SKN-1 is indispensable for protection against Aβ-induced proteotoxicity by a selenopeptide derived from Cordyceps militaris

Oxidative stress (OS) and disruption of proteostasis caused by aggregated proteins are the primary causes of cell death in various diseases. Selenopeptides have shown the potential to control OS and alleviate inflammatory damage, suggesting promising therapeutic applications. However, their potential function in inhibiting proteotoxicity is not yet fully understood. To address this gap in knowledge, this study aimed to investigate the effects and underlying mechanisms of the selenopeptide VPRKL(Se)M on amyloid β protein (Aβ) toxicity in transgenic Caenorhabditis elegans. The results revealed that supplementation with VPRKL(Se)M can alleviate Aβ-induced toxic effects in the transgenic C. elegans model. Moreover, the addition of VPRKL(Se)M inhibited the Aβ aggregates formation, reduced the reactive oxygen species (ROS) levels, and ameliorated the overall proteostasis. Importantly, we found that the inhibitory effects of VPRKL(Se)M on Aβ toxicity and activation of the unfolded protein are dependent on skinhead-1 (SKN-1). These findings suggested that VPRKL(Se)M is a potential bioactive agent for modulating SKN-1, which subsequently improves proteostasis and reduces OS. Collectively, the findings from the current study suggests VPRKL(Se)M may play a critical role in preventing protein disorder and related diseases.

A156 LOW COMPLICATION RATE IN THE OUTPATIENT INTRAJEJUNAL LEVODOPA/CARBIDOPA INTESTINAL GEL CLINICAL PROGRAM

Background

Levodopa/carbidopa intestinal gel (LCIG) is a formulation that is delivered continuously through a percutaneous endoscopy gastro-jejunal tube (PEG-J) for the treatment of patients with advanced Parkinson’s disease (PD). LCIG significantly reduces periods of increased motor symptoms without troublesome dyskinesia. Adverse events related to this treatment have been attributed to PEG-J insertion and the device used for LCIG delivery, rather than to the LCIG preparation itself. To date, the data evaluating long-term efficacy and safety of PEG-J insertion for LCIG administration in the outpatient setting is limited.

Aims

The aim of this study is to describe short and long-term adverse events (AEs) associated with outpatient PEG-J tube insertion for LCIG administration at our centre.

Methods

A retrospective chart review was performed of all PD patients who underwent PEG-J insertion for LCIG therapy at Toronto Western Hospital from March 2011 to October 2019. All AEs associated with PEG-J insertion were collected including procedure and tube related complications, hospital admissions, emergency room (ER) visits and deaths. Data was analyzed using descriptive statistics.

Results

A total of 58 patients were identified and included in the final analysis. 37 (64%) male, with a mean age of 74 years +/-6.17. The mean duration of PD diagnosis prior to PEG-J insertion was 16.5 years +/-2.0. Mean time from PEG-J insertion to data collection was 37.5 months +/- 19.3. 30 (51%) patients had post-procedural abdominal pain or site pain. This pain improved with over the counter analgesics. 9 (16%) had possible site infection; 6 received oral antibiotics and 3 had the tube replaced. 19 (33%) developed granulation tissue, with only 2 patients requiring tube exchange. 32 (55%) had their tube removed or exchanged secondary to PEG-J malfunction. No ER visits related to the PEG-J were recorded. During the data collection period, 12 (21%) patients died for reasons unrelated to PEG-J insertion. There were no reported serious adverse events (SAEs), including post-procedure perforation, bleeding, fistula formation, development of intra-abdominal collections or buried bumper syndrome.

Conclusions

This study demonstrates the absence of serious AEs associated with outpatient PEG-J insertion for LCIG administration in patients with advanced PD. The most common short-term AE was post-procedural pain. The most common long-term AE was related to PEG-J malfunction requiring replacement. This study supports that the current method of outpatient PEG-J insertion for the administration of LCIG is safe in patients with advanced PD.

Funding Agencies

None

A123 GASTROINTESTINAL SYMPTOMS AND DISORDERS OF GUT BRAIN INTERACTION ARE COMMON IN PATIENTS WITH EHLERS-DANLOS SYNDROME (EDS) IN TERTIARY REFERRAL CENTER

Background

Ehlers Danlos Syndrome (EDS) is a group of rare connective tissue disorders. Gastrointestinal (GI) symptoms such as abdominal pain, nausea, vomiting, bloating and altered bowel habits are common in patients with EDS. Specifically, disorders of gut brain interaction (DGBI) appear to be more common in this patient population. The University Health Network (UHN) has the first and only multi-disciplinary clinic, including specialized gastroenterology services, in Canada for the management of EDS.

Aims

The aim of this study is to describe the GI symptoms and DGBI that are present in our cohort of EDS patients.

Methods

A retrospective chart review of all EDS who were seen in the gastroenterologist clinic of the GoodHope EDS clinic at UHN were reviewed from November 1, 2017 to September 26, 2019. Demographic information including age, sex and EDS subtype were collected. GI symptoms that were collected include constipation, diarrhea, fecal incontinence, nausea, vomiting, bloating, abdominal pain, early satiety, heart burn, dysphagia and regurgitation. A physician made diagnosis of irritable bowel syndrome (IBS) was recorded. Descriptive statistics were performed.

Results

The charts of 79 EDS patients were reviewed; 4 were excluded due to missing data. 75 patients were included in the final analysis. 93.3% of patients were female with a mean age of 36.4 +/- 12.5 years. Of these 75 patients, 43 (57.3%) had EDS-hypermobile subtype, 13 (17.3%) EDS-classic, 3 (4%) EDS-vascular, 3 (4%) unknown EDS subtype and 13 (17.3%) were categorized as having a hypermobile spectrum disorder. The most common GI symptoms observed in this patient group included abdominal pain in 85.5%, bloating in 64.4%, heartburn in 61.8%, constipation in 57.9%, nausea in 50%, diarrhea 43.4%, dysphagia in 43.4%, regurgitation in 34.2%, early satiety in 32.89%, vomiting in 30.2%,and fecal incontinence in 13.1%. It was also observed that 50.7% (n=38) had a physician made diagnosis of IBS. Of these patients with IBS, 16 (42.1%) had IBS constipation, 12 (31.5%) had IBS mixed, and 10 (26.3%) had IBS diarrhea.

Conclusions

Our study demonstrated that GI symptoms are common in patients with EDS. In our cohort, abdominal pain is the most commonly reported GI symptom, though other various GI symptoms are also reported in high numbers. DGBI are also common, with IBS being much more common than what has been reported in the general population. Further studies are needed to better understand the pathophysiology and impact of these GI symptoms and DGBI in patients with EDS.

Funding Agencies

UNH Foundation Goodhope Fund

Cardiotoxicity of forchlorfenuron (CPPU) in zebrafish (Danio rerio) and H9c2 cardiomyocytes

Forchlorfenuron (CPPU), as a plant growth regulator or herbicide/pesticide, is widely used in agriculture worldwide. It is adopted by most farmers due to its high efficacy for boosting size and improving the quality of fruit. However, CPPU was implicated in, and gained notoriety due to an incident of exploding watermelon that occurred in 2011. Subsequently, the wider community became aware of the potential risks it posed to living organisms and the ecosystem. In this study, we evaluated the effects of CPPU on the survival, cardiac morphology and function, as well as hematopoietic system, of zebrafish (Danio rerio). Notably, CPPU (2.5-12.5 μg/ml) induced cardiac morphology deformation, cardiac contractile dysfunction and erythrocyte reduction in zebrafish. Consistently, the mRNA expression levels of several cardiac and hematopoietic gene markers (myl7, gata4, mef2c, amhc, vmhc and gata1) were altered by CPPU treatment. In addition, CPPU caused cytotoxicity, cytoskeleton destruction and reduced corresponding proteins (Myl7, Gata4 and Mef2c) expression in H9c2 cardiomyocytes in vitro. Taken together, this study has identified the cardiotoxicity of CPPU in different experimental models and enhanced our understanding on the mechanism underlying the toxicity of CPPU to living organisms.

ANP in regulation of arterial pressure and fluid-electrolyte balance: lessons from genetic mouse models

The recent development of genetic mouse models presenting life-long alterations in expression of the genes for atrial natriuretic peptide (ANP) or its receptors (NPR-A, NPR-C) has uncovered a physiological role of this hormone in chronic blood pressure homeostasis. Transgenic mice overexpressing a transthyretin-ANP fusion gene are hypotensive relative to the nontransgenic littermates, whereas mice harboring functional disruptions of the ANP or NPR-A genes are hypertensive compared with their respective wild-type counterparts. The chronic hypotensive action of ANP is determined by vasodilation of the resistance vasculature, which is probably mediated by attenuation of vascular sympathetic tone at one or several prejunctional sites. Under conditions of normal dietary salt consumption, the hypotensive action of ANP is dissociated from the natriuretic activity of the hormone. However, during elevated dietary salt intake, ANP-mediated antagonism of the renin-angiotensin system is essential for maintenance of blood pressure constancy, inasmuch as the ANP gene "knockout" mice (ANP -/-) develop a salt-sensitive component of hypertension in association with failure to adequately downregulate plasma renin activity. These findings imply that genetic deficiencies in ANP or natriuretic receptor activity may be underlying causative factors in the etiology of salt-sensitive variants of hypertensive disease and other sodium-retaining disorders, such as congestive heart failure and cirrhosis.

Effect of external ultrasound postliposuction: a side-to-side comparison study

BACKGROUND

External ultrasound (EUS) has been used as a therapeutic modality for more than 30 years by multiple medical specialists, primarily for stimulating the repair of soft tissue injuries and relieving pain. It has also been used to treat postoperative swelling after liposuction. There are no controlled studies documenting the objective and subjective effects of EUS following liposuction.

OBJECTIVE

The purpose of this preliminary study was to evaluate the role of EUS in the relief of postoperative symptoms following traditional tumescent liposuction.

METHODS

Twenty-five patients underwent tumescent liposuction of the abdomen or hips. Within 2 weeks after the procedure, a double-blind study was initiated in which EUS therapy was applied at therapeutic energies to one-half of the treated area, while the other side was treated with placebo settings. Patients were treated biweekly for a total of six to eight treatments. Both objective and subjective parameters were assessed during the subsequent side-by-side evaluations by the patient and observer.

RESULTS

After four treatments, 18 of 25 patients had the same postoperative symptoms on each side. Two had fewer symptoms on the EUS side and five were worse on the EUS side. After completion of all treatments, 17 of 25 again had the same symptoms on the therapeutic and placebo sides. Three had improved symptoms and five were worse on the EUS side. The subjective findings revealed that all patients believed the treatment helped significantly on both the placebo and EUS-treated sides.

CONCLUSION

EUS after liposuction of the abdomen at the study parameters provided no objective benefit compared to placebo in postoperative recovery. Patient acceptance and perception of benefit are high. Further studies are needed to determine the optimal timing and energies required for therapeutic value.

Cutaneous laser resurfacing

Cutaneous resurfacing with the new generation of carbon dioxide and erbium lasers has recently come into favor for the treatment of facial rhytides, photodamage, and scarring. The precise control of these resurfacing lasers over the extent of tissue vaporization minimizes thermal damage to the skin while maximizing therapeutic efficacy. Proper use of resurfacing lasers is contingent upon a complete understanding of their clinical, histologic, and ultrastructural effects, as well as an appreciation of the principles of laser safety. An organized approach to the preoperative, intraoperative, and postoperative management of the patient undergoing laser resurfacing will be provided, including a discussion of prevention and treatment of postoperative side effects and complications. (J Am Acad Dermatol 1999;41:365-89.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the clinical, histologic, and ultrastructural effects of resurfacing lasers and be able to discuss the preoperative, intraoperative, and postoperative management of patients undergoing laser resurfacing.

Chronic regulation of arterial blood pressure in ANP transgenic and knockout mice: role of cardiovascular sympathetic tone

OBJECTIVE

Atrial natriuretic peptide (ANP) lowers arterial blood pressure (ABP) chronically, in association with vasodilation of the resistance vasculature. The mechanism mediating the chronic relaxant effect of ANP is likely indirectly mediated by interactions with tonic vasoeffector mechanisms, inasmuch as the resistance vasculature is relatively insensitive to direct cGMP-mediated relaxation by ANP. On the basis of evidence that ANP has widespread sympatholytic activity, the current study investigated whether the chronic hypotensive effect of ANP is mediated by attenuation of tonic cardiovascular sympathetic tone.

METHODS

Total plasma catecholamine concentration and changes in basal ABP and heart rate (HR) following autonomic ganglionic blockade were measured as indices of underlying sympathetic nerve activity in hypotensive ANP-overexpressing transgenic mice (TTR-ANP), hypertensive ANP knockout mice (-/-) and the genetically-matched wild type (NT and +/+, respectively) control mice. Pressor and chronotropic responses to norepinephrine infusion were measured in ganglion-blocked mice of all genotypes, and norepinephrine receptor binding was assessed in representative tissues of -/- and +/+ mice, in order to determine whether peripheral adrenergic receptor responsiveness is altered by ANP-genotype.

RESULTS

Basal ABP was significantly lower in TTR-ANP and higher in -/- compared to their wild-type controls. Basal HR did not differ significantly between mutant and control mice. Autonomic ganglionic blockade reduced ABP and HR in all genotypes, however, the relative decrease in ABP was significantly smaller in TTR-ANP and greater in -/- mice than in their respective controls. Total plasma catecholamine was significantly higher in -/- than in +/+ mice but did not differ significantly between TTR-ANP and NT mice. Norepinephrine infusion during ganglionic blockade elicited quantitatively similar pressor and chronotropic responses in mutant and control mice. Tissue norepinephrine binding did not differ significantly between -/- and +/+ mice.

CONCLUSIONS

The present study shows that differences in endogenous ANP activity in mice, resulting in chronic alterations in ABP are accompanied by directional changes in underlying cardiovascular sympathetic tone, and suggests that the chronic vasodilator effect of ANP is, at least partially, dependent on attenuation of vascular sympathetic tone, possibly at a prejunctional site(s).

Pulsed dye laser treatment of warts: an update

BACKGROUND

Warts are a therapeutic challenge. New studies indicate that pulsed dye laser therapy may be effective, with clearance rates of 72 to 93%.

OBJECTIVE

To determine clearance rate in pulsed dye laser treatment of warts and compare our rate to those of other published studies.

METHODS

Thirty-three patients with 96 warts received pulsed dye laser treatment for recalcitrant plantar, digital, peri- and subungual, and body warts.

RESULTS

Forty-eight percent of patients had complete wart clearance; 45% partially cleared. Sixty-nine percent of those who cleared remained wart-free for an average of 11 months. Mean fluence was 9.4 J/cm2, with an average of 3.4 treatments. Body and palmar warts responded best, digital and peri- and subungual next, and plantar lesions worst. No significant side effects were observed.

CONCLUSION

Pulsed dye laser is an effective treatment option for recalcitrant warts with an excellent side effect profile. However, our response rates were not as high as those previously reported, and we feel that further studies would be useful.

Hair removal using a pulsed-intense light source

Many new laser and light sources have been developed for removal of unwanted body and facial hair. A multiple wavelength pulsed-intense light source (Epilight) has been shown to be effective for long-lasting hair removal. This system is most effective on patients with dark hair and light skin. Further studies are needed to fully elucidate the role of the pulsed-intense light source in permanent hair removal.

Analysis of interdigital spaces during mouse limb development at intervals following amniotic sac puncture

A spectrum of limb abnormalities ranging from adactyly, syndactyly, acrosyndactyly to nail hypoplasia was encountered in mouse embryos subjected to amniotic sac puncture at the corresponding gestational stage when human chorionic villus sampling (cvs) would normally be performed clinically. Previous skeletal studies revealed that, apart from the occasional incidence of fusion of 2 distal phalanges, syndactyly usually only affected the soft tissues within the interdigital spaces. A similar situation was also observed in cases of adactyly; while the skeletal elements of the digits were present, the soft tissues in the interdigital spaces failed to separate. A transient period of bradycardia is induced, possibly secondary to compression of the embryo by the extraembryonic membranes and uterine muscles following amniotic sac puncture. These factors, we believe, produce temporary hypoxia/ischaemia of the distal extremities, and may lead to the modification of the interdigital mesenchymal tissues within the autopods. In order to investigate the mechanism(s) underlying soft tissue syndactyly, limbs recovered at 0.5, 4, 8, 12, 24, or 36 h following amniotic sac puncture (ASP) were examined histologically. Vascular disruption in the form of localised areas of haemorrhage, vascular dilatation and congestion and the presence of fluid-filled cavities occurred in relation to the marginal vein and vascular plexus in the interdigital spaces. It is hypothesised that this interfered with the normal equilibrium of the preset programs of mitosis/cell death and apoptosis within the mesenchymal cells of the interdigital spaces. Apoptosis in these areas was inhibited in the majority of the experimental limbs analysed 4 h after ASP. Instead of undergoing necrosis/apoptosis, increased mitotic activity was usually observed from 8 h following ASP at the sites where apoptosis would normally be expected to be seen. The aberrant fate of the interdigital mesenchyme following ASP and the underlying mechanism(s) involved are discussed, as is the critical importance of an adequate vascular supply to the interdigital spaces during the morphogenesis of the autopod. We believe that this report contributes to understanding the mechanism(s) which lead to syndactyly following ASP, and the limb defects occasionally seen following cvs when this is undertaken during early gestation.

Short-pulse carbon dioxide laser resurfacing in the treatment of rhytides and scars. A clinical and histopathological study

BACKGROUND

Previous studies have shown the efficacy of short-pulse carbon dioxide (CO2) lasers in the treatment of rhytides and scars. To date, there have been few studies examining the histological aspects of these treatments.

OBJECTIVE

The purpose of this study was to perform a prospective clinical and histopathological study of CO2 laser resurfacing for improvement of facial rhytides and scars.

METHODS

A total of 23 patients were studied. Clinical improvement was evaluated both pre- and postoperatively using photographs and optical profilometry. Skin biopsies of rhytides were also obtained.

RESULTS

Postoperatively, rhytides and scars both demonstrated significant increases in clinical improvement scores. Results from optical profilometry studies reflected these results. Skin biopsies from rhytides posttreatment demonstrated increases in collagen layer thickness. Improvement was sustained as late as 1 year following treatment.

CONCLUSIONS

Histopathological studies suggest improvement of rhytides and scars by CO2 laser resurfacing may be attributed to new collagen formation following treatment.

A clinical and histologic evaluation of two medium-depth peels. Glycolic acid versus Jessner's trichloroacetic acid

BACKGROUND

Chemical peels using alpha hydroxy acids have become one of the most frequently requested dermatologic procedures. The use of glycolic acid in superficial chemical peels is now well established. However, the role of glycolic acid in medium-depth chemical peels has yet to be elucidated.

OBJECTIVE

We performed a clinical and histologic comparison of 70% glycolic acid versus Jessner's solution as part of a medium-depth chemical peel using 35% trichloroacetic acid (TCA).

METHODS

Thirteen patients with actinic keratoses, solar lentigines and fine wrinkling were evaluated prospectively. Each patient was treated with 70% glycolic acid plus 35% TCA (GA-TCA) to the right face and Jessner's solution plus 35% TCA (JS-TCA) to the left face. Clinical and histologic changes were evaluated at 7, 30, and 60 days postoperatively.

RESULTS

Clinically, the GA-TCA peel was effective in treating photodamaged skin. The GA-TCA peel was slightly more efficacious in removing actinic keratoses (clinical response score = 1.5) than the JS-TCA peel (clinical response score = 1.0). Histologically, the GA-TCA peel caused the formation of a slightly thicker Grenz zone (mean = 0.053 mm) 60 days postpeel than the JS-TCA peel (mean = 0.048 mm) (not statistically significant). The GA-TCA peel caused more neoelastogenesis than the JS-TCA peel, while the JS-TCA peel resulted in more papillary dermal fibrosis and neovascularization than the GA-TCA peel.

CONCLUSION

The GA-TCA peel is a new medium-depth chemical peel that is effective in treating photodamaged skin.

The removal of cutaneous pigmented lesions with the Q-switched ruby laser and the Q-switched neodymium: yttrium-aluminum-garnet laser. A comparative study

BACKGROUND

The Q-switched ruby laser (QSRL) (694 nm) has been used successfully in the removal of tattoos and a variety of cutaneous pigmented lesions. The frequency-doubled Q-switched neodymium:yttrium-aluminum-garnet laser (QSNd:YAG) (1064 and 532 nm) has also been shown to be effective in the treatment of tattoos, however, little has been published regarding the QSNd:YAG laser in the removal of cutaneous pigmented lesions.

OBJECTIVE

The purpose of this study is to compare the efficacy and side effect profile of the QSRL and the frequency-doubled QSNd:YAG lasers in the removal of cutaneous pigmented lesions, including lentigines, café-au-lait macules, nevus of Ota, nevus spilus, Becker's nevus, postinflammatory hyperpigmentation, and melasma.

METHODS

Twenty patients with pigmented lesions were treated with the QSRL and the frequency-doubled QSNd:YAG lasers. Clinical lightening of the lesion was assessed 1 month after a single treatment. Side effects and patient satisfaction were also evaluated.

RESULTS

A minimum of 30% lightening was achieved in all patients after only one treatment with either the QSRL or the frequency-doubled QSNd:YAG laser. The QSRL seems to provide a slightly better treatment response than the QSNd:YAG laser. Neither laser caused scarring or textural change of the skin. Most patients found the QSRL to be more painful during treatment, but the QSNd:YAG laser caused more postoperative discomfort.

CONCLUSION

Both the QSRL and the frequency-doubled QSND:YAG laser are safe and effective methods of treatment of epidermal and dermal pigmented lesions.

Distinction of class II MHC+ Langerhans cell-like interstitial dendritic antigen-presenting cells in murine dermis from dermal macrophages

Dermal cells are capable of initiating contact-hypersensitivity responses but the precise identification of the antigen-presenting cell within murine dermis is lacking. Class II major histocompatibility complex (MHC)+ cells with dendritic shape and lacking endothelial factor VIII but expressing the dendritic antigen-presenting cell marker NLDC-145 were observed in the perivascular and interstitial dermis of BALB/c and C3H/HeN skin. The heterogeneous class II MHC+ cells could be divided into two subsets: each was class II MHC+ CD45+ (bone marrow derived) GR-1- (non-neutrophil/macrophage) CD3- (non T), but one subset was CD11b+ (beta 2 integrin) and the other was CD11b-. Ultrastructural examination of class II MHC+ cells revealed the presence of a Langerhans cell-like/indeterminant cell subset with indented nuclei, dendritic morphology, active cytoplasm, and dense intermediate filaments. Phagolysomes and Birbeck granules were not observed in such cells, indicating these were distinct from dermal macrophages and from classical epidermal Langerhans cells, respectively. Cells with a monocyte/macrophage ultrastructural appearance were also noted, likely representing the class II MHC subset expressing CD11b and Ly6c (monocyte/endothelial antigen). Dermal cells in suspension were capable of processing and presenting large protein antigens to antigen-specific T-cell hybridomas; dermal cells also induced the syngeneic mixed lymphocyte reaction. The dermal antigen-presentation activities were totally abrogated by removal of class II MHC+ cells, but not by removal of CD11b+ cells or Ly6c+ cells, indicating that potent antigen-presenting cell activity was restricted to the class II MHC+ CD11b- Ly6c- subset (Langerhans cell-like/indeterminant cells). In conclusion, within a complex array of dermal leukocytes a murine dermal class II MHC+ cell population expressing a Langerhans cell-like/dendritic antigen-presenting cell phenotype and exhibiting potent antigen processing and presenting activity can be identified. The positioning of potent interstitial dendritic antigen-presenting cells at the interface of the vasculature with the dermal interstitium provides rapid access to an antigen-presenting cell as T cells first egress into the skin.

Cutaneous dermal Ia+ cells are capable of initiating delayed type hypersensitivity responses

The presence of Langerhans cells (LC) within the epidermis has been shown to be critical for inducing T-cell-mediated immune responses in the skin. The purpose of this study was to assess whether cells in the dermis can initiate T-cell-mediated delayed-type hypersensitivity responses in vivo. Initially, back skins from C3H mice were trypsinized to remove the epidermis. The dermis was enzymatically dispersed and filtered to obtain a cell suspension. However, dermal cells exposed to trypsin were contaminated with numerous disaggregated hair follicles. These hair follicles contained Ia+ cells (presumably LC), and upon haptenation in vitro with trinitrophenyl, initiated contact hypersensitivity reactions in vivo. We therefore used dispase in place of trypsin to prevent follicular disaggregation and to allow preparation of dermal cell suspensions free of hair follicles. These hair follicle-free dermal cells were haptenated with trinitrophenyl and injected intradermally. Elicitation of contact hypersensitivity by epicutaneous painting 6 d later revealed the mean +/- SEM incremental ear-swelling response to be 53 +/- 8 mm X 10(-3). In contrast, mice sensitized by injection with dermal cells depleted of Ia+ cells demonstrated only 10 +/- 1 mm X 10(-3) of ear swelling. Thus, like dendritic LC of the epidermis, perivascular dendritic Ia+ cells of the dermis are capable of initiating T-cell-mediated contact hypersensitivity in vivo and may be highly relevant for presentation of antigen to T cells trafficking through the dermis.

E. coli and M. luteus DNA topoisomerase I can catalyze catenation of decatenation of double-stranded DNA rings

Escherichia coli and Micrococcus luteus DNA topoisomerase I are found to promote catenation of double-stranded DNA rings. At low DNA concentration dimeric catenanes are the major catenated products; at high DNA concentration or when spermidine is present, catenanes containing more than two rings are formed. There is no requirement of extensive sequence homology between the conponent rings forming a catenane; dimeric catenanes between Pseudomonas phage PM2 DNA and E. coli plasmid pBR322 are readily formed. The formation of a dimeric catenane by these type I topoisomerases, however, requires the presence of at least one preexisting single-chain scission in one of the two component rings. This is in contrast to the cases with the type II DNA topoisomerases which can form catenanes made of covalently closed rings only. The catenanes formed by the type I enzymes can be unlinked by the same enzymes, or by DNA gyrase, a type II enzyme, upon dilution of the isolated catenanes. The catenation and decatenation of duplex DNA rings adds a fourth type of reaction promoted by these type I DNA topoisomerases to the three reported previously: relaxation of superhelical DNA, interconversion between single-stranded DNA rings with and without knots and the intertwining of single-stranded DNA rings of complementary sequences into a covalently closed duplex ring with a high linking number. All four topoisomerization reactions involve the crossing of one DNA strand through a transient break of another DNA strand. The new reaction reported here suggests that such a crossover event might not require pairing of complementary nucleotide sequences.