Microvascular Unit Research Articles

Dermal Microvascular Units in Domestic Pigs (Sus scrofa domestica): Role as Transdermal Passive Immune Channels.

The dermal microvascular unit (DMU) is a perivascular functional unit in the dermis. It is composed of microvascular and capillary lymphatics surrounded by immune cells. In this study, jet needle-free injection system was used to injected biocompatible carbon nanoparticles into the cervical skin of domestic pigs (Sus scrofa domestica) and assessed the morphological distribution of DMUs by hematoxylin erythrosine staining, immunohistochemistry (IHC), and transmission electron microscopy (TEM), and TEM was also used to observe the ultrastructural changes of DMUs after jet needle-free injection. Following our study, we identified DMUs in the dermis stratum papillare and similar structures in the dermis stratum reticulare, but the aggregation of CD68+ and CD1a+ cells in the dermis stratum papillare of DMUs by IHC confirmed that DMUs act as reservoirs of dermal immune cells, while similar structures in the dermis stratum reticulare should not be considered as DMUs. Ultrastructure of DMUs was revealed by TEM. Marvelous changes were found following xenobiotics attack, including the rearrangement of endothelial cells and pericytes, and the reactivity of immune cells. Novel interstitial cell telocyte (TC) was also identified around the microvasculature, which may have been previously known as the veil cell. Our results successfully identified the distribution of DMUs in the skin of domestic pigs, which might act as reservoirs of immune cells in the skin and play a role in immune surveillance and immune defense.

Myofibre injury induces capillary disruption and regeneration of disorganized microvascular networks.

Injury to skeletal muscle disrupts myofibres and their microvascular supply. While the regeneration of myofibres is well described, little is known of how the microcirculation is affected by skeletal muscle injury or its recovery during regeneration. Nevertheless, the microvasculature must also recover to restore skeletal muscle function. We aimed to define the nature of microvascular damage and time course of repair during muscle injury and regeneration induced by the myotoxin BaCl2 . To test the hypothesis that microvascular disruption occurred secondary to myofibre injury, isolated microvessels were exposed to BaCl2 or the myotoxin was injected into the gluteus maximus (GM) muscle of mice. In isolated microvessels, BaCl2 depolarized smooth muscle cells (SMCs) and endothelial cells while increasing intracellular calcium in SMCs but did not elicit death of either cell type. At 1day post-injury (dpi) of the GM, capillary fragmentation coincided with myofibre degeneration while arteriolar and venular networks remained intact; neutrophil depletion before injury did not prevent capillary damage. Perfused capillary networks reformed by 5dpi in association with more terminal arterioles and were dilated through 10dpi. With no change in microvascular area or branch point number in regenerating capillary networks, fewer capillaries aligned with myofibres and were no longer organized into microvascular units. By 21dpi, capillary orientation and microvascular unit organization were no longer different from uninjured GM. We conclude that following their disruption secondary to myofibre damage, capillaries regenerate as disorganized networks that remodel into microvascular units as regenerated myofibres mature. KEY POINTS: Skeletal muscle regenerates after injury; however, the nature of microvascular damage and repair is poorly understood. Here, the myotoxin BaCl2 , a standard experimental method of acute skeletal muscle injury, was used to investigate the response of the microcirculation to local injury of intact muscle. Intramuscular injection of BaCl2 induced capillary fragmentation with myofibre degeneration; arteriolar and venular networks remained intact. Direct exposure to BaCl2 did not kill microvascular endothelial cells or smooth muscle cells. Dilated capillary networks reformed by 5days post-injury (dpi) in association with more terminal arterioles. Capillary orientation remained disorganized through 10dpi. Capillaries realigned with myofibres and reorganized into microvascular units by 21dpi, which coincides with the recovery of vasomotor control and maturation of nascent myofibres. Skeletal muscle injury disrupts its capillary supply secondary to myofibre degeneration. Reorganization of regenerating microvascular networks accompanies the recovery of blood flow regulation.

Free flap surgery in osteoradionecrosis of the head and neck

: Osteoradionecrosis (ORN) following radiation therapy is a much-feared complication of the treatment of head and neck cancer. Free flap reconstruction in the ORN patient has specific challenges for the surgeon. From 2014 to 2020 the Head and Neck Microvascular unit of the Oral and Maxillofacial Surgery Division at Jackson Health/University of Miami treated 149 ORN patients with free flap reconstruction. The fibula free flap (n=65) and anterior lateral thigh free flap (6n=1) were the workhorse flaps in our series comprising 44% and 41% of the total flap surgeries. A total of 13 cases (8.7%) involved performing 2 flaps in the same operation. Thirty cases had recorded complications with one flap loss (0.7%) and one case of partial necrosis (0.7%) of the flap. The most common complications encountered were flap congestion with 8 cases (5%), 5 cases of flap dehiscence,4 cases of neck hematoma (2.6%) and 3 cases of infection of the flap reconstruction site (3%). The average length of stay was 8.2 days. In this paper we present our approach to reconstruction in these patients and the lessons we have learned. Though this surgery is complex and has greater risks than free flap surgery in the “virgin” neck, our experience demonstrates that good outcomes can be achieved consistently with a structured approach.

Multiphoton-Guided Creation of Complex Organ-Specific Microvasculature.

Engineering functional human tissues in vitro is currently limited by difficulty replicating the small caliber, complex connectivity, cellularity, and 3D curvature of the native microvasculature. Multiphoton ablation has emerged as a promising technique for fabrication of microvascular structures with high resolution and full 3D control, but cellularization and perfusion of complex capillary-scale structures has remained challenging. Here, multiphoton ablation combined with guided endothelial cell growth from pre-formed microvessels is used to successfully create perfusable and cellularized organ-specific microvascular structures at anatomic scale within collagen hydrogels. Fabrication and perfusion of model 3D pulmonary and renal microvascular beds is demonstrated, as is replication and perfusion of a brain microvascular unit derived from in vivo data. Successful endothelialization and blood perfusion of a kidney-specific microvascular structure is achieved, using laser-guided angiogenesis. Finally, proof-of-concept hierarchical blood vessels and complex multicellular models are created, using multistep patterning with multiphoton ablation techniques. These successes open new doors for the creation of engineered tissues and organ-on-a-chip devices.

Epithelioid Fibrous Histiocytoma: A Concise Review.

Epithelioid fibrous histiocytoma (EFH) is a rare lesion believed to arise from dermal microvascular unit fibroblasts and dendritic histiocytes. EFH has long been considered a morphologic variant of benign fibrous histiocytoma (dermatofibroma), with prominent epithelioid cytomorphology that can mimic both vascular and melanocytic neoplasms. The molecular basis for the relationship between EFH and benign fibrous histiocytoma has remained largely unknown, with some authors suggesting that EFH represents an entity that is biologically distinct from benign fibrous histiocytoma. Recent molecular studies have identified the presence of recurrent anaplastic lymphoma kinase (ALK) gene rearrangements, a phenomenon that has not been described in benign fibrous histiocytoma. These new molecular findings highlight the uniqueness of this rare tumor and may prove useful as a diagnostic tool for differentiation from other histologic mimics.

Duration of type 2 diabetes mellitus and pulmonary function tests: a correlative study

Diabetes mellitus (DM) encompasses a group of metabolic disorders characterized by elevated levels of plasma glucose leading to macro- and micro-vascular damages to target organs. According to IDF, India had 73 million population of diabetes in 2017, and this figure may rise to 134 million adults by 2045 International Diabetes Federation, 2017. Since the alveolar capillary network in the lung is a large micro-vascular unit, microangiopathy may be targeting lungs along with other organs. To correlate pulmonary function tests with duration of type 2 diabetes mellitus. The cross-sectional study was conducted on one hundred six patients of type 2 diabetes mellitus who met the inclusion and exclusion criteria. Diabetic cases were categorized on the basis of duration of disease. RMS Helios 401 computerized spirometer was used to assess pulmonary functions. Statistical tests employed include t test, ANOVA, and correlation coefficient analysis. The mean duration of disease for patients with diabetes was 10.17 ± 5.16 year. There was a significant negative correlation between the parameters of lung function test (p value < 0.05) with duration of diabetes. We found that pulmonary functions have inverse relationship with increase in duration of type 2 diabetes mellitus.

Insights on Microvascular Flow Regulation in Microvascular Units: A Computational Modeling Study

BackgroundRegulation of RBC oxygen delivery and plasma flow is a critical function of the microcirculation. Given the complexity of microvascular networks, mathematical modeling has been an essential adjunct for understanding physiological principles. Many studies have simulated flow through branching arteriolar networks or isolated groups of capillaries, but the completed microvascular units (MVU) ‐ from terminal arteriole, through a capillary bundle, and into a post‐capillary venule ‐ has rarely been studied. Modeling this fundamental microvascular structure will help describe how capillary networks interface with the broader microcirculation and provide insight into properties of flow regulation on this scale.MethodsWe constructed an idealized MVU and applied a dual‐phase steady‐state blood flow model to solve for RBC and plasma flow. We incorporated physiologic parameters that were varied individually while keeping all of the other variables constant: (i) number of parallel capillaries in a bundle (4–10 capillaries), (ii) capillary length (50–600 micron), (iii) arteriolar inflow hematocrit (0.1–0.5), (iv) arteriolar diameter (6–18 micron), (v) venular diameter (6–18 micron), and (vi) driving pressure across the MVU. Mean and coefficient of variation (CV) were calculated for RBC flow, plasma flow, and tube hematocrit (HT) for all parallel capillaries.ResultsPlasma flow is significantly more variable than RBC flow in capillaries for all test cases in this study. Increasing the number of capillaries per bundle decreased the mean RBC and plasma flow but increased total flow through the MVU; plasma flow CV (17%–54%) and HT CV (19%–52%) increased substantially while RBC flow CV was much less affected (4%–9%). Increasing capillary length reduced mean RBC flow, plasma flow, and HT nonlinearly with an inflection point occurring at capillary lengths of 200 microns or greater. Increasing arteriolar inflow hematocrit reduced RBC flow CV (16% vs 2%) and increased plasma flow CV (26%–36%). Increases to arteriolar and venular diameter above 10 microns had little effect on the magnitude or distribution of RBC and plasma flow through the MVU. Changes to the driving pressure across the MVU had a linear effect on RBC and plasma flow with no effect on the relative distribution between capillaries.ConclusionsThis study provides insight into how the biophysical properties of the microcirculation may influence flow regulation through completed microvascular units. Pre‐ and post‐capillary microvessels appear optimized for diameters less than 10 microns. Modifications to driving pressure provide a much more straight forward method of flow regulation than alterations to vessel diameter. Future work will compare these results against in vivo capillary measurements with heterogeneous spatial geometry and explore modeling approaches for multiple interconnected MVU. Example of one idealized microvascular unit included in the study; this microvascular unit has 6 parallel capillaries with length 300 microns.imageExample of one idealized microvascular unit included in the study; this microvascular unit has 6 parallel capillaries with length 300 microns.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of capillary pericytes in the integration of spontaneous Ca2+ transients in the suburothelial microvasculature in situ of the mouse bladder.

In the bladder suburothelial microvasculature, pericytes in different microvascular segments develop spontaneous Ca2+ transients with or without associated constrictions. Spontaneous Ca2+ transients in pericytes of all microvascular segments primarily rely on the cycles of Ca2+ uptake and release by the sarco- and endoplasmic reticulum. The synchrony of spontaneous Ca2+ transients in capillary pericytes exclusively relies on the spread of depolarizations resulting from the opening of Ca2+ -activated chloride channels (CaCCs) via gap junctions. CaCC-dependent depolarizations further activate L-type voltage-dependent Ca2+ channels as required for the synchrony of Ca2+ transients in pericytes of pre-capillary arterioles, post-capillary venules and venules. Capillary pericytes may drive spontaneous Ca2+ transients in pericytes within the suburothelial microvascular network by sending CaCC-dependent depolarizations via gap junctions. Mural cells in the microvasculature of visceral organs develop spontaneous Ca2+ transients. However, the mechanisms underlying the integration of these Ca2+ transients within a microvascular unit remain to be clarified. In the present study, the origin of spontaneous Ca2+ transients and their propagation in the bladder suburothelial microvasculature were explored. Cal-520 fluorescence Ca2+ imaging and immunohistochemistry were carried out on mural cells using mice expressing red fluorescent protein (DsRed) under control of the NG2 promotor. NG2(+) pericytes in both pre-capillary arterioles (PCAs) and capillaries developed synchronous spontaneous Ca2+ transients. By contrast, although NG2-DsRed also labelled arteriolar smooth muscle cells, these cells remained quiescent. Both NG2(+) pericytes in post-capillary venules (PCVs) and NG2(-) venular pericytes exhibited propagated Ca2+ transients. L-type voltage-dependent Ca2+ channel (LVDCC) blockade with nifedipine prevented Ca2+ transients or disrupted their synchrony in PCA, PCV and venular pericytes without dis-synchronizing Ca2+ transients in capillary pericytes. Blockade of gap junctions with carbenoxolone or Ca2+ -activated chloride channels (CaCCs) with 4,4'-diisothiocyanato-2,2'-stilbenedisulphonic acid disodium salt prevented Ca2+ transients in PCA and venular pericytes and disrupted the synchrony of Ca2+ transients in capillary and PCV pericytes. Spontaneous Ca2+ transients in pericytes of all microvascular segments were abolished or suppressed by cyclopiazonic acid, caffeine or tetracaine. The synchrony of Ca2+ transients in capillary pericytes arising from spontaneous Ca2+ release from the sarco- and endoplasmic reticulum appears to rely exclusively on CaCC activation, whereas subsequent LVDCC activation is required for the synchrony of Ca2+ transients in pericytes of other microvascular segments. Capillary pericytes may drive spontaneous activity in the suburothelial microvascular unit to facilitate capillary perfusion.

Epidermal growth factor prevents oligomeric amyloid-β induced angiogenesis deficits in vitro

Cerebrovascular dysfunction is a critical component of Alzheimer’s disease (AD) pathogenesis. Oligomeric amyloid-β42 (oAβ42) is considered a major contributor to AD progression. However, data are limited on the role of oAβ42 in brain endothelial cell vessel degeneration/angiogenesis, including the interaction with angiogenic mediators. Thus, the current study determined the effect of oAβ42 on angiogenesis in vitro, utilizing single brain endothelial cell cultures and triple cultures mimicking the microvascular unit (MVU: brain endothelial cells, astrocytes, and pericytes). oAβ42 dose-dependently reduced angiogenesis and induced vessel disruption. Critically, epidermal growth factor prevented oAβ42-induced deficits, implicating angiogenic pathways as potential therapeutics for AD.

Molecular determinants of blood-brain barrier permeation.

The blood-brain barrier (BBB) is a microvascular unit which selectively regulates the permeability of drugs to the brain. With the rise in CNS drug targets and diseases, there is a need to be able to accurately predict a priori which compounds in a company database should be pursued for favorable properties. In this review, we will explore the different computational tools available today, as well as underpin these to the experimental methods used to determine BBB permeability. These include in vitro models and the in vivo models that yield the dataset we use to generate predictive models. Understanding of how these models were experimentally derived determines our accurate and predicted use for determining a balance between activity and BBB distribution.

Effect of type 2 diabetes mellitus on pulmonary function.

Type 2 diabetes mellitus (T2DM) is a metabolic disease with debilitating effects on multiple organs. The alveolar-capillary network in the lung is a large microvascular unit which may be affected by T2DM-associated microangiopathy. This retrospective study investigated whether type 2 diabetes mellitus (T2DM) affected pulmonary function. Of the 584 patients enrolled in the study, 292 had T2DM and 292 did not. Forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), maximum voluntary ventilation (MVV) and total lung capacity (TLC) are values as percent of predicted, as well as FEV₁/FVC ratio which were values measured. FEV₁, FVC, FEV₁/FVC ratio, MVV, and TLC were significantly lower in T2DM than in non-T2DM (P-values < 0.010). Multiple linear regression analysis found that for the entire study population fasting plasma glucose levels was negatively associated with FEV₁, FVC, FEV₁/FVC ratio and maximum voluntary ventilation (P-values < 0.030). Patients with T2DM were negatively associated with total lung capacity (P-values = 0.025). Multiple linear regression analysis found for patients with T2DM that fasting plasma glucose was negatively associated with FEV₁, FVC, FEV₁/FVC ratio and maximum voluntary ventilation (P-values < 0.020). In T2DM patient, height was negatively correlated with FEV₁ and FVC (all P-values < 0.020), triglycerides were negatively correlated with FEV₁/FVC ratio (P-values = 0.048), and creatinine was negatively correlated with total lung capacity (P-values = 0.017). In summary, T2DM is associated with impaired pulmonary function consistent with obstructive ventilation pattern and fasting plasma glucose is an independent risk factor of reduced pulmonary function.

A Tribute to Sergio Stagnaro: A Scientific Odyssey

Sergio Stagnaro, an Italian scientist and medical doctor, 1931, graduated in Medicine and Surgery and specialized (1959) in Blood, Gastrointestinal and Metabolic Diseases. During the last six decades he undertook a transdisciplinar research dedicated to clinical diagnosis and primary prevention of the most severe human pathologies such as cancer, diabetes, hypertension, cardiovascular and neurodegenerative diseases. By means of a bed-side diagnosis using just the common stethoscope, his research was oriented to get useful qualitative information from the nonlinear behavior of human biological systems. He developed his original method re-evaluating the old semeiotic technique termed ‘Auscultatory Percussion’, re-interpreted with the aid of modern sciences such as deterministic chaos and quantum biophysics, updated as ‘Auscultatory Percussion Reflex Diagnostics’. This original method permitted to collect accurate and exhaustive study cases visiting more than 100,000 patients in the second half of the last century. The data interpretation gives new light about the pathophysiology of several congenital degenerative diseases since birth, when there is just only their inherited real risk, involving and uniting different disciplines such as chemistry and physics, biology and genetics, mathematics and microangiology. Among the various discoveries of Dr, Stagnaro, we remember Congenital Acidosic Enzymo-Metabolic Histangiopathy (CAEMH), Quantum Biophysical Semeiotics (QBS) Constitutions( in particular the Oncological Terrain), and their related Inherited Real Risks (IRR), pathological Endoarteriolar Blocking Devices (EBDs), Tissue Microvascular Unit (TMU) and ‘Clinical Microangiology’. Sergio Stagnaro is the father of the ‘Single Patient Based Medicine’, re-evaluating the relationship between Medical Doctors and patients, by means of a new not-invasive diagnostic medicine termed ‘Venus Medicine’, in alternative to the invasive ‘Mars Medicine’ in current usage, . His last discoveries are related to primary and pre-primary prevention as given by the ‘blue therapy’, a new medical approach oriented to heal QBS Constitutions and Inherited Real Risks, with the use of both innovative nanotechnologies and ancient natural treatments. A Tribute to this Italian scientist is given by medical doctors, scientists, writers, philosophers, poets and patients, highlighting his relevant human and scientific contribute to mankind. NeuroQuantology | June 2013 | Volume 11 | Issue 2 | Page 289-304

Whole microvascular unit deletions in dermatomyositis

ObjectivesThe pathophysiology of dermatomyositis (DM) remains unclear, combining immunopathological mechanisms with ischaemic changes regarded as a consequence of membranolytic attack complex (MAC)-induced capillary destruction. The study is a reappraisal of...

Vascular permeability modulation at the cell, microvessel, or whole organ level: towards closing gaps in our knowledge

Multiple processes modulate net blood-to-tissue exchange in a microvascular unit in normal and pathophysiological conditions. These include mechanisms that control the number and type of microvessels perfused, the balance of adhesion and contractile forces that determine the conductance of the spaces between endothelial cells to water and solutes, the pressure and chemical potential gradients determining the driving forces through these conductive pathways, and the organization of barriers to macromolecules in the endothelial glycocalyx. Powerful methods are available to investigate these mechanisms at the levels of cultured endothelial monolayers, isolated microvessels, and the microvascular units within intact organs. Here we focus on current problems that limit the integration of our knowledge of mechanisms investigated in detail at the cellular level into a more complete understanding of modulation of blood-to-tissue exchange in whole organs when the endothelial barrier is exposed to acute and more long-term inflammatory conditions. First, we review updated methods, applicable in mouse models of vascular permeability regulation, to investigate both acute and long-term changes in permeability. Methods to distinguish tracer accumulation due to change in perfusion from real increases in extravascular accumulation are emphasized. The second part of the review compares normal and increased permeability in individually perfused venular microvessels and endothelial cell monolayers. The heterogeneity of endothelial cell phenotypes in the baseline state and after exposure to injury and inflammatory conditions is emphasized. Lastly, we review new approaches to investigation of the glycocalyx barrier properties in cultured endothelial monolayers and in whole-body investigations.

Introduction: Stockholm stroke symposium – from genes to acute care

The acute stroke research field is dynamic and exciting with several clinical breakthroughs, which give reason for optimism. There is gradually a broader understanding of the genetic linkage with different aspects of stroke. As a majority of stroke cases are caused by thrombo-embolism with blocking of one or more of the cerebral arteries, the obvious acute treatment strategy is to remove the occluded vessel and thereby restore the aerobic metabolism provided that neuroimaging analyses reveal the presence of rescuable ischaemic tissue. On January 28-29, 2009, the Journal of Internal Medicine arranged a 2-day symposium entitled Stockholm stroke symposium - from genes to acute care. In this issue of JIM, five comprehensive reviews from this symposium are presented. These include the genetic factors in the aetiology and treatment of ischaemic stroke, the interplay between microvessels, neurons and glia (i.e., the microvascular unit) in the setting of acute stroke, a critical review of various neuroimaging techniques to visualize ischaemic tissue that is still viable (the ischaemic penumbra), recanalization strategies by means of intravenous thrombolysis as well as future recanalization techniques by, for example, intra-arterial or mechanical thrombolysis and sonothrombolysis by a transcranial approach.

Ischaemic brain damage after stroke: new insights into efficient therapeutic strategies. International Symposium on Neurodegeneration and Neuroprotection.

The International Symposium on Neurodegeneration and Neuroprotection was organized by S. Klumpp with the support of an international advisory board, and was held in Muenster, Germany, between 23 and 26 July 2006. This meeting was a continuation of the International Symposium on Pharmacology of Cerebral Ischemia series. ![][1] At the International Symposium on Neurodegeneration and Neuroprotection in Muenster, Germany, around 50 scientists and clinicians from all over the world presented their most recent data on mechanisms of neuronal cell death after cerebral ischaemia, potential therapeutic strategies and ongoing clinical trials. In addition, emerging topics in this field were discussed, such as the important role of the microvascular unit, brain injury‐induced immunodeficiency and reversible phosphorylation. In particular, protein kinases and phosphatases are becoming the focus of stroke research, as reversible phosphorylation has a crucial role in the fine‐tuning of many biochemical pathways, including cell death and survival signalling. This symposium reflected the impressive progress that has been made in experimental and clinical research on ischaemic brain damage over the past few years, and provided an encouraging outlook on new targets and therapeutic approaches. A main focus of the symposium was on the complex mechanisms of ischaemic brain injury, which involve energy failure, excitotoxicity, the accumulation of reactive oxygen species (ROS), programmed cell death and inflammatory processes. Several speakers showed that the biochemical hallmarks of apoptosis can be observed in models of neurodegenerative diseases, including the regulation of apoptotic factors, mitochondrial dysfunction and the release of cytochrome c or apoptosis‐inducing factor (AIF), activation of caspases and DNA fragmentation. C. Wasterlain (Los Angeles, CA, USA) showed that neuronal cell death after ischaemia also displayed features of apoptosis and necrosis in the same cell, indicating that ‘programmed necrosis’ contributes to infarct development after stroke. The cytotoxic accumulation of intracellular calcium has been established as a … [1]: /embed/graphic-1.gif

The inflammatory response in drug‐induced acute urticaria: ultrastructural study of the dermal microvascular unit

Drug exposure is one of the main aetiologies of urticaria and represents the second most common cause in acute urticarias. Studies involving the ultrastructural aspects of urticaria are relatively rare in the literature. Most of the articles published report on skin biopsies of experimentally induced urticaria, and acute urticaria has been studied even less from a morphological point of view. The aims of this study were to observe ultrastructural cell characteristics in five patients with drug-induced acute urticaria and possible aspects of the inflammatory skin response. Clinical manifestations, light microscopy and transmission electron microscopy were evaluated. With light microscopy, a mild perivascular lymphocyte-monocyte infiltrate was observed with few neutrophils and dermal oedema in skin biopsies of five patients. With electron microscopy, a mild vascular dilatation was observed, with platelets in the lumen and several lymphocytes and dendritic cells close to the superficial dermal vessels. Some mast cells appeared normal, whereas others were granule-depleted. In some areas, mast cells, lymphocytes and satellite dendritic cells were closely associated, as well as some macrophages. A significant number of plasma cells, eosinophils and polymorphonuclear neutrophils were not observed; however, the presence of lymphocytes and macrophages was significant. The epidermis and the dermal-epidermal junction were preserved, except for a discrete oedema in keratinocytes. The ultrastructural aspect of drug-induced acute urticaria is similar to that observed in urticaria caused by Urtica dioica, intradermal histamine and cold urticaria. The presence of the cellular triad with mast cells, dendritic (or satellite) cells and lymphocytes suggests a functional interaction of these cells. These findings support the possible existence of mechanisms in the dermis that may participate in protective and/or injurious vasocentric immune reactions.

Blood Flow Calculations in 3D Microvascular Networks Reconstructed from Multi‐Photon Microscopy

Laser scanning multi-photon microscopy (MPM) makes it possible to obtain detailed, three-dimensional images of tissue microvascular geometry. When combined with mathematical models of network blood flow and mass transport, this data will be extremely useful in estimating local oxygen delivery capabilities and correlating them with direct measures of tissue oxygenation. The objectives of this study were to reconstruct 3D microvascular networks imaged with MPM, and perform theoretical calculations of blood flow in the reconstructed networks. An intravital 3D angiogram of a complete microvascular unit in the mouse hindlimb, including feeding arterioles, capillary segments and collecting venules, was used as the basis for this study. Algorithms for skeletonizing the microvascular network and determining network connectivity and vessel diameters were implemented. The reconstructed network and a previously developed blood flow model were used to calculate steady-state hemodynamics in the network. In the future, these results will be refined using experimental measures of 3D network hemodynamics. Financial Support: HSFC, MSFHR, CIHR/HSFC IMPACT Fellowships (RMB).

Möglichkeiten und Grenzen der Mikrogefäßdarstellung

Vessel systems and the microvascular unit may be studied by a variety of morphological techniques which enable improved structure-function analyses. Two-dimensional light and electron microscopic sectioning techniques with and without specific markers are complemented by 3D vascularisation and perfusion study techniques. Static ex vivo modalities still prevail, however, the future will be dominated by intravital high-resolution techniques.

ISVD‐1 Highlights of the skin immune system

Similar to intestine and pulmonary tissue, skin is in contact with the environment and hence, requires efficient immune surveillance. The concept of skin‐associated lymphoid tissue (SALT) was first introduced in 1978. The skin immune system (SIS) with its cellular and humoral components and the associated draining lymph nodes fulfills the three major functions of the innate and adaptive immune system: (1) induction of the primary immune response; (2) expression of immunity to previously encountered antigens (memory); and (3) avoidance of deleterious immune responses to nonthreatening antigens (tolerance). The cellular components of the SIS include dendritic antigen‐presenting cells (Langerhans cells and dermal dendritic cells), skin‐homing αβ‐T lymphocytes and γδ‐T lymphocytes, keratinocytes and their environment, the microvascular unit (endothelial cells of the dermal postcapillary venules), neural cells and dendritic neural processes, and the draining lymph node with its high endothelial venules. Humoral components of the SIS are defensins, complement components, immunoglobulins, cytokines, chemokines, fibrinolysin, eicosanoids and neuropeptides. Important characteristics and functions of these components and their interactions with each other will be discussed with regard to normal skin versus recruitment phase, retention phase and resolution phase associated with inflammatory conditions. The discussion will primarily focus on cutaneous dendritic antigen‐presenting cells, cutaneous lymphocytes and their homing into the skin, and keratinocytes. Moreover, the importance of the microvascular unit in relation to leukocyte recruitment and migration will be discussed.