Endothelial Basal Lamina Research Articles

Neutrophil extravasation in rat mesenteric venules induced by the chemotactic peptide N-formyl-methionyl-luecylphenylalanine (fMLP), with special attention to a barrier function of the vascular basal lamina for neutrophil migration.

The present study was performed to investigate morphologically the process of neutrophil extravasation induced by the synthetic bacterial peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) in venules of the rat mesentery by the combined use of intravital microscopy and transmission electron microscopy (TEM). Special attention was given to the interaction of the neutrophils with the endothelial cells and endothelial basal lamina. By intravital microscopy, the rolling and adhesion of leukocytes were observed within 3 min in preparations activated by fMLP. Neutrophils remained in the vascular wall for more than 30 min even after penetration of the endothelium. In this period, neutrophils migrating between endothelial cells and their basal lamina were often observed by TEM. After 40 min application of fMLP, some of the migrating neutrophils parted from the vessel wall into the surrounding connective tissues. There were neutrophils which passed through the small pore of the basal lamina with a cytoplasmic constriction. These findings indicate that the endothelial basal lamina acts as a physical barrier against neutrophil extravasation, thus resulting in the transient retainment of neutrophils beneath the endothelial cells of the venular wall.

Neurodegeneration in Striatum Induced by the Mitochondrial Toxin 3-Nitropropionic Acid: Role of Matrix Metalloproteinase-9 in Early Blood-Brain Barrier Disruption?

Blood-brain barrier (BBB) dysfunction is a potential mechanism involved in progressive striatal damage induced by the mitochondrial excitotoxin, 3-nitropropionic acid (3-NP). After activation by proteases and free radicals, matrix metalloproteinases (MMPs), particularly MMP-9 and -2, can digest the endothelial basal lamina leading to BBB opening. Using CD-1 mice, we show that MMP-9 expression by zymography is increased in the injured striatum compared with the contralateral striatum 2 hr after 3-NP injection [133.50 +/- 57.17 vs 50.25 +/- 13.56; mean +/- SD of optical densities in arbitrary units (A.U.); p < 0.005] and remains elevated until 24 hr (179.33 +/- 78.24 A.U.). After 4 hr, MMP-9 expression and activation are accompanied by an increase in BBB permeability. MMP inhibition attenuates BBB disruption, swelling, and lesion volume compared with vehicle-treated controls. There is a clear spatial relationship between MMP-9 expression and oxidized hydroethidine, indicating reactive oxygen species (ROS) production. Furthermore, transgenic mice that overexpress copper/zinc-superoxide dismutase (SOD1) show decreased lesion size and edema along with decreased immunoreactivity for MMP-9, compared with wild-type littermates (lesion: 38.8 +/- 15.1 and 53.3 +/- 10.3, respectively, p < or = 0.05; edema: 21.8 +/- 11.2 and 35.28 +/- 11, respectively, p < or = 0.05; MMP-9-positive cells: 352 +/- 57 and 510 +/- 45, respectively, p < or = 0.005), whereas knock-out mice deficient in SOD1 display significantly greater swelling (48.65 +/- 17; p < or = 0.05). We conclude that early expression and activation of MMP-9 by ROS may be involved in early BBB disruption and progressive striatal damage after 3-NP treatment.

Angiogenin distribution in human term placenta, and expression by cultured trophoblastic cells.

Human angiogenin is a 14-kDa secreted protein with angiogenic and ribonucleolytic activities. Angiogenin is associated with tumour development but is also present in normal biological fluids and tissues. To further address the physiological role of angiogenin, we studied its expression in situ and in vitro, using the human term placenta as a model of physiological angiogenesis. Angiogenin was immunodetected by light and transmission electron microscopy, and its cellular distribution was established by double immunolabelling with cell markers including von Willebrand factor, platelet/endothelial cell adhesion molecule-1 (PECAM-1), CD34, Tie-2, vascular endothelial cadherin (VE-cadherin), vascular endothelial growth factor receptor-2 (VEGF-R2), erythropoeitin receptor (Epo-R), alpha-smooth muscle actin, CD45, cytokeratin 7, and Ki-67. Angiogenin immunoreactivity was detected in villous and extravillous trophoblasts, the trophoblast basement membrane, the endothelial basal lamina, foetal blood vessels, foetal and maternal red blood cells, and amnionic cells. Its expression was confirmed by in situ hybridisation with a digoxygenin-labelled cDNA probe and reverse transcriptase-polymerase chain reaction amplification. Villous cytotrophoblasts, isolated and differentiated in vitro into a functional syncytiotrophoblast, expressed and secreted angiogenin. Given its known biological activities in vitro and its observed pattern of expression, these data suggest that, in human placenta, angiogenin has a role not only in angiogenesis but also in vascular and tissue homeostasis, maternal immune tolerance of the foetus, and host defences.

Matrix metalloproteinases correlate with alveolar-capillary permeability alteration in lung ischemia-reperfusion injury.

Matrix metalloproteinases (MMPs) are able to degrade the endothelial basal lamina and increase vascular permeability. In a porcine model of isolated-reperfused lung, we studied the alveolar-capillary permeability and the zymographic expression of MMP-9 and MMP-2 in the bronchoalveolar lavage fluid of lungs submitted ex vivo to ischemia in three preservation solutions [modified Euro-Collins (EC), low-potassium-dextran, modified-blood]. Twenty-two pigs were randomly divided into three groups according to the preservation solution used. One lung of each pig was rapidly reperfused and analyzed (control lung) although the other lung was reperfused and analyzed after 8 hr of ischemia (ischemic lung). Alveolar-capillary permeability, evaluated by the transferrin leak index, was increased after 8 hr of ischemia compared with controls in the three groups, but was significantly higher in the modified EC group. In the EC group, after 8 hr of ischemia, both proMMP-9 and MMP-9 increased significantly (8.8- and 22-fold, respectively) compared with controls and this increase correlated with the transferrin leak index. Neither proMMP-9 nor MMP-9 increased with the other two preservation solutions. The MMP-2 increase after ischemia was smaller and was also restricted to the EC group. MMP expression is enhanced during lung ischemia-reperfusion, especially in the presence of EC and this phenomenon correlates with the alteration of alveolar-capillary permeability.

The structure of endometrial microvessels.

Recent studies have provided substantial evidence to highlight abnormalities in the structure of endometrial microvessels in users of progestogen-only contraception. Structural changes alone are unlikely to lead to breakthrough bleeding, but appear to be associated with a reduction in vessel integrity, and may reflect alterations in the control and growth of endometrial microvessels in those exposed to exogenous progestogens. In users of low-dose progestogens, immunohistochemical studies have demonstrated changes in superficial endometrial vascular morphology, density and in endometrial migratory cell populations. In Norplant users the endometrial endothelial basal lamina is deficient in the initial months of exposure, when bleeding problems are most common. The basal lamina refers to the very thin structure consisting mostly of collagen IV and laminin seen underlying endothelial and epithelial cells at the electron microscope level. In addition, hysteroscopic studies have demonstrated increased fragility of superficial vessels. Changes in endometrial microvascular anatomy associated with normal menstruation have been reviewed, and are compared with those seen following contraceptive steroid exposure. Likely mechanisms of breakthrough bleeding such as increased superficial vascular fragility and the possible alterations in endometrial vascular structure leading to this are discussed.

Pulmonary edema in fatal heroin overdose: immunohistological investigations with IgE, collagen IV and laminin — no increase of defects of alveolar-capillary membranes

Pulmonary edema complicating heroin overdosage is a well recognized entity and regarded as the major mechanism contributing to death in heroin addicts. It’s pathogenesis is unknown, several mechanisms are discussed: hypoxia-induced increase of pulmonary capillary permeability, depressed myocardial contractility, centrally induced respiratory depression, primary toxic effects on the alveolar capillaries and acute anaphylactic shock. The present study included opiate-related deaths ( n=23) and a control group of sudden cardiovascular deaths ( n=12) to verify the hypothesis, that defects of the alveolar capillary membranes and/or an acute anaphylactic reaction leads to pulmonary congestion, edema and hemorrhages. Lung specimens were obtained from these 35 autopsies of persons autopsied in the Institute of Forensic Medicine, University of Bonn, in 1997 and 1998. All specimens were examined with hematoxylin–eosin, prussian blue and investigated with immunohistological methods using primary antibodies against collagen IV, laminin and IgE. Defects of the basal laminae of the alveoli were found, demonstrated by laminin and collagen IV, and the number of IgE-positive cells was counted in both groups. There was an increased but not significant number of IgE-positive cells in the heroin-group and defects of the epithelial and endothelial basal laminae were found in both groups without significant differences.

Advances in the Vascular Pathophysiology of Ischemic Stroke

The cerebral vascular supply is constructed to protect the cerebral hemispheres and brainstem from the consequences of blood flow cessation. Reversal of blood flow around local obstructions is a feature of the microvascular beds of the striatum and cerebral cortex. Cerebral capillaries of these beds consist of endothelial cells, basal lamina, and astrocyte end-feet that sit in close apposition. The interaction of astrocytes with neurons indicates the close relationship of microvessels to neurons. These relationships are altered when blood flow ceases in the supplying artery. Increased endothelial cell permeability and endocytoses lead to edema formation, and matrix degradation is associated with hemorrhage. Autoregulation is lost. Ischemia initiates leukocyte adhesion receptor expression, which is promoted by cytokine generation from the neuropil and activated monocytes. “Preactivation” may further augment the inflammatory responses to ischemia. The activation of cerebral microvessels by ischemia is heterogeneous, involving alterations in integrin–matrix interactions, leukocyte-endothelial cell adhesion, permeability changes, and the “no-reflow” phenomenon due to platelet activation, fibrin formation, and leukocyte adhesion. Ischemia produces swelling of the microvascular endothelium, and rapid detachment and swelling of the astrocyte end-feet. Ischemic injury targets the microvasculature, where the inflammatory responses are initiated and contribute to tissue injury.

Mast Cells Migrate from Blood to Brain

It is well established that mast cells (MCs) occur within the CNS of many species. Furthermore, their numbers can increase rapidly in adults in response to altered physiological conditions. In this study we found that early postpartum rats had significantly more mast cells in the thalamus than virgin controls. Evidence from semithin sections from these females suggested that mast cells were transiting across the medium-sized blood vessels. We hypothesized that the increases in mast cell number were caused by their migration into the neural parenchyma. To this end, we purified rat peritoneal mast cells, labeled them with the vital dyes PKH26 or CellTracker Green, and injected them into host animals. One hour after injection, dye-filled cells, containing either histamine or serotonin (mediators stored in mast cells), were located close to thalamic blood vessels. Injected cells represented approximately 2-20% of the total mast cell population in this brain region. Scanning confocal microscopy confirmed that the biogenic amine and the vital dye occurred in the same cell. To determine whether the donor mast cells were within the blood-brain barrier, we studied the localization of dye-marked donor cells and either Factor VIII, a component of endothelial basal laminae, or glial fibrillary acidic protein, the intermediate filament found in astrocytes. Serial section reconstructions of confocal images demonstrated that the mast cells were deep to the basal lamina, in nests of glial processes. This is the first demonstration that mast cells can rapidly penetrate brain blood vessels, and this may account for the rapid increases in mast cell populations after physiological manipulations.

Early appearance of activated matrix metalloproteinase-9 and blood–brain barrier disruption in mice after focal cerebral ischemia and reperfusion

Blood–brain barrier (BBB) disruption is thought to play a critical role in the pathophysiology of ischemia/reperfusion. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that can degrade all the components of the extracellular matrix when they are activated. Gelatinase A (MMP-2) and gelatinase B (MMP-9) are able to digest the endothelial basal lamina, which plays a major role in maintaining BBB impermeability. The present study examined the expression and activation of gelatinases before and after transient focal cerebral ischemia (FCI) in mice. Adult male CD1 mice were subjected to 60 min FCI and reperfusion. Zymography was performed from 1 to 23 h after reperfusion using the protein extraction method with detergent extraction and affinity-support purification. MMP-9 expression was also examined by both immunohistochemistry and Western blot analysis, and tissue inhibitors to metalloproteinase-1 was measured by reverse zymography. The BBB opening was evaluated by the Evans blue extravasation method. The 88-kDa activated MMP-9 was absent from the control specimens, while it appeared 3 h after transient ischemia by zymography. At this time point, the BBB permeability alteration was detected in the ischemic brain. Both pro-MMP-9 (96 kDa) and pro-MMP-2 (72 kDa) were seen in the control specimens, and were markedly increased after FCI. A significant induction of MMP-9 was confirmed by both immunohistochemistry and Western blot analysis. The early appearance of activated MMP-9, associated with evidence of BBB permeability alteration, suggests that activation of MMP-9 contributes to the early formation of vasogenic edema after transient FCI.

The demonstration of immunoreactive dystrophin and its developmental expression in perivascular astrocytes

Immunoreactivity of dystrophin family proteins was observed in the astrocytes of the adult and immature rat hippocampus and cerebral cortex by using Dys2, a monoclonal antibody recognizing both 427 kDa and short dystrophin isoforms. As revealed by light and electron microscopy, immunostaining of the ribosomal apparatus and of pericapillary endfeet was particularly pronounced in the adult. In the pericapillary astrocyte processes immunostaining appeared between postnatal days 10 and 20, and reached the intensity seen in the adult by postnatal day 30. In the pericapillary astrocyte process, the membrane facing the endothelial basal lamina was the earliest structure to show the immunoreaction. At later stages, the pericapillary astrocyte process was gradually filled up with immunoprecipitate. Findings suggest that dystrophins are expressed coinciding with the development of the blood–brain barrier, and it is assumed that they contribute to the formation of this system.

Modulation of fibronectin expression in the central nervous system of Lewis rats with experimental autoimmune encephalomyelitis.

Fibronectin (FN), a large family of plasma and extracellular matrix (ECM) glycoproteins, plays an important role in leukocyte migration. In normal central nervous system (CNS), a fine and delicate mesh of FN is virtually restricted to the basal membrane of cerebral blood vessels and to the glial limitans externa. Experimental autoimmune encephalomyelitis (EAE), an inflammatory CNS demyelinating disease, was induced in Lewis rats with a spinal cord homogenate. During the preclinical phase and the onset of the disease, marked immunolabelling was observed on the endothelial luminal surface and basal lamina of spinal cord and brainstem microvasculature. In the paralytic phase, a discrete labelling was evident in blood vessels of spinal cord and brainstem associated or not with an inflammatory infiltrate. Conversely, intense immunolabelling was present in cerebral and cerebellar blood vessels, which were still free from inflammatory cuffs. Shortly after clinical recovery minimal labelling was observed in a few blood vessels. Brainstem and spinal cord returned to normal, but numerous inflammatory foci and demyelination were still evident near the ventricle walls, in the cerebral cortex and in the cerebellum. Intense expression of FN in brain vessels ascending from the spinal cord towards the encephalon preceded the appearance of inflammatory cells but faded away after the establishment of the inflammatory cuff. These results indicate an important role for FN in the pathogenesis of CNS inflammatory demyelinating events occurring during EAF.

Renal cell carcinomas and pancreatic adenocarcinomas produce nidogen in vitro and in vivo.

The production of nidogen by four renal cell carcinoma (RCC) and three pancreatic adenocarcinoma (PAc) cell lines has been studied in cell culture and in xenografted tumours in nude mice. In RCC cells, immunoreactivity for nidogen was seen only after exposure to monensin to induce cytoplasmic accumulation of secretory proteins. In PAc cells, immunoreaction was also detectable in control cells. Immunoblotting of control and monensin-exposed cells and immunoprecipitation of culture media of radioactively labelled cells demonstrated the production of nidogen polypeptide of Mr ca. 150000 by six of the seven cell lines. Basement membranes (BMs) and stroma of the xenografted tumours derived from these six cell lines demonstrated immunoreactivity for both human and mouse nidogen, as revealed with species-specific antibodies. The ability of the cells to produce nidogen in vitro and deposit in vivo was positively correlated with high histological grade of the xenografted tumours, although the small number of cell lines studied calls for further studies to confirm this. The distribution of nidogen in human RCC and PAc specimens was also studied by immunohistochemistry. There was strong immunoreactivity for nidogen in tumour stroma, BM of carcinoma cell nests, and endothelial basal lamina, but no conclusions could be drawn regarding histological grade and immunostaining patterns, because stromal production could not be ruled out. The results show that nidogen is produced by human carcinoma cells both in vitro and in vivo.

Pulmonary Gas Exchange in Life-Long Nonsmoking Patients with Diabetes mellitus

In a companion paper, we have found that the alveolar epithelial basal lamina, endothelial basal lamina and both fused were significantly thicker in 6 autopsied diabetics than in 6 control subjects. The purpose of the present work was to assess whether these lesions have detrimental effects on gas exchange. We investigated 20 life-long nonsmoking subjects: 10 healthy subjects and 10 insulin-dependent diabetics. All of them had one to four diabetic complications of the following organs: kidney, retina, nerves or arteries. Their pulmonary gas exchange and their transfer factor were measured at rest and during two levels of submaximal exercise. Spirometric data, specific airway conductance, transfer factor, transfer coefficient, oxygen consumption and arterial blood gases were normal and almost identical in both groups. In conclusion, the thickening of lung basal laminae has no detrimental effect on pulmonary gas exchange in insulin-dependent diabetics with peripheral complications.

Sentries at the gate: chemokines and the blood-brain barrier.

The blood-brain barrier (BBB) isolates the CNS from the rest of the organism. The anatomic foundation of this structure is a syncytium of cerebrovascular endothelial cells sealed together by tight junctions. The endothelial basal lamina, located at the abluminal side of endothelium, borders the perivascular (Virchow-Robin) space. The perivascular space is continuous with the subarachnoid compartment and is itself bordered by the glia limitans, formed by astrocytic and microglial end feet. Within the perivascular space, on either side of the endothelial basal lamina, dwell a unique population of phagocytic cells variously termed perivascular macrophages, perivascular microglia, perivascular c:ells or pericytes. These cells form a first line of defense once the BBB is breached. Astrocytes are also important for BBB development and function: their processes attach to the basement membrane shared with the endothelial cells and perivascular cells. The close contact between astrocytes and brain endothelial cell...

Distribution of the alpha1 to alpha6 chains of type IV collagen in bovine follicles.

During follicular development the proliferative and differentiated state of the epithelioid granulosa cells changes, and the movement of fluid across the follicular basal lamina enables the formation of an antrum. Type IV collagen is an important component of many basal laminae. Each molecule is composed of three alpha chains; however, six different type IV collagen chains have been identified. It is not known which of these chains are present in the follicular basal lamina and whether the type IV collagen composition of the basal lamina changes during follicular development. Therefore, we immunolocalized each of the six chains in bovine ovaries using antibodies directed to the nonconserved non-collagenous (NC) domains. Additionally, dissected follicles were digested with collagenase to release the NC domains, and the NC1 domains were then detected by standard Western immunoblot methods. The follicular basal lamina of almost all primordial and preantral follicles was positive for all type IV collagen alpha chains. Colocalization of type IV collagen and factor VIII-related antigen allowed for discrimination between the follicular and endothelial basal laminae. Type IV collagen alpha1, alpha2, alpha3, alpha4, and alpha5 chains were present within the follicular basal lamina of only a proportion of antral follicles (17 of 22, 20 of 21, 15 of 18, 14 of 28, and 12 of 23, respectively), and staining was less intense than in the preantral follicles. Staining for the alpha1 and alpha2 chains was diffusely distributed throughout the theca in regions not associated with recognized basal laminae. The specificity of this immunostaining for alpha1 and alpha2 chains of type IV collagen was confirmed by Western immunoblots. As well as being detected in the basal lamina of approximately half of the antral follicles examined, type IV collagen alpha4 also colocalized with 3beta-hydroxysteroid dehydrogenase-immunopositive cells in the theca interna. Type IV collagen alpha6 was detected in the basal lamina of only one of the 16 antral follicles examined. Thus, the follicular basal lamina changes in composition during follicular development, with immunostaining levels being reduced for all type IV collagen chains and immunoreactivity for type IV collagen alpha6 being lost as follicle size increases. Additionally, immunoreactivity for alpha1 and alpha2 appears in the extracellular matrix of the theca as it develops.

Ultrastructural evidence of peripheral neuropathy in spontaneous hyperglycemic Otsuka Long-Evans Tokushima Fatty rats: histopathological similarity to human diabetic neuropathy

The ultrastructure in the peripheral nerves of spontaneous hyperglycemic rats and of two cases of human diabetic neuropathy was compared using electron microscopy. Experimental animals were Otsuka Long-Evans Tokushima Fatty (OLETF) rats, bred to reveal spontaneous hyperglycemia and glucosuria after 20 weeks of age. The ultrastructural findings in the peripheral nerves of OLETF rats consisted of destructive changes of the myelin sheath, followed by axonal degeneration and basal laminal thickening of Schwann cells covering small-caliber axons. These alternations in the endoneurium were associated with the later onset of capillary vasculopathy, which revealed duplication of endothelial basal lamina and proliferation of microvilli at the luminal surface. It was characteristic that these histological alterations were apparently distinguished according to the duration of hyperglycemia between 10 and 30 weeks of age. The two human diabetic cases, who had suffered from non-insulin-dependent diabetes mellitus (NIDDM) for a considerable period, had undergone amputation of the leg following the onset of severe neuropathic ulcerative necrosis. Biopsied specimens from peripheral nerves revealed perineurial thickening, proliferation of endoneurial collagen tissue, loss of myelinated fibers, extension of Schwann cell processes with occasional “onion-bulb” formation, and endoneurial vascular basal laminal thickening. The results of these comparative histological studies suggested that the alterations occurring in peripheral nerve tissue of experimental diabetic OLETF rats may reflect the early pathological changes of human diabetic neuropathy.

Vascular involvement in cutaneous sarcoidosis.

Sarcoidosis is a systemic granulomatous disease with systemic vascular involvement, that is, granulomatous angiitis and microangiopathy. To determine if there is vascular involvement in cutaneous sarcoidosis, we examined 42 skin specimens taken from 32 patients with cutaneous lesions of sarcoidosis. Cutaneous sarcoidosis was prevalent in older females with high serum angiotensin-converting enzyme (ACE) levels. Most skin lesions appeared during the following-up of sarcoidosis. Granulomatous angiitis was present in 12 specimens of sarcoid skin lesions (30.8%). Eight of the 12 specimens showed venous involvement in the dermis. There was no correlation between the incidence of granulomatous angiitis and the gross pattern of cutaneous sarcoidosis. Immunohistochemically, thrombomodulin was negative in the vascular endothelium close to the granuloma or a periphlebitis lesion. Electron microscopy revealed endothelial swelling, luminal narrowing, and basal lamina layering of the basement membrane in the capillaries and venules in the dermis. These findings demonstrated that granulomatous angiitis and microangiopathy coexist in cutaneous sarcoidosis.

Cyclosporin nephrotoxicity in heart and lung transplant patients.

Twenty-two patients with heart, lung or heart and lung transplants maintained on cyclosporin for periods ranging from 3 months to 10 years developed renal insufficiency which was investigated by renal biopsy. The histopathological changes were: (i) severe vascular and glomerular damage due to thrombotic microangiopathy (TM); (ii) a form of focal segmental glomerulosclerosis (FSGS); (iii) glomerular ischaemia. Rather than being separate entities, these changes appeared to represent a spectrum of pathology, some biopsies showing all three forms of glomerular injury. In all cases the glomerular changes were accompanied by arteriolar and arterial pathology, and we identified novel ultrastructural changes in the arteriolar endothelial basal lamina. Tubular atrophy was a consistent feature, the severity of which reflected the severity of the glomerular sclerosis, and which appeared to be a consequence of glomerular loss. Our findings are consistent with the nephrotoxic effects of cyclosporin being mediated chiefly via damage to preglomerular vessels and glomerular capillary endothelium. From an analysis of the clinical aspects of these cases, the effects of cyclosporin appear to be to some extent idiosyncratic, and therefore not entirely preventable, but strict monitoring of blood cyclosporin levels is essential to minimize the risk of permanent renal damage. Monitoring urinary protein in addition to plasma creatinine may detect the onset of FSGS, as proteinuria precedes creatinine elevation.

Fibroblasts Are in a Position to Provide Directional Information to Migrating Neutrophils during Pneumonia in Rabbit Lungs

Previous findings have shown that pulmonary fibroblasts are associated with preexisting holes in the endothelial and epithelial basal laminae through which neutrophils appear to enter and leave the interstitium as they migrate from capillaries to alveoli. To determine their role in neutrophil migration, fibroblast organization within the interstitium was assessed by transmission electron microscope observations of serial-sectioned rabbit lung tissue. Interstitial fibroblasts were found to physically interconnect the endothelial basal lamina holes to epithelial basal lamina holes. Morphometric assessment of rabbit lung tissue instilled withStreptococcus pneumoniaerevealed that approximately 70% of the surface area density of migrating neutrophils is in close contact (15 nm or less) with interstitial fibroblasts and extracellular matrix elements (30 and 40%, respectively). Although migrating neutrophils were close enough to adhere to both fibroblasts and extracellular elements, the interstitial fibroblasts are organized in a manner that would allow them to provide directional information to the neutrophils. A model illustrating this process is proposed.

Neutrophil Migration through Preexisting Holes in the Basal Laminae of Alveolar Capillaries and Epithelium during Streptococcal Pneumonia

The purpose of this study was to determine whether or not there are preexisting holes in the endothelial and epithelial basal laminae of alveolar walls and to determine the path taken by neutrophils as they migrate from the capillaries to the airspace of the alveoli during inflammation. Using transmission electron microscopy and serial thin sections of normal rabbit and mouse lung, we have demonstrated the presence of slit-like holes in the capillary basal laminae and round holes in the basal laminae of type 2 pneumocytes. The slits in the capillary basal laminae were observed at the intersection of the thick and thin walls where endothelium, pericytes, and fibroblasts make close contact. The round holes in the type 2 cell basal laminae were observed at sites of close contact with fibroblasts. Neutrophils were observed to migrate through these slits and holes during streptococcal pneumonia in rabbit lungs. We conclude that during inflammation in the lung, migrating neutrophils displace pericytes and fibroblasts from the slits in the capillary basal lamina and then crawl through these slits into the alveolar interstitium. We postulate that neutrophils find their way to type 2 pneumocytes by following interstitial fibroblasts. We believe that neutrophils displace fibroblasts from their close contacts with the type 2 cells and then crawl through the holes in the basal lamina into the basal lateral space of the type 2 cells. From there, neutrophils migrate into the alveolar airspace.