Medullasin enhances human natural killer cell activity.

Medullasin, a new serine protease found in bone marrow cells, increased markedly human natural killer cell activity. Whereas the natural killer cell activity measured immediately after the treatment with medullasin remained almost on the same level as the control, an incubation at 37 degrees C for several hours increased markedly the natural killer cell activity of the lymphocytes treated with medullasin. Enhancement of the natural cytotoxicity was caused by the treatment with physiologic concentrations of the protease (5-20 micrograms/ml). Inhibitors of medullasin such as phenylmethylsulfonyl fluoride and elastatinal prevented the activation of natural cytotoxicity. Depletion of lymphocytes bearing Fc receptors for IgG abolished the enhancement of natural killer cell activity by medullasin. Interferon activity was not detected in the supernatant of lymphocyte cultures stimulated with medullasin. The medullasin enhanced further the natural killer cell activity of lymphocytes stimulated with interferon. Medullasin activity was detected neither in unstimulated nor stimulated (by concanavalin A or phytohemagglutinin) human lymphocytes. The protease was released easily from human mature granulocytes into culture medium. It is considered from these results that the level of human natural killer cell activity is regulated by medullasin released by mature granulocytes.     

Cloned cell lines with natural killer activity. Specificity,function, and cell surface markers

Cell lines with natural killer (NK) activity grown from native spleen cells cultured in medium conditioned by spleen cells proliferating in the presence of concanavalin A (Con A) were characterized. One NK cell line was cloned and assayed on several human and mouse NK-sensitive targets to analyze whether target specificities segregate upon cloning. Results showed that NK clones display target specificities identical to NK cells in normal spleen. This suggests that NK cells have no clonally distributed specific receptors to a given target. They may, however, have receptors which recognize identical antigens on all NK-sensitive targets or may possess multiple receptors for different target specificities. NK lines could not be demonstrated to possess activity in antibody-dependent cell-mediated cytotoxicity, nor did they effect mutual lysis. In the presence of Con A, NK cells exhibited dramatically enhanced lysis of NK-sensitive targets but only a slight increase in lysis of NK-insensitive targets. This indicates that the degree of lysis of an NK target is a function of two variables: effector binding to the target and target sensitivity to lysis. Furthermore, it suggests that the affinity of the putative antigen receptors on NK effectors must be rather weak. Cell surface marker analysis reveals that NK cell lines are Thy 1.2+, Lt-1-2-, T200+, asialo GM1+, and asialo GM2+. These markers distinguish NK cells from cytolytic thymus-derived lymphocytes, without resolving the question of classification within a give hematopoietic cell lineage.     

Unraveling human natural killer cell deficiency

NK cells are a component of the innate immune system identified in animals as serving an essential role in antiviral immunity. Establishing their role in human health has been challenging, with the most direct insight coming from the study of NK cell-deficient individuals. However, NK cell deficiencies are rare, and more research is needed. In this issue of the JCI, two independent groups of researchers have simultaneously identified the genetic cause of a human NK cell deficiency as mutation in the MCM4 gene, encoding minichromosome maintenance complex component 4. These reports suggest a critical role for the minichromosome maintenance helicase complex in NK cells and NK cell-mediated host defense.     

Induction of lymphokine-activated killer and natural killer cell activities from cryopreserved lymphocytes

Lymphokine-activated killer (LAK) and natural killer (NK) cells were studied for their capacity to retain cytotoxicity after cryopreservation. LAK cells were generated by a 4-day culture of lymphocytes with recombinant interleukin-2 (rIL-2). Cytotoxicity was measured by 51Cr-release assay at effector:target ratios of 10:1 to 80:1. Cryopreserved LAK cells retained 58.8 to 87.4 percent of cytotoxicity, as compared with that in fresh control cells. Cryopreserved NK cell activity against K562 and Molt-4 targets was 45.7 to 67.9 percent of the respective values of the fresh control cells. The responsiveness of NK cells to polyinosinic-polycytidilic acid (poly I:C), interferon-alpha (IFN-alpha), or rIL-2 remained intact. Activated NK cell activity after poly I:C or IFN-alpha stimulation and that after rIL-2 were, respectively, comparable to and higher than the endogenous NK cell activity of the fresh cells. The composition of lymphocyte subsets as determined by flow cytometry using monoclonal antibodies did not change after cryopreservation, indicating that cellular loss of the given subsets did not occur during the procedure. The retention of substantial levels of cytotoxicity in cryopreserved LAK and NK cells may make them promising candidates as cytotoxic effector cells.     

Cocaine increases natural killer cell activity.

The administration of epinephrine to humans increases natural killer (NK) cell activity and numbers. If endogenous catecholamines regulate NK cells, then their activity should be increased by cocaine, an agent that potentiates endogenous catecholamines. We investigated the in vivo effect of cocaine on NK cell activity and on the distribution of lymphocyte subsets, including NK cells. Intravenous cocaine (0.6 mg/kg) produced a three- to fourfold increase in NK cell activity in peripheral blood. The increase was accompanied by a marked and selective increase in circulating NK cells, as identified by the Fc receptor (Leu-11). Normal saline and benzoylecgonine, a major metabolite of cocaine, had little effect on NK cell activity or on levels of Leu-11+ cells. Other lymphocyte subpopulations were not increased by cocaine. The time course of the alterations in NK cell numbers and activity paralleled plasma levels of cocaine. In vitro cocaine did not increase NK cell activity. Our results indicate that cocaine selectively alters the activity and distribution of the NK lymphocyte subset. Because cocaine increases the activity of endogenous catecholamines, these findings suggest that human NK cells are selectively regulated by the sympathetic nervous system.     

Antibacterial activity of human natural killer cells

The in vitro effects of human NK cells on viability of Gram-negative and Gram-positive bacteria was investigated. PBLs depleted of glass-adherent cells showed a significant antibacterial activity that was increased as the concentration of NK cells became higher. Leu-11-enriched cells exhibited the most efficient bactericidal activity. Stimulation of NK cells with staphylococcal enterotoxin B for 16 h produced a significant increase in the antibacterial activity of all NK cells tested. The antibacterial activity of monocyte-depleted cells and Leu-11-enriched cells was also enhanced after culturing in vitro for 16-24 h without exogenous cytokines. Dependence of the antibacterial activity on the presence of serum in the culture medium was not found. Ultrastructural studies revealed close contact between NK cell membranes and bacteria, no evidence of phagocytosis, and extracellular bacterial ghosts, after incubation at 37 degrees C. Supernatants from purified NK cells exhibited potent bactericidal activity with kinetics and target specificity similar to that of effector cells. These results document the potent antibacterial activity of purified NK cells and suggest an extracellular mechanism of killing.     

A novel 120-kD surface antigen expressed by a subset of human lymphocytes. Evidence that lymphokine-activated killer cells express this molecule and use it in their effector function

A human cell clone (SF-16) displaying strong cytolytic activity against fresh tumor target cells was used for production of murine mAbs against surface antigens expressed by lymphokine-activated killer (LAK) cells and their peripheral blood precursors. The preliminary screening of hybridoma supernatants was performed according to the ability to bind SF-16 cells. Selected mAbs were further analyzed for their reactivity with several T and B cell lines and with peripheral blood T and non-T cell populations. A selected mAb, termed anti-LAK-1, only reacted with some T cell lines and with 15-30% of PBMC. Approximately 10-15% E- rosetting (T) cells and 40-50% E-rosette-negative cells were LAK-1+, as determined by cytofluorometric analysis. As the fluorescence distribution of LAK-1 antigen was clearly bimodal, LAK-1+ and LAK-1- cells could be separated by FACS. Positive cells were composed of large granular lymphocytes (LGL), whereas negative cells were mostly small lymphocytes and monocytes without LGL. After culture in rIL-2, purified LAK-1+ (but not LAK-1-) cells acquired the ability to lyse NK-resistant fresh melanoma target cells. In addition, only the LAK-1+ fraction of PBMC cultured for 5 d in rIL-2 lysed fresh tumor targets, thus indicating that the LAK-1 antigen is expressed also on LAK effector cells. Unlike some other LGL/NK cell markers, LAK-1 antigen is characterized by a stable expression: thus, LAK-1+ cell populations cultured for up to 20 d in rIL-2 maintained the LAK-1 antigen expression, whereas HNK-1 and, partially, CD16 were lost. Finally the cytolytic activity of LAK effector cells generated from PBMC cultured for 3 d in rIL-2 was susceptible to inhibition by the anti-LAK-1 mAb.     

Functional consequences of interleukin 2 receptor expression on resting human lymphocytes. Identification of a novel natural killer cell subset with high affinity receptors

In this study, we have used radiolabeled IL-2 binding assays, Northern blot analysis, immunofluorescent flow cytometry and cell sorting, as well as proliferation and cytotoxicity assays to perform an extensive phenotypic and functional characterization of the IL-2 receptor in normal resting human peripheral blood lymphocytes. Our results indicate that almost all T cells (greater than 98%) express neither the high affinity IL-2 receptor nor the functional intermediate affinity p75 chain of the IL-2 receptor without prior activation. In contrast, most NK cells constitutively express the isolated intermediate affinity p75 IL-2 receptor. In addition, a subpopulation of NK cells, distinguished by high density expression of the NKH1 antigen, constitutively express the high affinity IL-2 receptor, in addition to an excess of the isolated intermediate affinity p75 IL-2 receptor. These NKH1bright+ cells exhibit a brisk proliferative response to IL-2, similar to that seen with antigen-activated T cells, yet do so in the absence of any known antigenic stimuli. No other resting peripheral blood lymphocyte population, including CD4+, CD8+, and CD20 cells, exhibits this property. The intermediate affinity p75 IL-2 receptor, as it exists in its isolated form on resting NK cells, does not transduce a growth signal equivalent to that seen in NK cells expressing the high affinity IL-2 receptor, despite doses of IL-2 that are known to fully saturate the isolated p75 chain. This strongly suggests that additional structural or functional components are involved in generating the proliferative response following the binding of IL-2 to the high affinity heterodimeric form of the IL-2 receptor. The constitutive expression of this functional high affinity IL-2 receptor on a small population of resting NK cells provides further evidence in support of a role for these cells in the host's early defense against viral infection or malignant transformation, before the more delayed but specific T cell response.     

Decreased natural killer cell activity in late-onset hypogammaglobulinaemia

1. Natural killer cell activity and monocyte cytotoxicity was evaluated in three subgroups of patients with primary hypogammaglobulinaemia (ten patients with late-onset, eight with X-linked and five with early-onset disease) and in two patients with secondary late-onset hypogammaglobulinaemia against the K-562 erythroleukaemia, the CaCo-2 colon carcinoma and the HGT-1 gastric carcinoma cell lines and compared with the results found in healthy control subjects. 2. The natural killer cell activity, both spontaneous and after stimulation with recombinant gamma-interferon, was found to be decreased in patients with late-onset hypogammaglobulinaemia. The natural killer cell activity in this subgroup was found to be impaired in 60% of the patients (P less than 0.05). Within the other forms of primary hypogammaglobulinaemia a decreased natural killer cell activity was found to be less frequent (33%). 3. The lectin-mediated cytotoxicity by phytohaemagglutinin resulted in a similar maximal cytotoxicity in patients and control subjects. 4. The cytotoxicity of monocytes, spontaneous and after recombinant gamma-interferon stimulation, was found to be normal in all patients with hypogammaglobulinaemia. 5. The impaired natural killer cell activity which was found in patients with late-onset hypogammaglobulinaemia may contribute to the increased susceptibility to infections and to the increased incidence of malignancies in this subgroup of patients with primary hypogammaglobulinaemia.     

Functional abnormalities of circulating natural killer cell subpopulations in patients with dilated cardiomyopathy.

We investigated abnormalities in natural killer (NK) cells in the myocardium and circulating blood of 38 patients with idiopathic dilated cardiomyopathy (DCM), 18 patients with hypertrophic cardiomyopathy, 8 patients with primary amyloidosis, and 12 age-matched normal control subjects. Immunohistochemical staining of myocardial biopsies revealed a significantly greater number of CD57-positive NK cells in patients with DCM than that in controls (3.7 +/- 2.7 v.s. 1.9 +/- 1.6, p < 0.05). The New York Heart Association functional class, left ventricular ejection fraction, myocardial fiber diameter, and interstitial fibrosis volume fraction did not differ significantly between the DCM patients who died within five years of diagnosis and the 31 surviving DCM patients. However, there were significantly fewer CD57-positive NK cells in patients who died than in surviving patients (p < 0.05). There were no significant differences in the peripheral NK cell activity or the number of NK subset cells between the 16 patients with DCM (n = 16) and the 12 age-matched normal controls. In normal controls, the number of some NK cell subpopulations (CD16+, CD57+, CD16+ CD57+, and CD8+ CD57+ cells) were positively correlated with NK cell activity. In patients with DCM, there was no correlation between the number of NK cell subpopulations and NK cell activity. Our findings indicate that functional abnormalities exist in NK cell subpopulations in patients with DCM, and that these abnormalities may be related to the pathogenesis of DCM.     

Preservation of natural killer and interleukin-2 activated killer cell activity in ataxia-telangiectasia with T cell deficiency

Peripheral blood mononuclear cells (PBMs) from 6 patients with ataxia-telangiectasia (AT) were studied by 5 kinds of cell-mediated cytotoxicity systems. Decrease in cell mediated lympholysis (CML) activity to allogeneic lymphocytes was observed in all 6 AT patients who had low numbers of OKT-3+ cells. These patients also showed decreased proliferative responses to phytohemagglutinin stimulation and allogeneic lymphocytes. In contrast, antibody-dependent cell-mediated cytotoxicity (ADCC) activity and natural killer (NK) activity were comparable with those in normal controls. In addition, PBMs from these AT patients activated by in vitro stimulation with allogeneic PBMs or interleukin-2 were able to acquire lytic activity against NK-insensitive target cells. The phenotypes of these effectors determined by complement-mediated lysis were OKT-3- and Leu-11+, suggesting that they were derived from NK cell lineage. Thus, AT patients with severe T cell defects were found to maintain a normal range of NK, ADCC, MLC-activated and lymphokine-activated killer activity.     

Decreased natural killer cell activity in patients with zinc deficiency with sickle cell disease

Zinc deficiency is associated with depression of a number of immune responses. To assess the relationship of zinc and natural killer activity, we studied natural killer activity in adults with sickle cell disease and in two normal volunteers rendered zinc deficient by dietary restriction. Natural killer activity was significantly lower in patients with sickle cell disease and zinc deficiency (5.1 +/- 2.9 lytic units per 10(6) cells) than in controls (11.7 +/- 5.0 lytic units per 10(6) cells). In the two volunteers, natural killer activity declined during zinc restriction and returned to near initial levels with zinc repletion. These results suggest that zinc deficiency is associated with a lowering of natural killer activity.     

In vivo expression of natural killer cell inhibitory receptors by human melanoma-specific cytolytic T lymphocytes.

Natural killer (NK) receptor signaling can lead to reduced cytotoxicity by NK cells and cytolytic T lymphocytes (CTLs) in vitro. Whether T cells are inhibited in vivo remains unknown, since peptide antigen-specific CD8(+) T cells have so far not been found to express NK receptors in vivo. Here we demonstrate that melanoma patients may bear tumor-specific CTLs expressing NK receptors. The lysis of melanoma cells by patient-derived CTLs was inhibited by the NK receptor CD94/NKG2A. Thus, tumor-specific CTL activity may be decreased through NK receptor triggering in vivo.     

A transformation-associated 130-kD cell surface glycoprotein is growth controlled in normal human cells

Two characteristics of cell surface molecules involved in the regulation of cell proliferation are altered expression in relation to growth phase in normal cells and overexpression in transformed cells. Here, we describe a similar pattern of expression for a 130-kD cell surface glycoprotein (gp 130) in human cells. Synthesis and cell surface expression of gp130 were greatly increased in both virally and chemically transformed fibroblasts, fibrosarcomas, a squamous cell carcinoma of the skin, and T cell leukemia lines. Furthermore, gp130 expression was induced in serum-starved fetal fibroblasts by serum stimulation, and in fresh T cells by various activating agents. Expression in response to serum stimulation was associated primarily with the transition from a quiescent state (G0) into the cell cycle (G1).     

High hepatic natural killer cell activity in murine lupus

This study demonstrates a profound elevation of NK activity, as measured by cytotoxicity to YAC-1 targets in a 4-h incubation 51Cr-release assay, of freshly isolated hepatic NPC from both MRL/lpr and (NZB X NZW)F1 mice. This marked increase was not observed in splenic or peripheral blood NK. The hepatic NK were nonadherent, radioresistant, Ly-1-,2-, and AGM1+. Furthermore, biologic response modifiers can further augment hepatic NK activity in these autoimmune strains.     

Alterations in human natural killer cell activity and monocyte cytotoxicity induced by zinc deficiency

Zinc deficiency alters lymphocyte and monocyte function in man and animals. A patient with isolated zinc deficiency was found to have lymphopenia (420 lymphocytes/microliter), depressed T-cell mitogen response (48% of normal control), increased numbers of circulating T-suppressor cells (OKT8 reactive cells) and decreased circulating T-helper cells (OKT4 reactive cells). Activity of the patient's natural killer (NK) cells was 1 lytic unit/10(6) cells (normal 10 to 40), and monocyte cytotoxicity (MC) was four times that of normal controls. Zinc repletion in vivo improved the peripheral lymphocyte count, corrected the abnormal OKT8-to-OKT4 ratio, normalized T-cell response to mitogen, improved NK function, and lowered MC to control values. A divalent cation chelator, 1,10-orthophenanthroline (OP), was used to simulate zinc deficiency in vitro. T-cells exposed to OP are nonresponsive to mitogen unless zinc is added. NK function of lymphocytes from normal donors exposed to OP was depressed in a time- and dose-dependent manner. NK activity of peripheral blood lymphocytes (PBL) from 12 normal donors exposed to 50 microM OP for 16 hr was 10.3 +/- 7 lytic units/10(6) cells (mean +/- S.E.M.) vs. 32.6 +/- 14 for cells incubated in medium alone. When monocytes were exposed for 16 hr to 50 microM OP, however, MC significantly increased to a range two to five times that of control. OP-induced alterations of lymphocyte and monocyte function was reversed by the addition of 50 microM zinc but not calcium or magnesium. Since NK activity and MC are thought to be important in host tumor immunity, alterations in zinc metabolism may have important implications for human tumor immune surveillance mechanisms.     

A novel subset of human lymphocytes with a T cell receptor-gamma complex

We have previously characterized a CD3+ T cell receptor (TCR) alpha/beta- human fetal cloned cell line, termed F6C7, which surface-expresses a CD3-associated gamma chain identified by anti-NKFi, an mAb with a restricted clonotypic reactivity. Here, we have produced an additional antibody, anti-Ti-gamma A, which recognizes a public epitope of the gamma molecule defined by anti-NKFi. Ti-gamma A is present on approximately 3% of circulating lymphocytes with a wide range (1-15%) among 30 healthy individuals tested. Two-color immunofluorescence experiments performed with anti-Ti-gamma A and BMA 031 mAb (a reagent specific for the TCR-alpha/beta receptor) showed that surface expression of Ti-alpha/beta and Ti-gamma A is mutually exclusive. Moreover, it was found that most Ti-gamma A+ cells are CD2+, CD3+, CD4-, CD5+, NKH1-, HLA class II-negative. In contrast, the expression of the CD8 molecule on these T lymphocytes appears to be variable from one individual to another. Finally, we found that Ti-gamma A+ cells represent a majority of peripheral lymphocytes that express CD3 proteins but not the TCR-alpha/beta heterodimer. The delineation of this unique lymphocyte subset should help further studies on the biology of cells with a CD3-associated gamma complex.     

Suppressive effects of pentoxifylline on natural killer cell activity.

The methylxanthine derivative pentoxifylline, widely used as a hemorrheologic agent in the treatment of peripheral vascular disease, is now being evaluated for potential applications in patients with cancer. Recent studies have shown that pentoxifylline can modulate a number of neutrophil functions at in vitro concentrations of at least 50 micrograms/ml. Using a standard51chromium-release assay, we studied the suppressive effects of pentoxifylline on natural killer (NK) cell activity and found that pentoxifylline, at concentrations of 50 and 100 micrograms/ml, suppressed the in vitro NK cell activity of healthy volunteers by 25% and 75%, respectively. Postreaction supernatants from chromium-release studies were then assayed for prostaglandin E2 (PGE2) and tumor necrosis factor-alpha (TNF-alpha) by using enzyme-linked immunosorbent assay. Concentrations of both PGE2 and TNF-alpha were increased by more than five times in those assay wells containing pentoxifylline. Moreover, the addition of 1 microgram/ml indomethacin to the NK assay system containing pentoxifylline, completely inhibited PGE2 production and abrogated the pentoxifylline-induced NK suppression. The addition of PGE2 (1 x 10(-6) mol/L) to the assay system suppressed NK activity, whereas addition of 1 or 10 ng/ml TNF-alpha did not. Theophylline, another methylxanthine, failed to suppress NK activity like pentoxifylline at equimolar concentrations. Our studies provide the first evidence that concentrations of pentoxifylline of at least 50 micrograms/ml suppressed NK cell function by inducing PGE2 synthesis from effector peripheral-blood mononuclear cells.     

Mode of regulation of natural killer cell activity by interferon

Whereas xenogeneic tumors such as baby hamster kidney or HeLa cells grow in nude mice, the same cells persistently infected with a variety of viruses are rejected. Spleen cells from normal nude mice were found to be induced to produce interferon and to exert natural killer (NK) activity on virus persistently infected (PI) tumor cells, and not on uninfected parental cells in vitro. The phenotype of the interferon-producing cells and the NK effector cells was found to be the same namely, Qa 5(+), Ly 5(+), ganglio-N- tetraosylceramide, with 35 percent of the NK cells also expressing Thy 1.2. NK activity against virus PI tumor cell lines could be nonspecifically augmented both in vivo and in vitro by prior contact with virus PI tumor cells. It was unambiguously demonstrated with chemically homogeneous mouse interferon that interferon, and not a contaminant, was responsible for the augmentation of NK activity in vitro. Studies on the mode of interferon action in augmenting NK activity revealed that the target cell for interferon action was serologically distinct from the NK effector cell. Anti-Ly 5 + complement (C)-treated spleen cells were depleted of NK activity and the ability to produce interferon, but, upon incubation with interferon for 1-3 h, regained both NK activity and susceptibility to anti-Ly 5 + C. Treatment with anti-Qa 5 + C eliminated NK activity, which could not be restored by the addition of interferon. We conclude that interferon produced by Ly 5(+) cells in response to virus PI tumor cells acts on Ly 5(-) precursor cells and induces their differentiation into functional Ly 5(+) NK effector cells.     

A novel anti-Vpre-B antibody identifies immunoglobulin-surrogate receptors on the surface of human pro-B cells

Vpre-B and lambda 5 genes, respectively, encode V-like and C-like domains of a surrogate immunoglobulin light chain (psi L). Such psi L complex is expressed in early progenitor B (pro-B) cells, before conventional immunoglobulin heavy (microH) and light (L) chains are produced. We raised a wide panel of monoclonal antibodies (mAbs) against soluble recombinant Vpre-B proteins to study early events in human B cell development. One of these antibodies, B-MAD688, labeled surrogate Ig-complexes on the surface of microH- pro-B cell lines and normal bone marrow cells in immunofluorescence assays. Immunoprecipitations using surface-labeled pro-B cells and B-MAD688 mAb indicated that human psi L is associated with high molecular weight components homologous to the surrogate heavy (psi H) chains described in mouse. Using B-MAD688 and SLC2 mAbs, we were able to distinguish between psi H psi L and microH psi L complexes on the surface of human pro-B and later precursor, pre-B, cells. The finding of psi H psi L complexes in mouse and man lead us to hypothesize a role for psi H- containing receptors in B cell development.