Structural transformation with "negative volume expansion": chemical bonding and physical behavior of TiGePt.

The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.

Passalidae (Coleoptera: Scarabaeoidea) of the Biogeographical Province of Chocó and the West Andean Region of Colombia, with the Description of Two New Species.

We present a synopsis of the Passalidae of the Chocó biogeographical province and the western slopes of the Western Andean range of Colombia as a result of field collections, examination of entomological collections, and review of the literature. We record a total of 41 species, provide an identification key, and, for the 39 species for which we were able to examine specimens, include a diagnosis and collecting data. Two new species of Passalus (Pertinax) are described and illustrated. The species of this region compose 42% of the passalid species known for Colombia. The richness of species and the high degree of endemism (34%) indicate the faunistic importance of this area, which is closely related to the fauna of lowland Central America.

Interleukin 7 is a potent co-stimulator of myelin specific T cells that enhances the adoptive transfer of experimental autoimmune encephalomyelitis.

Interleukin 7 (IL-7), originally described as a B cell growth factor, has recently been found to play a critical role in T and B lymphocyte development and function. This study evaluated the effects of IL-7 on myelin specific T cells. IL-7 strongly enhanced proliferation of proteolipid protein (PLP) 139-151 specific T cells in association with elevated secretion of the T cell growth factor IL-2. Co-stimulation with IL-7 preferentially increased the levels of pro-inflammatory cytokines secreted by PLP 139-151 specific T cells and adoptive transfer of these cells into naive recipients induced a profound enhancement of experimental autoimmune encephalomyelitis, an animal model for the human disease multiple sclerosis. These results suggest that IL-7 may be a critical co-stimulatory factor that enhances the extrathymic expansion of inflammatory T cells and may play an important role in the pathogenesis of a number of inflammatory autoimmune disorders.

Gender differences in experimental autoimmune encephalomyelitis develop during the induction of the immune response to encephalitogenic peptides.

Multiple sclerosis (MS) strikes women more often than men. Gender differences in experimental autoimmune encephalomyelitis (EAE) parallel those seen in MS. We utilized the adoptive transfer model of EAE to determine the role of gender on the induction and effector phases of disease. PLP 139-151-sensitized spleen cells from female SJL mice were more effective at transferring disease than male cells. However, there were no gender differences in the frequency of PLP 139-151-specific T cells. PLP 139-151-specific female T cell lines induced more severe disease than male T cell lines. Disease severity was more strongly linked to the sex of the donor T cells, indicating that gender influences the immune response primarily during the induction phase.

Androgens alter the cytokine profile and reduce encephalitogenicity of myelin-reactive T cells.

Adoptive transfer of proteolipid protein 139-151-specific T cell lines was used to examine the role of androgens in regulating T cell cytokine secretion and the severity of experimental autoimmune encephalomyelitis (EAE) in the SJL mouse. In this study, we found that T cells from female mice transferred more severe EAE than T cells from male mice and that gender differences in clinical disease were due, at least in part, to differences in donor T cell cytokine secretion. T cell lines were selected from proteolipid protein 139-151-immunized female SJL mice in the presence or absence of exogenous androgens. Androgen-selected T cell lines secreted less IFN-gamma and more IL-10 than untreated cell lines. Clinical disease induced by the adoptive transfer of androgen-selected T cell lines was less severe than disease induced with untreated T cell lines. Furthermore, androgen treatment of naive TCR transgenic T cells, during their first encounter with Ag, resulted in a shift in the balance of Th1/Th2 cytokines. This phenotype was maintained during subsequent stimulations in the absence of androgen. These results suggest that androgen present in the lymphoid microenvironment during the induction of an immune response can alter the development of effector T cells and may play an important role in governing gender differences in the immune response and susceptibility to autoimmune disorders.

Gender differences in protection from EAE induced by oral tolerance with a peptide analogue of MBP-Ac1-11.

Mechanisms that contribute to increased female susceptibility to multiple sclerosis can be studied in the murine model of experimental autoimmune encephalomyelitis (EAE). In this report, we compared oral tolerance induction in male and female B10.PL mice using fed myelin basic protein (MBP) Ac1-11 peptide or a high-affinity analogue, Ac1-11[4Y]. We found that fed Ac1-11[4Y] peptide, but not native Ac1-11, could limit cellular infiltration into the central nervous system (CNS) and protect male mice from EAE, an effect that was completely obviated by castration. In contrast, female mice could not be orally tolerized or protected from EAE with either peptide. Tolerance induction in males was reflected by the appearance of Ac1-11[4Y]-reactive splenocytes that produced a sharply increased ratio of transforming growth factor (TGF)-beta:interleukin (IL)-2 and induced bystander suppression. These data directly demonstrate gender differences in regulatory T cells, and support the concept that androgens are involved in governing oral tolerance to EAE.