The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides.

PURPOSE: The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range. PROCEDURES: To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects. RESULTS: Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV. CONCLUSION: Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.

Impact of peripheral immune status on central molecular responses to facial nerve axotomy.

When facial nerve axotomy (FNA) is performed on immunodeficient recombinase activating gene-2 knockout (RAG-2-/-) mice, there is greater facial motoneuron (FMN) death relative to wild type (WT) mice. Reconstituting RAG-2-/- mice with whole splenocytes rescues FMN survival after FNA, and CD4+ T cells specifically drive immune-mediated neuroprotection. Evidence suggests that immunodysregulation may contribute to motoneuron death in amyotrophic lateral sclerosis (ALS). Immunoreconstitution of RAG-2-/- mice with lymphocytes from the mutant superoxide dismutase (mSOD1) mouse model of ALS revealed that the mSOD1 whole splenocyte environment suppresses mSOD1 CD4+ T cell-mediated neuroprotection after FNA. The objective of the current study was to characterize the effect of CD4+ T cells on the central molecular response to FNA and then identify if mSOD1 whole splenocytes blocked these regulatory pathways. Gene expression profiles of the axotomized facial motor nucleus were assessed from RAG-2-/- mice immunoreconstituted with either CD4+ T cells or whole splenocytes from WT or mSOD1 donors. The findings indicate that immunodeficient mice have suppressed glial activation after axotomy, and cell transfer of WT CD4+ T cells rescues microenvironment responses. Additionally, mSOD1 whole splenocyte recipients exhibit an increased astrocyte activation response to FNA. In RAG-2-/- + mSOD1 whole splenocyte mice, an elevation of motoneuron-specific Fas cell death pathways is also observed. Altogether, these findings suggest that mSOD1 whole splenocytes do not suppress mSOD1 CD4+ T cell regulation of the microenvironment, and instead, mSOD1 whole splenocytes may promote motoneuron death by either promoting a neurotoxic astrocyte phenotype or inducing Fas-mediated cell death pathways. This study demonstrates that peripheral immune status significantly affects central responses to nerve injury. Future studies will elucidate the mechanisms by which mSOD1 whole splenocytes promote cell death and if inhibiting this mechanism can preserve motoneuron survival in injury and disease.

Alloprimed CD8(+) T cells regulate alloantibody and eliminate alloprimed B cells through perforin- and FasL-dependent mechanisms.

While it is well known that CD4(+) T cells and B cells collaborate for antibody production, our group previously reported that CD8(+) T cells down-regulate alloantibody responses following transplantation. However, the exact mechanism involved in CD8(+) T cell-mediated down-regulation of alloantibody remains unclear. We also reported that alloantibody production is enhanced when either perforin or FasL is deficient in transplant recipients. Here, we report that CD8(+) T cell-deficient transplant recipient mice (high alloantibody producers) exhibit an increased number of primed B cells compared to WT transplant recipients. Furthermore, CD8(+) T cells require FasL, perforin and allospecificity to down-regulate posttransplant alloantibody production. In vivo CD8-mediated clearance of alloprimed B cells was also FasL- and perforin-dependent. In vitro data demonstrated that recipient CD8(+) T cells directly induce apoptosis of alloprimed IgG1(+) B cells in co-culture in an allospecific and MHC class I-dependent fashion. Altogether these data are consistent with the interpretation that CD8(+) T cells down-regulate posttransplant alloantibody production by FasL- and perforin-dependent direct elimination of alloprimed IgG1(+) B cells.

Digital radiographic measurement of the main bronchi: a pilot study.

BACKGROUND: Conventional chest radiographs do not afford consistently good visualisation of the main bronchi and sub-carinal angle. Improved visualisation would facilitate accurate measurement of the airways, definition of normal radiographic anatomy and, possibly, earlier identification of extrinsic compression or displacement. AIM: The main objective of this study was to establish whether the paediatric main bronchi and sub-carinal angle could be measured consistently on AP supine chest images obtained using a specific digital radiographic system (DRS). SUBJECTS AND METHODS: The proximal bronchial diameters were measured on supine DRS chest images of 102 children between the ages of 6 months and 13 years. RESULTS: The left and right main bronchi could be seen clearly and measured in over 90% of cases, with intraclass correlation co-efficients of reliability indicating high intra- and inter-observer agreement. The sub-carinal angle had lower intra- and inter-observer agreement. CONCLUSION: Supine chest images acquired using DRS facilitate accurate measurement of the main bronchi and sub-carinal angle in children. Further work is required to establish population-specific age-related norms for bronchial dimensions. These could serve as reference standards for early detection of deviations from normal.

Inhibition of experimental periodontitis by a topical boron-based antimicrobial.

AN0128 is a boron-containing compound with antibacterial and anti-inflammatory properties. To test its potential effectiveness in treating periodontal disease, we induced experimental periodontitis in the rat by placing ligatures and assessed the impact of AN0128 and positive and negative controls by micro-CT and histologic measurements. The formation of an inflammatory infiltrate was measured in hematoxylin-and-eosin-stained sections. Daily application of AN0128 (1%) compared with controls reduced bone loss by 38 to 44% (P < 0.05), while vehicle alone had no effect (P > 0.05). The reduction in bone loss with AN0128 was similar to that achieved with a NSAID, ketorolac, and Total toothpaste containing triclosan. AN0128 also reduced the level of gingival inflammation 42% compared with the ligature only (P < 0.05), whereas vehicle alone had no effect (P > 0.05). The results indicate that AN0128 significantly reduces the formation of an inflammatory infiltrate and reduces bone loss, measured histologically and by micro-CT.

Hospital-acquired pneumonia: microbiological data and potential adequacy of antimicrobial regimens.

Adequate antimicrobial therapy is a main approach employed to decrease the mortality associated with hospital-acquired pneumonia (HAP). All methods that optimise empirical treatment without increasing antibiotic selective pressure are relevant. Categorisation of patients according to HAP time of onset, severity and risk factors (American Thoracic Society (ATS) classification) or duration of mechanical ventilation and prior antibiotics (Trouillet's classification) are two such methods. The aim of this study was to catagorise patients with HAP according to these classifications and to determine the frequency of resistant pathogens and the most adequate antimicrobial regimens in each group. A total 124 patients with bacteriologically proven HAP were studied. The ATS classification categorised patients by increasing frequency of resistant pathogens from 0-30.3%. The ATS empirical antibiotic recommendations appeared valid but proposed combinations including vancomycin for 72.5% of patients. Trouillet's classification categorised patients into four groups with a frequency of resistant pathogens from 4.9-35.6%. Vancomycin was proposed for 48.5% of patients. The American Thoracic Society classification appears to be more specific than Trouillet's for predicting the absence of resistant causative pathogens in hospital-acquired pneumonia but could lead to a greater use of vancomycin. Stratification combining the two classifications is an interesting alternative.

Norepinephrine and beta 2-adrenergic receptor stimulation regulate CD4+ T and B lymphocyte function in vitro and in vivo.

Historically, norepinephrine and the sympathetic nervous system have been associated with the "fight or flight" response, and they also contribute to the regulation of autonomic activity within the body, such as cardiovascular function. In addition, evidence over the past 30 years suggests that norepinephrine may also regulate the function of immune cells that protect the body against pathogens. The presence of sympathetic nerve fibers and the release of norepinephrine within lymphoid organs represent a mechanism by which signals from the central nervous system may influence immune cell function. The T cell-dependent antibody response is essential to successful host defense against numerous environmental pathogens. It is during this response that CD4+ T and B lymphocytes are activated to produce cytokines and antibody, respectively, leading to immune competence and protection. The goal of this review is to discuss the evidence supporting the release of norepinephrine within lymphoid organs and the expression of the beta2-adrenergic receptor by CD4+ T and B lymphocytes. We also discuss the mechanisms by which beta2-adrenergic receptor stimulation affects the level of cytokine and antibody produced by these cells both in vitro and in vivo. In cases where conflicting findings have been reported, we discuss potential variables that may have contributed to these conflicting findings. To conclude, we discuss the disease- and health-specific implications of the basic research being done in the area of sympathetic nervous system regulation of T and B lymphocyte function.

Mortality due to ventilator-associated pneumonia: impact of medical versus surgical ICU admittance status.

PURPOSE: The purpose of this study was to compare the prognosis of medical versus surgical patients developing ventilator-associated pneumonia (VAP). MATERIALS AND METHODS: An observational cohort study included 125 consecutive patients exhibiting VAP. Incidence of death occurred at two different times: during intensive care unit (ICU) stay and during hospital stay. RESULTS: Eighty-seven patients were included in the medical group and 38 in the surgical group. On ICU admission and at the time of VAP onset, most collected data, such as demographic parameters, severity of underlying diseases, and current illness, risk factors forVAP development andVAP characteristics were similar in the two groups. Mortality rates during ICU and hospital stays were not significantly different in medical (49%, 56%) and surgical (55%, 61%) groups. In multivariate logistic regression model adjusting for main factors of VAP mortality, surgical admittance status demonstrated no significant impact on mortality assessed during ICU stay (AOR = 1.6; 0.6 - 4.3 CI) and during hospital stay (AOR = 1.6; 0.6 - 4.2 CI). CONCLUSIONS: In this series, after adjustment for mortality confounding factors, medical versus surgical admittance status was not a significant determinant of VAP mortality.

Neodymium:YAG treatment of interlenticular opacification in a secondary piggyback case.

Interlenticular opacification (ILO) developed 7 months after secondary acrylic piggyback lens implantation in which the anterior lens was placed in the bag. This resulted in glare and a hyperopic shift. Treating the ILO with the neodymium:YAG laser successfully reduced the glare and corrected the hyperopic shift.

Pupillary capture of the optic in secondary piggyback implantation.

Two patients who received a minus-power intraocular lens implanted as a secondary piggyback to correct pseudophakic myopia experienced pupillary optic capture following dilation in the early postoperative period. Both cases were successfully managed by pressing the optic back into the ciliary sulcus and constricting the pupil with pilocarpine.

Amelioration of neurotoxic effects of HIV envelope protein gp120 by fibroblast growth factor: a strategy for neuroprotection.

Approximately two thirds of patients with human immunodeficiency virus encephalitis (HIVE) show cognitive impairment and neurodegeneration, while one third are cognitively unimpaired and their neuronal populations are preserved. Thus, it is possible that these individuals might have the capacity to produce neurotrophic factors capable of protecting neurons against the deleterious effects of HIV. In this context, the main objective of this study was to determine whether fibroblast growth factor 1 (FGF1) is protective against HIV. For this purpose levels of FGF1 immunoreactivity were determined in the frontal cortex of 35 AIDS cases subdivided into 4 groups according to the presence or absence of HIVE and neurodegeneration. In cases without both HIVE and neurodegeneration, mild to moderate levels of FGFI immunoreactivity were observed in pyramidal neurons, while in cases with HIVE but without neurodegeneration, levels were significiantly elevated. In contrast, individuals with both HIVE and neurodegeneration showed low levels of neuronal FGF1 immunoreactivity. Furthermore, studies in primary human neuronal cultures treated with the HIV envelope protein-gp120 in the presence or absence of FGF1 showed that FGF1 was protective against gpl20 neurotoxicity in a dose-dependent manner. Taken together, these results support the notion that upregulation of certain neurotrophic factors, such as FGF1, might protect the central nervous system from the neurotoxic effects of HIV.

IFN-gamma production by Th1 cells generated from naive CD4+ T cells exposed to norepinephrine.

During activation in vivo, naive CD4(+) T cells are exposed to various endogenous ligands, such as cytokines and the neurotransmitter norepinephrine (NE). To determine whether NE affects naive T cell differentiation, we used naive CD4(+) T cells sort-purified from either BALB/c or DO11.10 TCR-transgenic mouse spleens and activated these cells with either anti-CD3/anti-CD28 mAbs or APC and OVA(323-329) peptide, respectively, under Th1-promoting conditions. RT-PCR and functional assays using selective adrenergic receptor (AR) subtype antagonists showed that naive CD4(+) T cells expressed only the beta 2AR subtype to bind NE and that stimulation of this receptor generated Th1 cells that produced 2- to 4-fold more IFN-gamma. This increase was due to more IFN-gamma produced per cell upon restimulation instead of more IFN-gamma-secreting cells, as determined by IFN-gamma-specific immunofluorescence and enzyme-linked immunospot. In contrast, Th1 cell differentiation was unaffected when naive T cells were exposed to NE and activated either in the presence of a neutralizing anti-IL-12 mAb or by APC from IL-12-deficient mice. Moreover, the addition of IL-12 to the IL-12-deficient APC cultures restored the ability of NE to increase Th1 differentiation. Taken together, these results indicate that a possible link may exist between the signaling pathways used by NE and IL-12 to increase naive CD4(+) T cell differentiation to a Th1 cell.

Cytokine production by naive and primary effector CD4+ T cells exposed to norepinephrine.

We recently showed that clones of Th1 cells, but not Th2 cells, expressed a functional beta-2-adrenergic receptor (beta2AR) and that either norepinephrine or the beta2AR agonist terbutaline stimulated this receptor to modulate the level of Th1 cytokines produced. In the present study, we show that norepinephrine and terbutaline stimulate the beta2AR to decrease the level of IL-2 produced by freshly isolated murine splenic naive CD4+ T cells from either Balb/C or DO11.10 transgenic mice and activated polyclonally with anti-CD3 and anti-CD28 mAbs. In contrast, the level of cytokines produced by primary effector Th1 and Th2 cells were unaffected when norepinephrine, terbutaline, or cAMP analogs were added at the time of restimulation. These results suggest that a diversity exists among CD4+ T-cell subsets with respect to the level of adrenergic receptor expression, responsiveness to cAMP, stage of cell differentiation, or a combination of the above.

Damage and repair of DNA in HIV encephalitis.

Neuronal damage and dementia are common sequelae of HIV encephalitis. The mechanism by which HIV infection of CNS macrophages results in neuronal damage is not known. We examined the brains from 15 AIDS autopsies (8 with HIV encephalitis and 7 without) and 4 non-infected control autopsies for the presence of DNA strand breaks, for associated changes in the expression of the DNA repair enzymes KU80 and Poly (ADP-ribose) polymerase (PARP), and for accumulation of amyloid precursor protein (APP). Abundant DNA damage was observed with terminal transferase-mediated dUTP nick end-labeling (TUNEL), however, there was no morphologic evidence of significant neuroglial apoptosis. The DNA repair enzyme KU80 was immunocytochemically detectable in neuronal and glial cells in autopsy brains from patients with and without HIV encephalitis; however, in cases with HIV encephalitis the staining was more prominent than in the infected or non-infected controls without encephalitis. There was no difference in KU80 immunostaining in oligodendroglia from autopsies with and without encephalitis. Immunostaining for PARP was more intense in gray and white matter of cases with HIV encephalitis. No clear spatial relationship existed between expression of DNA repair enzymes and the spatial proximity of microglial nodules or HIV-infected macrophages. The cytoplasm of cortical and subcortical neurons immunostained for APP Stronger cortical neuronal APP staining was observed in cases without HIV encephalitis. Staining of deep gray matter neurons was similar, irrespective of the presence or absence of encephalitis. While foci of intense APP staining were noted in white matter not related to HIV infection, they were associated with foci of opportunistic infections (e.g. due to CMV or PML). We conclude that damaged DNA and altered patterns of expression of DNA repair proteins and APP are common findings in the brains of AIDS patients at autopsy, but do not have a spatial relationship to HIV-infected macrophages.

Kinetics of facial motoneuron loss following facial nerve transection in severe combined immunodeficient mice.

We have recently shown that cells of the acquired immune system are crucial components of motoneuron survival after injury (Serpe et al. [1999] J. Neurosci. 19:RC7). The goal of the present study was to determine the kinetics of facial motoneuron (FMN) loss in wild-type, scid, and reconstituted scid mice after a right facial nerve axotomy at the stylomastoid foramen. Scid mice showed a significant decrease in FMN survival at all weekly postoperative (wpo) times. One, two, four, and ten wpo, ipsilateral FMN survival in scid mice was 90% +/- 1.8%, 84% +/- 1.3%, 52% +/- 3.7%, and 45% +/- 2.5%, respectively, of the contralateral, unoperated side. In contrast, FMN loss after axotomy in wild-type and reconstituted scid mice was not observed until 4 wpo (86% +/- 2.5% and 83% +/- 3.5%, respectively) relative to the contralateral, unoperated side. However, the levels of FMN in both wild-type and reconstituted scid mice were significantly higher than those in the nonreconstituted scid at 4 wpo. By 10 wpo, FMN survival in both wild-type and reconstituted scid mice had continued to decline significantly (60% +/- 2.1% and 58% +/- 3.1%, respectively) relative to the contralateral, unoperated side but were still significantly higher than that of the nonreconstituted scid at 10 wpo. Several important controls were also added to this study. Because the scid mutation is present in all cells (although it specifically results in a loss of V(D)J recombination mechanisms, we wanted to rule out the actual DNA mutation as causal in FMN loss). To accomplish this, we used the recombinase-activating gene-2 knockout (RAG-2 KO) mouse model, in which the RAG-2 has been disrupted and prevents maturation of T and B cells. As with the scid model, there was a significant loss of FMN at 4 wpo in the RAG-2 KO that could be reversed with whole splenocyte reconstitution. We also compared FMN numbers in nonaxotomized facial nuclei from both scid and RAG-2 KO mice relative to wild-type controls. No differences in normal numbers of FMN were found in either the mutation or the gene knockout model. The ability of T and B lymphocytes to rescue FMN from cell death after peripheral nerve injury supports the hypothesis that cells of the acquired immune system produce neurotrophic factors or neurocytokines to support neuronal survival until target reconnection occurs.

Stimulation of the B cell receptor, CD86 (B7-2), and the beta 2-adrenergic receptor intrinsically modulates the level of IgG1 and IgE produced per B cell.

Our findings using B cells from either wild-type, CD86-deficient, or beta 2-adrenergic receptor (beta2AR)-deficient mice suggest three mechanisms by which the level of IgG1 and IgE production can be increased on a per cell basis. Trinitrophenyl-specific B cells enriched from unimmunized mouse spleens were pre-exposed to Ag and/or the beta 2AR ligand terbutaline for 24 h before being activated by either a beta 2AR-negative Th2 cell clone or CD40 ligand/Sf9 cells and IL-4 in the presence or absence of an anti-CD86 Ab. Data suggest that the first mechanism involves a B cell receptor (BCR)-dependent up-regulation of CD86 expression that, when CD86 is stimulated, increases the amount of IgG1 and IgE produced in comparison to unstimulated cells. The second mechanism involves a BCR- and beta 2AR-dependent up-regulation of CD86 to a level higher than that induced by stimulation of either receptor alone that, when CD86 is stimulated, further increases the amount of IgG1 and IgE produced. The third mechanism is BCR-independent and involves a beta 2AR-dependent increase in the ability of a B cell to respond to IL-4. Flow cytometric and limiting dilution analyses suggest that the increase in IgG1 and IgE occurs independently from the isotype switching event. These findings suggest that the BCR, the beta 2AR, and CD86 are involved in regulating IL-4-dependent IgG1 and IgE production.