Do natural killer cells engage in regulated reactions against self to ensure homeostasis?

Tumor Immuno-Environment in Cancer Progression and Therapy

The approvals of Provenge (Sipuleucel-T), Ipilimumab (Yervoy/anti-CTLA-4) and blockers of the PD-1 - PD-L1/PD-L2 pathway, such as nivolumab (Opdivo), pembrolizumab (Keytruda), or atezolizumab (Tecentriq), have established immunotherapy as a key component of comprehensive cancer care. Further, murine mechanistic studies and studies in immunocompromised patients have documented the critical role of immunity in effectiveness of radio- and chemotherapy. However, in addition to the ability of the immune system to control cancer progression, it can also promote tumor growth, via regulatory T cells (Tregs), myeloid-derived dendritic cells (MDSCs) and tumor associated macrophages (TAM), which can enhance survival of cancer cells directly or via the regulation of the tumor stroma.An increasing body of evidence supports a central role for the tumor microenvironment (TME) and the interactions between tumor stroma, infiltrating immune cells and cancer cells during the induction and effector phase of anti-cancer immunity, and the overall effectiveness of immunotherapy and other forms of cancer treatment. In this chapter, we discuss the roles of key TME components during tumor progression, metastatic process and cancer therapy-induced tumor regression, as well as opportunities for their modulation to enhance the overall therapeutic benefit.

Natural killer activity: early days, advances, and seminal observations

This manuscript describes the early history of NK cell discovery, with emphasis on the events in the first decade of NK cell studies, 1972-1982. The authors highlight some of the earliest and most important observations that would later prove to be milestones in the study of NK cells and their activity.

Activation or suppression of bactericidal activity of macrophages during a graft-versus-host reaction against I-A and I-J-region differences, respectively

Systemic graft-versus-host reactions (GVHR) were induced in F1 heterozygous mice by injecting 10(8) parental lymphocytes. The Anti-Thy 1.2-sensitive, T-cell mediated activation of macrophages was assessed by their increased capacity to destroy a facultative intracellular bacterium Listeria monocytogenes. The difference in MHC regions causing a GVHR that induced high levels of macrophage activation mapped to I-A. In contrast, differences at K or D, in any of the other H-2 subregions or in the non-H-2 background, including Mls alone or in combination, did not induce a GVHR leading to macrophage activation, unless these differences were combined with a difference at I-A. The numbers of parental cells needed to activate macrophages via a GVHR caused by I-A vs. non-I-A differences, varied at least 30- to 100-fold. When parental cells were injected into F1 offspring of parents differing at I-J, growth of Listeria was enhanced significantly; this negative effect on macrophages was not seen when parental combinations differing at I-A alone were compared with those differing at I-A plus I-J or I-J plus other H-2 regions.

Enhancement of natural killer cell activation and antibody-dependent cellular cytotoxicity by interferon-alpha and interleukin-12 in vaginal mucosae Sivmac251-infected Macaca fascicularis

We studied the innate immune system of Cynomolgus monkeys (Macaca fascicularis) experimentally infected via the vaginal mucosae with a virulent simian immunodeficiency virus isolate SIVmac251. Animals were evaluated for their natural killer (NK) cell activity, and for their antibody-dependent cellular cytotoxicity. NK cells from SIVmac251-infected macaques show impaired NK cell activity compared to cells from uninfected animals. Subsequent treatment of NK cells with interferon-a (IFN-alpha) or interleukin-12 (IL-12) alone partially restored the NK activity. However, either treatment of NK cells with both IFN-alpha and IL-12 completely reversed the impairment of cytotoxicity induced by simian immunodeficiency virus (SIV) infection. Incubation of NK cells from infected but not from uninfected monkeys with IFN-alpha and IL-12 for 8 days increased the percentage of CD16+/CD56+ cells twofold to five-fold and enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. Thus IFN-alpha and IL-12 greatly enhance both the NK cell and ADCC activities of peripheral blood cells from SIVmac251-infected animals and increase the number of NK cells in longer term culture. The combined effect of IFN-alpha and IL-12 in enhancing NK cell activity may provide a novel therapeutic approach for the restoration of depressed NK cell activity observed in human immunodeficiency virus (HIV)-infected patients.

Inhibitory effect on natural killer activity of microphthalmia transcription factor encoded by the mutant mi allele of mice

The mouse mi locus encodes a basic-helix-loop-helix-leucine zipper-type transcription factor, microphthalmia transcription factor (MITF). Mice of mi/mi genotype express a mutant form of MITF (mi-MITF), whereas mice of tg/tg genotype have a transgene in the 5' flanking region of the mi gene and do not express MITF. Although the mi/mi mouse is deficient in natural killer (NK) activity, it was found that the tg/tg mouse was normal in this respect. To know the cause, spleen cells of both genotypes were compared. Although the proportion of spleen cells expressing an NK cell marker, NK1.1, was comparable in both mice, the proportion of large granular lymphocytes decreased only in mi/mi mice. The difference between mi/mi and tg/tg mice was reproducible in the culture supplemented with interleukin-2. Moreover, the perforin gene expression was reduced in mi/mi-cultured spleen cells. Wild-type (+) MITF transactivated, but mi-MITF suppressed, the perforin gene promoter through the NF-P motif, a strong cis-acting element. However, neither +-MITF nor mi-MITF bound the NF-P motif. Instead, 2 nuclear factors that bound the NF-P motif were retained in the cytoplasm of mi/mi-cultured spleen cells. In addition, overexpression of mi-MITF resulted in cytoplasmic retention of the 2 NF-P motif-binding factors in cytotoxic T lymphocytes. The presence of mi-MITF rather than the absence of +-MITF appeared to lead to poor transactivation of the NF-P motif by intercepting NF-P motif-binding factors. This inhibitory effect of mi-MITF may cause the deficient cytotoxicity of NK cells in mi/mi mice. (Blood. 2001;97:2075-2083)

Reversal of human immunodeficiency virus type 1 protein-induced inhibition of natural killer cell activity by alpha interferon and interleukin-2

A recombinant fusion peptide, Env-Gag, derived from the human immunodeficiency virus type 1 (HIV-1) genome corresponding to a defined portion of the envelope (Env) and internal core (Gag) proteins was examined for immunoregulatory effects on the cytotoxic activity of natural killer (NK) cell-enriched, large granular lymphocytes (LGL) from healthy donors. Percoll-separated, NK cell-enriched LGL precultured for 24 h with Env-Gag at 10- and 50-ng/ml concentrations, which significantly stimulated lymphocyte proliferation, caused significant suppression of NK cell activity. Denatured Env-Gag did not cause any effect on the NK cell activity of LGL. Two other control peptides, one derived from the Escherichia coli vector used to clone the HIV Env-Gag fusion peptide and the other derived from a non-HIV-1 viral antigen (rubeola virus), did not produce any observable effect on the NK cell activity of LGL, demonstrating the specificity of the effect produced by Env-Gag. Subsequent treatment of LGL with alpha interferon (IFN-alpha) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-alpha and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-alpha and IL-2 in enhancing NK cell activity may provide a novel therapeutic approach to the restoration of depressed NK cell activity observed in HIV-infected patients.

SCID mouse models of human stem cell engraftment

The discovery of the severe combined immunodeficiency (scid) mouse mutation has provided a tool for establishment of small animal models as hosts for the in vivo analysis of normal and malignant human pluripotent hemopoietic stem cells. Intravenous injection of irradiated scid mice with human bone marrow, cord blood, or G-CSF cytokine-mobilized peripheral blood mononuclear cells, all rich in human hemopoietic stem cell activity, results in the engraftment of a human hemopoietic system in the murine recipient. This model has been used to identify a pluripotent stem cell, termed "scid-repopulating cell" (SRC) that is more primitive than any of the hemopoietic stem cell populations identified using the currently available in vitro methodology. In this review, we describe the development and use of this model system, termed Hu-SRC-SCID, and summarize the discoveries that have resulted from the investigation of human stem cells in this model. Finally, we detail the recent extension of the original Hu-SRC-SCID model system based on the C.B-17-scid mouse as the murine host to the Hu-SRC-NOD-SCID model based on the NOD-scid mouse as the host. The engraftment of human stem cells in the Hu-SRC-NOD-SCID model is enhanced over that observed in the Hu-SRC-SCID model and results in exceptionally high levels of human hemopoietic cells in the murine recipient. Future directions to further improve the Hu-SRC-NOD-SCID model system and the potential utility of this model in the preclinical and diagnostic arenas of hematology and oncology are discussed.

The potential role of NK cells in the separation of graft-versus-tumor effects from graft-versus-host disease after allogeneic bone marrow transplantation

Allogeneic bone marrow transplantation (BMT) is being increasingly used for the treatment of a variety of cancers ranging from leukemias to breast cancer. However, significant obstacles currently limit the efficacy of this treatment procedure. The predominant two are the occurrence of graft-versus-host disease (GVHD) and relapse from the cancer. While regimens exist that prevent the occurrence or severity of GVHD, these same regimens also increase the rate of relapse. Conversely, most attempts to reduce the relapse rate also result in increased GVHD. The use of NK cells as an adoptive immunotherapy after BMT is attractive for several reasons. NK cells exhibit antitumor effects both in vitro and in animal models and may, therefore, promote graft-versus-tumor (GVT) effects to remove minimal residual disease after allogeneic BMT. NK cells have also been shown to promote hematopoietic engraftment and donor cell reconstitution after allogeneic BMT in mice. The effects of NK cells on hematopoiesis are believed to be due to the hematopoietic growth factors they can produce after activation. Another advantage in using NK cells is that they can prevent the occurrence of GVHD after allogeneic BMT in mice. This effect is mediated at least in part by the immunosuppressive cytokine, transforming growth factor beta (TGF-beta). BMT studies in mice also indicate that the beneficial effects of NK cells are optimal if they are administered soon after the transplant. Thereafter, NK cells and, more importantly, IL-2, which is used to activate them, are detrimental and can exacerbate the subsequent GVHD. Thus, the use of activated NK cells after allogeneic BMT may provide GVT effects without inducing GVHD.

Murine natural killer cell differentiation: past, present, and future

Natural killer cells are bone marrow-derived lymphocytes capable of lysing a variety of target cells without prior exposure. While the biological activities and function of mature NK cells have been extensively investigated, the differentiation of NK cells from primitive hematopoietic stem cells is poorly understood. Recently, we have reported on the identification of a highly enriched bone marrow population capable of repopulating recipient mice with mature NK cells. In this review, we will summarize our findings and those of others in an attempt to clarify the current status of murine natural killer cell differentiation.

Bovine NK and LAK susceptibility is independent of class I expression on B lymphoblastoid variants

Numerous tumors express low or no class I molecules, resulting in their avoidance of recognition and destruction by different effector cells of the immune system. Using a parent and two MHC class I mutant cell lines, we have tested the role of MHC class I molecules in natural killer (NK) cells, lymphokine activated killer (LAK) cells and cytotoxic T lymphocytes (CTLs). Both class I expressing parent cells and class I loss mutants were insensitive to NK cell lysis as assayed, regardless of the amount of class I molecules on the target cell surface. However, LAK cells demonstrated higher cytolysis on these target cells than NK cells, suggesting different mechanisms of target cell recognition or different levels of lytic activity by these two effector cell populations. Up-regulation of class I expression on the target surface by gamma interferon (gamma-IFN) had little influence on NK and LAK susceptibility, indicating there was no correlation between class I expression and bovine NK or LAK cytolysis. However, allogeneic CTLs mediated a lytic pattern distinct from NK and LAK cells, in which target sensitivity to allogeneic CTLs correlated with the amount of class I molecules expressed on the cell surface. Additionally, effector-target cell conjugation studies demonstrated that target class I expression was not involved in NK and LAK cells binding to targets. These results demonstrate that NK and LAK cytolysis of these two class I mutant cell lines is independent of the amount of class I molecules expressed on the target cell surface.

Cytokine cross-talk between phagocytic cells and lymphocytes: relevance for differentiation/activation of phagocytic cells and regulation of adaptive immunity

Cytokines represent one of the most important elements in the communication among different cell types. They play an increasingly better understood role in the communication among hematopoietic cells and in particular in the reciprocal regulation of effector cell types of innate or natural resistance (phagocytic cells and Natural Killer (NK) cells) and those of adaptive immunity (T and B lymphocytes). Lymphocytes produce several cytokines with either stimulatory (e.g., colony stimulatory factor) or suppressive (e.g., tumor necrosis factors and interferons) effects on proliferation of early hematopoietic cells. Many of these cytokines, alone or acting in synergistic combinations, also have a differentiation-inducing ability on immature myeloid cells and act as powerful potentiators of the cellular functions of terminally differentiated phagocytic cells. The communication between lymphocytes and phagocytic cells is not unidirectional, as phagocytic cells produce factors that regulate lymphocyte activation. In addition to their role as antigen presenting cells expressing costimulatory accessory molecules and secreting cytokines (e.g., IL-1, IL-6, TNF), phagocytic cells have been recently shown to produce Natural Killer cell Stimulatory Factor (NKSF/IL-12). IL-12 is a heterodimeric cytokine with important modulatory functions on cytotoxicity of NK and T cells, lymphocyte proliferation, lymphokine production, and development of T helper cell subsets. These communications between phagocytic cells and lymphocytes are further regulated by negative and positive feedback mechanisms that contribute to maintain the homeostasis of the system in physiologic conditions and to govern the changes in this equilibrium needed for the response to infectious or other foreign agents.

Analysis of peripheral blood lymphocyte cell surface density of functional and activation associated markers in young and old hemodialysis patients

Aging has been associated with specific shifts in various peripheral blood immune competent cell subsets. As part of pre-transplant immune profile evaluation possible parallel age-related changes in mean T-cell surface density of several cluster differentiation and activation linked antigens were into 2 groups: group 1-114 patients 40 years old or younger and group 2-36 patients 55 years old or older. Peripheral blood CD3+, DR+, CD3+DR+, CD4+, CD4+DR+, CD8+, CD8+DR+, CD56+, CD8+CD56+, CD3+IL-2-R+ and CD3+TR+ (interleukin-2 and transferrin receptors bearing CD3+ cells respectively), all mononuclear cells expressing IL-2-R and TR, and CD4+CD45+ cell subsets were analyzed and enumerated by 2-color flow cytometry. Subset relative levels as well as absolute counts were recorded. Cell surface density computation was performed using a computerized mathematical model based on fluorescence intensity vector analysis and cell size score determination based on light scatter pattern from raw data obtained by flow cytometry studies. Younger age was significantly associated with higher absolute cell count of CD3+ (p < 0.001), DR+ (p < 0.05), CD4+ (p < 0.01), CD8+ (p < 0.005), CD3+IL-2-R+ (p < 0.05), CD3+TR+ (p < 0.03) and IL-2-R+ (p < 0.05). Older patients had a slightly higher mean absolute count of CD4+CD45+ subset (p not significant) and significantly higher mean count for CD8+CD56+ cell subset (p < 0.001). When cell subset levels were compared between the 2 groups as the relative fraction of cells expressing a given marker out of all mononuclear cells gated out by flow cytometry, younger age was significantly associated with higher levels of CD3+ (p < 0.005), CD8+ (p < 0.001), CD4+DR+ (p < 0.004), CD3-TR+ (p < 0.05) and CD8+IL-2-R+ (p < 0.05). In contrast, slightly higher subset levels of CD56+ (p not significant), and significantly elevated levels of CD8+CD56+ (p < 0.0019) and CD4+CD45+ (p < 0.004) were observed in the older patients. Cell surface density analysis showed that younger patients had higher mean density per cell of CD3 (p < 0.05), CD8 (p < 0.001), IL-2-R on CD3+ cells (p < 0.05) and TR on CD3+ cells (p < 0.05). Mean cell surface density of CD56 on all CD56+ cells as well as on CD8+ cells was higher in older individuals (p < 0.001 and p < 0.003, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Activated natural killer cells suppress myelopoiesis in mice with severe combined immunodeficiency

The in vivo effect of natural killer (NK) cell activation on autologous myelopoiesis was studied in an environment deficient of functional T and B cells. Administration of 3,6-bis[2-(Dimethylamino)-ethoxy]-9H-xanthen-9-one dihydrochloride) Tilorone) or recombinant interleukin-2 (rIL-2) to mice with severe combined immunodeficiency (C.B.-17 scid/scid) resulted in an increase in YAC-1 lysis by their splenocytes as well as bone marrow cells. Recombinant IL-2 furthermore led to a fivefold increase in the cellularity of the spleen. When assayed against human NK/lymphokine-activated killer (LAK) target, K562 cell line, the IL-2-activated mouse cells exhibited no cytotoxicity across the species barrier. Both agents induced a profound suppression of myelopoietic progenitor cells as measured in a 7-day granulocyte-macrophage colony forming cell (GM-CFC) assay. We conclude that the presence of neither functional T nor B cells is necessary for NK cells to mediate inhibition of myelopoiesis in the autologous host.

Impaired NK response of cancer patients to IFN-alpha but not to IL-2: correlation with serum immunosuppressive acidic protein (IAP) and role of suppressor macrophage

In vitro NK responses of cancer patients (N = 21) to rIFN-alpha A and rIL-2 were examined. The serum concentration of IAP (immunosuppressive acidic protein) was determined in parallel. Five out of seven patients whose serum IAP contents were within the normal range (270 micrograms/ml to 470 micrograms/ml), had their NK activities significantly augmented by rIFN-alpha A and rIL-2. On the other hand, NK cells from ten out of fifteen patients whose serum IAP concentrations were 650 micrograms/ml or more, were not activated by rIFN-alpha A. NK cells of these fifteen patients yet were capable of responding to rIL-2. NK cells from cancer patients, however, became responsive to rIFN-alpha A by either removal of adherent cells or treatment with indomethacin. Therefore, macrophages in PBMC of cancer patients with high serum IAP levels seem to selectively suppress NK response to rIFN-alpha A by an indomethacin-sensitive mechanisms. It was further shown that PGE2 was not the mediator of this suppression.

Pidotimod stimulates natural killer cell activity and inhibits thymocyte cell death

Experiments were performed to analyze the possible effect of the immunomodulating agent Pidotimod (3-L-pyroglutamyl-L-thiazolidine-4-carboxylic acid) on mouse Natural Killer (NK) cell activity and glucocorticoid hormone(GCH)-induced thymocyte apoptosis. The results indicate that in vivo treatment with Pidotimod (200 mg/Kg ip for 5 days) causes a significant increase in NK activity and in vitro treatment produces a significant reduction of dexamethasone-induced thymocyte apoptosis. This inhibition appears to be dose-dependent and is also evident against TPA or Ca(++)ionophore-induced apoptosis.

Differences in murine gut-associated lymphoid tissues in generating broadly nonspecific cytotoxic cells in response to interferon alpha A/D and interleukin 2

We examined the response of cells of murine gut-associated lymphoid tissues to agents that augment the activity of natural killer (NK) cells. Specifically, we studied the effect of polyinosinic: polycytidylic acid (Poly I:C) in vivo, and recombinant interferon alpha A/D (rIFN alpha A/D) and recombinant interleukin 2 (rIL2) in vitro on lymphoid cells of mesenteric lymph nodes (MLN) and Peyer's patches (PP) in generating cytotoxicity against NK-sensitive (YAC-1) and NK-insensitive (B16BL6) tumor targets. The effect of these agents on spleen cells was examined for comparison with their effect on MLN and PP cells and as a positive control. MLN and PP cells lacked spontaneous NK activity: however, NK activity could be augmented to different levels by the three agents. The treatment of mice in vivo with Poly I:C induced considerable cytotoxicity in the spleen and MLN but only a weak cytotoxic response in PP. The in vitro enhancement of NK activity by rIFN alpha A/D was strong in the spleen, intermediate in MLN, and consistently poor in PP. The weak NK augmentation by rIFN alpha A/D in PP was not restricted to a single mouse strain. PP cells from five strains of mice responded poorly to rIFN alpha A/D. Furthermore, NK augmentation by rIFN alpha A/D in PP cells did not improve after passing the responder cells through nylon wool, indicating that the lack of augmentation of NK activity was not the result of a preponderance of B cells or the masking of NK cells by adherent lymphoid populations in PP. In contrast to weak augmentation of NK activity by rIFN alpha A/D, considerable IL2-induced lymphocyte-activated killer (LAK) activity against NK-insensitive B16BL6 tumor cells was induced in PP. Limiting-dilution analysis showed that the frequency of LAK precursors in the MLN and PP was not markedly different from that of the spleen. The differences among spleen, MLN, and PP lymphoid populations in generating the broadly nonspecific cytotoxic effector cells in response to rIFN alpha A/D or rIL2 may result from differences in the pools of different pre-NK cells or to differential sensitivity of the same pool of pre-NK cells to rIFN alpha A/D and rIL2 in different anatomical locations.

Differential sensitivity of head and neck cancers to non-major histocompatibility-restricted killer cell activity

Cell lines derived from squamous cell carcinoma of the upper aerodigestive tract (head and neck cancer) were phenotypically characterized with regard to differential sensitivity to nonmajor histocompatibility restricted (non-MHCr) killer cell activity. Requirements for detectable lysis of the cell lines in a standard chromium release assay included either isolation of fresh enriched Leu 19+ large granular lymphocytes (both Leu 19+CD3+ and Leu 19+CD3- populations) or interleukin-2 (IL-2) stimulation of peripheral blood lymphocytes (PBL). In neither circumstance could lytic activity be identified among Leu 19- populations. With PBL IL-2 stimulation significant differential sensitivity to lysis expressed by the head and neck cancer cell lines (P less than 0.001 by analysis of variance) was identified and maintained regardless of PBL source, i.e., PBL from healthy controls and three differing populations of head and neck cancer patients categorized by disease status and treatment. One factor associated with a cell line's increased sensitivity was degree of tumor differentiation, poorly differentiated tumors (as defined by intermediate filament cytochemical staining [decreased keratin and increased vimentin]) being more sensitive. Furthermore, as tumor cell lytic sensitivity increased, major histocompatibility complex (MHC)-class I antigen expression diminished concurrently. In 1 of 4 cell lines tested, however, pretreatment of tumor cells with interferon-gamma induced diminished lytic sensitivity independent of changes in MHC-class I expression, indicating factors not related to MHC-class I expression are likewise relevant. In previous studies we defined the in vivo prognostic significance of non-MHCr killer cell cytotoxicity activity against K562 targets, diminished activity being principally predictive of metastatic disease development in persons with poorly differentiated head and neck cancers. This report extends these observations by demonstrating in vitro that poorly differentiated head and neck cancer target cells are highly sensitive to changes in lytic function expressed by Leu 19+ non-MHCr effector cells.

Characterization of Corynebacterium parvum-induced suppressor cells of mouse NK and ADCC activity

Treatment of mice with Corynebacterium parvum (Cp) resulted in a substantial decrease in natural killer activity in the spleen at 10 days. The decrease in cytotoxicity was associated with the presence of splenic nonadherent (NA) suppressor cells, capable of inhibiting natural as well as antibody-dependent cellular cytotoxicity (ADCC). The nonadherent suppressor cells appeared to be null cells, lacking detectable expression of Thy 1, L3T4 (CD4), Lyt 2 (CD8), or asialo-GM1 and could be physically separated from cells with NK activity by centrifugation on Percoll discontinuous density gradients. Our results indicate that Cp can negatively modulate cytolytic functions of NK cells by inhibiting the effector phase of cytotoxicity.

Acute rejection of allogeneic hemopoietic progenitors by genetically resistant mice

Natural resistance to hemopoietic allograft results in functional elimination of the graft from the host within 24 to 48 h. The resistance is specific and is directed to the cell surface target structures of an unidentified nature. These determinants are controlled by the major histocompatibility complex-linked hemopoietic histocompatibility (Hh) loci and expressed by cells of the hemopoietic system. In this study, the susceptibility of various hemopoietic progenitors, as well as the nature and the kinetics of the early rejection process, were examined by directly following the functional survival of the grafted progenitors by periodic sampling. In both F1 hybrid and inbred allogeneic hosts, multipotential progenitors for granulocyte-erythrocyte-monocyte-megakaryocyte lineages, bipotential progenitors for granulocyte-monocyte lineages and unipotential progenitors of erythrocyte, granulocyte and monocyte were susceptible to elimination. Therefore, within the limited range of comparisons, neither the lineage, nor the degree of commitment or differentiation determines the susceptibility of hemopoietic progenitors to resistance. Functional elimination of the grafted progenitors from the recipient spleen was irreversible upon cultivation in semisolid medium. The frequency of seeding in the spleen at 3 h was comparable in resistant and susceptible hosts; elimination commenced shortly afterwards and by 24 h after transplantation less than 10% of clonogenic progenitors remained functional. Activation of natural killer cells strengthened pre-existing resistance, but did not convert genetically susceptible mice to resistant. Therefore, the resistance is dependent on an effector mechanism with predetermined specificity.

Intestinal intraepithelial and splenic natural killer cell responses to eimerian infections in inbred chickens

Splenic and intestinal natural killer (NK) cell responses were assessed in chickens inoculated with Eimeria parasites. The NK cell activities of both splenic and intestinal intraepithelial lymphocytes (IELs) decreased to a subnormal level during the early phase of eimerian infections but returned to normal or slightly higher than normal levels at about 1 week after the primary inoculation. Lymphocytes obtained from the lamina propria did not show any detectable level of NK cell activity during or following eimerian infections. Significant increases in splenic and intestinal IEL NK cell activities were seen during the early phase of secondary infection. The increase in the IEL NK cell activity that was seen shortly following secondary eimerian infection was accompanied by a substantial increase in the number of IELs expressing the asialo-GM1 antigen. Host strain differences in both splenic and IEL NK cell responses were detected following primary eimerian infections. These results suggest that both splenic and intestinal IEL NK cells may play an important role in the host defense against intestinal protozoan infections.

Development of thymocytes in organ culture: migrant cells with natural killer cell characteristics

During organ culture of foetal thymic lobes, up to 5% of the thymic cells migrate out of the lobes and a majority of these have phenotypic characteristics of thymocytes or macrophages. Interleukin-2 (IL-2) increases the number of these migrant cells, and cytotoxic cells can be detected which display natural killer cell surface markers. In contrast, although cytotoxic activity can be detected in cells from adult thymic fragments cultured with IL-2, the cytotoxic activity is not detected with natural killer sensitive target cells. The appearance of natural killer-like cells during the culture of foetal thymic lobes suggests that they are involved in differentiation events which occur at this time in the thymus.

Production of hematopoietic colony-stimulating factors by human natural killer cells

We have analyzed the ability of highly purified preparations of human NK cells to produce CSF. NK cells, purified by negative selection from 10-d cultures of PBMC incubated with irradiated B-lymphoblastoid cell lines, were stimulated with rIL-2, FcR(CD16) ligands (particulate immune complexes or anti-CD16 antibodies bound to Sepharose), a combination of CD16 ligands and rIL-2, or the phorbol diester phorbol dibutyrate (PDBu) together with the Ca2+ ionophore A23187. Both rIL-2 and CD16 ligands induce accumulation of GM-CSF mRNA in NK cells and the combined effect of the two stimuli is synergistic. Maximal accumulation of GM-CSF mRNA is observed after PDBu/A23187 stimulation. The participation of contaminant T cells in the observed expression of the GM-CSF gene is excluded because CD16 ligands do not stimulate T cells and CD3 ligands, powerful stimulators of T cells, are inactive on NK cells. Accumulation of CSF-1 mRNA is observed only in NK cells stimulated with both CD16 ligands and rIL-2, whereas accumulation of IL-3 mRNA is observed only in NK cells stimulated with PDBu/A23187. Transcripts of the G-CSF, IL-1 alpha, and IL-1 beta genes were never detected in NK cells in these experiments. The kinetics of accumulation of GM-CSF and CSF-1 mRNA in NK cells stimulated with CD16 ligands and rIL-2 peaked at 2-4 h and was slower than that of TNF and IFN-gamma mRNA, which peak at 1 h. GM-CSF was precipitated from the supernatant fluids of NK cells stimulated with PDBu/A23187 and its biological activity was demonstrated by the ability of the supernatants to sustain proliferation of the TALL-101 cell line or CML blasts. Biological activity of IL-3 and CSF-1 was demonstrable in supernatant fluids of NK cells stimulated with PDBu/A23187 and CD16 ligands/rIL-2, respectively.

The mechanism of inhibition of alveolar macrophages on autologous blood natural killer cell activity

We investigated the mechanism of suppressive effect of alveolar macrophages (AM) on autologous blood NK cell activity in healthy nonsmokers (NS) and smokers (S). A 50 percent additional concentration of AM both in NS and S inhibited NK cell activity significantly (p less than 0.05). The degree of inhibition was not different in NS and S. Effects of prostaglandins (PG) and oxygen radicals were studied separately on the NK cell activity in the presence of AM. Indomethacin, catalase, or thiourea did not reverse inhibition of NK cell activity, but superoxide dismutase (SOD) prevented this phenomenon. These results suggest that the inhibition of NK cell activity by AM may be caused by O2 release rather than PG, H2O2, and OH.

Effect of Biostim (RU 41.740) on natural killer cell generation from bone marrow precursors

We have evaluated the possible effect of RU 41.740 (Biostim), a mixture of two glycoproteins extracted from K. pneumoniae, on the in vitro interleukin-2 (IL-2)-induced generation of NK cells from bone marrow (BM) precursors and on the in vivo reconstitution of splenic NK activity in lethally irradiated (9 Gy) and BM reconstituted mice. Our results show that RU 41.740 is able to augment the generation of NK cells when added (1-0.01 micrograms/ml) to normal or 5-fluorouracil-resistant BM, cultured in the presence of recombinant IL-2. Also, in vivo treatment of lethally irradiated mice, transplanted with syngeneic BM cells, with RU 41.740 (1-0.1 mg/kg i.v.) from day 0 through day 4 after BM graft, resulted in a significant augmentation of NK activity reconstitution.

Depletion of catecholamines with alpha-methyl-p-tyrosine suppresses splenic NK cell activity

The effects of depleting the tissue catecholamines with alpha-methyl-p-tyrosine (AMPT, an inhibitor of catecholamine synthesis) on the splenic NK cell cytotoxic activity were assessed both in vivo and in vitro. Treatment with i.p. doses of AMPT (3-500 mg/kg) produced a dose-related suppression in the splenic NK cytotoxic activity in many mouse strains. For an i.p. dose of 300 mg/kg of AMPT, the splenic NK cell activity began to fall 1 h after AMPT injection. The splenic NK cell activity reached its maximal level at 3 h, accompanied by a severe depletion of norepinephrine contents in the spleen. Both the NK activity and the splenic norepinephrine content returned to their control levels at 24 h. Direct addition of AMPT (up to 2500 micrograms/ml) to the cultured mouse spleen cells in vitro resulted in no NK suppression. However, when the serum obtained from the AMPT-treated mice was added to the cultured mouse spleen cells of the AMPT-untreated mice, the splenic NK cytotoxic activity was greatly suppressed. In addition, natural killing by spleen cells from AMPT-untreated mice was not reduced by the addition of spleen cells from AMPT-treated mice. No evidence of AMPT-induced cellular suppressors of natural killing could be detected. It was also found that both the splenic NK cell activity and the effector-target cell conjugation activity were suppressed by treatment with AMPT. These observations indicate that depleting the tissue catecholamines with AMPT results in the release of certain humoral factors which can suppress both the effector-target cell conjugation activity and the splenic NK cell activity in mice.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Immunoregulation of human natural killer cells (NK) by corticosteroids: inhibitory effect of culture supernatants

Peripheral blood lymphocytes were separated into HNK-1+ and HNK-1- subpopulations and examined for the effects of prednisolone (PRD) on natural killer cell activities in vitro. Preculture of HNK-1+ lymphocytes with PRD (10(-6) to 10(-8) mol/L) for 72 hours resulted in a significant reduction of cytotoxic functions. When peripheral blood lymphocytes were first precultured with PRD and then separated into HNK-1+ and HNK-1- subpopulations, both could suppress the target binding and lytic activities of fresh large granular lymphocytes with the HNK-1+ cells demonstrating greater inhibition than the HNK-1- cells. Moreover, PRD-treated cells demonstrated greater suppression of target binding and cytotoxicity than identical subpopulations cultured without PRD. Culture supernatants of lymphocytes treated with 10(-6) to 10(-9) mol/L concentrations of PRD contain PRD-induced soluble suppressor factor that significantly inhibited the natural killer activity of allogeneic lymphocytes against different targets. PRD-induced soluble suppressor factor was not cytotoxic itself, and suppression was evident at various effector-to-target cell ratios. These studies indicate that in addition to being directly immunosuppressive, corticosteroids may also induce immunoregulatory lymphocytes to secrete a suppressive lymphokine.

Immunoregulation of lymphokine-activated killer cells

The in vitro effects of Concanavalin A (Con A) and prednisolone (PRD) on the cytotoxic functions of lymphocytes and the generation of lymphokine-activated killer (LAK) cells were investigated. Con A at concentrations ranging from 1 to 40 micrograms/ml did not significantly affect the cytotoxicity of LAK cells when added directly to the effector and target cell mixture in a 4-hr 51Cr release assay. The generation and lytic capacity of LAK cells were significantly affected by Con A in a dose-dependent manner when lectin was added at the initiation of culture. Suppression of LAK cell activity was demonstrable at effector: target (E:T) cell ratios. Lymphocyte cultures incubated with PRD at concentrations ranging from 10(-9) to 10(-4) M showed a decrease in both the numbers of and activity of LAK cells using a variety of target cells. Pretreatment of target cells with either PRD or Con A did not affect their sensitivity to lysis by LAK cells and incubation of lymphocytes with Con A did not induce autoreactive cytotoxic or suppressor cells directed against LAK cell activity. Thus while PRD and Con A can inhibit the generation of LAK cells, they also directly inhibit their specific cytotoxic activity on a per cell basis. These results suggest that like other cytotoxic cells, LAK cells are also under active immunologic control.

Comparison of NK activity in mouse spleen and peripheral blood lymphocytes

Natural killer (NK) cells originating in mouse peripheral blood were studied with regard to their lytic activity against YAC-1 target cells and to their expression of asialo-GM1 marker on their surface. In Balb/c, CBA/LAK and A/J mice, PBL were found to be approximately twice as effective as splenocytes. Splenic and peripheral NK cells were shown by flow cytometry to have similar lytic potential per cell; the difference in NK activity found in the spleen and in PBL was solely due to the differences in the size of the NK cell population found in the two sites. Strain distribution of NK activity in PBL followed the same pattern observed in splenocytes. The difference in NK activity between CBA and Balb/c mice was shown to be due to the fact that the lytic potential per NK cell was approximately twice as high in the former.

Inhibition of natural killer cell-mediated lysis of tumor cells by normal and regenerating bone marrow

The natural killer (NK) cells which can lyse certain tumor cells during brief incubation in vitro have also been postulated to be the cells responsible for natural resistance to transplanted hemopoietic cells in vivo. To test this hypothesis, we have now measured: 1) the ability of bone marrow cells to compete with tumor cells as targets for spleen NK cells and 2) the effect of a brief incubation with spleen cells on the hemopoietic grafting potential of bone marrow cells. Firstly, when CBA/J mouse spleen cells were incubated with 51Cr-labelled YAC tumor cells together with DBA/2 mouse bone marrow cells, tumor cell lysis was reduced compared with incubation of spleen cells with tumor cells alone. Tumor cell lysis was even less when post-irradiation regenerating bone marrow was used. Secondly, C57B1/6 mouse bone marrow cells incubated with an excess of DBA/2 mouse spleen cells showed a reduced ability to produce hemopoietic spleen colonies in irradiated 129/J mice, whereas incubation with either thymus cells or fewer spleen cells produced no such effect. The results show that, when incubated with spleen cells under the conditions of a standard NK cell assay, regenerating bone marrow cells competitively inhibit the killing of YAC tumor cells and bone marrow progenitor cells are rendered ineffective in their hemopoietic colony-forming potential (CFU-s). These findings suggest that certain hemopoietic progenitor cells and YAC tumor cells can both serve as targets for NK cells, consistent with the view that the spontaneous cytolysis of tumor cells in vitro and natural resistance to bone marrow transplantation in vivo are mediated by cells of a common lineage.

In vivo function of natural killer cells as regulators of myeloid precursor cells in the spleen

In order to study the in vivo effect that natural killer (NK) cells may have on hematopoietic precursor cells in the autologous host, NK-depleted mice were constructed by injection of an anti-NK-1.1 monoclonal antibody. Only the spleen, and not the bone marrow, of such NK-depleted mice shows an increase in the number of myeloid precursur cells able to form colonies in soft agar as compared to control mice with normal levels of NK activity. The increase in number of hematopoietic immature cells due to lack of a regulatory cell (i.e. NK cell) is selective for the committed myeloid precursur cells, and not evident for erythroid or pluripotent progenitor cells. This is direct evidence in support of the hypothesis that NK cells in the autologous host serve as a regulator of extramedullary myelopoiesis.

Effect of interleukin 2 on fetal thymocytes in organ cultures: generation of lymphokine-activated killer cells

Cells with cytolytic activity can be detected in mouse fetal thymic lobes cultured in the presence of interleukin 2 for 6 days. The lymphokine-activated killer cells from 14-day fetal thymic lobes are relatively resistant to treatment with anti-Ly-2 antibody and complement (CD8-) but sensitive to anti-Thy-1 and complement treatment (Thy-1+). They display major histocompatibility complex-unrestricted killing, lysing both syngeneic and allogeneic tumor cells, but will not lyse human xenogenic target cells. Low levels of cytotoxic activity can be detected in thymic lobes from Day 12-13 embryos and this activity increases with embryonic age. While the events which lead to the inhibition of normal maturation of fetal thymocytes by inclusion of IL-2 in fetal thymus organ cultures are unknown, the appearance of cytotoxic cells raises the question of whether they are involved in the normal intrathymic cell death process.

Role of interferons in natural killer cell generation from primitive bone marrow precursors

We studied the possible role of interferons (IFNs) on the interleukin-2 (IL-2)-dependent development of mouse natural killer (NK) cells from undifferentiated bone marrow (BM) precursors. Results indicate that alpha-IFN is able to synergize with IL-2 in the induction of lytic effectors. The stimulating effect of alpha-IFN is dose-dependent and is also obtained when BM cells are pretreated shortly before culturing. The precursor cells are resistant to treatment with 5-fluorouracil (FU, 150 mg/kg i.v.). Treatments which have been shown to eliminate more differentiated cells but spare less differentiated BM precursors, are asialoGM1-, Thy1+, Lyt1- and Lyt2-. Effector cells generated by culturing with IL-2 and alpha-IFN are typical NK cells in that they lyse only NK-susceptible targets. These are Thy1+, asialoGM1+, Lyt5+, Lyt1- and Lyt2-. These data suggest that alpha-IFN may represent a maturational signal for the generation of NK cells from undifferentiated BM precursors.

Regulation of natural killer activity

Cells mediating natural killer (NK) activity mediate lysis against a variety of tumor cells and may serve as important effector cells in host resistance to infection. NK active cells are present in virtually all individuals and can be rapidly activated by a wide range of stimuli. Their activities are non-MHC restricted and do not depend on sensitization by antigens, a prerequisite for specific immunity. Several important components of the immunoregulation of NK active cells are: 1) positive or negative signals that regulate the expression of NK activity, and 2) the ability of these cells to function as immunoregulatory cells. The majority of the agents that activate NK activity fall into two basic categories; the interferons and interleukin-2. This review will concentrate on studies regarding these two agents, and will primarily discuss the results obtained with recombinant molecules.

Differential effects of beta-endorphin fragments on human natural killing

The endogenous opiate peptide, beta-endorphin, has two effects on human natural killing (NK). Preincubation of effector lymphocytes with between 10(-7) and 10(-11) M beta-endorphin increases NK. Preincubation with lower concentrations results in a reduction in NK. Endorphin peptides containing an unmodified N-terminal sequence, and which are known to bind only to opiate receptors, increase NK. Sequences reported to bind only to nonopiate receptors reduce NK.

Interleukin 2 enhances cytotoxic cell function in vitro after T-cell depleted marrow transplantation

After T-cell depleted marrow transplantation, there is a rapid recovery of cytotoxic effector cells, with activity against targets not susceptible to killing by 'resting' natural killer cells. These targets include Epstein-Barr virus transformed B cells and leukaemic cell lines. Activated killer cell function declines by 3 months after transplantation. We find that when CD3 negative effector cells are obtained from these patients and cultured in vitro with interleukin 2 there is a further enhancement of cytotoxic activity against a range of target cells in the early post-transplant period, and a restoration of high level cytotoxic activity to effector cells obtained 3 months or more after the procedure. These results may have relevance to attempts to reduce the incidence of leukaemic relapse, and EBV + ve lymphoma outgrowth after T-cell depleted BMT.

Selective inhibition of human natural killing and antibody-dependent cellular cytotoxicity by a polyanion

A high molecular polyanion, Liquoid, was found to inhibit at nontoxic concentrations (12-50 micrograms/ml) the natural killing (NK) and the antibody-dependent cellular cytotoxic (ADCC) activity of human peripheral blood mononuclear cells selectively. Whereas NK of the K 562 target cell was slightly or not at all affected, the spontaneous lysis of PDe-B-1, an EBV-transformed B-cell line, was strongly inhibited or even completely abolished. ADCC activity could only be inhibited by Liquoid if the target cells were mycoplasma-free, while the polyanion had no effect when mycoplasma-contaminated target cells were used. Liquoid did not alter the target binding capacity of the NK effector cells and did not activate monocytes or induce other suppressive cells. Alpha interferon, but neither beta nor gamma interferon, was able to neutralize the NK reduction. These results suggest that Liquoid inhibits a target cell-related, selective process in the post-binding stage of NK cell lysis.

The effect of radiotherapy on the natural killer (NK)-cell activity of cancer patients

The aim of this study was to determine the effect of radiotherapy on peripheral blood natural killer (NK)-cell number and activity in 15 patients with cancer, prior to the commencement and at the completion of radiotherapy. The following observations were made. Prior to radiotherapy NK activity could not be correlated with the stage of malignancy. In all patients with advanced disease and with subnormal baseline NK activity, the outcome of radiotherapy was unfavorable. Following radiotherapy to sites including the mediastinum, patients had decreased NK activity compared with those receiving treatment to other sites. This decrease was not related to the dose of radiotherapy or stage of malignancy. The tumor response was favorable in most patients whose NK activity decreased as a result of radiotherapy. The decrease in NK activity may be associated with a decrease in the percentage of NK (N901) cells in the peripheral blood. The reduction in NK activity in those patients receiving mediastinal irradiation may be due to the large volume of blood which transits the field, so that the NK cells, or their more radiosensitive precursors, may be damaged and/or differentiation inhibited. Thus, these new observations show that radiotherapy does indeed affect the NK activity in cancer patients predominantly when the irradiation site includes the mediastinum.

Inhibition of postbinding target cell lysis and of lymphokine-induced enhancement of human natural killer cell activity by in vitro exposure to ultraviolet B radiation

In vitro exposure of human peripheral blood mononuclear cells (PBMC) to ultraviolet B (uvB) radiation has been shown to inhibit natural killer (NK) cell-mediated cytotoxicity in a dose-dependent fashion. The purpose of this study was to examine the manner by which uvB produced these deleterious effects. Inhibition of NK activity was not due to lethal injury to NK cells since the viability of cell populations enriched for NK activity was greater than 90% with the uvB doses employed. uvB appeared to directly affect NK cells since procedures which removed suppressor mechanisms, such as removal of monocytes and pharmacologic inhibition of the cyclooxygenase pathway, failed to reverse the response. Furthermore, no suppression of activity of unirradiated NK cells could be produced by coincubation of unirradiated NK cells with uv-irradiated NK cells. When the single cell assay for binding and killing was employed to determine at which stage in the lytic sequence inhibition occurred, it was found that binding was normal but lysis of bound targets and the recycling capacity of active NK cells were markedly reduced. At uvB doses above 50 J/m2, both interferon alpha (IFN-alpha) and interleukin 2 (IL-2) were ineffective in augmenting NK cell-mediated cytotoxic reactions after cells had been irradiated with uvB. Furthermore, incubation of NK cells with IFN-alpha prior to irradiation failed to protect against the inhibitory effects. These studies provide evidence that in vitro exposure of NK cells to uvB radiation inhibits their function by a direct nonlethal effect and that this inhibition occurs selectively at the postbinding stage of target cell lysis.

Relationship of cytotoxic activity of natural killer cells to growth rates and serum zinc levels of female RIII mice fed zinc

This study examined a) the dietary zinc (Zn) requirement of RIII female weanling mice and b) the cytotoxicity of murine natural killer (NK) cells obtained from spleens of these mice fed varying levels of Zn. Zn was fed in a biotin-enriched egg albumen diet in amounts ranging from 0.9 to 40.4 micrograms/g diet. During a 28-day growth assay, maximum carcass growth was obtained with a diet containing 5.4 micrograms Zn/g diet. Maximal serum levels of Zn, however, were observed in mice fed diets containing 3.4 micrograms Zn/g diet. The cytotoxic activity of NK cells obtained from spleens of selected treatment groups was maximal at 40.4 micrograms Zn/g diet and was significantly higher (p less than or equal to 0.05) than that observed in spleens from mice fed diets that maximized carcass growth rates and serum Zn concentrations. It is concluded that female RIII mice have a dietary Zn requirement for growth similar to that observed for other murine strains but considerably lower than that reported for the rat. Our findings also suggest that RIII NK cells are particularly sensitive to dietary Zn intake: the optimal functional activity of these cells may result from intake of Zn higher than that necessary to maximize carcass growth and serum Zn concentrations.

Regulation of hematopoiesis by T lymphocytes and natural killer cells

T lymphocytes and natural killer (NK) cells exert both stimulatory and suppressive effects that regulate growth and differentiation of hematopoietic cells. Activated T and NK cells have been demonstrated in different pathological states of bone marrow failure and are proposed to play a role in the pathogenesis of the disease. T and NK cells have also been shown to be responsible for bone marrow graft rejection in both allogeneic and syngeneic donor/recipient combinations. Lymphocytes can regulate hematopoietic cell growth by direct cellular contact or by releasing soluble factors, such as colony-stimulating factors, immune interferon, lymphotoxin, and tumor necrosis factor, active on hematopoietic precursor cells.

Differential effect of hybrid resistance on the localization of virus-immune effector T cells to spleen and brain

The hybrid resistance (Hr) effect operates in the lymphocytic choriomeningitis (LCM) in vivo transfer model to inhibit both the level of cytotoxicity T lymphocyte (CTL) generation in spleen and the induction of inflammation in cerebrospinal fluid (CSF). The effect is seen when LCM virus-immune T cells that are homozygous for H-2Db are injected into virus-infected, immunosuppressed recipients that are heterozygous for this allele, or into radiation chimeras that express an appropriate F1 phenotype. Evidence that Hr to T-cell transfer is cell-dose-dependent and tends to diminish with age was found in both chimeric and normal F1 mice. Inhibition of the capacity of injected T cells to cause meningitis is a more sensitive measure of Hr than is the further stimulation of CTL effectors in recipient lymphoid tissue. The injection of large numbers of H-2b virus-immune T cells into (H-2k X H-2bF1----H-2k) virus-infected recipients did not induce any cellular extravasation into CSF, though potent H-2b-restricted CTL effectors were generated in recipient spleen. Evidence of minimal inflammatory process was found in one experiment where these chimeras were given a comparable dose of (H-2b X H-2d)F1 immune spleen cells. Development of this T-cell-mediated immunopathological process depends essentially on the expression of the appropriate H-2 restriction element on radiation-resistant host cells which, in this case, presumably constitute part of the physiological barrier between blood and CSF.

Natural killer cell regulation of age-related and type-specific variations in antibody responses to pneumococcal polysaccharides

Pretreatment of mice with anti-asialo GM1, which has been shown to deplete NK cytolytic activity without affecting cytotoxic T cells or macrophages, increased the weak anti-PPS 6 responses of adult mice to levels similar to that of their anti-PPS 3 responses, and increased the weak-to-absent anti-PPS 3 and anti-PPS 6 responses of weanling mice to the same levels as achieved by adult mice. By contrast, pretreatment with poly(IC), which augments NK activity, resulted in a 14-fold reduction in the anti-PPS 3 responses of adult mice. The enhancement of anti-PPS responses in mice treated with anti-asialo GM1 was due to inactivation or depletion of NK cells, and not T suppressor cells, since this enhancement occurred in athymic nude mice as well as in euthymic mice. In addition, strains of mice with low or absent endogenous NK activity were found to have considerably stronger anti-PPS responses than strains of mice with normal NK activity. NK depletion enhanced anti-PPS 6 IgM but not IgG response, and resulted in a true increase in antibody production rather than an alteration in the time course of the response. These findings indicate that NK cells physiologically downregulate anti-PPS responses, and that age-dependent and type-specific variations in these responses are primarily determined by NK regulatory effects.

Generation of mouse natural killer (NK) cell activity: effect of interleukin-2 (IL-2) and interferon (IFN) on the in vivo development of natural killer cells from bone marrow (BM) progenitor cells

The possible effect of IL-2, alpha,beta-IFN and poly I:C (an IFN inducer) administration on the generation of NK cells of LI and BM-reconstituted animals was investigated. B6D2F1 mice were LI (9.5 Gy) by total-body irradiation and reconstituted by i.v. injection of different doses (ranging from 10(6) to 2 X 10(7)) of syngeneic BM, after which the levels of splenic NK activity were evaluated on days 4, 7, 9, 12 and 14 after LI and BM graft. After a marked decline on day 4 (no detectable NK activity at any effector to target ratio tested), NK activity gradually returned, reaching the levels of untreated controls on day 9. Groups of LI and BM-reconstituted mice were also treated i.p. with mouse or human recombinant IL-2 from day 0 through day 3 (15-50 U/day/mouse) after BM transplantation. It appears that an earlier reconstitution of NK activity occurs in IL-2-treated animals as compared to medium-injected controls. LI and BM-reconstituted animals were also treated i.p. with alpha,beta-IFN (10(4) U/mouse) or Poly I:C (1 mg/kg/mouse) from day 0 through day 3, and the splenic NK activity was evaluated at 4, 7, 9, 12 and 14 days after LI and BM graft. Our data indicate that in vivo administration of IFN or Poly I:C was able to cause an earlier maturation of NK activity as measured on days 7 and 9 after LI. In contrast, when the NK activity of IFN-treated animals was compared with that of controls 14 days after LI and BM graft, a significant inhibition was found due to the induction of suppressor cells. Pre-treatment of donor BM with Poly I:C or IFN was also able to induce a more rapid reconstitution of NK activity of recipient mice. The NK activity reconstitution paralleled the increase in the number of splenic LGL. A synergistic effect was obtained when LI mice were transplanted with Poly I:C-pre-treated BM and then treated with IL-2. The effector cell in the IFN and IL-2 treated chimeras is a typical NK cell: asialo GM-1+, Thy 1 +/-, Lyt 1-, Lyt 2- and reactive only against NK-susceptible targets. These data suggest that IL-2 as well as IFN may represent maturational signals in the in vivo physiological regulation of growth and differentiation of BM NK stem-cells.