A comparison of surface moisture budget and structural equation models in high latitudes: evapotranspiration and atmospheric drivers

Thesis (M.S.) University of Alaska Fairbanks, 2021Arctic soil moisture is one of the most impactful and unknown aspects of the Arctic climate system. As the climate changes, surface soil moisture can impact water supplies, wildfire risk, and vegetation stress, all of which have consequences for terrestrial ecosystems and human activities. The present analysis is intended to (1) document seasonal and interannual variations of surface moisture fluxes in the Arctic region and (2) clarify the drivers of variations of net Precipitation minus Evapotranspiration (P-ET) across Arctic tundra and boreal vegetation and permafrost status. Forty-five flux tower sites were examined across boreal and tundra ecosystems across the Arctic and sub-arctic. The surface moisture budget at boreal forest sites in permafrost areas generally shows a moisture deficit in late spring and early summer, followed by a moisture surplus from late summer into autumn. The annual net P-ET is generally positive but can vary interannually by more than an order of magnitude. A factor analysis found the primary drivers of variations in evapotranspiration to be radiative fluxes, air temperature, and relative humidity, while a path analysis found windspeed to have the largest independent influence on evapotranspiration. Overall, the ET at boreal forest sites shows a stronger dependence on relative humidity, and ET at tundra sites shows the stronger dependence on air temperature. These differences imply that tundra sites are more temperature-limited and boreal sites are more humidity-dependent. Relative to nearby unburned sites, the recovery time of ET after disturbance by wildfire was found to vary from several years on the Alaska tundra to nearly a decade in the Alaska boreal forest.National Science Foundation, Office of Polar Programs Grant ARC-183013

Immune Responses in Healthy and Allergic Individuals Are Characterized by a Fine Balance between Allergen-specific T Regulatory 1 and T Helper 2 Cells

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-γ–, 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-β 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

Novel treatment strategies and regulation of IgE-mediated allergic disease.

Allergic symptoms such as rhinoconjunctivitis, asthma or gastrointestinal symptoms, triggered by inhaled or ingested allergens cross-linking allergen-specific IgE on mast cells or basophils, are defined as IgE-mediated allergy. The major allergens from birch pollen (Bet v 1) and cat dander (Fel d 1) are two common allergens eliciting allergic disease. Allergen-specific immunotherapy (SIT) is the only curative treatment for IgE-mediated allergy. It is long-lasting and involves repeated injections of crude allergen extracts. Successful SIT modifies a number of allergen-associated immunological responses. SIT has been shown to induce IL-10 producing regulatory T-cells (Treg), allergen-specific T- and B-cell anergy as well as blocking antibodies. Although effective, SIT is associated with a risk for treatment side effects. This has led to the development of novel treatment strategies, such as modified recombinant allergens with reduced allergenicity (hypoallergens) and new means of antigen delivery. The general aim of this thesis is to investigate regulation of allergic immune responses and how novel strategies for SIT affect those responses. The first article describes an eight injection short-course SIT study with Bet v 1 hypoallergens; where 27 birch pollen allergic patients participated. The major findings were that SIT with genetically modified Bet v 1 hypoallergens induced allergen-specific neutralizing antibodies and reduced immediate skin reactivity as well as the number of IL-5 and IL-13 producing cells. Even though rBet v 1 hypoallergen treatment exhibited typical immunological features of successful allergen-specific immunotherapy, there was no increase in the number of IL-10 producing cells after treatment. In the second study we therefore decided to evaluate the role of the suppressive cytokines IL-10 and TGFb as well as natural FOXP3+ Treg cells in immune-regulation of allergic immune responses. We found that unlike Treg cells from non-allergic controls, Treg cells from birch pollen-allergic patients displayed an impaired ability to suppress birch-pollen stimulated effector cells. Neutralization of IL-10 in CD4+CD25+ Treg cell and CD4+CD25- effector cell co-cultures induced a significant increase of TNFa secretion, suggesting that IL-10 and TNFa may have counter-acting properties in the periphery, where IL-10 promotes tolerance and suppression by Treg cells and TNFa promotes inflammatory responses. In the third and fourth article, recombinant (r) Fel d 1 was coupled to the novel adjuvant carbohydrate based particles (CBPs) and investigated in a mouse model sensitized to Fel d 1. Pre-treatment with CBP-rFel d 1 was able to induce antigen-specific T-cell tolerance and shift immunoglobulin production from an IgE to an IgG2a type of response. Antigen-coupled CBPs also demonstrated improved antigen depot-effects with prolonged antigen-exposure, when compared to the most commonly used adjuvant in vaccine preparations for humans; aluminum hydroxide. Furthermore, CBP-rFel d 1 was tested in a treatment protocol for SIT, where it was able to modulate the allergic immune response in rFel d 1 sensitized mice without adverse effects. Thus, CBPs ability to promote induction of potent immune responses and to deliver allergens without risk of systemic allergen spreading are beneficial properties of an adjuvant aimed to be used in allergen-specific immunotherapy. Possibly, CBPs coupled to infectious or auto-immune antigens could be applied as an adjuvant to prevent other types of diseases. In conclusion, the work presented in this thesis has shed new light on in vivo function of two conceptually different approaches to improve allergen-specific immunotherapy. The thesis has also contributed to increased understanding regarding regulation of allergic immune-responses, thus providing a basis for further research

Diagnosis of Atmospheric Drivers of High-Latitude Evapotranspiration Using Structural Equation Modeling

Evapotranspiration (ET) is a relevant component of the surface moisture budget and is associated with different drivers. The interrelated drivers cause variations at daily to interannual timescales. This study uses structural equation modeling to diagnose the drivers over an ensemble of 45 high-latitude sites, each of which provides at least several years of in situ measurements, including latent heat fluxes derived from eddy covariance flux towers. The sites are grouped by vegetation type (tundra, forest) and the presence or absence of permafrost to determine how the relative importance of different drivers depends on land surface characteristics. Factor analysis is used to quantify the common variance among the variables, while a path analysis procedure is used to assess the independent contributions of different variables. The variability of ET at forest sites generally shows a stronger dependence on relative humidity, while ET at tundra sites is more temperature-limited than moisture-limited. The path analysis shows that ET has a stronger direct correlation with solar radiation than with any other measured variable. Wind speed has the largest independent contribution to ET variability. The independent contribution of solar radiation is smaller because solar radiation also affects ET through various other drivers. The independent contribution of wind speed is especially apparent at forest wetland sites. For both tundra and forest vegetation, temperature loads higher on the first factor when permafrost is present, implying that ET will become less sensitive to temperature as permafrost thaws

Low levels of endotoxin enhance allergen-stimulated proliferation and reduce the threshold for activation in human peripheral blood cells

Background: Endotoxins, comprised of bacterial cell wall lipopolysaccharides (LPS), have been reported to have both protective and exacerbating effects on the development and maintenance of allergic disease in humans and on markers of allergic inflammation in animal models of allergy. In this study, we investigated the effect of low concentrations of LPS on human peripheral blood mononuclear cells (PBMC) stimulated with the major cat allergen Fel d 1. Methods: Extensive purification of recombinant (r) Fel d 1 yielded essentially endotoxin-free rFel d 1 (0.2 ng LPS/mg protein). PBMCs prepared from 15 subjects having IgE to cat ( gt 0.7 kU(A)/l) and 8 subjects IgE negative to cat were stimulated with 2, 10 or 25 mu g/ml of rFel d 1 in the presence or absence of 50 pg/ml LPS. Proliferation was measured after 7 days of culture and supernatants were analyzed for IFN gamma, IL-5 and IL-10. Results: LPS (50 pg/ml) increased rFel d 1-stimulated proliferation of PBMCs both from subjects IgE-positive and subjects negative to cat allergens. PBMCs from 13 of the subjects did not proliferate in response to stimulation with 2 and 10 mu g/ml rFel d 1 alone but did so in the presence of LPS. Moreover, LPS increased the levels of rFel d 1-stimulated IFN gamma in cultures from cat-negative subjects, IL-5 from cat-positive subjects and IL-10 from both groups. Conclusion: Very low doses of LPS enhance proliferation and decrease the apparent threshold level for cell activation, prompting careful evaluation of allergen stimulated T cell activation in vitro. Copyright (C) 2007 S. Karger AG, Basel

Structural characterization of the tetrameric form of the major cat allergen Fel d 1

Felis domesticus allergen 1(Fel d 1) is a 35 kDa tetrameric glycoprotein formed by two heterodimers which elicits IgE responses in 95% of patients with allergy to cat. We have previously established in vitro conditions for the appropriate folding of recombinant Fel d 1 using a direct linkage of chain I to chain 2 (construct Fel d 1 (1 + 2)) and chain 2 to chain 1 (construct Fel d 1 (2 + 1)). Although the crystal structure of Fel d 1 (2 + 1) revealed a striking structural similarity to that of uteroglobin, a steroid-inducible cytokine-like molecule with anti-inflammatory and immunomodulatory properties, no functional tetrameric form of Fel d I could be identified. Here we present the crystal structure of the Fel d I (1 +2) tetramer at 1.6 angstrom resolution. Interestingly, the crystal structure of tetrameric Fel d I reveals two different calcium-binding sites. Symmetrically positioned on each side of the Fel d 1 tetramer, the external Ca2+ -binding sites correspond to a putative Ca2+- binding site previously suggested for uteroglobin. The second Ca2+-binding site lies within the dimerization interface, stabilizing the formation of the Fel d 1 tetramer, and inducing important local conformational changes that directly govern the shape of two water-filled cavities. The crystal structure suggests a potential portal for an unknown ligand. Alternatively, the two cavities could be used by the allergen as a conditional inner space allowing for the spatial rearrangement of centrally localized side-chains, such as Asp130, without altering the overall fold of the molecule. The striking structural similarity of the major cat allergen to uteroglobin, coupled to the identification in the present study of a common Ca2+ -binding site, let us speculate that Fel d I could provoke an allergic response through the modulation of phospholipase A2, by sequestering Ca ions in a similar manner as previously suggested for uteroglobin. (c) 2007 Elsevier Ltd. All rights reserved