Systematic evaluation of cellular radiosensitivity parameters

Cellular radiosensitivity parameters of the track structure theory of Katz and co-workers are evaluated from a sum of squares minimizing computer program for nonlinear models. Based on these observations, suggestions are presented for efficient experiment design for the determination of these parameters from track-segment bombardments of high LET radiations.     

Antigen-specific CD8+ T cell subset distribution in lymph nodes draining the site of herpes simplex virus infection

Inoculation with replicating virus leads to an increase in T cell numbers within lymph nodes that drain the site of infection. This increase has been associated with a nonspecific proliferation of bystander cells, with only a minority thought to be directed to the infectious agent. Such an assumption is largely based on precursor cytotoxic T lymphocyte (CTL) estimations using limiting dilution analysis. Recently, studies using more advanced molecular approaches have suggested that such functionally derived precursor frequencies considerably underestimate the proportion of T cells specific for the antigen under investigation. We have defined T cell receptor sequences characteristic of CTL populations directed to a dominant determinant of the herpes simplex virus (HSV) glycoprotein B (gB). In this investigation, we used this receptor signature as a probe to directly monitor changes occurring within lymph nodes draining the sites of active infection with HSV. We found that although lymph node CD8+ T cell numbers increase as a consequence of HSV infection, the majority of these cells are small resting cells that are not enriched for gB-specific receptors. In contrast, a significant proportion of activated T cells are highly enriched for CTL bearing gB-specific receptors. Our results are therefore consistent with a nonspecific migration of CTL precursors into the lymph nodes draining the site of infection, followed by the activation and proliferation of the antigen-specific subset that normally makes up a small proportion of the naive T cell repertoire.     

Patterning activities of vertebrate hedgehog proteins in the developing eye and brain

BACKGROUND: The hedgehog (hh) family of secreted signaling proteins is responsible for developmental patterning in a variety of systems, including the neural tube, limbs and somites. Within the neural tube, at the level of the spinal cord, products of the vertebrate gene sonic hedgehog (shh) are proposed to function as a ventral patterning influence, with the capability of inducing floor plate and motor neurons. RESULTS: We report the isolation of tiggy-winkle hedgehog (twhh), a novel member of the zebrafish hh gene family. Both twhh and shh are expressed in the ventral midline of the embryonic zebrafish neural tube and brain, but twhh expression becomes limited to the neural tube, whereas shh is also expressed in the notochord. Both genes are expressed in the developing brain, in domains that include a discrete region in the floor of the diencephalon, located between the sites of the future optic stalks. Using pax-2 and pax-6 as markers of proximo-distal fate within the developing eye, we found that ectopic expression of either hh gene promoted proximal fates and suppressed distal fates. In contrast, proximal fates were lost in cyclops mutant embryos, which lack twhh- and shh-expressing forebrain cells. Both twhh and shh proteins undergo autoproteolytic processing in vivo; a fragment corresponding to the amino-terminal cleavage product was sufficient to carry out all signaling activities associated with twhh in eye and brain development. CONCLUSIONS: These findings suggest that secreted signals encoded by members of the hedgehog gene family, emanating from the ventral midline of the neural tube, not only play important roles in dorso-ventral patterning of the brain but also appear to constitute an early patterning activity along the proximo-distal axis of the developing eyes.     

Effects of feeding on protein turnover in healthy children and in children with cystic fibrosis

In 24 patients presenting with 55 renal lesions (mean size, 20.8 mm), single-breath-hold (SBH) fast spin-echo (FSE) techniques allowing T1 and T2 images to be produced within 20 and 23 sec, respectively, were compared with routine non-breath-hold (NBH) spin-echo (SE) T1 and NBH-FSE T2 sequences. Contrast-to-noise ratios (CNRs) measured from SBH-FSE T1 images were an average of 97% higher than their NBH counterparts (P = .0001) and allowed an improved lesion conspicuity in 80% of the cases (P = 0.0001). For T2 imaging, SBH-FSE and NBH-FSE sequences were not statistically different with respect to lesion conspicuity (P = .55) and CNR values (P = .19). This was observed despite a 35% average decrease in CNR of SBH-FSE compared to NBH-FSE images. By reducing respiratory motion artifacts while preserving SE-like image contrast, SBH-FSE techniques have the potential to replace routine NBH sequences for an optimal diagnosis of renal masses.     

A characterization of first-generation flowable composites

A plethora of new low-viscosity composite resin materials, or flowable composites, have been marketed during the last two years, but little has been published about them. The authors describe research in which they compared the properties--filler, depth or cure, flow, wear, compressive strength, diametral tensile strength, indented biaxial flexure strength and toughness--of flowable and hybrid composites. Mechanical property tests (ISO 4049, ISO/DIS 6872) of eight flowable composites and two hybrid composites were conducted. The flowable composite with the least flow was similar to traditional composites. Mechanical properties were generally about 60 to 90 percent of those of conventional composites. The authors conclude that flowable materials should be used with caution in high-stress applications for restorative dentistry.