The Nitric Oxide Pathway Provides Innate Antiviral Protection in Conjunction with the Type I Interferon Pathway in Fibroblasts

The innate host response to virus infection is largely dominated by the production of type I interferon and interferon stimulated genes. In particular, fibroblasts respond robustly to viral infection and to recognition of viral signatures such as dsRNA with the rapid production of type I interferon; subsequently, fibroblasts are a key cell type in antiviral protection. We recently found, however, that primary fibroblasts deficient for the production of interferon, interferon stimulated genes, and other cytokines and chemokines mount a robust antiviral response against both DNA and RNA viruses following stimulation with dsRNA. Nitric oxide is a chemical compound with pleiotropic functions; its production by phagocytes in response to interferon-γ is associated with antimicrobial activity. Here we show that in response to dsRNA, nitric oxide is rapidly produced in primary fibroblasts. In the presence of an intact interferon system, nitric oxide plays a minor but significant role in antiviral protection. However, in the absence of an interferon system, nitric oxide is critical for the protection against DNA viruses. In primary fibroblasts, NF-κB and interferon regulatory factor 1 participate in the induction of inducible nitric oxide synthase expression, which subsequently produces nitric oxide. As large DNA viruses encode multiple and diverse immune modulators to disable the interferon system, it appears that the nitric oxide pathway serves as a secondary strategy to protect the host against viral infection in key cell types, such as fibroblasts, that largely rely on the type I interferon system for antiviral protection

CATALYTIC COMBUSTION OF PROPANE IN A MEMBRANE REACTOR WITH SEPARATE FEED OF REACTANTS .2. OPERATION IN PRESENCE OF TRANS-MEMBRANE PRESSURE-GRADIENTS

This is the second communication of a series dealing with an experimental and modelling study on propane catalytic combustion in a membrane reactor with separate feed of reactants. In paper I the behaviour of the reactor in the absence of trans-membrane pressure gradients was presented and discussed. Attention is here focused on the reactor behaviour when pressure differences are applied over the membrane, resulting in a convective flow through the membrane itself. By these means, a major conversion enhancement (up to more than 300%) is achievable compared to the case in which only diffusive mass transfer controls the reactor performance. However, above certain pressure differences (> 1 bar), this is obtained at the price of noticeable slip of unconverted reactants across the membrane. The experimental results are in good agreement with the predictions of an isothermal model based on the numerical solution of differential mass balances across the membrane, employing a Stefan-Maxwell expression for diffusive fluxes and a d'Arcy law for convective ones

Absorption accompanied with chemical reaction in trickle-bed reactors

A new development in the field of internals in packed columns is the use of structured packing types. Recently, a new structured packing type coated with a thin alumina layer (KATAPAKTM) has been developed. In this report, the results of an experimental and theoretical study concerning the possible applicability of this new packing material for hydrogenation processes in a trickle-bed reactor is presented. The palladium catalyzed hydrogenation of α-methylstryrene is used as a model reaction to study hydrodynamics and mass transfer characteristics in a trickle-bed reactor under reactive conditions. Converstions at several process conditions are measured in a pilot plant in which 3 mm spheres as well KATAPAKTM is applied as packing materials. A comparison of the results of some physical absorption experiments with the results of hydrogenation experiments showed that the resistance in series model—in which the total resistance against mass transfer is calculated from the separate resistances—is not valid in systems where heterogeneous reactions at the solid surface can enhance the mass transfer-rate at the gas-liquid interphase. With the aid of a developed trickle-bed reactor model, based on liquid diffusion, simultaneous reaction at the solid surface and zero volume mixing points, the mass transfer phenomena in trickle-bed reactors in conditions where the resistance in series model fails can be explained and described. The numerically solved model calculates the hydrogen profiles in the liquid films of the reactor and over all single pass conversions at several process conditions. These conclusions are confirmed by the results of the simulation of a model reactor, i.e. the laminar film reactor with a catalytically active wall. From the results of the measurements it could be concluded that in trickle-flow conditions, the application of KATAPAKTM does not significantly improved on the overall performance of trickle-bed reactors. The increase of the physical absorption rate due to better mass transfer characteristics of structured packings compared to dumped packing types—as reported in literature—will be eliminated to a certain extent in reactive systems due to the enhancement effect of heterogeneous reactions in trickle-flow operation.