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- Akdis, M, et al.
(författare)
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Immune responses in healthy and allergic individuals are characterized by a fine balance between allergen-specific T regulatory 1 and T helper 2 cells
- 2004
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 0022-1007 .- 1540-9538. ; 199:11, s. 1567-1575
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms by which immune responses to nonpathogenic environmental antigens lead to either allergy or nonharmful immunity are unknown. Single allergen-specific T cells constitute a very small fraction of the whole CD4(+) T cell repertoire and can be isolated from the peripheral blood of humans according to their cytokine profile. Freshly purified interferon-gamma-, interleukin (IL)-4-, and IL-10-producing allergen-specific CD4(+) T cells display characteristics of T helper cell (Th)1-, Th2, and T regulatory (Tr)1-like cells, respectively. Tr1 cells consistently represent the dominant subset specific for common environmental allergens in healthy individuals; in contrast, there is a high frequency of allergen-specific IL-4-secreting T cells in allergic individuals. Tr1 cells use multiple suppressive mechanisms, IL-10 and TGF-beta as secreted cytokines, and cytotoxic T lymphocyte antigen 4 and programmed death 1 as surface molecules. Healthy and allergic individuals exhibit all three allergen-specific subsets in different proportions, indicating that a change in the dominant subset may lead to allergy development or recovery. Accordingly, blocking the suppressor activity of Tr1 cells or increasing Th2 cell frequency enhances allergen-specific Th2 cell activation ex vivo. These results indicate that the balance between allergen-specific Tr1 cells and Th2 cells may be decisive in the development of allergy.
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- Zhong, C. J., et al.
(författare)
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Capacity Bounds for AF Dual-hop Relaying in G Fading Channels
- 2012
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 61:4, s. 1730-1740
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ergodic capacity of amplify-and-forward (AF) dual-hop relaying systems in composite Nakagami-m/inverse-Gaussian fading channels. This type of fading, which is known in the literature as G fading, has recently attracted increasing research interest due to its ability to better approximate the Nakagami-m/lognormal model, compared with the Nakagami-m/gamma model. We study both fixed-and variable-gain relaying systems and present analytical upper and lower bounds for the ergodic capacity of dual-hop relaying systems with not necessarily identical hops; these bounds provide an efficient means to evaluate the ergodic capacity of AF dual-hop relaying systems over G fading channels. We also establish sufficient conditions for the existence of the bounds, depending on the values of the fading parameters. In both cases, our simulation results demonstrate that the proposed upper and lower bounds remain relatively tight for different fading conditions.
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| 9. |
- Zhong, C. J., et al.
(författare)
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Generic Ergodic Capacity Bounds for Fixed-Gain AF Dual-Hop Relaying Systems
- 2011
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Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 60:8, s. 3814-3824
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Tidskriftsartikel (refereegranskat)abstract
- This paper elaborates on the ergodic capacity of fixed-gain amplify-and-forward (AF) dual-hop systems, which have recently attracted considerable research and industry interest. In particular, two novel capacity bounds that allow for fast and efficient computation and apply for nonidentically distributed hops are derived. More importantly, they are generic since they apply to a wide range of popular fading channel models. Specifically, the proposed upper bound applies to Nakagami-m, Weibull, and generalized-K fading channels, whereas the proposed lower bound is more general and applies to Rician fading channels. Moreover, it is explicitly demonstrated that the proposed lower and upper bounds become asymptotically exact in the high signal-to-noise ratio (SNR) regime. Based on our analytical expressions and numerical results, we gain valuable insights into the impact of model parameters on the capacity of fixed-gain AF dual-hop relaying systems.
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