Estimating the average distribution of Antarctic krill Euphausia superba at the northern Antarctic Peninsula during austral summer and winter.

This study was performed to aid the management of the fishery for Antarctic krill Euphausia superba. Krill are an important component of the Antarctic marine ecosystem, providing a key food source for many marine predators. Additionally, krill are the target of the largest commercial fishery in the Southern Ocean, for which annual catches have been increasing and concentrating in recent years. The krill fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has endorsed a new management framework that requires information about the spatial distribution and biomass of krill. Here, we use krill density estimates from acoustic surveys and a GAMM framework to model habitat properties associated with high krill biomass during summer and winter in the northern Antarctic Peninsula region, an area important to the commercial fishery. Our models show elevated krill density associated with the shelf break, increased sea surface temperature, moderate chlorophyll-a concentration and increased salinity. During winter, our models show associations with shallow waters (< 1500 m) with low sea-ice concentration, medium sea-level anomaly and medium current speed. Our models predict temporal averages of the distribution and density of krill, which can be used to aid CCAMLR's revised ecosystem approach to fisheries management. Our models have the potential to help in the spatial and temporal design of future acoustic surveys that would preclude the need for modelled extrapolations. We highlight that the ecosystem approach to fisheries management of krill critically depends upon such field observations at relevant spatial and temporal scales. Supplementary Information: The online version contains supplementary material available at 10.1007/s00300-022-03039-y.

Innate immune responses in viral encephalitis.

The innate immune system is multifaceted, comprised of preformed factors, cells, and many proteins and lipid mediators produced by those cells. In the CNS these are critical in initiation and amplification of the inflammatory response and in the subsequent elicitation of the specific T cell response to viral encephalitis. Cells that are resident in brain parenchyma and peripheral cells that are recruited both play key roles in the hosts's responses. Unlike the peripheral compartments, in the CNS, non-cytolytic means of eliminating viral infections have been critical, since, in contrast to columnar epithelial cells, neurons are non-renewing. When the innate immune responses are inefficient or absent in viral encephalitis, pathology is more likely. Much more work remains to elucidate all of the critical cells and their mediators, as well as to develop new therapies for infections of the CNS.

Leukotrienes play protective roles early during experimental VSV encephalitis.

Leukotrienes (LT) are potent lipid mediators of inflammation. 5-Lipoxygenase (5-LO) is the key enzyme in the conversion of arachidonic acid to LT. There are four LT: LTB(4), LTC(4), LTD(4) and LTE(4). LT have been extensively studied in airway inflammation but little is known about their roles in viral infection in the CNS. LTB(4) is a chemoattractant for neutrophils. In this work, we studied the roles of LT in acute vesicular stomatitis virus (VSV) encephalitis. Two methods were used to disrupt 5-LO activity: mice were treated with Zileuton, an enzyme antagonist, or 5-LO genetic knockout mice were used. We found that inhibition or deletion of 5-LO resulted in: (a) impaired process of neutrophil infiltration into the CNS early during viral infection; (b) fewer neurons expressed nitric oxide synthase-1 (NOS-1); (c) higher viral titers 1 day after viral infection; and (d) increased disruption of blood brain barrier (BBB). Our studies suggest that LT are important innate immune players during VSV pathogenesis and are beneficial to the host in early control of viral replication in the CNS.

The role of interleukin-18 in vesicular stomatitis virus infection of the CNS.

Intranasal application of vesicular stomatitis virus (VSV) results in the initial infection of the olfactory receptor neurons and a rapid progression of the virus through the mouse central nervous system (CNS). Interleukin-18 (IL-18) is an 18.3-kd cytokine that induces interferon gamma (IFN-gamma) production in mice. IL-18 is synthesized as an inactive precursor that is cleaved and activated by caspase-1/interleukin-1beta converting enzyme (ICE). IL-18 shares several biological properties with IL-12, including the ability to induce IFN-gamma production in T lymphocytes and natural killer (NK) cells. In the CNS, microglia and astrocytes produce IL-18 and IL-12. We have previously shown that IL-12 promotes recovery from VSV encephalitis. This led us to examine the potential role of IL-18 in the pathogenesis of VSV encephalitis. We show that both IL-18 and caspase-1 mRNA are consistently present in the CNS of mice. The addition of exogenous IL-18 to cell cultures does not affect the production of VSV, and addition of exogenous IL-18 at the time of infection does not alter the morbidity or mortality of BALB/c mice. In vitro studies with neutralizing monoclonal antibody to IL-18 had no effect. From these results we conclude that in this system and under the experimental conditions used, unlike IL-12 and IFN-gamma, IL-18 does not play a significant role in the host response to VSV infection.

NSAID treatment suppresses VSV propagation in mouse CNS.

Cyclooxygenase (COX) is the key enzyme in the conversion of arachidonic acid to prostaglandins. COX has two isoforms: COX-1, the constitutively expressed form, and COX-2, the inducible form. Prostaglandins are mediators of many critical physiological and inflammatory responses, but little is known about their roles during a viral infection in the central nervous system (CNS). We used non-selective inhibitors of COX, aspirin and indomethacin, and a selective antagonist of COX-2, celecoxib, to study the role of prostaglandins in Vesicular Stomatitis Virus (VSV) induced encephalitis. We found that the inhibition of COX antagonizes VSV propagation both in vitro and in vivo. In addition, aspirin and celecoxib both prevented the disruption of the blood brain barrier in VSV-infected mice. In vitro experiments showed that the effect of COX inhibition was at least partially mediated by increased production of Nitric Oxide (NO), a molecule known to inhibit VSV replication. When NO production was inhibited by N(omega)-nitro-L-methyl-arginine-ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, the difference in viral titer between aspirin (or celecoxib)-treated and the control cells was abolished. VSV-infected mice treated with celecoxib expressed more NOS-1 and produced more NO in their CNS compared to the controls. Our data suggest that the product(s) of COX have antagonistic effect(s) on NO production in the mouse CNS.

Regulation of the BBB during viral encephalitis: roles of IL-12 and NOS.

Intranasal infection of mice by Vesicular Stomatitis Virus (VSV) often leads to breakdown of the blood-brain barrier (BBB). The role of Interleukin 12 (IL-12) and nitric oxide synthase (NOS) was examined here. Wild-type (WT), NOS-1 knockout (KO), and NOS-3 KO mice were infected with VSV and treated with either IL-12 or medium. IL-12 treatment of uninfected hosts did not result in pathology. In contrast with WT and NOS-1 KO mice, where extensive gross and ultrastructural correlation of BBB breakdown were evident following infection, in NOS-3 KO mice, integrity of the BBB was observed. Thus NOS-3 activity in astrocytes, endothelial cells, or ependymal cells may play an essential role in regulating the BBB.

Mechanisms of cytokine-mediated inhibition of viral replication.

In this report, the role of nitric oxide synthase (NOS) and IL-12 administration in inhibition of vesicular stomatitis virus (VSV) from infected neuroblastoma cells was examined. We previously have shown that cytokine treatment of cells results in the induction of NOS-1, and this is associated with a 2 log inhibition of VSV production. We performed these studies to examine the mechanism by which viral replication is suppressed. Neuroblastoma cells (NB41A3) were treated with either IL-12 or medium and subsequently infected with VSV. Viral protein and mRNA were isolated from these cells, and their levels were measured by Western or Northern blots, respectively. mRNA levels were decreased modestly, but viral proteins were decreased substantially in cells pretreated with IL-12, suggesting that the inhibitory effect of NO is working at the translational level. Cytokine treatment of cells was not associated with oxidative stress. The viral proteins also were nitrosylated. These data suggest that the mechanism of NO inhibition of viral replication occurs through translational interference and posttranslational modifications of viral components.

Neuronal expression of NOS-1 is required for host recovery from viral encephalitis.

The role of nitric oxide synthase (NOS) in host defense and clearance of vesicular stomatitis virus (VSV) from the central nervous system (CNS) was examined. NOS-1, NOS-2, and NOS-3 knockout mice were infected with VSV and were treated with either IL-12 or medium. IL-12 treatment resulted in substantially decreased VSV titers in wildtype and NOS-3 knockout mice, but had a marginal effect in the NOS-1 and NOS-2 knockout mice. NOS-1 expression in neurons was associated with survival from VSV infection. The data indicate that the enzyme activity is local, since NOS-2 expression in microglia and inflammatory macrophages and NOS-3 expression in astrocytes, endothelial cells, and ependymal cells did not compensate.

Delayed administration of interleukin-12 is efficacious in promoting recovery from lethal viral encephalitis.

Vesicular stomatitis virus (VSV) applied intranasally to mice initially infects the olfactory receptor neurons, and then spreads quickly to the rest of the central nervous system (CNS). Previously, we have shown that the cytokine interleukin-12 (IL-12) has a significant survival and recovery promoting effect in mice infected with VSV when administered at the time of infection. The question of whether IL-12 is efficacious under the more clinically relevant condition of post-infection administration was explored. The data show that when IL-12 is administered post-infection, it is as effective as at the time of infection.

Viral replication in olfactory receptor neurons and entry into the olfactory bulb and brain.

This communication describes our ongoing studies of the interaction of the mouse host and vesicular stomatitis virus (VSV). When VSV is applied to the nasal neuroepithelium, it initially replicates in olfactory receptor neurons, and is transmitted along the olfactory nerve to the central nervous system (CNS) within 12 hours. In the olfactory bulb, the virus replicates invasively through the layers of the olfactory bulb, reaching the olfactory ventricle by day 4-5 post infection, and the hindbrain by day 8 post infection. In mice, infection may result in a 50% mortality rate. The crucial host innate and specific immune responses responsible for restricting viral propagation and caudal spread of the virus will be discussed. The efficacy of interleukin-12 (IL-12) treatment for enhanced viral clearance and promotion of host recovery are described along with the implications for treatment of human encephalitis. The hosts' response to infection is also regulated by the sex of the host, and the age at infection. The role of specific mucosal humoral immunity and systemic cellular immunity in prevention of infection are described.

IL-12 and viral infections.

Interleukin-12 activates natural killer cells and promotes the differentiation of Th1 CD4+ cells; it is a critical factor in viral immunity. IL-12 is secreted by antigen presenting cells including dendritic cells, macrophages and astrocytes, both in tissues and in secondary lymphoid organs. Experimental studies have shown that administration of the cytokine rapidly activates both innate and specific immune responses; this results in enhanced host cellular responses and generally, promotes clearance of virus and host recovery from infection. The observations of many laboratories, studying viral immunity to both RNA and DNA based pathogens, are summarized.

IFN-gamma is not required in the IL-12 response to vesicular stomatitis virus infection of the olfactory bulb.

In this report, the role of IFN-gamma in host defense to exogenous IL-12 and clearance of vesicular stomatitis virus (VSV) from the central nervous system was examined. Wild-type and IFN-gamma knockout mice infected with VSV were treated with IL-12 or medium. In both groups, IL-12 treatment resulted in 1) substantially decreased VSV titers in brain homogenates and diminished immunohistochemical detection of VSV Ags in tissue sections; 2) induction of types 1, 2, and 3 nitric oxide synthase; and 3) induction of MHC molecules and rapid infiltration of both T cells and NK cells. These results suggest that IFN-gamma production, both systemically and in the olfactory bulb, contributes to but is not essential for clearance of VSV from the brain. Neutralization of TNF-alpha in IFN-gamma knockout mice mice treated with IL-12 was accompanied by the same immunohistochemical changes, implying that neither IFN-gamma nor TNF-alpha was required. In vitro studies using purified IL-12 or IFN-gamma in culture medium induced nitric oxide synthase isoforms in neurons, glia, and macrophages, and MHC II on glia and macrophages. These data suggest that IL-12 directly activates neurons to promote viral clearance in vivo.

Interleukin-12 promotes recovery from viral encephalitis.

Infusion of interleukin-12 (IL-12) enhances recovery from lethal experimental vesicular stomatitis virus (VSV) infection of the central nervous system (CNS). Interleukin-12 treatment resulted in: 1) increased survival frequency; 2) faster recovery from weight loss; 3) substantially decreased VSV titers in brain homogenates and diminished immunohistochemical detection of VSV antigens in tissue sections; 4) earlier and increased CNS expression of types 1, 2, and 3 nitric oxide synthase (NOS) and both major histocompatibility complex (MHC) class I and class II antigens; 5) earlier and increased blood and CNS levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). These results suggest that IL-12 enhances recovery from VSV infection of the CNS.

Activation of type III nitric oxide synthase in astrocytes following a neurotropic viral infection.

Type III nitric oxide synthase (type III NOS), also known as endothelial cell nitric oxide synthase (eNOS or ecNOS or NOS-3), is a constitutively expressed, calcium- and calmodulin-dependent, isoform of NOS. Its expression has been localized to endothelial cells and a subset of neurons in the brain. We report here that resident astrocytes of the central nervous system (CNS) of mice express type III NOS. Following an experimental neurotropic viral infection, the expression of type III NOS on reactive astrocytes increases substantially, predominantly in virally infected regions of the brain. This upregulation of type III NOS expression is also evident following cytokine treatment in vitro. The intraperitoneal (i.p.) administration of IL-12, a potent activator of IFN-gamma and TNF-alpha production, results in a substantial increase in type III NOS immunoreactivity in astrocytes. Cytokine-mediated activation of type III NOS is observed in vitro following exposure of a C6 glioma cells, which constitutively express type III NOS, to IL-12, IFN-gamma, and TNF-alpha treatment. We conclude that astrocytes of the murine CNS express type III NOS, which may be positively regulated by a number of cytokines following viral infection. Type III NOS expression by astrocytes represents a novel source of nitric oxide in the brain. It may be important in regulating perfusion and maintaining the blood-brain barrier. Given the intimate association of astrocytes with endothelial cells and neurons, increased activity of type III NOS following viral infection may be beneficial in inhibition of viral infection in neighboring cells.

Interferon-gamma induced type I nitric oxide synthase activity inhibits viral replication in neurons.

Type I NOS expression increases in OB neurons during VSV infection. Immunocytochemical staining of NB41A3 cells indicates constitutive expression of interferon (IFN)-gamma receptor and type I NOS. IFN-gamma treatment of NB41A3 cells increased NO production and type I NOS protein. In vitro replication of VSV, polio virus type I, and Herpes Simplex virus type I (HSV-1) is significantly inhibited by IFN-gamma induced type I NOS and antagonized by NOS inhibitors. In contrast, while IFN-gamma treatment inhibited influenza and Sindbis virus replication, a different pathway(s) was involved. The isoform-selective NOS inhibitor. 7-nitroindazole (7NI) was used to treat mice, resulting in a 10-fold higher titer of virus in brain homogenates, and abrogated the recovery-promoting effect of interleukin-12 treatment. Thus, IFN-gamma induced type I NOS activity may play an important role in host immunity against neurotropic viral infections.