Determination of a quantitative relationship between material properties, process settings and screw feeding behavior via multivariate data-analysis.

In this study, a quantitative relationship between material properties, process settings and screw feeding responses of a high-throughput feeder was established via multivariate models (PLS). Thirteen divergent powders were selected and characterized for 44 material property descriptors. During volumetric feeder trials, the maximum feed capacity (FCCmax), the relative standard deviation on the maximum feed capacity (RSDFCmax), the short term variability (STRSD) and feed capacity decay (FCdecay) were determined. The gravimetric feeder trials generated values for the mass flow rate variability (RSDLC), short term variability (STRSD) and refill responses (Vrefill and RSDrefill). The developed PLS models elucidated that the material properties and process settings were clearly correlated to the feeding behavior. The extended volumetric feeder trials pointed out that there was a significant influence of the chosen screw type and screw speed on the feeding process. Furthermore, the process could be optimized by reducing the feeding variability through the application of optimized mass flow filters, high frequency vibrations, independent agitator control and optimized top-up systems. Overall, the models could allow the prediction of the feeding performance for a wide range of materials based on the characterization of a subset of material properties greatly reducing the number of required feeding experiments.

Modeling HIV transfer between dendritic cells and T cells: importance of HIV phenotype, dendritic cell-T cell contact and T-cell activation.

OBJECTIVE: To study the requirements for HIV transfer between dendritic cells (DC) and CD4 T cells, using an in vitro model, combined with flow cytometry. METHODS: Immature DC and macrophages (MA) were generated from monocytes. After infection, DC or MA were cultured alone or with purified CD4 T cells. Intracellular HIV was measured, using (1) the monocyte (MO)-tropic AD8 HIV, endowed with enhanced green fluorescent protein (EGFP); and (2) intracellular staining of laboratory HIV strains and clones from primary isolates. RESULTS: (1) Clone AD8-EGFP infected DC and MA with equal efficiency, but the virus was preferentially transferred from DC to autologous T cells. (2) DC were more productively infected with R5/NSI, as compared to X4/SI, HIV, but both HIV phenotypes were easily transmitted to autologous T4 cells. (3) HIV-infected DC transferred the virus to T cells across a semi-permeable membrane, if the T cells were in contact with non-infected DC. (4) Co-culture of T cells with autologous non-infected DC induced T-cell activation. HIV-infected DC selectively increased HLA-DR on T cells and HLA-DR (+) T cells were preferential targets for HIV transfer. (5) Resting Ba-L-infected CD4 T cells were able to transmit the virus 'inversely' to co-cultured DC. CONCLUSION: HIV transfer between monocyte-derived dendritic cells and autologous CD4 T cells was directly demonstrated using flow cytometry. The transfer proceeded in both directions, depended on cellular contact and was associated with partial T-cell activation. This model, representing relevant in vivo targets of HIV, is useful to further investigate interactions between HIV, DC and T cells, without the need for primary ex vivo DC.

The HIV-2 genotype and the HIV-1 syncytium-inducing phenotype are associated with a lower virus replication in dendritic cells.

During sexual transmission, HIV infects the mucosal dendritic cells and is transferred to CD4 T cells. Whether HIV variants of a particular genetic (sub)type or phenotype selectively infect dendritic cells (DC) or are preferentially transferred to T cells remains highly controversial. To avoid the cumbersome use of primary dendritic cells, in vitro dendritic cell models were generated from precursors, either hematopoietic progenitor cells (HPC) or monocytes (MO). Productive infection in the dendritic cells and transfer of the virus to T cells was assessed for a range of HIV variants. HPC-derived dendritic cells (HPC-DC) were more susceptible to HIV-1 than to HIV-2 isolates. The HIV-1 group O strains were more productive in HPC-DC than group M, but amongst the latter, no subtype-related difference was observed. Both non-syncytium-inducing (NSI) and SI HIV isolates and lab strains could productively infect HPC-DC, albeit with a different efficiency. Adding blocking antibodies confirmed that both CCR-5 and CXCR-4 co-receptors were functional. Biological HIV-1 clones of the NSI/R5 phenotype infected more readily HPC-DC than SI/X4 clones. MO-derived dendritic cells were, however, more exclusive in their preference for NSI/R5 clones. Some HIV variants, that did not grow readily in HPC-DC alone, could be rescued by adding resting or pre-activated T cells. The present data show that HIV-2 isolates and SI clones replicate less in model-DC, but no preference for a particular HIV-1 subtype was evident. Co-culture with T cells could "correct" a limited growth in dendritic cells. Clearly, both intrinsic dendritic cell susceptibility and enhancement by T cells are explained only partly by HIV genotype and phenotype. The in vitro dendritic cell models seem useful tools to further unravel interactions between HIV, DC, and T cells.

Decreased CD40 ligand induction in CD4 T cells and dysregulated IL-12 production during HIV infection.

During HIV infection various cytokines are overproduced in early stages, whereas in advanced disease cytokines of the T helper 1 type (e.g. interferon-gamma (IFN-gamma)) are selectively deficient. During antigenic stimulation, the production of type-1 cytokines is enhanced by IL-12, secreted by antigen-presenting cells (APC) after their interaction with activated CD4 T cells. Two factors are essential in this process: priming APC with IFN-gamma and triggering the CD40 receptor on APC by CD40 ligand (CD40L). In view of the importance of this pathway, we compared its regulation in HIV-infected and control subjects. After cross-linking of the T cell receptor (TCR)/CD3 complex, the proportional expression of CD40L was similar on CD4+ T cells from controls and from patients with high circulating CD4 T counts (> 500/microl), but CD40L up-regulation was significantly reduced in patients with more advanced disease. Simultaneous triggering of the costimulatory receptor CD28 on T cells through its natural ligand CD80 partly corrected the CD40L defect in patients with intermediate CD4 T counts (200-500), but not in AIDS patients. Early production of IFN-gamma was preserved in lymphocytes from HIV+ patients. The expression of CD40 on peripheral monocytes from HIV+ subjects was increased in a disease stage-related fashion. Stimulation of mononuclear cells through cell-bound CD40L and soluble IFN-gamma induced significantly higher IL-12 in cultures from patients with > 200 circulating CD4 T cells, whereas IL-12 production was marginally decreased in cultures from patients with < 200 CD4 T cells, compared with healthy control cultures. In conclusion, our data suggest that impaired CD40L induction on CD4 T cells contributes to deficient type-1 responses through decreased IL-12 production in AIDS infection, whereas enhanced CD40-mediated IL-12 production in less advanced stages might contribute to increased levels of various cytokines in early disease