Relaxation and dephasing in a two-electron 13C nanotube double quantum dot.

We use charge sensing of Pauli blockade (including spin and isospin) in a two-electron 13C nanotube double quantum dot to measure relaxation and dephasing times. The relaxation time T1 first decreases with a parallel magnetic field and then goes through a minimum in a field of 1.4 T. We attribute both results to the spin-orbit-modified electronic spectrum of carbon nanotubes, which at high field enhances relaxation due to bending-mode phonons. The inhomogeneous dephasing time T{2} is consistent with previous data on hyperfine coupling strength in 13C nanotubes.

Role of 2CT cell receptor residues in the binding of self- and allo-major histocompatibility complexes.

T cell clone 2C recognizes the alloantigen L(d) and the positive selecting major histocompatibility complex (MHC), K(b). To explore the molecular basis of T cell antigen receptor (TCR) binding to different peptide/MHC (pMHC) complexes, we performed alanine scanning mutagenesis of the 2C TCR. The TCR energy maps for QL9/L(d) and SIYR/K(b) were remarkably similar, in that 16 of 41 Valpha and Vbeta alanine mutants showed reduced binding to both ligands. Several TCR residues varied in the magnitude of energy contributed to binding the two ligands, indicating that there are also unique interactions. Residues in complementarity determining region 3alpha showed the most notable differences in binding energetics among the ligands QL9/L(d), SIYR/K(b), and the clonotypic antibody 1B2. Various lines of evidence suggest that these differences relate to the mobility of this loop and point to the key role of conformational dynamics in pMHC recognition.

Mapping the energy of superantigen Staphylococcus enterotoxin C3 recognition of an alpha/beta T cell receptor using alanine scanning mutagenesis.

Binding of the T cell receptor (TCR) to a bacterial superantigen (SAG) results in stimulation of a large population of T cells and subsequent inflammatory reactions. To define the functional contribution of TCR residues to SAG recognition, binding by 24 single-site alanine substitutions in the TCR Vbeta domain to Staphylococcus aureus enterotoxin (SE) C3 was measured, producing an energy map of the TCR-SAG interaction. The results showed that complementarity determining region 2 (CDR2) of the Vbeta contributed the majority of binding energy, whereas hypervariable region 4 (HV4) and framework region 3 (FR3) contributed a minimal amount of energy. The crystal structure of the Vbeta8.2-SEC3 complex suggests that the CDR2 mutations act by disrupting Vbeta main chain interactions with SEC3, perhaps by affecting the conformation of CDR2. The finding that single Vbeta side chain substitutions had significant effects on binding and that other SEC3-reactive Vbeta are diverse at these same positions indicates that SEC3 binds to other TCRs through compensatory mechanisms. Thus, there appears to be strong selective pressure on SAGs to maintain binding to diverse T cells.

Role of the T cell receptor alpha chain in stabilizing TCR-superantigen-MHC class II complexes.

Superantigens (SAGs) activate T cells by simultaneously binding the Vbeta domain of the TCR and MHC class II molecules on antigen-presenting cells. The preferential expression of certain Valpha regions among SAG-reactive T cells has suggested that the TCR alpha chain may modulate the level of activation through an interaction with MHC. We demonstrate that the TCR alpha chain is required for maximum stabilization of the TCR-SAG-MHC complex and that the alpha chain increases the half-life of the complex to match those of TCR-peptide/MHC complexes. The site on the TCR alpha chain responsible for these effects is CDR2. Thus, the overall stability of the TCR-SAG-MHC complex is determined by the combination of three distinct interactions: TCR-SAG, SAG-MHC, and MHC-TCR.

Perceptions of childbirth: are women properly informed?

This paper is the second of two examining the differing perceptions of childbirth between women and medical professionals. It has been suggested that the differing views have led to a position where medical knowledge and frames of reference are accepted and legitimated by a system which leaves women feeling alienated and dissatisfied with the conduct of delivery. This paper takes the discussion forward by reviewing the recommendations of the Changing Childbirth document, asking whose responsibility it is to inform women about their condition and treatment, examining the importance of continuity of care to the information-sharing process, the impact that this could have on women's ability to exercise informed choice and, ultimately, assessing whether change is possible.

The conflict between lay and professional views of labour.

This paper is one of two reviewing the evidence of differing perceptions of pregnancy and labour between medical professionals and the women who are consumers of maternity services, and how those perceptions have changed over the years. The author points out the existence of power imbalances, which can be argued as being at the root of the expert maternity committee's report, Changing Childbirth. The second article will look at the impact of the report on this situation.

Incidence of Pneumocystis carinii antigenemia in ambulatory cancer patients.

Although the existence of subclinical Pneumocystis carinii infection in pediatric patients with solid tumors or hematologic malignancies has been documented, similar data are lacking in adults. In addition, data are needed to define the epidemiology of this agent in adult malignancies to assess the validity of the methodology employed in antigen detection, and to elucidate the value of these methods in the diagnosis, prophylaxis, and prognosis of P carinii infection in adults with cancer. The study was designed to determine the incidence of P carinii antigenemia in ambulatory patients with solid tumors or hematologic malignancies. The authors also sought to determine if antigenemia as detected by a counterimmunoelectrophoresis test correlated with any clinical parameter. Patients included in the study were ambulatory, asymptomatic, afebrile, adult cancer patients seen in the clinic for follow-up or treatment. Coded sera were electrophoresed against high-titered rabbit antiserum to P carinii organisms. Two hundred forty-seven patients were studied, including 172 hematologic malignancies (average age, 57 years), 109 men and 63 women; 75 solid tumors (average age, 55 years), 39 women and 36 men. One hundred three healthy adults served as controls. Only five patients had positive antigen (2%). All of these patients had hematologic malignancies and were women. None of the control sera were antigen-positive. We conclude that the incidence of P carinii antigenemia in asymptomatic adults with neoplastic disease is extremely low. A positive P carinii antigen in the absence of clinical symptoms most likely represents subclinical infection. Positive antigen does not always indicate active disease, but probably reflects mobilization of antigen during generalized inflammatory response or possible pulmonary insult. In making the decision to treat consideration should be given to clinical presentation and history.