A lymphocyte homing receptor (L-selectin) mediates the in vitro attachment of lymphocytes to myelinated tracts of the central nervous system.

Lymphocytes enter lymph nodes by first adhering to high endothelial venules, an adhesive event mediated by a lectinlike lymphocyte receptor (L-selectin). Previously, it was shown with an in vitro assay that lymphocytes preferentially adhere to myelin-rich regions in brain sections. Here, using a recombinant form of L-selectin as an immunohistochemical reagent, we demonstrate potential ligands for L-selectin in myelinated regions of the central but not the peripheral nervous system. Using several antibodies and phorbol ester downmodulation of the receptor, we establish that L-selectin on human lymphocytes has a primary involvement in lymphocyte adherence to the myelinated regions. On mouse lymphocytes, the contribution of L-selectin appears to be partial. These findings raise the possibility that leukocyte targeting to myelin-rich regions, via a L-selectin dependent mechanism, may be a factor in the pathogenesis of certain central nervous system demyelinating diseases.

A homing receptor-IgG chimera as a probe for adhesive ligands of lymph node high endothelial venules.

The binding of lymphocytes to high endothelial venules (HEV) within peripheral lymph nodes (pln) is thought to be mediated by a lectinlike adhesion molecule termed the pln homing receptor (pln HR). The cloning and sequencing of cDNAs encoding both murine and human pln HR revealed that these adhesion molecules contain protein motifs that are homologous to C-type or calcium dependent lectin domains as well as to epidermal growth factor (egf) and complement-regulatory protein domains. We have produced a novel, antibody-like form of the murine HR by joining the extracellular region of the receptor to a human IgG heavy chain. This antibody-like molecule is capable of recognizing carbohydrates, blocking the binding of lymphocytes to pln HEV, and serving as a histochemical reagent for the staining of pln HEV. This murine HR-IgG chimera should prove useful in analyzing the distribution of the HR ligand(s) in normal as well as in inflammatory states.

Demonstration that a lectin-like receptor (gp90MEL) directly mediates adhesion of lymphocytes to high endothelial venules of lymph nodes.

Lymphocyte migration from the blood into most secondary lymphoid organs is initiated by a highly selective adhesive interaction with the endothelium of specialized blood vessels known as high endothelial venules (HEV). The propensity of lymphocytes to migrate to particular lymphoid organs is known as lymphocyte homing, and the receptors on lymphocytes that dictate interactions with HEV at particular anatomical sites are designated "homing receptors". Based upon antibody blockade experiments and cell-type distribution studies, a prominent candidate for the peripheral lymph node homing receptor in mouse is the approximately 90-kD cell surface glycoprotein (gp90MEL) recognized by the monoclonal antibody MEL-14. Previous work, including sequencing of a cDNA encoding for this molecule, supports the possibility that gp90MEL is a calcium-dependent lectin-like receptor. Here, we show that immunoaffinity-purified gp90MEL interacts in a sugar-inhibitable manner with sites on peripheral lymph node HEV and prevents attachment of lymphocytes. Lymphocyte attachment to HEV in Peyer's patches, a gut-associated lymphoid organ, is not affected by gp90MEL. The results demonstrate that gp90MEL, as a lectin-like receptor, directly bridges lymphocytes to the endothelium.

Endocytosis by endothelial phagocytes: uptake of bovine serum albumin-gold conjugates in bone marrow.

The endocytic function of the endothelial cells of the venous sinuses ("sinusoids") in rat bone marrow was investigated. Marrow sinusoidal endothelial cells (MSEC) were exposed to pulse injections of bovine serum albumin-gold (BSA-Au) conjugates in vivo and examined after timed intervals by electron microscopy. BSA-Au particles were rapidly taken up by MSEC. Within 1 min, BSA-Au was internalized by means of coated pits and vesicles (exclusively) and processed through pleomorphic endosomes to dense bodies known to be secondary lysosomes. In this processing, no involvement of the Golgi apparatus was observed. The continuous association of BSA with gold throughout endocytic processing to lysosomes was verified by immunolabeling with anti-BSA antibody. Although the nature of the affinity mediating endocytosis of BSA-Au by MSEC, in particular the possibility of specific adsorption of BSA and receptor involvement, remains to be established, it is suggested that marrow sinusoidal endothelial cells internalize the albumin-coated particles and process them through to lysosomal structures for purposes of degrading the albumin component.

Preservation of ultrastructure in bone marrow with a glutaraldehyde-artificial blood perfusate.

A method of perfusion-fixation of bone marrow using a commercially available blood substitute as a vehicle for glutaraldehyde has been developed. Low magnification observations of sections by transmission electron microscopy revealed a high degree of integrity throughout the hematopoietic tissue. The continuity and fine structure of the sinusoidal endothelial cells were well preserved as evidenced by exclusion of ruthenium red/OsO4, and occasionally, stages of blood cell egress (diapedesis) across the sinusoidal lining were observed. The quality of fixation of cellular organelles was judged to be equal or superior to that obtained with the use of conventional buffer-based fixatives.

Backscattered electron imaging for the life sciences: introduction and index to applications - 1961 to 1980.

Backscattered electron imaging (BEI) in a scanning electron microscope has been used in biological investigation since 1961. Originally used for imaging specimen surfaces during x-ray microanalysis, applications of this method accelerated rapidly with the recognition of its potential for selective imaging of heavy metal stained biological structures, including those labelled by cytochemical methods. This use of backscattered imaging, to view heavy metal stained structures in cells and tissues, has become the predominate BEI application in the life sciences. This paper presents a brief introduction to BEI as it relates to the use of the scanning microscope for histo - and cytochemistry. Biological applications reported in the years 1961-1980 are cited and indexed by subject and author(s).

Nuclear envelope invaginations in hamster pyramidal cells during development and aging.

Nuclear envelope invaginations were observed in pyramidal cell nuclei of the hamster frontal cortex during development and aging. These invaginations which began to appear at 10 day did not recede at maturity as has been observed in certain other cell types, but persisted in the adult hamster and during subsequent aging. Morphometric data showed a significant increase in the number of nuclear envelope invaginations and in their length per unit of the nucleus. This increase was positively correlated with age until 500 days and is suggestive of a continued high metabolic activity that did not subside following the rapid growth phase of the pyramidal neurons.