A ligation-independent sequencing method reveals tRNA-derived RNAs with blocked 3' termini.

Despite the numerous sequencing methods available, the diversity in RNA size and chemical modification makes it difficult to capture all RNAs in a cell. We developed a method that combines quasi-random priming with template switching to construct sequencing libraries from RNA molecules of any length and with any type of 3' modifications, allowing for the sequencing of virtually all RNA species. Our ligation-independent detection of all types of RNA (LIDAR) is a simple, effective tool to identify and quantify all classes of coding and non-coding RNAs. With LIDAR, we comprehensively characterized the transcriptomes of mouse embryonic stem cells, neural progenitor cells, mouse tissues, and sperm. LIDAR detected a much larger variety of tRNA-derived RNAs (tDRs) compared with traditional ligation-dependent sequencing methods and uncovered tDRs with blocked 3' ends that had previously escaped detection. Therefore, LIDAR can capture all RNAs in a sample and uncover RNA species with potential regulatory functions.

No-touch saphenous vein: current understanding of the conduit 'less handled'.

PURPOSE OF REVIEW: The no-touch technique is an established method to harvest the saphenous vein (NT-SV), which is the most commonly used conduit in coronary artery bypass grafting. Herein, we summarize the foundational evidence, as well as highlight recent innovations and ongoing clinical trials involving NT-SV. RECENT FINDINGS: Through preservation of perivascular tissue for atraumatic handling and omission of manual distension, the NT-SV maintains endothelial nitrous oxide synthase levels and experiences less vascular smooth muscle cell activation, which translates to slower progression of atherosclerosis and less size mismatch of the graft and target vessel. These biomolecular advantages allow NT-SV to provide superior graft patency compared to conventional skeletonized saphenous vein and approximating that of the radial artery. Nonetheless, the clinical benefits of NT-SV for mortality and reduction in major adverse cardiac and cerebrovascular events are insufficiently studied in the long-term. The drawback of NT-SV is the short-term harvest site complications, which may potentially be addressed by the advent of endoscopic no-touch technique. SUMMARY: NT-SV is a promising conduit, and its role will be further clarified in upcoming clinical trials and as follow-up lengthens. However, conduit selection and harvest technique should ultimately be personalized to the individual patient.

Risk of in-hospital Deterioration for Children with Single Ventricle Physiology.

Children with single ventricle physiology (SV) are at high risk of in-hospital morbidity and mortality. Identifying children at risk for deterioration may allow for earlier escalation of care and subsequently decreased mortality.We conducted a retrospective chart review of all admissions to the pediatric cardiology non-ICU service from 2014 to 2018 for children < 18 years old. We defined clinical deterioration as unplanned transfer to the ICU or inpatient mortality. We selected children with SV by diagnosis codes and defined infants as children < 1 year old. We compared demographic, vital sign, and lab values between infants with and without a deterioration event. We evaluated vital sign and medical therapy changes before deterioration events.Among infants with SV (129 deterioration events over 225 admissions, overall 25% with hypoplastic left heart syndrome), those who deteriorated were younger (p = 0.001), had lower baseline oxygen saturation (p = 0.022), and higher baseline respiratory rate (p = 0.022), heart rate (p = 0.023), and hematocrit (p = 0.008). Median Duke Pediatric Early Warning Score increased prior to deterioration (p < 0.001). Deterioration was associated with administration of additional oxygen support (p = 0.012), a fluid bolus (p < 0.001), antibiotics (p < 0.001), vasopressor support (p = 0.009), and red blood cell transfusion (p < 0.001).Infants with SV are at high risk for deterioration. Integrating baseline and dynamic patient data from the electronic health record to identify the highest risk patients may allow for earlier detection and intervention to prevent clinical deterioration.

Recommend with caution: A meta-analysis investigating papillary thyroid carcinoma tumor progression under active surveillance.

BACKGROUND: Papillary thyroid carcinoma (PTC) is an indolent disease with favorable outcomes. The non-surgical treatment approach known as active surveillance (AS) has been introduced as an alternative treatment instead of the traditional thyroidectomy. However, 10-15 % of PTC tend to progress. We sought to determine factors predicting the progression of PTC under AS. METHODS: A systematic search was performed in January 2022 using PubMed, Embase, Google Scholar, Web of Science, and ScienceDirect. PRISMA guidelines were used by multiple reviewers to extract study characteristics (author name, publication date, journal name, country, institution, and study design), as well as main outcomes and measures. A combination of utilization of thyroid replacement therapy, baseline tumor size and volume, follow-up tumor size and volume, and the presence of lymph node metastasis and its distribution, as well as surveillance duration, were the main measures of this study. RESULTS: Nine studies with 4166 patients were included, of which 354 showed tumor progression during AS (15 %; 95%CI = 7 % - 23 %). The average follow-up period was 41.58 months. The mean tumor maximum diameter was 8.54 mm (95%CI = 7.04-10.03). Tumor progression was most commonly secondary to an increase in volume by ≥50 % (75 %; 95%CI = 68 % - 80 %), then increase in diameter by ≥3 mm (41 %; 95%CI = 13 % - 76 %), and finally the development of lymph node metastasis (13 %; 95%CI = 9 % - 19 %). Approximately only 2 % of all patients thus developed new lymph node metastasis. Patient age, sex, and tumor size were not associated with higher risks of tumor progression. 12 % of AS patients eventually underwent surgery, though only 40 % (95%CI = 27 % - 53 %) of these patients displayed tumor progression. CONCLUSIONS: Our meta-analysis determined a tumor progression rate of 15 % in patients who underwent AS management, 13 % of which (2 % of all patients) developed lymph node metastasis. We found no protective or risk factors for tumor progression, and that almost half of all patients who underwent delayed surgery did so for reasons other than tumor progression. While not biopsying small (<1 cm) or very low suspicious nodules is already recommended, AS may be an appropriate treatment option in patients appropriately counseled, considering the low risk of advanced tumor progression but also the considerable patient population who fail to adhere to treatment. Alternatively, in aim of preventing overtreatment in patients who would rather take proactive measures against their low-risk carcinoma, minimally-invasive ablation techniques may be an attractive option.

Radiofrequency Ablation of Indeterminate Thyroid Nodules: The First North American Comparative Analysis.

Thyroid nodules can be classified as benign, malignant, or indeterminate, the latter of which make up 10-30% of nodules. Radiofrequency ablation (RFA) has become an attractive and promising therapy for the treatment of benign thyroid nodules. However, few studies have investigated the safety and efficacy of RFA for the management of indeterminate thyroid nodules. In this study, 178 patients with thyroid nodules diagnosed as benign (Bethesda II) or indeterminate (Bethesda III/IV) by preoperative cytopathological analysis were included. Patients in the benign and indeterminate cohorts had similar thyroid nodule volume reduction rates at 65.60% and 64.20%, respectively (p = 0.68). The two groups had similar nodular regrowth rates, at 11.2% for benign nodules and 9.40% for indeterminate nodules (p = 0.72). A total of three cases of transient dysphonia were reported. RFA of indeterminate thyroid nodules was comparable to that of benign thyroid nodules in all parameters of interest, including volume reduction rate. To our best knowledge, our work is the first North American analysis comparing benign and indeterminate thyroid nodules and suggests RFA to be a promising modality for the management of indeterminate thyroid nodules.

Evolution of IgA nephropathy in Singapore over four decades and a comparison of two cohorts from the first and fourth decade.

OBJECTIVE: In this study, we trace the changes in the clinical and histological pattern of IgA nephritis (IgAN) in Singapore as it has evolved over 4 decades and compare the clinical, demographic, histological, and renal outcome of patients with IgAN from the 1st decade and the 4th decade. MATERIALS AND METHODS: This is a retrospective study of all histologically proven IgAN diagnosed between 1976 and 2018. Clinical, laboratory, and histological characteristics between the 1st and the 4th decade, including treatment which could influence the disease progression and renal outcome of these two groups, were compared. We used the Oxford classification to compare the renal biopsy changes for these 2 decades as we were able to retrieve 125 renal biopsy tissues for the 1st cohort of IgAN studied in the 1970s for the comparative study. RESULTS: The commonest clinical presentation throughout the first 3 decades was asymptomatic hematuria and proteinuria (63, 52, and 49%, respectively). In the 4th decade, nephrotic syndrome (31%) was the commonest followed by asymptomatic hematuria and proteinuria (30%), hypertension (21%), and chronic renal failure (11%). The data showed that treatment can modify the Oxford MEST - Crescent scores. Renin-angiotensin system (RAS) blockers modified the S scores, immunosuppressants modified the T and C scores, and combination therapy with RAS blockers and immunosuppressants modified the E, S, and T scores. CONCLUSION: The Oxford MEST classification offers a robust and expressive classification for early and late disease progression with respect to the development of end-stage renal disease (ESRD). E and S seem to be indices of continuing disease activity with progressive glomerulosclerosis, probably still amenable to therapy, but T was a predictive indicator for those destined for ESRD and no longer amenable to therapy.

Changes in primary glomerulonephritis in Singapore over four decades
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This review of 3,289 native kidney biopsies over the past four decades in Singapore documents the changing pattern of biopsy-proven glomerulonephritis (GN)from that of a third world country to that of a developed nation. In the 1st decade, mesangial proliferative GN was the most common form of primary GN, similar to the Asian region. In the 2nd decade, the percentage of mesangial proliferative GN decreased, but membranous GN became more common, as was seen in China and Thailand. In the 3rd decade, focal segmental glomerulosclerosis (FSGS) and membranous nephropathy continued to rise, but it was only recently, in the 4th decade, that FSGS prevalence increased dramatically, although membranous nephropathy continues to increase in some Asian countries. In the last decade in Singapore, Malaysia, and Japan, prevalence of IgA nephritis has decreased but remains the most common GN. The percentage of FSGS continues to increase in many countries like in Italy, United States of America, United Kingdom, China, and Malaysia. We surmise that socioeconomic factors play significant roles in the evolution of the renal biopsy pattern.
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Liver paired exchange: Can the liver emulate the kidney?

Kidney paired exchange (KPE) constitutes 12% of all living donor kidney transplantations (LDKTs) in the United States. The success of KPE programs has prompted many in the liver transplant community to consider the possibility of liver paired exchange (LPE). Though the idea seems promising, the application has been limited to a handful of centers in Asia. In this article, we consider the indications, logistical issues, and ethics for establishing a LPE program in the United States with reference to the principles and advances developed from experience with KPE. Liver Transplantation 24 677-686 2018 AASLD.

The case against imminent death donation.

PURPOSE OF REVIEW: Imminent death donation (IDD) is a proposal to procure organs from patients prior to the withdrawal of life support, which is anticipated to lead to death. In this review, we outline substantial concerns that the transplant community should consider when deliberating the possibility of practicing IDD. RECENT FINDINGS: Although there are several compelling theoretical and intuitive reasons to support IDD, its application has been hindered because of inadequate definitions or protocols. A lack of published reports limits empirical data about the practice. Discussion on the topic has not adequately addressed potential harms to the donor, involvement of stakeholders, or the threat to public trust. SUMMARY: Although IDD has been proposed as a method to increase the number of organs or improve end-of-life care, the proposal currently poses more risk than benefit for patients and the transplant community. Until the major barriers to implementation of IDD are addressed, the transplant community should invest its efforts to increase the organ supply elsewhere.

Robotic single-site adrenalectomy.

INTRODUCTION: Technological advances have brought about robotic single-site (RSS) cholecystectomy and hysterectomy. The application of RSS to additional procedures requires careful assessment of the surgeon learning curve, the technological limitations, patient selection criteria and associated outcomes. METHODS: Patient demographics, BMI, surgical indications, adrenal size, OR times, length of stay, postoperative pain and complications were assessed. RESULTS: Thirty-three patients underwent RSS-A by a single surgeon with 53 % being male, mean age 54 ± 16 years and mean BMI of 32.7. There were 18 left, 10 right, and 5 bilateral procedures for a total of 38 adrenal glands removed (mean tumor size 3.2 cm). There were 5 conversions to a laparoscopic approach, and two to open approach. The necessity for conversion was not associated with age, BMI, tumor size, surgical side or pathology (p > 0.05). The patients who underwent successful unilateral RSS-A had a profile of mean age 55, BMI 31, tumor size 3 cm, and a mean operative time of 118 ± 25.8 min. Pain scores were <4 (10 point scale) in 67 % of patients. 74 % of patients were discharged on POD 1 and 96 % were discharged by POD 2. An assessment of the quartile learning curve for the unilateral RSS-A showed operative times decreased from a mean of 124 to 103 min after 21 cases (p = 0.05). CONCLUSION: Patients with functioning and non-functioning tumors, along with those with obesity can safely be treated with RSS-A. The surgeon learning curve was associated with shortened operative times and not increased complication rates.

A Multimodal Imaging Protocol, (123)I/(99)Tc-Sestamibi, SPECT, and SPECT/CT, in Primary Hyperparathyroidism Adds Limited Benefit for Preoperative Localization.

INTRODUCTION: Focused parathyroidectomy in primary hyperparathyroidism (1°HPT) is possible with accurate preoperative localization and intraoperative PTH monitoring (IOPTH). The added benefit of multimodal imaging techniques for operative success is unknown. METHOD: Patients with 1°HPT, who underwent parathyroidectomy in 2012-2014 at a single institution, were retrospectively reviewed. Only the patients who underwent the standardized multimodal imaging workup consisting of (123)I/(99)Tc-sestamibi subtraction scintigraphy, SPECT, and SPECT/CT were assessed. RESULTS: Of 360 patients who were identified, a curative operation was performed in 96%, using pre-operative imaging and IOPTH. Imaging analysis showed that (123)I/(99)Tc-sestamibi had a sensitivity of 86% (95% CI 82-90%), positive predictive value (PPV) 93%, and accuracy 81%, based on correct lateralization. SPECT had a sensitivity of 77% (95% CI 72-82%), PPV 92% and accuracy 72%. SPECT/CT had a sensitivity of 75% (95% CI 70-80%), PPV of 94%, and accuracy 71%. There were 3 of 45 (7%) patients with negative sestamibi imaging that had an accurate SPECT and SPECT/CT. Of 312 patients (87%) with positive uptake on sestamibi (93% true positive, 7% false positive), concordant findings were present in 86% SPECT and 84% SPECT/CT. In cases where imaging modalities were discordant, but at least one method was true-positive, (123)I/(99)Tc-sestamibi was significantly better than both SPECT and SPECT/CT (p < 0.001). The inclusion of SPECT and SPECT/CT in 1°HPT imaging protocol increases patient cost up to 2.4-fold. CONCLUSION: (123)I/(99)Tc-sestamibi subtraction imaging is highly sensitive for preoperative localization in 1°HPT. SPECT and SPECT/CT are commonly concordant with (123)I/(99)Tc-sestamibi and rarely increase the sensitivity. Routine inclusion of multimodality imaging technique adds minimal clinical benefit but increases cost to patient in high-volume setting.

Radiofrequency ablation as a treatment modality for primary hyperparathyroidism: a systematic literature review.

Background: Primary hyperparathyroidism (pHPT) is an endocrine disorder typically characterized by elevated serum calcium and elevated parathyroid hormone (PTH). While parathyroidectomy is the standard treatment, non-operative intervention such as radiofrequency ablation (RFA) has been adopted as an alternative for the management of pHPT, as it has been utilized in other endocrine glands such as thyroid and adrenal. In this literature review, we aim to evaluate the current practice of RFA for pHPT. Methods: A systematic literature search using PubMed, Web of Science, and Embase through June 2022 was conducted. Studies included in the review consisted of patient cohorts who had an unequivocal diagnosis of pHPT and underwent the treatment of pHPT with RFA. When more than one study was published from a similar cohort of patients, only the study with the most number of patients was considered. Studies included were assessed for bias using the critical appraisal instruments from the Joanna Briggs Institute (JBI) System. Results: A total of 14 studies describing 167 parathyroid glands treated in 163 patients were reviewed. The overall cure rate was 91.2%, with 5 patients undergoing more than one ablation. The most common adverse effect encountered was temporary dysphonia. Incomplete ablation and missed multiglandular disease were the most common reasons for RFA treatment failure. Conclusions: RFA may be an effective and safe alternative to parathyroidectomy in select patients with a well-localized, well-located parathyroid adenoma. Additional long-term data are needed to refine its role in the pHPT treatment algorithm.

Viral cardiovascular surgical diseases: global burdens, challenges and opportunities.

Globally, more than one billion people are vulnerable to neglected tropical diseases, many of which have viral origins and cardiovascular implications. Access to cardiovascular care is limited in countries where these conditions are endemic. Six billion people lack access to safe, timely and affordable cardiac surgical care, whereby over 100 countries and territories lack a single cardiac surgeon. Moreover, while clinically unique, the surgical consequences of neglected cardiovascular diseases with viral origins have been poorly described in the current literature. This review provides an overview of the global burden of viral cardiovascular disease, describes access to cardiac surgical care in regions where these conditions are endemic, and further highlights surgical consequences and considerations to manage patients requiring cardiac surgical care.

[Box: see text].

Decision analysis in cardiac surgery: a scoping review and methodological primer.

OBJECTIVES: Randomized controlled trials are the gold standard for evidence generation in medicine but are limited by their real-world generalizability, resource needs, shorter follow-up durations and inability to be conducted for all clinical questions. Decision analysis (DA) models may simulate trials and observational studies by using existing data and evidence- and expert-informed assumptions and extend analyses over longer time horizons, different study populations and specific scenarios, helping to translate population outcomes to patient-specific clinical and economic outcomes. Here, we present a scoping review and methodological primer on DA for cardiac surgery research. METHODS: A scoping review was performed using the PubMed/MEDLINE, EMBASE and Web of Science databases for cardiac surgery DA studies published until December 2021. Articles were summarized descriptively to quantify trends and ascertain methodological consistency. RESULTS: A total of 184 articles were identified, among which Markov models (N = 92, 50.0%) were the most commonly used models. The most common outcomes were costs (N = 107, 58.2%), quality-adjusted life-years (N = 96, 52.2%) and incremental cost-effectiveness ratios (N = 89, 48.4%). Most (N = 165, 89.7%) articles applied sensitivity analyses, most frequently in the form of deterministic sensitivity analyses (N = 128, 69.6%). Reporting of guidelines to inform the model development and/or reporting was present in 22.3% of articles. CONCLUSION: DA methods are increasing but remain limited and highly variable in cardiac surgery. A methodological primer is presented and may provide researchers with the foundation to start with or improve DA, as well as provide readers and reviewers with the fundamental concepts to review DA studies.

Combined ion beam irradiation platform and 3D fluorescence microscope for cellular cancer research.

To improve particle radiotherapy, we need a better understanding of the biology of radiation effects, particularly in heavy ion radiation therapy, where global responses are observed despite energy deposition in only a subset of cells. Here, we integrated a high-speed swept confocally-aligned planar excitation (SCAPE) microscope into a focused ion beam irradiation platform to allow real-time 3D structural and functional imaging of living biological samples during and after irradiation. We demonstrate dynamic imaging of the acute effects of irradiation on 3D cultures of U87 human glioblastoma cells, revealing characteristic changes in cellular movement and intracellular calcium signaling following ionizing irradiation.

Caring for Each Other: A Resident-Led Peer Debriefing Skills Workshop.

Background: Inadequate time and space to process critical incidents contribute to burnout. Residents do not regularly participate in emotional debriefs. An institutional needs assessment revealed only 11% of surveyed pediatrics and combined medicine-pediatrics residents had participated in a debrief. Objective: The primary objective was to increase resident comfort in participation in peer debriefs after critical incidents from 30% to 50% with implementation of a resident-led peer debriefing skills workshop. Secondary objectives included increasing resident likelihood of leading debriefs and comfort in identifying symptoms of emotional distress. Methods: Internal medicine, pediatrics, and medicine-pediatrics residents were surveyed for baseline participation in debriefs and comfort in leading peer debriefs. Two senior residents became trained debrief facilitators and led a 50-minute peer debriefing skills workshop for co-residents. Pre- and post-workshop surveys assessed participant comfort in and likelihood of leading peer debriefs. Surveys distributed 6 months post-workshop assessed resident debrief participation. We implemented the Model for Improvement from 2019 to 2022. Results: Forty-six (77%) and 44 (73%) of the 60 participants completed the pre- and post-workshop surveys. Post-workshop, residents' reported comfort in leading debriefs increased from 30% to 91%. The likelihood of leading a debrief increased from 51% to 91%. Ninety-five percent (42 of 44) agreed that formal training in debriefing is beneficial. Almost 50% (24 of 52) of surveyed residents preferred to debrief with a peer. Six months post-workshop, 22% (15 of 68) of surveyed residents had led a peer debrief. Conclusions: Many residents prefer to debrief with a peer after critical incidents that cause emotional distress. Resident-led workshops can improve resident comfort in peer debriefing.

The Association of Race and Ethnicity with Mortality in Pediatric Patients with Congenital Heart Disease: a Systematic Review.

CONTEXT: Congenital heart disease (CHD) is a common condition with high morbidity and mortality and is subject to racial and ethnic health disparities. OBJECTIVE: To conduct a systematic review of the literature to identify differences in mortality in pediatric patients with CHD based on race and ethnicity. DATA SOURCES: Legacy PubMed (MEDLINE), Embase (Elsevier), and Scopus (Elsevier) STUDY SELECTION: English language articles conducted in the USA focused on mortality based on race and ethnicity in pediatric patients with CHD. DATA EXTRACTION: Two independent reviewers assessed studies for inclusion and performed data extraction and quality assessment. Data extraction included mortality based on patient race and ethnicity. RESULTS: There were 5094 articles identified. After de-duplication, 2971 were screened for title and abstract content, and 45 were selected for full-text assessment. Thirty studies were included for data extraction. An additional 8 articles were identified on reference review and included in data extraction for a total of 38 included studies. Eighteen of 26 studies showed increased risk of mortality in non-Hispanic Black patients. Results were heterogenous in Hispanic patients with eleven studies of 24 showing an increased risk of mortality. Results for other races demonstrated mixed outcomes. LIMITATIONS: Study cohorts and definitions of race and ethnicity were heterogenous, and there was some overlap in national datasets used. CONCLUSION: Overall, racial and ethnic disparities existed in the mortality of pediatric patients with CHD across a variety of mortality types, CHD lesions, and pediatric age ranges. Children of races and ethnicities other than non-Hispanic White generally had increased risk of mortality, with non-Hispanic Black children most consistently having the highest risk of mortality. Further investigation is needed into the underlying mechanisms of these disparities so interventions to reduce inequities in CHD outcomes can be implemented.

CD34+ progenitor to endothelial cell transition in post-pneumonectomy angiogenesis.

In many species, pneumonectomy triggers compensatory lung growth that results in an increase not only in lung volume, but also in alveolar number. Whether the associated alveolar angiogenesis involves the contribution of blood-borne progenitor cells is unknown. To identify and characterize blood-borne progenitor cells contributing to lung growth after pneumonectomy in mice, we studied wild-type and wild-type/green fluorescence protein (GFP) parabiotic mice after left pneumonectomy. Within 21 days of pneumonectomy, a 3.2-fold increase occurred in the number of lung endothelial cells. This increase in total endothelial cells was temporally associated with a 7.3-fold increase in the number of CD34(+) endothelial cells. Seventeen percent of the CD34(+) endothelial cells were actively proliferating, compared with only 4.2% of CD34(-) endothelial cells. Using wild-type/GFP parabiotic mice, we demonstrated that 73.4% of CD34(+) cells were derived from the peripheral blood. Furthermore, lectin perfusion studies demonstrated that CD34(+) cells derived from peripheral blood were almost uniformly incorporated into the lung vasculature. Finally, CD34(+) endothelial cells demonstrated a similar profile, but had enhanced transcriptional activity relative to CD34(-) endothelial cells. We conclude that blood-borne CD34(+) endothelial progenitor cells, characterized by active cell division and an amplified transcriptional signature, transition into resident endothelial cells during compensatory lung growth.

Alveolar macrophage dynamics in murine lung regeneration.

In most mammalian species, the removal of one lung results in dramatic compensatory growth of the remaining lung. To investigate the contribution of alveolar macrophages (AMs) to murine post-pneumonectomy lung growth, we studied bronchoalveolar lavage (BAL)-derived AM on 3, 7, 14 and 21 days after left pneumonectomy. BAL demonstrated a 3.0-fold increase in AM (CD45(+), CD11b(-), CD11c(+), F4/80(+), Gr-1(-)) by 14 days after pneumonectomy. Cell cycle flow cytometry of the BAL-derived cells demonstrated an increase in S + G2 phase cells on days 3 (11.3 ± 2.7%) and 7 (12.1 ± 1.8%) after pneumonectomy. Correspondingly, AM demonstrated increased expression of VEGFR1 and MHC class II between days 3 and 14 after pneumonectomy. To investigate the potential contribution of peripheral blood cells to this AM population, parabiotic mice (wild-type/GFP) underwent left pneumonectomy. Analysis of GFP(+) cells in the post-pneumonectomy lung demonstrated that by day 14, less than 1% of the AM population were derived from the peripheral blood. Finally, AM gene transcription demonstrated a significant shift from decreased transcription of angiogenesis-related genes on day 3 to increased transcription on day 7 after pneumonectomy. The increased number of locally proliferating AM, combined with their growth-related gene transcription, suggests that AM actively participate in compensatory lung growth.

Cross-circulation and cell distribution kinetics in parabiotic mice.

Blood-borne nucleated cells participate not only in inflammation, but in tissue repair and regeneration. Because progenitor and stem cell populations have a low concentration in the blood, the circulation kinetics and tissue distribution of these cells is largely unknown. An important approach to tracking cell lineage is the use of fluorescent tracers and parabiotic models of cross-circulation. Here, we investigated the cross-circulation and cell distribution kinetics of C57/B6 GFP(+)/wild-type parabionts. Flow cytometry analysis of the peripheral blood after parabiosis demonstrated no evidence for a "parabiotic barrier" based on cell size or surface characterstics; all peripheral blood cell subpopulations in this study reached equilibrium within 14 days. Whole blood fluorescence analysis indicated that the mean exchange flow rate was 16 µl/h or 0.66% of the circulating blood volume per hour. Studies of peripheral lymphoid organs indicated differential cell distribution kinetics. Some subpopulations, such as CD8(+) and CD11c(+), equilibrated in both lymph nodes and spleen indicating a residence time <28 days; in contrast, other lymphocyte subpopulations, such as B220(+) and CD4(+) cells, had not yet reached equilibrium at 28 days. We conclude that parabiosis can provide important insights into defining tissue distribution, residence times, and recirculating pools using fluorochrome markers of cell lineage.