Natural killer activity in the rat. II. Analysis of surface antigens on LGL by flow cytometry

With the use of monoclonal antibodies and continuous flow microfluorometry, we have examined the cell surface antigenic characteristic of rat large granular lymphocytes (LGL) and compared them with monocytes, T cells, and polymorphonuclear leukocytes (PMN). The antigenic profile of rat LGL was of particular interest because these cells have been shown to be highly associated with natural killer (NK) activity. This analysis of enriched populations demonstrated that rat LGL are in antigenically distinct population of cells that share some characteristics with monocytes, T cells, and PMN. Essentially all of the cells in the enriched LGL population expressed with W3/13, OX-8, leukocyte-common (L-C), and asialo GM1 antigens. A portion of these cells were also positive with a monoclonal Ab against the ART-1a antigen. In contrast, few LGL expressed the Ia, W3/25, surface immunoglobulin (sIg), or Thy 1.1 antigens. Monocytes demonstrated a pattern of reactivity similar to LGL but were found to by OX-8 negative. As previously reported, a portion of the T cells were found to express ART-1a, W3/25, and/or OX-8. These results demonstrate that rat LGL are not typical T cells, B cells, monocytes, or PMN. However, the sharing of antigenic markers by LGL with some T cells and monocytes raises the possibility that LGL may be in the development lineage of 1 of these populations.

Natural killer cells: their roles in defenses against disease

Natural killer cells are a recently discovered subpopulation of lymphoid cells that are present in most normal individuals of a range of mammalian and avian species. Natural killer cells have spontaneous cytolytic activity against a variety of tumor cells and some normal cells, and their reactivity can be rapidly augmented by interferon. They have characteristics distinct from other types of lymphoid cells and are closely associated with large granular lymphocytes, which comprise about 5 percent of blood or splenic leukocytes. There is increasing evidence that natural killer cells, with the ability to mediate natural resistance against tumors in vivo, certain virus and other microbial diseases, and bone marrow transplants, may play an important role in immune surveillance.

Human large granular lymphocytes: spontaneous and interferon-boosted NK activity against adherent and nonadherent tumor cell lines

Human natural killer (NK) cells against K-562 tumor cells have been morphologically identified as large granular lymphocytes (LGL). We have investigated whether LGL are also responsible for NK activity against a variety of adherent and nonadherent tumor cell lines. LGL-enriched fractions, obtained by centrifugation of nonadherent mononuclear cells on discontinuous density gradients of Percoll, contained high levels of spontaneous and interferon- (IFN) boosted NK activity against each of the target cells tested. In contrast, the LGL-depleted functions, which contain most of the typical small lymphocytes, were devoid of NK activity and did not develop appreciable activity after treatment with IFN. The ability of the different fractions to exert NK activity correlated with their capacity to form conjugates with nonadherent tumor cells. Reconstitution of the different fractions with macrophages did not increase the NK activity of already cytotoxic fractions and did not induce appreciable activity in the LGL-depleted fractions. On the other hand, mixtures of highly cytotoxic and nonreactive cell fractions did not reveal the presence of suppressor cells for NK in the nonreactive fractions. Taken together, our data demonstrate that both spontaneous and IFN-boosted NK activity is confined to the LGL-enriched fractions and suggest that LGL are the main effector cells exerting NK cytotoxicity against a variety of adherent as well as nonadherent tumor cell lines.

Human large granular lymphocytes: spontaneous and interferon-boosted NK activity against adherent and nonadherent tumor cell lines

Human natural killer (NK) cells against K-562 tumor cells have been morphologically identified as large granular lymphocytes (LGL). We have investigated whether LGL are also responsible for NK activity against a variety of adherent and nonadherent tumor cell lines. LGL-enriched fractions, obtained by centrifugation of nonadherent mononuclear cells on discontinuous density gradients of Percoll, contained high levels of spontaneous and interferon- (IFN) boosted NK activity against each of the target cells tested. In contrast, the LGL-depleted functions, which contain most of the typical small lymphocytes, were devoid of NK activity and did not develop appreciable activity after treatment with IFN. The ability of the different fractions to exert NK activity correlated with their capacity to form conjugates with nonadherent tumor cells. Reconstitution of the different fractions with macrophages did not increase the NK activity of already cytotoxic fractions and did not induce appreciable activity in the LGL-depleted fractions. On the other hand, mixtures of highly cytotoxic and nonreactive cell fractions did not reveal the presence of suppressor cells for NK in the nonreactive fractions. Taken together, our data demonstrate that both spontaneous and IFN-boosted NK activity is confined to the LGL-enriched fractions and suggest that LGL are the main effector cells exerting NK cytotoxicity against a variety of adherent as well as nonadherent tumor cell lines.

Augmentation of natural and antibody-dependent cell-mediated cytotoxicity by pure human leukocyte interferon

Augmentation of the cytolytic activity of human natural killer cells and of antibody-dependent cell-mediated cytotoxicity has been attributed to human interferons. With the purification to homogeneity of human leukocyte interferon, it became possible to test directly whether pure interferon could increase the activity of these effector cells. Treatment of purified blood mononuclear cells with pure interferon resulted in substantial increases in natural killer cell activity and in antibody-dependent cell-mediated cytotoxicity. Concentrations of 10-100 units/ml of antiviral activity were sufficient to augment appreciably natural killer cell activity.

Characteristics of human large granular lymphocytes and relationship to natural killer and K cells

Recent evidence, has demonstrated an association between a subpopulation of peripheral blood mononuclear cells, morphologically identified as large granular lymphocytes (LGL), and natural killer (NK) activity. We have now evaluated more directly the role of LGL in both NK activity and antibody- dependent cellular cytotoxicity (ADCC), by using highly enriched populations of LGL, obtained by centrifugation of peripheral blood mononuclear cells on Percoll discontinuous density gradients. Both spontaneous and interferon- augmented NK and ADCC activities were exclusively associated with the LGL- enriched, low density fractions. The majority of LGL formed conjugates with NK-susceptible and antibody-coated target cells. Approximately 20 percent of small conventional lymphocytes also formed conjugates with the target cells for NK, but this was not associated with cytotoxic activity. Virtually all LGL were found to have receptors for the Fc portion of IgG (FcgammaR). The frequency of LGL among blood leukocytes was 2-6 percent. LGL could be enriched to an average purity of 95 percent by combining discontinuous density gradient centrifugation with subsequent adsorptions of the low density fractions on monolayers of immobilized immune complexes. About 50 percent of LGL were found to be FcgammaR-bearing T cells (T(G)), forming low affinity rosettes with sheep erythrocytes at 4 degrees C. Only 10-20 percent of LGL formed high affinity rosettes with sheep erythrocytes at 29 degrees C. LGL could be enriched to a purity of more than 90 percent by depleting high affinity rosette-forming cells from low density Percoll fractions. LGL were only a subpopulation of T(G) cells, because some lymphocytes with conventional morphology also adhered to the immobilized immune complex monolayers and formed high affinity rosettes with sheep erythrocytes. Separation of these cells from LGL by discontinuous density gradient centrifugation indicated that they are not cytotoxic, suggesting a morphological and functional subdivision of T(G) cells. The verification in this study that virtually all human NK and K cells have a characteristic morphology adds a useful parameter to the monitoring of human lymphocytes, and the ability to purify these cells by simple physical procedures should be invaluable in their further characterization.

Augmentation of human natural killer cell activity by interferon: conditions required for boosting and characteristics of the effector cells

Human effector cells of natural killer (NK) activity have been augmented by pretreatment with a partially purified preparation of interferon (IFN-beta). Using the 4-hr 51Cr release assay to measure cytotoxicity, the boosted effector cells, as well as the spontaneous NK cells, were nonphagocytic cells with receptors for the Fc portion of IgG. Augmentation of cytolytic activity occurred: (1) in medium with either fetal calf serum and human serum; (2) in the presence of absence of monocytes; (3) in both sheep RBC rosette-forming and non-rosette-forming populations; and (4) when only the effector cells were pretreated with interferon. This last observation led to the finding that less than or equal to 5 min of contact at 37 degrees C, 22 degrees C, or 4 degrees C with interferon was necessary for augmentation of cytotoxicity. Augmentation kinetics demonstrated significant boosting of NK activity in peripheral blood leukocytes and highly NK-enriched Percoll fractions after 1 hr of contact with IFN-beta or pure IFN-alpha-Collectively, these results indicate that NK boosting with interferon: (1) occurs after a rapid temperature-independent binding to the effector cells; and (2) has a rapid effect on the cytolytic process.

Augmentation of human K-cell activity with interferon

Our laboratory recently reported that interferon (IF) could augment human antibody-dependent cellular cytotoxicity (ADCC) and cytotoxicity by natural killer (NK) cells. Although there is general agreement that IF can boost the activity of human NK cells, two laboratories have reported a failure to boost ADCC. We have therefore examined in more detail the effects of IF on human ADCC. We have found, by several lines of evidence, that IF can indeed appreciably augment the activity of K cells, the subpopulation of lymphocytes that mediate ADCC: (1) human leucocyte IF, purified to homogeneity, boosted ADCC: (2) IF augmented ADCC against target cells that were completely resistant to NK activity; and (3) the ADCC activity of leukaemic cells from a patient with chronic lymphocytic leukaemia (CLL) which lacked any detectable NK activity was boosted by IF. These results are consistent with the hypothesis that human NK and K cells are the same subpopulation of lymphocytes and that the mechanisms regulating their activity are similar. However, the absence of NK activity in the CLL patient strongly supports the idea that not all FcR-positive cells are NK and that ADCC effectors devoid of NK may exist. However, further evidence is required to analyse this point.

Selective depletion of human natural killer cells on monolayers of target cells

The specificity of human natural killer (NK) cells recently has been evaluated by examining direct cytotoxic reactions against a variety of target cells and by cold target inhibition assays. Although these studies have provided evidence for the multiplicity of NK antigens, they did not indicate whether NK cells were heterogeneous, with subpopulations recognizing different specificities. We have examined this issue by using a tumor cell-monolayer adsorption technique that allowed the removal of NK-reactive cells by adsorption to monolayers of various NK-sensitive target cells. After depletion of cells capable of binding to a particular monolayer, the remaining cells were tested for cytotoxicity against a panel of 5 target cells. With several donors, the monolayers were effective in depleting most or all reactivity against the same target cell but only removed a portion of reactivity against some other target cells. The patterns of reactivity after adsorption, although varying among the donors, were consistent upon repeat testing of the same donor. To account for the reactivities of the various donors that remained after adsorption, it was necessary to postulate at least 7 antigenic specificities. These results indicate that human NK cells may be heterogeneous, with each subpopulation recognizing different antigenic specificities on target cells.

Selective depletion of human natural killer cells on monolayers of target cells

The specificity of human natural killer (NK) cells recently has been evaluated by examining direct cytotoxic reactions against a variety of target cells and by cold target inhibition assays. Although these studies have provided evidence for the multiplicity of NK antigens, they did not indicate whether NK cells were heterogeneous, with subpopulations recognizing different specificities. We have examined this issue by using a tumor cell-monolayer adsorption technique that allowed the removal of NK-reactive cells by adsorption to monolayers of various NK-sensitive target cells. After depletion of cells capable of binding to a particular monolayer, the remaining cells were tested for cytotoxicity against a panel of 5 target cells. With several donors, the monolayers were effective in depleting most or all reactivity against the same target cell but only removed a portion of reactivity against some other target cells. The patterns of reactivity after adsorption, although varying among the donors, were consistent upon repeat testing of the same donor. To account for the reactivities of the various donors that remained after adsorption, it was necessary to postulate at least 7 antigenic specificities. These results indicate that human NK cells may be heterogeneous, with each subpopulation recognizing different antigenic specificities on target cells.

Effects of metabolic inhibitors on spontaneous and interferon-boosted human natural killer cell activity

Human natural killer (NK) cell activity can be augmented by pretreatment with partially purified preparations of human interferon (IF). Studies have now been performed to determine the metabolic processes required for and involved in spontaneous NK activity and augmentation of cytotoxicity. A 4-hr 51Cr release cellular cytotoxicity assay was used to measure the NK activity, and peripheral blood leukocyte cells (PBL) were treated with: a) x-ray or mitomycin C; b) actinomycin D; or c) emetine, cycloheximide, pactamyhcin, or puromycin to assess the roles of DNA, RNA, and protein synthesis, respectively, in spontaneous NK activity and in boosting by IF. Prolonged incubation (18 hr) of PBL after blockage of synthesis of DNA almost completely abrogated NK activity; however, NK activity could be partially or totally restored to these populations by incubation of the effector cells for 1 hr at 37 degrees C with IF. Blockage of DNA synthesis for 1 hr had no effect on spontaneous NK activity or on boosting by IF. Inhibition of RNA synthesis also had no effect on spontaneous NK activity. Treatment of PBL with actinomycin before exposure to IF prevented boosting, but treatment with the RNA synthesis inhibitor after boosting with IF for 5 to 6 hr no longer had an appreciable effect on cytotoxicity. The effect of protein synthesis inhibitors on spontaneous NK activity was dependent on the inhibitor selected. Emetine and puromycin totally abrogated spontaneous NK activity at concentrations of inhibitor that blocked 3H-leucine incorporation 90% or more. In contrast, cycloheximide and pactamycin had only minimal effects on spontaneous NK activity but totally abrogated the boosting of IF.

Effects of metabolic inhibitors on spontaneous and interferon-boosted human natural killer cell activity

Human natural killer (NK) cell activity can be augmented by pretreatment with partially purified preparations of human interferon (IF). Studies have now been performed to determine the metabolic processes required for and involved in spontaneous NK activity and augmentation of cytotoxicity. A 4-hr 51Cr release cellular cytotoxicity assay was used to measure the NK activity, and peripheral blood leukocyte cells (PBL) were treated with: a) x-ray or mitomycin C; b) actinomycin D; or c) emetine, cycloheximide, pactamyhcin, or puromycin to assess the roles of DNA, RNA, and protein synthesis, respectively, in spontaneous NK activity and in boosting by IF. Prolonged incubation (18 hr) of PBL after blockage of synthesis of DNA almost completely abrogated NK activity; however, NK activity could be partially or totally restored to these populations by incubation of the effector cells for 1 hr at 37 degrees C with IF. Blockage of DNA synthesis for 1 hr had no effect on spontaneous NK activity or on boosting by IF. Inhibition of RNA synthesis also had no effect on spontaneous NK activity. Treatment of PBL with actinomycin before exposure to IF prevented boosting, but treatment with the RNA synthesis inhibitor after boosting with IF for 5 to 6 hr no longer had an appreciable effect on cytotoxicity. The effect of protein synthesis inhibitors on spontaneous NK activity was dependent on the inhibitor selected. Emetine and puromycin totally abrogated spontaneous NK activity at concentrations of inhibitor that blocked 3H-leucine incorporation 90% or more. In contrast, cycloheximide and pactamycin had only minimal effects on spontaneous NK activity but totally abrogated the boosting of IF.

Characterization of a suppressor T-cell chronic lymphocytic leukemia with ADCC but not NK activity

A patient with T-cell chronic lymphocytic leukemia (T-CLL) is reported whose cells demonstrate in vitro suppression of normal lymphocyte mitogen stimulation. The patient, who remains in Rai's clinical stage 0 on no therapy after more than 24 mo of observation, has shown a less aggressive clinical course than is usually attributed to T-CLL. His peripheral blood lymphocytes (PBL) were characterized by functional assays as well as surface markers. Over 90% of the patient's PBL formed rosettes with sheep erythrocytes and were lysed by two T-cell-specific antisera plus complement, while less than 1% bore surface immunoglobulins, and only 3% had complement receptors. In addition, 45% of the PBL demonstrated Ia-like antigens, more than 50% expressed a receptor for the Fc portion of IgG(T gamma), and most of the sheep erythrocyte rosettes were inhibited by theophylline. The patient's cells failed to respond to several mitogens and they caused marked suppression of lymphoproliferative responses to normal PBL to phytohemagglutinin (PHA) and concanavalin A (Con-A). The patient's lymphocytes also exhibited antibody-dependent cytotoxic activity (ADCC) against antibody-coated nucleated target cells, but lacked demonstrable natural killer (NK) activity. This patient's T-CLL cells appear to represent the clonal expansion of a subset of T cells with a previously undescribed pattern of suppressor and cytotoxic activities.

Brief communication: technical modifications of the human agarose microdroplet leukocyte migration inhibition assay

Direct leukocyte migration inhibition assays using the capillary tube technique can be used to demonstrate cell-mediated immunity in vitro. Unfortunately, the cumbersome nature of this technique makes it time consuming and difficult to perform. Similar results have been obtained using the direct agarose microdroplet leukocyte migration inhibition assay. In this paper, modifications of the agarose technique are outlined which insure standardization of droplets and ease of performance of the assay. Additionally a technique is described to reduce the time required for calculation of results.

Role of interferon in augmentation of natural and antibody-dependent cell-mediated cytotoxicity

Natural killer (NK) activity in rats and NK and antibody-dependent cell-mediated cytotoxicity in mice have been shown to be rapidly augmented by in vivo treatment with a variety of viruses and immune adjuvants. Poly I:C and other interferon inducers also caused boosting in NK-cell activity, with peak levels occurring at about the time of peak interferon levels. Crude and purified virus-induced interferon itself had strong boosting effects in mice, both when inoculated in vivo and when incubated briefly with normal spleen cells. The in vitro activation by interferon or by poly I:C was completely abrogated by anti-interferon. Interferon also appears to play a central role in augmentation of human NK-cell activity. Inoculation of normal volunteers with influenza virus or of a patient with poly I:C produced rapid boosting. In vitro incubation of peripheral blood mononuclear cells with various interferon preparations for 1 hour or overnight usually produced an appreciable increase in lytic activity.

Natural cytotoxic reactivity of rat lymphocytes against gross virus-induced tumor cell lines as measured by [125I]iododeoxyuridine and tritiated proline microcytotoxicity assays

Mononuclear cells from rat spleens that mediate "natural" cytotoxicity are described, and the subpopulation responsible for this activity is partially identified. These naturally cytotoxic cells have been designated "N-cells" and appear to be lymphocytes that lack both detectable immunoglobulin and complement receptors and are therefore not mature B-cells. They are different from the classic "null cells", which have immunoglobulin and/or complement recepters. This subpopulation of cells is responsible for the natural activity present is normal spleens and in spleens from immunized animals. These results indicate that the same subpopulation of cells responsible for natural activity in the short-term assays is also responsible for natural activity in the long-term microcytotoxicity assays reported here. In addition, these mononuclear cells are active against both nonadherent cells and monolayer targets. Natural activity as measured by the long-term assays appears to be somewhat less age specific than that reported previously with the short-term chromium assay. Appropriate base lines are described in an attempt to better document natural activity in these assays. This natural activity must be closely monitored in any system purporting to measure cell-mediated cytotoxicity.