Phase coexistence and electric-field control of toroidal order in oxide superlattices

Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO₃/SrTiO₃ superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a₁/a₂ phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities.

Direct observation of thermal relaxation in artificial spin ice

We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state to the ground state. On plotting vertex-type populations as a function of time, we can characterize the relaxation, which occurs in two stages, namely a string and a domain regime. Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations.

Neuroendocrine gene polymorphisms and susceptibility to juvenile idiopathic arthritis

OBJECTIVE

To investigate the involvement of neuroendocrine candidate genes in the aetiopathogenesis of juvenile idiopathic arthritis (JIA).

METHODS

Single-nucleotide polymorphisms and intragenic microsatellite markers within five neuroendocrine candidate genes (CRH, CBG, CYP19, ESR1, PRL) were investigated in 463 clinically characterized UK Caucasian JIA patients and a panel of 276 unrelated, healthy UK Caucasian controls.

RESULTS

None of the polymorphisms investigated showed any statistically significant associations with JIA.

CONCLUSIONS

The lack of association with polymorphisms of these neuroendocrine genes suggests that they are not involved in susceptibility to JIA.

In vitro cytokine production of TNFalpha and IL-13 correlates with acute liver transplant rejection

Individuals may differ in their capacity to produce cytokines. Since cytokines play a key role in allograft rejection, we investigated whether inter-individual differences in cytokine production by in vitro stimulated PBMC are related to the occurrence of acute liver transplant rejection. Our study group comprised 49 liver transplant recipients and 30 healthy individuals. Rejection, which occurred within one month after liver transplantation, was defined in 22 patients ("rejectors") as biopsy-proven rejection, treated with high dose prednisolone. Patients who never experienced rejection episodes were termed as "nonrejectors" (n=27). PBMC of healthy individuals and of liver transplant recipients, collected late after transplantation (mean 3.5 years), were cultured in the presence and absence of Concanavalin A. The production of TNF-alpha, IFN-gamma, IL-10, and IL-13 was measured in supernatant after 1, 2, 3, 4, and 7 days of cell culture. In cell culture, stimulated PBMC of rejectors were found to produce significantly higher levels of TNF-alpha, while there was a trend towards higher production of IFN-gamma and IL-10 as compared to nonrejectors. After grouping patients into high or low cytokine producers based upon reference levels of the healthy individuals using multivariate analysis it was found that occurrence of acute liver transplant rejection correlated to high production of TNF-alpha and low production of IL-13. After stimulated cell culture PBMC of liver transplant recipients show a differential production of TNF-alpha and IL-13 which is correlated with the occurrence of acute liver transplant rejection.

Cytokine gene polymorphisms and susceptibility to juvenile idiopathic arthritis. British Paediatric Rheumatology Study Group

OBJECTIVE

To investigate the involvement of candidate cytokine genes in the pathogenesis of juvenile idiopathic arthritis (JIA).

METHODS

Single nucleotide polymorphisms and intragenic microsatellite markers within 8 candidate cytokine genes (interleukin-1alpha [IL-1alpha], IL-2, IL-4, IL-6, IL-10, interferon-alpha1 [IFNA1], interferon-gamma [IFNG], and interferon regulatory factor 1 [IRF-1]) were investigated in 417 Caucasian patients with clinically characterized JIA and a panel of 276 unrelated, healthy Caucasian controls, all from the United Kingdom.

RESULTS

A novel 3'-untranslated region (3'UTR) polymorphism in IRF-1 was found to be associated with susceptibility to JIA (corrected P = 0.002). No significant association with IL-1alpha, IL-2, IL-4, IL-6, IL-10, IFNA1, or IFNG was observed.

CONCLUSION

An association between JIA and a previously unreported 3'UTR polymorphism of IRF-1 was observed. This association was not found to be specific to any particular JIA subgroup. This suggests that IRF-1 may contribute to a common pathogenesis shared by all JIA patients, regardless of clinical phenotype. This is most likely to be a genetic contribution to the chronic inflammatory process that underlies JIA pathology.

Antinuclear antibodies in early onset pauciarticular juvenile chronic arthritis (JCA) are associated with HLA-DQB1*0603: a possible JCA-associated human leucocyte antigen haplotype

A panel of 43 early onset pauciarticular (EOPA) juvenile chronic arthritis (JCA) patients have been typed for human leucocyte antigens (HLA) DRB1, DPB1, DQA1 alleles, and DQB1*0603 status using molecular-based methods. Increased frequencies of DRB1*08 [odds ratio (OR) 7.7, 95% confidence interval (CI) 2.6-22.3], DRB1*11 (OR 3.1, 95% CI 1.2-8.1), DRB1*1301 (OR 7.7, 95% CI 2.6-22.3), DPB1*0201 (OR 3.5, 95% CI 1.6-8.0), DQA1*0103 (OR 4.4, 95% CI 1.5-13.3), DQA1*0501 (OR 2.9, 95% CI 1.3-6.6), DQA1*0601 (OR 30, 95% CI 3.6-241) and DQB1*0603 (OR 7.3, 95% CI 3.0-17.6) were found in the EOPA-JCA group compared with Caucasoid controls. Stratification of the EOPA-JCA group into antinuclear antibody (ANA) positive (n = 18) and ANA negative (n = 25) individuals revealed that ANA positivity was only associated with DRB1*1301 (OR 4.2, 95% CI 1.0-17.3), DPB1*0201 (OR 4.0, 95% CI 1.0-15.7) and DQB1*0603 (OR 11.5, 95% CI 2.5-53.4). Further analysis of the relative contributions of HLA antigens to ANA status revealed that DQB1*0603 determined the primary HLA effect. No apparent interaction between DQB1*0603 and DRB1*1301 or between DQB1*0603 and DPB1*0201 was found to contribute to the association with ANA. We suggest that those ANA positive individuals with a restricted HLA background, (DQB1*0603 positive), defines a group of EOPA-JCA patients which will be especially valuable in the characterization of the ANA associated with EOPA-JCA.

Twin concordance rates for rheumatoid arthritis: results from a nationwide study

We report the concordance rate for RA in a nationwide study of 91 monozygotic (MZ) and 112 dizygotic (DZ) pairs. Twin pairs were recruited from both a national media campaign and a 2-month prospective inquiry of all UK rheumatologists. Disease status was established following a structured clinical and serological appraisal, together with radiological assessment where necessary. Zygosity was confirmed using DNA fingerprinting. In all, 14 (15.4%) of the MZ and four (3.6%) of the DZ pairs were disease concordant (risk ratio: 4.3 95% CI 1.5 to 12.6). There was no difference in the concordance between the media and clinical derived twins. Further the excess MZ concordance persisted after adjusting for age, age at disease onset, sex and rheumatoid factor status. Analysing the data in relation to the timing of disease onset in the first affected twin showed that subsequent disease risk in the initially unaffected co-twins of the MZ affected probands increased with increasing duration of follow-up. We conclude that the overall MZ concordance at 15% is lower than the 30% figure normally quoted from a study some 30 years ago and sets a ceiling at the potential genetic contribution to disease susceptibility.