TCR revision generates functional CD4+ T cells

CD4(+)Vβ5(+) peripheral T cells in C57BL/6 mice respond to encounter with a peripherally expressed endogenous superantigen by undergoing either deletion or TCR revision. In this latter process, cells lose surface Vβ5 expression and undergo RAG-dependent rearrangement of endogenous TCRβ genes, driving surface expression of novel TCRs. Although postrevision CD4(+)Vβ5(-)TCRβ(+) T cells accumulate with age in Vβ5 transgenic mice and bear a diverse TCR Vβ repertoire, it is unknown whether they respond to homeostatic and antigenic stimuli and thus may benefit the host. We demonstrate in this study that postrevision cells are functional. These cells have a high rate of steady-state homeostatic proliferation in situ, and they undergo extensive MHC class II-dependent lymphopenia-induced proliferation. Importantly, postrevision cells do not proliferate in response to the tolerizing superantigen, implicating TCR revision as a mechanism of tolerance induction and demonstrating that TCR-dependent activation of postrevision cells is not driven by the transgene-encoded receptor. Postrevision cells proliferate extensively to commensal bacterial Ags and can generate I-A(b)-restricted responses to Ag by producing IFN-γ following Listeria monocytogenes challenge. These data show that rescued postrevision T cells are responsive to homeostatic signals and recognize self- and foreign peptides in the context of self-MHC and are thus useful to the host.     

Assessing the long-term impact of land-use and land-cover changes on soil erosion in Ethiopia’s Chemoga Basin using the RUSLE model

Soil erosion is one of the primary causes of environmental degradation worldwide. The Chemoga Basin—the highlands region in northwestern Ethiopia—has experienced accelerated soil erosion due to changes in land-use and land-cover (LULC) in recent decades. The Revised Universal Soil Loss Equation (RUSLE) model was used to quantify the impact of LULC changes on soil loss in the study area. Satellite images from 1987 and 2017 were used to characterize the spatial patterns of LULC changes. All RUSLE factors were mapped on a 30?m ×?30 m grid to reflect the natural and environmental conditions of the study area. An expansion of agricultural lands occurred between 1987 and 2017, while the area of natural vegetation cover such as woodlands and grasslands declined. Forest cover has recovered in recent years as a result of afforestation and eucalyptus plantations. Reflecting LULC changes, the total soil loss in the study area was estimated at 2,087,894 t year^–1 in 1987, which increased to 2,112,093 t year^–1 in 2017. Agricultural lands accounted for 89.3% and 90.1% of the total soil loss in 1987 and 2017, respectively. The results showed that slope gradient and elevation are important factors in agricultural land conversion, and thereby influence soil erosion. An understanding of the impact of LULC changes on soil erosion potential is crucial for establishing government policy and action plans to conserve natural resources in erosion-prone areas of the Ethiopian highlands.