Natural killer function in flow cytometry: identification of human lymphoid subsets able to bind to the NK sensitive target K562

Natural killer cells in female infertility and recurrent miscarriage: a systematic review and meta-analysis

INTRODUCTION Embryo implantation is a complex process involving maternal hormonal changes, immune responses and maturational events in the embryo. A pregnancy could fail when these events are not synchronized. It is speculated that in women, an elevation of natural killer (NK) cells may have an effect on reproductive performance, and NK cell levels in blood are currently being used as a diagnostic test to guide the initiation of therapies in patients with infertility. METHODS We conducted a systematic review to evaluate the (i) levels of NK cells in blood and endometrium in infertile versus fertile women, (ii) association between NK cells and IVF outcome, (iii) levels of NK cells in blood and endometrium in women with recurrent miscarriage (RM) versus controls. The following electronic databases were searched: Medline, EMBASE, Cochrane Library, Web of Science and National Research Register. RESULTS A total of 22 studies were included. Meta-analysis of studies that evaluated peripheral and uterine NK (uNK) cell percentages in infertile versus fertile women showed no significant difference between the two groups [standardized mean difference (SMD) -0.33; 95% confidence intervals (CI) -1.06, 0.4; P = 0.37; SMD -1.82; 95% CI -4.80, 1.17; P = 0.23 respectively]. Pooling of studies that reported peripheral NK cells as numbers showed significantly higher NK cell numbers in infertile women compared with fertile controls (SMD 3.16; 95% CI 1.07, 5.24; P = 0.003). Meta-analysis of studies that evaluated the role of NK cells in IVF outcome showed no significant difference in live birth rates in women with elevated NK cells or NK cell activity compared with women without elevated peripheral NK cells or NK cell activity (NK activity assessed using a cytotoxicity assay) (relative risk 0.57; 95% CI 0.06, 5.22; P = 0.62). Meta-analysis of studies that evaluated peripheral NK cell percentages in women with RM versus controls showed significantly higher NK cell percentages in women with RM (SMD 1.36; 95% CI 0.04, 2.69; P = 0.04). Meta-analysis of studies that evaluated peripheral NK cell numbers showed significantly higher NK cell numbers in women with RM compared with controls (SMD 0.81; 95% CI 0.47, 1.16; P < 0.00001). Meta-analysis of studies that evaluated uNK cells showed no significant difference in women with RM compared with controls (SMD 0.40; 95% CI -1.24, 2.04; P = 0.63). CONCLUSIONS Further research is needed before NK cell assessment can be recommended as a diagnostic tool in the context of female infertility or RM. There is no clear explanation as to why the results differ when data for NK cells are expressed as numbers or a percentage. On the basis of current evidence, NK cell analysis and immune therapy should be offered only in the context of clinical research.

Restoring the functional immunogenicity of chronic lymphocytic leukemia using epigenetic modifiers

Chronic lymphocytic leukemia (CLL) is a malignancy arising from immune cells (B-lymphocytes) endowed with intrinsic antigen-presenting capabilities. Such a function however is lost during malignant transformation and CLL cells are well known for their inability to process and present antigens to the T-cell arm of the immune system. Instead, malignant CLL cells elicit a vast array of immune regulatory mechanisms conducive to T-cell dysfunction and immunosuppression. Previously, we have shown that treatment of CLL cells with the demethylating agent 5-aza-2'-deoxycytidine unleashed target antigen expression. Here we show for the first time that combining two epigenetic modifiers, 5-aza-2'-deoxycytidine and the histone deacetylase inhibitor LAQ824 effectively restores the immunogenicity of CLL cell lines as well as primary cells obtained from CLL patients. Indeed, such a combination induces the expression of novel and highly antigenic cancer-testis antigens (CTAs) and costimulatory molecules. These changes facilitate the formation of robust supramolecular activation complexes (SMAC) between CLL cells and responder T-cells leading to intracellular signaling, lytic granule mobilization, and polarization of functional and relevant T-cell responses. This cascade of T-cell activating events triggered by CLL cells with restored APC function, points to combined epigenetic modifier treatment as a potential immunotherapeutic strategy for CLL patients.

Distribution of several activating and inhibitory receptors on CD3-CD16+ NK cells and their correlation with NK cell function in healthy individuals

The aim of this study was to estimate the distribution and density of a representative set of activating and inhibitory receptors on gated natural killer (NK) cells, as well as on their bright and dim subsets, and to correlate the receptor expression with NK cell activity for healthy individuals on CD3(-)CD16(+) NK cells. We show that in 43 healthy controls NK cell activity against K562 target cells was 37.34% (E:T, 80:1) by standard chromium release assay. The expression of receptors on NK cells and their subsets was analyzed by flow cytometry. The cytotoxic CD3(-)CD16(bright) NK subset constituted 78.97%, while the regulatory CD3(-)CD16(dim) NK subset constituted 21.03% of NK cells. We show the distribution of NKG2D, CD161, CD158a, and CD158b receptors on CD3(-)CD16(+) NK cells in peripheral blood lymphocytes (PBLs), on gated NK cells, and on the CD3(-)CD16(bright) and CD3(-)CD16(dim) subsets. Contrary to CD158a and CD158b killer immunoglobulin-like receptors (KIRs), there is a significant positive correlation of NKG2D and CD161 expression with NK cytotoxicity. We show the kinetics of change in CD3(-)CD16(+)NK/K562 conjugate composition, together with the stronger target binding capacity of CD16(bright) NK cells. Furthermore, we show that after coculture of PBLs with K562 the expression of CD107a, a degranulation marker, on CD3(-)CD16(+)NK cells and subsets is time dependent and significantly higher on the cytotoxic CD3(-)CD16(bright) NK subset. The novel data obtained regarding expression of NK cell activating and inhibitory receptors for healthy individuals may aid in detecting changes that are associated with various diseases.

CD28 costimulation provided through a CD19-specific chimeric antigen receptor enhances in vivo persistence and antitumor efficacy of adoptively transferred T cells

Chimeric antigen receptors (CAR) combine an antigen-binding domain with a CD3-zeta signaling motif to redirect T-cell specificity to clinically important targets. First-generation CAR, such as the CD19-specific CAR (designated CD19R), may fail to fully engage genetically modified T cells because activation is initiated by antigen-dependent signaling through chimeric CD3-zeta, independent of costimulation through accessory molecules. We show that enforced expression of the full-length costimulatory molecule CD28 in CD8(+)CD19R(+)CD28(-) T cells can restore fully competent antigen-dependent T-cell activation upon binding CD19(+) targets expressing CD80/CD86. Thus, to provide costimulation to T cells through a CD19-specific CAR, independent of binding to CD80/CD86, we developed a second-generation CAR (designated CD19RCD28), which includes a modified chimeric CD28 signaling domain fused to chimeric CD3-zeta. CD19R(+) and CD19RCD28(+) CD8(+) T cells specifically lyse CD19(+) tumor cells. However, the CD19RCD28(+) CD8(+) T cells proliferate in absence of exogenous recombinant human interleukin-2, produce interleukin-2, propagate, and up-regulate antiapoptotic Bcl-X(L) after stimulation by CD19(+) tumor cells. For the first time, we show in vivo that adoptively transferred CD19RCD28(+) T cells show an improved persistence and antitumor effect compared with CD19R(+) T cells. These data imply that modifications to the CAR can result in improved therapeutic potential of CD19-specific T cells expressing this second-generation CAR.

Priming with Dendritic Cells Can Generate Strong Cytotoxic T Cell Responses to Chronic Myelogenous Leukemia Cells In Vitro

Dendritic cells (DC) are antigen-presenting cells that can elicit potent antigen-specific responses. Since the development of techniques to cultivate these cells from peripheral blood, there has been a great deal of interest in their use in immunotherapeutic strategies. Here we show that morphologically, phenotypically, and functionally characteristic DC can be generated in vitro from peripheral blood mononuclear cells (PBMC) isolated from frozen apheresis product (AP) of cancer patients. These DC, when pulsed with whole-tumor lysate, protein, or RNA from a chronic myelogenous leukemia (CML) cell line, can induce anti-CML specific cytotoxicity in vitro by autologous cytotoxic T lymphocytes (CTL). RNA and protein-pulsed DC were more effective than lysate-pulsed DC at inducing cytotoxicity at low effector:target (E:T) ratios. These results were comparable to those obtained when fresh healthy peripheral blood was used as the source of PBMC, indicating that neither the malignant state of the patient nor the storage period detrimentally affected the generation or functionality of DC. CML cells were found to increase their level of MHC class I expression after exposure to CTL and pulsed DC thereby becoming better targets. These investigations lend support for the utilization of DC to generate anti-tumor responses in CML.

Simultaneous flow cytometric measurement of K-562 megakaryocytic differentiation and CD56+ large granular lymphocyte cytotoxicity

K-562 cells have the capacity to undergo multi-lineage differentiation, which may be crucial to their ability to serve as target reservoirs for CD56+ large granular lymphocytes (LGL). Conventional techniques using chromium release assays to measure lymphocyte-mediated cytotoxicity suffer from disadvantages, including radioactive contamination and the inability to simultaneously determine K-562 and/or CD56+ lymphocyte phenotypes. We illustrate here a three-color flow cytometric method providing for the simultaneous evaluation of K-562-CD56+ LGL binding, K-562 cell viability, and the status of K-562 cell differentiation. Phorbol 12-myristate 13-acetate (PMA) engenders megakaryocytic differentiation in K-562 cell populations, as measured by presentation of the beta(3) integrin (gpIIIa, CD61), while maintaining a negative expression of MHC-I and MHC-II molecules. Using the auto-fluorescence of K-562 cells, flow cytometry can be used to demonstrate a significant decrease in CD56+ LGL activity against K-562 cells in populations pre-incubated with PMA. The capacity of three-color flow cytometry to measure lymphocyte-target cell binding and cell death kinetics, while simultaneously determining target cell phenotype, permits the specific localization of CD61-expressing K-562 cells to areas inconsistent with CD56+ LGL-mediated patterns of lysis.

Deficiency in circulating natural killer (NK) cell subsets in common variable immunodeficiency and X-linked agammaglobulinaemia

Absolute and relative NK cell numbers were determined in peripheral whole blood by flow cytometry in patients with common variable immunodeficiency (CVID) (n = 55) and X-linked agammaglobulinaemia (XLA) (n = 19) on regular immunoglobulin (IVIG) therapy. Absolute CD3-CD16+ NK cell numbers were significantly reduced in CVID patients (median 108/microl, range 23-815), compared with normal subjects (n = 60) (289/microl, range 56-640, P < 0.001). Total lymphocyte concentrations were significantly lower in CVID (median 1587/microl, range 523-7519) compared with normal subjects (median 2019/microl, range 1124-3149, P = 0.004), with the percentage of NK cells also being significantly decreased (median 7.5%, range 3.0-33. 0%, compared with 14.2%, range 2.6-30.8%, P < 0.001). In XLA, absolute NK cell numbers (median 140/microl, range 32-551, P < 0. 001) but not relative numbers were significantly reduced compared with normal controls. We excluded the possibility that IVIG interferes with in vitro binding of CD16 MoAbs. Further analysis of NK cell subsets showed a deficiency of both CD16+ and CD56+ cells in CVID, most marked in the CD3-CD8dim subpopulation, which may be due to increased homing of these cells to the gut. Serial studies on a small number of patients suggest that IVIG therapy has no short-term effect on NK cells, although we cannot exclude an effect with prolonged use. Although there are no obvious clinical effects of the NK depletion in CVID and XLA, this may be a factor in their predisposition to cancer.

Importance of the CD3 marker for evaluating changes in rhesus macaque CD4/CD8 T-cell ratios

BACKGROUND

Until recently, there were no CD3 antibodies that crossreacted with rhesus macaque T cells. Consequently, studies relying on CD8 counts or CD4/CD8 ratios enumerated this subpopulation on the basis of CD8+ or CD8bright+ staining. We used a rhesus-specific, anti-CD3 antibody to better define the CD8+ T-cell population, and to show the effects of better measurements on CD4/CD8 ratios and changes in T cells as macaques age.

METHODS

We used three-color flow cytometry to measure CD4 and CD8 populations with and without CD3 costaining. Venous blood samples were obtained from 52 colony-bred macaques between 2 months and 9 years of age.

RESULTS

The CD8+ T cells defined by CD3 and CD8 double staining were approximately 60% of all cells that were stained by CD8 alone. Improved detection of this lymphocyte subset showed that CD4/CD8 ratios were close to the range of 1.5-2.0. Declining CD4/CD8 ratios during aging are predominantly due to decreasing CD4+ T-cell counts.

CONCLUSIONS

Better quantitation of the CD8+ T-cell population showed that the CD4/CD8 ratio was not inverted as had been reported, but is actually very similar to the values observed in human beings. Although the two species differ in the pattern of CD8 expression, the general immune system characteristics are very similar.

Differential production of IFN-gamma, analyzed at the single-cell level, by specific subsets of human NK and T cells from healthy and HIV(+) subjects

BACKGROUND

Interferon gamma is a cytokine that plays a central role in immunity, and is physiologically secreted by T and NK cells under appropriate stimuli during the immune response. By means of flow cytometry, we performed a single cell analysis of interferon gamma producing NK cells and their surface phenotype in normal and HIV(+) individuals that show several defects of cytokine production and cellular immunity.

METHODS

PBMC or purified NK cells were stimulated for 1-12 h with PMA/ionomycin in the presence of monensin, subsequently stained for surface CD56 and CD3 or CD8, and for intracytoplasmic IFN-gamma, and analysed by flow cytometry.

RESULTS

Our results show that CD56(+) NK cells are more efficient interferon gamma producers than T cells. Moreover, within the CD56(+) NK cell population, those that co-express low density CD8 are the best producers. Finally, we show that NK cells during HIV infection are more massively recruited to interferon gamma production than those from normal subjects.

CONCLUSIONS

Both in the normal and HIV(+) subjects, a higher percentage of NK cells than T cells can produce IFN-gamma although differences can be identified within the NK cells subset in terms of IFN-gamma production. The production of IFN-gamma is fully achievable in the HIV(+) subjects, which is consistent with their elevated plasmatic levels of the cytokine. The possibility that NK cells that produce interferon gamma could represent a functionally distinct population committed to the production of this cytokine, is discussed.

Determination of parameters that characterize effector-target conjugation of human NK and LAK cells by flow cytometry

Effector-target conjugation between different cell populations of human NK cells and K562 tumor cells has been studied from binding isotherms obtained from data of effector (alpha) and target (beta) conjugate frequencies measured by flow cytometry analysis at different effector-to-target ratios. Non-linear and linear regression methods were applied to these isotherms to calculate the binding parameters that characterize the process of conjugation, namely, the maximum effector and target conjugate frequencies, the dissociation constant of the conjugates formed, the binding units and the area under the binding isotherms. The results obtained show that: (1) flow cytometry analysis of effector-target conjugation is faster, unbiased and more suitable than microscopic counting of conjugates, thereby permitting the analysis of larger number of conjugates in shorter times, (2) the binding parameters derived from conjugate frequencies obtained by flow cytometry analysis differ from those obtained by microscopy, (3) the discrepancies between the two methods are due to the presence of several cells engaged in multicellular conjugates that are detected as single particles by flow cytometry and (4) the analysis of population distributions of the conjugates formed at different values of the effector-to-target ratio permit the above discrepancies to be corrected.

Determination of natural killer cell function by flow cytometry

Natural killer cells (NK cells) are a subset of peripheral blood lymphocytes that mediate non-major histocompatibility complex-restricted cytotoxicity of foreign target cells. The "gold standard" assay for NK cell activity has been the chromium release assay. This method is not easily performed in the clinical laboratory because of difficulties with disposal of radioactive and hazardous materials, short reagent half-lives, expense, and difficulties with assay standardization. We describe a flow cytometric assay for the clinical measurement of NK cell activity. This study compared the chromium release assay and the flow cytometric assay by using clinically relevant specimens. There were no significant differences between the two assays in the measurement of lytic activity for 17 peripheral blood specimens or in reproducibility in repeated samplings of healthy individuals. We also established a normal range of values for NK activity in healthy adults and identified a small cluster of individuals who have exceptionally high or low levels of NK activity. The flow cytometric assay was validated by testing specimens from subjects expected to have abnormally low levels of NK activity (pregnant women) and specimens from healthy individuals in whom the activity of NK cells was enhanced by exposure to interleukin-2 or alpha interferon. Treatment with these agents was associated with a significant increase in NK activity. These results confirm and extend those of others, showing that the flow cytometric assay is a viable alternative to the chromium release assay for measuring NK cell activity.

Flow cytometric measurement of NK cell immunoconjugates by pulse width processing

Pulse width analysis, in flow cytometry, has been widely used for optimal cell size resolution in cell kinetics analysis. Pulses, generated by scattered light or fluorescence of cells, are electronically analyzed for their height and width. The information generated from these two properties of the pulses is utilized to distinguish signals from single cells vs. signals from cell clumps or aggregates. Pulse width, unlike pulse height, is more sensitive to differences in cell diameter, and therefore can discriminate very small differences in it, which pulse height cannot. We have exploited this property of pulse widths to measure immunoconjugates between NK cells and their targets. Discrimination of the free target cells from the conjugated ones is possible by the pulse widths of only light scatter signals, both forward and/or orthogonal. This resolution was not obtained if pulse height of the same signals was visualized. Using this resolution it was possible to distinguish single cells from the aggregates between target and effector cells. We propose that this is a better method for distinguishing conjugates than the method in which prior vital staining of cells is used.

Flow cytometric determination of intracellular calcium changes in human peripheral blood mononuclear cells during conjugation to tumour cell lines

Using a flow cytometric assay, conjugate formation between human peripheral blood mononuclear cells (PBMC) and three different human tumour cell lines has been analysed. Changes in the intracellular calcium levels of PBMC were monitored using the calcium sensitive dye Fluo-3. Target cell populations were distinguished by forward scatter or following loading with the fluorescent dye, SNARF-1. Intracellular calcium was expressed as a ratio of fluorescence of conjugated to unconjugated PBMC and followed for ten minutes after initiation of conjugation. The results demonstrate an apparent increase in intracellular calcium in PBMC conjugated to the NK-sensitive cell line K562, and that the kinetics and magnitude of this response varied considerably between individuals. Tumour cells which were resistant to lysis (as determined in a 4 h chromium release assay) were also capable of eliciting a calcium response from PBMC. Although the induction of a rise in intracellular calcium was therefore not correlated with cytotoxicity, it was greater in IL-2-activated PBMC upon exposure to the same target cell lines as PBMC.

Standardization of a micro-cytotoxicity assay for human natural killer cell lytic activity

Cytotoxicity assays are widely used to evaluate the functional activity of NK and T cells against tumour target cells and the release of radioactive sodium chromate from labelled target cells is still the most commonly used marker of target lysis in culture supernatants. We describe here the standardization of a micro-cytotoxicity test in which the number of cytolytic effector and tumour target cells have been decreased by a factor of 10. The release obtained by 500 tumour target cells was compared with the release obtained by 5000 target cells in the standard cytotoxicity assay for target:effector cell ratios from 1:1 to 1:100. Both gamma and beta emissions of the 51Cr isotope were evaluated to determine the assay release. The results obtained by the micro-cytotoxicity assay (500 target cells) were comparable to those of the standard assay (5000 target cells) and 51Cr release evaluation using the gamma counter was the most sensitive method of determining lytic activity using 500 tumour target cells. beta counter evaluation using solid phase scintillation was found to be a reproducible alternative method, even if the lytic curves cannot be compared with those obtained using the traditional method.

Flow cytometric analysis of natural killer cell function as a clinical assay

The 51Cr release assay has been the method of choice in analyzing natural killer cell (NK) function. Previous FCM cytotoxicity assays of NK activity have had numerous disadvantages that discouraged clinicians from attempting to evaluate NK function by flow cytometry. We demonstrate the effectiveness of using PKH-26, a stable membrane dye, to label the K562 target cells and propidium iodide intercalation into killed target cell DNA to determine the percentage of target cells killed by effector NK cells from the peripheral blood or bone marrow. This method compares favorably with the 51Cr release assay and is quicker and easier to perform. The percentage of cytotoxicity of NK cells (CD3- CD56+ and/or CD16+) from 10 normal subjects and 10 HIV-infected children are reported to demonstrate the feasibility of studying NK function in clinical populations by FCM. The potentiation of cytolysis by alpha-interferon and interleukin 2 in vitro was also compared between these two study groups. In addition, a patient whose leukemic blasts expressed CD56+ was also studied for NK activity using this flow cytometric assay. The benefits of using this flow cytometric approach to clinically assess NK function are discussed.

Cytokine activity after allogeneic bone marrow transplantation. V. Analysis of IL-2 and IFN production by isolated CD4+ and CD8+ cells

Previous studies from this laboratory have shown that PBMC from recipients of an HLA-identical sibling bone marrow transplant produce levels of IL-2 which are 10-100-fold lower than those produced by the same number of PBMC from healthy controls, whereas production of IFN-gamma is normal. The present study examined IL-2 and IFN production over a range of cell numbers for PBMC and for isolated CD4+ and CD8+ cells for controls and marrow transplant recipients. There was a 5-fold lower IL-2 production in marrow transplant recipient CD8+ cells compared with equivalent numbers of control cells, whereas no difference was found in IL-2 production by CD4+ cells. In contrast, IFN production by CD4+ cells from marrow transplant recipients was 4-fold higher than in controls, whereas CD8+ cells from both populations produced similar amounts of IFN. When the observed production of cytokine by PBMC was compared with the expected production based on the CD4+ and CD8+ content of the PBMC, control values were similar, but the expected values for both cytokines were approximately 2-fold higher than the observed values for marrow transplant recipients. The results suggest that the capacity of T cells from marrow transplant recipients to produce IL-2 and IFN is not impaired, but that the frequency of cytokine-producing cells may be reduced, and that a negative interaction present in recipient PBMC, eliminated by isolating T-cell subsets, is responsible for the observed low levels of cytokine production.

Subtraction of autofluorescent dead cells from the lymphocyte flow cytometric binding assay

Flow cytometry allows the quantitative analysis of lymphocyte-target cell conjugates and the identification of the lymphocyte subset involved in the binding phenomenon. We recently described a methodology to identify the effector cells bound to K562 targets based on target cell autofluorescence coupled with lymphocyte staining by means of fluorescent monoclonal antibodies. Here we describe an implementation of the methodology that allows the subtraction of spontaneously dead targets to which lymphocytes may or may not adhere, thereby preventing the overestimation of the binding phenomenon and limiting its evaluation to living effector-target conjugates, thus preserving the specificity of the phenomenon.

Flow cytometric method for simultaneous detection of lymphocyte-K562 conjugates and immunophenotyping of the conjugate forming cells

A flow cytometric method for the simultaneous quantification and immunophenotyping of conjugates formed by human peripheral blood lymphocytes (PBL) and K562 cells has been developed. The method uses three fluorescent probes. One of the fluorescent probes (F-18) is used for labeling of PBL prior to incubation with K562 cells. After incubation the cells are treated with monoclonal antibodies labeled with phycoerythrin and Red613, respectively. The combination of F-18 fluorescence and light scattering signals enables identification and quantification of the conjugates while the fluorescence of the monoclonal antibodies provides information about the phenotype of the conjugate forming cells. Results obtained using different monoclonal antibodies are presented. The highest conjugate forming capacity has been found in the CD56+CD8+ population while the CD4+CD8- population has shown the lowest capacity to form conjugates. The influence of a washing step on the conjugate formation is discussed. The possibility to use the method in combination with a cytotoxicity assay is indicated.

The impairment of natural killer function in the healthy aged is due to a postbinding deficient mechanism

In order to study the fine mechanisms that underlie the impairment of non-MHC-restricted cytolytic activity which occurs during human aging, we examined by multiparametric flow cytometry the binding and lytic activities of human natural killer cells. The flow analysis revealed a striking increase of the CD16+8- subset, together with a significant decrease of CD8bright cells and total T cells (CD3+). Aging had no influence on the CD8dim subset. The total lytic activity expressed by PBL as well as their binding efficiency to K562 targets were moderately but not significantly increased in the elderly. In contrast, the cytotoxicity of the single target-bound natural killer cell (i.e., lytic efficiency) was deeply impaired in aged subjects, suggesting that the NK functional impairment observed in aging is located at postbinding level.

Antibodies to adhesion molecules inhibit the lytic function of MHC-unrestricted cytotoxic cells by preventing their activation

We evaluated the effect of the antibodies to adhesion molecules CD2, CD11a/CD18 (LFA-1), and CD56 (N-CAM) on MHC-unrestricted cytotoxicity mediated by polyclonal NK cells and LAK cells or by CD3+ or CD3- cytolytic cell clones against a panel of tumor cell targets selected according to expression or absence of the corresponding ligands. We show that (i) antibodies to CD11a/CD18 and, to a lesser extent, antibodies to CD2 inhibit target cell lysis, whereas anti-CD56 antibodies exert little if any effect; (ii) in a model system using polyclonal NK/LAK cells as effectors and K562 or HL60-R (NK-resistant) cells as targets, inhibition of cytotoxicity occurs without a significant impairment of effector to target cell binding; (iii) the cytotoxic function of CD3+ or CD3- cytotoxic cell clones is inhibited differentially by antibodies to adhesion molecules; (iv) conjugates formed in the presence of antibodies which inhibit target cell lysis display a significant reduction of target to effector cell contact surface; and (v) this may lead to defective activation of effector cells, as indicated by lack of redistribution of the microtubular apparatus. We conclude that (i) MHC-unrestricted cytotoxicity is regulated by a number of molecular interactions that span far beyond our present knowledge and that it is strictly dependent on the surface phenotype of the effector cell and of the target cell; (ii) in certain types of effector/target cell interactions, antibodies to adhesion molecules do not prevent conjugate formation but reduce the extent of cell-to-cell surface contact which, in turn, leads to defective activation of the effector cell and, therefore, to inhibition of target cell lysis.

Human NK cells in health and disease: clinical, functional, phenotypic and DNA genotypic characteristics

Natural killer (NK) cells are the subject of great current interest because of their possible (in vivo) role in tumour cell surveillance and killing, and because of the potential application of cytokine-modulated NK cells in cancer immunotherapy. In addition, clonal proliferations of NK-associated (NKa) cell populations represent a high proportion of chronic (non-B) lymphoid malignancies and abnormal (both clonal and non-clonal) NKa components are being increasingly reported in association with diverse clinical pictures such as autoimmune disease. This communication extensively reviews what is presently known regarding normal and leukaemic NKa phenotypic diversity, the mechanisms of NK-mediated cytolysis, the role of NK cells in malignancy, and the diagnostic and cellular aspects of malignant NKa proliferations.