Unique Type I Interferon Responses Determine the Functional Fate of Migratory Lung Dendritic Cells during Influenza Virus Infection

Migratory lung dendritic cells (DCs) transport viral antigen from the lungs to the draining mediastinal lymph nodes (MLNs) during influenza virus infection to initiate the adaptive immune response. Two major migratory DC subsets, CD103+ DCs and CD11bhigh DCs participate in this function and it is not clear if these antigen presenting cell (APC) populations become directly infected and if so whether their activity is influenced by the infection. In these experiments we show that both subpopulations can become infected and migrate to the draining MLN but a difference in their response to type I interferon (I-IFN) signaling dictates the capacity of the virus to replicate. CD103+ DCs allow the virus to replicate to significantly higher levels than do the CD11bhigh DCs, and they release infectious virus in the MLNs and when cultured ex-vivo. Virus replication in CD11bhigh DCs is inhibited by I-IFNs, since ablation of the I-IFN receptor (IFNAR) signaling permits virus to replicate vigorously and productively in this subset. Interestingly, CD103+ DCs are less sensitive to I-IFNs upregulating interferon-induced genes to a lesser extent than CD11bhigh DCs. The attenuated IFNAR signaling by CD103+ DCs correlates with their described superior antigen presentation capacity for naïve CD8+ T cells when compared to CD11bhigh DCs. Indeed ablation of IFNAR signaling equalizes the competency of the antigen presenting function for the two subpopulations. Thus, antigen presentation by lung DCs is proportional to virus replication and this is tightly constrained by I-IFN. The “interferon-resistant” CD103+ DCs may have evolved to ensure the presentation of viral antigens to T cells in I-IFN rich environments. Conversely, this trait may be exploitable by viral pathogens as a mechanism for systemic dissemination

Chaotic Behaviour of Gas-Solids Flow in the Riser of a Laboratory-Scale Circulating Fluidized Bed

A cold model of a circulating fluidized bed with a 0.030-m-ID, 2.77-m-high riser was operated in a wide range of operating conditions. Several solids were tested front 57 mu m to 1,830 mu m in size and from 1,100 kg/m(3) to 2,540 kg/m(3) in density. Pressure fluctuations were measured at several points along the riser, and time series were processed to evaluate chaotic invariants (Kolmogorov entropy and correlation dimension). Axial profiles of average values of pressure and voidage were also evaluated. At fixed operating conditions, the Kolmogorov entropy changed along the riser, which appeared to be a function of the local voidage and showed a minimum when voidage decreases from 1.00 until about 0.90. Changes of the Kolmogorov entropy with local voidage were interpreted based on interactions among solids and gas turbulence structures. Three regions were identified in the voidage range investigated: particles-controlled region, clusters-controlled region and bottom-bed-controlled region

Fluidization Regimes and Transitions from Fixed Bed to Dilute Transport Flow

Characterization by means of Kolmogorov entropy shows that the dynamics of the bottom bed in small size circulating fluidized bed risers are significantly different from the dynamics of the dense bottom bed in large size risers and, as a consequence, two types of circulating regimes are introduced: the exploding bubble bed for large risers and the circulating 'slugging' bed for small risers, the latter at high superficial gas velocities. In a pictorial fluidization diagram ten gas-solid fluidization regimes are given, seven of which are experimentally identified with the Kolmogorov entropy by varying the superficial gas velocity, riser solids holdup and diameter (or width) of the riser: bubbling bed, slugging bed, exploding bubble bed, intermediate turbulent bed, circulating 'slugging' bed, intermediate dilute flow, and dilute transport flow. No transition could be identified between the exploding bubble bed at captive conditions and the exploding bubble bed at circulating conditions in the dense bottom bed of the two largest facilities in this study. This suggests that the dense bottom bed in large size risers can be considered as a bubbling bed. A turbulent bed was found in none of the facilities of this study with the Geldart B solids used. As well as by the Kolmogorov entropy ( chaos analysis), the hydrodynamics have been characterized by amplitude of pressure fluctuations, while a solids distribution analysis has also been carried out. The study has been made in four (circulating) fluidize beds of different size and design, all operated with 0.30 mm silica sand. The dimensions of the fluidized bed risers are 1.47 x 1.42 x 13.5 m, 0.70 x 0.12 x 8.5 m, 0.12 m i.d. x 5.8 m, and 0.083 m i.d. x 4.0 m. (C) 1998 Elsevier Science S.A