Counter-regulation of T helper 1 cell proliferation by nitric oxide and interleukin-2

Selenium Mitigates Ammonia-Induced Neurotoxicity by Suppressing Apoptosis, Immune Imbalance, and Gut Microbiota-Driven Metabolic Disturbance in Fattening Pigs

Ammonia could be regarded as one detrimental pollutant with an acrid smell in livestock sheds. So far, the pig breeding industry became the main source of atmospheric ammonia. Previous literature demonstrated that excessive ammonia inhalation might cause a series of physiological damage to multiple organs. Unfortunately, the toxicity mechanisms of gaseous ammonia to the porcine nervous system need further research to elucidate. Selenium (Se) involves in many essential physiological processes and has a mitigative effect on the exogenous toxicant. There were scant references that corroborated whether organic Se could intervene in the underlying toxicity of ammonia to the hypothalamus. In the present study, multi-omics tools, ethology, and molecular biological techniques were performed to clarify the detailed mechanisms of relaxation effects of L-selenomethionine on ammonia poisoning. Our results showed that ammonia inhalation caused the clinical symptoms and the increment of positive apoptosis rate in the hypothalamus with the dysfunction of mitochondrial dynamics factors, while obvious mitochondria structure defects were observed. In parallel, the inflammation medium levels and gut microbes-driven metabolism function were altered to mediate the neurotoxicity in fattening pigs through the initiation of inflammation development. Interestingly, L-selenomethionine could attenuate ammonia toxicity by activating the PI3K/Akt/PPAR-γ pathway to inhibit the mitochondria-mediated apoptosis process, blocking the abnormal immune response and the accumulation of reactive oxygen species in the nucleus. Meanwhile, Se could enhance the production performance of fattening sows. Taken together, our study verified the novel hypothesis for the toxicity identification of aerial ammonia and provided a therapeutic strategy for the treatment of occupational poisoning.

iNOS is essential to maintain a protective Th1/Th2 response and the production of cytokines/chemokines against Schistosoma japonicum infection in rats

Humans and a wide range of mammals are generally susceptible to Schistosoma infection, while some rodents such as Rattus rats and Microtus spp are not. We previously demonstrated that inherent high expression levels of nitric oxide (NO), produced by inducible nitric oxide synthase (iNOS), plays an important role in blocking the growth and development of Schistosoma japonicum in wild-type rats. However, the potential regulatory effects of NO on the immune system and immune response to S. japonicum infection in rats are still unknown. In this study, we used iNOS-knockout (KO) rats to determine the role of iNOS-derived NO in the immune system and immunopathological responses to S. japonicum infection in rats. Our data showed that iNOS deficiency led to weakened immune activity against S. japonicum infection. This was characterized by the impaired T cell responses and a significant decrease in S. japonicum-elicited Th2/Th1 responses and cytokine and chemokine-producing capability in the infected iNOS-KO rats. Unlike iNOS-KO mice, Th1-associated cytokines were also decreased in the absence of iNOS in rats. In addition, a profile of pro-inflammatory and pro-fibrogenic cytokines was detected in serum associated with iNOS deficiency. The alterations in immune responses and cytokine patterns were correlated with a slower clearance of parasites, exacerbated granuloma formation, and fibrosis following S. japonicum infection in iNOS-KO rats. Furthermore, we have provided direct evidence that high levels of NO in rats can promote the development of pulmonary fibrosis induced by egg antigens of S. japonicum, but not inflammation, which was negatively correlated with the expression of TGF-β3. These studies are the first description of the immunological and pathological profiles in iNOS-KO rats infected with S. japonicum and demonstrate key differences between the responses found in mice. Our results significantly enhance our understanding of the immunoregulatory effects of NO on defensive and immunopathological responses in rats and the broader nature of resistance to pathogens such as S. japonicum.

Schistosomiasis is a zoonosis that affects more than 200 million people worldwide. A wide range of mammals, including mice, are permissive hosts of Schistosoma and develop chronic disease characterized by egg-granuloma formation and fibrosis after infection. Rats, on the other hand, are non-permissive hosts and develop efficient immune responses to eliminate the worms. Interestingly, schistosome eggs elicit a dominant Th2 immune response within mouse hosts, whereas rats with schistosomiasis develop a significant Th2 response in the absence of available egg production. The Th2 response in rats seems to play an essential role in the protection of the host against Schistosoma. So far, the factors that lead to the different immune responses to Schistosoma infection in both hosts have not been demonstrated. In this study, our results show that an iNOS-dependent mechanism maintains the function of the immune system in rats by modulating CD4⁺ T cell-mediated Th1/Th2-associated cytokine responses and chemokine production. Additionally, the absence of iNOS led to slow clearance of parasites, increases in the development of worms, and an exacerbation of granuloma formation and fibrosis in rats. Furthermore, high levels of NO in rats can promote the development of fibrosis induced by inflammation (rapid inflammatory repair). Therefore, this study demonstrates that the difference in iNOS levels between mice and rats is responsible for the different immune responses and outcomes induced by schistosome infection in both hosts.

Proper cold stimulation starting at an earlier age can enhance immunity and improve adaptability to cold stress in broilers

The effects of long-term cold stimulation on the immune function of ileum and adaptability to cold stress in broilers were examined. A total of 360 Arbor Acres broilers was divided into 3 groups and four replicates per group. C (control) was reared in normal thermal environment. C-3 and C-12 (treatments) were kept in cold condition of 3 or 12°C lower than the temperature of C from days 8 to 42. At day 42, all the groups were exposed to an acute cold stress challenge, designated as S, S-3, and S-12. The mRNA levels of immune molecules and heat shock proteins as well as oxidative stress-related indicators in ileum tissues, and immunoglobulins contents in serum were examined at 14, 42, and 43 d of age. The C-3 regimen had no adverse effect on production performance, whereas the C-12 regimen reduced the production performance relative to C (P < 0.05). At day 42, C-3 had higher levels of immune indexes (P < 0.05), whereas C-12 had lower levels than C (P < 0.05). No differences in levels of oxidative stress-related indicators were found between C and C-3 at day 42 (P > 0.05). S-3 had higher levels of immune indexes and lower levels of oxidative stress-related indicators (P < 0.05), as compared to S and S-12. The results suggest that 34 d of cold stimulation at 3°C lower than the normal temperature had no adverse impacts on production performance but enhanced the immunity of ileum and adaptability to acute cold challenge in broilers.

Oxidative stress and immunotoxic effects of bisphenol A on the larvae of rare minnow Gobiocypris rarus

Bisphenol A (BPA), a known endocrine disrupting chemical, is ubiquitous in the aquatic environment and can pose risk to the health of aquatic organisms. Studies on immunotoxicity of BPA in aquatic organisms are limited. In this study, rare minnow (Gobiocypris rarus) larvae were exposed to 1, 225 and 1000μg/L BPA for 7 days. Inflammatory effects of BPA exposure were assessed from the increased production of nitric oxide (NO) and reactive oxygen species (ROS), the change of iNOS mRNA and other TLRs-associated immune gene expression. Our findings provide evidences that different concentrations of BPA can induce a toxic response in fish to produce reactive free radicals which can affect the function of T lymphocytes and decrease the transcription levels of cytokine genes. The excess production of H2O2, induced oxidative stress and suppressed TLR4/NF-κB signaling, leading to immunosuppressive effects in fish larvae. The present results suggest that BPA has the potential to induce oxidative stress accompanied by immunosuppression in rare minnow larvae.

Selenium deficiency influences the gene expressions of heat shock proteins and nitric oxide levels in neutrophils of broilers

The aim of the present study was to investigate the effects of selenium (Se) deficiency on the expressions of heat shock proteins (Hsp90, 70, 60, 40, and 27) and nitric oxide (NO) levels in neutrophils of broilers. One hundred eighty 1-day-old broilers were randomly assigned into two groups and were fed on a low-Se diet (0.008 mg/kg Se) or a control diet (0.2 mg/kg Se), respectively. Then, the messenger RNA (mRNA) levels of Hsp90, 70, 60, 40, and 27, induced nitric oxide synthase (iNOS), and NO levels were examined. The results showed that Se deficiency increased the mRNA levels of Hsps and iNOS and induced higher level of NO in chicken neutrophils (P < 0.05). It showed that the expression of Hsp40 increased higher than other Hsps in neutrophils, which indicated that it might play the crucial protective role in neutrophils. In addition, correlation analysis showed that iNOS had the biggest correlation with Hsp60, which indicated that Hsp60 might play an important function in inhibiting the production of NO, and the correlation coefficient between Hsp60 and Hsp70 was over 0.9, which indicated that they might have a synergistic effect. These results suggested that the level of NO and Hsp expression levels in neutrophils can be influenced by Se deficiency. And Hsp40 might play the crucial protective role in neutrophils induced by Se deficiency.

Effectiveness of the immunomodulatory extract of Kalanchoe pinnata against murine visceral leishmaniasis

Previously, we described the protective action of the immunomodulatory extract of Kalanchoe pinnata (Kp) in murine and human cutaneous leishmaniasis. In the present study, we investigated the effectiveness of Kp against visceral leishmaniasis, using the BALB/c mouse model of infection with Leishmania chagasi. Mice receiving oral daily doses of Kp (400 mg/kg) for 30 days displayed significantly reduced hepatic and splenic parasite burden, when compared with untreated animals. Protectiveness was accompanied by a reduction in parasite-specific IgG serum levels, and impaired capacity of spleen cells to produce IL-4, but not IFN-γ and nitric oxide upon antigen recall in vitro. The reference drug Pentostam (72 mg/kg) given by the intra-peritoneal route on alternate days produced an anti-leishmanial effect similar to oral Kp. Our findings show that the oral efficacy of Kp, seen previously in murine cutaneous leishmaniasis, extends also to visceral leishmaniasis caused by L. chagasi, a difficult to treat and lethal disease of man.

Nitric oxide-releasing compounds inhibit the production of interleukin-2, -4 and -10 in activated human lymphocytes

In the present study, we investigated the effects of nitric oxide donors, GEA 3162 (1,2,3,4-oxatriazolium,5-amino-3(3,4-dichlorophenyl)-chloride), GEA 3175 (1,2,3,4-oxatriazolium,3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl) sulfonyl]amino]-, hydroxide inner salt) and S-nitroso-N-acetylpenicillamine (SNAP), on the production of Th1 [interleukin (IL)-2] and Th2 (IL-4 and IL-10) type cytokines in activated human lymphocytes. Lymphocytes were stimulated with concanavalin A or a combination of thapsigargin and phorbol myristate acetate in the absence or in the presence of nitric oxide donors. Concanavalin A induced expression of IL-2 mRNA and production of IL-2, and the combination of thapsigargin and phorbol myristate acetate induced expression of IL-4 and IL-10 mRNAs and production of IL-4 and IL-10. These effects were inhibited by the nitric oxide donors in a dose-dependent manner, GEA 3162 and GEA 3175 being more potent than SNAP on a molar basis. The results show that nitric oxide donors have immunomodulatory properties in both Th1- and Th2-derived responses.

Enhanced antiviral antibody secretion and attenuated immunopathology during influenza virus infection in nitric oxide synthase-2-deficient mice

NOS2 gene-deficient (NOS2−/−) mice are less susceptible than wild-type (NOS2+/+) mice to infection with Influenza A virus. Virus titres in the lungs of influenza-infected NOS2−/− mice are significantly lower than those in NOS2+/+ mice, with enhanced viral clearance in NOS2−/− mice dependent on gamma interferon (IFN-γ). The current study was undertaken to ascertain the role of specific components of the immune response in promoting virus clearance in influenza-infected NOS2−/− mice. Levels of T cell- and natural killer cell-mediated cytotoxicity in the lungs of virus-infected mice were not significantly different between NOS2+/+ and NOS2−/− mice. However, virus-infected NOS2−/− mice produced higher levels of virus-specific IgG2a antibody. Furthermore, more viable B cells and plasmablasts, along with greater levels of IFN-γ, were found in NOS2−/− splenocyte cultures stimulated with B-cell mitogens. In addition to the early reduction in virus titres, clinical symptoms and proinflammatory cytokine production were attenuated in NOS2−/− mice. Thus, NOS2−/− B cells are capable of responding rapidly to influenza virus infection by proliferating and preferentially producing antibody of the IgG2a subtype. The relationship between viral load and the development of immunopathology is discussed.

Nitric oxide and cell proliferation

Nitric oxide (NO*) has been proposed to be a physiological modulator of cell proliferation, able to promote in most cases cell cycle arrest. In this review I explore the molecular basis of this mechanism of action. The modulatory action of NO* on the intracellular concentration of cGMP and the machinery directly involved in the control of cell cycle progression, including the expression and activity of diverse cyclins and cyclin-dependent kinases, their physiological inhibitors, and the master transcriptional regulator retinoblastoma protein, will be discussed. The role of NO* in proliferation mediated by tyrosine kinase receptors such as the epidermal growth factor receptor and downstream signalling pathways will also be considered. Finally, the involvement of NO* in proliferative processes relevant for normal development will be outlined.

Estrogen regulation of nitric oxide and inducible nitric oxide synthase (iNOS) in immune cells: implications for immunity, autoimmune diseases, and apoptosis

Nitric oxide plays a central role in the physiology and pathology of diverse tissues including the immune system. It is clear that the levels of nitric oxide must be carefully regulated to maintain homeostasis. Appropriate levels of nitric oxide derived from iNOS assist in mounting an effective defense against invading microbes. Conversely, inability to generate nitric oxide results in serious, even fatal, susceptibility to infections. Further, dysregulation or overproduction of nitric oxide has been implicated in the pathogenesis of many disorders, including atherosclerosis, neurodegenerative diseases, inflammatory autoimmune diseases, and cancer. Therefore, depending upon the levels of nitric oxide generated, the potential exists for nitric oxide to behave like a "double-edged" biological sword. Taking these issues into consideration, it is thus pivotal to understand the regulation of nitric oxide. Nitric oxide is regulated by many endogenous factors including hormones such as estrogens. While the effects of estrogen on the generation of nitric oxide in non-immune tissues are relatively well documented, the effect of estrogen on iNOS/nitric oxide in immune cells is only now becoming apparent. Our laboratory has recently shown that estrogen treatment of mice markedly upregulates the levels of iNOS mRNA, iNOS protein, and nitric oxide in activated splenocytes. This upregulation of nitric oxide is in part mediated through interferon-gamma (IFN-gamma), a pro-inflammatory cytokine that is enhanced by estrogen. These findings are important considering that estrogens are not only involved in regulation of normal immune responses, but also are implicated in many autoimmune and inflammatory diseases. To date, there are no reviews on the effects of estrogen on immune tissue-derived nitric oxide and therefore this review will address this critical gap in the literature. Given the increasing importance of immune-tissue-derived iNOS in health and disease, studies on estrogen-induced regulation of iNOS may offer a better understanding of diseases and aid in devising new therapeutic interventions.

A novel theory: biological processes mostly involve two types of mediators, namely general and specific mediators

A great number of papers have shown that free radicals as well as bioactive molecules can play a role of mediator in a wide spectrum of biological processes, but the biological actions and chemical reactivity of the free radicals are quite different from that of the bioactive molecules, and that a wide variety of bioactive molecules can be easily modified by free radicals due to having functional groups sensitive to redox, and the significance of the interaction between the free radicals and the bioactive molecules in biological processes has been confirmed by the results of some in vitro and in vivo studies. Based on these evidence, this article presented a novel theory about the mediators of biological processes. The essentials of the theory are: (a) mediators of biological processes can be classified into general and specific mediators; the general mediators include two types of free radicals, namely superoxide and nitric oxide; the specific mediators include a wide variety of bioactive molecules, such as specific enzymes, transcription factors, cytokines and eicosanoids; (b) a general mediator can modify almost any class of the biomolecules, and thus play a role of mediator in nearly every biological process via diverse mechanisms; a specific mediator always acts selectively on certain classes of the biomolecules, and may play a role of mediator in different biological processes via a same mechanism; (c) biological processes are mostly controlled by networks of their mediators, so the free radicals can regulate the last consequence of a biological process by modifying some types of the bioactive molecules, or in cooperation with these bioactive molecules; the biological actions of superoxide and nitric oxide may be synergistic or antagonistic. According to this theory, keeping the integrity of these networks and the balance between the free radicals and the bioactive molecules as well as the balance between the free radicals and the free radical scavengers would be of vital importance for physiological processes, and disturbance of these networks and balances would be a critical factor of pathological processes. Therefore, the investigators who want to get a deep and full understanding of the mechanism of a biological process should pay attention to the roles of both free radical and bioactive molecule species, and the free radical scavengers, which are used for health protection, such a vitamin E and carotenoid, should be taken in a suitable dosage.

A nitric oxide releasing derivative of flurbiprofen inhibits experimental autoimmune encephalomyelitis

Nitric oxide (NO)-releasing non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to have a safer profile and additional anti-inflammatory and immuno-modulatory properties compared to parent compounds. Preventive treatment of experimental autoimmune encephalomyelitis (EAE)-induced in C57BL/6 mice by immunization with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55-with the NO-releasing derivative of flurbiprofen HCT1026 delayed disease onset and significantly decreased disease severity. HCT1026 treatment was associated to (i) decreased mRNA levels of pro-inflammatory cytokines, caspase-1, and iNOS in blood cells; (ii) decreased ability of encephalitogenic T cells to proliferate; (iii) reduced number of central nervous system (CNS)-infiltrating T cells; (iv) decreased axonal loss and demyelination; (v) increased CD4(+) CD69(-) CD25(+) regulatory T cells in the spleen.

Pharmacological assessment of the role of nitric oxide in mice infected with lethal and nonlethal species of malaria

This pharmacological investigation sought to determine whether nitric oxide (NO) had an antiparasitic effect and/or mediated pathology in mice infected with nonlethal P. chabaudi or lethal P. berghei. Nitric oxide synthase (NOS) inhibitors were evaluated for their ability to inhibit the rise in reactive nitrogen intermediates (RNI) induced by bacterial lipopolysaccharide (LPS) in mice. The more effective compound, aminoguanidine (AG) inhibited the rise in RNI induced by P. chabaudi and increased mortality, but had no effect on parasitaemia. Inducers and donors of NO were screened for their ability to increase RNI and the most effective agents evaluated for their ability to modify P. berghei infection. S-Nitrosoglutathione had little effect, but LPS decreased parasitaemia and mortality. An inconsistent relationship is evident between the abilities of these agents to modify NO activity and their effects on malaria in mice. Increased mortality in mice with P. chabaudi treated with AG indicates a reduction in resistance. The absence of an effect on parasitaemia by a NOS inhibitor or NO donor indicates either RNI have insignificant antimalarial action in vivo or the efficacy of the compounds is inadequade. Resistance to P. berghei in LPS-treated mice demonstrates an antiparasitic effect, but this may be attributable to factors other than NO.

The production of nitric oxide in EL4 lymphoma cells overexpressing growth hormone

Growth hormone (GH) is produced by immunocompetent cells and has been implicated in the regulation of a multiplicity of functions in the immune system involved in growth and activation. However, the actions of endogenous or lymphocyte GH and its contribution to immune reactivity when compared with those of serum or exogenous GH are still unclear. In the present study, we overexpressed lymphocyte GH in EL4 lymphoma cells, which lack the GH receptor (GHR), to determine the role of endogenous GH in nitric oxide (NO) production and response to genotoxic stress. Western blot analysis demonstrated that the levels of GH increased approximately 40% in cells overexpressing GH (GHo) when compared with cells with vector alone. The results also show a substantial increase in NO production in cells overexpressing GH that could be blocked by N(G)-monomethyl-L-arginine (L-NMMA), an L-arginine analogue that competitively inhibits all three isoforms of nitric oxide synthase (NOS). No evidence was obtained to support an increase in peroxynitrite in cells overexpressing GH. Overexpression of GH increased NOS activity, inducible nitric oxide synthase (iNOS) promoter activity, and iNOS protein expression, whereas endothelial nitric oxide synthase and neuronal nitric oxide synthase protein levels were essentially unchanged. In addition, cells overexpressing GH showed increased arginine transport ability and intracellular arginase activity when compared with control cells. GH overexpression appeared to protect cells from the toxic effects of the DNA alkylating agent methyl methanesulfonate. This possibility was suggested by maintenance of the mitochondrial transmembrane potential in cells overexpressing GH when compared with control cells that could be blocked by L-NMMA. Taken together, the data support the notion that lymphocyte GH, independently of the GH receptor, may play a key role in the survival of lymphocytes exposed to stressful stimuli via the production of NO.

Expression of inducible nitric oxide synthase (iNOS) mRNA in target organs of lethal and non-lethal strains of murine malaria

Nitric oxide (NO) is a putative mediator of the immunological and/or pathological responses to malaria, consequently it is a potential target for novel drug therapy. Numerous cell types increase expression of inducible nitric oxide synthase (iNOS) under inflammatory conditions, the most relevant stimuli being cytokines and endotoxins. In this study the expression of iNOS mRNA in several target organs (brain, liver, spleen) of malaria have been investigated in MF1 mice during lethal Plasmodium (P.) berghei and non-lethal P. c. chabaudi infection. In P. berghei malaria, iNOS mRNA decreased in liver and was unchanged in spleen during the period of rising parasitaemia, but increased in both organs late in the infection, when parasitaemia was high and death imminent. In mice infected with P. c. chabaudi, spleen iNOS mRNA increased progressively throughout the early, peak and recovery periods of parasitaemia, but decreased in liver. Brain iNOS mRNA decreased in samples collected throughout the time courses of both infections. Hence it is evident that changes in iNOS mRNA in murine malaria depend upon the tissue, day of infection, degree of parasitaemia and strain of Plasmodium. These data indicate induction of iNOS mRNA in the spleen has a role in combating these strains of Plasmodium in MF1 mice. Failure to clear lethal P. berghei parasitaemia was associated with increased iNOS mRNA expression in the liver, which may contribute to the pathology of this malaria.

Nitric oxide and reactive nitrogen intermediates during lethal and nonlethal strains of murine malaria

The virulence of Plasmodia depends partly on the strain of parasite and partly on the host. In this study, Plasmodium berghei N/13/1A/4/203 caused the death of mice, whereas Plasmodium chabaudi chabaudi AS was not lethal. Current opinion is that nitric oxide (NO) and other reactive nitrogen intermediates (RNI) are produced in several host organs during malaria to resist infection or produce tissue damage. NO and RNI production in blood or plasma, brain, liver and spleen in MF1 mice was investigated during P. berghei and P. c. chabaudi infection, in order to help determine whether changes in NO production are beneficial or detrimental to the host in vivo. NO production was measured both directly and indirectly as nitrites and nitrates, to represent RNI. No changes in blood NO were detected in P. berghei infected mice, but increases were observed in brain, liver and spleen. In P. c. chabaudi infected mice, rises in NO concentration were observed in blood and spleen, whereas a decline in liver NO was seen, but there were no changes in brain. Liver contained the highest concentration of RNI, but increasing concentrations were seen in both plasma and spleen in both P. berghei and P. c. chabaudi infected mice. These results show that NO and RNI production alters during murine malaria. The changes depend upon the tissue, the day of infection, the degree of parasitaemia, the strain of Plasmodia and the method of measuring NO biosynthesis. Lethal P. berghei induced NO production in the mid and late stages of infection in mice when parasitaemia was high, whereas in nonlethal P. c. chabaudi infection, NO production was increased in the early and late stages when parasitaemia was low. These data are consistent with a role for NO in the protection of the MF1 mouse against Plasmodia. Failure to clear the parasite is associated with evidence of increased NO production in brain and liver, which may contribute to the pathology of malaria, but this hypothesis requires confirmation from other experimental approaches.

Enhancing effect of an inhibitor of nitric oxide synthesis on bacillus Calmette-Guerin-induced macrophage cytotoxicity against murine bladder cancer cell line MBT-2 in vitro

We studied the effect of an inhibitor of nitric oxide (NO) synthesis, N(G)-monomethyl-L-arginine (L-NMMA), on the Bacillus Calmette-Guérin (BCG)-induced antitumor activity of murine peritoneal exudate cells (PEC) against murine bladder cancer cell line MBT-2 in vitro. L-NMMA enhanced BCG-induced cytotoxic activity of PEC, as well as interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha production. The L-NMMA-induced enhancement was due to the prolonged survival of BCG in macrophages, because no enhancement of cytotoxicity was observed and neither IFN-gamma nor TNF-alpha production was significantly enhanced by killed BCG. Anti-TNF-alpha antibody (Ab) and anti-IFN-gammaAb reduced the L-NMMA-induced enhancement of the cytotoxicity. The depletion of T cells from PEC reduced the production of both IFN-gamma and TNF-alpha, as well as the enhancement of cytotoxicity induced by viable BCG plus L-NMMA. These results suggest that L-NMMA has an enhancing effect on BCG-induced macrophage cytotoxicity and the enhancement is partially mediated by T cells and their soluble products. Accordingly, NO inhibitor should be a valuable adjunct to BCG immunotherapy for bladder cancer.

The inflammatory and cytotoxic effects of a nitric oxide releasing cream on normal skin

We describe the pro-inflammatory and cytotoxic effects of nitric oxide in vivo in human skin. Nitrite and ascorbic acid were mixed on the skin of 12 normal volunteers, three times daily, to release nitric oxide. Exposure to nitric oxide was varied by randomizing the concentration of nitrite and duration of application. Nitric oxide treated skin showed significant increases in cells expressing CD3, CD4, CD8, CD68, neutrophil elastase, ICAM-1, VCAM-1, nitrosotyrosine, p53, and apoptotic cells compared with skin treated with ascorbic acid alone. There was no significant increase in mast cells. Following application of nitric oxide there were significantly fewer CD1a positive Langerhans cells in the epidermis. These appeared to lose dendritic morphology and migrate from the epidermis. There was no significant difference in staining for Ki-67, a marker related to proliferating cell nuclear antigen, between active and control skin but staining was greater after exposure to higher dose nitric oxide than the low dose. Apoptosis, cytotoxicity, and p53 staining were relatively greater after 48 h exposure than after 24 h. These results suggest that nitric oxide is pro-inflammatory and is toxic to DNA, leading to the accumulation of p53 and subsequent apoptosis. High-dose nitric oxide paradoxically led to a smaller increase in macrophages and T cells than low dose suggesting an immunosuppressive effect of higher levels.

Different Doses of Adenoviral Vector Expressing IL-12 Enhance or Depress the Immune Response to a Coadministered Antigen: the Role of Nitric Oxide

Joint immunization with two recombinant adenoviruses, one expressing hepatitis C virus (HCV) core and E1 proteins and another expressing IL-12 (RAdIL-12), strongly potentiates cellular immune response against HCV Ags in BALB/c mice when RAdIL-12 was used at doses of 1 × 105–1 × 107 plaque-forming units. However, cellular immunity against HCV Ags was abolished when higher doses (1 × 108 plaque-forming units) of RAdIL-12 were used. This immunosuppressive effect was associated with marked elevation of IFN-γ and nitric oxide in the serum and increased cell apoptosis in the spleen. Administration of N-nitro-l-arginine methyl ester (l-NAME), an inhibitor of nitric oxide synthase, to mice that received high doses of RAdIL-12 was lethal, whereas no apparent systemic toxicity by l-NAME was observed in those immunized with lower doses of the adenovirus. Interestingly, in mice immunized with recombinant adenovirus expressing core and E1 proteins of HCV in combination with RAdIL-12 at low doses (1 × 107 plaque-forming units), l-NAME inhibited T cell proliferation and CTL activity in response to HCV Ags and also production of Abs against adenoviral proteins. In conclusion, gene transfer of IL-12 can increase or abolish cell immunity against an Ag depending of the dose of the vector expressing the cytokine. IL-12 stimulates the synthesis of NO which is needed for the immunostimulating effects of IL-12, but apoptosis of T cells and immunosuppression ensues when IFN-γ and NO are generated at very high concentrations.

A dichotomous role for nitric oxide in protection against blood stage malaria infection

Nitric oxide (NO) is cytotoxic and cytostatic to blood stage malaria parasites in vitro, but the precise mechanism(s) by which it mediates an effect in vivo is not known. In particular, whether or not control of acute parasitemia depends on the presence of NO is unclear. We have shown previously that blocking NO synthesis at the time of its induction may cause an increase in peak primary parasitemia during infection of mice with Plasmodium chabaudi, suggesting that NO may be parasiticidal in vivo. However, as recent data indicate that NO suppresses Th1 cell proliferation in vitro by downregulating IL-2 production, we have investigated whether this immunoregulatory function of NO affects its capacity for anti-malarial activity. Treatment of P. chabaudi-infected mice with the iNOS inhibitor aminoguanidine hemisulfate (AG) starting just prior to the peak of primary parasitemia caused a significant elevation and extension of the acute infection and led to a partial but significant abrogation of the suppression of spleen cell proliferation to both mitogen and specific antigen observed when NO synthesis was not blocked. In the absence of NO, levels of IL-2, but not of IFN-gamma, TNF-alpha, or of any Th2-regulated cytokines examined, increased significantly. However, when AG treatment was brought forward to the early ascending phase of primary parasitemia, significantly increased levels of IFN-gamma and TNF-alpha, as well as of IL-2, were observed over those for infected control mice similarly treated with phosphate-buffered saline. Moreover, despite the absence of NO, parasitemias of AG-treated mice were not significantly elevated. The effect of AG therefore appeared to be dependent upon the timing of its administration in vivo. We propose that during malaria infections, there is a dynamic balance between the regulatory and anti-parasitic roles of NO. While the immunosuppressive function of NO leads to a downregulation in vivo of production of IL-2, and indirectly of IFN-gamma and TNF-alpha, this perceived weakening of the host cell-mediated immune response is in part masked by the protective anti-malarial effects of NO itself.

Inducible nitric oxide synthase-deficient mice develop enhanced type 1 cytokine-associated cellular and humoral immune responses after vaccination with attenuated Schistosoma mansoni cercariae but display partially reduced resistance

High levels of nitric oxide (NO) are produced by inducible nitric oxide synthase (iNOS) in response to activating signals from Th1-associated cytokines and play an important role in cytotoxicity and cytostasis against many pathogenic microorganisms. In addition to its direct effector function, NO serves as a potent immunoregulatory factor. NO produced by gamma interferon-activated macrophages immobilizes and kills Schistosoma mansoni larvae, and several studies have indicated a role for this pathway in protective immunity against this parasite. The potential regulatory influence of NO in immunity to S. mansoni is less well understood. In this study, we have used iNOS-deficient mice to determine the role of NO in mice vaccinated with irradiated cercariae of S. mansoni. We show by enzyme-linked immunosorbent assay and reverse transcriptase PCR analysis that vaccinated iNOS-deficient mice develop exacerbated type 1 cytokine responses in the lungs, the site where resistance to infection is primarily manifested. In addition, parasite-specific immunoglobulin G2a (IgG2a) and IgG2b antibody responses were significantly increased in vaccinated iNOS-deficient animals and total IgE antibody levels in serum were decreased relative to those in wild-type controls. Surprisingly, since resistance in this vaccine model is largely Th1 dependent and since Th1-related cellular and humoral immune responses were found to be exacerbated in vaccinated iNOS-deficient mice, vaccine-elicited protective immunity against challenge infection was found to be reduced. These findings demonstrate that iNOS plays a paradoxical role in immunity to S. mansoni, both in the effector mechanism of resistance and in the down regulation of the type 1 cytokine response, which is ultimately required for NO production.

Calcium-dependent nitric oxide synthase activity in rat thymocytes

We examined the conversion of L-[3H]arginine to L-[3H]citrulline in lysate from rat thymocytes, which was dependent on Ca2+ and cofactors (FAD, BH4, NADPH). Removal of Ca2+ of the medium, reduced the total L-[3H]citrulline formation by about 97%. The L-[3H]citrulline formation was completely inhibited by the NO synthase inhibitors, NG-nitro-L-arginine and NG-monomethyl-L-arginine, with values for IC50 of 1.2 microM and 19.4 microM, respectively. In intact thymocytes, the L-[3H]citrulline formation was dependent on the intracellular Ca2+ ([Ca2+]i) concentration. Increasing the extracellular free-Ca2+ concentration up to 1.5 mM, was accompanied by an increase in [Ca2+]i inside the thymocytes and there was a parallel increase in the intracellular L-[3H]citrulline formation, which reached a maximal value of 371.2 nM of [Ca2+]i. Addition of NG-nitro-L-arginine to the medium, completely inhibited the formation of L-[3H]citrulline. The immunolabeling study revealed that 15% of the thymocytes isolated from rat thymus constitutively expressed the endothelial isoform of NO synthase.

Immunoregulation of malarial infection: balancing the vices and virtues

Malaria continues to extract an incalculable cost on human morbidity and mortality throughout tropical and subtropical regions of the world, and effective control measures are urgently needed. Despite considerable efforts in recent years to develop subunit vaccines targeted at various stages of the Plasmodium life-cycle, the commercial availability of a vaccine is still a distant prospect. One of the underlying difficulties hindering successful vaccine design is our incomplete knowledge of the precise type(s) of immune response to aim for, and then how to achieve it. A greater appreciation of the mechanisms of protective immunity, on the one hand, and of immunopathology, on the other, should provide critical clues on how manipulation of the immune system may best be achieved. Ten years have passed since the identification of the Th1/Th2 paradigm for distinguishing CD4+ T cells according to cytokine secretion patterns which determine their function. This review summarises our progress towards understanding the broad spectrum of immune responsiveness to the blood stages of the malaria parasite during experimental infections in mice and highlights the way in which examination of rodent malarias provides a powerful tool to dissect the interaction of Th1 and Th2 cells during an immune response to an infectious disease agent. It is proposed that the pliability of rodent systems for investigating immunoregulation provides valuable insight into the balance between protection and pathology in human malaria and throws light on the factors involved in the modulation of vaccine-potentiated immunity.