Effects of protein kinase C (PK-C) activators and inhibitors on human large granular lymphocytes (LGL): role of PK-C on natural killer (NK) activity

Effects of adenylyl cyclase and protein kinase A inhibition on signaling enzymes in natural killer cells: comparison to tributyltin

Natural killer (NK) cells are lymphocytes capable of destroying tumor cells and virally-infected cells without prior sensitization. In a previous study, we found that inhibition of adenylyl cyclase (AC) or cAMP-dependent protein kinase (PKA) decreased the ability of NK cells to destroy tumor cells. We also found that the environmental contaminant tributyltin (TBT), at concentrations of 300 500 nM, decreased tumor-cell lysis by NK cells, as well as their intracellular levels of cAMP. This suggested that the decreases in cAMP associated with TBT (300 500 nM) may, in part, be responsible for loss of cytotoxic function. Here, we investigated the effects of inhibition of AC or PKA on enzymes that are required in the NK tumorolytic process and compared them to those of TBT exposure. The enzymes studied were: the protein tyrosine kinase (PTK), syk; phospholipase C gamma1 (PLCg1); and the mitogen activated protein kinase (MAPK), p44/42. Exposure of NK cells to the AC inhibitor 2?,5?-dideoxyadenosine (DDA) significantly increased the total level of PLCg1 by 67% after 60 min and the level of p44/42 by about 30%. Exposure to the PKA inhibitor H-89 significantly increased the levels of the phosphorylated (activated) p44/42 (90%) after 60 min. Exposure to TBT increased the levels of PLCg1 by about 50%. Previously, we found that exposure to TBT increased the phosphorylation of p44/42 within 5 min. These results indicate that AC inhibition caused alterations of the levels of key enzymes, while decreased PKA activity caused an increase in p44/42 activation. They also suggest that the effects of decreased levels of cAMP on these key cytotoxic signaling proteins may overlap, to a very limited extent, with those of TBT.

Activation of protein kinase C and protein kinase D in human natural killer cells: effects of tributyltin, dibutyltin, and tetrabromobisphenol A

Up to now, the ability of target cells to activate protein kinase C (PKC) and protein kinase D (PKD) (which is often a downstream target of PKC) has not been examined in natural killer (NK) lymphocytes. Here we examined whether exposure of human NK cells to lysis sensitive tumor cells activated PKC and PKD. The results of these studies show for the first time that activation of PKC and PKD occurs in response to target cell binding to NK cells. Exposure of NK cells to K562 tumor cells for 10 and 30 min increased phosphorylation/activation of both PKC and PKD by roughly 2-fold. Butyltins (tributyltin (TBT), dibutyltin (DBT)) and brominated compounds (tetrabromobisphenol A (TBBPA)) are environmental contaminants that are found in human blood. Exposures of NK cells to TBT, DBT, or TBBPA decrease NK cell lytic function in part by activating the mitogen-activated protein kinases (MAPKs) that are part of the NK lytic pathway. We established that PKC and PKD are part of the lytic pathway upstream of MAPKs and thus we investigated whether DBT, TBT, and TBBPA exposures activated PKC and PKD. TBT-activated PKC by 2-3-folds at 10 min at concentrations ranging from 50 to 300 nM while DBT caused a 1.3-fold activation at 2.5 µM at 10 min. Both TBT and DBT caused an approximately 2-fold increase in phosphorylation/activation of PKC. Exposures to TBBPA caused no statistically significant changes in either PKC or PKD activation.

Role of protein kinase C in TBT-induced inhibition of lytic function and MAPK activation in human natural killer cells

Human natural killer (NK) cells are lymphocytes that destroy tumor and virally infected cells. Previous studies have shown that exposure of NK cells to tributyltin (TBT) greatly diminishes their ability to destroy tumor cells (lytic function) while activating mitogen-activated protein kinases (MAPK) (p44/42, p38, and JNK) in NK cells. The signaling pathway that regulates NK lytic function appears to include activation of protein kinase C(PKC) as well as MAPK activity. TBT-induced activation of MAPKs would trigger a portion of the NK lytic signaling pathway, which would then leave the NK cell unable to trigger this pathway in response to a subsequent encounter with a target cell. In the present study we evaluated the involvement of PKC in inhibition of NK lysis of tumor cells and activation of MAPKs caused by TBT exposure. TBT caused a 2–3-fold activation of PKC at concentrations ranging from 50 to 300 nM (16–98 ng/ml),indicating that activation of PKC occurs in response to TBT exposure. This would then leave the NK cell unable to respond to targets. Treatment with the PKC inhibitor, bisindolylmaleimide I, caused an 85% decrease in the ability of NK cells to lyse tumor cells, validating the involvement of PKC in the lytic signaling pathway. The role of PKC in the activation of MAPKs by TBT was also investigated using bisindolylmaleimide I. The results indicated that, in NK cells where PKC activation was blocked, there was no activation of the MAPK, p44/42 in response to TBT.However, TBT-induced activation of the MAPKs, p38 and JNK did not require PKC activation. These results indicate the pivotal role of PKC in the TBT-induced loss of NK lytic function including activation of p44/42 by TBT in NK cells.

Increases in cytosolic calcium ion levels in human natural killer cells in response to butyltin exposure

This study investigated whether exposures to butyltins (BTs), tributylin (TBT), and dibutyltin (DBT) were able to alter cytosolic calcium levels in human natural killer (NK) cells. Additionally, the effects of cytosolic calcium ion increases on the activation state of mitogen-activated protein kinases (MAPKs) in NK cells were also investigated. NK cells are an intital immune defense against the development of tumors or viral infections. TBT and DBT are widespread environmental contaminants, due to their various industrial applications. Both TBT and DBT have been shown to decrease the ability of NK cells to lyse tumor cells (lytic function). TBT has also been shown to activate MAPKs in NK cells. The results of this study indicated that TBT increased cytosolic calcium levels by as much as 100% after a 60-min exposure to 500 nM TBT, whereas DBT increased cytosolic calcium levels to a much smaller extent (and required higher concentrations). The results also indicated that increases in cytosolic calcium could activate MAPKs but only for a short period of time (5 min), whereas previous studies showed that activation of MAPKs by TBT last for at least 6 h. Thus, it appears that TBT-stimulated increases in cytosolic calcium might contribute to, but are not fully responsible for, TBT-induced activation of MAPKs.

Decreased adenylyl cyclase and cAMP-dependent protein kinase activities inhibit the cytotoxic function of human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumor cells and virally infected cells without prior sensitization. Elevation of cyclic 3', 5' adenosine monophosphate (cAMP) levels in NK cells is known to cause dramatic inhibition of NK cytolytic function. However, the effect of lowering cellular levels of cAMP on the cytolytic function of natural killer (NK) cells has not been studied. The current study investigated the effects of inhibiting adenylyl cyclase (AC) or cAMP-dependent protein kinase (PKA) activities on the ability of NK cells to lyse K562 tumor cells, and on the activation of NK-cell phospholipase C (PLC) by tumor targets. Exposure of NK cells to the AC inhibitors MDL-12,330A (MDL) or 2',5',-Dideoxyadenosine (DDA) completely blocked their ability to destroy K562 tumor cells. Further, target-induced stimulation of NK-cell PLC was inhibited by as much as 90% when NK cells were treated with the AC inhibitors. Treatment of NK cells with the PKA inhibitor, H-89, caused essentially complete inhibition of cytotoxic function while decreasing target-induced stimulation of PLC by about 50%. Additionally, exposure to the organotin compound, tributyltin (TBT), which decreases cAMP levels in NK cells (as much as 80%) caused a decrease in cytotoxic function by as much as 90%. These data suggest that decreased levels of cAMP may cause very significant loss of NK cytotoxic function and that this may be mediated by decreased PKA activity. These data coupled with previous work revealing that increased cAMP levels inhibit NK cytotoxic function, suggest that tight regulation of cAMP levels is critical to NK cell function.

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

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

Dependence of Both Spontaneous and Antibody-Dependent, Granule Exocytosis-Mediated NK Cell Cytotoxicity on Extracellular Signal-Regulated Kinases

Extracellular signal-regulated kinases (ERK, also known as mitogen-activated protein kinases) are serine-threonine kinases transducing signals elicited upon ligand binding to several tyrosine kinase-associated receptors. We have reported that ERK2 phosphorylation and activation follows engagement of the low affinity receptor for the Fc portion of IgG (CD16) on NK cells, and is necessary for CD16-induced TNF-α mRNA expression. Here, we analyzed the involvement of ERK in NK cell-mediated cytotoxicity and IFN-γ expression induced upon stimulation with targets cells, coated or not with Abs. Our data indicate that, as with immune complexes, ERK2 phosphorylation occurs in human primary NK cells upon interaction with target cells sensitive to granule exocytosis-mediated spontaneous cytotoxicity, and that this regulates both target cell- and immune complex-induced cytotoxicity and IFN-γ mRNA expression. A specific inhibitor of mitogen-activated protein kinase kinase reduced both spontaneous and Ab-dependent cytotoxicity in a dose-dependent manner involving, at least in part, inhibition of granule exocytosis without affecting effector/target cell interaction and rearrangement of the cytoskeleton proteins actin and tubulin. Involvement of ERK in the regulation of Ca2+-dependent cell-mediated cytotoxicity was confirmed, using a genetic approach, in primary NK cells infected with a recombinant vaccinia virus encoding an ERK inactive mutant. These data indicate that the biochemical pathways elicited in NK cells upon engagement of receptors responsible for either spontaneous or Ab-dependent recognition of target cells, although distinct, utilize ERK as one of their downstream molecules to regulate effector functions.

Jatrophone and 12-O-tetradecanoyl phorbol-13-acetate antagonism of stimulation of natural killer activity and lymphocyte proliferation

We have recently reported that the diterpene jatrophone antagonizes the effects of phorbol ester in pharmacogical studies. In order to investigate further whether this action is associated with an inhibition of protein kinase C activity, we examined the effect of jatrophone on the stimulation of lymphocyte activities which are dependent on the protein kinase C pathway. Jatrophone (0.02-0.32 microM) caused concentration-dependent and equipotent inhibition of human lymphocyte proliferation induced by 5 micrograms/ml of phytohemagglutinin or by a combination of 100 ng/ml of 12-O-tetradecanoyl phorbol-13-acetate (TPA) plus 0.15 microM ionomicyn, with IC50 values (and their 95% confidence limits) of 53.4 (42.6-65.3) nM and 48.4 (39.4-59.8) nM, respectively. Jatrophone also blocked, in a concentration-dependent fashion, the murine lymphocyte proliferation stimulated by 5 micrograms/ml of concanavalin A, with an IC50 value of 63.5 (51.2-76.5) nM. The inhibition was not due to a toxic effect as the pre-incubation of lymphocytes for 48 h with 0.32 microM jatrophone did not impair the proliferation after removal of the diterpene from the culture medium. Human lymphocytes when pre-treated with 10 ng/ml TPA had a 3 times higher spontaneous natural killer activity against K562 cells and an increased expression of CD69. In addition, jatrophone inhibited both spontaneous and TPA-stimulated natural killer activity and the expression of CD69. Jatrophone concentrations that inhibited 75% of lymphocyte proliferation did not impair the intracellular increase in Ca2+ flux in lymphocytes stimulated by phytohemagglutinin. These results indicate that jatrophone is a potent inhibitor of activation of lymphocytes, probably through inhibition of the protein kinase C pathway.

Tumour necrosis factor-alpha induces an increase in susceptibility of human glioblastoma U87-MG cells to natural killer cell-mediated lysis

The mechanism by which tumour necrosis factor (TNF)-alpha increases the susceptibility of U87-MG human glioblastoma cells to lysis by natural killer (NK) cells was studied. Treatment with TNF-alpha (100 units ml-1) for 48 h enhanced the susceptibility of tumour cells to lysis by NK cells. Increased susceptibility to lysis was associated with enhanced expression of intercellular adhesion molecule 1 (ICAM-1) and HLA class I antigen. Antisense ICAM-1 oligonucleotide inhibited lysis by NK cells of TNF-alpha-treated tumour cells. In contrast, acid treatment following TNF-alpha treatment increased lysis by NK cells. These findings indicate that TNF-alpha treatment of glioblastoma cells increased their susceptibility to lysis by NK cells, since ICAM-1 up-regulation would have more profound effects on NK susceptibility than would HLA class I antigen up-regulation.

Opposite effects of amiloride and amiloride analogues on activation of natural killer cytotoxicity by the phorbol ester TPA and gamma-interferon

Amiloride, a K(+)-sparing diuretic used as an Na+/H+ exchange inhibitor, blocked the activation of human natural killer (NK) activity against K562 cells by either the phorbol ester TPA or gamma-interferon. However, this stimulation was not blocked by 5-(N,N-hexamethylene)amiloride, a potent inhibitor of Na+/H+ exchange. Spontaneous NK activity was inhibited by this amiloride analogue as well as by 5-(N-methyl-N-guanidinocarbonylmethyl) amiloride, another potent inhibitor of exchange, but only in concentrations 30-80 times higher than those used to inhibit Na+/H+ exchange. The analogue phenamil amiloride blocked NK activity in concentrations found to inhibit epithelial Na+ channels, whereas tetrodotoxin, the specific inhibitor of voltage-dependent Na+ channels, had no effect. These results indicate that Na+/H+ exchange is not essential either for spontaneous NK activity or for its activation by TPA and gamma-interferon. They also suggest the involvement of voltage-independent Na+ channels in NK activity.

Phorbol 12-myristate 13-acetate induces resistance of human melanoma cells to natural-killer- and lymphokine-activated-killer-mediated cytotoxicity

Human melanoma cells are sensitive to the lytic activity of natural killer (NK) and lymphokine-activated killer (LAK) cells in vitro. The events resulting in tumour cell killing by lymphocytic effectors have not been completely clarified, and the same target cell determinants regulating responsiveness to immune cytolysis have not yet been identified. Indeed, changes in the differentiative status of leukemia cells as well as in the expression of major histocompatibility complex (MHC) antigens have been described to modulate sensitivity to cytotoxic effectors; moreover surface expression of adhesion factors or extracellular matrix proteins by the cancer cells can promote the activation of the cytolytic effectors and has been described to correlate with tumour cell sensitivity to cytolytic cells. We reasoned that treatment with differentiation inducers could modulate melanoma cell sensitivity to NK and LAK cells. The present study demonstrates that human melanoma GLL-19 cells, when treated with the phorbol diester phorbol 12-myristate 13-acetate (PMA) in vitro, undergo growth inhibition and neuron-like differentiation. Moreover, PMA treatment induces an evident inhibition of GLL-19 cell sensitivity to NK- and LAK-mediated cytotoxicity. GLL-19 cells express constitutively MHC class I antigens. PMA treatment, however, does not modify the expression of MHC class I and class II DR antigens in human melanoma GLL-19 cells. We have finally evaluated the effects of PMA on the expression at the cell surface of adhesion factors such as ICAM-1, and extracellular matrix proteins such as collagen IV, laminin and fibronectin; we have also studied the expression of the integrin vitronectin receptor, a membrane receptor for adhesive proteins. While adhesion factors and extracellular matrix proteins appear to play an important role in the interaction between immune effector and tumour target, it can be supposed that the modulation of such membrane-associated proteins or glycoproteins induces NK and LAK resistance in cancer cells. We indeed found that PMA treatment induced in GLL-19 a marked reduction of membrane expression of collagen IV and ICAM-1; moreover PMA reduced the cell membrane expression of the integrin vitronectin receptor. On the other hand, membrane expression of fibronectin and laminin was not affected by PMA. These data indicate that the acquisition of a NK- and LAK-resistant phenotype by GLL-19 cells occurs together with cell differentiation, down-regulation of membrane expression of collagen IV, ICAM-1 and vitronectin receptor, but in the absence of changes in MHC antigens.

Inhibition of the calpain-mediated proteolysis of protein kinase C enhances lytic activity in human NK cells

Recent evidence from our laboratory has demonstrated that NK/LAK cell activation of human lymphocytes is protein kinase C (PKC)-dependent. Here, we have investigated the translocation of PKC in human NK cells exposed to sensitive targets or to PMA, a phorbol ester. In NK cells exposed to K562 for 6 hr, we observed a weak translocation of PKC whereas in NK cells exposed to PMA more than 90% of cytosolic PKC was translocated to the membrane in less than 5 min. Stimulation of NK cells with an NK-resistant target, however, did not translocate PKC even after 6 hr. Translocation of PKC to the membrane was followed by the appearance of PKM, the cytosolic calcium/phospholipid (Ca2+/PL)-independent form of PKC. The conversion of PKC to PKM was mediated by calpain, an intracellular calcium-dependent thiol proteinase. When we used two inhibitors of calpain, calpain inhibitor I (CI-I) and calpain inhibitor II (CI-II), both caused a dose-related enhancement of NK-CMC when the inhibitors were present throughout the 3-hr chromium release assay. This enhancement could be circumvented by PMA or by the PKC inhibitor H-7. CI-I and CI-II added together caused a greater increase in NK-CMC than when each was added alone. CI-I and CI-II also enhanced antibody-dependent cell-mediated cytotoxicity (ADCC), substantiating further our previous contention that the activation of both NK-CMC and ADCC may involve a common lytic pathway. Activation of NK cells with IL-2 for 18 hr at 37 degrees C was inhibited in the presence of CI-I. To investigate a possible feedback inhibition mechanism due to the buildup of PKC, we examined phosphatidylinositol (PI) metabolism in NK cells activated by IL-2 in either the presence or the absence of CI-I. We observed a significant decrease in PI turnover when NK cells, activated in the presence of IL-2 and CI-I, were stimulated with K562 as compared to NK cells activated by IL-2 alone, then stimulated with K562.

Phorbol myristate acetate corrects impaired NK function of old mice

Previous studies indicated that natural killer (NK) activity in mice declined with age. In this report, we investigated the basis for the decreased activity of NK cells in older mice. Our results demonstrated that phorbol myristate acetate (PMA)--an activator of protein kinase C (PKC)--corrects the impaired NK function of older animals. The per cent increase of NK activity post treatment with PMA is 226-261% at effector:target (E:T) ratio = 100:1 compared with control untreated cells. The effect of PMA was shown to be dose dependent. A maximum increase in NK activity was achieved at approximately 10-15 nM PMA. Treatment with PMA does not result in increased binding of NK cells to YAC-1 targets as demonstrated by single-cell assay. In addition, treatment of young NK cells with 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H-7), a very potent PKC inhibitor, significantly suppressed NK activity (65% of control). Therefore, we conclude that the age-related decline in murine NK activity may reside in the early signalling events leading to triggering of PKC.

Microglial cell-mediated anti-Candida activity: temperature, ions, protein kinase C as crucial elements

An in vitro established microglial cell line, BV-2, constitutively exhibits high levels of anti-Candida activity. To elucidate the cascade of events leading to the accomplishment of such activity, we studied its dependence on temperature and ion availability. The role of protein kinases has also been studied by the specific inhibitors, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7) and N-(2-guanidinoethyl)-5-isoquinoline sulfonamide hydrochloride (HA 1004). We found that (a) the BV-2 cell/Candida conjugate formation is a discrete step, temperature-, ion- and protein kinase-independent; (b) the phagocytic event, which is protein kinase-independent, is significantly impaired by temperature decrease and ion deprivation; (c) the fulfillment of anti-Candida effects is strictly dependent upon temperature, ion availability and functional protein kinase. Functional protein kinase C, but not other kinases, is required for the accomplishment of anti-Candida activity, which, in fact, is selectively abrogated by H7 but not HA. Furthermore, protein kinase C activators, such as 12-O-tetradecanoylphorbol 13-acetate (TPA) or 1-oleoyl-2-acetyl glycerol (OAG), consistently potentiate BV-2 cell-mediated anti-Candida activity, the phenomena being dose-dependent. These results indicate that the multistep events leading a microglial cell to express anti-Candida activity can be dissected and differentiated for biochemical and biological demands, the latest along the cascade being the most demanding steps.

Basic fibroblast growth factor and interleukins 4 and 6 stimulate the release of IFN-gamma by individual NK cells

Both the secretory and cytotoxic activity of natural killer (NK) cells are known to be regulated by such cytokines as interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In the present study we have used the reverse hemolytic plaque assay to investigate either the direct effects of the protein kinase activator, phorbol myristate acetate (PMA), or exposure to recombinant human interleukins 2, 4, and 6 (IL-2, IL-4, and IL-6) tumour necrosis factor alpha (TNF-alpha) and basic fibroblast growth factor (bFGF) on the release of IFN-gamma by individual, immunoidentified NK cells isolated from peripheral blood. This sensitive immunoassay was adapted and coupled with immunocytochemistry not only to immunophenotype and enumerate cells secreting IFN-gamma in a given cell population, but also to quantify the amount of this cytokine released per individual cell. These studies have confirmed mononuclear cells with the morphology of large granular lymphocytes and the immunophenotype of CD3-/CD16+ NK cells to be the predominant source of spontaneously released IFN-gamma in vitro. In contrast to this, fewer than 2% of the CD3+ T cells secreted detectable levels of this cytokine during the assay, irrespective of the stimulus applied. Whilst TNF-alpha had no significant effect on IFN-gamma release by NK cells, a 6-hr exposure to IL-2 or PMA stimulated an increase in the amount secreted per single cell. Furthermore, bFGF and interleukins 4 and 6 elicited a marked, dose-dependent stimulation of IFN-gamma secretion by this cell type. However, exposure to these cytokines did not alter the number of cells capable of releasing detectable levels of IFN-gamma during the assay. These studies demonstrate that (i) both the spontaneous and stimulated release of IFN-gamma by NK cells can be visualized and quantified at the single-cell level using this sensitive immunoassay, and (ii) bFGF and interleukins 2, 4, and 6, but not TNF-alpha, are potent stimulants of IFN-gamma secretion by CD3-/CD16+ NK cells.

An improved in vitro assay to quantitate chemotaxis of rat peripheral blood large granular lymphocytes (LGL)

We have developed an improved method to study the directed migration, or chemotaxis, of rat peripheral blood large granular lymphocytes (LGL) in vitro. A modified Boyden chamber technique was used to measure chemotaxis of LGL through polycarbonate filters that had been coated with different basement membrane components. LGL were found to adhere to collagen types I and IV, laminin and fibronectin. However, only collagen type IV was not in itself chemotactic for LGL. Migrated cells could be identified both morphologically and phenotypically as LGL on collagen type IV-coated filters after incubation with a chemotactic stimulus. LGL were found to display chemotaxis to a number of different stimuli, including the classical chemoattractant agents N-formyl-methionyl-leucyl-phenylalanine, leukotriene B4, and complement fragments present in activated sera. However, the degree of response to these stimuli was much less than that of isolated peripheral blood neutrophils or monocytes. In contrast, all three cell types showed increased chemotaxis to the diacyl glycerol analog 1-oleoyl 2-acetyl glycerol (OAG), which induced a 4-14 fold stimulation of migration. Induction of chemotaxis of LGL by OAG was time and dose-dependent, as confirmed using checkerboard assays. In summary, we have developed a rapid, quantitative method to measure chemotaxis of LGL in vitro. This technique may now be utilized to identify naturally occurring chemoattractants for LGL and to study the intracellular and regulatory events associated with LGL migration.

Cadmium inhibits spontaneous (NK), antibody-mediated (ADCC) and IL-2-stimulated cytotoxic functions of natural killer cells

Cadmium (Cd2+), an environmental contaminant, has been shown to inhibit, even if not totally, natural killer (NK) cell-mediated cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood lymphocytes in a dose- and time-dependent manner. The presence of Cd2+ during the early period of the cytotoxic assay was needed to obtain maximal inhibition. Preincubation of either effector or target cells with Cd did not result in any inhibitory effect. Cd2+ also inhibited the cytotoxic activities of effector cells prestimulated with IL-2 for 18 h or 4 days, which mostly consist of NK cells. Our results indicate that Cd2+ did not block effector-target conjugate formation, but rather interfered with the hydrolysis of phosphoinositides, as shown by the decrease of inositol trisphosphate (IP3), which is known to release stored Ca2+.

HIV infection and natural killer cytotoxicity in hemophilic patients

In this study we analyzed the ability of peripheral blood mononuclear cells (PBMC) from hemophilic patients (He) with negative or positive serology for the human immunodeficiency virus (HIV), to increase natural killer (NK) cytotoxicity upon stimulation with physiological and non physiological agents. Purified interleukin-2 (IL-2), the interferon (IFN)-inducer polyinosinic polycytidylic acid (PIC), recombinant alpha- and gamma-IFN and the protein kinase activator phorbol myristate acetate (PMA) were used as stimulatory agents. The NK functional response was correlated with the presence of PBMC bearing phenotypic markers of activated cells (IL-2 receptor, IL-2R) and of different NK cell maturation stages. Our results demonstrate that NK effector cells with slight lytic activity (Leu 7+ CD16-) predominated in HIV+ He patients. On the other hand the occurrence of IL-2R positive cells was similarly high in both HIV+ and HIV- individuals and was probably more related to chronic replacement treatment with Factor VIII or Factor IX concentrates than to HIV infection. The ability to respond to physiological NK regulators such as IL-2 and IFNs, or to the IFN-inducer PIC was impaired in HIV+ He, especially in HIV+ LAS individuals, suggesting that the inability of these cells to increase NK cell activity after appropriate induction was due to an intrinsic defect. Since phosphoinositide turnover and subsequent protein kinase C activation are thought to be part of the physiological mechanism of NK cytotoxicity, we studied the effect of PMA on PBMC from each group of patients. The ability to respond to PMA was lost only in PBMC from HIV+ LAS patients, indicating that impairment of the NK lytic mechanism progresses as the disease gets worse.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of the natural killer cell deficiency in AIDS

Deficiency in natural killer (NK) cell activity is a common feature of acquired immune deficiency syndrome (AIDS). This is part of a general immune dysfunction in AIDS and may lead to progression of the disease, since NK cells are known to be involved in protection against tumors and against viral infections. The lack of immunological surveillance by NK cells of the growth of pathogens that activate the HIV-1 tat infectivity gene may also favor progression to AIDS. The pathogenesis of NK cell deficiency in AIDS is not known. Previous studies have shown that NK cells from AIDS patients are able to bind but not to lyse the target cell line K562. This results from an inability to rearrange the cytoskeleton microtubular (MT) system and to release the natural killer cytotoxic factor (NKCF). This report by Maria Caterina Sirianni and colleagues evaluates the possible mechanisms leading to this NK cell deficiency.

Measurement of cytokine release by human cells. A quantitative analysis at the single cell level using the reverse haemolytic plaque assay

The reverse haemolytic plaque assay has been adapted to detect and measure the release of such cytokines as interleukin-1, -2 and -6, GM colony-stimulating factor or interferon-gamma by individual human cells derived from either peripheral blood or enzymatically dispersed breast carcinomas. Since each of these peptides is released by more than one cell type, this in vitro assay has been coupled with immunocytochemistry to identify the particular cell type(s) contributing to the release of each cytokine. This technique is useful in (i) obviating the need for purification of a given cell type prior to estimating cytokine release, and (ii) evaluating quantitative differences in secretion amongst cells of a particular type. Such a method has the additional advantage over most alternative methods applied at the single cell level in that the cells remain viable at the end of the assay and can be used in further studies. This assay thus provides a powerful new tool in the investigation of the role of cytokines in both the normal modulation of the immune system and the development of such diseases as neoplasia.