Our interpretation that there are no endothelial cells in this compartment is based on the morphological picture of blood oozing into the buds at this tissue location, the lack of TEK expression, and the change in diameter of the channels in the honeycomb region, all of which suggest that this compartment is defined simply by channels consisting of extracellular matrix proteins.
It is unclear whether these honeycomb regions are part of the marginal sinus, although hemodynamic data Table 1 would suggest that they are sinus like. Indeed, these structures seem more akin to the perifollicular zone recently reported in the human spleen These structures were not seen in corrosion casts of the spleen, and it was assumed that this was due to the digestion process during the casting procedure. If this is the case, it is possible that a similar perifollicular structure may occur in the mouse and may be the honeycomb region in which we see cells firmly adhering.
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Clearly this structure is within the white pulp, as cells begin rolling from within the transfluosphere region and firmly adhere near its terminus. Figure 9 is a schematic of our current understanding of the vascular entry into the white pulp. Further characterization of this novel tissue compartment will provide important insights into the factors governing leukocyte behavior in cells newly entering the splenic white pulp both under homeostatic conditions and in the setting of microbial infection or systemic inflammatory diseases.
Schematic diagram of T lymphocyte entry into the white pulp. Blood enters the central arteriole from large arterial vessels. On the basis of our data, the blood then enters pulsating vessels indicated by the dark gray ovals suggesting a muscular sheath. These vessels then divide into smaller terminal vessels, which give rise to the honeycomb-like regions of the white pulp, which lack a TEK-expressing endothelial layer.
It is unclear from our data whether these regions are part of the marginal sinus, as in A , or are closer to the center of the lymphoid nodule, as shown in B. The gray arrowheads indicate the path of T cells. The draining of blood from these honeycomb areas is unclear and is indicated by the dashed lines and question marks. Our hemodynamic data suggest that specific carbohydrate selectin -based interactions could be possible between migrating lymphocytes and the spleen microvasculature.
Cellular rolling velocities were calculated before and after adhesion molecule blockade to determine whether CD49d or L-selectin plays any role in migration to the spleen. Both of these molecules have been reported to be important in the MLN; however, neither has ever been shown to be important in the spleen although, as mentioned previously, no adhesion molecules have ever been associated with a loss of splenic cellularity 3 , 5 , 9 , , 27 , 39 , 43 , With the use of L-selectin-deficient T lymphocytes with or without CD49d blockade, we were unable to alter the rolling velocities or adhesion of cells in the spleen.
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Therefore, we conclude that these adhesion molecules play little, if any, role in homing to the spleen. Indeed, we speculate that the majority of the adhesive events in the spleen are due to mechanical interactions, possibly controlled by the autonomic nervous system via the pulsating vessels ; however, further investigations will be needed to verify this assertion. Although our data were not revealing for the spleen, they do give some insight into the relative importance of these molecules in the MLN.
The differences and similarities between secondary lymphoid organs are shown in Table 2. Abrogation of both adhesion molecules led to a significant increase in lymphocyte velocity in the MLN. This is similar to what has been reported in Peyer's patches, the organ with which the MLN has the most in common. Movement of lymphocytes into the spleen, however, was unaffected by blocking L-selectin or CD49d, even though the terminal vessels had hemodynamic properties similar to the MLN HEV.
Therefore, our data show that neither of these molecules plays a dominant role in T cell rolling in the spleen. Furthermore, our data indicate that a significant component of T cell adhesion in the spleen is likely due to mechanical effects. Table 2. Comparison of T lymphocyte migration characteristics in secondary lymphoid organs.
MAdCAM-1, mucosal addressin cell adhesion molecule We have further defined the vasculature of the spleen, showing that blood flow initially goes from pulsating vessels into terminal vessels and finally into terminal buds or honeycombs. In the terminal bud region, channels are found that lack a TEK-expressing endothelial cell lining, and this is where lymphocytes firmly adhered.
On the basis of hemodynamic values, however, we postulate that rolling interactions of lymphocytes take place in the terminal vessels, immediately proximal to the buds. Although L-selectin and CD49d are important in the migration of T lymphocytes into the MLN HEV, these adhesion molecules are not involved in rolling and adherence of T lymphocytes in the vascular channels of the white pulp of the spleen. While this region has a WSR similar to bone marrow sinusoids, it is unclear whether it does represent the marginal sinus. Specifically, the lack of TEK-expressing endothelium and the larger vessel size suggest that this discrete structure is not the marginal sinus, which separates the white pulp from the red pulp.
Further investigations are being directed at better understanding this unique compartment, which is not found in other secondary lymphoid organs. We thank Dale F. Osborne and Michelle Rohlfing for excellent technical assistance, Carlene Zindl for helpful discussions, and Dr. Charles Parker for the critical review of the manuscript. This work was supported by a Barnes-Jewish Foundation grant to M. Grayson , AI to D. Chaplin , and GM to R. Hotchkiss , and the Alan A. Wolff Foundation. Address for reprint requests and other correspondence: M.
Grayson, Washington Univ. School of Medicine, Campus Box , S. Euclid Ave. Louis, MO E-mail: wheeze allergist. The costs of publication of this article were defrayed in part by the payment of page charges. Section solely to indicate this fact. First published February 13, ; Journal home Ahead of Print Issues. Archive of all online content. January July Articles in Press. Volume Issue 1. Volume Issue 6. Volume Issue 5. Volume Issue 4. Volume Issue 3. Volume Issue 2. Volume Issue Volume Issue 9. Volume Issue 8. Volume Issue 7. Submit Subscribe. This Journal. Quick Search in Journals Search this journal.
Journal Menu. Mitchell H. Grayson Divisions of Allergy and Immunology,. Richard S. Louis, Missouri ; and. Irene E. Karl Metabolism, and. Michael J. David D. This is the final version - click for previous version. Export citation Add to favorites Get permissions Track citations. Download figure Download PowerPoint. In vivo-activated CD4 T cells upregulate CXC chemokine receptor 5 and reprogram their response to lymphoid chemokines.
Lymphocyte homing and leukocyte rolling and migration are impaired in L-selectin-deficient mice. Distinct roles of L-selectin and integrins alpha 4 beta 7 and LFA-1 in lymphocyte homing to Peyer's patch-HEV in situ: the multistep model confirmed and refined. Lymphocyte migration in lymphocyte function-associated antigen LFA deficient mice. Lymphocyte homing and homeostasis.
Pertussis toxin inhibits migration of B and T lymphocytes into splenic white pulp cords. Susceptibility to infection and altered hematopoiesis in mice deficient in both P- and E-selectins. Scanning electron microscopy SEM studies of the spleen—normal and pathological. Scan Electron Microsc Pt. Visualization of specific B and T lymphocyte interactions in the lymph node. Confocal fluorescent intravital microscopy of the murine spleen. Cell-free rolling mediated by L-selectin and sialyl Lewis x reveals the shear threshold effect.
Mice lacking expression of secondary lymphoid organ chemokine have defects in lymphocyte homing and dendritic cell localization. A B-cell-homing chemokine made in lymphoid follicles activates Burkitt's lymphoma receptor Relevance of L-selectin shedding for leukocyte rolling in vivo.
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Handbook of Fluorescent Probes and Research Chemicals. Identification of a human peripheral lymph node homing receptor: a rapidly down-regulated adhesion molecule. In situ demonstration of intraepithelial lymphocyte adhesion to villus microvessels of the small intestine. Alpha 3 beta 1 integrin has a crucial role in kidney and lung organogenesis.
The roles of L-selectin, beta 7 integrins, and P-selectin in leukocyte rolling and adhesion in high endothelial venules of Peyer's patches. Characterization of E-selectin-deficient mice: demonstration of overlapping function of the endothelial selectins. Dynamics of T lymphocyte responses: intermediates, effectors, and memory cells. Rolling of lymphocytes and neutrophils on peripheral node addressin and subsequent arrest on ICAM-1 in shear flow.
Are murine marginal-zone macrophages the splenic white pulp analog of high endothelial venules? Leukocyte rolling and extravasation are severely compromised in P selectin-deficient mice. Hematopoietic progenitor cell rolling in bone marrow microvessels: parallel contributions by endothelial selectins and vascular cell adhesion molecule 1 J Exp Med —, J Exp Med September 7, , p.
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Total body irradiation causes profound changes in endothelial traffic molecules for hematopoietic progenitor cell recruitment to bone marrow. Adhesion and homing of blood-borne cells in bone marrow microvessels. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes, which are described further in a later section.
Reticular tissue is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver Figure 3. Reticular cells produce the reticular fibers that form the network onto which other cells attach. Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to stretching. There are two major categories of dense connective tissue: regular and irregular. Dense regular connective tissue fibers are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fiber orientations.
Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibers are parallel. Dense regular elastic tissue contains elastin fibers in addition to collagen fibers, which allows the ligament to return to its original length after stretching. The ligaments in the vocal folds and between the vertebrae in the vertebral column are elastic.
In dense irregular connective tissue, the direction of fibers is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. In some tissues, fibers crisscross and form a mesh. In other tissues, stretching in several directions is achieved by alternating layers where fibers run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibers. Dense irregular elastic tissues give arterial walls the strength and the ability to regain original shape after stretching Figure 4.
Connective Tissue: Tendinitis Your opponent stands ready as you prepare to hit the serve, but you are confident that you will smash the ball past your opponent. As you toss the ball high in the air, a burning pain shoots across your wrist and you drop the tennis racket. That dull ache in the wrist that you ignored through the summer is now an unbearable pain.
The game is over for now. After examining your swollen wrist, the doctor in the emergency room announces that you have developed wrist tendinitis. She recommends icing the tender area, taking non-steroidal anti-inflammatory medication to ease the pain and to reduce swelling, and complete rest for a few weeks. She interrupts your protests that you cannot stop playing.
She issues a stern warning about the risk of aggravating the condition and the possibility of surgery. She consoles you by mentioning that well known tennis players such as Venus and Serena Williams and Rafael Nadal have also suffered from tendinitis related injuries. What is tendinitis and how did it happen? Tendinitis is the inflammation of a tendon, the thick band of fibrous connective tissue that attaches a muscle to a bone. The condition causes pain and tenderness in the area around a joint.
On rare occasions, a sudden serious injury will cause tendinitis. Most often, the condition results from repetitive motions over time that strain the tendons needed to perform the tasks. Persons whose jobs and hobbies involve performing the same movements over and over again are often at the greatest risk of tendinitis. In all cases, overuse of the joint causes a microtrauma that initiates the inflammatory response. Tendinitis is routinely diagnosed through a clinical examination.
In case of severe pain, X-rays can be examined to rule out the possibility of a bone injury. Severe cases of tendinitis can even tear loose a tendon. Surgical repair of a tendon is painful. Connective tissue in the tendon does not have abundant blood supply and heals slowly. While older adults are at risk for tendinitis because the elasticity of tendon tissue decreases with age, active people of all ages can develop tendinitis.
Young athletes, dancers, and computer operators; anyone who performs the same movements constantly is at risk for tendinitis. Although repetitive motions are unavoidable in many activities and may lead to tendinitis, precautions can be taken that can lessen the probability of developing tendinitis.
For active individuals, stretches before exercising and cross training or changing exercises are recommended. For the passionate athlete, it may be time to take some lessons to improve technique. All of the preventive measures aim to increase the strength of the tendon and decrease the stress put on it. With proper rest and managed care, you will be back on the court to hit that slice-spin serve over the net. Watch this animation to learn more about tendonitis, a painful condition caused by swollen or injured tendons.
Two major forms of supportive connective tissue, cartilage and bone, allow the body to maintain its posture and protect internal organs. The distinctive appearance of cartilage is due to polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. Cartilaginous tissue is avascular, thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of cartilaginous tissues.
The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage Figure 5. Hyaline cartilage , the most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans. Under the microscope, tissue samples appear clear. The surface of hyaline cartilage is smooth. Both strong and flexible, it is found in the rib cage and nose and covers bones where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation.
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A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. Fibrocartilage is tough because it has thick bundles of collagen fibers dispersed through its matrix. The knee and jaw joints and the the intervertebral discs are examples of fibrocartilage. Elastic cartilage contains elastic fibers as well as collagen and proteoglycans. This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their initial shape.
The external ear contains elastic cartilage. Bone is the hardest connective tissue. It provides protection to internal organs and supports the body. Both components of the matrix, organic and inorganic, contribute to the unusual properties of bone.
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Without collagen, bones would be brittle and shatter easily. Without mineral crystals, bones would flex and provide little support. Osteocytes, bone cells like chondrocytes, are located within lacunae. The histology of transverse tissue from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal.
Bone is a highly vascularized tissue. Unlike cartilage, bone tissue can recover from injuries in a relatively short time. Cancellous bone looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than compact bone and found in the interior of some bones and at the end of long bones. The porcine model could potentially allow for the large-scale production of high-quality human hepatocytes needed in order for bioartificial livers to be incorporated into clinical use.
About 38, people in the United States die each year from liver disease, according to the Centers for Disease Control and Prevention. Liver transplantation has been the go-to option for treatment, but it comes with many risks and isn't always an option, due to compatibility and availability of donor livers," Dr. This content does not have an English version. This content does not have an Arabic version. Bioartificial liver: Potential to avoid transplant. Related Content.
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