Reactions of the subunits of the class II major histocompatibility complex molecule IAd.

Major histocompatibility complex (MHC) class II molecules are heterodimers formed by noncovalent linkage of alpha and beta chains. It has been shown that the subunits of the MHC class II molecules IAd and IEk bind antigenic peptides as well as antigenic peptides labeled with fluorescent probes. Laser scanning fluorescence microscopy on SDS/polyacrylamide gels demonstrates that the subunit-peptide complexes of IAd are stable over a wide pH range. Below pH 5.3 the heterodimer of IAd dissociates into the free chains, which still bind antigenic peptides such as the 18-amino acid peptide obtained by a tyrosine addition to a chicken ovalbumin peptide, Ova-(323-339)Y. The stability of preformed subunit complexes with fluorescein-labeled Ova-(323-339)Y was investigated by using high-performance size exclusion chromatography and epifluorescence microscopy. Each subunit forms a long-lived complex, both in detergent solutions and in reconstituted lipid bilayers. At 37 degrees C and pH 7.0 the dissociation half-time of the beta-subunit-peptide complex was determined to be 28 hr and that of the alpha-subunit-peptide complex was 10 hr. In contrast to the dissociation of the peptide from the IAd heterodimer, the half-times for dissociation of the peptide from the separate chains are not decreased at pH 5.0.     

Equilibration rates in lipid monolayers

A theoretical analysis is given for the rate of change of domain sizes in lipid monolayers at the air–water interface. The calculation is applicable to liquid domains formed from binary mixtures of lipids that form two coexisting liquid phases. Under conditions where the two lipid molecules have approximately equal areas, the equilibration rate does not involve macroscopic hydrodynamic flow in the subphase but rather depends on the diffusion coefficient of the lipid molecules. The calculation shows that the equilibration rate in binary mixtures of cholesterol and phosphatidylcholine is remarkably slow, the radius of a typical 20-μm diameter domain changing by as little as a part in a million per second. Under these circumstances, equilibration times of the order of days or weeks are expected. Even with such long times, the final state reached by the monolayer will in general be a state of metastable equilibrium, rather than true equilibrium.     

Clonal dysregulation of the antibody response to tetanus-toxoid after bone marrow transplantation

After bone marrow transplantation (BMT), a prolonged dysregulation of humoral immunity can be observed. In the present study, we investigated whether this is reflected in an abnormal production of specific antibodies (Ab) to the T-cell-dependent recall antigen tetanus-toxoid (TT). The study group consisted of children receiving transplants of an unmodified allogeneic graft and of adults receiving either a T-cell- depleted allogeneic or an unmodified autologous BM graft. Findings were compared with those in healthy controls. In pediatric graft recipients, who were routinely revaccinated early after BMT, the Ab response was quantitatively superior to that in adult graft recipients who did not receive early revaccination. In the majority of graft recipients, the time period after vaccination required to reach the peak level of antibodies was prolonged and the number of responding TT-specific B- cell clones was markedly decreased in comparison with controls. In controls, a low frequency of dominant B-cell clones may produce low quantities of homogeneous Ab components (H-Ab) against a heterogeneous background. However, in BM graft recipients, "overshooting" of Ab production by separate B-cell clones was observed, resulting in the development of H-Ab at a relatively high concentration. These abnormalities were present up to 10 years after BMT, irrespective of either the age of the recipient, the modulation of the graft, or the vaccination schedule used. It is hypothesized that the dysregulated Ab production is the consequence of activation of a restricted number of resting memory B cells, present in germinal centers, repopulating gradually after BMT. Our data show that routine revaccination early after BMT improves the humoral immune response. However, because of a clonally dysregulated Ab production, long-lasting qualitative defects may be present even after normalization of Ab titers.     

Noninvasive assessment of coronary vasodilation using magnetic resonance angiography

OBJECTIVES: The purpose of this study was to investigate the use of coronary magnetic resonance angiography (MRA) for assessing human epicardial coronary artery vasodilation. BACKGROUND: Coronary vasodilation plays a vital role in the human coronary circulation. Previous studies of epicardial coronary vasodilation have used invasive coronary angiography. Coronary MRA may provide an alternative noninvasive method to directly assess changes in coronary size. METHODS: Thirty-two subjects were studied: 12 patients (age 55 +/- 18 years) and 20 healthy subjects (age 34 +/- 4 years). High-resolution multi-slice spiral coronary MRA (in-plane resolution of 0.52 to 0.75 mm) was performed before and after sublingual nitroglycerin (NTG). Quantitative analysis of coronary vasodilation was performed on cross-sectional images of the right coronary artery (RCA). A time-course analysis of coronary vasodilation was performed in a subset of eight subjects for 30 min after NTG. Signal-to-noise ratio was also measured on the in-plane RCA images. RESULTS: Coronary MRA demonstrated a 23% increase in cross-sectional area after NTG (16.9 +/- 7.8 mm2 to 20.8 +/- 8.9 mm2, p <0.0001), with significant vasodilation between 3 and 15 min after NTG on time-course analysis. The MRA measurements had low interobserver variability (< or =5%) and good correlation with X-ray angiography (r=0.98). The magnitude of vasodilation correlated with baseline cross-sectional area (r=0.52, p=0.03) and age (r=0.40, p=0.019). Post-NTG images also demonstrated a 31% improvement in coronary signal-to-noise ratio (p = 0.002). CONCLUSIONS: Nitroglycerin-enhanced coronary MRA can noninvasively measure coronary artery vasodilation and is a promising noninvasive technique to study coronary vasomotor function.     

Nursing home staff perspectives on adoption of an innovation in goals of care communication

Nursing homes (NH) are important settings for end-of-life care, but limited implementation may impede goals of care discussions. The purpose of this study was to understand NH staff perceptions of adoption and sustainability of the Goals of Care video decision aid for families of residents with advanced dementia. Study design was a cross-sectional survey of staff at 11 NHs in North Carolina who participated in the Goals of Care (GOC) cluster randomized clinical trial. Staff perceived the GOC decision aid intervention as a positive innovation; it was perceived as more compatible with current practices by male staff, nurses, and more experienced NH staff. Perceptions were correlated with experience, implying that experience with an innovative approach may help to promote improved GOC communication in nursing homes. Nurses and social work staff could be effective champions for implementing a communication technique, like the GOC intervention.     

Anisotropic molecular motion on cell surfaces.

Photobleaching in a two-dimensional periodic pattern has been used to characterize the motion of succinylconcanavalin A receptors on the surfaces of mouse fibroblasts. These receptors were found to exhibit anisotropic two-dimensional diffusion in adherent cells having parallel stress fibers. Diffusion coefficients of the order of 10(-11) cm2/sec and 10(-12) cm2/sec were measured for diffusive motions parallel and perpendicular to these fibers. The determination of the anisotropic motion used a two-dimensional Fourier analysis. A study was made of the effect of changes in cell shape on the photobleach pattern.     

The value of plasmid studies in the epidemiology of infections due to drug-resistant Salmonella wien.

Since 1969 strains of Salmonella wien that are resistant to multiple antibacterial drugs have caused widespread epidemics of enteritis in Europe and North Africa. Of 113 British strains examined between January 1970 and January 1977, 67 were multi-resistant. These strains and 22 strains from six other countries were examined to determine their plasmid content. Two plasmids were found in the vast majority of strains: an FIme factor, conferring resistance to ampicillin, chloramphenicol, kanamycin, streptomycin, spectinomycin, sulfonamides, and tetracyclines (ACKSSpSuT), and a nonautotransferring plasmid of resistance type ASSu. The FIme plasmids have dual incompatibility: they are incompatible with group FI factors and with the MP10 plasmid of Salmonella typhimurium, which belongs to a separate group. Other plasmids found in S. wien included principally a ColIa factor and an autotransferring plasmid that codes for ampicillin resistance and belongs to compatibility group I2. The similarity in plasmid content of strains isolated in widely separated areas suggests that they have a clonal origin.     

Changing the model of radiography practice in the UAE: A snapshot of a profession in transition

IntroductionThis study forms part of a needs assessment in relation to the challenges United Arab Emirates (UAE) radiographers face as they move beyond the role of a technician, and their learning needs to facilitate role advancement. It presents a snapshot of the workforce in terms of qualifications, clinical experience, and responsibilities, as it transitions towards an Emirati, led profession. The results will aid the radiography workforce to embrace a broader role within medical imaging and radiographic practice in the UAE.MethodsAn electronically distributed cross-sectional study was conducted among radiographers in the UAE. The questionnaire captured radiographer demographics, qualifications, professional experience, postgraduate training, professional development plans, and their interest in future role developments.Results272 radiographers were invited to participate with a response rate of 68% (n = 185). Thirty-four (18%) radiographers were UAE nationals with the remainder educated overseas. BSc qualifications were held by 153 (82.7%) and had 6–20 years of experience. There were 12 masters’ qualified and two with doctoral qualifications. Modality vendors were significant providers of professional development. Improved job satisfaction and the development of an Emirati led radiography profession were identified as the main gains for role advancement by 171 (92.4%) respondents.ConclusionCurrently, UAE radiographers work within traditional professional boundaries focussing on image acquisition under direct radiologist supervision. At the same time, many respondents revealed they had embraced advanced practice roles after appropriate education and training.Implications for practiceThe findings suggest an Emirati led profession requires the creation of a distinct professional body to represent the interests of radiographers, more investment in postgraduate education, and the creation of a career structure that encompasses positive role development.