Spontaneous human lymphocyte-mediated cytotoxicity against tumor target cells. IX. The quantitation of natural killer cell activity

Cellular cytotoxicity assessed by the 51Cr release assay. Biological interpretation of mathematical parameters

This study deals with the interpretation of primary data of the 51Cr release assay for cellular cytotoxicity. In particular the dose-effect relationship between increasing numbers of lymphoid cells and the percentage of target cells killed has been considered. The number of target cells killed depends on the frequency and the activity of cytotoxic cells. These two parameters are often not distinguished from each other, which causes confusion and frequently results in vague descriptions of cytotoxicity data. Because in many cases not all cells in the target cell population can be lysed, we recommend the introduction of the plateau value for target cell kill. This maximum of target cell kill is a measure of the frequency of lysable target cells, but also depends on the cytotoxic cell activity. Description of the dose-effect curve by y = A(1 - e-kx) allows the simultaneous calculation of the maximum kill (A) and the frequency of cytotoxic cells (k) in the lymphoid cell population (x). Results are presented which indicate that A and k represent totally independent biological parameters the use of which permits a more objective description of cytotoxicity data.

Natural killer cell function and interferon generation in patients with primary immunodeficiencies

Patients with primary immunodeficiency disorders were evaluated for three aspects of natural defense: natural killer (NK) cells which lyse HSV-infected fibroblasts [NK(HSV-FS)], NK cells which lyse K562 tumor targets [NK(K562)], and interferon-alpha generation. In addition, capacity to make interferon upon challenge with other commonly used inducers was also evaluated. Most patients with severe combined immunodeficiency disease (SCID) and deficits of both T- and B-cell function demonstrated normal NK function with one or both targets. Six of eight SCID patients generated interferon-alpha at or below the lower limit of normal while only two made clearly normal levels. Six of 10 patients with Wiskott-Aldrich syndrome (WAS) had normal NK(K562) and five of 10 generated normal levels of interferon-alpha but all had severely deficient NK(HSV-FS). Patients with Bruton's agammaglobulinemia demonstrated normal NK and interferon generation, as did patients with common variable immunodeficiency, even when subdivided into patients with T-cell proliferative deficiencies and those with only hypogammaglobulinemia. Natural defense parameters may help categorize patients with SCID and WAS and help define these heterogeneous diseases.

Natural killer cell activity in murine muscular dystrophy. III. NK-sensitive myoblast cells and lack of NK activity in beige/dystrophic hybrid mice

The NK-susceptibility of dystrophic mouse myoblast cells was investigated. Spleen cells from 8- to 10-week-old normal (+/+) and dystrophic (dy2J/dy2J) male C57BL/6J mice were fractionated on Percoll density gradients and the cells at each density interface were incubated with either 51Cr-labeled YAC-1 or myoblast cells in a 6 hr 51Cr-release assay. Myoblast target cells were obtained from either heterozygous (+/dy2J) or homozygous (dy2J/dy2J) muscle cultures or a transformed tetraploid myoblast line (M14D2). The data indicate that the interface between the 50 and 60% (1.060-1.075 g/ml) Percoll density fractions of spleen cells from either normal or dystrophic mice contains the largest proportion of asialo GM-1 positive and NK-1 positive cells displaying NK activity. Myoblast cells from either heterozygous (phenotypically normal) or homozygous dystrophic mice were not significantly different in susceptibility to NK-mediated lysis by Percoll enriched normal or dystrophic mouse NK cells. However, dystrophic mouse spleen cells had the highest NK activity against both myoblast targets as compared with normal mouse spleen cells. The transformed myoblast cell line, M14D2, was significantly less susceptible to NK-mediated lysis by dystrophic mouse spleen cells when compared with freshly cultured myoblast target cells. Target cell binding studies revealed that conjugate forming cells from the 50% Percoll density interface of dystrophic mouse spleen cells were approximately twofold greater than that of normal mouse spleen cells against either heterozygous or homozygous dystrophic mouse myoblast targets. Cold target inhibition studies revealed that the natural killing of dystrophic mouse myoblast cells was due to a YAC-1 reactive NK cell. Breeding experiments between C57BL/6J homozygous "beige" (bgJ/bgJ) mutant mice and dystrophic (dy2J/dy2J) mice produced beige/dystrophic hybrid mice which displayed clinical symptoms of the dystrophy process by 3 to 4 weeks of age. Spleen cells from these hybrid mice showed no significant differences in NK activity against YAC-1 target cells when compared with homozygous beige mice. Taken together, these results demonstrate the first reported evidence that murine myoblasts are susceptible to NK-mediated lysis. In addition, the data indicate that although dystrophic mouse NK cells recognize myoblast cells as targets, the NK cell studies with the beige/dystrophic hybrid mice do not indicate a direct in vivo role for NK cells in the dystrophy process.

The effect of acute and chronic leukapheresis on the natural killer (NK) cell function of normal human volunteers

Twenty-two normal volunteers had approximately eight, 2-hr-long leukapheresis procedures over a 2-year period and their natural killer (NK) cell function was prospectively measured. The NK activity of the preprocedure peripheral blood (pre-PB) was found to correlate well with the NK activity of the inital leukocytes removed by leukapheresis (I-Leuk). When the I-Leuk specimens were compared with the leukapheresis specimens removed at the termination of leukapheresis (T-Leuk), T-Leuk showed a consistent 10% increase in NK activity. When the pre-PB and the I-Leuk values were analyzed for each donor over the 2 years of the study, 18 donors revealed no significant change from their baseline NK activity, two donors showed a minimal increase in NK cell activity, and two donors displayed a minimal decrease in NK cell activity. We conclude that although leukapheresis appears acutely to boost NK cell activity, this increase is transient and small in magnitude. Most importantly, repeated leukapheresis does not appear adversely to effect this important effector function in normal donors.

Impaired neonatal natural killer-cell activity to herpes simplex virus: decreased inhibition of viral replication and altered response to lymphokines

Human adult natural killer (NK) cells were recently demonstrated to inhibit herpes simplex virus (HSV) replication in vitro. In this study we compared the ability of newborn and adult NK cells to inhibit HSV replication. Cord blood mononuclear cells (MNCs) from healthy, term newborns and MNCs from adults were analyzed for their percentage of Leu-11+ cells and compared in vitro for their NK-cell activity against HSV-infected fibroblasts and the tumor cell line K562. Cord blood MNCs, compared with adult MNCs, had significantly lower percentages of Leu-11+ cells (5 vs 11%; P less than 0.01), less anti-K562 NK activity (6 vs 54 lytic units/10(7) cells; P less than 0.001), and less anti-HSV NK activity (5 vs 52% HSV plaque inhibition; P less than 0.02). Comparing individual neonates and adults with equal percentages of Leu-11+ cells, neonatal MNCs still had less NK activity against either target. When Leu-11+ MNCs were isolated using the fluorescence-activated cell sorter, neonatal Leu-11+ MNCs still inhibited HSV replication less than adult Leu-11+ MNCs (P less than 0.01). MNCs from some neonates had significant anti-K562 NK activity but poor anti-HSV NK activity, suggesting either nonidentical NK-cell subpopulations or specific suppression. Whereas neonatal NK activity against K562 was always augmented by prior exposure to either interferon (IFN) or interleukin-2 (IL-2), the neonatal NK activity against HSV-infected cells was only augmented for half of the neonates tested. Endogenous production of alpha-IFN and gamma-IFN by MNCs exposed to HSV-infected fibroblasts was the same for cells from neonates or from HSV-seronegative adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural killer cell response to interferons

The availability of recombinant interferons has facilitated a comparison of the in vitro effects of interferon-alpha and -gamma upon human natural killer (NK) cells. In the absence of interferon high and low NK responders exist. Repeated testing of the same individuals revealed different but stable NK patterns to in vitro addition of interferon-alpha and -gamma Furthermore, the NK cell response patterns differed depending on whether the interferons were administered in combination or separately. These studies suggest new complexities that must be addressed in the planning and execution of clinical interferon trials. The pattern of responsiveness of human NK cells to interferon-alpha or -gamma or both is highly variable, but stable, within a given individual.

Immunological effects of recombinant interferon alfa-2a in patients with disseminated melanoma

Twenty patients with disseminated melanoma were treated with interferon alfa-2a, given by intramuscular (IM) injection three times a week in escalating doses from 15 to 50 X 10(6) U/m2. Of 18 patients considered evaluable, two had complete remission and in two others the disease was stabilized. Laboratory tests 6 hours after injection of interferon alfa-2a indicated a marked lymphopenia and a reduction in natural killer (NK) cell activity. Sequential changes (measured before injection of interferon alfa-2a on days 3, 10, and 31) consisted of neutropenia, thrombocytopenia, and a slight increase in OKT4 positive T cells compared with OKT8 positive T cells. NK activity against the K562 target cells was increased in most patients during the first week of treatment, returning to near or below pretreatment levels thereafter. This response contrasted with a delayed increase against melanoma target cells in 10 patients. The latter correlated with an increase in mitogen-stimulated interleukin-2 (IL2) production, and may indicate that the cytotoxic activity resulted from lymphokine-activated killer (LAK) cells. Changes in cortisol levels may explain some effects on the immune system, such as depression of IL2 and immunoglobulin production in vitro, and the differences noted in clinical responses during the present study compared with those observed with interferon alfa-2b given by intravenous (IV) injection in 5-day cycles. These results suggest that interferon alfa-2a has antitumor activity in certain melanoma patients, in particular those with metastases to pulmonary or subcutaneous sites. Assays of IL2 production and LAK activity may assist in the selection of patients who respond to interferon alfa-2a and help to optimize treatment regimens.

Defective postbinding lysis underlies the impaired natural killer activity in factor VIII-treated, human T lymphotropic virus type III seropositive hemophiliacs

We investigated the diminished natural killer (NK) activity in human T lymphotropic virus type III (HTLV-III) seropositive hemophiliacs. Despite normal percentages of NK cells, lymphocytes from five hemophiliacs showed impaired NK activity against K-562 tumor cells in 4-h chromium release microcytotoxicity assays. For example, at an effector-to-target cell ratio of 10:1, cells from patients caused 21.7 +/- 2.5% lysis of tumor targets compared with 47.9 +/- 5.1% lysis by cells from controls (mean +/- SEM, P less than 0.005). Cells from patients were as cytotoxic in 18 h as were cells from controls in 4 h. Binding to tumor targets was not impaired since 11.0 +/- 1.5% of cells from patients and 11.1 +/- 1.3% of cells from controls bound to K-562 cells. Patients' binding cells, however, showed defective killing of attached tumor cells at all time points tested from 0 to 18 h. At 4 h, for example, patients' cells had lysed 10.9 +/- 2.1% of attached tumor cells compared with 26.3 +/- 3.3% lysis by controls' cells (P less than 0.005). The percentage of lymphocytes which were active NK cells (i.e., cells that bound and lysed a tumor cell) was always lower for patients than for controls (1.17 +/- 0.25% vs. 2.82 +/- 0.33%, P less than 0.005). Two methods for estimating recycling of effector cells against multiple target cells demonstrated that active NK cells from patients could recycle as well as those from controls (approximately 3-4 times in 4 h). Mixing experiments showed no evidence for cellular suppression of NK activity. The lytic function of NK cells from HTLV-III seropositive hemophiliacs is thus heterogeneous. This is characterized by a defect in post-binding lysis, with relative sparing of binding capability and recycling capacity.

Human natural killer cell lysis of virus-infected cells. Relationship to expression of the transferrin receptor

Natural killer (NK) cells lyse tumor and virus-infected cells yet the nature of the target structure they recognize is unknown. A normal host cell glycoprotein, the transferrin receptor (TfR), has been proposed as a target structure on tumor cells. We therefore investigated whether changes in the number or physiological recycling of the TfR, consequent on virus infection, were related to the differential susceptibility of virus-infected cells to NK lysis. There was a direct correlation between TfR expression, susceptibility to NK lysis and ability to act as cold target competitors, for human fibroblasts infected with RNA and DNA viruses (cytomegalovirus, herpes simplex, polio, vaccinia and Semliki Forest virus). The NK lysis of human cytomegalovirus-infected fibroblasts was studied in more detail. NK lysis was increased coincident with human cytomegalovirus early antigen expression and this susceptibility to lysis was associated with increased total and recycling TfR but only a slight increase in surface TfR expression. In addition, susceptibility of uninfected human fibroblasts to NK lysis directly correlated with TfR number. However, we were unable to inhibit NK lysis by either excess iron-saturated Tf or affinity-purified TfR. We conclude that there is a direct correlation between total TfR expression and susceptibility to NK lysis of human virus-infected cells; however, the NK target structure on virus-infected cells is probably not the TfR itself.

Cortisol at physiological concentrations and prostaglandin E2 are additive inhibitors of human natural killer cell activity

The effects of cortisol and prostaglandin E2 on preparations of human peripheral blood mononuclear cells that mediate natural killer cytotoxicity were evaluated. Natural killer cell activity was measured using 51Cr-labelled K562 target cells and effector to target cell (E:T) ratios of 50:1, 25:1, 12.5:1 and 6:1. In vitro preincubation of mononuclear cell preparations for 20 h with 1 X 10(-8) to 1 X 10(-5) M cortisol resulted in a significant decrease of natural killer cell activity. The magnitude of the suppression was directly related to the steroid concentration and inversely related to the E:T ratio. Exposure of cortisol-treated mononuclear cells to 1 X 10(-6) M prostaglandin E2 resulted in a significantly higher level of inhibition than after treatment with the two agents singularly. In contrast, the concomitant incubation with 1 X 10(-5) to 1 X 10(-4) M theophylline, or with 1 X 10(-6) to 1 X 10(-5) M isobutyl-methylxanthine, two widely used phosphodiesterase inhibitors, failed to demonstrate a significant enhancement of cortisol-induced suppression. Prostaglandin E2-dependent inhibition, on the other hand, was more intense after the inhibition of phosphodiesterase activity. Taken together, these results show that cortisol at physiological concentrations has the property of depressing human natural killer cell activity in vitro and suggest that endogenous glucocorticoids play a role in the in vivo regulation of this natural cytotoxicity. Additionally, cortisol and prostaglandin E2 are additive inhibitors of natural killer cell activity. Since the effect of cortisol in our experiments was not changed by theophylline or isobutyl-methylxanthine it is conceivable that the hormone acts at a level different from the adenylate cyclase/phosphodiesterase system.

Recombinant leukocyte A interferon therapy for advanced hairy cell leukemia. Therapeutic and immunologic results

Hairy cell leukemia is a lymphoproliferative disorder characterized clinically by cytopenias. Standard therapy following variable periods of disease stability consists of splenectomy that often restores normal hematologic parameters for periods ranging from weeks to years. Fifteen patients (five without prior splenectomy or chemotherapy) were treated with 3 X 10(6) units per day of recombinant leukocyte A interferon and 14 of 15 patients completed eight weeks of therapy and were evaluated for response. There was one complete and 12 partial responses for an overall response rate of 93 percent. All of these patients' conditions have remained in complete or partial remissions and they continue to receive interferon with a median follow-up of six months. Coincident with the normalization of peripheral blood counts was a return of natural killer activity and normalization of immunologic surface markers as determined by monoclonal antibodies. This study confirms and extends earlier observations with natural alpha-interferon and indicates that recombinant leukocyte A interferon in low daily doses is also very effective treatment for hairy cell leukemia. In fact, it may be the best single modality of therapy for inducing both hematologic and immunologic recovery of these patients and deserves consideration as initial therapy.

Characterization of culture-induced cytotoxicity from human peripheral lymphocyte subpopulations

Cultured human lymphocyte subpopulations can generate cytotoxicity against K562 leukemia target cells under certain conditions. Such cytotoxicity arises during mixed leukocyte culture or in medium containing fetal calf serum (FCS), mitogenic factors, or interleukin 2. We cultured peripheral blood lymphocytes (PBL) in FCS-containing medium after fractionation of these cells on a Percoll discontinuous density gradient. Higher density cell fractions generated culture-induced spontaneous cytotoxicity (CIC) after 2-3 days in culture. CIC was not due to a loss of suppressor cells during fractionation since culture of PBL prior to fractionation yielded the same results. At least some CIC was associated with the differentiation of higher density cells to newly appearing lower density cells during culture. Most CIC required cells with the HNK-1- OKT3- OKM1+ phenotype. Culture-induced cytotoxicity has some similarities to the previously described lymphokine-activated killing but some important differences are also discussed.

Phase II study of vaccinia melanoma cell lysates (VMCL) as adjuvant to surgical treatment of stage II melanoma. II. Effects on cell mediated cytotoxicity and leucocyte dependent antibody activity: immunological effects of VMCL in melanoma patients

Patients with stage II melanoma were vaccinated with vaccinia virus-induced melanoma cell lysates (VMCL). The vaccine contained viable vaccinia virus, membranous fragments and no intact nuclei. A number of antigens defined by monoclonal antibodies were detected in the vaccine including the ganglioside GD3 and DR antigens. Administration of the vaccine was associated with depression of natural killer cell activity against melanoma and K562 target cells in the first 3-6 months of treatment. Leucocyte dependent antibody (LDA) activity against melanoma cells was induced or increased in titre in approximately half of the patients studied. Continued vaccination was associated in a number of patients with a decrease in LDA titres. Studies on a small sample of patients revealed that this was associated with the development of serum factors which inhibited LDA activity. LDA activity appeared directed to non-MHC antigens on melanoma cells which were of at least two specificities. One specificity which was shared with antigens on a number of non-melanoma carcinoma cells was removed by absorption on fetal brain and may be similar to oncofetal antigens described by other workers. Reactivity against melanocytes was induced in some patients and may underline the development of vitiligo in several patients. These results suggest that vaccines prepared from VMCL may be a favourable method for increasing immune responses against melanoma.

Studies on the mechanism of specificity of human natural killer cells for tumor cells: correlation between target cell transferrin receptor expression and competitive activity

Previous studies to determine the nature of the specificity of natural killer (NK) cells for leukemic cells indicated that functional transferrin (Tf) receptors may be one of the determinants recognized by NK cells. To further investigate these observations, the relationship between cellular Tf receptor expression and ability to compete with a control K562 cell preparation in a standard chromium release assay was studied. K562 cells were selected at different phases of growth by removing cells from tissue culture at 1, 3, and 5 days postfeeding. Under these conditions, K562 cells, respectively, displayed relatively high, medium, and low numbers of Tf receptors and corresponding competitive activity against a control K562 cell preparation. K562 cells were modified by either trypsin, heat, or sodium butyrate (differentiation inducer) pretreatment. An NK-resistant clone was also studied. There was a good correlation between Tf receptor expression and cold competitive activity of the above K562 cell preparations (r = 0.82, P less than 0.01). The different tumor target cell lines, K562, Molt-4, Raji, HL-60, and MeWo, which would be expected to express different ranges of specificity, did not show a significant correlation between Tf receptor expression and their cold competitive activities against Cr-51-labeled K562 cells. Rabbit reticulocytes which express high numbers of Tf receptors were tested for their ability to compete with K562 cells for NK cells. These cells were able to compete with K562 cells while mature rabbit red blood cells which do not express Tf receptors did not compete well. These findings support the contention that the Tf receptor may be involved in NK cell recognition of some tumor cells.

Natural killer cell activity in multiple sclerosis and myasthenia gravis

Because of the potential role of Natural Killer (NK) cells in viral immunity and immunoregulation, we have undertaken a study of NK activity of peripheral blood lymphocytes from both Multiple Sclerosis (MS) and Myasthenia Gravis (MG) patients, two chronic diseases in which a viral etiology and an induced autoregulatory abnormality are strongly implicated. No significant difference between the mean NK activity in MS patients and controls was observed. A difference was observed between the NK activity of female MG patients and female controls, but no difference was seen between male MG patients and controls.

Segregation of the NK-sensitive phenotype in human x mouse somatic cell hybrids reveals separate genetic control of recognition and postrecognition determinants

In an attempt to investigate the nature of tumor cell-derived membrane surface determinants involved in natural killer cell (NK) recognition or postrecognition events, we have constructed human X mouse interspecies somatic cell hybrids. Highly NK-sensitive (NKs) human tumor cells were fused with NK resistant (NKr) mouse fibroblasts (LMTK-) in polyethylene glycol and selected in hypoxanthine/aminopterin/thymidine medium and ouabain. Hybrids generated from NKs erythroleukemia cells (K-562) or NKs retinoblastoma cells (Y-79) with LMTK- displayed an intermediate NK-sensitive phenotype. One Y-79 X LMTK- hybrid (YL-22) retained a high level of susceptibility to NK binding and cytolysis, as determined by 51Cr release and in cold-target inhibition assays. On the other hand, human NKr RAJI cells generated NK-resistant hybrids when fused with LMTK- fibroblasts. Four hybrids (KL-12, YL-2, YL-22, and YL-43) displaying consistent NK sensitivity were subsequently cloned by limiting dilution. Various hybrid clones derived from the KL-12 hybrid (K-562 X LMTK-) demonstrated a range of NK-sensitive phenotypes. However, the uncloned KL-12 and most cloned lines derived from this hybrid competed against 51Cr-labeled K-562 targets as well as unlabeled K-562 parental cells, regardless of their NK-sensitive phenotype. These findings raise the possibility that chromosomal segregation may be affecting a postbinding step in this hybrid system. The NK-sensitive hybrids exhibited a limited number of human chromosomes as assessed by quinacrine banding. Furthermore, human transferrin receptor (TfR) expression, as monitored by flow cytometry using the B3/25 monoclonal antibody, demonstrated no clear correlation with NK sensitivity or competitive ability in either KL or YL hybrid clones, thus arguing against the involvement of the TfR in human NK recognition. These results suggest that the NK-sensitive phenotype in human tumor cells may be regulated by genes encoded by a limited number of human chromosomes.

Studies on natural, antibody-dependent, and interleukin-2-activated killer-cell activity of a patient with mucolipidosis III as a test of the mannose-6-phosphate lytic acceptor hypothesis

The natural (NK), antibody-dependent (K), and interleukin-2-generated (LAK) killer-cell activity of a patient with mucolipidosis III (ML III; an autosomal recessive defect in UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase) was studied to determine whether or not the defect in the phosphorylation of lysosomal enzyme mannose residues resulted in a failure of target-cell lysis, as would be predicted from recent studies showing NK inhibition by phosphorylated sugars, especially mannose-6-phosphate. The patient was studied in parallel with normal donors known to be at the high and low extremes of NK activity. The following results were obtained: NK activity was markedly elevated against K562, Molt-4, human fibroblasts, HL-60, and MeWo to levels approximately one to two times that of our previous highest donor and five times the mean of normal donors previously tested. Interleukin-2-generated killer-cell activity and antibody-dependent cell-mediated cytotoxicity against antibody-coated P815 cells were normal and increased, respectively. HNK-1-positive cells were normal in frequency (7.3 +/- 1.7%), while lytic conjugates were proportional to activity (3.9 +/- 0.6 vs 2.7 +/- 0.4% for the "high" donor), and this was attributable to an increased proportion of lytic cells. The addition of fresh serum from the ML III patient had no effect on the NK activity of normal donors and the effects of preincubation with interferon (enhancement), monensin (inhibition), fructose-6-phosphate (inhibition), and mannose-6-phosphate (inhibition) were identical to those seen using lymphocytes from normal donors. Studies on the NK activity of the parents and two normal female siblings showed that the father's NK activity was high, the mother's was low, and both siblings' was intermediate but low. The data obtained suggest that the inability of lymphocytes to phosphorylate lysosomal enzyme mannose residues had no effect on NK-, K-, or LAK-cell function and that the mechanism of target-cell lysis is independent of either a mannose-6-phosphate-bearing lytic moiety or a mannose-6-phosphate-dependent ligand mechanism.

Low doses of interferon alpha result in more effective clinical natural killer cell activation

To define critical parameters concerning interferon (IFN) effects upon natural killer (NK) cells in vivo, we gave cancer patients serial weekly intramuscular injections of purified lymphoblastoid IFN in six doses ranging from 10(5) to 3 X 10(7) U. Dose sequences were determined by randomly allocating patients to one of six levels in a latin square ordering scheme. NK cell stimulation, a threefold peak increase above preinjection levels of cytolysis (P = 0.022), occurred in peripheral mononuclear cells (PMC) sampled 24 h postinjection, of 3 X 10(6) U, but was not detectable at any dose in PMC sampled 7 d postinjection. No blunting occurred in NK cell responsiveness to repeated injection of IFN dosages a second time at or several weeks after study completion. At IFN doses of 3 X 10(6), 10(7), and 3 X 10(7) U, a negative correlation existed between the amount of IFN injected and the average extent of NK cell activation (r = -0.423, P less than 0.05). This contrasted with the progressively increasing response of NK cells to in vitro incubation with increasing concentration of up to 3,000 U/ml of IFN. Overnight culturing of PMC sampled before IFN injections resulted in a mean 1.9-fold increase in cytolytic activity (P = 0.0005) and a mean 53% decrease in variance (P = 0.024) between serial preinjection NK cell activity determinations. Cell separation procedures may, therefore, have resulted in NK cell inactivation, from which overnight culturing permitted recovery. We found that maximal NK cell activation at a low IFN dose, decreasing NK cell responsiveness at higher doses, and the need to culture PMC to efficiently detect NK cell boosting may account for disparities in reported effects of IFN on NK cell function.

The analysis of measurements of murine natural killer cell activity

Several methods of analysing murine NK response measurements have been compared in order to select a quantitative objective measure of NK activity . The fitting of data from 51chromium release experiments to the formula y=A(1-e-kx)((termed the "k method" and shown by Pross et al. (J. Clin. Immunol. (1981) 1,51) to be beneficial in analysing human the NK response) has been particularly evaluated. Computer simulated curves as well as experimental NK dose response curves were analysed testing data in which a plateau level of chromium release had not been reached. Results obtained by the "k method" were very dependent on both the portion of the curve used for the analysis and on small deviations of the data from the theoretical form of the equation. In the analysis of murine NK response the "k method" has no clear advantage over other methods.

The sensitivity of placental trophoblast cells to intraplacental and allogeneic cytotoxic lymphocytes

The NK-susceptibility of trophoblast cells to allogeneic and autologous intraplacental natural killer (NK), antibody-dependent (K), and mitogen-induced cell-mediated cytotoxicity was studied, using untreated and neuraminidase-treated trophoblast cells from normal, full-term deliveries. The work was preceded by systematic studies of placental cell separation and labelling techniques, and the effects of these techniques on the NK target, K562. The results indicated that maternal NK cells are present among intraplacental lymphocytes, but that their activity is lower than that of peripheral blood lymphocytes and they are not stimulated by interferon to the same extent as peripheral blood lymphocytes (PBL). Trophoblast cells were rarely susceptible to allogeneic NK cells, with low cytotoxicity at high effector-target cell ratios in only two of five experiments. Interferon (IF)-boosted NK cells mediated some cytolysis of trophoblasts in three of four experiments, but high effector/target cell ratios were also required for the effect to be observed. The trophoblast cells could be lysed, however, by K cells and lectin-induced cytotoxicity. Removal of surface sialic acid by neuraminidase treatment of the trophoblast cells had little effect on the susceptibility of these cells to unstimulated NK cells (one of four experiments), but resulted in susceptibility to IF-boosted NK cells in four of four experiments. Normal trophoblast cells did not compete in IF-NK(K562) assays and neuraminidase-treated cells competed weakly in only one of three such experiments, indicating that the NK "target structure" is only weakly expressed on human trophoblast cells. Intraplacental lymphocytes lysed autologous trophoblast cells to a lower extent than allogeneic PBL.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cytotoxic cells generated from in vitro cultures of murine bone marrow cells

Bone marrow cells cultured for 5-6 days generate cytotoxic activity against a number of natural killer (NK)-susceptible tumor cells. In this study, these bone marrow cytotoxic cells were compared to cells with NK activity obtained either from spleen cells activated in vitro with interferon (IFN-alpha/beta) or mitogen or from peritoneal exudate cells (PEC) obtained 4 days after bacillus Calmette-Guerin (BCG) infection. Splenic and PEC cytotoxic cells were shown to be Thy 1.2+, NK 1.1+, Asialo GM+1, Lyt 1.2-, Lyt 2.2-. In contrast, bone marrow cytotoxic cells were Thy 1.2+, NK 1.1-, Lyt 1.2-, Lyt 2.2- and expressed low levels of Asialo GM1 antigen (Asialo GM +/- 1). Precursor cells for bone marrow cytotoxic activity were shown to be Thy 1.2-, NK 1.1-, Lyt 1.2-, Lyt 2.2- but also expressed low levels of Asialo GM1 antigen (Asialo GM +/- 1). Cytotoxic activity for both bone marrow and spleen cells peaked in the low-density fractions of discontinuous Percoll density gradients. The cytotoxic activity of these bone marrow cells was augmented by pretreatment with IFN (-alpha/beta, -gamma) or soluble factors (IFN free) from activated EL-4 thymoma cells. Surprisingly, the ability of bone marrow cells to generate high levels of cytotoxic activity following in vitro culture appeared to be associated primarily with mice which were of the H-2b haplotype.

Natural killer activity against cultured human neural tumor and fetal brain cells

Ten human neural tumor lines and three established from normal human brain were analyzed for sensitivities to natural killer (NK) cytolysis. Compared to MOLT-4, fetal brain cells were sensitive, but those from adult brain and eight of ten neural tumor cell lines demonstrated marked NK resistance. The frequencies of target-binding cells (TBC) and single-cell lysis of glioma cells bound within tumor cell conjugates demonstrated that the resistance of two lines was explained either by a decrease in the frequencies of TBC or reduced ability of bound NK cells to lyse the tumor cell conjugates. A third resistant line demonstrated decreases in both TBC and tumor cell conjugate lysis. Two glioma lines with less NK resistance had greater frequencies of TBC or conjugate lysis than the resistant lines. Thus, NK resistance can result from decreased recognition of targets, diminished NK lysis of bound targets, or a combination of both.

Response of resting human peripheral blood natural killer cells to interleukin 2

The present study shows that recombinant interleukin 2 (IL-2) purified to homogeneity induces a rapid and potent enhancement of spontaneous cytotoxicity of human peripheral blood lymphocytes. The cells mediating cytotoxicity after 18-h treatment with IL-2 have surface markers of natural killer (NK) cells and are generated from the peripheral blood subset containing spontaneous cytotoxic cells. A parallel production of gamma interferon (IFN-gamma) is induced by recombinant IL-2 (rIL-2), and NK cells appear to be the major producer cells, whereas T cells are unable to produce IFN-gamma under these experimental conditions. However, the kinetics of the enhancement of cytotoxicity are faster than those of IFN-gamma production, and monoclonal anti-IFN-gamma antibodies do not suppress this effect, making it unlikely that the IFN-gamma produced is responsible for the enhancement. The enhancement of NK cell activity induced by rIL-2 precedes any proliferative response of the lymphocytes, which is instead observed in longer-term cultures of both NK and T cells.

Natural killer cell activity in women at "high risk" for breast cancer, with and without benign breast syndrome

This study is an analysis of natural killer cell (NK) function in 155 women repeatedly tested over a 5-year period while attending breast screening clinics because of one or more of the following risk factors: family history-breast cancer in a close female relative (relative risk = 1.2-9); personal history-early menarche, non-parity, late menopause, etc. (relative risk = 1.3-3); clinical benign breast syndrome-localized and diffuse (relative risk = 2-4). Contrary to expectations, the high-risk group as a whole had significantly higher than normal relative NK function vs K562 (1.21 +/- 0.06 vs 1.00 +/- 0.06) (p less than 0.02). Division into subgroups showed that the NK activities in patients with positive family histories, personal histories, or both, were exactly the same as normal values and that the increased NK function in the high-risk group as a whole was due to those donors with benign breast syndrome (BBS). This group was also subdivided and the results were compared with the high-risk patients with no BBS. The NK activity of the group having diffuse BBS (1.67 +/- 0.05, n = 32) was significantly higher than that of the "No BBS" group (1.07 +/- 0.07, n = 102) (p less than 0.025). A paired "t'-test performed on data from 7 patients who had no BBS and diffuse BBS at different times showed a significant difference of p less than 0.001, suggesting that the elevated NK activity is a reaction to the hormonal factors which cause this condition.

Human autologous rosettes. IV. Their relation with interleukin 2 activity production and natural killer cells in cancer patients

Peripheral blood lymphocytes (PBL) of solid-tumor-bearing cancer patients produced a lower interleukin 2 (IL-2) activity after lectin stimulation than did those from normal subjects. Moreover natural killer (NK) cell activity and autologous rosette forming (ARF) cell rate are found significantly correlated with IL-2 production in these patients. No direct relation is observed between ARF cell ratio and NK cell activity in a given patient. A central role for IL-2 in cancer patient immune dysfunctions is suggested. Two lines of pathogenetic mechanisms are documented. First, PBL exhibited cellular function defects, namely, autologous receptor expression, IL-2 production, and NK activity. Second, these dysfunctions involved, at least partly, plasma factors. The possibility of specific deficiency, (e.g., thymic factors) is not documented. Conversely it is demonstrated that patient plasma contain immunosuppressive factor(s) that block(s) IL-2 production and ARF cell expression. Involvement of ARF cell receptor in T-cell activation is discussed.

Prospective study of natural cytotoxicity in peripheral blood of patients with nonlymphoid solid malignancies

Natural killer (NK) cells have been implicated as an initial immunosurveillance mechanism for carcinogenesis in humans. Work in the murine system as well as the findings of depressed NK activity in patients with advanced malignancies and the discovery of increased incidences of cancer in humans congenitally deficient in NK ability have supported this. Few prospective studies have demonstrated a prognostic change in NK activity with respect to malignant disease course. In 32 healthy donors, NK activity against K562 was determined. No race or sex difference existed with respect to NK cell function. Esophageal (5), bronchogenic (3), breast (3), cervical (3), and endometrial (1) cancer patients who had received no prior chemotherapy were compared to controls. All patients subsequently received radiotherapy. Prior to such treatment NK activity could not be associated with stage of malignancy. Of the 15 patients studied, 11 were sequentially followed. Five of eight patients with stable or improving clinical courses as assessed by weight and Karnofsky scores were found to have increasing NK activity. Two of three patients with poor clinical courses presented with subnormal killing which never rose to normal while the third declined to subnormal before expiring. Esophageal, cervical, and endometrial carcinoma patients all presented with low or subnormal NK activity. Of these, only cervical and endometrial cancer patients exhibited an increase to normal levels.

The standardization of NK cell assays for use in studies of biological response modifiers

This paper deals with the standardization of human natural killer (NK) cell assays for the sequential evaluation of patients with various disease states, or who are being treated with biological response modifiers. The method is described for the calculation of lytic units which results in numbers proportional to effector cell activity. It is shown that normal donors are relatively consistent in their cytotoxicity, making it possible to use a 'bank' of normal controls against which patients data can be normalized. Cryopreserved lymphocytes, as well as fresh lymphocytes, can be used as controls. Under the usual conditions for recovering cryopreserved lymphocytes, NK activity is markedly reduced; but by preincubation of the lymphocytes at 37 degrees C for 5 h or more the activity is recovered. A number of currently used methods for the selection of controls are described and discussed with respect to their practicality and validity. The principle problem with currently used methods is the necessity for a large number of controls so that a uniform distribution of NK activity about the 'true' normal is assured. The method which we advocate in this paper is based on the selection of normal control donors from a group of individuals who have been tested repeatedly over several months or years and whose NK activity relative to normal donors as a whole can be stated with reasonable confidence. These values are then used as correction factors which are applied to the relevant control donor's cytotoxicity every time that that person is used. In any particular experiment the mean of the corrected control lytic unit values is used as the denominator for the calculation of patient NK activity relative to normal. This method can be applied 'retrospectively' if a variety of donors have been used repeatedly. Two 'tests' of the methodology are described, with the following results: (1) the relative NK activity of a randomly selected group of normal women, whose data were handled as if they were a patient population, was approximately one, and (2) complete Freund's adjuvant, administered intradermally to patients with resected lung cancer, caused an increase in natural killer cell activity compared to pretreatment levels. The use of these methods should make it possible to derive meaningful NK results which are comparable from laboratory to laboratory.

Effect of isoprinosine on natural killer cell activity of blood mononuclear cells in vitro and in vivo

Addition of isoprinosine to cultures of blood mononuclear cells was shown to inhibit natural killer (NK) cell activity against the K562 myeloid cells and melanoma cells. This appeared to be due to inhibitory influences of monocytes in that after removal of adherent cells isoprinosine appeared to stimulate NK activity. Similar effects were noted on T cells separated by E rosette procedures. Administration of isoprinosine in vivo had variable effects on NK activity during drug administration but there was a significant increase in NK activity 3 days after cessation of the drug. These changes in NK activity may reflect different threshold levels of the drug on suppressor and NK cell populations and the relative proportions of different lymphocyte populations in individual subjects. Further studies with a wider range of drug doses and more frequent monitoring of responses are required to further evaluate the effect of isoprinosine on NK activity.

The effect of lysed and nonviable target cells on the experimentally determined kinetic parameters for natural and antibody-dependent cytotoxicity

In previous studies, we have demonstrated that kinetic assays of natural and antibody-dependent cellular cytotoxicity reactions can be used to obtain simultaneously estimates for both the frequency and lytic activity of the NK or K cells that lyse a given target cell. In order to generate useful information from kinetic cytotoxicity assays, it is imperative that suitable experimental conditions be used and consideration be given to factors that may alter the values of experimentally determined kinetic parameters. In this paper we derive equations to predict the effects of unlabeled inhibitor cells on the values obtained for KappM and Vmax. We further demonstrate that these equations can be used to interpret data obtained in the presence of a fixed concentration of added inhibitor cells and to correct for the apparent inhibition of cytotoxicity caused by nonviable cells present in 51Cr-labeled target cell preparations. We also predict that high concentrations of lysed target cells will cause product inhibition, present experimental evidence in support of this prediction, and present a method that can be used to test and correct for inhibition by lysed target cells. These results should provide for the more accurate determination of kinetic parameters for natural and antibody-dependent cytotoxicity reactions, and thereby more accurate quantification of effector cell frequency and activity.

An enzyme-release assay for natural cytotoxicity

A sensitive enzyme-release assay for natural cytotoxicity is described. The kinetic determination of the amount of the enzyme lactate dehydrogenase (LDH) released from lysed target cells was determined to provide a sensitive and precise measure of natural cytotoxicity when used in conjunction with appropriate controls and calculational methods. Values for the percentage of cytotoxicity or kinetic parameters determined by this method were identical, within experimental error, to values determined in parallel 51Cr release assays. Moreover, it was found that the spontaneous release of LDH from the target cells tested was considerably lower than the spontaneous release of 51Cr. This enzyme-release cytotoxicity assay is convenient, inexpensive, and precise, and should be applicable to the study of other cytotoxicity reactions, including antibody-dependent and T-cell mediated reactions.

Role in nude mice of interferon and natural killer cells in inhibiting the tumorigenicity of human hepatocellular carcinoma cells infected with hepatitis B virus

The human hepatoma cell line, PLC/PRF/5, which is persistently infected with hepatitis B virus (HBV), has integrated HBV-DNA, secretes HBV surface antigen (HBsAg), and does not grow readily in congenitally athymic (nu/nu) mice. The present investigation was undertaken to ascertain whether the low tumorigenicity of this cell line was governed by a host immune response and/or was related to expression of HBsAg. Subcutaneous injection of 4-5 X 10(6) cells into BALB/c nude mice produced localized encapsulated tumors with morphologic features of primary hepatocellular carcinoma in 25% of the animals within 29-40 d. No tumor growth was observed at lower cell inocula. In contrast, SK-HEP-1, an HBV-negative human hepatoma cell line, produced tumors at 1-5 X 10(6) cells inocula in 66% of the animals. Immunosuppression of mice with antilymphocyte serum (ALS) or irradiation increased tumor incidence in mice inoculated with 1 X 10(6) PLC/PRF/5 cells to almost 100% and produced local invasiveness. Immunosuppression also reduced the latency, i.e., time to tumor appearance, and increased mean tumor weight. These results suggest that tumorigenicity was limited by the host immune response. The nature of the response was delineated by treating nude mice challenged with tumor cells with sheep anti-mouse interferon globulin (anti-IFN). When 2 X 10(6) cells were injected, tumor growth occurred in 75% of anti-IFN-treated mice, whereas controls injected with the same number of cells, but not receiving anti-IFN, failed to develop tumors. The tumors in the anti-IFN-treated mice were highly invasive and the latency period until tumor appearance was reduced to 3-5 d. An inverse correlation was found between susceptibility of the hepatoma cells to natural killer (NK) activity in vitro and resistance to tumor growth in vivo. In vitro cytotoxicity for PLC/PRF/5 cells was eliminated by anti-NK 1.1 and complement, establishing the effector cell as an NK cell. NK cell activity 14 d after inoculation of mice with PLC/PRF/5 cells was augmented against PLC/PRF/5 target cells but not against SK-HEP-1 cells. Treatment of mice with ALS, irradiation, or anti-IFN abolished NK activity against PLC/PRF/5 cells. Co-cultivation of nude mouse spleen cells with PLC/PRF/5 but not with HBsAg or SK-HEP-1 cells induced secretion of murine IFNalpha. These results suggest that the IFN/NK cell system may play a role in limiting tumorigenicity and invasiveness of HBV-infected human hepatocellular carcinoma cells by a mechanism similar to that found for other cells persistently infected with viruses.

Lymphotoxin amplification of tumor growth inhibition is specific for natural killer cells but not for macrophages

Lymphotoxin augments the susceptibility of tumorigenic guinea-pig cells to natural killer (NK) cell cytolysis in vitro but does not directly stimulate either NK cell or macrophage cytolytic action. The question whether lymphotoxin enhances the susceptibility of tumorigenic guinea-pig cells to cytolysis or other means of growth inhibition in vivo by syngeneic NK cells or macrophages was, therefore, examined using a modified tumor cell neutralization (Winn) assay. Mineral oil-, thioglycollate- or casein-induced peritoneal leukocytes, but not the macrophages isolated from the elicited leukocytes obtained from nonimmunized strain 2/N guinea-pigs, effected enhanced cytolysis of lymphotoxin-treated guinea-pig benzo (a)pyrene-induced 104CI tumor cells in vitro. Neither guinea-pig splenic NK cells nor oil-induced peritoneal macrophages alone inhibited the growth of 104CI cells as tumors in vivo when admixed with 104CI cells and injected into guinea-pigs. However, when the 104CI cells were treated with lymphotoxin before addition of effector cells, NK cells but not macrophages significantly reduced tumor growth in vivo. Therefore, the ability of lymphotoxin to increase the sensitivity of tumor cells to destruction mediated by natural leukocytes is specific for NK cells as compared to macrophages. This form of lymphokine amplification of natural leukocyte cytotoxicity may be one mechanism by which natural and acquired immunity serves or fails to prevent cancer and should be an important consideration in therapeutic approaches to eradicate or control tumor growth.

Quantification of natural cytotoxicity by human lymphocyte subpopulations isolated by density: heterogeneity of the effector cells

Natural cell mediated cytotoxicity has been expressed as percent cytotoxicity, as the slope of the titration curve obtained by testing different effector: target cell ratios, and as lytic units. Objections can be raised to each method as used. The present report involves the study of cytotoxicity by subpopulations of lymphocytes obtained by Percoll density gradient centrifugation. The subpopulations vary greatly in cytotoxic activity, making accurate comparisons by traditional means difficult. A method was therefore developed for making objective comparisons between activities of subpopulations of lymphocytes. Cytotoxicity titration curves, which were sigmoidal on linear-linear plots, were found to best fit the sigmoidal curves described by the Von Krogh equation. A best fitting scale family of curves having the identical maximum cytotoxicity and shape parameter was fitted simultaneously to cytotoxicity measurements obtained by titrating all subpopulations of effector cells obtained from each patient. Values expressing relative cytotoxicities were obtained from the ratios of the scale parameters of the different curves or by obtaining lytic units from the fitted curves. In addition to the enriched natural cytotoxic activity found among the lighter cells obtained by Percoll density gradient centrifugation, activity was also increased among cells sedimenting at the very bottom of the gradient. This was found in subpopulations of cells obtained from 16/21 gradients in tests against K562 and in subpopulations obtained from both of 2 gradients in tests against Daudi cells. These findings are consistent with the existence of at least 2 subpopulations of lymphocytes which can mediate natural cytotoxicity, and which are separable by density.

The biology of the human natural killer cell

Natural killer (NK) cells in the human are a population of large granular lymphocytes (LGL) with at least one unique surface antigen not expressed on cells of other lineages. NK-target-cell interaction appears to involve carbohydrate recognition and, following binding, the NK cells are induced to generate O2-, transmethylate membrane phospholipids, and activate phospholipase A2. Some or all of these activities trigger a cascade of events which ultimately leads to the secretion of a substance toxic to the target cell. A variety of genes controls various steps in this cytolytic pathway. There is a good deal of evidence in the mouse, and some in the human, that NK cells play a role in host surveillance against tumor development, resistance to viral infections, and, possibly, hematopoietic regulation.

Human newborns are deficient in natural killer activity

The peripheral blood natural killer (NK) activity of newborns was found to be significantly less than that of adults. In mixing experiments newborn cells inhibited adult NK activity in only one of nine instances. Interferon treatment in vitro increased newborn NK activity to an even greater degree than adult NK activity. These findings imply that diminished newborn NK activity is due not to inhibitory cells or lack of pre-NK cells but rather to deficient in vivo activation of pre-NK cells. This deficiency may be a major factor in the increased susceptibility of newborns to certain virus infections.

Lymphotoxin enhances the susceptibility of neoplastic and preneoplastic cells to natural killer cell mediated destruction

Treatment of neoplastic guinea-pig cells for 1-14 days with 300 units of guinea-pig lymphotoxin/ml medium enhanced 2- to 5-fold their susceptibility to natural killer (NK) cell-mediated cytotoxicity as measured by 4 h 51Cr and 72 h [3H]-thymidine-release assays. The NK susceptibility of human neoplastic and guinea-pig non-neoplastic cells refractory to guinea-pig lymphotoxin growth-inhibitory activity was unchanged after lymphotoxin treatment. Lymphotoxin preparations were free of detectable interferon and the enhancing activity copurified with lymphotoxin during diafiltration and isoelectric focusing. Treatment of NK cells with lymphotoxin preparations also augmented NK-mediated lysis but that activity did not copurify with lymphotoxin. As with neoplastic cells, lymphotoxin-sensitive preneoplastic cells previously treated with ultraviolet light, a chemical carcinogen, or carcinogen and the tumor-promoting agent tetradecanoylphorbol-acetate also exhibited lymphotoxin enhancement to NK-cell destruction. Thus, the immunologic hormone lymphotoxin enhances the susceptibility of lymphotoxin-sensitive cells to NK-cell destruction, indicating that these two natural immune mediators, lymphotoxin and NK cells, have the potential in concert to regulate carcinogenesis and neoplastic growth.

Studies of human natural killer cells. I. In vivo parameters affecting normal cytotoxic function

The results of natural killer cell (NK) studies on 539 normal healthy donors tested from once to 213 times over a seven-year time span have been presented. NK activity did not vary with donor blood group, Rh type or (in a small sample) HLA type. There was a slight but significant increase in NK activity from birth to adulthood, and between males an females. The male/female difference was present at birth and persisted through adulthood. The relative NK activity of individual donors tested repeatedly over many years was remarkably consistent in spite of variability in the absolute cytotoxicity observed. The expression of NK data in terms of relative NK was found to be superior to other methods, and the values obtained were found to be independent of the NK-sensitive target cell used. Although age and sex differences in NK activity are slight, their existence should be considered when studies of NK activity in patients are analysed.

Studies of human natural killer cells. III. Neutropenia associated with unusual characteristics of antibody-dependent and natural killer cell-mediated cytotoxicity

A 52-year-old Caucasian man with chronic neutropenia and recurrent infections was found to have an increased proportion of peripheral T lymphocytes having Fc receptors for IgG (T gamma ). Although levels of antibody-dependent cell-mediated cytotoxicity (ADCC) and "natural" killing (NK) by unfractionated lymphocytes were similar to those of a control donor, the frequency of KN cells was markedly increased. Removal of E rosette-forming cells eliminated both NK and ADCC by the patient's peripheral blood, in marked contrast to the enhanced cytotoxicity seen with control lymphocytes. Both normal and patient ADCC and NK functions were removed by depletion of Fc receptor-bearing cells. These depletion experiments proved that all of the patient's killer cells were E rosette-forming T gamma cells, in contrast to the heterogeneous pattern of null gamma and T gamma killer cells seen in the blood of normal donors. The homogeneity of the T gamma proliferation suggested that ADCC and NK were mediated by the same cell type, albeit acting by different mechanisms. The addition of the patient's serum and lymphocytes to chromium-labelled normal granulocytes caused a low but significant level of cytotoxicity, indicating that the patient's neutropenia may have been caused by a similar mechanism in vivo. There was no evidence of complement-dependent serum antibody-mediated neutrophil lysis, but one serum sample taken over the course of the patient's disease agglutinated granulocytes from four of five donors tested.

A simple and economical device for the rapid collection of multiple supernates from cytotoxicity experiments

The construction and use of a single semiautomatic device for collecting equal aliquots of supernates after radioisotope release assays of cellular cytotoxicity are described. This device simultaneously removes an aliquot of the supernate from each of the 12 wells in one row of a microtiter plate, and transfers these aliquots directly to disposable tests tubes for insertion into a gamma-counter. Results obtained using this device were more reproducible than manual methods for supernate collection.

Improved quantification of cellular cytotoxicity reactions: determination of kinetic parameters for natural cytotoxicity by a distribution-free procedure

A distribution-free statistical procedure for estimating kinetic parameters for cellular cytotoxicity reactions is described. Estimates of cytotoxic activity obtained using this procedure are considerably more precise than percent cytotoxicity values, lytic unit values, and V max values determined by least-squares analysis of the same sets of experimental data. Application of this procedure to the study of natural cytotoxicity allows for precise quantitative comparisons of the lytic activity of different lymphocyte preparations for a given target cell line, of a single lymphocyte preparation for different target cell lines, or of a given lymphocyte and target cell combination under different experimental conditions. This procedure, which does not involve a more complex experimental protocol than other methods, should also allow for more accurate assessment of the relative cytotoxic activity of lymphocytes obtained from patient populations.

Countercurrent distribution of human peripheral blood lymphocytes: isolation of a subpopulation enriched with natural killer and K cells

Aqueous solutions of dextran and of poly(ethylene glycol) when mixed give rise to two-phase systems suitable for the separation by partitioning of cells based on subtle differences in their membrane surface properties. Human peripheral blood mononuclear cells were obtained by centrifuging blood over Hypaque-Ficoll and removing the cells from the cushion. Clean lymphocytes were then isolated by velocity sedimentation of the mononuclear cells. Lymphocytes were subjected to countercurrent distribution (i.e., a multiple extraction procedure) in a two-polymer aqueous phase system which separates cells primarily on the bases of surface charge-associated properties. It was found that a small subpopulation of cells with highest partition coefficient (presumably highest surface charge-associated properties) contain virtually all of the natural killer (NK) and K cell activities.