The Early Devonian Rhynie hot spring system is the oldest known and is of the low sulphidation type. It extends for at least 1.5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments, plant-bearing sinters and andesitic lavas. The age of sedimentation and hydrothermal activity has been determined by palynological (Pragian) and radiometric (396 f 12 Ma) techniques. The outlier is a half graben with a complex stepped western margin.The Devonian rocks show intense hydrothermal alteration along the fault zone.The main alteration minerals are quartz, K-feldspar, calcite, hematite and illitic and chloritic clays. Multiple chert veining and brecciation are widely developed, and geyserite and vent material are also present. Pyrite occurs in veins and all alteration facies. Sinters and altered rocks contain high concentrations of Au, As, Sb, Hg, W and MO. Gold occurs in arsenian pyrite and as sub-micron particles in oxidized rocks.The fluid(s) responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water. However, incursions of high temperature (300-440°C) magmatic fluids occurred with SD -65960 and S'*O around +8.59~. 634S (pyrite) and initial *' Sr/%r ratios (vein calcite) lie mainly within the ranges +3.4%0 to +8.5% and 0.71138 to 0.71402 respectively. These data indicate that late Proterozoic Dalradian metasediments are a likely source for S and Sr but other sources are possible. 613C values for caliche and vein calcite imply derivation of carbon from non-organic sources.The Rhynie cherts were deposited from a low salinity fluid of probable meteoric origin (S1'Ochen +13.1% to +16.5%) which had interacted with the basement rocks and sediments (high Xe/Ar, Br/CI and I/Cl ratios). Plant-bearing chert yielded an 40Ar/39Ar ratio (292.1 f 0.6) significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere.

Glucocorticoids are highly effective in the treatment of allergy and asthma and inhibit the synthesis of IL‐4, IL‐5 and IL‐13 by disease‐promoting CD4+ Th2 cells. CD8+ T cells also synthesize these cytokines, and the aim of this study was to investigate how glucocorticoids effect cytokine production by these cells. When CD8+ T cells are stimulated with anti‐CD3 and IL‐2 plus IL‐4 or dexamethasone, production of the anti‐inflammatory cytokine IL‐10 is low in both primary and secondary cultures restimulated with anti‐CD3 and IL‐2 alone. However, when both are present, a synergistic effect on IL‐10 synthesis is observed. The additional presence of antigen‐presenting cells (APC) in the priming culture maintains IL‐10 levels, but inhibits IL‐4 and IL‐5 production. CD4+ T cells develop a similar glucocorticoid‐induced phenotype. These cells demonstrate regulatory activity and inhibit CD4+ T cell activation in an IL‐10‐dependent manner. Earlier reports show glucocorticoids promote a Th2 phenotype by effects on purified naive T cells or pretreatment of APC. This study demonstrates, more critically, that when APC are present, glucocorticoids induce CD4 and CD8 T cell populations synthesizing high levels of IL‐10, but greatly reduced amounts of disease‐promoting IL‐4 and IL‐5.