Role of protein kinase C in mediating alpha-1-adrenoceptor-induced negative inotropic response in rat ventricles

The aim of this study was to determine the effect of protein kinase C (PKC) activation on intracellular Ca(2+) transient and its relation to alpha(1)-adrenoceptor (alpha(1)-AR)-stimulated negative inotropic response in rat ventricles. The electromechanical responses to phenylephrine (PE) in rat ventricular muscles were concomitantly examined using the conventional microelectrode method. The responses of intracellular Ca(2+) transient and cell contractions to PE in the absence of certain pharmacological interventions were ascertained in fura-2-loaded myocytes. The influence of PE on L-type Ca(2+) current (I(Ca,L)) was also examined using a voltage clamp in a whole-cell configuration. PE did not alter the action potential parameters during the negative inotropic phase. The negative inotropic effect (NIE) was inhibited by prazosin, chloroethylclonidine (CEC) and staurosporine, but was insensitive to pertussis toxin. Desensitization of PKC after prolonged pretreatment of rat ventricles with PDBu also abolished the NIE of PE. Caffeine modulated the NIE, but thapsigargin did not. The evoked intracellular Ca(2+) transient and cell contraction were initially decreased by PE, while I(Ca,L) was not altered. Prazosin and staurosporine significantly inhibited the responses. Our data indicated that alpha(1)AR-mediated NIE in rat ventricular muscles was due to the decrease of intracellular Ca(2+) transients by the modulation of PKC on Ca(2+)-releasing channels signaling through a CEC-sensitive alpha(1)AR subtype.

Degeneration of the cerebellar dentate nucleus in corticobasal degeneration: neuropathological and morphometric investigations

To resolve the controversy regarding the involvement of the dentate nucleus in corticobasal degeneration (CBD), an entire profile of the dentate nucleus was exposed in a sagittal plane and divided into four fields, and the number of neurons in each filed was counted separately using a computer-assisted analyzer in five cases of CBD and compared to those from seven age-matched controls. The size of the nucleus and the number of neurons were significantly reduced in all five cases of CBD. The neuronal loss had a definite regional predilection, more severe in the caudolateral neodentatum than in the rostromedial palaeodentatum, and was accompanied by grumose degeneration and astrogliosis which paralleled the severity of the neuronal loss. Thus, the dentate nucleus appears to be a cardinal target in CBD.

Distinct pattern of neuronal degeneration in the fetal rat brain induced by consecutive transplacental administration of methylmercury

The transplacental neurotoxicity of methylmercury (MeHg) on the fetal rat brain was studied. Adult female rats were administered 1, 2 or 3 mg/kg/day methylmercury chloride (MMC) orally for either 5 or 12 days, and were then mated. They were subsequently administered MMC in the same manner until the end of gestation. On embryonic day 22, a proportion of the fetal brains were histologically examined. Neuronal degeneration of varying degree was detected consistently in the brain stem, cingulate cortex, thalamus and cerebral basal area, including the hypothalamus. The distribution pattern of neuronal damage was different from those in rats treated with MeHg in the postnatal or adult stages. This finding suggests that pathomechanisms in MeHg intoxication operate distinctively in the fetal brain. The offspring derived from dams treated with 1 mg/kg/day MMC for 5 pregestational days and throughout pregnancy survived with inherent brain lesions. This experimental model could be a useful tool for research on the neurotoxicity of MeHg in the human fetal brain.

Regulation of the UNC-5 netrin receptor initiates the first reorientation of migrating distal tip cells in Caenorhabditis elegans

Cell migrations play a critical role in animal development and organogenesis. Here, we describe a mechanism by which the migration behaviour of a particular cell type is regulated temporally and coordinated with over-all development of the organism. The hermaphrodite distal tip cells (DTCs) of Caenorhabditis elegans migrate along the body wall in three sequential phases distinguished by the orientation of their movements, which alternate between the anteroposterior and dorsoventral axes. The ventral-to-dorsal second migration phase requires the UNC-6 netrin guidance cue and its receptors UNC-5 and UNC-40, as well as additional, UNC-6-independent guidance systems. We provide evidence that the transcriptional upregulation of unc-5 in the DTCs is coincident with the initiation of the second migration phase, and that premature UNC-5 expression in these cells induces precocious turning in an UNC-6-dependent manner. The DAF-12 steroid hormone receptor, which regulates developmental stage transitions in C. elegans, is required for initiating the first DTC turn and for coincident unc-5 upregulation. We also present evidence for the existence of a mechanism that opposes or inhibits UNC-5 function during the longitudinal first migration phase and for a mechanism that facilitates UNC-5 function during turning. The facilitating mechanism presumably does not involve transcriptional regulation of unc-5 but may represent an inhibition of the phase 1 mechanism that opposes or inhibits UNC-5. These results, therefore, reveal the existence of two mechanisms that regulate the UNC-5 receptor that are critical for responsiveness to the UNC-6 netrin guidance cue and for linking the directional guidance of migrating distal tip cells to developmental stage advancements.

Generation of sheep X (sheep X mouse) heterohybridoma cell line expressing the beta-1 integrin membrane molecule

Sheep are an important biological model in such diverse areas as immunology and reproductive biology. The limitation of sheep as an experimental model is the absence of reliable cell lines. To establish cell lines that express functional sheep membrane molecules, we produced a sheep x mouse heterohybridoma by fusion of sheep efferent lymph T cells with the murine myeloma cell line NS1. A cloned heterohybridoma fusion partner was selected by treatment with 8-azaguanine. The resulting cell line HL1/385 was selected for hypoxanthine/aminopterin/thymidine (HAT) sensitivity and growth efficiency. The HL1/385 cell line was used as a back-fusion partner into lectin-stimulated efferent T lymphocytes. The back-fusion approach produced more than 50 heterohybrid cell lines with high growth efficiency. The expression of physiological levels of the sheep beta-1 integrin cell surface molecule on the HT4/6 cell line was stable for months in culture. These results suggest that somatic heterohybrids may provide a reliable source of cell lines for sheep studies in vitro.

Nigral degeneration in a case of amyotrophic lateral sclerosis: evidence of Lewy body-like and skein-like inclusions in the pigmented neurons

This report describes a 58-year-old man who exhibited the clinical features of amyotrophic lateral sclerosis (ALS) at autopsy, 1 year after clinical onset of the disease. Neuropathologically, in addition to degeneration of the upper and lower motor neurons, marked degeneration of the substantia nigra with the appearance of Lewy body-like inclusions (LBI) and skein-like inclusions (SLI) were observed in the remaining pigmented neurons. An immunohistochemical study revealed that both LBI and SLI were immunopositive for ubiquitin. Ultrastructurally, LBI in the substantia nigra were composed of randomly arranged 15 nm thick tubular structures associated with ribosome-like granules, similar to those of LBI in the lower motor neurons. SLI in the substantia nigra were composed of curved bundles of 5 nm thick filaments (thinner than those comprising the SLI in the lower motor neurons). We believe that degeneration of the substantia nigra could be one of the degenerative processes involved in ALS.

Neighborhoods and child maltreatment: a multi-level study

OBJECTIVE

To better understand how neighborhood and individual factors are related to child maltreatment.

METHOD

Using an ecological framework, a multi-level model (Hierarchical Linear Modeling) was used to analyze neighborhood structural conditions and individual risk factors for child abuse and neglect. Parents (n = 400) of children under the age of 18 were systematically selected from 20 randomly selected census-defined block groups with different risk profiles for child maltreatment report rates. Parents were administered the Neighborhood Environment for Children Rating Scales, the Child Abuse Potential Inventory, the Zimet measure of social support, and the Conflict Tactics Scales as a measure of childhood experience with violence.

RESULTS

Neighborhood factors of impoverishment and child care burden significantly affect child abuse potential after controlling for individual risk factors. However, neighborhood effects are weaker than they appear to be in aggregate studies of official child maltreatment reports. Variation in child abuse potential within neighborhoods is greater than between neighborhoods. However, adverse neighborhood conditions weakend the effects of known individual risk and protective factors, such as violence in the family of origin.

CONCLUSIONS

If individual potential for child maltreatment is more evenly distributed across neighborhoods than reported maltreatment, then neighborhood and community play an important, if as yet unspecified, role in child maltreatment. Multi-level models are a promising research strategy for disentangling the complex interactions of individual and contextual factors in child maltreatment.

Sensitivity of the slow component of the delayed rectifier potassium current (IKs) to potassium channel blockers: implications for clinical reverse use-dependent effects

The slow delayed rectifier potassium current (I(Ks)) is unique in its slow activation and deactivation kinetics. It is important during cardiac repolarization, especially when the heart rate is fast. We compared the effects of quinidine, procainamide, sotalol, and amiodarone on I(Ks) and correlated the findings with the clinical reverse use-dependent effects of potassium channel blockers. Human minK RNA was obtained by reverse transcription-polymerase chain reaction using explanted human heart. The RNA was injected into Xenopus oocytes for heterologous expression of I(Ks). A two-electrode voltage clamp technique was performed to investigate the I(Ks). We demonstrated that quinidine, sotalol and procainamide had no effects on I(Ks) up to a concentration of 300 microM while amiodarone inhibited I(Ks) in a concentration-dependent manner starting from 10 microM. The inhibition by amiodarone was state-dependent with gradual unblocking after depolarization. The degree of inhibition was 53% immediately after depolarization and 19% at the end of a 5-second depolarization. I(Ks) is 30 times more sensitive to amiodarone than to quinidine, sotalol, and procainamide. Quinidine, sotalol and procainamide have reverse use-dependent effects while amiodarone does not. This is compatible with the hypothesis that no inhibition of I(Ks) at clinical concentrations contributes to the clinical reverse use-dependent effects.

Ethanol increases endothelial nitric oxide production through modulation of nitric oxide synthase expression

Moderate alcohol consumption has been shown to reduce the risk of ischemic heart disease potentially through its effect on specific endothelial-derived compounds. We tested the hypothesis that ethanol increases the expression of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production in bovine aortic endothelial cells (BAEC). Primary cultures of BAEC grown to confluence under standard conditions were treated 3-6 h with 0.1% ethanol in the presence of indomethacin. Ethanol induced a significant increase in both basal and stimulated NO production as determined by chemiluminescence method. This effect was accompanied by a rapid increase of eNOS protein and mRNA expression levels. eNOS mRNA increased two-fold within 3 h and gradually declined, but the increased levels of mRNA persisted for >24 h. A similar increase of eNOS expression was observed in human umbilical endothelial cells exposed to ethanol. These results demonstrate that ethanol augments both basal and stimulated NO production and that this effect is associated with increased eNOS protein and mRNA expression levels. The data are consistent with the hypothesis that the reduced incidence of ischemic heart disease associated with alcohol may be related, at least in part, to the modulation of vascular endothelial cell production of NO.

Liver regeneration is transiently impaired in urokinase-deficient mice

To test the hypothesis that urokinase-type plasminogen activator (uPA) plays an important role in liver regeneration in vivo, partial hepatectomy was performed on wild-type and uPA-deficient (uPA-/-) mice. Mice were studied at 24, 44, and 96 h and at 8 days and 4 wk post-partial hepatectomy for evidence of regeneration, as measured by mitotic indexes and [3H]thymidine incorporation. In wild-type mice, thymidine incorporation peaked at 44 h and this index was reduced by 47% in uPA-/- mice (P = 0.02). By 8 days, however, liver mass was comparable in both groups. Histological analysis revealed the presence of focal areas of fibrin deposition and cellular loss by 24 h that were more severe and prevalent in uPA-/- mice than in wild-type mice (62 and 23%, respectively; chi2 = 3.939, P = 0.047). In contrast, regeneration was not impaired in uPA receptor (uPAR)-deficient mice at 24 and 44 h. Taken together, these data indicate that uPA, independent of its interaction with the uPAR, plays an important role in liver regeneration in vivo.

Pilomotor seizures

We report pilomotor seizures in two patients who had piloerection or gooseflesh spreading in a pattern like the 'Jacksonian march', confined ipsilaterally to the lesion side. The first patient presented this in conjunction with complex partial seizures. Left anterior temporal lobectomy abolished pilomotor and other seizures. Pathological study demonstrated hippocampal sclerosis. A meningioma near the left sphenoid region, incompletely removed, is the likely cause of pilomotor seizures in the second patient. Carbamazepine reduced these attacks. To our knowledge, hippocampal sclerosis and meningioma have never been linked to pilomotor seizures.

Impoverishment and child maltreatment in African American and European American neighborhoods

Although it is well documented that child maltreatment exerts a deleterious impact on child adaptation, much less is known about the precise etiological pathways that eventuate in child abuse and neglect. This paper reports on a multimethod ecological study of the relationship between neighborhood structural factors and child maltreatment reports in African American and European American census tracts. The study had two major components. First, in an aggregate analysis, the effects of four measures of community structure (impoverishment, child care burden, instability, and geographic isolation) on child maltreatment report rates were examined separately for predominantly African American (n = 94) and predominantly European American (n = 189) census tracts. Impoverishment in particular had a significantly weaker effect on maltreatment rates in African American than in European American neighborhoods. Second, focused ethnographies were conducted in four selected census tracts with child maltreatment report rates in the highest and lowest quartiles. Ethnographic data point to the importance of the social fabric in accounting for differences in child maltreatment report rates by predominant neighborhood ethnicity.

Selective involvement of large motor neurons in the spinal cord of rats treated with methylmercury

Mercury is thought to be a possible epidemiological factor for the pathogenesis of motor neuron disease, since it has been reported that metallic, inorganic and organic mercury causes a syndrome clinically resembling amyotrophic lateral sclerosis. We administered 10 mg/kg/day methylmercury chloride to adult rats for 10 consecutive days. The hind-limbs became flaccid and atrophic, and 14 out of the 34 rats had died by the 18th day after methylmercury treatment began. Light microscopical examination of the large motor neurons in the spinal anterior horn revealed cytoplasmic vacuolation and loss of Nissl substance on the 14th day, and neuronophagia appeared on the 16th day. On the 18th day, the loss of large motor neurons was almost complete, whereas small to medium-sized neurons were preserved. Silver acetate autometallography to detect mercury revealed the selective accumulation of mercury in the large motor neurons. These findings suggest that although a high dose is required, organic mercury can cause the definite loss of large spinal motor neurons in rats.

Sp1 sites mediate activation of the plasminogen activator inhibitor-1 promoter by glucose in vascular smooth muscle cells

This study was designed to characterize the direct effects of hyperglycemia on plasminogen activator inhibitor-1 (PAI-1) expression in cultured vascular smooth muscle cells. Glucose induced dose- and time-dependent increases of PAI-1 mRNA expression in rat aortic smooth muscle (RASM) cells in vitro. Using a series of luciferase reporter gene constructs containing PAI-1 5'-flanking sequence (from -6.4 kilobase to -42 base pairs (bp)) transfected into RASM, we found that glucose (25 mM) consistently induced a 4-fold increase in luciferase activity, with the response localized to sequence between -85 and -42 bp. Mutagenesis of two putative Sp1-binding sites located in the region of interest essentially obliterated the glucose-response. Electrophoretic mobility shift assays with radiolabeled oligonucleotides containing the two putative Sp1-binding sites from PAI-1 promoter and nuclear extracts from RASM cells revealed that glucose treatment markedly changed the mobility pattern of the major protein-DNA complexes. Supershift assay showed that transcription factor Sp1 was present in the complexes under control and hyperglycemic conditions. These results suggest that glucose regulates PAI-1 gene expression in RASM cells through an effect on two adjacent Sp1 sites located between -85 and -42 bp of the PAI-1 5'-flanking region and that the release of a transcriptional repressor from the Sp1 complexes may explain the activation of the PAI-1 gene under high glucose conditions in RASM cells.

Effect of selective substitution of 5-bromocytosine on conformation of DNA triple helices

Three triplex DNAs containing 5-bromocytosine[BrC] were studied by vibrational spectroscopy and molecular modelling. Firstly, three oligodeoxypyrimidines of 5'-(TC)3-T4-(BrCT)3 [CBrC], 5'-(TBrC)3-T4-(CT)3 [BrCC] and 5'-(TBrC)3-T4-(BrCT)3 [BrCBrC] were synthesized and then reacted with an oligodeoxypurine of 5'-(AG)3 at pH=4.5 in phosphate buffer respectively to form three comparative hairpin triplex named CY,YC and YY. The results of FT-Raman and IR revealed that YY is almost in A-like form, CY and YC are combinations of A-like form and B-like form, but A-form dominates in CY while B-form is equivalent as A-form in YC. The result is consistent with the theoretical analysis.

[Experimental study on the role of the pedicle of the subdermal vascular network skin flap]

OBJECTIVE

The experiment was to investigate the role of the pedicle of the subdermal vascular network skin flap.

METHODS

Ten healthy white pigs, weighting from 20 to 25 kg were used. The subdermal vascular network skin flap and the traditional skin flap were designed and created on each side of the animal's flank. The traditional skin flap on the contralateral side of the flank was used as control. Flap survival was studied by gross observation and ECT examination of isotope distribution.

RESULTS

There were significant differences between the two groups in mean survival length and area (P < 0.05). In both groups the radioactive isotope gathering is restricted proximally with a ratio of length to width of (1-1.5):1.

CONCLUSION

The presence of the pedicle of the subdermal vascular network skin flap makes no difference compared the traditional skin flap.

An unusual meningioma variant with glial fibrillary acidic protein expression

We studied a recurrent meningioma located in the right frontal lobe. The tumor showed high cellularity and the cells had plump, hyalinous cytoplasm. Immunohistochemically, almost all the tumor cells were positive for epithelial membrane antigen and vimentin, and unexpectedly, glial fibrillary acidic protein (GFAP). Ultrastructural investigation revealed abundant 8- to 10-nm filaments in the cytoplasm. Conspicuous interdigitations with numerous desmosomes were present. Frequently, intracellular and intercellular lumina lined by microvilli were also found. We considered the present case to be an unusual variant of meningioma with GFAP expression. A few cases of meningioma with triple expression of GFAP, vimentin and cytokeratin have been reported previously. However, the present case showed obvious pathological differences from these, and had no immunoreactivity for cytokeratin.

[Multiple brain metastasis of bronchial atypical carcinoid: unusual MR imaging, case report]

We reported a case of a 76-year-old male who suffered from gait disturbance. His first MR image showed multiple masses in the cerebellum and cerebrum. After 50Gy of whole brain irradiation the masses downsized, but, after 8 months the patient was readmitted because of general convulsions. MRI on his second admission showed an enlargement of the multiple masses and reinforcement of the perifocal edema. One year after the onset, MRI revealed the unusual appearance of multiple obscure-marginated cystic masses, intratumoral hemorrhage, and intraventricular hemorrhage. Soon he died of complications from pneumonia. In the autopsy, a mass 4 x 5 cm in size was found in the right lung and multiple metastatic foci were found in the CNS, small intestine, and lymph nodes. The case was diagnosed as bronchial atypical carcinoid with multiple metastases.

Expression of connexin 43 in rat mandibular bone and periodontal ligament (PDL) cells during experimental tooth movement

Bone remodeling in response to force requires the coordinated action of osteoblasts, osteoclasts, osteocytes, and periodontal ligament cells. Coordination among these cells may be mediated, in part, by cell-to-cell communication via gap junctions. This study tests the hypothesis that the regulation of expression of connexin 43, a gap junction protein, is part of the transduction mechanism between force as applied to bone during orthodontic tooth movement and bone remodeling. To test this hypothesis, we examined connexin 433 expression in a rat model system of experimental tooth movement. To establish the model, we extracted maxillary first molars to initiate supra-eruption of opposing mandibular molars. The rats were killed at 0, 6, 12, 24, and 48 hrs post-extraction. The mandibles were removed, demineralized, and embedded in paraffin. To localize connexin 43 protein and mRNA, we used a specific antibody for immunohistochemistry and a specific cDNA probe for in situ hybridization. Western and Northern blot analyses were used to assess the specificity of the connexin 43 antibody and cDNA probe, respectively. We found connexin 43 protein expressed by osteoclasts (++ ++) and periodontal ligament cells (++ +) in compression zones, and by osteoblasts (++ ++) and osteocytes (++ ++) in tension zones of the periodontal ligament. In addition, connexin 43 mRNA was found in some bone and periodontal ligament cells. Connexin 43 protein was found, by densitometric analysis, to be higher in the periodontal ligament after exposure to force compared with controls (P < 0.001). The number of osteocytes expressing connexin 43 48 hrs after molar extraction was also significantly greater in bone subjected to tension when compared with controls (P < 0.001). The results of this study support the hypothesis that connexin 43 plays a role in the coordination of events during experimentally induced alveolar bone remodeling.

High PCNA index in meningiomas resistant to radiation therapy

PURPOSE

Meningiomas are common intracranial tumors, often well controlled with surgical resection alone. While the efficacy of radiation therapy in improving local control and progression-free survival is well documented, prognostic data substantiate factors that are predictive of poor local control following definitive radiation therapy. PCNA is a DNA polymerase expressed at the highest levels in the S-phase, the most resistant portion of the cell cycle to ionizing radiation in vitro. We investigated the possible correlation between the levels of PCNA expression and the clinical outcome of patients treated with definitive radiation therapy.

METHODS AND MATERIALS

Archival tissue was collected from 33 cases of meningioma treated at our institution for definitive radiation therapy between 1970 and 1990. Age-matched normal meningeal tissue and asymptomatic meningiomas removed at autopsy served as tissue controls. A standard ABC immumoperoxidase technique employing antibodies to PCNA, PC-10 (Dako, California) was used to stain specimen slides for PCNA. PCNA index was defined as the number of positive nuclei per 10 high-power fields at 400x magnification. Two independent observers scored the slides without prior knowledge of the cases at hand.

RESULTS

Patients with high PCNA index were less likely to be controlled by therapeutic radiation (p < 0.001, Kaplan-Meier). All patients with a PCNA index greater that 25 failed radiation therapy. Using multivariate analyses, malignant (but not atypical), histology and PCNA index were significant predictors of progression following radiation therapy (p < 0.05, log rank).

CONCLUSION

PCNA index may be a useful adjunct to more standard histopathologic criteria in the determination of meningioma local control and progression-free survival following therapeutic irradiation. Data on a more expanded population evaluated on a prospective basis will be needed before such criteria are routinely employed in the clinical setting.

[Clinical significance of beta 2-microglobulin content in nasopharyngeal secretion]

To study its clinical significance, beta 2-microglobulin (beta 2-MG) in nasopharyngeal secretion was examined using radioimmunoassasy methods in 73 patients with nasopharyngeal carcinoma (NPC), 30 with chronic nasopharyngitis and 30 normal control subjects. In 31 NPC patients, the examination was repeated before and after radiotherapy. The average concentrations of beta 2-MG were 4.87 +/- 2.51 mg/L in NPC group, 1.05 +/- 0.64 mg/L in chronic nasopharygitis group, and 0.85 +/- 0.32 mg/L in the control. The beta 2-MG concentration was higher in the NPC patients than in both chronic pharyngitis patients and normal subjects (P < 0.01). The concentration was lowered down in NPC patients after radiotherapy, and remained high when the treatment failed to control the condition. It seems that beta 2-MG level in nasopharyngeal secretion is closely related to the prognosis and recurrence of nasopharyngeal carcinoma.

[An autopsy case of amyotrophic lateral sclerosis with concomitant Alzheimer's and incidental Lewy body diseases]

We report a 72-year-old man with sporadic amyotrophic lateral sclerosis (ALS) who showed concomitant histopathology of Alzheimer's disease (AD) and incidental Lewy body disease. The patient presented at the age of 70 years with distal upper limb amyotrophy. Thereafter, gait disturbance and respiratory distress progressed. Neuropathological examination showed mild frontal lobe and anterior spinal root atrophy. There was moderate loss of upper and lower motor neurons, and Bunina bodies and skein-like inclusions were present in the spinal anterior horns and facial and hypoglossal nuclei, confirming the pathology of ALS. In addition, however, numerous amyloid plaques were observed throughout the entire cerebral neocortex, nucleus accumbens and amygdaloid body. Many neurofibrillary tangles were also evident in the medial temporal cortex. Moreover, the substantia nigra showed mild degeneration, and Lewy bodies were found in the substantia nigra, locus ceruleus, basal nucleus of Meynert and peripheral autonomic ganglia. Although neither parkinsonism nor dementia was noted during the clinical course, our final neuropathological diagnosis was sporadic ALS, AD and incidental Lewy body disease (or presymptomatic Parkinson's disease). Whether or not the coexistence of these three diseases in the same patient was merely coincidental is of considerable interest.

Induction of alloantigen-specific tolerance by B cells from CD40-deficient mice

Interaction between CD40 on B cells and CD40 ligand molecules on T cells is pivotal for the generation of a thymus-dependent antibody response. Here we show that B cells deficient in CD40 expression are unable to elicit the proliferation of allogeneic T cells in vitro. More importantly, mice immunized with CD40-/- B cells become tolerant to allogeneic major histocompatibility complex (MHC) antigens as measured by a mixed lymphocyte reaction and cytotoxic T-cell assay. The failure of CD40-/- B cells to serve as antigen presenting cells in vitro was corrected by the addition of anti-CD28 mAb. Moreover, lipopolysaccharide stimulation, which upregulates B7 expression, reversed the inability of CD40-/- B cells to stimulate an alloresponse in vitro and abrogated the capacity of these B cells to induce tolerance in vivo. These results suggest that CD40 engagement by CD40 ligand expressed on antigen-activated T cells is critical for the upregulation of B7 molecules on antigen-presenting B cells that subsequently deliver the costimulatory signals necessary for T-cell proliferation and differentiation. Our experiments suggest a novel strategy for the induction of antigen-specific tolerance in vivo.

Cyclin D1 induced apoptosis maintains the integrity of the G1/S checkpoint following ionizing radiation irradiation

Cell cycle "checkpoints" help to ensure the integrity of normal cellular functions prior to replicative DNA synthesis and/or cell division. Cell kinetic abnormalities, particularly arrests at the G1/S and G2/M cell cycle checkpoints, are induced following exposure to ionizing radiation in vitro. Following irradiation, cellular signaling pathways may lead to G1 arrest and/or apoptosis at the G1/S cell cycle transition point. Transfection of cyclin D1, a G1/S cyclin, into a rat embryo cells (REC) results in cellular populations that overexpress cyclin D1, are transformed morphologically, demonstrate an increased incidence of apoptosis, and are tumorigenic in immune-deficient mice. Despite such phenotypic changes, transfected cell populations maintain the integrity of the G1 checkpoint following ionizing radiation. The transfected cells overexpressing Cyclin D1 have a statistically significant increase in the incidence of apoptosis as compared to parental REC strains or mock-transfected REC. The work provides further evidence of Cyclin D1 playing a critical role in maintaining the integrity of the G1/S checkpoint, via the activation of apoptotic pathways following exposure to ionizing radiation in vitro.