RESUMO
It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km(3) rock) yr(-1), defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate.
RESUMO
Monocyte/macrophage differentiation was studied in biopsy samples of multiple sclerosis (MS) lesions obtained in the early course of the disease. Macrophages were identified by immunocytochemistry using a panel of antibodies recognizing different macrophage-activation antigens. The number of cells stained with each antibody was related to the demyelinating activity of the lesions as detected by the presence of myelin degradation products. The pan-macrophage marker Ki-M1P revealed the highest numbers of macrophages in early and late active lesions. Lower numbers were encountered in inactive, demyelinated, or remyelinated lesions. The acute stage inflammatory macrophage markers MRP14 and 27E10 were expressed in either only early active (MRP14) or early and late active (27E10) lesions, thus allowing the identification of actively demyelinating lesions. The chronic stage inflammatory macrophage marker 25F9, in contrast, showed increasing expression with decreasing lesional activity. These findings indicate a differentiated pattern of macrophage activation in MS lesions and allow the staging of demyelinating lesions in routinely fixed and paraffin-embedded tissue.