University of Cologne

About: University of Cologne is a education organization based out in Cologne, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 32050 authors who have published 66350 publications receiving 2210092 citations. The organization is also known as: Universität zu Köln & Universitatis Coloniensis.

Evolutionary and somatic selection of the antibody repertoire in the mouse

Abstract: The repertoire of antibody variable (V) regions has been subject to evolutionary selection, affecting both the diversity of V region genes in the germline and their expression in the B lymphocyte population and its subsets. In ontogeny, contact with an antigen leads to the expansion of B cells expressing antibodies complementary to it. In a defined phase of B cell differentiation, new sets of V regions are generated from the existing repertoire through somatic hypermutation. Cells carrying advantageous antibody mutants are selected into the memory compartment and produce a stable secondary response upon reexposure to the antigen.

2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia

Abstract: The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) ...

Thermodynamics of spin S = 1 / 2 antiferromagnetic uniform and alternating-exchange Heisenberg chains

Abstract: The magnetic susceptibility ${\ensuremath{\chi}}^{*}(t)$ and specific heat $C(t)$ versus temperature t of the spin $S=1/2$ antiferromagnetic (AF) alternating-exchange ${(J}_{1}$ and ${J}_{2})$ Heisenberg chain are studied for the entire range $0l~\ensuremath{\alpha}l~1$ of the alternation parameter $\ensuremath{\alpha}\ensuremath{\equiv}{J}_{2}{/J}_{1}{(J}_{1},$ ${J}_{2}g~0,$ ${J}_{2}l~{J}_{1},$ ${t=k}_{\mathrm{B}}{T/J}_{1},$ ${\ensuremath{\chi}}^{*}=\ensuremath{\chi}{J}_{1}{/Ng}^{2}{\ensuremath{\mu}}_{B}^{2}).$ For the uniform chain $(\ensuremath{\alpha}=1),$ the high-accuracy ${\ensuremath{\chi}}^{*}(t)$ and $C(t)$ Bethe ansatz data of Kl\"umper and Johnston (unpublished) are shown to agree very well at low t with the respective exact theoretical low-$t$ logarithmic correction predictions of Lukyanov [Nucl. Phys. B $522,$ 533 (1998)]. Accurate $(\ensuremath{\sim}{10}^{\ensuremath{-}7})$ independent empirical fits to the respective data are obtained over t ranges spanning 25 orders of magnitude, $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}l~tl~5,$ which contain extrapolations to the respective exact $t=0$ limits. The infinite temperature entropy calculated using our $C(t)$ fit function is within 8 parts in ${10}^{8}$ of the exact value $\mathrm{ln}2.$ Quantum Monte Carlo (QMC) simulations and transfer-matrix density-matrix renormalization group (TMRG) calculations of ${\ensuremath{\chi}}^{*}(\ensuremath{\alpha},t)$ are presented for $0.002l~tl~10$ and $0.05l~\ensuremath{\alpha}l~1,$ and an accurate $(2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4})$ two-dimensional $(\ensuremath{\alpha},t)$ fit to the combined data is obtained for $0.01l~tl~10$ and $0l~\ensuremath{\alpha}l~1.$ From the low-$t$ TMRG data, the spin gap $\ensuremath{\Delta}(\ensuremath{\alpha})$ is extracted for $0.8l~\ensuremath{\alpha}l~0.995$ and compared with previous results, and a fit function is formulated for $0l~\ensuremath{\alpha}l~1$ by combining these data with literature data. We infer from our data that the asymptotic critical regime near the uniform chain limit is only entered for $\ensuremath{\alpha}\ensuremath{\gtrsim}0.99.$ We examine in detail the theoretical predictions of Bulaevskii [Sov. Phys. Solid State $11,$ 921 (1969)], for ${\ensuremath{\chi}}^{*}(\ensuremath{\alpha},t)$ and compare them with our results. To illustrate the application and utility of our theoretical results, we model our experimental $\ensuremath{\chi}(T)$ and specific heat ${C}_{\mathrm{p}}(T)$ data for ${\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ single crystals in detail. The $\ensuremath{\chi}(T)$ data above the spin dimerization temperature ${T}_{\mathrm{c}}\ensuremath{\approx}34\mathrm{K}$ are not in quantitative agreement with the prediction for the $S=1/2$ uniform Heisenberg chain, but can be explained if there is a moderate ferromagnetic interchain coupling and/or if J changes with T. Fitting the $\ensuremath{\chi}(T)$ data using our ${\ensuremath{\chi}}^{*}(\ensuremath{\alpha},t)$ fit function, we obtain the sample-dependent spin gap and range $\ensuremath{\Delta}{(T=0)/k}_{\mathrm{B}}=103(2)\mathrm{K},$ alternation parameter $\ensuremath{\delta}(0)\ensuremath{\equiv}(1\ensuremath{-}\ensuremath{\alpha})/(1+\ensuremath{\alpha})=0.034(6)$ and average exchange constant ${J(0)/k}_{\mathrm{B}}=640(80)\mathrm{K}.$ The $\ensuremath{\delta}(T)$ and $\ensuremath{\Delta}(T)$ are derived from the data. A spin pseudogap with magnitude $\ensuremath{\approx}0.4\ensuremath{\Delta}(0)$ is consistently found just above ${T}_{\mathrm{c}},$ which decreases with increasing temperature. From our ${C}_{\mathrm{p}}(T)$ measurements on two crystals, we infer that the magnetic specific heat at low temperatures $T\ensuremath{\lesssim}15\mathrm{K}$ is too small to be resolved experimentally, and that the spin entropy at ${T}_{\mathrm{c}}$ is too small to account for the entropy of the transition. A quantitative analysis indicates that at ${T}_{\mathrm{c}},$ at least 77% of the entropy change due to the transition at ${T}_{\mathrm{c}}$ and associated order parameter fluctuations arise from the lattice and/or charge degrees of freedom and less than 23% from the spin degrees of freedom.

UV-induced reactive oxygen species in photocarcinogenesis and photoaging.

Abstract: The increase in UV irradiation on earth due to the stratospheric ozone depletion represents a major environmental threat to the skin increasing its risk of photooxidative damage by UV-induced reactive oxygen species (ROS). Increased ROS load has been implicated in several pathological states including photoaging and photocarcinogenesis of the skin. Large efforts have been made to better define the involvement of distinct ROS in photocarcinogenesis and photoaging. Both pathological processes share common features; however, they reveal unique molecular characteristics which finally determine the fate of the cell and its host. As well as causing permanent genetic changes involving protooncogenes and tumor suppressor genes, ROS activate cytoplasmic signal transduction pathways that are related to growth differentiation, senescence, transformation and tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in biochemical and clinical characteristics of photocarcinogenesis and photoaging. A decrease in the ROS load by efficient sunscreens and/or otherwise protective agents may represent a promising strategy to prevent or at least minimize ROS induced cutaneous pathological states.

Expression of p16 protein identifies a distinct entity of tonsillar carcinomas associated with human papillomavirus.

Abstract: Recent analyses of head and neck squamous cell carcinomas revealed frequent infections by oncogenic human papillomavirus (HPV) type 16 in tonsillar carcinomas. Concerning involvement of risk factors, clinical course of the disease, and prognosis there are strong indications arguing that the HPV-positive tonsillar carcinomas may represent a separate tumor entity. Looking for a surrogate marker, which in further epidemiological studies could replace the laborious and expensive HPV detection and typing we analyzed p16 protein expression in 34 tonsillar carcinoma for correlation to HPV status and load of viral DNA. p16 has been shown to be of diagnostic value for clinical evaluation of cervical dysplasia. We found 53% of the tested tonsillar carcinomas to be HPV-positive. Fifty-six percent of all tumors tested were immunohistochemically positive for the p16 protein. In 16 of 18 of the HPV-positive carcinomas diffuse p16 expression was observed. In contrast, only one of the HPV-negative carcinomas showed focal p16 staining (P < 0.001). As determined by laser-assisted microdissection and quantitative real-time polymerase chain reaction, p16 expression correlated with the presence of HPV-DNA in the individual tumor specimens. Clinical outcome analysis revealed significant correlation of p16 expression with increased disease-free survival (P = 0.02). These data indicate that p16 is a technically simple immunohistological marker, applicable for routine pathological histology, and its prognostic value for survival is fully equivalent to HPV-DNA detection.