Steady Motions of Rigid Body Satellites in a Central Gravitational Field

Numerous studies have been conducted on equilibrium orientations of objects moving under the influence of a central gravitational field. The results of many of these studies conclude that equilibrium conditions exist only when one of the principal axes coincides with the radius vector. Furthermore, these results assume that the center of force is located within the orbit plane, thereby tracing a great circle orbit. While these previous works have approximated the gravitational potential, this study examines relative equilibrium obtained by retaining an exact expression for the potential of a spherical primary body, as shown in a recent paper by Wang, Maddocks, and Krishnaprasad. The exact dynamic equations for the motion of a finite rigid body in an inverse square gravitational force field are investigated. Only circular orbits for a specific satellite model consisting of six masses connected by three massless rigid rods are considered. The system dynamics are comprised of seven nonlinear equations, which were numerically solved on a Cray computer. The existence of equilibrium orientations which establish non-great circle orbits was verified and other interesting results were noted. The operational significance of these results was also examined

Actinobacillus pleuropneumoniae Possesses an Antiviral Activity against Porcine Reproductive and Respiratory Syndrome Virus

Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. This phenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) and porcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The main objective of this project was to study the in vitro interactions between these two pathogens and the host cells in the context of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolar macrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed by an infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV preinfection did not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicity effect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPL and PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviral activity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (,1 kDa). The antiviral activity was also observed in SJPL cells infected with swine influenza virus but to a much lower extent compared to PRRSV. More importantly, the PRRSV antiviral activity of App was also seen with PAM, the cells targeted by the virus in vivo during infection in pigs. The antiviral activity might be due, at least in part, to the production of interferon c. The use of in vitro experimental models to study viral and bacterial co-infections will lead to a better understanding of the interactions between pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools

Identification of a new cell line permissive to porcine reproductive and respiratory syndrome virus infection and replication which is phenotypically distinct from MARC-145 cell line

Background Airborne transmitted pathogens, such as porcine reproductive and respiratory syndrome virus (PRRSV), need to interact with host cells of the respiratory tract in order to be able to enter and disseminate in the host organism. Pulmonary alveolar macrophages (PAM) and MA104 derived monkey kidney MARC-145 cells are known to be permissive to PRRSV infection and replication and are the most studied cells in the literature. More recently, new cell lines developed to study PRRSV have been genetically modified to make them permissive to the virus. The SJPL cell line origin was initially reported to be epithelial cells of the respiratory tract of swine. Thus, the goal of this study was to determine if SJPL cells could support PRRSV infection and replication in vitro. Results The SJPL cell growth was significantly slower than MARC-145 cell growth. The SJPL cells were found to express the CD151 protein but not the CD163 and neither the sialoadhesin PRRSV receptors. During the course of the present study, the SJPL cells have been reported to be of monkey origin. Nevertheless, SJPL cells were found to be permissive to PRRSV infection and replication even if the development of the cytopathic effect was delayed compared to PRRSV-infected MARC-145 cells. Following PRRSV replication, the amount of infectious viral particles produced in SJPL and MARC-145 infected cells was similar. The SJPL cells allowed the replication of several PRRSV North American strains and were almost efficient as MARC-145 cells for virus isolation. Interestingly, PRRSV is 8 to 16 times more sensitive to IFNα antiviral effect in SJPL cell in comparison to that in MARC-145 cells. PRRSV induced an increase in IFNβ mRNA and no up regulation of IFNα mRNA in both infected cell types. In addition, PRRSV induced an up regulation of IFNγ and TNF-α mRNAs only in infected MARC-145 cells. Conclusions In conclusion, the SJPL cells are permissive to PRRSV. In addition, they are phenotypically different from MARC-145 cells and are an additional tool that could be used to study PRRSV pathogenesis mechanisms in vitro

<i>AppΔapxIΔapxIIC</i> cell culture supernatant and PRRSV effects on mRNA quantification of type I (IFNα, IFNβ) and type II (IFNγ) interferons.

<p>qRT-PCR results expressed in relative expression (ΔΔCT) for IFNα (A), IFNβ (B) and IFNγ (C) in SJPL cells. The cells were mock infected or infected with 0.5 MOI of PRRSV for 4 hours then treated without or with <i>AppΔapxICΔapxIIC</i> cell culture supernatant for 48 hours. Poly (I:C) and LPS were used as positive controls. Data labeled with superscripts of different letters indicates that these sets of data are statistically different (P<0.05).</p

Antiviral activity of <i>AppΔapxIΔapxIIC</i> supernatant against several animal DNA and RNA viruses in SJPL infected cells.

<p>All experiences were performed at least 2 times.</p><p>Statistical <i>P</i> value compared to <i>AppΔapxIΔapxIIC</i> untreated cells: <i>P</i> = 0.15.</p><p>Statistically significative compared to <i>AppΔapxIΔapxIIC</i> untreated cells: *<i>P</i><0.05, **<i>P</i><0.01, ***<i>P</i><0.001.</p><p>Statistically significative compared to other viruses: <i>^aP</i><0.01.</p

Bacterial adherence over time of <i>Appwt</i> or <i>AppΔapxIΔapxIIC</i> in PRRSV co-infected SJPL and MARC-145 cells.

<p>SJPL (A) and MARC-145 (B) cells were infected with or without PRRSV at an MOI of 0.5 during 72 hours, and then cells were co-infected with <i>Appwt</i> or <i>AppΔapxIΔapxIIC</i> at an MOI of 10. Bacterial adherence was measured in CFU per well after 1, 2 and 3 hours post bacterial infection as described in Auger <i>et al</i>., 2009 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098434#pone.0098434-Auger1" target="_blank">[20]</a>. Values are presented as ± Standard Deviation (SD). No statistical significance was obtained following two-away ANOVA analysis. All experiments were repeated 3 times.</p

<i>AppΔapxIΔapxIIC</i> cell culture supernatant <1 kDa fraction antiviral activity against PRRSV.

<p>Detection of the N viral protein in PRRSV infected SJPL cells by immunofluorescence. SJPL cells were infected with 0.5 MOI of PRRSV for 4 hours then incubated with DMEM culture medium alone (DMEM) (A) or either a DMEM culture medium fraction of <1 kDa (DMEM <1 kDa) (B) or a <i>AppΔapxIΔapxIIC</i> cell culture supernatant <1 kDa fraction (<i>App</i><1 kDa) (C) added to complete SJPL culture medium for 48 hours. White scale bar represents 200 µm. Pictures were taken at 100X magnification.</p

Cytotoxicity over time of <i>Appwt</i> or <i>AppΔapxIΔapxIIC</i> in PRRSV co-infected SJPL and MARC-145 cells.

<p>SJPL (A and B) and MARC-145 cells (C and D) were infected with or without PRRSV at an MOI of 0.5 during 72 hours, and then cells were co-infected with <i>App</i> (for 1 or 2 hours) (A and C, respectively) or with <i>AppΔapxIΔapxIIC</i> (for 4, 5 and 6 hours) (B and D, respectively) at an MOI of 10. Cytotoxicity was measured in % using lactate dehydrogenase (LDH) CytoTox assay <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098434#pone.0098434-Auger1" target="_blank">[20]</a>. Values are presented as ± Standard Deviation (SD). Two-away ANOVA analysis was used to obtain statistical data. *<i>P</i><0.05. All experiments were performed 3 times.</p