Multiple mechanisms of lymphocyte-mediated killing

Mechanism of norepinephrine-mediated inhibition of human NK cytotoxic functions: inhibition of cytokine secretion, target binding, and programming for cytotoxicity

Norepinephrine (NE) has been shown to inhibit human peripheral blood-derived natural-killer (NK) cell cytotoxicity (NKCC) in vitro. We demonstrate in this study that NE not only inhibits IL-2-activated NKCC but antibody-dependent cellular cytotoxicity (ADCC) as well. NK cytotoxicity by purified NK cells against K562 (NKCC) and against Raji cells (ADCC) were inhibited by NE (1-100 microM) by more than 50% in a 4-h (51)Cr release assay. The mechanism underlying the inhibition has been examined. NK cytotoxicity is dependent on target recognition and formation of NK-target conjugates, and activation by IL-2 is dependent on the secretion of cytokines (such as TNF-alpha) by NK cells. We hypothesized that the inhibition of NK functions by NE may be due to disruption of NK-target conjugation, blocking programming for lysis, and/or inhibition of cytokine secretion. Pretreatment of human peripheral blood mononuclear cells (PBMC) with NE for 15 min significantly reduced the binding to K562 cells by CD16(+) NK lymphocytes. In the presence of K562 cells, NE down-regulated the expression of CD16 (FcgammaRIII) by human PBMC, an NK cell receptor responsible and necessary for ADCC and cytokine secretion. We also demonstrate that NE inhibited the IL-2-mediated up-regulation of the activation marker CD69. At concentrations of 10(-6) to 10(-5) M, NE inhibited TNF-alpha, IFN-gamma, and GM-CSF secretion by NK cells, which are essential for IL-2-driven NK maturation and functions. In addition, using single-cell analysis, NE pretreatment of lymphocytes reduced the frequency of killer cells in the NK-K562 conjugate population in a concentration-dependent manner, indicating an inhibition of the programming for lysis by NK cells. In summary, these data demonstrate that NE-induced inhibition of NK cytotoxicity is manifested at multiple levels, including a modification of NK cell receptor ligation to target cells, blockade of NK cytokine secretion necessary for NK maturation and differentiation, and inhibition of the target-induced activation of the cytotoxic mechanism(s) in NK cells. Thus, sympathetic activation, as often induced experimentally, may profoundly impair natural cellular immunity through varied measurable pathways.

Genetic identity and differential expression of p38.5 (Haymaker) in human malignant and nonmalignant cells

Previous studies from our laboratory revealed a novel protein of 38.5 kD on the surface of malignant cell lines of hematopoetic origin that exhibit susceptibility to naive natural killer (NK) cell-mediated lysis. In contrast, p38.5 was not detected on the surface of NK cell-resistant carcinoma cell lines or normal cells. We now report that this protein is differentially expressed, intracellularly, in malignant cell lines of both hematopoetic and epithelial origin compared with nonmalignant cells. To characterize p38.5 further, we used a previously developed antipeptide antibody (anti-11-mer) to probe cDNA expression libraries and subsequently performed 5' extension by rapid amplification of cDNA ends (RACE). Sequence analyses of these cDNA clones reveal open reading frames (ORFs) that include the previously identified 11-mer peptide from purified, native p38.5 and that have identical sequences to a gene of unknown function on chromosome 19. Nucleotide sequence data obtained from these cDNA clones, as well as analysis of the genomic sequence, permitted design of primers for reverse transcriptase-polymerase chain reaction (RT-PCR) that resulted in a cDNA clone encoding an ORF of 361 amino acids; the clone was identical to a sequence encoded by an unpublished mRNA in GenBank. Anti-p38.5 antibody against the 11-mer peptide encoded in exon 5 and against a 25-mer peptide encoded in exon 1 both reacted with the same protein in immunoprecipitation studies, providing further evidence of identity. RT-PCR and Northern blot analyses both demonstrated p38.5 gene transcripts in normal cells, nonmalignant cell lines and malignant cell lines of epithelial as well as hematopoietic origin. Semiquantitative studies revealed a greater level of p38.5 gene transcription in malignant cell lines compared with nonmalignant cells. Immunoblot analyses of protein expression confirmed and extended the latter studies by revealing substantially greater levels of the 38.5 kD protein in whole cell extracts of malignant cell lines compared with nonmalignant cells. Quantitative differences in detection of the 38.5 kD protein and mRNA in NK susceptible- hematopoietic malignancies compared with NK resistant-carcinomas were not observed. These experiments suggest that the p38.5 gene (Haymaker) is widely expressed in human cells of different tissue origins but that elevated expression is associated with the malignant phenotype.

Involvement of granule-mediated apoptosis in the cyclic changes of the normal human endometrium

Our objective is to investigate the involvement of granule-mediated apoptosis in the cyclic changes of the endometrium. We demonstrated the localization of CD56, perforin, granzyme B and caspase-3 in the endometrium by immunohistochemistry. We also confirmed the localization of perforin by immuno-electron microscopy, and demonstrated apoptosis in endometrial glandular cells by TdT-mediated dUTP-biotin nick end labeling (TUNEL) and electron microscopy. Uterine CD56-positive natural killer (NK) cells expressed perforin and granzyme B in its cytoplasm. Uterine NK cells increased significantly in the endometrial stroma during the secretory phase, and peaked during the late secretory phase. These cells started decreasing in number during the menstrual period. In endometrial glandular cells, caspase-3 and TUNEL-positive cells increased significantly from the late secretory phase, with apoptosis reaching a peak during the menstrual period. Using electron microscopy, we observed uterine NK cells with chromatin rich, segmented nuclei and intracytoplasmic granules in the stroma obtained from late secretory phase endometria. These cells extended projections to the lining of endometrial glandular cells and attached to form a cell-to-cell contact. In addition, nuclear chromatin was observed to have already cohered and small cytoplasmic organelles were beginning to disappear, suggesting that these endometrial glandular cells were undergoing apoptosis. Utilizing immuno-electron microscopy, intracytoplasmic granules in uterine NK cells were stained with anti-perforin antibody. The findings of this study suggest that granule-mediated apoptosis in endometrial glandular cells induced by NK cells expressing perforin and granzyme B may be associated with the onset of menstruation.

T-cell-rich large-B-cell lymphomas contain non-activated CD8+ cytolytic T cells, show increased tumor cell apoptosis, and have lower Bcl-2 expression than diffuse large-B-cell lymphomas

The factor(s) responsible for the reduced B cell number and increased T cell infiltrate in T-cell-rich large-B-cell lymphomas (TCRBCLs) have not been well characterized. We studied 18 TCRBCLs and 12 diffuse large-B-cell lymphomas (DLBCLs) to compare the 1) predominant T cell subpopulation(s), 2) expression of cytotoxic granule proteins (TIA-1 and granzyme B), 3) level of tumor cell apoptosis (Apoptag system, Oncor, Gaithersburg, MD), and 4) expression of Ki-67 (Mib-1) and apoptosis-related proteins (fas (CD95), bcl-2, and p53). T cells in TCRBCLs and DLBCLs were predominantly CD8+ T cells expressing alphabeta T-cell receptors and TIA-1 (16 of 18 TCRBCLs with >50% TIA-1+ small lymphocytes) but lacking granzyme B (16 of 18 TCRBCLs with <25% granzyme B+ small lymphocytes). Scattered apoptotic tumor cells (confirmed with CD20 co-labeling) were present in 15 of 18 TCRBCLs, with 14 of 15 cases having <10% apoptotic cells. No apoptotic cells were seen in 12 of 12 DLBCLs. In 16 of 16 immunoreactive TCRBCLs, <25% tumor cells were bcl-2+, whereas 6 of 12 DLBCLs had >50% bcl-2+ tumor cells. CD95 (fas) expression was also lower, with 3 of 18 (16.7%) TCRBCLs versus 4 of 12 (33%) DLBCLs having >25% CD95+ tumor cells. TCRBCLs and DLBCLs had similar levels of p53 and Ki-67 (Mib-1) expression. Thus, T cells in TCRBCLs are non-activated cytotoxic T lymphocytes (TIA-1+, granzyme B-). Tumor cell apoptosis (perhaps cytotoxic T cell mediated) may partly account for the decreased number of large (neoplastic) B cells in TCRBCLs, but other factors (ie, decreased bcl-2 expression) may also be needed.

Histone-induced damage of a mammalian epithelium: the role of protein and membrane structure

In a previous report [T. J. Kleine, A. Gladfelter, P. N. Lewis, and S. A. Lewis, Am. J. Physiol. 268 (Cell Physiol. 37): C1114-C1125, 1995], we found that the cationic DNA-binding proteins histones H4, H1, and H5 caused a voltage-dependent increase in the transepithelial conductance in rabbit urinary bladder epithelium. In this study, results from lipid bilayer experiments suggest that histones H5-H1 and H4 form variably sized conductive units. Purified fragments of histones H4 and H5 were used to determine the role of histone tertiary structure in inducing conductance. Isolated COOH- and NH2-terminal tails of histone H4, which are random coils, were inactive, whereas the central alpha-helical domain induced a conductance increase. Although the activities of the central fragment and intact histone H4 were in many ways similar, the dose-response relationships suggest that the isolated central domain was much less potent than intact histone H4. This suggests than the NH2- and COOH-terminal tails are also important for histone H4 activity. For histone H5, the isolated globular central domain was inactive. Thus the random-coil NH2- and COOH-terminal tails are important for H5 activity as well. These results indicate that histone molecules interact directly with membrane phospholipids to form a channel and that protein tertiary structure and the degree of positive charge play an important role in this activity.

A new class of antigen-specific killer cells

A new class of antigen-specific killer cells that combines the features of antibody-mediated and cell-mediated immunity was designed. The principle and feasibility of this strategy are illustrated by creating an antigen-specific killer cell to produce and secrete targeted antibody-toxin molecules that recognize and kill human immunodeficiency virus (HIV)-1-infected cells. The transduced lymphocytes, which were able to produce and secrete the targeted toxin proteins, remained viable due to the lack of the target antigen on the cell surface. These transduced cells were found to have selective and potent cytotoxicity to the HIV-infected cells. This approach combines the specificity of antibodies, extreme potency of toxins, and effector-cell properties of T-cells to generate a new class of potent antigen-specific killer cells, which may have broad applications for the treatment of viral infection and other diseases. This study demonstrates the principle that mammalian cells can be genetically modified to produce targeted toxins, indicating that in vivo production of targeted toxins can be achieved to locally or systematically destroy targeted cells.

Human T-lymphocyte serine proteases (granzymes) 1, 2, and 3 mediated DNA fragmentation in susceptible target cells

We reported the characterization of three serine proteases (granzymes 1, 2, and 3) from human cytotoxic T lymphocytes. In this study, human granzymes 1, 2, and 3 were purified from the cytoplasmic granules of lymphokine activated killer (LAK) cells by gel filtration and cation exchange chromatography. Human perforin was purified by phenyl superose and heparin-agarose chromatography. Each purified granzyme was used with purified perforin to study DNA fragmentation in target cells of both human and murine origin. As measured by agarose gel electrophoresis and [125I]dUrd assay, the granzymes induced oligonucleosomal DNA fragmentation and [125I]dUrd release respectively from various target cells. Murine target cells were generally more susceptible to nuclear DNA release than were human targets. Both enzyme activity and nuclear DNA breakdown were significantly inhibited by 3,4-dichloroisocoumarin (DCI) or by heat inactivation of each granzyme. Perforin alone or granzyme alone failed to fragment nuclear DNA in various target cells. We conclude that human granzymes are an important family of effector molecules that with perforin induce DNA fragmentation in susceptible target cells.

The derivation of binding parameters from effector and target conjugate frequency data using linear and non-linear data-fitting transformations. Application of such transformations to the NK-MOLT4 and NK-K562 effector-target systems

Effector-target conjugation is described quantitatively by binding isotherms which are characterized by three parameters, the maximum effector and target conjugate frequencies, alpha max and beta max, and the dissociation constant of the conjugates formed, KD. In this paper the application of non-linear data-fitting techniques, as well as linear transformations of the binding isotherms that permit us to use standard regression analysis, has been tested to calculate estimates of these parameters in the NK-MOLT4 and NK-K562 effector-target systems. Both unweighted and weighted data were used to calculate alpha max, beta max and KD for six different donors which were used as a source of NK cells. The results obtained have shown that these regression methods are useful for revealing potential disparities between binding efficiencies in effector-target systems.

Perforin: structure and function

Perforin is a cytolytic mediator produced by killer lymphocytes, and is stored in and released by cytoplasmic granules. The protein is partially homologous to the terminal components of the membrane attack complex of complement and produces pores of up to 20 nm in diameter on target membranes. Its genomic and protein structures have recently been unraveled, and its function elucidated through the availability of genetically engineered, perforin-deficient mice. Here Chau-Ching Liu, Craig M. Walsh and John Ding-E Young briefly outline certain biochemical and molecular features of perforin, and discuss the still-evolving issues concerning the relevance of perforin and Fas in cell killing.

Human granzyme B is essential for DNA fragmentation of susceptible target cells

We have partially characterized the granules of the human NK cell line, YT-INDY, and assessed granule-mediated lysis and DNA fragmentation of assorted targets. Biochemical studies demonstrated significant quantities of granzyme B (asp-ase) and a heretofore undescribed chymase but no tryptase (i.e., granzyme A or 3) or distinct met-ase. YT-INDY expressed mRNA for granzyme B, perforin and CCPX. The existence of perforin was confirmed by immunoblot. The granules lysed both human and murine NK-sensitive and NK-resistant targets. YT-INDY and NK3.3, two human cytotoxic cells, were also lysed. EGTA reduced lysis by only 50%, suggesting that a perforin-independent lytic pathway is associated with the granules. In addition, 4-(2-aminoethyl) benzenesulfonylfluoride hydrochloride (AEBSF), an inhibitor that selectively blocked the chymase and 3,4-dichloroisocoumarin (DCI), an inhibitor that inactivated both chymase and asp-ase activities, marginally affected lysis. By gel electrophoresis and 125I-labeled deoxyuridine release assay, only murine cells (SP2/0 and YAC-1) underwent DNA fragmentation, and cleavage was completely inhibited by DCI, whereas EGTA, AEBSF and aurintricarboxylic acid (ATA) had no effect. The results, therefore, underscore the central role of granzyme B in granule-mediated DNA fragmentation, emphasize that the protease acts via an ATA-resistant endonuclease pathway and stress that nucleolysis does not invariably accompany granule-mediated cytolysis. Finally, ATA inhibited the asp-ase activity of isolated but not granule-associated granzyme B. ATA, therefore, is not a specific endonuclease inhibitor and results obtained with ATA should be viewed cautiously.

A novel ligand in lymphocyte-mediated cytotoxicity: expression of the beta subunit of H+ transporting ATP synthase on the surface of tumor cell lines

Extracellular adenosine triphosphate (eATP) has been suggested to play a role in lymphocyte-induced tumor destruction. We now provide evidence that a protein responsible for ATP synthesis in mitochondria may also play a physiologic role in major histocompatibility complex-independent, lymphocyte-mediated cytotoxicity. A 51.5-kD protein (p51.5) bearing structural and immunologic characteristics of the beta subunit of H+ transporting ATP synthase (E.C. 3.6.1.34, beta-H+ATPase, published molecular mass of 51.6 kD) was detected on the plasma membrane of three different human tumor cell lines studied. NH2-terminal amino acid sequence analysis of purified p51.5 from K562 tumor cells revealed 100% homology of 16 residues identified in the first 21 positions to the known sequence of human mitochondrial beta-H+ ATPase. Antibody directed against a 21-mer peptide in the ATP binding region of beta-H+ ATPase (anti-beta) reacted with only one band on Western blots of whole tumor extracts and tumor membrane extracts suggesting that the antiserum reacts with a single species of protein. Anti-beta reacted with the cell membranes of tumor cells as determined by fluorescence-activated flow cytometry and immunoprecipitated a 51.5-kD protein from surface-labeled neoplastic cells (but not human erythrocytes and lymphocytes). Purified p51.5 bound to human lymphocytes and inhibited natural killer (NK) cell-mediated cytotoxicity. Furthermore, anti-beta treatment of the K562 and A549 tumor cell lines inhibited NK (by > 95%) and interleukin 2-activated killer (LAK) cell (by 75%) cytotoxicity, respectively. Soluble p51.5 upon binding to lymphocytes retained its reactivity to anti-beta suggesting that the ATP binding domain and the lymphocyte-receptor binding domain reside in distinct regions of the ligand. These results suggest that beta-H+ ATPase or a nearly identical molecule is an important ligand in the effector phase (rather than the recognition phase) of a cytolytic pathway used by naive NK and LAK cells.

Binding units (BU) and the area under binding isotherms (AUI). New indices of effector-target conjugation

New methods for simplified quantitation of effector-target conjugation have been developed. The binding unit (BU) is defined as the number of target cells required to bind a specified percentage of effector cells. The number of binding units is determined from binding isotherms in which effector conjugate frequencies are measured by holding constant the number of effector cells and by varying the number of target cells. Alternately, a binding unit can be defined as the number of effector cells required to bind a specified percentage of target cells. In this case, BU is computed from binding isotherms in which target conjugate frequencies are measured at different values of effector cells by holding constant the number of target cells. Also, the area under the curve (AUI) of these isotherms is another index that can be used as an overall measure of the binding capacity in an effector-target system. The experimental values of BU and AUI determined from effector and target isotherms agree well with theoretical predictions based on our previously developed binding model (J. Immunol. Methods (1992) 155, 133-147). The relationship between BU and AUI, and procedures to determine these parameters are shown. The value of these indices to express effector-target conjugation quantitatively has been confirmed by determining the values of BU and AUI for the NK-K562 effector-target system.

Heat-shock proteins protect cells from monocyte cytotoxicity: possible mechanism of self-protection

We have previously shown that major heat-shock protein (hsp 70) protects WEHI-S tumor cells from cytotoxicity mediated by tumor necrosis factor alpha (TNF-alpha) and TNF-beta. In the present study, the effect of altered expression of hsp70 and low molecular weight heat-shock protein, hsp27, on tumor cell sensitivity to monocytes and lymphokine-activated killer (LAK) cells was studied. Constitutive and stable expression of transfected human hsp70 rendered cells almost completely resistant to monocytes. Conversely, inhibition of endogenous hsp70 by expression of antisense hsp70 RNA enhanced the sensitivity of cells to monocyte-mediated killing. Surprisingly, overexpression of human hsp27, which does not protect WEHI-S cells from TNF killing, conferred partial resistance to monocytes. Only approximately 60% of monocyte-mediated killing of WEHI-S cells could be blocked by neutralizing TNF-alpha antibody or immunoglobulin G-TNF receptor chimeric protein, suggesting the presence of both TNF-dependent and TNF-independent lytic mechanisms. As free radicals have been suggested to be mediators of monocyte cytotoxicity, we tested the sensitivity of transfected cells to oxidative stress. Overexpression of either hsp70 or hsp27 rendered cells partially resistant to hydrogen peroxide. No significant changes in the susceptibility of cell lines overexpressing hsp70 or hsp27 to cytotoxicity mediated by LAK cells were observed. Interestingly, monocytes but not LAK cells contained detectable levels of hsp27 and hsp70 in nonstressed conditions. Taken together, these data indicate that hsp70 protects tumor cells from TNF-mediated monocyte cytotoxicity and that both hsp27 and hsp70 confer resistance to TNF-independent, probably free radical-mediated lysis by monocytes. Moreover, hsp27 and hsp70 may provide monocytes with a protective mechanism against their own toxicity.

Effector-target interactions: saturability, affinity and binding isotherms. A study of such interactions in the human NK cell-K562 tumour cell system

Effector-target interactions at the cell-to-cell level have been studied. This has revealed that saturability, i.e., the existence of a finite number of specific receptor sites, applies to both the effector and target cell populations and plays a key role in the formation of conjugates. As a result, two maximum conjugate frequencies, alpha max and beta max, are recognised for the effector and target cell populations, respectively. The dissociation constant of the conjugates formed, KD, characterizes effector-target affinity. This constant, together with the maximum conjugate frequencies, are the three parameters which make it possible to describe the binding process quantitatively. The existence of binding isotherms for effector-target interactions has been demonstrated. These isotherms contain all the relevant information necessary to interpret quantitatively the formation of conjugates. Quantitative procedures to determine the three binding parameters are described together with the modifications necessary to use Scatchard plots in the analysis of conjugate frequencies in these kinds of cell-to-cell interactions. A quantitative study of these interactions in the NK-K562 tumour cell system has been performed. For this purpose, nine different cell source donors were used to test the model proposed. Relationships with related phenomena--CMC and the adhesion process--are also discussed.

Highly restricted expression of a stromal cell determinant in mouse bone marrow in vivo

B lymphocyte precursor cells in mouse bone marrow develop in close association with stromal cells which provide essential growth signals. To identify molecules that may normally play a role in this interaction we have examined the in vivo binding of a new monoclonal antibody (mAb) (KMI6) that recognizes a determinant on a bone marrow stromal cell line (BMS2) in vitro. Flow cytometric and radioautographic evaluations revealed that the antigen recognized by KMI6 is represented on the surface of an extremely small number of cells in bone marrow cell suspensions from adult mice. An apparent molecular mass of 110 kD was obtained by surface labeling of a stromal cell clone and immunoprecipitation. Purified mAb KMI6 labeled with 125I was then given intravenously to young C3H/HeJ mice. Unbound mAb was washed out by cardiac perfusion and femoral bone marrow was examined by light and electron microscope radioautography. KMI6 labeling was heavy on the plasma membrane of many stromal cells, especially those located towards the outer subosteal region. The KMI6-labeled stromal cells were usually associated with cells of lymphoid morphology which they often completely surrounded. The labeling was restricted to areas of stromal cell plasma membranes in contact with lymphoid cells. The lymphoid cells themselves, as well as macrophages and other hemopoietic cells, failed to bind mAb KMI6 significantly. Stromal cells in bone marrow depleted of hemopoietic cells by gamma-irradiation (9,5 Gy) bound mAb KMI6 at reduced intensity. The results demonstrate that the KMI6 determinant, a 110-kD protein, is expressed on bone marrow stromal cells in vivo. Its restriction to areas of interaction with lymphoid cells suggests a role in forming microenvironmental niches of B lymphopoiesis. The surface membrane of individual stromal cells may thus be functionally polarized towards interacting B cell precursors and other hemopoietic cells.

Identification and functional characterization of a TIA-1-related nucleolysin

We recently reported the molecular cloning of a cytotoxic granule-associated RNA-binding protein designated TIA-1. The ability of recombinant TIA-1 to induce DNA fragmentation in permeabilized cells suggested that this protein is the granule component responsible for inducing apoptosis in cytolytic lymphocyte (CTL) targets. Here we report the characterization of a cDNA encoding a TIA-1-related protein designated TIAR. The deduced amino acid sequence of TIAR reveals it to be a 42-kDa protein possessing three RNA-binding domains and a carboxyl-terminal auxiliary domain. Although the RNA-binding domains of TIA-1 and TIAR share greater than 85% amino acid homology, their carboxyl-terminal auxiliary domains are only 51% homologous. The carboxyl terminus of TIAR contains a lysosome-targeting motif, indicating that TIAR is probably a cytotoxic granule-associated protein. Like TIA-1, purified recombinant TIAR induced DNA fragmentation in permeabilized target cells. Although immunoblotting analysis of post-nuclear supernatants revealed TIA-1 protein to be restricted to CTLs, PCR analysis revealed the expression of TIA-1 and TIAR mRNA transcripts in a wide variety of cell types. Our data suggest that the granules of CTLs contain at least two candidate nucleolysins involved in CTL killing.

On the kinetics and optimal specificity of cytotoxic reactions mediated by T-lymphocyte clones

Using the chromium release assay and the single cell assay in agarose, we study the cytotoxic reaction of the MHC-restricted T lymphocyte clones P89:15 and P1:3, which recognize distinct but specific tumour antigens on the surface of syngeneic P815 mastocytoma cells. We propose a mathematical model which describes these experiments, accounts for the strongly non-Michaelian behaviour of the reaction and permits us to estimate the kinetic parameters characterizing effector-target conjugation and lethal hit delivery. The results show that the binding and lytic activity of effector cells is modulated by the number of targets bound to them. The binding of a second target by an effector having already a target bound is facilitated; on the other hand, an effector having bound two targets delivers a lethal hit more slowly than one with a single target bound. We investigate the role of these kinetic properties in the competition between the process of tumour progression due to cancer cell replication and the process of tumour regression due to T lymphocyte cytotoxic activity. For both clones, we estimate the effector-target ratio beyond which rejection prevails. This ratio is nine times larger for P1:3 than for P89:15. Furthermore, our analysis suggests that there exists an optimal specificity minimizing this ratio. Deviations from this optimum, be it in the sense of an increase or decrease of specificity, tends to stabilize the tumoural state: a situation which in the broader context of the immune response evolution and regulation can be viewed as an immune response dilemma.

A polyadenylate binding protein localized to the granules of cytolytic lymphocytes induces DNA fragmentation in target cells

Cytolytic lymphocytes (CTLs) are characterized by their inclusion of cytoplasmic granules containing effector molecules such as perforin and the serine proteases. Here we describe the cDNA cloning and functional characterization of two related isoforms of a cytolytic granule protein designated TIA-1. Sequence analysis reveals that the 40 kd TIA-1 isoform (rp40-TIA-1) is structurally related to the poly(A)-binding proteins, possessing three RNA-binding domains and a carboxy-terminal, glutamine-rich auxiliary domain. The 15 kd TIA-1 isoform, the major species present in cytolytic granules, appears to be derived from the carboxy-terminal auxiliary domain of rp40-TIA-1 by proteolytic processing. Both natural and recombinant TIA-1 were found to induce DNA fragmentation in digitonin permeabilized thymocytes, suggesting that these molecules may be the granule components responsible for inducing apoptosis in CTL targets.

Anti-CD3 antibody-induced activated killer cells: cytokines as the additional signals for activation of killer cells in effector phase to mediate slow lysis

This study examines the role of cytokines in activating the effector cells to mediate slow lysis. After activation of splenocytes by alpha CD3, further culturing the cells in the absence of alpha CD3 resulted in the generation of activated killer cells (CD3-AK-) to mediate slow lysis. In contrast to fast lysis which was not affected by a PKC inhibitor H-7, slow lysis was inhibited. These findings suggested that a PKC-dependent activation phase preceded the lytic phase in slow lysis. To explore the mechanism for activating the lytic machinery in slow lysis, we examined the roles of cytokines in these reactions. First, it was found that alpha IL-2 or an alpha IL-2/alpha IL-4 combination inhibited slow lysis but had no effect on fast lysis. Secondly, IL-2, IL-4, or TNF alpha converted a noncytolytic CD3-AK- cells to mediate slow lysis, but they did not augment fast lysis. IL-2 and IL-4 had additive effect, and TNF alpha synergized with IL-2 to further augment the CD3-AK- cytolytic activity. Exogenous IL-6 and INF did not have any appreciable effect on the cytolytic activity of the killer cells. Besides TNF alpha, these cytokines were not directly cytotoxic to the target cells, indicating that they were not cytotoxic factors per se. Treatment with cycloheximide for 24 hr abrogated the cytolytic activities of CD3-AK cells, suggesting that a cytotoxic factor(s) was continuously synthesized to be stored in activated killer cells and was catabolized within 24 hr. Our results indicated that in the effector phase of slow lysis, after activating the CD3-AK- cells by the first signal (appropriate target cells), IL-2 and/or IL-4 appeared to be the second signal to initiate a cascade of events which triggered the release of other cytokines (e.g., TNF). This process resembles the secondary (memory) type of immune response. These events lead to full activation of the killer cells and converted the preformed cytotoxic factors into active form to initiate the lytic reaction and completed the lytic process.

BLT-esterase activity following in vitro and in vivo activation of human lymphocytes with interleukin-2. In vivo IL-2 induces BLT-esterase

BLT-esterase and cytolytic activity by human in vitro and in vivo generated Lymphokine Activated Killer (LAK) cells were measured. Lysates made from peripheral blood lymphocytes (PBL) of both normal donors and cancer patients receiving IL-2 therapy were assayed for BLT-esterase activity in a spectro-photometric assay. Cytotoxicity of PBL was measured in a 51Cr-release assay. Both BLT-esterase activity and cytotoxicity increased when normal-donor PBL were stimulated in vitro with IL-2, with greater activities at higher IL-2 concentrations. The activities also increased over time, peaking at 6 days of in vitro stimulation. Patient PBL had increased BLT-esterase and cytotoxic activities after 4 weeks of in vivo IL-2 treatment. This association of BLT-esterase activity and cytotoxicity with IL-2 activation is consistent with the model that LAK cytotoxicity is mediated by secretion of BLT-esterase associated cytolytic granules. Lymphocytes obtained after in vivo IL-2 treatment and cultured for 3-4 hours in IL-2 show markedly augmented cytotoxic activity but no increase in their BLT-esterase activity. These results indicate that the increased cytotoxicity observed after this brief pulse of in vitro IL-2 following in vivo IL-2 treatment must result from effects of IL-2 other than the production of more esterase-containing cytolytic granules.

Cytotoxic T lymphocyte (CTL)-mediated cytolysis proceeds in the absence of Na+/H+ antiport activity: regulation of cytosolic pH by the Na+/H+ antiport in a cloned CTL

Cytotoxic T lymphocyte (CTL)-mediated cytolysis of specifically bound target cells (TC) is thought to be triggered by cross-linking the T-cell antigen receptor (TcR). Biochemical events associated with TcR cross-linking include increased intracellular calcium levels [Ca2+]i, hydrolysis of phosphatidylinositol (PI), and an increase in intracellular pH [pH]i. Whereas CTL-mediated cytolysis of some TC is calcium-dependent, and PI hydrolysis is speculated to trigger the CTL lethal hit via activation of PKC, little is known about changes in [pH]i relating to activation of the lethal hit stage. We report regulation of [pH]i in a cloned CTL by the electroneutral Na+/H+ antiport during activation with PMA and specific antigen-bearing TC. Furthermore, using 5-(N-methyl-N-isobutyl) amiloride (MIBA), a potent antiport inhibitor, we demonstrate that Na+/H+ exchange is not required for activation of CTL cytolytic activity.

T lymphocyte participation in acute serum sickness glomerulonephritis in rabbits

The extent and timing of glomerular T lymphocyte infiltration was studied in acute serum sickness (AcSS) glomerulonephritis (GN) in rabbits. AcSS was initiated by a single intravenous injection of bovine serum albumin (BSA). Rabbits developed circulating BSA anti-BSA immune complexes, and rapid immune elimination of the circulating antigen was associated with the deposition of immune complexes in the kidney and the onset of a diffuse endocapillary proliferative GN. On the day of immune elimination (defined as when less than 1% of the injected antigen remained in the circulation), rabbits developed significant proteinuria (98 +/- 36 mg/24 h; normal 14 +/- 1 mg/24 h, P less than 0.01), glomerular macrophage accumulation (44.3 +/- 21.1 macrophages per glomerulus [mac/glom]; normal 0.28 +/- 0.18 mac/glom, P less than 0.01), and a significant glomerular T lymphocyte influx (3.0 +/- 0.9 cells/glomerular cross-section [c/gcs]; normal 0.47 +/- 0.13 c/gcs; P less than 0.005). On the day prior to immune elimination, increased T cells numbers were observed in some rabbits (2.4 +/- 2.1 c/gcs) together with a minor macrophage presence (7.6 +/- 3.6 mac/glom) and minimal proteinuria (17.6 +/- 3 mg/24 h). These studies demonstrate the influx of T lymphocytes together with macrophages at the onset of proteinuria in serum sickness nephritis and are consistent with a role for cell-mediated immunity in the pathogenesis of this lesion.

Marijuana components suppress induction and cytolytic function of murine cytotoxic T cells in vitro and in vivo

Killer lymphocytes play a major role in host defense against tumors and infectious diseases. Previously, we reported that delta-9-tetrahydrocannabinol (THC) and II-hydroxy-delta-9-tetrahydrocannabinol (II-hydroxy-THC) suppressed the cytolytic activity of cultured natural killer (NK) cells. Also, we showed that the drugs appeared to be affecting a stage in the killing process subsequent to the binding of the killer cell to the target cell. In the present report, we have extended these studies to an examination of the effect of cannabinoids on the activity of cytotoxic T lymphocytes (CTLs). The cytolytic activity of CTLs generated by cocultivation with either allospecific stimulators or TNP-modified-self stimulators were suppressed by both THC and II-hydroxy-THC treatment. Allospecific CTLs generated in vivo were also inhibited by an in vitro exposure to either THC or II-hydroxy-THC, and the sensitivity of these cells to drug effects appeared to be greater than the sensitivity of the in vitro generated CTLs. Suppression of cytolytic function by THC and II-hydroxy-THC was maximal after a 4-h drug treatment, suggesting that the drug effects were inducible and therefore required a finite period of time to develop maximally. As seen in previous studies involving NK cells, drug treatment of mature CTLs appears to have little effect on the binding capacity of these cells for the target. However, the maximal killing capacity of the cells and the frequency of CTLs were significantly reduced by drug treatment. In addition to suppressing the cytolytic activity of mature effector CTLs, we also show that drug treatment inhibits both the proliferation of lymphocytes responding to an allogeneic stimulus and the maturation of these lymphocytes to mature CTLs. Similarly, CTL activity developing in vivo could be inhibited by THC injection. These results suggest that CTLs are inhibited by cannabinoids by at least two mechanisms. First, the cytolytic activity of mature killers is suppressed at some point beyond the binding to the target cell. Second, the cannabinoids appear to suppress the normal development of these mature effector cells from less mature precursor cells.

Characterization of pancreatic T lymphocytes associated with beta cell destruction in the non-obese diabetic (NOD) mouse

Pancreatic beta cell destruction in the non-obese diabetic (NOD) mouse is mediated by T lymphocytes and macrophages and accelerated by cyclophosphamide. We purified pancreatic T lymphocytes from the NOD mouse for comparative phenotypic and functional analysis with T lymphocytes from spleen, peripheral blood and regional lymph nodes. Pancreatic T lymphocytes from NOD-Wehi mice, which have an incidence of spontaneous diabetes of less than 5%, had a CD4:CD8 ratio of 1.25 +/- 0.23 compared with 2.44 +/- 0.31 for peripheral blood lymphocytes. After cyclophosphamide, the CD4:CD8 ratio of pancreatic lymphocytes increased to 2.30 +/- 0.24 at day 7. T lymphocytes bearing IL-2 receptors increased two- to three-fold in number and their secretion of GM-CSF/IL-3 and IFN-gamma increased to a maximum on day 7. Pancreatic insulin content and mRNA levels declined sharply between days 10 and 12, at which time the majority of pancreatic T lymphocytes in hyperglycaemic mice were CD8+ (CD4:CD8 ratio 0.63 +/- 0.04 compared to 4.14 +/- 1.05 in peripheral blood). The pancreatic T lymphocyte CD4:CD8 ratio in prediabetic NOD-Lt mice, which have an incidence of spontaneous diabetes of about 60% at 150 days, was similar to that in untreated NOD-Wehi mice, but 25% of their pancreatic CD8 T lymphocytes were IL-2-receptor positive. Thus, significant changes in the phenotype of NOD pancreatic T lymphocytes following cyclophosphamide were not reflected in peripheral blood or spleen T lymphocytes. The earliest change after cyclophosphamide was an increase in activated, predominantly CD4+ T lymphocytes; with the development of beta cell destruction and hyperglycaemia, pancreatic T lymphocytes were, as in human IDDM, predominantly CD8+.

T cell-T cell killing is induced by specific epitopes: evidence for an apoptotic mechanism

Epstein-Barr virus-specific cytotoxic T lymphocyte clones were shown to be an effective target for their own lysis when incubated in the presence of their specific epitopes but not in the presence of irrelevant epitopes. The mode of cell killing appeared to be by apoptosis and was prevented by previously described inhibitors of the process. Degranulation, as measured by serine esterase activity, was involved in this form of T cell-T cell killing. This is the first report of T cell-T cell killing by apoptosis and is only observed in the presence of a specific epitope. This result may be of significance in the use of peptide-based vaccines.

Ultrastructure of IL2-stimulated tumor-infiltrating lymphocytes showing cytolytic activity against tumor cells

Tumor-infiltrating lymphocytes (TIL) obtained from tumor tissue and pleural effusion of breast carcinoma were cultured with interleukin-2 (IL2) and thus activated. The ultrastructure of TIL stimulated by IL2 to kill various breast carcinoma cells was then investigated. Freshly isolated TIL cultured with autologous tumor cells for 48 h without IL2 were small, round and showed neither binding to nor killing of tumor cells. TIL stimulated to proliferate by IL2 became effector cells and showed cytotoxicity against tumor cells. Ultrastructurally, the effector TIL resembled large granular lymphocytes, and adhered to tumor cells through interdigitation or close apposition of the two plasma membranes accompanied by spot-like close membrane contacts. At the site of each spot-like contact, there was a 5-nm intercellular space. The morphology of the TIL processes did not differ from those of LAK and other CTL or NK cell processes during contact, invagination or the killing of target cells. The granules in TIL were considered to participate in the cytotoxic effect. Phenotypically heterogeneous TIL, CD8+/CD57- and CD8+/CD57+, adhered to autologous tumor cells and MCF7 (human breast carcinoma cell line). However, it was unclear which cell or cells acted as the effector for tumor-cell killing.

Cyclosporin A renders target cells resistant to immune cytolysis

Exposure of cytolytically susceptible human target cells with therapeutic concentrations of the immunosuppressive drug cyclosporin A renders these cells highly resistant to T cell-mediated, natural killer (NK) cell-mediated, and complement-mediated cytolysis. The resistance is dose dependent, time dependent and reversible. The resistance is accompanied by target cell growth inhibition as measured by thymidine uptake. Surprisingly, target cell growth inhibition induced by serum depletion is associated with cell-mediated cytolytic resistance. These data suggest that cyclosporin A (CsA) may block some target cell biochemical pathway(s) important in the suicidal cytolytic process which is (are) linked to some G0/G1 cell cycle events. In addition, these results suggest that the increased risk of Epstein-Barr virus (EBV)-associated lymphoproliferative disease in human organ transplant recipients may be contributed to by CsA-induced resistance of EBV-transformed B lymphocytes to immune cytolysis. In the post-transplant setting, CsA probably blocks T cell-dependent responses to EBV-transformed B lymphocytes (Bird, A.G., McLachlan, S.M. and Britton, S., Nature 1981, 289: 300) yet leaving the NK cell and antibody-dependent responses intact (Shao-Hsien, C. et al. Transplantation 1983. 35: 127). However, given the direct effect of CsA upon EBV-transformed B lymphocytes, these cells would be rendered resistant to nearly all forms of cytolytic immune control (cytotoxic T lymphocyte, natural killer, antibody-dependent cell-mediated cytotoxicity, complement). Unregulated EBV-transformed B lymphocytes may then proliferate in the CsA-treated host thus leading to a polyclonal B cell hyperplasia. Our data would suggest that this early pre-malignant process is likely to be reversible following CsA dose reduction. Indeed, EBV-dependent polyclonal B cell hyperplasia is seen in early post-transplant lymphoproliferative disorders (Hanto, D.W., et al., Transplantation 1989, 47: 458). Furthermore, in some cases CsA dose reduction does lead to disease regression (Starzl, T., et al., Lancet 1984. i: 583). However, further progression of the disease probably occurs following chromosomal changes leading to oncogene activation and might be resistant to CsA dose reduction.

T cell targeting in cancer therapy

Targeting of immune cells by bispecific antibodies has proven a powerful tool for the investigation of cellular cytotoxicity, lymphocyte activation and induction of cytokine production, as well as to represent an innovative form of immunotherapy for the treatment of cancer. The hallmark of this approach is the use of the specificity of monoclonal antibodies to join target and immune cells by virtue of the dual specificity of bispecific antibodies for the two entities. More precisely the bispecific antibody has two different binding sites, which are capable of recognizing tumor associated antigens on the one hand and lymphocyte activation sites on the other. This process of crosslinking results in the activation of the lymphocyte and triggering of its lytic machinery, as well as lymphokine production. A major advantage of this therapeutic modality is, that use is made of the normal cellular immune defence system and therefore is only associated with minor toxicity. The distinct lymphocyte populations, which can be used for adoptive immunotherapy and the various bispecific antibody preparations, as well as the chimeric immunoglobulin/T cell receptor construction are the major topics of this review.

Ultrastructural analysis of apoptosis induced by the monoclonal antibody anti-APO-1 on a lymphoblastoid B cell line

Apoptosis (programmed cell death) is the most common form of death in eukaryotic cells. We recently described a monoclonal antibody, anti-APO-1, which induces apoptosis of cells from the human B-lymphoblastoid line SKW 6.4 and of cells from a variety of other human lymphoid cell lines. This model of apoptosis was now studied ultrastructurally. SKW 6.4 cells undergoing apoptosis showed the following morphological changes: condensation of the cytoplasm and karyoplasm, formation of large electron-opaque aggregates of the chromatin lining the nuclear membrane, "blebbing" of the cell membrane at an early stage of apoptosis, and dilatation of the mitochondria. Two hours after adding anti-APO-1, the nuclear membrane was ruptured. Occasionally, large vesicular enlargement of endoplasmic reticulum or Golgi appeared in the cytoplasm. Finally, total breakdown of all cell membranes and cellular disintegration was observed.

Suppression of target cell proliferation by natural killer cells

The cytolytic effects of natural killer (NK) cells have been extensively studied in recent years. In the present study we have investigated the cytostatic effects of NK cells. Human peripheral blood lymphocytes from healthy volunteers were used as a source of effector cells, and the cell lines K562, U937, U1285, and Molt-4 were used as target cells. Effector cells were enriched for NK cells using Percoll gradients and depleted of NK cells on Percoll gradients or by using Leu-19 antibodies and magnetic beads. By monitoring cell numbers during co-culture of effector cells and K562, it was found that after an initial phase of cell killing for 3 h target cell numbers remained stable during the following 24-48 h. In a microcytotoxicity assay measuring inhibition of uptake of [3H]thymidine, the four target cell types were shown to have different NK sensitivity; inhibition of greater than or equal to 80% was obtained for K562 and U937 at an effector to target cell (E/T) ratio of 30:1, 50% for U1285, and 30% for Molt-4. This inhibition was shown to be partly a direct effect on DNA synthesis for all cell lines, as incorporation of [3H]thymidine was decreased in cocultured target cells compared with an equal number of target cells alone. Inhibition of DNA synthesis was thus not directly related to cell death and was also observed for the Molt-4 cell line that was not killed. A cell division assay, with target cells in agarose and effector cells in a liquid upper layer, showed a decline in the rate of target cell divisions. Effects on the cell cycle were studied on latent-phase cells. It was shown that effector cells delayed the onset of DNA synthesis. This anti-proliferative effect was observed for several days, but cell growth then gradually resumed. The effector cells were identified as CD56-positive large granular lymphocytes (LGL). Double-layer cultures and experiments using effector cell supernatants demonstrated that the growth-inhibitory effect could be mediated by soluble factors, and the production of such factors was stimulated by exposure to a small proportion of target cells (50:1). Studies with specific antibodies indicated that growth inhibition was not mediated by alpha interferon (IFN-alpha) but it was partly mediated by tumour necrosis factor alpha (TNF-alpha). It is concluded that NK cells have a growth-inhibitory effect that is distinct from the cytolytic effect and this activity is probably mediated by several soluble factors including TNF-alpha.

Comparison of the effects of purified human alpha 1-antichymotrypsin and alpha 1-proteinase inhibitor on NK cytotoxicity: only alpha 1-proteinase inhibitor inhibits natural killing

While an inhibitory effect on natural killer (NK) cell activity was demonstrated with partially purified alpha 1 Achy, neither highly purified alpha 1 Achy from two healthy donors nor from one patient with giant-cell arteritis, which carries more highly branched glycans, inhibited the NK cytotoxicity. Our purification procedure, based on immunoaffinity chromatography and gel filtration, was not in question since the pure alpha 1-proteinase inhibitor (alpha 1PI) prepared in our laboratory by using a similar procedure continued to inhibit the NK cytotoxicity. If an inhibitory effect not related to antiprotease activity occurs with alpha 1PI, it is surprising that it is not shared by alpha 1 Achy which, like alpha 1PI, belongs to the serpin family and which possesses a strong structural homology with alpha 1PI. Our finding that alpha 1PI is able to affect human NK cytotoxicity while alpha 1 Achy (even with more highly branched glycans) is unable to suggests that events controlling NK activity may involve other enzymes than chymotrypsin-like enzymes.

Anti-CD3 antibody-induced activated killer cells subsets of killer cells that mediate fast or slow lytic reactions

The present study has characterized two sets of alpha CD3-induced activated killer cells (CD3-AK). A 2 to 4-h 51Cr release assay or triton-treated 125IUdR release assay demonstrated that CD3-AK cultured in the continuous presence of alpha CD3 (CD3-AK+) mediated fast lysis. A 20-h 51Cr or 125I-deoxyuridine release assay demonstrated that CD3-AK cultured in the absence of alpha CD3 (CD3-AK-) mediated slow lysis. Activating the TCR-CD3 complex of CD3-AK- cells with alpha CD3 for 2 h enabled the killer cells to mediate fast lysis. The activation process was inhibited by H-7, a protein kinase C (PKC) inhibitor. Conversely, removal of alpha CD3 from CD3-AK+ cell cultures for 24 h resulted in almost complete loss of the ability of CD3-AK+ cells to mediate fast lysis, but they still retained the ability to mediate slow lysis. It appeared that constant perturbation of CD3 by alpha CD3 maintained the CD3-AK+ cells in an active state, and thus, they were able to mediate fast lysis. On the other hand, activation by a 2-h incubation with PMA could convert the noncytolytic CD3-AK- cells to be cytolytic in slow lysis and to augment the slow lytic reactions mediated by CD3-AK- cell with low cytolytic activity. These results were confirmed by triton-treated 125IUdR release assay which could detect early DNA-release. Thus it appeared that activation of CD3-AK cells with T cell activation signals that bypassed TCR (such as PMA) could induce slow lysis. In the effector phase of lytic reactions, the fast lytic reaction was relatively resistant to inhibition by H-7, whereas the slow lytic reaction was susceptible to H-7 inhibition, indicating that fast lysis was PKC independent and slow lysis was PKC dependent. It was further found that H-7 inhibition was at an early stage of slow lysis, suggesting that a PKC dependent activation process preceded the PKC independent lytic process. These findings indicated that the CD3-AK- cells were in a less activated state which required further activation to turn on their lytic machinery to initiate the lytic reaction.

Mechanism of killing by virus-induced cytotoxic T lymphocytes elicited in vivo

The mechanism of lysis by in vivo-induced cytotoxic T lymphocytes (CTL) was examined with virus-specific CTL from mice infected with lymphocytic choriomeningitis virus (LCMV). LCMV-induced T cells were shown to have greater than 10 times the serine esterase activity of T cells from normal mice, and high levels of serine esterase were located in the LCMV-induced CD8+ cell population. Serine esterase was also induced in purified T-cell preparations isolated from mice infected with other viruses (mouse hepatitis, Pichinde, and vaccinia). In contrast, the interferon inducer poly(I.C) only marginally enhanced serine esterase in T cells. Serine esterase activity was released from the LCMV-induced T cells upon incubation with syngeneic but not allogeneic LCMV-infected target cells. Both cytotoxicity and the release of serine esterase were calcium dependent. Serine esterase released from disrupted LCMV-induced T cells was in the form of the fast-sedimenting particles, suggesting its inclusion in granules. Competitive substrates for serine esterase blocked killing by LCMV-specific CTL, but serine esterase-containing granules isolated from LCMV-induced CTL, in contrast to granules isolated from a rat natural killer cell tumor line, did not display detectable hemolytic activity. Fragmentation of target cell DNA was observed during the lytic process mediated by LCMV-specific CTL, and the release of the DNA label [125I]iododeoxyuridine from target cells and the accompanying fragmentation of DNA also were calcium dependent. These data support the hypothesis that the mechanism of killing by in vivo-induced T cells involves a calcium-dependent secretion of serine esterase-containing granules and a target cell death by a process involving nuclear degradation and DNA fragmentation.

Identification of hemolytic granules isolated from human myocardial cells

Human myocardial cells from fresh autopsy material contained granules which possessed hemolytic activity against guinea pig and rabbit erythrocytes. The hemolytic granules, which had a density of 1.02 and a diameter of 200-300 nm, were recovered as a microsome fraction from subcellular homogenates of human myocardial cells by differential centrifugation in 300 mM sucrose containing 0.1 mM PMSF and 10 mM EDTA. The membrane lesions caused by the granules were ring-like structures with an internal diameter of about 10-17 nm, analogous to that caused by perforin- and complement-induced lysis. However, the requirement for divalent cation differed from that for perforin-induced lysis, since the microsome-mediated lysis occurred in the presence of EDTA.

Ultrastructural changes during lysis of L929 target cells by class II-restricted influenza virus-specific murine cytotoxic T-lymphocyte clones

Lysis of virus-infected L929 target cells transfected with the H-2 class II IAk gene by class II-restricted influenza virus-specific murine cytotoxic T lymphocyte (CTL) clones was studied by electron microscopy and compared with lysis of L929 cells by class I-restricted CTL clones. T lymphocytes predominantly approached the basal surface of target cells grown on a plastic dish and also approached uninfected L929 target cells, although virus maturation exhibited no polarity with respect to the cell surface site. After incubation for 30 min, the target cell nuclei began to change: chromatin became irregularly redistributed and aggregated, and the nuclei appeared swollen. Later, electron-dense and -light areas of nuclei became segregated, and the cytoplasm became disorganized with many vacuoles. The ultrastructural changes of target cells during lysis by class I- and class II-restricted CTL clones appeared to be similar. These findings and other cytotoxicity data of class I and class II CTLs are discussed.

Cytopathic action of Naegleria fowleri amoebae on rat neuroblastoma target cells

The axenically cultured, weakly pathogenic Naegleria fowleri LEE and the highly pathogenic, mouse passaged N. fowleri LEEmp are cytopathic for B103 rat nerve cells in culture. Cytopathogenicity was measured by release of radiolabeled rubidium or radiolabeled chromium from B103 target cells. Cytopathogenicity was time-dependent for up to 18 h and dependent upon amoebae effector to nerve cell target ratios of less than 1:1. Release of 51Cr from B103 cells by either LEE or LEEmp amoebae was enhanced by addition of calcium or magnesium to medium free of these divalent cations but the ion-channel inhibitor, verapamil, or the ionophore A23187 and phorbol myristate acetate did not alter release of 51Cr from B103 cells cocultured with the amoebae. Cycloheximide or actinomycin D impaired release of 51Cr from B103 target cells injured by either LEE or LEEmp amoebae. Both strains of amoebae were fractionated by glass bead disruption and high speed centrifugation into membrane and soluble fractions. Each fraction was incubated with either 86Rb or 51Cr labeled nerve cells. The membrane fraction from LEEmp was more active than the soluble fraction in facilitating rubidium and chromium release. In contrast, the soluble fraction from LEE was more active than the membrane fraction in facilitating rubidium release from radiolabeled target cells. The sequential release of 86Rb and 51Cr from target cells rather than the simultaneous release of the two isotopes indicates that target cell death is due to the release of ions followed later by the release of large macromolecules. The results indicate that N. fowleri amoebae injure nerve cells by two alternate mechanisms, trogocytosis or contact-dependent lysis.

Murine trophoblast cells are not killed by tumor necrosis factor-alpha

Purified midgestation murine trophoblast cannot be killed by a variety of cell-mediated effector mechanisms, with the exception of highly lytic effectors such as lymphokine-activated killer cells. We now report that this trophoblast population is also resistant to tumor necrosis factor (TNF)-alpha.

Genomic organization of the mouse pore-forming protein (perforin) gene and localization to chromosome 10. Similarities to and differences from C9

Genomic clones encompassing the entire coding region of the mouse lymphocyte pore-forming protein gene (Pfp) have been isolated and used to determine its intron-exon organization. In contrast to C9, Pfp has a simple structure, consisting of only three exons (two of which encode polypeptide), a large 5' intron, and a single, smaller intron that is situated approximately one-third of the way through the protein-coding portions of the gene. The regions encoding the homologous domains of PFP and C9 are encoded on exons 7, 8, 9, and 10 of C9, but form only approximately half of the open reading frame of exon III in Pfp. Although encoding polypeptides with related functions, the two genes possess such sharply contrasting structures as to suggest that their analogous regions may have risen independently, by a process of convergent evolution. Using a panel of somatic cell hybrid cell lines, Pfp has been mapped to chromosome 10.

Effects of heat shock on cytolysis mediated by NK cells, LAK cells, activated monocytes and TNFs alpha and beta

We have recently shown that a heat treatment of a murine target cell line, WEHI 164, induces resistance to lysis mediated by tumour necrosis factors alpha (TNF-alpha) and beta (TNF-beta). In the present study the effect of the heat shock of target cells on cytotoxicity mediated by natural killer cells (NK cells), lymphocyte-activated killer cells (LAK cells), activated monocytes, TNF-alpha, and TNF-beta was investigated. First, WEHI 164 cell line and six human cell lines (ME 180, K 562, U 937, HeLa, MCF7, and SK-OV 3) were screened for their sensitivity to different forms of lysis, and then sensitive cell lines were heat-treated. Pretreatment of target cells at 42 degrees C for 45-60 min also rendered human target cell lines more resistant to lysis by rTNFs, and the acquired resistance was accompanied by an increased resistance to activated monocytes, but not to NK cells or LAK cells. Thus, the heat-induced resistance mechanisms capable of protecting target cells from lysis by rTNFs and by activated monocytes do not elicit resistance to lysis by NK cells and LAK cells, supporting the hypothesis that mediators other than TNFs are involved in NK cell- and LAK cell-mediated killing.

Cancer, cytokines, and cytotoxic cells: interleukin-2 in the immunotherapy of human neoplasms

Modern immunotherapy of human cancer has evolved as a rapidly expanding field of clinical and experimental research. Employing the systemic application of recombinant interleukin-2 (IL-2) in humans, Rosenberg and colleagues from the National Cancer Institute reported the regression of advanced metastatic tumors in approximately 10%-30% of patients treated. The additional adoptive transfer of autologous patient-derived activated lymphocytes was performed to enhance therapeutic efficacy. While the exact mechanisms of IL-2 based immunotherapy in cancer remain unclear, it has been hypothesized that both the IL-2 activated lymphocyte and its secretory products such as interferon-gamma or tumor-necrosis factor beta may contribute to the lysis of tumor cells in vivo. Accordingly, research has been directed toward enhancing both the activation state and the specificity of IL-2 induced killer cells in humans. Based on in vitro and animal data, the retransfusion of tumor-infiltrating lymphocytes has been shown to mediate the regression of metastatic neoplasms in up to 50% of patients receiving systemic IL-2. Considerable toxicity from the use of high-dose IL-2 has prompted attempts to develop low-dose regimens which allow for the outpatient treatment of patients presenting poor prognosis. While in most clinical trials involving IL-2, patient follow-up has been short, and no or only limited data have become available from controlled prospective and randomized clinical studies, IL-2 has shown some promise in patients with metastatic renal cell cancer or malignant melanoma. Novel approaches toward the improvement of clinical efficacy of IL-2 include local (e.g., intracavitary) application or combinations with other cytokines such as interferon-alpha or cytostatic drugs.

A new model for lethal hit delivery by cytotoxic T lymphocytes

Human cytotoxic T lymphocyte (CTL) granules contain an electron-dense core and small membrane vesicles. By immuno-electron microscopy, molecules relevant to CTL-target cell (TC) interactions have been identified on the membranes of the dense core and small vesicles within the granule. Moreover, perforin, the component implicated in the lethal hit, and serine esterases are localized within these granule substructures. In this article Peter Peters and colleagues argue that these observations necessitate a revision of the current model for lethal hit delivery. They suggest that the cytotoxic mediators exocytosed into the cleft between CTL and TC are not in soluble form, but rather are membrane-enveloped. The presence of the CD3-T-cell receptor (TCR) complex, CD8 and possibly other relevant molecules on these membranes may ensure unidirectional delivery of the lethal compounds to the TC.

Evidence that protein kinase C activation is essential for killing by IL-2-activated lymphocytes

Previous pharmacological evidence has suggested that activation of protein kinase C (PKC) is necessary for T and natural killer (NK) killing of different target cells. In the present study we find, using interleukin 2 (IL-2)-activated lymphocytes (LAK cells), that phosphorylation of a well-characterized 80-kDa PKC substrate increases during conjugation to target cells. Furthermore, down-regulation of PKC by pretreatment with the active phorbol esters PDB (24 h) or PMA (2 h), but not with the inactive phorbolester PDD, simultaneously inhibits killing by LAK cells. H-7, an inhibitor of PKC, also inhibited LAK-cell killing without affecting the target-effector cell conjugate formation. We also demonstrate that pretreatment of target cells with phorbol ester (PMA) decreases killing, suggesting that PKC activation in the target cell population may also influence killing although the effect may vary depending on the particular target cell used. We conclude that PKC activation is essential for triggering of lysis in LAK cells.