Phorbol esters enhance spontaneous cytotoxicity of human lymphocytes, abrogate Fc receptor expression, and inhibit antibody-dependent lymphocyte-mediated cytotoxicity

Phorbol esters with tumor promoter activity enhance the spontaneous cytotoxicity of human lymphocytes against a variety of target cell lines, with an efficiency that correlates with their potency as tumor promoters or skin irritants. Analysis of surface marker expression of the lymphocytes cytotoxic after treatment with phorbol ester identified the cytotoxic cell subset as that containing natural killer cells. Although gamma-interferon (IFN gamma) is produced by T cells treated with phorbol esters, IFN gamma is probably not the mediator of enhancement of natural killer cell activity, because anti-IFN gamma antibodies failed to block this enhancement. Spontaneous cell-mediated cytotoxicity is inhibited when phorbol esters are present during the cytotoxic assay, but is enhanced when the effector cells are pretreated with these agents. On the other hand, antibody-dependent cytotoxicity mediated by lymphocytes is inhibited by phorbol ester pretreatment of the effector cells or by phorbol esters present during the cytotoxic assay. Treatment of lymphocytes with phorbol esters at 37 degrees C, but not at 4 degrees C, completely abrogates in 1 to 2 hr the expression of the receptor for the Fc fragment of IgG, as detected by rosette formation with IgG-sensitized erythrocytes and by reactivity with anti-Fc receptor antibodies. The inhibition of antibody-dependent cytotoxicity by phorbol esters is probably secondary to their effect on the Fc receptor.     

Divergence in activation by poly I:C of human natural killer and killer cells

Summary Interferons consistently enhance spontaneous cellular cytotoxicity (SCC) mediated by natural killer (NK) cells. More controversial is the ability of interferons to enhance antibody-dependent cellular cytotoxicity (ADCC) mediated by killer (K) cells. Since NK and K cells appear to represent overlapping subpopulations of lymphocytes, the present study was undertaken to examine in greater detail the relationship between NK and K cell functional modulation by the potent interferon inducer, poly I:C. Utilizing peripheral mononuclear cells from a panel of 21 healthy individuals, treatment in vitro with poly I:C resulted in modulation of both SCC and ADCC. SCC was significantly enhanced in 52 of a series of 55 trials (95%), whereas ADCC was significantly enhanced in parallel in only 18 of the trials (33%). Cells which mediated enhanced ADCC were plastic-nonadherent, which is characteristic of K cells. SCC was consistently enhanced in all but two of the 14 individuals who were tested two or more times. By contrast, the ability of poly I:C to enhance ADCC varied between trials in 11 of these individuals. In the other three, ADCC enhancement never occurred. No correlation existed between SCC and ADCC augmentation despite use of the same target cell to assess the two lytic activities in parallel. Poly I:C exclusively enhanced SCC in 36 trials (65%) and exclusively enhanced ADCC in two trials (4%). Discordance between SCC and ADCC enhancement also occurred in three of eight trials (38%) in which lymphocytes were treated directly with interferon a. Results in long-term (18-h) ⁵¹Cr-release assays indicated that poly I:C accelerated the kinetics of ADCC without affecting the proportion of target cells lysed by K cells. By contrast, an increased proportion of target cells was killed by poly I:C-stimulated NK cells. These results suggest that the controversy concerning relative interferon effects upon NK and K cells derives from differences both quantitative and qualitative in nature. K cell activity is enhanced but at a relatively low frequency. Enhancement of NK cell activity is selective in the sense that it occurs independently of and with greater frequency than enhancement of K cell activity. Distinct biological mechanisms may, therefore, be involved in regulation and expression of NK and K cell activation by interferons.     

IL-27 Enhances the Expression of TRAIL and TLR3 in Human Melanomas and Inhibits Their Tumor Growth in Cooperation with a TLR3 Agonist Poly(I:C) Partly in a TRAIL-Dependent Manner

Interleukin (IL)-27 is a member of the IL-6/IL-12 cytokine family and possesses potent antitumor activity, which is mediated by multiple mechanisms. Toll-like receptor (TLR)3 is the critical sensor of the innate immune system that serves to identify viral double-stranded RNA. TLR3 is frequently expressed by various types of malignant cells, and recent studies reported that a synthetic TLR3 agonist, polyinosinic-polycytidylic acid [poly(I:C)], induces antitumor effects on malignant cells. In the present study, we have explored the effect of IL-27 on human melanomas and uncovered a previously unknown mechanism. We found that IL-27 inhibits in vitro tumor growth of human melanomas and greatly enhances the expression of TNF-related apoptosis inducing ligand (TRAIL) in a dose-dependent manner. Neutralizing antibody against TRAIL partly but significantly blocked the IL-27–mediated inhibition of tumor growth. In addition, IL-27 and poly(I:C) cooperatively augmented TRAIL expression and inhibited tumor growth. The cooperative effect could be ascribed to the augmented expression of TLR3, but not retinoic acid-inducible gene-I or anti-melanoma differentiation-associated gene 5, by IL-27. The inhibition of tumor growth by the combination was also significantly abrogated by anti-TRAIL neutralizing antibody. Moreover, IL-27 and poly(I:C) cooperatively suppressed in vivo tumor growth of human melanoma in immunodeficient mice. Taken together, these results suggest that IL-27 enhances the expression of TRAIL and TLR3 in human melanomas and inhibits their tumor growth in cooperation with poly(I:C), partly in a TRAIL-dependent manner. Thus, IL-27 and the combination of IL-27 and poly(I:C) may be attractive candidates for cancer immunotherapy.     

Natural killing can be independent of interferon generated in vitro

PBL produce interferon in response to culture with the tumor cell line K562, but this production of interferon does not correlate with natural cytotoxicity. A basal level of natural killing is independent of interferon generated in vitro. We base this conclusion on the following findings: (i) natural killing and interferon level are not temporally correlated; (ii) preincubation of lymphocytes at 37 °C greatly reduces their ability to produce interferon but does not affect their lytic capacity against K562; and, (iii) addition of an anti-interferon antibody has no effect on NK. We conclude that NK against K562 is not dependent upon or correlated with the level of interferon generated during in vitro assay.     

Sequential metabolic events and morphological changes during in vivo large granular lymphocyte activation and proliferation

Interferon (IFN) and IFN inducers are known to boost natural killer (NK) activity in vivo and in vitro. In vivo enhancement of NK activity results from activation of preexisting NK cells as well as from an increased number of large granular lymphocytes (LGL), with a portion of them undergoing cell division. Our study was addressed to analyze the sequence of metabolic events occurring within the LGL population of Fischer rats treated with poly(I:C), as an IFN inducer. The increase in cytotoxic activity and LGL number in the peripheral blood already reached maximal levels by 12 hr after poly(I:C) injection, remained on a plateau 24 to 48 hr later, then slightly decreased on Day 4, and returned to control levels by Day 6. A similar kinetics was observed for RNA synthesis. In contrast DNA synthesis first increased at 24 hr, peaked at 48 hr, then decreased on Day 4, and was not detectable on Day 6. Percoll fractionation resulted in 92-97% of LGL in fraction 1, and cells in this fraction accounted for the increase of cytotoxicity as well as for newly synthesized RNA and DNA. However, LGL recovered on Day 1 or 2 after poly(I:C) stimulation displayed quite heterogeneous morphology, and a number of mitotic configurations were seen on Day 2 within the LGL population. Our results indicate that the boosting of NK activity by poly(I:C) is always associated with an increase in LGL numbers, the enhanced lytic capacity is associated in vivo with new RNA synthesis by the NK cells, and only in a later phase NK cell proliferation may account for the increase in LGL numbers.     

Natural cytotoxicity in lymphatic metastasis

Summary The survival of cloned variants of the BSp73 tumor differing in susceptibility to natural killer (NK) and macrophage-mediated cytotoxicity in vitro was evaluated in syngeneic animals. The cytocidal effect was assayed by whole-body determination of (¹²⁵I)5-iodo-2-deoxyuridine (¹²⁵IUdR) retention in intact animals and in animals depleted of phagocytes and/or radiation-sensitive lymphocytes. The following results were obtained: (1) In the peritoneal cavity, survival of the susceptible tumor cells (variant AS) was significantly higher in rats pretreated with radiation and silica than in untreated rats. (2) Cold target competition, response modification by C. parvum, and correlation of label excretion with survival of animals supported the notion that excretion rates of radioactivity were in fact determined by natural cytotoxicity in vivo. (3) Tumor cells resistant to natural cytotoxicity in vitro (variant ASML) were nevertheless killed in vivo (IP) by NK cells and macrophages. (4) Additional elements of tumor cell destruction were active upon IV injection of both AS- and ASML-derived cells, since rapid label excretion was observed irrespective of irradiation and silica treatment or addition of excess unlabeled competitor cells.The apparent increase in susceptibility of ASML cells in vivo might be due to a shift in phenotype induced by microenvironmental factors. No evidence was gained that differences in metastatic capacity exhibited by the variants might relate to differential action of natural cytotoxicity on these cells.     

Regulation of human natural killing. II. Protective effect of interferon on NK cells from suppression by PGE2

Activation of human natural killer (NK) cells in vitro with interferon (IFN) and poly I:C results in a partial loss of sensitivity of these cells to suppression by PGE2. The acquired resistance to suppression can be induced with the large granular lymphocytes (LGL) in the absence of monocytes. With K562, HSB, and CEM used as NK target cells, the IFN-induced resistance to suppression by PGE2 is observed with all three target cells. Furthermore, ADCC activity of IFN-activated cells against tumor (SB-TNP) and erythroid (CRC-TNP) target cells is also less susceptible to suppression by PGE2. The dual effect of IFN on NK cells is prompt; the augmentation of NK activity and the acquired resistance to suppression by PGE2 can be seen after 3 hr of treatment with IFN. Both of these characteristics seem to be quite stable for at least 24 hr. Spleen cells from mice (CBA, C3H, and BALB/c nude) treated in vivo with poly I:C also acquire partial resistance to suppression by PGE2. Our data therefore suggest that IFN-stimulated NK cells are protected from suppression by PGE2. Biologically, the IFN-induced protective effect may be beneficial to host resistance to neoplasia.     

Suppression of Lewis carcinoma metastasis in mice by an interferon-inducing vasodilator curantil

The intravascular (iv) or intramuscular (im) inoculations of a suspension of Lewis carcinoma cells induced metastatic tumor nodules in the lungs of C57Bl/6 mice. The administration of curantil (dipyridamole) (500 mg per 20 g-mouse, per os) once a week beginning one day after iv tumor cells inoculation (2 X 10(5) cells) reduced 4-fold the number of tumor nodules. The administration of curantil one day after im tumor cells inoculation (2 X 10(6) cells) reduced 2-fold the number of tumor nodules. The combined treatment of curantil (4-, 10-days after inoculation) and well-known inducer of interferon poly I:poly C (50 mg per 20 g-mouse, 1-, 7-, 14-days after inoculation tumor cells) had no synergistic effect.     

Preferential involvement of mitochondria in Toll-like receptor 3 agonist-induced neuroblastoma cell apoptosis,but not in inhibition of cell growth

Double-stranded RNA (dsRNA) can mediate its therapeutic effect through Toll-like receptor 3 (TLR3) expressed on tumor cells including neuroblastoma. We used synthetic dsRNA polyinosinic-polycytidylic acid [Poly(I:C)] as a TLR3 agonist to treat TLR3-expressing SK-N-AS neuroblatoma (NB) cells. We found up-regulation of endoplasmic reticulum (ER) stress proteins glucose-regulated protein 78 and inositol-requiring enzyme 1. Bafilomycin A1, an inhibitor of ER function, effectively blocked poly(I:C)-induced activation of caspase-8, -9, and -3, MnSOD and glutathione peroxidase 1 and reduced poly(I:C)-induced SK-N-AS apoptosis. Pan caspase inhibitor and inhibitor of caspase-9, but not of caspase-8, inhibited poly(I:C)-induced activated caspase-3 expression. Rho zero (ρ⁰)-SK-N-AS cells were resistant to poly(I:C)-induced mitochondrial reactive oxygen species production and apoptosis, but not to inhibition of cell growth, as compared to parent SK-N-AS cells. Taking together, these findings suggest that mitochondria are preferentially involved in poly(I:C)-induced NB cell apoptosis, but not in inhibition of cell growth. A crosstalk between mitochondria and ER is implicated.     

Natural resistance in mice against Friend leukemia cells. II. Studies with in vivo passaged interferon-sensitive and interferon-resistant cell clones

Experiments were designed to test the presence of antitumor natural resistance (NR) in DBA/2 mice against highly oncogenic in vivo passaged histocompatible Friend leukemia cells (FLC-V). NR was measured in vivo as rapid clearance of radiolabeled cells from different organs or as growth inhibition in lethally irradiated mice. Interferon-sensitive (745) or interferon-resistant (3C18) lines were used. Organ clearance studies showed that young recipients eliminate cells more rapidly than old mice. Moreover, depressive (e.g., cyclophosphamide or carrageenen) or enhancing (e.g., poly (I:C) or Friend leukemia virus infection) agents of NR function modulate accordingly leukemia cell clearance. Similar results were obtained testing tumor growth in lethally irradiated hosts, although modulating agents were substantially less effective in this system. Both FLC-745-V and FLC-3C18-V lines were equally susceptible to NR. Therefore, these data provide further support to the hypothesis that exogenous IFN capable of suppressing the growth of both lines could act via enhancement of the NR function.     

Selenium and immune cell functions. II. Effect on lymphocyte-mediated cytotoxicity

Selenium (Se) is an essential nutritional factor with a chemopreventive potential. This study examined the ability of C57BL/6J mice, maintained for 8 weeks on Se-deficient (0.02 ppm Se), normal (0.20 ppm Se), or Se-supplemented (2.00 ppm Se) Torula yeast-based diets, to generate cytotoxic lymphocytes (CTL) and to destroy tumor cells. CTL were generated in vivo by intraperitoneal immunization with P815 cells and in vitro by allogeneic stimulation of cells from animals maintained on a normal diet in media supplemented with 1 x 10(-9) to 1 x 10(-6) M Se (as selenite). Lymphocytes from animals maintained on the Se-supplemented diet had a greater ability to destroy tumor cells than lymphocytes from animals maintained on the normal diet, whereas Se deficiency reduced the cytotoxicity. The effects on cytotoxicity were accompanied by parallel changes in the levels of lymphotoxin produced. The greatest enhancement of tumor cytodestruction occurred with supplementation of 1 x 10(-7) M Se, whereas with 1 x 10(-6) M there was inhibition of the cytotoxic responses. The stimulatory effect of Se occurred during the phase of CTL generation rather than during the lytic phase of cytotoxicity. These results indicated that Se supplementation enhances CTL generation and the ability of a host to destroy malignant cells, whereas Se deficiency has the opposite effect.     

Induction of natural killer cell activity of thoracic duct lymphocytes by polyinosinic-polycytidylic acid (poly(I:C)) or interferon

Natural killer (NK) cell activity of thoracic duct lymphocytes (TDL) was examined in normal mice and in mice treated with polyinosinic-polycytidylic acid (poly(I:C) and interferon (IFN). TDL from mice treated with phosphate-buffered saline (PBS) expressed little or no NK cell activity against YAC-1 target cells at effector-to-target ratios of up to 200:1, even after in vitro treatment with murine L-cell IFN. In contrast, TDL from poly(I:C)- or IFN-treated mice expressed significant NK activity, which correlated with the significantly higher NK activity of splenocytes from these mice compared to the NK activity of splenocytes from PBS-treated mice. These data indicate that although TDL from normal mice express no detectable NK cell activity, NK cell activity can be induced in TDL by in vivo treatment with poly(I:C) or IFN.     

The viral mimic, polyinosinic:polycytidylic acid, induces fever in rats via an interleukin-1-dependent mechanism

Polyinosinic:polycytidylic acid (poly I:C) is a synthetic double-stranded RNA that is used experimentally to model viral infections in vivo. Previous studies investigating the inflammatory properties of this agent in rodents demonstrated that it is a potent pyrogen. However, the mechanisms underlying this response have not been fully elucidated. In the current study, we examined the effects of peripheral administration of poly I:C on body temperature and cytokine production. Male rats were implanted with biotelemetry devices and randomly assigned to one of the following three groups: poly I:C + saline, poly I:C + interleukin-1 receptor antagonist (IL-1ra), or saline + saline. Maximal fever of 1.6 degrees C above baseline was observed 3 h after an intraperitoneal injection of poly I:C (750 microg/kg). Pretreatment with IL-1ra diminished this response by >50% (maximum body temperature = 0.6 degrees C above baseline). Plasma IL-6 concentration increased fivefold 2 h post-poly I:C compared with saline-injected rats; levels returned to baseline 4 h postinjection. Pretreatment with IL-1ra prevented this rise in IL-6. Plasma tumor necrosis factor (TNF)-alpha was also increased more than fourfold 2 h postinjection but remained unaffected by IL-1ra treatment. IL-1beta and cyclooxygenase-2 mRNA were significantly upregulated in the hypothalamus of poly I:C-treated animals. Finally, poly I:C decreased food intake by 30%, but this response was not altered by pretreatment with IL-1ra. These results suggest that poly I:C induces fever, but not anorexia, through an IL-1 and prostaglandin-dependent mechanism.     

The immunological basis of tumor rejection: the absolute dependence of the effector arm on sensitized T cells after chemoimmunotherapy of a murine sarcoma

The mechanisms of tumor rejection were investigated by using a therapeutic model system involving treatment of C57BL/6J (B6) mice bearing the syngeneic MCA/76-9 or the unrelated MCA/76-64 sarcomas with cytoxan and tumor-sensitized T lymphocytes. Separated tumor-associated T lymphocytes (TAL) and tumor-associated macrophages (TAM) isolated from the regressing tumors 8 to 10 days after combination therapy expressed relatively specific cytotoxicity in vitro, whereas the unseparated tumor-associated cells (TAC), consisting of a mixture of TAL and TAM, expressed nonspecific cytotoxicity. TAM-mediated cytotoxicity was not dependent on the presence of TAL, as shown by T cell depletion of TAM or TAC cultures with the use of monoclonal anti-Thy-1 or anti-Lyt-2 antibody and complement. In contrast, the nonspecific cytotoxicity was dependent on the presence of T cells. In vivo assays using the Winn test failed to confirm certain aspects of the in vitro data. Without exception, the TAC inhibited tumor growth in an immunologically specific manner, having no effect on the growth of the unrelated B6 sarcoma. T cell depletion completely abrogated in vivo cytotoxicity. Specificity of tumor growth inhibition was confirmed in a bystander experiment in which TAC were mixed with both tumor cell types and were injected into recipient B6 mice. Tumors grew under these conditions, but the tumor that grew consisted only of those tumor cells toward which TAC cytotoxicity was not specifically directed. A bioassay indicated that the specifically immune antitumor effects at the site of regression were initiated between days 3 and 7 after combination therapy. By days 7 and 9, few tumorigenic stem cells could be detected at the tumor site. However, T cell depletion of the TAC isolated on days 8 to 10 resulted in enhanced tumor growth when the depleted TAC were injected into recipient mice. The conclusions reached were that tumor rejection was absolutely dependent on T cell participation at the tumor site, and that if TAM were involved, they required the presence of TAL and did not express nonspecific antitumor cytotoxicity. Indeed, the accelerated tumor growth seen in the absence of TAL suggested the possibility that TAM were growth stimulatory.     

Immunomodulation of human leukocytes by staphylococcal enterotoxin A: augmentation of natural killer cells and induction of suppressor cells

Staphylococcal enterotoxin A (SEA), a protein isolated from culture supernatants of Staphylococcus aureus, is a potent T-cell mitogen and an inducer of interferon-gamma (IFN-gamma). We report here that SEA exhibits a number of significant in vitro immunomodulatory functions. In vitro treatment of human peripheral blood monocyte-depleted lymphocytes with SEA resulted in significant augmentation of their natural killer cytotoxicity against target cells from hemopoietic (K562, Daudi) or solid (melanoma, lung, colon) human tumor cell lines. SEA was found to be more effective than interferons-alpha (natural or Escherichia coli-derived) in augmenting natural killer (NK) cytotoxicity of peripheral blood lymphocytes. Studies on the kinetics of the augmentation revealed a significant increase of NK within 3 hr of in vitro treatment with SEA at 37 degrees C. A neutralizing monoclonal antibody specific for human IFN-gamma did not affect the augmentation of natural killer cytotoxicity by SEA, suggesting that SEA augmented natural killer cytotoxicity primarily by a mechanism not involving induction of interferon-gamma. Furthermore, in vitro treatment with SEA resulted in significant augmentation of antibody-dependent cell-mediated cytotoxicity and of natural killer-like cytotoxicity, generated in mixed lymphocyte culture, against the K562 targets. Induction of suppressor cells to proliferative responses of autologous or allogeneic mononuclear cells to phytohemagglutinin (PHA) or to allogeneic cells in mixed lymphocyte culture was observed after in vitro treatment of peripheral blood mononuclear leukocytes with SEA for 24 or 48 hr at 37 degrees C. In addition, the presence of SEA in mixed lymphocyte cultures (MLC) resulted in significant inhibition of the generation of specific T-cell-mediated cytotoxicity in MLC. These results suggest that SEA, which may be involved in S. aureus infections and in treatment with extracorporeal perfusion systems over S. aureus columns, can regulate a number of significant lymphoid functions.     

Poly(I:C) enhances the susceptibility of leukemic cells to NK cell cytotoxicity and phagocytosis by DC

α active specific immunotherapy aims at stimulating the host's immune system to recognize and eradicate malignant cells. The concomitant activation of dendritic cells (DC) and natural killer (NK) cells is an attractive modality for immune-based therapies. Inducing immunogenic cell death to facilitate tumor cell recognition and phagocytosis by neighbouring immune cells is of utmost importance for guiding the outcome of the immune response. We previously reported that acute myeloid leukemic (AML) cells in response to electroporation with the synthetic dsRNA analogue poly(I:C) exert improved immunogenicity, demonstrated by enhanced DC-activating and NK cell interferon-γ-inducing capacities. To further invigorate the potential of these immunogenic tumor cells, we explored their effect on the phagocytic and cytotoxic capacity of DC and NK cells, respectively. Using single-cell analysis, we assessed these functionalities in two- and three-party cocultures. Following poly(I:C) electroporation AML cells become highly susceptible to NK cell-mediated killing and phagocytosis by DC. Moreover, the enhanced killing and the improved uptake are strongly correlated. Interestingly, tumor cell killing, but not phagocytosis, is further enhanced in three-party cocultures provided that these tumor cells were upfront electroporated with poly(I:C). Altogether, poly(I:C)-electroporated AML cells potently activate DC and NK cell functions and stimulate NK-DC cross-talk in terms of tumor cell killing. These data strongly support the use of poly(I:C) as a cancer vaccine component, providing a way to overcome immune evasion by leukemic cells.     

Effect of acute or daily cocaine administration on cellular immune response and virus infection in mice

The effects of in vivo cocaine administrations on cellular cytotoxicity were studied. Cocaine induced a dose-related immunosuppression of natural killer cell activity, with maximal depression at 1-5 mg/kg. In addition, the degree of inhibition following a single intraperitoneal (i.p.) or intravenous cocaine dose (acute treatment, 1 mg/kg) was similar to that after repeated administration (subchronic treatment: 1 mg/kg/day i.p. for 7 consecutive days or subcutaneous administration by Alzet 2001 osmotic minipumps). T cells from cocaine-treated mice failed to generate cytotoxic T lymphocytes (CTL) in mixed lymphocyte cultures and acute or subchronic cocaine treatment also inhibited CTL generation in vivo. On the other hand, acute administration induced a very rapid (24-hour) inhibition of natural cytotoxicity, with a return to normal within 72 h after treatment. By contrast, repeated doses led to more protracted immunologic consequences and a delayed recovery (144 h). The effect of cocaine on susceptibility to influenza virus (PR8) infection was also investigated. Both acute and subchronic treatment significantly decreased resistance to PR8 infection. The results clearly indicate that cocaine has a potent suppressive effect on cellular immunity and that abuse can adversely affect the outcome of infectious diseases.     

Potential role of natural killer cells in controlling tumorigenesis by human T-cell leukemia viruses.

Human T-cell leukemia virus (HTLV) is the etiologic agent of adult T-cell leukemia (ATL), a malignancy of T lymphocytes that is characterized by a long latency period after virus exposure. Intraperitoneal inoculation of severe combined immunodeficient (SCID) mice with HTLV-transformed cell lines and ATL tumor cells was employed to investigate the tumorigenic potential of HTLV type I (HTLV-I)-infected cells. In contrast to inoculation of ATL (RV-ATL) cells into SCID mice, which resulted in the formation of lymphomas, inoculation of HTLV-I- and HTLV-II-transformed cell lines (SLB-I and JLB-II cells, respectively) did not result in tumor formation. Immunosuppression of SCID mice, either by whole-body irradiation or by treatment with an antiserum, anti-asialo GM1 (alpha-AGM1), which transiently abrogates natural killer cell activity in vivo, was necessary to establish the growth of tumors derived from HTLV-transformed cell lines. PCR and flow cytometric studies reveal that HTLV-I-transformed cells are eliminated from the peritoneal cavities of inoculated mice by 3 days postinoculation; in contrast, RV-ATL cells persist and are detected until the mice succumb to lymphoma development. The differing behaviors of HTLV-infected cell lines and ATL tumor cells in SCID mice suggest that ATL cells have a higher tumorigenic potential in vivo than do HTLV-infected cell lines because of their ability to evade natural killer cell-mediated cytolysis.     

Activity of dsRNA-dependent protein kinase in rat lymphoid cells under the effect of X-ray irradiation

The activity of dsRNA-dependent protein kinase, which is the key enzyme of the interferon signal system, was studied in the rat spleen and thymus lymphocytes under the influence of X-ray irradiation at 0.5 and 1 Gy doses and interferon inducers administration. An increase of the enzyme activity was established in the presence of FGA, concanavaline A, poly(I).poly(C) in vitro. The effect is intensified under the irradiation by 0.5 Gy dose. The protein kinase activity in lymphocytes is amplified in proportion to poly(I).poly(C) concentration, that was most pronounced in the irradiated animals. The comparative analysis of the action of interferon inducers on the dsRNA-dependent protein kinase activity was carried out. Two biological systems were used: in vivo (when the preparations were injected to the experimental animals) and in vivo (under the preincubation of isolated lymphocytes with the inducers). It was shown that the combined action of radiation and interferon inducers causes the stimulation of dsRNA-dependent protein kinase activity.