Anti-viral strategies of cytotoxic T lymphocytes are manifested through a variety of granule-bound pathways of apoptosis induction

Cytotoxic T cells and natural killer cells together constitute a major defence against virus infection, through their ability to induce apoptotic death in infected cells. These cytolytic lymphocytes kill their targets through two principal mechanisms, and one of these, granule exocytosis, is essential for an effective in vivo immune response against many viruses. In recent years, the authors and other investigators have identified several distinct mechanisms that can induce death in a targeted cell. In the present article, it is postulated that the reason for this redundancy of lethal mechanisms is to deal with the array of anti-apoptotic molecules elaborated by viruses to extend the life of infected cells. The fate of such a cell therefore reflects the balance of pro-apoptotic (immune) and anti-apoptotic (viral) strategies that have developed over eons of evolutionary time.

The 2-5A system in viral infection and apoptosis

The 2-5A system is an established endogenous antiviral pathway. Interferon treatment of cells leads to an increase in basal, but latent, levels of 2-5A-dependent RNase (RNase L) and the family of 2'-5' oligoadenylate synthetases (OAS). Double-stranded RNA, thought to be derived from viral replication intermediates, activates OAS. Activated OAS converts ATP into unusual short 2'-5' linked oligoadenylates called 2-5A [ppp5'(A2'p5')2A]. The 2-5A binds to and activates RNase L which cleaves single stranded RNA with moderate specificity for sites 3' of UpUp and UpAp sequences, and thus leads to degradation of cellular rRNA. During apoptosis, generalized cellular RNA degradation, distinct from the differential expression of mRNA species that may regulate specific gene expression during apoptosis, has been observed. The mechanism of RNA breakdown during apoptosis has been commonly considered a non-specific event that reflects the generalized shut down of translation and homeostatic regulation during cell death. Due to the similar RNA degradation that occurs during both apoptosis and viral infection we investigated the potential role of RNase L in apoptosis. To investigate whether RNase L activity could lead to apoptosis, NIH3T3 cells were transfected with a lac-inducible vector containing the human RNase L gene. Treatment of these cells with isopropylthiogalactoside (IPTG) caused loss of cell viability that was confirmed as an apoptotic cell death by morphological and biochemical criteria. Similarly, specific allosteric activation of endogenous RNase L by introduction of 2-5A directly into L929 cells also induced apoptosis. In L929 cells poly(I).poly(C) treatment in combination with interferon caused an increase in apoptosis whereas neither interferon or double stranded RNA alone altered cell viability. Therefore, increased expression or activation of RNase L causes apoptosis. Inhibition of RNase L, specifically with a dominant negative mutant, suppressed poly(I)Ypoly(C)-induced apoptosis in interferon-primed fibroblasts. Poliovirus, a picornovirus with a single-stranded RNA genome, causes apoptosis of HeLa cells. Expression of the dominant negative inhibitor of RNase L in HeLa prevented virus-induced apoptosis and maintained cell viability. Thus, reduction or inhibition of RNase L activity prevents apoptosis. Both apoptosis and the 2-5A system can provide defense against viral infection in multicellular organisms by preventing production and therefore spread of progeny virus. RNase L appears to function in both mechanisms, therefore, initiation of apoptosis may be one mechanism for the antiviral activity of the 2-5A system.

Manganese superoxide dismutase (MnSOD) and autoantibodies against MnSOD in acute viral infections

Sera of 146 patients with acute EBV, HAV, HBV, CMV, HSV, and rubella virus infections, and sera from 35 healthy controls were tested for the antioxidant enzyme manganese superoxide dismutase (MnSOD). An enzyme immunoassay that detects all isomeres of the enzyme was developed. The mean MnSOD value of healthy controls was 107 ng/ml. In HAV, HBV and EBV infections characterized by viral replication in internal organs, there was an average 5-fold rise of serum MnSOD, whereas in viral infections with low direct cytopathogenity, such as rubella, CMV and HSV, the MnSOD levels showed only minor rises. These sera were also tested for autoantibodies against MnSOD using a novel sensitive indirect enzyme immunoassay. The average IgM anti-MnSOD concentration in sera of healthy controls was 112 GU. In sera of patients with acute HBV, CMV, HSV or rubella virus infections IgM anti-MnSOD values were only slightly raised above the cut-off level. In contrast, in some patients with acute EBV infections anti-MnSOD concentrations rose up to 20-fold of normal values. In HAV infections the same phenomenon was observed in patients who had reactivated EBV infections. These findings indicate that EBV may facilitate the B-cell response to MnSOD. These autoantibodies may inhibit the protective function of MnSOD and prolong the disease by oxygen injury. Our concept on the pathogenic effect of the autoantibodies against MnSOD emphasizes the importance of the antioxidant enzyme in viral infections.

The role of HMT (histamine N-methyltransferase) in airways: a review

Histamine N-methyltransferase (HMT) expressed in the epithelial and endothelial cells of the airways is a principal enzyme degrading histamine in the body. This brief review summarizes the recent advances in molecular biology related to the pathophysiological role of HMT in regulating airway functions.

Astrovirus infection in hatchling turkeys: alterations in intestinal maltase activity

Two experiments were conducted to determine intestinal disaccharidase activity in 1-day-old commercial turkey poults inoculated with astrovirus. Small intestinal samples were collected on days 0.5, 1, 3, and 7 postinoculation (PI) in Expt. 1 and on days 7, 10, and 14 PI in Expt. 2 and evaluated for specific maltase activity (SMA). Astrovirus infection was verified on day 7 PI by immune electron microscopy of intestinal contents. Inoculated poults developed diarrhea and a transient, significant decrease in intestinal SMA. SMA was significantly (P < 0.05) lower in astrovirus-inoculated poults than in control poults throughout the entire small intestine from day 3 through day 7 PI. However, SMA had returned to normal in inoculated poults by day 10 PI and was significantly higher than control values (P < 0.05) in all sections of the small intestine, except in the proximal jejunum, by day 14 PI. Decreased SMA caused by astrovirus infection resulted in disaccharide maldigestion, malabsorption, and subsequent osmotic diarrhea. As astrovirus was cleared from the intestinal tract, SMA was restored and diarrhea was resolved.

[2'-5' olygoadenylate synthetase activity in peripheral facial paralysis]

Interferons are produced in response to viral infection and play an important part in defense by their antiviral effects. An interferon-induced enzyme, 2'-5' oligoadenylate synthetase (2-5AS) also takes an important part of the system of defense against viral infections, and its activity elevates in nonspecific viral infections. This study was designed to evaluate the usefulness of examining serum 2-5AS activity and peripheral blood WBC 2-5AS (WBC 2-5AS) as diagnostic aids of viral infections that cause facial paralysis. Samples were obtained from 83 patients with Bell's palsy, 20 with Ramsay Hunt syndrome, 74 healthy individuals, and a total of 177 subjects. In 177, we measured serum 2-5AS level in 123 subjects, WBC 2-5AS level in 57, and both in 25. Serum 2-5AS levels in Bell's palsy (60 cases) ranged from 20 to 146 pmol/dl (average: 38.5). The range in Ramsay Hunt syndrome (13) was 20-333 (average: 59.0), and in healthy controls (50), it was 20-128 (average: 41.4). WBC 2-5AS level ranged from 20 to 5900 pmol/dl (average: 733.2) in Bell's palsy (23 cases), from 20-4540 (average: 1371.4) in Ramsay Hunt syndrome (7), and from 20-903 (average: 294.5) in healthy individuals (24). There were no statistically significant differences in serum 2-5AS activities. Otherwise, there was significant difference (p < 0.01) between healthy individuals and Patients with Ramsay Hunt syndrome in WBC 2-5AS activity. In Bell's palsy, 3 cases (13.0%) with markedly high WBC 2-5AS levels existed.(ABSTRACT TRUNCATED AT 250 WORDS)

Group II phospholipase A2 in sera of febrile patients with microbiologically or clinically documented infections

Group II phospholipase A2 (PLA2-II) is an inflammatory enzyme, which has been shown to be an acute-phase protein and to correlate with the severity of sepsis. In a prospective study, the concentration of PLA2-II in the sera of 46 patients with sepsis and nonseptic bacterial and viral infections was measured by a fluoroimmunoassay. The serum concentration of PLA2-II in patients with infections (median, 164.5 micrograms/L; range, 5.07-1,740 micrograms/L) was elevated 46-fold above normal concentrations (median, 3.61 micrograms/L; range, 1.32-25.25 micrograms/L). The concentration of PLA2-II was higher in patients with sepsis (median, 284.5 micrograms/L; range, 12.95-1,574 micrograms/L) and nonseptic bacterial infections (median, 210.6 micrograms/L; range, 5.07-1,740 micrograms/L) than in those with viral infections (median, 46.78 micrograms/L; range 11.46-275.9 micrograms/L) (P = .0042). The concentration of PLA2-II correlated well with the concentration of C-reactive protein (CRP) (r = .613, P = .0001) but not with the concentration of pancreatic PLA2 (r = .089, P = .365). Measuring the serum concentration of PLA2-II is useful as an adjunct to the determination of CRP concentrations for differentiating bacterial from viral infection.

Therapeutic potential of protein kinase C inhibitors

The serine/threonine protein kinase, protein kinase C (PKC) is a family of closely related isoforms which are physiologically activated by diacylglycerol generated by the binding of a variety of agonists to their cellular receptors. Free fatty acids may also play a role in activating PKC. The enzyme apparently mediates a wide range of signal transduction processes in cells and, therefore, inhibitors directed selectively against PKC may have wide-ranging therapeutic potential. This review highlights the evidence that inappropriate activation of PKC occurs in a number of disease states. Such evidence, however, is often seriously flawed because it relies on the use of phorbol esters, which are potent and direct PKC activators but may not mimic the physiological triggering of the enzyme in cells, or on the use of non-selective protein kinase inhibitors such as H7 and staurosporine. A new generation of bis-indolylmaleimides, derived from the lead provided by staurosporine, shows a high degree of selectivity for PKC over closely related protein kinases and such agents may provide more appropriate tools to investigate the role of PKC in cellular processes.

Thymidine kinases: the enzymes and their clinical usefulness

Thymidine kinases (TK) convert thymidine, or deoxythymidine (dT) to the respective monophosphate. TK occurs in many different procaryotic and eucaryotic species and different TK isoenzymes are found within the same eucaryotic cell. One isoenzyme (foetal, cytoplasmic, TK1) is associated with cell division while the other (adult, mitochondrial, TK2) is cell cycle independent. The relative isoenzyme activities in a tissue thus reflect the fraction of proliferating cells. The gene encoding TK1 has been cloned for many species and regulation of its expression is known to be complex. Increases in TK activity appear to correlate with the presence of human neoplasia and disease progression and regression have been reported to correlate with TK levels in many cancer types. TK estimations in human lymphoproliferative diseases have implicated this enzyme as an early marker of maldifferentiation. TK levels may also be increased in non-dividing mammalian cells infected with RNA or DNA viruses. Some virus encoded TK has been shown to differ biochemically, immunologically and in substrate specificity from the corresponding TK isoenzymes in target host cells thus facilitating the development of specific antiviral therapeutics. Further, TK1 in leukemic cells may differ biochemically from normal cellular TK1 such that tumor-specific TK may provide a target for tumor detection and therapy. TK quantitation has conventionally been performed in assays of enzyme activity using radiolabeled (3H or 125I) nucleoside substrates. The development of TK1-specific, non-radioisotope based immunoassays and the measurement of TK mRNA in tumour tissue using TK (DNA or RNA) probes may prove sufficiently valuable to be incorporated into the routine clinical management of human cancer.

Induction of a novel protein kinase in pupae of the silkworm Bombyx mori after infection with nuclear polyhedrosis virus

Protein kinases induced by Bombyx mori nuclear polyhedrosis virus in pupae of the silkworm B. mori were examined by activity gel analysis using phosvitin as a protein substrate. The method involved PAGE of the soluble fraction from pupae under native conditions and in the presence of SDS, followed by in situ renaturation of proteins and recovery of protein kinase activity in the intact gel. A novel protein kinase able to phosphorylate phosvitin was detected in the infected pupae from 2 days post-infection. This enzyme was not present in uninfected silkworms at any stage of the pupal period. The novel kinase activity was found by SDS-PAGE to be associated with a single polypeptide with an apparent M(r) of 50K. However, on electrophoresis under native conditions its activity was associated with a set of polypeptides with similar but not identical electrophoretic mobilities. Microheterogeneity of the catalytically active polypeptides suggests that the virus-induced protein kinase undergoes post-translational modification during the course of infection.

Effect of prostaglandin E2 on plasma lactic dehydrogenase activity in (NZB x NZW)F1 mice with a chronic infection of lactic dehydrogenase virus

The effect of prostaglandin E2(PGE2) on blood LDH values was investigated in (NZB x NZW)F1 mice with or without an established infection with lactic dehydrogenase virus (LDV). Plasma LDH decreased in infected mice treated with PGE2, but increased in infected mice treated with indomethacin, an inhibitor of PGE2. However no significant effect on LDH occurred in uninfected mice treated with PGE2 or indomethacin. To investigate the mechanisms of decreased LDH activities resulting from treatment with PGE2, clearance tests were performed. Clearance of LDH-5, but not LDH-1, was faster in PGE2-treated mice than in non-treated mice, whether or not they were infected with LDV. The results suggest that enhanced clearance of LDH-5 in mice treated with PGE2 may account for the fall in plasma LDH in LDV-infected mice.

Thymidine kinase: a tumor marker with prognostic value for non-Hodgkin's lymphoma and a broad range of potential clinical applications

Thymidine kinase (TK) is a cellular enzyme which is involved in a "salvage pathway" of DNA synthesis. It is activated in the G1/S phase of the cell cycle, and its activity has been shown to correlate with the proliferative activity of tumor cells. Additionally, certain viruses are able to induce cellular TK production and activity. Clinical studies have reported elevated serum TK levels in a variety of neoplasias. The majority of these studies concerned hematologic malignancies. TK seems to be a useful marker in non-Hodgkin's lymphoma, where it correlates with clinical staging and provides significant prognostic information on (progression-free) survival. Preliminary results in acute myeloid leukemia indicate that pretreatment serum TK values may predict the response to the first induction chemotherapy. Moreover, serum TK appears to have some clinical value in such solid tumors as prostate cancer, breast cancer, and small-cell lung cancer, whereas it is not a reliable marker of non-small-cell lung cancer and brain tumors.

Enhanced clearance of lactic dehydrogenase-5 in severe combined immunodeficiency (SCID) mice: effect of lactic dehydrogenase virus on enzyme clearance

The lactic dehydrogenase (LDH) level in plasma and the clearance of LDH in C.B-17 scid (severe combined immunodeficiency; SCID) mice were compared with those in C.B-17 or BALB/cCrSlc mice with or without lactic dehydrogenase virus (LDV) infection. The resting enzyme level in SCID mice showed little difference from that in C.B-17 or BALB/cCrSlc mice. The degree of increased plasma LDH level in SCID mice was lower than that in C.B-17 and BALB/cCrSlc mice after LDV infection. To assess the mechanisms of decrease in LDH elevation in SCID mice infected with LDV, virus replication was compared in SCID and BALB/cCrSlc mice. The infectivity titre of plasma in SCID mice was higher (more than 10 times) than that in BALB/cCrSlc mice. Moreover, the percentage of virus antigen positive Kupffer cells was higher in SCID mice than that in BALB/cCrSlc mice. The level of endogenous LDH release as a result of carbon tetrachloride treatment was similar in the SCID and BALB/cCrSlc mice. The clearance rate of endogenous LDH was greater in SCID mice than in BALB/cCrSlc mice with or without LDV infection. The rate of clearance of intravenously injected porcine LDH-5, but not porcine LDH-1, was enhanced in SCID mice as compared with that in BALB/cCrSlc mice. Furthermore, carbon clearance was higher in SCID mice than that in BALB/cCrSlc mice. These results suggest that the smaller increase of plasma LDH after infection might be due, at least in part, to the enhanced LDH-5 clearance function by macrophages in SCID mice.

Stimulation of thymidine kinase activity in baculovirus infected cells is not due to a virus-coded enzyme

A polyhedrin-positive recombinant autographa californica nuclear polyhedrosis virus (AcNPV) carrying a herpes simplex virus thymidine kinase gene under the control of the SynXIV promoter, a fusion of synthetic and linker-modified polyhedrin promoters, has been constructed. When this recombinant baculovirus was used to infect a variant of Spodoptera frugiperda cells deficient in thymidine kinase (TK-), a high level of TK activity was detected. These results, in conjunction with the demonstration that AcNPV could replicate in TK- S. frugiperda cells and no TK activity was found throughout infection, imply that the wild type virus-stimulated TK activity observed in S. frugiperda (TK+) cells is not contributed by a virus-coded enzyme.

Endomyocardial biopsy findings in cases with pericarditis or perimyocarditis

In order to determine the presence or absence of myocarditis in cases with viral or idiopathic pericarditis, a study was conducted as one of our series on endomyocardial biopsy. There were two groups of patients, pericarditis cases (n = 8), and patients with perimyocarditis (n = 6). In the former group, it was confirmed that cardiac sarcoplasmic enzymes were not released during the acute stage of the disease. In the latter, there was positive evidence of the enzyme release. Also, employing our method of categorizing the possibility of myocarditis at the histopathological level, we found that the category 'highly suggestive' of myocarditis was absent in all eight cases with pericarditis. However, in cases with perimyocarditis, this category was assigned in four out of six cases (67%), indicating a high incidence. The category, 'slightly suggestive', was seen in three cases of the former (38%) and two cases of the latter group (33%). It is concluded that in patients with pericarditis, the release of cardiac sarcoplasmic enzyme is an important diagnostic element in the diagnosis of perimyocarditis even if the clinical features reveal a predominance of pericarditis. In patients with perimyocarditis, progression to residual cardiac disease, such as conduction disturbance or congestive heart failure, is likely.

[Enzyme activity of interferon system in virus diseases]

The enzymes activities of interferon system at viral infections of different etiology/influenza, parainfluenza, hepatitis B with delta infection and urticaria chronica with respiratory and herpes infection/has been studied and evaluation of the noted changes in the enzymes activity is discussed. It is shown that the same pathological changes in enzymes activities of interferon system were observed at different viral infections.

[Elastase-alpha 1-proteinase inhibitor complex (E alpha 1 PI) and lactoferrin plasma concentrations in viral and bacterial infections]

Typical alterations of the white blood cell count are often missed during the acute course of infectious diseases. Activiation and degranulation of granulocytes are followed by elevation of E alpha 1 PI and lactoferrin plasma concentrations under these conditions. The aim of our study was the evaluation of the diagnostic significance of these granulocyte parameters in relation with the absolute granulocyte count in infected pediatric patients. A total number of 106 patients at the age of 1 day to 16 years were studied. 25 children suffered from viral, 26 from localized and 23 from systemic bacterial infections, 32 children exhibiting no signs of infection served as controls. Results of the study are given as medians and ranges. Total granulocyte count was elevated above controls (4.8; 2.2-12.7/nl) only in patients with localized bacterial infections (13.3; 5.5-36.5/nl). E alpha 1 PI and lactoferrin plasma concentrations correlated well (r = 0.72) and were found to be significantly elevated in patients with localized bacterial infections (856; 363-4820 micrograms/l and 748; 206-2078 micrograms/l) and septicemia respectively (661; 256-2078 micrograms/l and 871; 160-9550 micrograms/l). A clearcut differentiation of septic and locally infected patients was given by the ratio of E alpha 1 PI and total granulocyte counts. Significantly elevated E alpha 1 PI concentrations of patients exhibiting viral infections (295; 86-690 micrograms/l) may suggest effective granulocyte activation under this condition. Finally we conclude that E alpha 1 PI and lactoferin plasma concentration related to total granulocyte counts in infected patients may serve as a helpful indicator of granulocyte activation during the acute course of the disease.