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

FDA/PI flow cytometry assay of complement-mediated cytotoxicity of antibodies generated during xenotransplantation

BACKGROUND

A flow cytometry complement-mediated cytotoxicity assay (FCCA) using fluorescein diacetate (FDA) and propidium iodide (PI) to measure antibody-dependent toxicity is useful to determine the success of xenotransplant organs. We evaluated the validity of different mathematical models as a measure of cytotoxicity in FCCA.

METHODS

Sera from untreated baboons (n = 7) and from immunosuppressed animals (n = 5) undergoing different xenotransplantation protocols with pig organs were tested by endogenous FCCA and a similar assay also using exogenous complement, and the results were compared with those of a complement-dependent hemolytic assay to detect anti-pig antibodies (APHA). The influence of PI/FDA staining and the use of several mathematical models were analyzed.

RESULTS

For both groups of animals, we observed high correlations between the endogenous and exogenous FCCA pathways and between calculations based on PI and FDA staining. Of the four mathematical models tested--the Von Krogh equation, two exponential models, and area under the curve--the Von Krogh equation was the most appropriate in terms of goodness of fit and concordance with APHA.

CONCLUSIONS

FDA/PI FCCA is useful to measure endogenous and exogenous complement-mediated cytotoxicities, and it has advantages related to identification of potential new xenoantibodies. Although all four mathematical models produced acceptable solutions, the Von Krogh equation was the best option.

Novel employment of lactate dehydrogenase release from porcine aortic endothelial cells (PAEC) as a quantitative marker of cytotoxic activity in thermophilic Campylobacter spp. from human faecal isolates, poultry and environmental sources

The aim of this study was to employ a novel cytotoxicity assay based on primary porcine aortic endothelial cells in combination with a lactate dehydrogenase release assay to quantitatively determine differences in cytotoxin production between Campylobacter jejuni, C. coli, C. lari and urease-positive thermophilic campylobacters (UPTC), isolated from human faeces, animals and environmental sources. Campylobacter isolates totalling 34 and comprising of C. jejuni (n = 24) C. coli (n = 5) and UPTC (n = 4) and C. lari (n = 1) were analysed. The cytotoxic response ranged from 32.15 to 64.47% and 33.08 to 59.41%, for C. jejuni from chicken and human isolates, respectively and there was no statistically significant difference (P > 0.05) in cytotoxic response between C. jejuni isolated from humans and chicken isolates (50.78% versus 50.55% cytotoxicity, respectively). However, there was a difference in response between C. jejuni and C. coli isolated from chickens (50.78% versus 33.22% cytotoxicity, respectively). The greatest cytotoxic response was obtained with the UPTC group of organisms examined (n = 4 isolates) (mean cytotoxic response = 57.11% cytotoxicity. Employment of this cytotoxin assay may help identify virulent strains in poultry that could potentially proceed to cause clinical problems for humans and thus intervention measures targeted at the reduction or elimination of such specific strains, may be sought.

Reconstruction of SEA-B7.1 double signals on human hepatocellular carcinoma cells and analysis of its immunological effect

Since transfection of established tumors with immunostimulatory genes, such as superantigens (SAg), a family of bacterial and viral proteins with strong immunostimulatory properties, can elicit antitumor immunity, direct transfection of tumors with genes of staphylococcal enterotoxin A (SEA) could probably set up a new way of immunological pathway. In our study, human hepatocellular carcinoma (HCC) cell lines stably transduced with SEA and B7.1/SEA fused genes, HHCCSEA and HHCCBS, were obtained by using the method of retroviral mediated gene transduction. The results showed that human HCC cells could express SEA gene. Although a tiny quantity of expression was detected, a robust immune response was promoted. The cytotoxicity of CTL on HHCCBS was the same as that on HHCCSEA. But the K(m) value of the reaction of the former was lower than that of HHCCSEA. Furthermore, the activity assay of T cells by ELISPOT demonstrated that HHCCBS could elicit more CTL activity than HHCCSEA and HHCCB7.1. It suggested that the affinity of T cells to HHCCBS was higher and the maxim velocity of reaction could be attained at an early stage of the reaction. Transduced HCC cells were also analyzed for HLA expression, and it was found that a majority of the cells expressed HLA-I molecules but no HLA-DR molecules. After blocking the HLA-I molecules by HLA-I mAb, the cytotoxicity of T lymphocytes dropped remarkably. The results suggested that SEA were mainly presented by HLA-I molecules, and that B7.1 and SEA could have synergistic action at the early stage of the reaction, but the relationship between them in the consequent process needs to be clarified.

Discrimination between NK and LAK cytotoxic activities of murine spleen cells by MTT assay: differential inhibition by PGE(2) and EDTA

In the present study we propose a mathematical approach to improve the analysis of NK and LAK activities measured by MTT assay adapted for murine cells. We found that to calculate NK activity, high E:T ratios should be used (up to 50:1) and the phenomenon fits to a linear least-squares analysis. However, 5-fold less effector cells (10:1, E:T) should be used to detect LAK activity and the phenomenon has a nonlinear exponential behavior. Using this approach, we showed that EDTA inhibits LAK but not NK activity whereas PGE(2) inhibits NK but not LAK activity. In conclusion, this analytical approach allowed the discrimination between NK and LAK activities and exposed differences between these two cytotoxic activities.

Computational models in immunological methods: an historical review

The utilization of computational models in immunology dates from the birth of the science. From the description of antibody-antigen binding to the structural models of receptors, models are utilized to bring fundamental understandings of the processes together with laboratory measurements to uncover implications of these data. In this review, an historical view of the role of computational models in the immunology laboratory is presented, and short mathematical descriptions are given of fundamental assays. In addition, the range of current uses of models is explored -- especially as seen through papers which have appeared in the Journal of Immunological Methods from volume 1 (1971/1972) to volume 208 (1997). Each paper which introduced a new mathematical, statistical, or computer simulation model, or introduced an enhancement to an instrument through a model in those volumes is cited and the type of computational model noted.

A non-radioisotopic human natural killer cell assay using rhodamine-123 fluorescent dye as labelling probe

A non-radioisotopic method for assessment of human natural killer (NK) cell activity in peripheral blood mononuclear cells (PBMC) was established by labelling K562 erythroleukemia target cells with a fluorescent dye, rhodamine-123 (Rh-123). The labelling and assay conditions were determined for minimizing spontaneous release (SR). In order to investigate whether NK activity assessed by measuring Rh-123 release agrees with the activity determined by a 51Cr release assay, the NK activity of PBMC was measured simultaneously by both assay methods. Statistical analysis demonstrates that NK activities determined by Rh-123 release correlate well with those measured by 51Cr release. The Rh-123 release assay under the conditions determined was found to be applicable to measurement of the enhanced NK activity resulting from pretreatment of effector leukocytes with interferon-alpha. It is concluded that the Rh-123 release assay with use of K-562 labelled target cells is practical for the assessment of human NK activity in laboratories where use of radioisotopes is not permitted or undesirable.

Glucocorticoid regulation of natural cytotoxicity: effects of cortisol on the phenotype and function of a cloned human natural killer cell line

The ability of glucocorticoids to suppress cellular immune functions, including the cytotoxic activity of natural killer cells, is well known. However, the molecular mechanism(s) of glucocorticoid-mediated suppression of cellular cytotoxicity mediated by natural killer cells is not understood. We have investigated the effects of cortisol on protein expression and cytotoxic function of natural killer cells using NK3.3, a well-characterized, cloned human natural killer cell line. Cortisol, at concentrations up to 2 microM, does not significantly alter the viability or proliferative capacity of NK3.3 cells. However, micromolar concentrations of cortisol induce the expression of a small set of proteins which are not synthesized by NK3.3 cells in the absence of cortisol, and repress the synthesis of another set of proteins including several phenotypic determinants and cytokines. In the presence of added cortisol, the synthesis of perforin mRNA was partially repressed. However, the most striking effect of cortisol on this NK clone was its repression of granzyme A synthesis. In conjunction with the downregulation of adhesion proteins, NK3.3 cells cultured in the presence of cortisol exhibit a reduced capacity to form conjugates with K562 target cells. Whereas cortisol treatment of NK3.3 cells causes an approximately 50% decrease in their ability to form conjugates with K.562 target cells, the cytotoxic function of these cells is completely abolished under the same conditions. This first report of hormonal regulation of granzyme expression and the strong correlation between granzyme A repression and cytotoxic function suggests that cortisol may regulate NK function by repression of granzyme A synthesis. In addition to demonstrating the significant influence of cortisol on natural killer cell function, these studies provide a model system for elucidation of molecular mechanism(s) whereby glucocorticoids repress cellular immune function, especially with respect to natural killer cells.

Mycoplasma arthritidis mitogen up-regulates human NK cell activity

While the effects of superantigens on T lymphocytes are well characterized, how superantigens interact with other immune cells is less clear. This report examines the effects of Mycoplasma arthritidis mitogen (MAM) on human natural killer (NK) cell activity. Incubation of peripheral blood mononuclear cells (PBMC) with MAM for 16 to 20 h augmented NK cytotoxicity (against K562) in a dose-dependent manner (P < or = 0.05). Superantigen-dependent cellular cytotoxicity, an activity of superantigen-activated cytotoxic T cells, was not involved in lysis of K562 cells because the erythroleukemic tumor target cells expressed no class II major histocompatibility complex by fluorescence-activated cell sorter analysis. Kinetic experiments showed that the largest increase in NK activity induced by MAM occurred within 48 h. Incubation with MAM caused a portion of NK cells to become adherent to tissue culture flasks, a quality associated with activation, and augmented NK activity was found in both adherent and nonadherent subpopulations. Experiments using cytokine-specific neutralizing antibodies showed that interleukin-2 contributed to enhancement of the NK activity observed in superantigen-stimulated PBMC. Interestingly, MAM was able to augment NK lysis of highly purified NK (CD56+) cells in the absence of other immune cells in 9 of 12 blood specimens, with the augmented lytic activity ranging from 110 to 170% of unstimulated NK activity. In summary, data presented in this report show for the first time that MAM affects human NK cells directly by increasing their lytic capacity and indirectly in PBMC as a consequence of cytokines produced by T cells. Results of this work suggest that, in vivo, one consequence of interaction with superantigen-secreting microorganisms may be up-regulation of NK lytic activity. These findings may have clinical application as a means of generating augmented NK effector cells useful in the immunotherapy of parasitic infections or neoplasms.

Inhibition of natural killer cell activity by therapeutic levels of theophylline

Theophylline, as used for the treatment of asthma and chronic obstructive pulmonary disease, may have several effects, including direct bronchodilation, improvement in diaphragmatic and ciliary function, and possibly immune modulation. In this study, we quantified the capacity for theophylline to inhibit natural killer (NK) cells and investigated the mechanism(s) that mediate this inhibition. Theophylline at 10 micrograms/ml and 20 micrograms/ml inhibited the tumoricidal activity of isolated peripheral blood lymphocytes (PBL) by 19 +/- 5% and 36 +/- 6%, respectively (n = 6). Using fluorescence-activated cell sorting, we purified NK cells from PBL and tested theophylline's effects on the kinetics of tumor lysis (Vmax) and on tumor binding. Theophylline at 20 micrograms/ml reduced Vmax by 40 +/- 9% but had no effect on tumor binding. We compared the effects of theophylline, which is both a phosphodiesterase (PDE) inhibitor and an adenosine receptor (AdR) antagonist, with agents that range from relatively pure AdR antagonists to pure PDE inhibitors. Inhibition of NK activity occurred only with PDE inhibitors. We also extracted lymphocyte PDE and observed a direct correlation (r2 = 0.99) between theophylline's activity as a PDE inhibitor and its capacity to inhibit NK activity. These results suggest that theophylline inhibits NK cytotoxicity through its activity as a PDE inhibitor. The clinical relevance of these findings awaits further study.

T cells and monocytes regulate the generation and functional activity of natural killer-derived lymphokine-activated killer cells

The lymphokine-activated killer (LAK) phenomenon is generally referred to as nonspecific, i.e., major histocompatibility complex (MHC)-unrestricted cytotoxicity against tumor cells generated by ex vivo culture of human peripheral blood lymphocytes with interleukin 2 (IL-2). In this study, we selectively purified and depleted cell subpopulations such as natural killer (NK) cells, T-lymphocytes and monocytes from fresh human peripheral blood by negative selection. While highly purified NK cells could be induced to acquire potent LAK activity in five-day culture with IL-2, the presence of T-lymphocytes and monocytes in NK cultures was needed in order to induce a significant expansion of cytotoxic effector cells over the culture period. Neither T cells nor monocytes by themselves were able to generate LAK cells in a standard five-day IL-2 culture. However, when added to highly purified NK cells prior to IL-2 incubation, a proportion of CD3+ T-lymphocytes was found to gain LAK-like killing activity. Monocytes, when cultured with IL-2 in the presence of NK cells and T-lymphocytes, did not appear to acquire LAK activity but were able to induce a dramatic increase in cytotoxic lymphocyte recovery after five days with IL-2. In summary, we could demonstrate that peripheral blood T-lymphocytes and monocytes are potent regulators of NK-dependent lymphokine (IL-2)-activated killing.

Calculation of lytic units for the expression of cell-mediated cytotoxicity

Over the past 10 years, the lytic unit has become the most common means by which activity is expressed in cell-mediated cytotoxicity assays. The strengths and weaknesses of the lytic unit as a summary of cytotoxicity are discussed, and computational methods reviewed. The fundamental "assumption of proportional effect" which is implicit in the interpretation of lytic units is described and empirically tested. Based on extensive data from the assay of human natural killer (NK) activity against K562 targets, simplified computational methods are recommended. The proposed methods are easily explained, may be made robust to occasional erratic data, and permit a reasonable interpretation of lytic units even when the assumption of proportional effect breaks down.

Antitumor effects of interleukin-2 and mismatched double-stranded RNA, individually and in combination, against a human malignant melanoma xenograft

The antitumor effects of recombinant interleukin-2 (rIL-2) and mismatched double-stranded RNA (dsRNA) were assessed in tissue culture and in a nude mouse model. Mismatched dsRNA did not show a direct antiproliferative effect against the human malignant melanoma cell line, BRO, in tissue culture. However, treatment of the BRO cells with up to 1000 units/ml rIL-2 in culture showed a slight increase in growth rate. Combined rIL-2/mismatched dsRNA treatment also demonstrated a similar slight enhancement of growth. Nude mice bearing subcutaneous tumors were treated by intraperitoneal injection of low doses (5000-20,000 units) of rIL-2 and mismatched dsRNA (500 micrograms). The in vivo tumor growth was significantly inhibited by the combined treatments (P less than 0.05) and survival was significantly increased (P less than 0.05). Measurement of cytotoxicity using splenocytes from treated animals showed significant augmentation of lytic activity against natural killer (NK)-sensitive YAC-1 cells in all rIL-2/mismatched dsRNA treatment groups, compared to the individual treatments or controls (P less than 0.05). Cytotoxicity of the splenocytes against the NK-resistant BRO cells was also augmented in animals treated with mismatched dsRNA and the highest rIL-2 dose utilized here (P less than 0.01). Renal, liver, and hematological toxicity was evaluated by measurement of blood urea nitrogen, creatinine, serum asparrtate aminotransferase, and a complete blood count with differential. There were no significant differences in these parameters in any of the treatment groups. Similarly, no differences in weight of the animals was seen in any treatment group. These results indicate that the combination of low-dose rIL-2 and mismatched dsRNA can potentiate host-mediated antitumor effects, yielding increased survival, without significant toxicity.

Potentiated lymphokine-activated killer cell activity generated by low-dose interleukin-2 and mismatched double-stranded RNA

Lymphokine-activated killer (LAK) cell activity was measured in human peripheral blood mononuclear cells (PBMC) treated in vitro for 3 days with recombinant interleukin-2 (rIL-2) and mismatched double-stranded RNA (dsRNA). Lytic activity was measured utilizing K562 (NK-sensitive) and 786-0 (NK-resistant) target cells. PBMC cultured with rIL-2 (10-1000 BRMP U/ml) alone showed concentration-dependent lytic activity against the 786-0 target cells, while cells cultured in unsupplemented medium or medium supplemented with mismatched dsRNA (200 micrograms/ml) alone could not lyse the 786-0 targets. The combination of mismatched dsRNA with suboptimal concentrations of rIL-2 (10-30 U/ml) showed enhancement of both natural killer (NK) and LAK cell activities. The uptake of [3H]thymidine by treated effector cells was dependent on time and rIL-2 concentration and was not increased in the cells treated with low-dose rIL-2/mismatched dsRNA, compared to those treated with low-dose rIL-2 or mismatched dsRNA alone. Similarly, changes in the expression of CD3, CD4, CD8, CD57, CD16 and CD25 cell surface antigens were independent or rIL-2 concentration and not altered by the presence of mismatched dsRNA. These results indicate that mismatched dsRNA can potentiate rIL-2-induced LAK cell activity by increasing the functional activity per cell, rather than by increasing the number of activated cells.

Peripheral tolerance induced in lymph nodes by syngeneic spleen cells inhibits generation of CTLs to hapten-altered self antigens but not to alloantigens

The immunological tolerance that is induced in lymph nodes that have been exposed to syngeneic spleen cells has been examined. Development of cytotoxic T lymphocytes was used to assess the immunological status of the lymph node cells. The tolerance was studied from the viewpoint of its induction, its activation, and its specificity. We had already reported that injecting either T or B cells of splenic origin into a regional lymph node environment a week prior to immunization for CTL to hapten-altered self antigens prevents development of the CTL. Here, we confirm that syngeneic splenic cells but not lymph node cells will induce the suppression provided that spleen cells are not coupled with hapten. We now report that splenic cells that cannot replicate or synthesize and secrete protein are capable of inducing the suppression. The data suggest a preformed surface marker peculiar to spleen cells and perhaps on cells that traverse the thymus induces local tolerance that is mediated by suppressor cells. Triggering the induced suppressor T cells (previously identified as CD8-) was achieved by syngeneic spleen cells as well as by H-2-compatible, Mls-disparate spleen cells but not by syngeneic lymph node cells or apparently by allogeneic spleen cells. Furthermore, triggering suppression was achieved by hapten-coupled syngeneic spleen cells whereas such cells would not induce the suppression. Thus, activating the suppressor cells requires reexposure to splenic cells of the proper MHC haplotype, unaltered or coupled with either TNP or FITC. Once triggered, the suppression was manifested toward CTL generation against hapten-coupled syngeneic antigens on either spleen or lymph node cells but not against allogeneic antigens. Thus, the specificity of the tolerance was directed to altered self antigens despite its induction by unaltered spleen antigen. Furthermore, for suppression to be seen the spleen antigen was not required to be on the hapten-coupled syngeneic cells used for the CTL immunization. The relationship of the splenic cell "antigen" to hapten-altered self antigens and to other surface markers and its site of acquisition within the body and its significance for cell homing have become intriguing questions of importance. This information has been discussed from the viewpoint of its applicability to autoimmune diseases as well as to cessation of inflammatory reactions that may be mediated by lymph node cells.

Hormone specific regulation of natural killer cells by cortisol. Direct inactivation of the cytotoxic function of cloned human NK cells without an effect on cellular proliferation

Corticosteroids have previously been reported to partially inhibit the natural cytotoxic activity of peripheral blood lymphocytes. However, since only a few percent of peripheral lymphocytes are natural killer (NK) cells, it has not been possible to determine whether corticosteroids directly inhibit NK cells or mediate this effect via other cell types. This report documents direct functional inactivation, but unimpeded proliferation, of cloned human NK cells by subphysiologic levels of cortisol. In contrast, high concentrations of testosterone, progesterone or estradiol had no significant effect on proliferation or cytotoxic activity of the cloned NK cells. The kinetics of inhibition of NK function by cortisol are consistent with a transcription-dependent mechanism.

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

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

Quantification of effector/target conjugation involving natural killer (NK) or lymphokine activated killer (LAK) cells by two-color flow cytometry

Precise estimates of the frequency of NK- and LAK-target conjugates were obtained by two-color flow cytometry using hydroethidine and calcein as intracellular labels for target cells and effector cells, respectively. These two dyes can easily be used with a standard single-laser flow cytometer with excellent signal separation and dye retention. Hydroethidine labeling did not alter target susceptibility, and calcein labeling did not significantly alter NK function. Excellent agreement was obtained between this flow cytometric method and visual estimation of the frequency of fresh or IL-2-activated human lymphocytes that form conjugates with K-562 target cells. The percentage of cloned NK or LAK cells that form conjugates with K-562 target cells was dependent on the E:T ratio, with extrapolated maximum conjugate frequencies (alpha max) of 40-50%. However, the frequency of lymphocytes forming conjugates with K-562 cells did not closely correlate with the cytolytic activity of a given lymphocyte population. This two color flow cytometric method employing a pair of fluorochromes that do not modify cell membranes or alter cell function in cytotoxicity assays should facilitate further studies of mechanisms involved in the initial stages of target cell recognition by NK and LAK cells.

Further characterization of PNK-E: a monoclonal antibody enhancing porcine natural killer cell activity

Monoclonal antibody PNK-E binds to approximately 15% of porcine peripheral blood lymphocytes (PBL) which are PT4 negative and PT8 positive. When cells from tissues of adult pigs are treated with PNK-E, enhancement of natural killer (NK) cell activity is observed from PBL and spleen cells, and a dramatic induction of NK activity is observed from bone marrow cells. With cells derived from tissues of neonatal piglets, PNK-E induces NK activity from PBL and bone marrow cells. To investigate the mechanism of PNK-E-mediated enhancement of NK, proliferation assays, calcium-pulse assays, single-cell assays, and kinetic analyses were performed. PNK-E did not induce proliferation of PBL. PNK-E could be added as late as 30 min prior to termination of Ca(2+)-pulse assays and still enhance NK activity. Using kinetic analysis PNK-E was found to increase the rate of NK lysis (Vmax) and rate of lytic programming per NK cell (k2). In addition, results from single-cell assays indicate that PNK-E activates a population of normally inactive effector cells. These results indicate that PNK-E enhances the lytic capacity of mature NK cells and induces a population of nonlytic cells to become highly cytolytic cells. Furthermore, the enhancing effects are immediate and do not require an induction period. Thus, PNK-E recognizes and activates a unique triggering molecule that is present on NK cells.

Simplified quantitation of cytotoxicity by integration of specific lysis against effector cell concentration at a constant target cell concentration and measuring the area under the curve

Experience with the lytic unit (LU) as a measure of cytolytic efficiency has indicated that its accuracy is limited, even if expressed in a logarithmic format. A new method of quantifying cytotoxicity from effector dilution assays is proposed: the area under the curve (AUC) of the Ig (E/T) ratio vs. percentage cytotoxicity plot, gives an overall measure of lytic efficiency. The AUC derived from the Briggs-Haldane kinetic model is dependent on both the kinetic parameters that determine the efficiency of effector cells (the Michaelis constant KM and the catalytic constant kcat). AUC provides an index of inhibition or stimulation of lysis, independent of whether the modulation is kinetically competitive, uncompetitive or the same AUC value. In practice the method may be applied to interpret simple cytotoxicity assay data, where effector cells are being used in standardised screening for modifiers of the cytolytic response. Illustrative data of LAK cytotoxicity influenced by dose of the LAK response modifiers IL-2, TGF beta, TDSF and 5-FU, show different relationships between lytic units, KM and AUC. These data also show a wide range in the Hill coefficient and would be consistent with a cooperative effect dependent on the effector cell efficacy. This confirms that using LU as a simple measure of cytolytic efficiency could be erroneous and suggest that cytolytic response modifiers can produce a variety of kinetic changes. The AUC method, however, provides a comparative measure of efficiency in these situations, independent of mechanism.

Natural killer cell function in children with malignant solid neoplasias

Natural killer (NK) cell numbers and lytic activity were determined in 40 children with various types of solid malignant neoplasias and in 25 control children by NKH-1 monoclonal antibody and cytotoxicity against K562 target cells, respectively. Patients were analyzed at the time of diagnosis before initiation of therapy and followed over a median time of 15.8 months. Mean NK cell numbers and lytic activity were similar among different types of tumor analyzed. Patients with localized disease (stages I, II; n = 25) also showed values not statistically different from those of patients in advanced disease (stages III, IV; n = 15). According to their response to therapy, patients were divided into three groups: group 1 (complete remission; n = 28), group 2 (partial remission; n = 5), and group 3 (progression of disease; n = 6). Patients in group 3 showed at the time of diagnosis a mean NK activity significantly lower than that of patients in groups 1 and 2 and control children (P = 0.007). The defect in NK cell lytic capacity in vitro observed in patients with progressive disease suggests that NK cells play a role in the control of neoplastic growth in vivo and may imply that some children with refractory progressive disease can benefit from immunomodulation destined to improve the lytic potential of NK cells.

HSV-1 enhances GvHR-associated parent anti-F1 alloreactivity in vivo and in vitro

The present studies were performed to demonstrate whether concurrent HSV-1 infection could enhance the immune alterations and dysfunction associated with P----F1-induced graft-versus-host reactions. Examination of phenotypic and functional parameters revealed that Gv-HR-related immune abnormalities in the (C3H.SW X H-2bm1)F1 recipient were dependent on the parental donor inoculum. Together with HSV-1 infection, virus was found to exacerbate the phenotypic changes and functional abnormalities induced in this GvHR model. In addition, the presence of concurrent HSV-1 was shown to augment the level of specific in vivo donor anti-host reactivity present in F1 recipient spleen cells. Moreover, in vitro studies demonstrated that HSV-1 also enhanced the levels of parent anti-F1 allospecific cytotoxic activity. In total, these findings support the hypothesis that viral exacerbation of GvHR is mediated by its enhancement of donor anti-host alloreactive responses.

Kinetics of cellular cytotoxicity mediated by a cloned human natural killer cell line

The kinetics of natural killer (NK) cytotoxicity mediated by the cloned interleukin 2 (IL 2)-dependent human natural killer cell line NK3.3 has been investigated. This cloned cell line exhibits strong cytotoxic activity that is restricted to NK target cells. The initial rate of lysis of K-562 target cells by these cloned NK cells was, as anticipated, substantially greater than that previously reported for human peripheral blood NK cell preparations. However, in contrast to the kinetics of NK cytolysis mediated by fresh peripheral NK cells, the rate of 51Cr-release declined substantially within 1 to 3 h after initiation of assays involving NK3.3 cells and reached a plateau value in experiments conducted for longer periods. The data obtained suggest that NK3.3 cells cannot readily recycle and kill multiple target cells. Based on a model involving one lethal hit per active NK3.3 cell, estimates for the frequency of cytolytic cells in NK3.3 cultures were computed and compared to estimates obtained by the application of a kinetic model previously described. The cytotoxic activity of the NK3.3 cells was also found to be highly dependent on the conditions used for propagation and assay of these cells and, when cultured under "standard" conditions, only a fraction of the cloned NK3.3 cells was capable of effecting lysis of K-562 target cells. However, for the most optimal conditions developed to date, each NK cell killed an average of 1 to 2 target cells before inactivation. Although no significant differences in viability or growth rate were observed for the three different conditions described, up to 300-fold differences in lytic activity were observed. The observed strong dependence of the lytic function of NK3.3 cells on culture conditions should prove valuable for further investigations of mechanisms governing the regulation and function of human NK cells.

Biology of natural killer cells

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

Kinetics of cellular cytotoxicity mediated by cloned cytotoxic T lymphocytes

Kinetic methods can provide significant information concerning the mechanism of cellular cytotoxicity reactions. Previous kinetic studies of cytotoxic T lymphocytes (Tc) have been hampered by the heterogeneity of the effector cell population tested. We therefore examined the kinetics of lysis mediated by cloned, IL 2 and antigen-dependent murine Tc cells with strong cytotoxic activity that is restricted to distinct tumor-associated antigens on P815 mastocytoma target cells. Initial velocity measurements for cytotoxicity mediated by these clones fit a simple Michaelian kinetic model. Specific activity values obtained from these initial rate measurements are compared to those obtained for polyclonal Tc preparations, NK cells, and activated killer cells. Whereas the initial rate of lytic programming mediated by these cloned cells was very rapid, the rate of cytolysis mediated by the cloned cells decreased significantly within one hour. Since this decrease was observed over a wide range of E:T ratios, it is unlikely to result from product inhibition or a significant decrease in the concentration of unlysed target cells, but may be due to a decrease in the rate of programming and/or effector cell recycling. These results indicate that a simple Michaelian kinetic model is not adequate for tumor cell cytolysis by Tc cells in vitro.

Kinetic analysis of Qa-1-specific cloned cytotoxic T lymphocytes: lytic parameters and evaluation of cellular inhibition

A kinetic analysis of lysis assay was used to compare cytolysis of target cells expressing different allelic Qa-1 determinants by a Qa-1b-specific cytotoxic T-lymphocyte clone (CTL). Although this clone specifically recognized the Qa-1b determinant it also recognized the Qa-1c and Qa-1d determinants to a lesser extent. The maximum rate of lysis against Qa-1b targets was 10-fold faster than against Qa-1c or -1d targets. The affinity of the CTL clone for the Qa-1b and -1c target cells was the same, but significantly less for Qa-1d targets. The pattern of inhibition observed for target and inhibitor cells in these experiments was competitive. These studies demonstrated a greater similarity between the Qa-1b and -1c determinants, compared with Qa-1d. Kinetic analysis of lytic reactions allowed for quantitative evaluation of the similarities and differences between various target cell populations to an extent not possible using conventional cell-mediated assays.

Kinetic analysis of cloned cytotoxic T lymphocyte reactivity against normal and leukaemic target cells

The kinetics of unrestricted killing of normal and leukaemic lymphocyte target cells by a Qa-1b-specific murine cytotoxic T lymphocyte (CTL) clone were evaluated in a manner analogous to enzyme kinetic assays in which the effector and target cells corresponded to the enzyme and substrate, respectively. In order to apply the enzyme-substrate analogy to clonal cytolytic reactions, it was first established that the lytic reactions exhibited initial steady-state velocity of lysis at the effector and target cell concentrations used. The lytic reaction maintained linearity for velocity of lysis during the first 90 min of incubation, then plateaued. Vmax (the maximal rate of target cell lysis achieved by a given effector population) and Km (the target cell number resulting in 1/2Vmax) values were determined over a wide range of target and effector cell concentrations. Both parameters were found to be directly proportional to the number of effector cells. At a given concentration of cloned CTL, the lytic parameters of Vmax and Km were not significantly different for normal or leukaemic target cells that express Qa-1b. Additional kinetic parameters for lysis of normal and leukaemic target cells by a cloned CTL were also compared. The lytic efficiency of the CTL clone (i.e. maximal killing rate with an infinite number of targets) and the intrinsic affinity between effector and target cells were the same with either normal or leukaemic targets. However, the maximal lysis of target cells at an infinite number of effectors was significantly less for normal compared with leukaemic targets. This suggests that the normal target cells were more heterogeneous in their expression of the target (Qa-1b) antigen. Enzyme-like kinetic analysis of cell-mediated lysis reactions can be useful for comparing the relative affinities of effector and target cells obtained from various sources.

Elevated antibody-dependent cell-mediated cytotoxicity and its inhibition by nicotinamide in the diabetic NOD mouse

Antibody-dependent cell-mediated cytotoxicity (ADCC) by splenic mononuclear cells was measured in female non-obese diabetic (NOD) mice and age-matched ICR mice. No significant difference in ADCC activities was observed between the two groups when all the NOD mice were pre-diabetic. ADCC activities in diabetic NOD mice were significantly higher than those in age-matched ICR mice (P less than 0.001). Nicotinamide, known to prevent the diabetes of the NOD mouse, strongly inhibited ADCC by the mononuclear cells from diabetic NOD mice. Kinetic studies revealed that the inhibition was non-competitive.

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.

Human major histocompatibility complex class I antigens: residues 61-83 of the HLA-B7 heavy chain specify an alloreactive site

A chemically synthesized peptide (sequence in text) homologous to residues 61-83 of the HLA-B7 heavy chain, induced antibodies that specifically recognized the HLA heavy chain-beta 2-microglobulin complex and the free heavy chain of the HLA-B7 antigen. These antibodies specifically immunoprecipitated the HLA-B7 beta 2-microglobulin complex solubilized from human lymphoblastoid cells by nonionic detergents and reacted with free HLA-B7 heavy chains in blots on nitrocellulose. These observations suggest that the antigenic conformation of this region of the HLA-B7 molecule is independent of the presence of beta 2-microglobulin and that amino acid residues 61-83 mimic an alloreactive site expressed by the HLA-B7 antigen.

Effects of diethylstilbestrol on human natural killer cells in vitro

Exposure of human peripheral blood lymphocytes to diethylstilbestrol (DES) in vitro resulted in inhibition of Natural Killer (NK) cell activity. DES inhibited NK activity in a dose and time-dependent manner with maximal effect after an 18 h exposure time. Significant reduction in cytotoxicity was obtained at concentrations of DES equal to or above 1 microM. The DES-induced inhibition of NK activity was reversible and totally abrogated within 18 h of culture in the absence of DES. Studies at the single cell level revealed that DES impaired the lytic activity of NK cells without interfering with recognition of target cells. The presence of indomethacin or aspirin during exposure to DES completely reversed the DES-induced inhibition of NK activity, indicating that a product of the cyclooxygenase system mediated the suppression.

Macrophage antitumor activity in vitro. Comparative analysis of cytolytic, cytostatic, and cytotoxic activities of mouse macrophages and human monocytes

Mouse peritoneal M phi and human blood monocytes were assayed for their antitumor activity in vitro with a cytolysis, a cytostasis and a cytotoxicity test performed in parallel. Both natural and stimulus-induced M phi antitumor capacities were assessed. Results indicate that natural cytolytic activity of unstimulated M phi is generally unable to restrict final tumor cell growth, since it is not coupled with cytostatic capacity. In contrast, exposure of M phi in vitro to either MAF or IFN-beta, besides augmenting M phi cytolytic capacity, induced a very significant cytostatic activity and thus efficiently restricted the survival of tumor cells.

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.

Modulation of natural killer cell activity in patients with atopic dermatitis

The peripheral blood lymphocytes of 36 adult patients with moderate to severe atopic dermatitis had reduced natural killer (NK) cell activity when measured against 51Cr-labeled K 562 cells. The decrease in NK cells activity was not related to the serum IgE level, but was related to the severity of the skin disease. Addition of autologous monocytes of the assay reduced the NK cell activity and concealed the enhancing effect of gamma-interferon addition in a 4-h assay. The NK cell activity of lymphocytes could be reduced in vitro by addition of prostaglandin E1, or increased by addition of gamma-interferon similar to lymphocytes from persons without atopic disease. Our present findings raise the possibility that the reduced NK cell activity may be secondary to the skin disease, and due to in vivo interaction between NK cells and monocytes, or to low numbers of NK cells in peripheral blood.

Effects of diethylstilbestrol and estramustine phosphate (estracyt) on natural killer cell activity and tumor susceptibility in male mice

The effects of estramustine phosphate (EMP) and diethylstilbestrol (DES) on natural killer (NK) cell activity, tumor growth, and artificial metastases were investigated in male C57BL/6 mice. Kinetic analysis and studies at the single-cell level indicated that EMP did not influence the number of NK cells but interfered with their lytic activity thereby reducing the actual killer capacity. NK cells from EMP-exposed animals responded normally to the interferon inducer Poly I:C which restored NK activity to control levels. Spleen cells from DES-treated animals had lytic activity comparable to that of control animals. However, more detailed analysis showed that DES reduced the number of lymphocytes able to recognize target cells, while the individual NK cell had an increased lytic activity and recycling capacity. Moreover, NK cells from DES-treated animals were refractory to poly-I:C stimulation, suggesting that they were prestimulated in vivo. The pertubations of the NK cell system induced by both EMP and DES were reversible and normalization of NK activity was reached within a week. The incidence of tumor takes after subcutaneous inoculation of the syngeneic Lewis lung carcinoma was increased in EMP as well as DES-treated animals. Artificial lung metastasis produced by intravenous injection of the same tumor was increased in EMP but not in DES-exposed animals.

The effect of 3-methylcholanthrene on mouse natural killer cells in vitro

The effect of the chemical carcinogen 3-methylcholanthrene (3-MCA) on mouse natural killer (NK) cells was tested in vitro applying kinetic analysis of the NK-tumor cell interaction. 3-MCA inhibited the lytic activity of spleen cells against YAC-1 target cells in a dose-dependent manner. Maximal inhibition, of Vmax was about 60% and a parallell decrease in KM values was observed. Inhibition was observed after 30 min preincubation of effector cells while pre-incubation of target cells had no effect. Inclusion of Indomethacin in the assay to exclude the possibility that prostaglandins induced by 3-MCA were the mediators of NK suppression had no effect. 3-MCA inhibited basal and interferon-activated NK lysis to about the same extent, while Vmax and KM values of effector cells pretreated with 3-MCA and assayed in the presence of interferon was close to control values. In a single cell assay for NK activity it was found that 3-MCA interfered with the lytic step of NK mediated lysis without affecting target binding. These data are in accordance with an earlier observation that a single injection of 3-MCA transiently inhibited mouse NK cells in vivo and evidence is presented that 3-MCA inhibits the lytic activity of a subpopulation of NK cells. The effects of 3-MCA were reversed by interferon.

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.

Kinetic analysis of the specificity of human natural cytotoxicity

Distribution-free analysis of kinetic data for cellular cytotoxicity reactions enables the precise determination of kinetic parameters for the lysis of target cells by individual lymphocyte preparations. This report presents results obtained when this method was used to quantitate the inhibition of human natural cytotoxicity by unlabelled (cold) target cells. In agreement with previous studies, we found that the natural cytotoxicity of a given target cell can be inhibited by heterologous as well as homologous unlabelled cells; however, the strongest inhibition was usually produced when the unlabelled inhibitor cells were homologous to the labelled target cells. The general pattern of inhibition observed for the target and inhibitor cells tested in these experiments was competitive, and when inhibitor cells were homologous to the labelled cells, the observed increase in Kappm agreed with theoretical predictions based on equations derived previously. These results support earlier reports of limited but not absolute antigenic specificity by subsets of human NK cells. Moreover, while Kappm values for cytotoxicity reactions are not simply related to antigen binding, quantitative analysis of the relative inhibition of cytotoxicity by heterologous versus homologous unlabelled cells provides useful estimates of the relative affinity of the effector cell subset(s) that kill a given target cell for various NK target cells.

Simultaneous determination of the concentration and lytic activity of effector cells that mediate natural and antibody-dependent cytotoxicity

Cellular cytotoxicity reactions can be studied in a manner analogous to that used to measure enzyme activity. This approach yields two parameters: Vmax, the maximal rate of target cell lysis that can be achieved by the lymphocyte preparation tested, and KMapp, the apparent Michaelis constant. By analogy to many enzyme-catalysed reactions, KMapp values for cytotoxicity reactions have generally been interpreted in terms of dissociation constants for the interaction of receptor sites on effector cells with antigens on the target cells. In this paper we demonstrate that experimentally determined KMapp values for natural or antibody-dependent cytotoxicity reactions are approximately equal to the concentration of NK or K effector cells in the lymphocyte preparation tested. This result makes possible the simultaneous determination of both effector cell frequency and lytic activity in a given lymphocyte preparation.

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.

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.