Spatial and molecular organization of lymph node T cell cortex: a labyrinthine cavity bounded by an epithelium-like monolayer of fibroblastic reticular cells anchored to basement membrane-like extracellular matrix.

Naive T cells encounter antigen-presenting cells within the cortex of lymph nodes to initiate primary immune responses. Within this T cell cortex is the reticular network (RN)--a system of collagen fibers and extracellular matrix (ECM) wrapped by fibroblastic reticular cells (FRC). We have investigated the distribution of various molecules, including ECM proteins and proteoglycans, in the T cell cortex of both human and rodent lymph node. We confirm and extend reports of matrix elements in the RN. In addition, we find that staining for the laminin-alpha3 chain and for tenascin reveals a 'hollow' reticular pattern, consistent with localization to the basement membrane-like covering of reticular fibers. In contrast, keratan sulfate is observed in a fine linear pattern within the RN, suggesting it is localized to the core of the fibers. Staining with the marker ER-TR7 indicates that FRC cover all identifiable ECM surfaces of the T cell cortex. Based on these findings and previous reports, we conclude that cortical lymphocytes migrate within a 'labyrinthine cavity' free of fibrillar ECM, distinguishing the T cell cortex from other loose connective tissues, and that the FRC lining of the cavity constitutes an epithelium-like boundary. We propose that this spatial organization facilitates ameboid leukocyte crawling along preformed paths of least resistance and that the basement membrane-like ECM of the FRC may facilitate fluid transport within the RN by limiting leakage from the fiber.

Lymph-borne chemokines and other low molecular weight molecules reach high endothelial venules via specialized conduits while a functional barrier limits access to the lymphocyte microenvironments in lymph node cortex.

Lymph-borne, soluble factors (e.g., chemokines and others) influence lymphocyte recirculation and endothelial phenotype at high endothelial venules (HEVs) in lymph node cortex. Yet the route lymph-borne soluble molecules travel from the subcapsular sinus to the HEVs is unclear. Therefore, we injected subcutaneously into mice and rats a wide variety of fluorophore-labeled, soluble molecules and examined their distribution in the draining lymph nodes. Rather than percolating throughout the draining lymph node, all molecules, including microbial lipopolysaccharide, were very visible in the subcapsular and medullary sinuses but were largely excluded from the cortical lymphocyte microenvironments. Exclusion prevailed even during the acute lymph node enlargement accompanying viral infection. However, low molecular mass (MW) molecules, including chemokines, did gain entry into the cortex, but in a very defined manner. Low MW, fluorophore-labeled molecules highlighted the subcapsular sinus, the reticular fibers, and the abluminal and luminal surfaces of the associated HEVs. These low MW molecules were in the fibers of the reticular network, a meshwork of collagen fibers ensheathed by fibroblastic reticular cells that connects the subcapsular sinus floor and the HEVs by intertwining with their basement membranes. Thus, low MW, lymph-borne molecules, including chemokines, traveled rapidly from the subcapsular sinus to the HEVs using the reticular network as a conduit.

The watermelon stomach: clinical presentation, diagnosis, and treatment.

The watermelon stomach syndrome is an increasingly recognized cause of persistent acute or occult gastrointestinal bleeding, typically in elderly women. This disorder often presents with severe iron deficiency anemia, and a variety of associated conditions including autoimmune disease, cirrhosis, achlorhydria, and hypochlorhydria. Diagnosis is made by the characteristic endoscopic appearance of visible linear watermelon-like vascular stripes in the antrum. Histology confirms the vascular nature of this disorder, showing dilated and thrombosed capillaries in the lamina propria, associated with reactive fibromuscular hyperplasia. The optimum treatment of choice is not known. Several treatment options, including surgical antrectomy, and endoscopic photocoagulation with Nd:Yag laser, heater probe therapy, and bipolar electrocautery, have yielded excellent results. Pharmacological agents have also been used to treat selected numbers of patients, most of which comprise a small number of case reports.

Cords, channels, corridors and conduits: critical architectural elements facilitating cell interactions in the lymph node cortex.

The lymph node cortex is a critical site for encounter between recirculating T cells and their specific antigens. Due to its extreme plasticity, little is understood of the underlying functional unit of the lymph node cortex, the paracortical cord. The idealized paracortical cord (approximately 100 microns by 1000 microns) stretches from a medullary cord to the base of a B-cell follicle. In cross-section, a cord can be visualized as a set of nested cylinders consisting of spaces bounded by cells. The spaces are: i) the lumen of the high endothelial venule (HEV), ii) perivenular channels-narrow potential spaces (0.1 micron) tightly encircling the HEV, iii) corridors-broad spaces (10-15 microns) constituting the majority of the parenchyma, and iv) the cortical sinus. In addition to these spaces for cell traffic, the conduit (fifth space) is a special delivery system for the transit of soluble factors to the HEV and emigrating lymphocytes. The cellular barriers between these spaces are high endothelium, fibroblastic reticular cells, or sinus-lining cells. This review describes the spaces of the paracortical cord and their cellular boundaries, outlines the movement of cells and fluids through these spaces, and discusses how this anatomy affects the efficiency of surveillance by T cells.

Sophisticated strategies for information encounter in the lymph node: the reticular network as a conduit of soluble information and a highway for cell traffic.

The lymph node is the crossroad in which soluble signals and cells carried by lymph meet lymphocytes emigrating from blood. Efficient interactions among these elements depend on the reticular network, which comprises reticular fibers, related extracellular matrix components, and associated fibroblastic reticular cells. This network provides a three-dimensional scaffold for attachment of APCs and pathways for the migration of T cells to these APCs. In addition, the network constitutes a miniature conduit system for bulk flow delivery of soluble molecules to distinct sites in the paracortex, particularly the high endothelial venule. The delivered mediators, such as chemokines, regulate the phenotype of the high endothelial venule, the recruitment of lymphocytes, and the behavior of the recruited lymphocytes. Thus, the reticular network is a multifunctional infrastructure that facilitates encounters of cells with other cells and factors necessary for effective and efficient immune surveillance.

A micropipette which allows in situ perfusion of arterioles and capillaries.

In order to investigate capillary physiology, a glass micropipette system was developed that allowed in situ perfusion of microvessels as well as rapid changes of perfusion solutions. Theta tube (WPI, Inc.; 1.5-mm o.d. glass stock capillary tubing which is divided into two hemicylindrical sides by a central glass septum) was pulled to a smaller diameter of approx 300-600 microns and inserted into the shank of a sharpened cannulating micropipette tip constructed from large-bore glass stock (1.6 mm i.d.). The resulting dead volume between the end of the Theta supply tube and the tip of the outer cannulating tip was approximately 90 nl. The perfusate was driven in a circuit from a pressurized feed reservoir down one side of the Theta supply tube pipette and back through the second side into a reservoir maintained at a lower pressure. The pressure gradient between the two reservoirs established a high-volume flow rate and subsequently a short perfusate transit time from the feed to the collection reservoir. The average pressure in the two reservoirs determined the pressure which drove the perfusate from the cannulating tip. At normal pressures and flows, the time required to change perfusion fluid composition at the pipette tip was less than 1 min, and discharge hematocrit of a red blood cell suspension was indistinguishable from the hematocrit measured in the feed reservoir.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the in vitro spermicidal activity of synthetic magainins.

Two synthetic magainins A and G are shown to have spermicidal activity. Transmission electron microscopic micrographs show that both magainins alter the plasma membranes of sperm and that these actions are rapid. Further studies will better delineate the contraceptive potential of synthetic magainins.

PIP: 2 synthetic magainins--A and G-- have been shown, through transmission electron microscopy, to have spermicidal activity. Magainins, a class of peptides isolated from the skin of the African clawed frog. I have been demonstrated to have wide spectrum in vitro antimicrobial activity. In this study, semen sample collected from 7 healthy volunteers were diluted with magainins A and G and then examined for spermiostatic activity. Sperm diluted only with saline were used as a control. Sperm assays indicated the potency of magainin A to be significantly greater than that of magainin G. Magainin A demonstrated spermiostatic activity at concentrations of 0.024-0.095 mg/mL compared to concentrations of 0.095-0.380 mg/mL for magainin G. A similar pattern was identified in the concentration of peptide required to inhibit sperm motility. Magainin A inhibited sperm motility when diluted in seminal plasma at concentrations of 0.77-1.54 mg/mL, while 1.54-3.08 mg/mL of magainin G were required to produce this effect. In the transmission electron microscopic studies, magainin-treated sperm cells incubated with either peptide consistently demonstrated denudation of the outer plasma membrane and partial disappearance of the acrosome, while sperm incubated in saline remained unaltered. It is hypothesized that magainins exert their spermicidal activity by disrupting the outer plasma membrane. The contraceptive potential of synthetic magainins should be explored through animal studies that measure the in vivo effects of seminal fluid and vaginal secretions on magainin activity and the effects of these agents on vaginal and cervical mucosa.