X-Ray Diffraction, Calorimetric and Dielectric Relaxation Study of the Amorphous and Smectic States of a Main Chain Liquid Crystalline Polymer

Los polímeros cristales líquidos (LCP) son sistemas complejos que forman mesofases que presentan orden orientacional y polímeros amorfos. Con frecuencia, el estado amorfo isotrópico no puede ser estudiado debido a la rápida formación de mesofases. En este trabajo se ha sintetizado y estudiado un nuevo LCP: poli(trietilenglicol metil p, p '-bibenzoato), PTEMeB. Este polímero presenta una formación de mesofase bastante lenta haciendo posible estudiar de forma independiente tanto los estados amorfo y de cristal líquidos. La estructura y las transiciones de fase del PTEMeB han sido investigados por calorimetría (DSC), con MAXS / WAXS con temperatura variable que emplean radiación de sincrotrón y con difracción de rayos X. Estos estudios han mostrado la existencia de dos transiciones vítreas, relacionadas con las fases amorfa y cristal líquido. Se ha realizado un estudio de relajación dieléctrica en amplios intervalos de temperatura y presión. Se ha encontrado que la transición vítrea dinámica de la fase amorfa es más lenta que la del cristal líquido. El estudio de la relajación ? nos ha permitido seguir la formación isoterma de la mesofase a presión atmosférica. Además, con el estudio el comportamiento dinámico a alta presión se ha encontrado que se produce la formación rápida de la mesofase inducida por cambios bruscos de presión. Liquid crystalline polymers (LCPs) are complex systems that include features of both orientationally ordered mesophases and amorphous polymers. Frequently, the isotropic amorphous state cannot be studied due to the rapid mesophase formation. Here, a new main chain LCP, poly(triethyleneglycol methyl p,p'-bibenzoate), PTEMeB, has been synthesized. It shows a rather slow mesophase formation making possible to study independently both the amorphous and the liquid crystalline states. The structure and phase transitions of PTEMeB have been investigated by calorimetry, variable-temperature MAXS/WAXS employing synchrotron radiation, and X-ray diffraction in oriented fibers. These experiments have pointed out the presence of two glass transitions, related to the amorphous or to the liquid crystal phases. Additionally, the mesophase seems to be a coexistence of orthogonal and tilted smectic phases. A dielectric relaxation study of PTEMeB over broad ranges of temperature and pressure has been performed. The dynamic glass transition turns out to be slower for the amorphous state than for the liquid crystal. Monitoring of the α relaxation has allowed us to follow the isothermal mesophase formation at atmospheric pressure. Additionally, the dynamical behavior at high pressures has pointed out the fast formation of the mesophase induced by sudden pressure changes.

Cathepsins B and D are dispensable for major histocompatibility complex class II-mediated antigen presentation

Antigen presentation by major histocompatibility complex (MHC) class II molecules requires the participation of different proteases in the endocytic route to degrade endocytosed antigens as well as the MHC class II-associated invariant chain (Ii). Thus far, only the cysteine protease cathepsin (Cat) S appears essential for complete destruction of Ii. The enzymes involved in degradation of the antigens themselves remain to be identified. Degradation of antigens in vitro and experiments using protease inhibitors have suggested that Cat B and Cat D, two major aspartyl and cysteine proteases, respectively, are involved in antigen degradation. We have analyzed the antigen-presenting properties of cells derived from mice deficient in either Cat B or Cat D. Although the absence of these proteases provoked a modest shift in the efficiency of presentation of some antigenic determinants, the overall capacity of Cat B−/− or Cat D−/− antigen-presenting cells was unaffected. Degradation of Ii proceeded normally in Cat B−/− splenocytes, as it did in Cat D−/− cells. We conclude that neither Cat B nor Cat D are essential for MHC class II-mediated antigen presentation.

Major histocompatibility complex class I-restricted T cells are required for all but the end stages of diabetes development in nonobese diabetic mice and use a prevalent T cell receptor α chain gene rearrangement

Nonobese diabetic (NOD) mice develop insulin-dependent diabetes mellitus due to autoimmune T lymphocyte-mediated destruction of pancreatic β cells. Although both major histocompatibility complex class I-restricted CD8+ and class II-restricted CD4+ T cell subsets are required, the specific role each subset plays in the pathogenic process is still unclear. Here we show that class I-dependent T cells are required for all but the terminal stages of autoimmune diabetes development. To characterize the diabetogenic CD8+ T cells responsible, we isolated and propagated in vitro CD8+ T cells from the earliest insulitic lesions of NOD mice. They were cytotoxic to NOD islet cells, restricted to H-2Kd, and showed a diverse T cell receptor β chain repertoire. In contrast, their α chain repertoire was more restricted, with a recurrent amino acid sequence motif in the complementarity-determining region 3 loop and a prevalence of Vα17 family members frequently joined to the Jα42 gene segment. These results suggest that a number of the CD8+ T cells participating in the initial phase of autoimmune β cell destruction recognize a common structural component of Kd/peptide complexes on pancreatic β cells, possibly a single peptide.

Self-antigen does not accelerate immature B cell apoptosis, but stimulates receptor editing as a consequence of developmental arrest

In pre-B lymphocytes, productive rearrangement of Ig light chain genes allows assembly of the B cell receptor (BCR), which selectively promotes further developmental maturation through poorly defined transmembrane signaling events. Using a novel in vitro system to study immune tolerance during development, we find that BCR reactivity to auto-antigen blocks this positive selection, preventing down-regulation of light chain gene recombination and promoting secondary light chain gene rearrangements that often alter BCR specificity, a process called receptor editing. Under these experimental conditions, self-antigen induces secondary light chain gene rearrangements in at least two-thirds of autoreactive immature B cells, but fails to accelerate cell death at this stage. These data suggest that in these cells the mechanism of immune tolerance is receptor selection rather than clonal selection.

Hodgkin and Reed–Sternberg cells in lymphocyte predominant Hodgkin disease represent clonal populations of germinal center-derived tumor B cells

Among the four subtypes of Hodgkin disease (HD), lymphocyte-predominant (LP) HD is now generally considered as a separate entity. The B cell nature of the typical Hodgkin and Reed–Sternberg (HRS) cells and their variants (L and H, lymphocytic and histiocytic cells) in LP HD has long been suspected, but the question of whether these cells represent a true tumor clone is unclear. We previously demonstrated clonal Ig gene rearrangements in one case of LP HD. In the present study, five cases of LP HD were analyzed by micromanipulation of single HRS cells from frozen tissue sections and DNA amplification of rearranged Ig heavy chain genes from those cells. Clonal V gene rearrangements harboring somatic mutations were detected in each case. In three cases ongoing somatic mutation was evident. This shows that HRS cells in LP HD are a clonal tumor population derived from germinal center B cells. The pattern of somatic mutation indicates that HRS cells in LP HD are selected for antibody expression. This, and the presence of ongoing mutation discriminates LP from classical HD.

A critical role of Lyn and Fyn for B cell responses to CD38 ligation and interleukin 5

CD38 ligation on mouse B cells by CS/2, an anti-mouse CD38 mAb, induced proliferation, interleukin 5 (IL-5) receptor α chain expression, and tyrosine phosphorylation of Bruton tyrosine kinase (Btk) from wild-type, but not from X chromosome-linked, immunodeficient mice. B cells from fyn-deficient (Fyn−/−) and lyn-deficient (Lyn−/−) mice showed an impaired response to mAb CS/2 for proliferation and IL-5 receptor α chain expression, and B cells from fyn/lyn double-deficient (Fyn/Lyn−/−) mice did not respond at all to mAb CS/2. The Btk activation by CD38 ligation was observed in B cells from Fyn−/− mice, and it was severely impaired in B cells from Lyn−/− and Fyn/Lyn−/− mice. CD38 expression on B cells from three mutant strains was comparable to that on control B cells. We infer from these results that both Fyn and Lyn are required and that their signals are synergistic for B cell triggering after CD38 ligation. Lyn is upstream of Btk activation in the CD38 signaling. Stimulation of B cells with IL-5 together with CD38 ligation induces not only IgM but also IgG1 secretion. Analysis of the synergistic effects of IL-5 and CD38 ligation on IgG1 secretion revealed the impaired IgG1 secretion of B cells from Lyn−/− and Fyn/Lyn−/− mice. These data imply that Lyn is involved in B cell triggering by CD38 ligation plus IL-5 for isotype switching.