells produce similar amounts of cytokines, and a minor Ly49s3(-)NKR-P1B(-) double-negative NK subset appears to be hyporesponsive based on its significantly lower IFN-gamma production. Collectively, our data demonstrate divergent profiles of NKR-P1B(+) and Ly49s3(+) NK cells, indicating distinct tasks in vivo.

In vivo acute depletion of CD8(+) T cells before murine cytomegalovirus infection upregulated innate antiviral activity of natural killer cells

In this study, we investigated the effect of depletion of CD8(+) T cells on the activity of natural killer (NK) cells at an early phase of murine cytomegalovirus (MCMV) infection. For CD8(+) T cell depletion, mice were intraperitoneally treated with anti-CD8 mAb, purified from 2.43 hybridoma, for 2 consecutive days before or after infection. Three days after infection, we found that an acute depletion of CD8(+) T cells before infection caused a significant decrease in the viral load in liver and spleen. This effect coincided with an increase in numbers of CD3(-) NK1.1(+) cells in spleen and their expression of the early activation molecule CD69. Although cytolytic activity of NK cells increased on day 3 of infection in CD8-depleted mice, the level of IFN-gamma decreased in serum and supernatant of cultured spleen cells. In contrast to the effect of acute depletion of CD8(+) T cells before infection, the depletion after infection had no effect on the viral load or number and cytolytic function of NK cells. Lack of effects of CD8(+) T cell depletion on the viral load and NK cytolytic activity is also observed in CD8(+) knockout mice. In conclusion, the results suggest that an acute depletion of CD8(+) T cells before MCMV infection effectively upregulated the antiviral activity of NK cells. This effect appears to be mediated through an increase in numbers, activation and cytolytic activity of NK cells.

Maintenance and reversibility of natural killer cell- and T cell-independent B lymphocyte xenotolerance in athymic nude rats

BACKGROUND

We previously described that a tolerogeneic regimen (TR) including (1) the infusion of a minced hamster heart suspension (MHH), (2) a single injection of an anti-natural killer (NK) cell serum (rabbit anti-asialo GM1 serum), and (3) a 4-week course of the B cell immunosuppressant leflunomide (20 mg/kg/ day) induced T cell-independent (T-I) B lymphocyte and NK cell tolerance for hamster xenoantigens in T-deficient athymic nude rats. In addition, the TR allowed for long-term hamster cardiac xenograft (Xg) survival when Xgs were transplanted 2 weeks (Day 0) after the initiation of the TR (started on Day - 14). The present study was undertaken to investigate some of the characteristics of this T-I xenotolerance in more detail.

METHODS

To investigate the duration of the effect of the TR on the T-I xenotolerance, hamster Xgs were transplanted at various times after initiation of the TR. To investigate whether the maintenance of the T-I xenotolerance depended on the presence of the graft, tolerated Xgs were removed on Day +28, and the subsequent evolution of the T-I xenotolerance as well as of second hamster Xg was followed. In addition, the reversibility of NK cell nonresponsiveness by recombinant interleukin-2 was investigated in vitro.

RESULTS

Xgs transplanted on day 0 or Day +7 showed long-term survival. However, all Xgs transplanted on Day +15, +30, and +60 were rapidly rejected. The latter rejection occurred in the absence of formation of anti-hamster immunoglobulin (Ig)M xenoreactive antibodies (xAbs) but correlated with the recovery of anti-hamster NK cell reactivity from day +14 on. Rejected Xgs showed infiltration of NK cells but absence of IgM xAbs or complement factor deposition. When tolerated first Xgs (transplanted on Day 0) were removed on Day +28, second hamster Xgs survived without treatment when transplanted 1 or 2 weeks later. However, second hamster Xgs transplanted 3 weeks after removal of the first Xgs were all rapidly rejected. Again, the latter rejection was characterized by the infiltration of the Xgs with NK cells and by the absence of anti-hamster IgM xAbs formation. Xenoreactive NK cell nonresponsiveness was not only shorter than xenoreactive B cell nonresponsiveness, but was also more fragile. This was evident from the fact that after addition of recombinant interleukin-2 in vitro, specific anti-hamster NK nonresponsiveness was easily broken.

CONCLUSIONS

NK cell and T-I B cell xenotolerance can be induced in T-deficient rats. Compared with B cell xenotolerance, the maintenance of NK cell xenotolerance is much shorter, more dependent on the presence of the graft, and easily reversible in vitro.

The role of natural killer cell mediated caspases activation in a graft-versus-host disease model of semiallogeneic small bowel transplantation

In the clinical setting of solid organ transplantation the event of graft-versus-host disease (GvHD) is rare and not easily predictable. Even intestinal and multivisceral transplants harbour a huge amount of immunocompetent cells and they do not exert a significantly higher risk to trigger serious GvH reactions. A series of our own experimental studies has been conducted to delineate the role of the host's innate immune system in the context of GvHD following parental to F1 hybrid semiallogeneic small bowel transplantation (SBTx). These results clearly demonstrated the immunological significance of the recipient's status of natural killer (NK) cell activity to counteract donor-derived lymphocytes and related cytotoxicity. NK cells and macrophages are both endowed with Ca2+-dependent receptors of the C-type lectin family which interact with a diversity of high-affinity oligosaccharide ligands expressed on potential target cells. One of these proteins of the C-type lectin family, termed NKR-P1, has been cloned and sequenced. Activation of NKR-P1 stimulates activation-induced cell death (AICD) of bound target cells. As intracellular mediators of apoptotic cell death a new family of cysteine proteases, the caspases, have been defined. These proteases appear to be involved in the initiation of apoptosis in response to a number of stimuli. This study was conducted to investigate the impact on the activity level of host NK cells and on target cell lysis of donor-derived lymphocytes after heterotopic semiallogeneic (parental [DA;RT1.aaav1] to F1 [DA x LEW;RT1.(1)]) small bowel transplantation using a rat model. The host's NK activity was either specifically activated (by use of polyinosinic:polycytodilic acid [poly-I:C]) or suppressed (by depletion of host NK cells after intraperitoneal administration of the NKR-P1 monoclonal antibody 3.2.3). The impact of NK-activity on the incidence of GvHD and the recipients' survival was correlated with the frequency of apoptotic cell death and related expression of caspases 1 (ICE) and 3 (CPP-32) from donor and recipient small bowel tissues. Our results confirm that depletion of NK cells in F1 host rats prior to parental small bowel transplantation significantly decreased the mean survival to 11.4 days versus 16.2 days of nondepleted F1 rats (p < 0.01). Conversely, activation of host NK activity with poly-I:C abrogated GvHD in all 12 recipient rats and led to long-term survival in seven of 12 animals. Long-term survival was associated with a substantially higher frequency of apoptotic cell death in donor and recipient small bowel and mesenteric lymph nodes. On day 10 after transplantation, Northern blot analysis of these tissues revealed profound upregulation of mRNA-specific gene expression for caspase 1 and 3 as potential mediators of programmed cell death of activated lymphocytes. Our findings emphasize the importance of NK cell associated innate immunity in the context of GvHD after semiallogeneic small bowel transplantation. Killing of alloreactive donor-derived lymphocytes was mediated by the NKR-P1 protein on NK cells and could be suppressed after pretreatment of F1 hosts with anti-NKR-P1 mAb 3.2.3. Moreover, NK cell-mediated apoptosis induced upregulation of caspases 1 and 3, thus elucidating the involvement of this protein in the context of caspase-mediated target cell killing.

Positive and negative MHC class I recognition by rat NK cells

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

Silicone-induced modulation of natural killer cell activity

Current controversy regarding the effects of silicone gel mammary implants on the immune system has led to increased focus on the potential biological activity of silicone materials. Studies were undertaken in the B6C3F1 mouse to evaluate the immunotoxicological effects of the following components of a mammary gel prosthesis: polydimethylsiloxane fluid, silicone gel, elastomer shell and a polyurethane implant cover. Material was implanted subcutaneously (s.c.) for either 10 or 180 days. The only toxicological or immunological parameter which differed from control values was the natural killer (NK) cell activity in gel implanted mice. In these animals, basal NK activity was decreased. NK activity was comparably inhibited in female Fischer 344 rats implanted with silicone gel following short term (14 or 30 days) as well as chronic (1 year) exposure. The response was variable in both the rat and mouse. Host resistance to B16F10 melanoma in the mouse is known to be related to NK activity. Despite suppression of NK activity following gel implantation, host resistance was unaltered. Inhibition of NK activity by the administration of anti-asialo GM1 indicated that resistance was not adversely affected until NK activity was decreased by 40 to 50%. As with basal NK activity, augmented NK activity was inhibited in gel implanted rats when compared to controls. Administration of polyinosinic:polycytidylic acid to gel implanted rats resulted in an increase of approximately 65% in NK activity compared to gel implanted controls. This level of augmented NK activity was significantly less than the level of augmented NK activity in vehicle implanted animals where 100% enhancement in NK activity was noted. The results of these studies indicate that (1) NK cytolytic activity is altered in two animal models, the mouse and rat, although the results were variable, that (2) the level of suppression noted in the mouse is ineffective when compared to the level of suppression required to alter host resistance to B16F10 melanoma and that (3) the gel implanted animals exhibit a suppressed response to NK augmentation.

Recruitment of alloreactive natural killer cells to the rat peritoneum by a transfected cell line secreting rat recombinant interleukin-2

In order to obtain large numbers of natural killer (NK) cells from single rats for functional studies, we have devised a method for the generation of IL-2-activated NK cells in vivo. Rats were implanted intraperitoneally with cell-impermeable diffusion chambers (DC) containing cultures of transfected Chinese hamster ovary (CHO) cells secreting rat recombinant interleukin-2 (rIL-2). This resulted in a dramatic increase in the peritoneal exudate cell (PEC) number with a peak (300-1000 x 10(6)) 1 week after implantation. The majority were mononuclear cells of which a large proportion were CD3-NKR-P1+ NK cells, but with substantial numbers of macrophages (M phi) and CD3+8+NKR-P1+ T cells also. The NK activity against standard tumor target cells was high among PEC from six different inbred rat strains tested. However, the NK cell-mediated reactivity against concanavalin A (ConA)-activated T cell blasts from a panel of major histocompatibility complex (MHC) congenic strains differed widely. PEC from some strains (PVG, LOU/C, and AO) efficiently lysed all the MHC-disparate lymphoblasts. In other strains (BN and LEW) more restricted allorecognition repertoires were observed, whereas PEC from one strain (DA) were unresponsive. The secretion of rat rIL-2 intraperitoneally did not lead to a significant increase in the IL-2 level in the blood or in the total number or activity of NK cells in blood and spleen. The present method represents a most potent technique for generating large numbers of functional rat NK cells and shows the high efficiency with which IL-2 can induce NK cell recruitment in vivo.

Interferon-alpha activates cytotoxic function but inhibits interleukin-2-mediated proliferation and tumor necrosis factor-alpha secretion by immature human natural killer cells

Natural killer (NK) cells play an important role in host defense mechanisms against infection and neoplasia. Interferon-alpha (IFN-alpha) has been shown to activate NK cells and to augment their cytotoxic activity, albeit its role in the maturation pathway of NK cells has not been elucidated. The present study examined whether IFN-alpha activates the immature NK subset (Free cells) to become cytotoxic and also ascertained whether IFN-alpha uses the same pathway of activation as that mediated by interleukin-2 (IL-2). Incubation of sorted Free cells overnight with IFN-alpha resulted in augmentation of their cytotoxic function against NK sensitive target cells. The enhanced cytotoxic activity was not accompanied by a new recruitment of NK-target binder cells but by an increase in the frequency of killer cells in the conjugate fraction. Activation of the Free subset by IFN-alpha resulted in upregulation of CD69, CD11b, and CD2 surface expression and stimulated secretion of IFN-gamma. Unlike IL-2, IFN-alpha did not stimulate the Free cells to proliferate or secrete TNF-alpha and activation of cytotoxicity and modulation of surface antigens by IFN-alpha were independent of TNF-alpha. The failure of IFN-alpha to stimulate secretion and proliferation by Free cells appeared to be mediated by negative signals. This was corroborated in experiments demonstrating that when Free cells were cultured with both IFN-alpha and IL-2, a significant inhibition was observed for both the IL-2 dependent secretion of TNF-alpha and proliferation. These results demonstrate that IFN-alpha serves as both an activator and a regulator of NK function. Further, activation of the immature Free NK cells by IL-2 and IFN-alpha proceeds by TNF-alpha- dependent and independent pathways, respectively. The findings also support our contention that the mechanism of activation of the cytotoxic machinery of NK cells is not linked to the mechanism of activation of cytokine secretion and/or proliferation.

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.

In vivo modulation of lymphokine-activated killer cell activity by cell wall components of Candida albicans

We have previously reported that inoculating CD2F1 mice intraperitoneally with five doses of 2 x 10(7) inactivated Candida albicans (CA) cells was associated with the induction of lymphokine-activated killer (LAK)-like effectors. In this study we investigated the ability of some purified cell wall components of CA (CA-CW) to induce LAK-like cells in vivo. Multiple administrations of glucan ghost (GG), a mannoprotein mixture (MP) and a low-protein mannan fraction (M) at variance with whole CA did not induce LAK-like cells in the peritoneal cavity. However, the broad-spectrum antitumor cytotoxicity induced by CA could be recalled to a high level by a booster dose of MP and M, but not GG, given up to 70 days after the multiple CA-treatment. This induced cytotoxicity was maximum when the booster was given on Day +14 after CA-treatment and minimum on Day +70. In CA-treated mice, inoculated on Day +30 with CA or MP, LAK-like cytotoxicity was already significantly increased 4 hr after the booster, but the maximum value was reached at 24 hr. Anti-mannan antibodies did not interfere with LAK-like cells induction by CA because splenectomy before CA-treatment or passive administration of anti-mannan antibodies had no effect on the rapid activation of cytotoxicity by CA or a booster dose of MP. Administration of recombinant human interleukin-2 (rhIL-2) to CA-treated mice induced a higher level of NK activity than that induced by the same dose in untreated control mice, but did not activate LAK-like effectors. The results indicate that LAK-like effectors are easily generated in the peritoneal cavity by a booster with a defined antigenic constituent of CA cell wall for a long period in CA-sensitized mice.

Cellular response to double-stranded RNA

The study of double-stranded RNA (dsRNA) encompasses a variety of fields. Basic research in this area has contributed to a greater mechanistic understanding of gene induction, tumor cell growth arrest, the establishment of antiviral states, and immunomodulation. Because of the possible clinical value of these molecules, physicians are now exploring the use of synthetic dsRNA to treat patients with cancer, HIV-1 disease, and immune dysfunction. Continued studies of the mechanisms of action of dsRNA are likely to suggest an even wider scope of clinical applications.

Lymphokine-activated killer cells, natural killer cells and cytokines

In the past year, natural killer cells have been the subject of much active investigation. The analysis of the effect of cytokines on the generation, proliferation and function of natural killer cells, and the definition of the lymphokines that they produce, have been particularly important areas of research in view of their possible application in adaptive immunotherapy, combined with biological response modifiers.