Meshwork Of Cells Research Articles

Dark neurons in the mouse brain: an investigation into the possible significance of their variable appearance within a day and their relation to negatively charged cell coats.

This study aims to investigate the occurrence and nature of dark neurons in the central nervous system under physiological conditions. Mouse brain tissues were perfusion-fixed with paraformaldehyde or glutaraldehyde at 4 h intervals during one day (3:00, 7:00, 11:00, 15:00, 19:00, 23:00). Paraffin sections were stained with the cationic colloidal iron method, and counterstained with nuclear fast red or carbolthionin. The dark neurons were readily distinguishable as their shrunken cell bodies stained densely with nuclear fast red or thionin. Some of the dark cells were coated with perineuronal sulfated proteoglycans; this coat, which formed a smoothly extended meshwork in light cells, presented spicule-like forms in the dark cells. The occurrence of dark cells in the retrosplenial cortex varied by the time of day: the incidence of the dark neurons was low (10-15%) at 11:00, 15:00 and 23:00, while it was significantly high (50-60%) at 3:00 and 19:00. Previous authors have ascribed the occurrence of dark neurons either to artifacts due to inappropriate fixation or to pathological damage. However, the present study strongly suggests that this type of neuron occurs under physiological conditions as reversible changes, and vary over a day, showing distinct peaks. These peaks occurred coincidentally while the mice were awake. Such morphological changes may be involved in the neuronal activation and exhaustion. Our view is consistent with the hypothesis (Tewari and Bourne, 1963) that the neurons take such dark profiles at certain stages of neurosecretion.

Orientation and three-dimensional organization of actin filaments in dividing cultured cells.

The current hypothesis of cytokinesis suggests that contractile forces in the cleavage furrow are generated by a circumferential band of actin filaments. However, relatively little is known about the global organization of actin filaments in dividing cells. To approach this problem we have used fluorescence-detected linear dichroism (FDLD) microscopy to measure filament orientation, and digital optical sectioning microscopy to perform three-dimensional reconstructions of dividing NRK cells stained with rhodamine-phalloidin. During metaphase, actin filaments in the equatorial region show a slight orientation along the spindle axis, while those in adjacent regions appear to be randomly distributed. Upon anaphase onset and through cytokinesis, the filaments become oriented along the equator in the furrow region, and along the spindle axis in adjacent regions. The degree of orientation appears to be dependent on cell-cell and cell-substrate adhesions. By performing digital optical sectioning microscopy on a highly spread NRK subclone, we show that actin filaments organize as a largely isotropic cortical meshwork in metaphase cells and convert into an anisotropic network shortly after anaphase onset, becoming more organized as cytokinesis proceeds. The conversion is most dramatic on the adhering ventral surface which shows little or no cleavage activity, and results in the formation of large bundles along the equator. On the dorsal surface, where cleavage occurs actively, actin filaments remain isotropic, showing only subtle alignment late in cytokinesis. In addition, stereo imaging has led to the discovery of a novel set of filaments that are associated with the cortex and traverse through the cytoplasm. Together, these studies provide important insights into the process of actin remodeling during cell division and point to possible additional mechanisms for force generation.

Sexually dimorphic expression of estrogen receptors, but not of androgen receptors in human fetal external genitalia.

Using immunohistochemistry, we investigated the distribution of androgen receptors (AR) and estrogen receptors (ER) in the external genitalia of human male and female fetuses at 18-22 weeks gestation. In the male, the corpus cavernosum, and the stroma of the inner prepuce, scrotum, and periphery of the glans were AR rich. The corpus spongiosum, a well defined structure that surrounds the penile urethra in the neonate, was not yet developed at this fetal age, but the periurethral mesenchyme (presumably the primordium of the corpus spongiosum) was intensely AR positive. In contrast, the epithelium of the preputial skin, penile shaft skin, and scrotal skin were AR negative. The urethral plate in the distal glans was nonpatent and was filled with a meshwork of AR-negative epithelial cells. Canalization of the AR-negative urethral plate was observed to begin where it joined the patent distal penile urethra, which was AR positive. Male external genitalia lacked ER, ruling out a direct influence of maternal estrogen on male genital development. Interestingly, female external genital structures contained AR, and the distribution of AR and staining intensity were strikingly similar to that in the male. The distribution of AR in the female provides a mechanism to explain how female external genitalia become masculinized if exposed to elevated androgen levels in the first trimester. Moreover, it implies that in the male, these AR indeed mediate androgen-dependent male external genital development. Female fetal external genitalia were also intensely ER positive in the stroma of the labia minora and in the periphery of the glans and inner prepuce. The presence of ER suggests that maternal estrogen may play a direct role in female external genital development, challenging the widely held view that female external genital development is passive because it can occur in the absence of fetal gonadal hormones.

Developmentally regulated and spatially restricted antigens of radial glial cells.

Radial glial cells, present in many parts of the embryonic vertebrate central nervous system (CNS), have been implicated in the guidance of neuroblasts from the ventricular zone to their laminar destinations. Moreover, radial glial cells may be progenitors of some CNS neurons and glia. To gain new insight into the structure and development of these cells, we have generated and characterized a panel of monoclonal antibodies that recognize radial glial cells of the chick optic tectum. Mice were immunized with homogenates of embryonic day (E) 10 tectum, and antibodies were analyzed by immunofluorescence and immunoblotting. We describe here three pairs of antibodies. 1) H5 and a previously generated antibody, R5 (Dräger et al., J. Neurosci. 4:2025, 1984), stain the whole extent of the radial glial cell from E7 to E20. In cultures prepared from E10 tecta, both stain a filamentous meshwork in glial cells but not in neurons. On immunoblots, both recognize a protein of approximately 52 kD that is closely related (or identical) to vimentin. 2) H28 and H29 stain radial glia between E7 and E14, but not later. Moreover, H28 and H29 staining is markedly more intense in the ventricular and intermediate zones than in the laminae of the tectal plate. Both of these antibodies recognize an intracellular epitope in cultured glial cells and a protein of approximately 35 kD on immunoblots. 3) H2 and H27 recognize antigens concentrated in the most superficial processes and endfeet of radial glia in late (E16-E20) embryos. They stain distinct structures in cultured glia, suggesting that they recognize distinct antigens. H27 recognizes a protein of approximately 29 kD on immunoblots. Thus antibodies H5 and R5 are good markers of radial glial cells at all stages, whereas the others define antigens that are developmentally regulated and localized to discrete domains. Together, these antibodies can be used to study temporal and spatial specializations of radial glia.

Periarterial lymphoid sheath in the rat spleen: a light, transmission, and scanning electron microscopic study.

The periarterial lymphoid sheath (PALS) in the rat spleen was studied by light, transmission, and scanning electron microscopy. The PALS was divided into three regions: the central region, peripheral region, and marginal zone bridging channel. In the central region, lymphocytes were easily washed away by perfusion. Large spaces were found between flat reticular cells or in large meshworks of stellate reticular cells; these may be deep lymphatic vessels. True lymphatic vessels were found in the central region near the hilus. In the marginal zone bridging channel, flat reticular cells surrounded the central artery in a circumferential pattern and formed channel-like spaces between the flat reticular cells. These spaces were connected with the meshwork of the red pulp reticular cells and may be a route for lymphocytes between the deep lymphatic vessels and the red pulp. In the peripheral region of the PALS, it was usually difficult to wash away free cells by perfusion, and free cells were found among the reticular cells. In places in the peripheral region, however, free cells were washed away. It is suggested that the lymph flow may start from the region surrounding the PALS, and that the peripheral region of the PALS may also be another route for lymphocyte migration.

Myxoid leiomyosarcoma of the ovary: Analysis of three cases

The first three cases of myxoid leiomyosarcoma occurring in the ovary are reported. Two cases in stage III were found in postmenopausal patients and a further case was found in stage I in a 32-year-old. All masses were large and gelatinous with cystic change, necrosis, and hemorrhage, but both uteri and ligaments and contralateral adnexa appeared normal. Microscopically, the tumors showed a predominantly reticular meshwork of elongated cells surrounded by abundant basophilic material. While electron microscopy proved inconclusive due to nondifferentiation, the use of monoclonal antibodies against smooth muscle actin demonstrated a smooth muscle type of differentiation. The differential diagnosis of this rare ovarian condition includes other myxoid ovarian lesions, such as ovarian edema, myxoma, endodermal sinus tumors, and the sarcomatous component of malignant mixed müllerian tumor and carcinosarcoma, as well as lymphovascular tumors. Since mitotic count due to decreased cellular density is unusually low in myxoid leiomyosarcoma, capsular rupture and clinical stage seem to be more reliable prognostic markers. The highly aggressive behavior of myxoid leiomyosarcoma parallels that of typical ovarian leiomyosarcoma. Two of the three patients in this series died of tumor at 13 and 24 months after diagnosis; the other patient is free of disease at 3 years after diagnosis.

Changes of cytokeratin filament organization in human and murine Mallory body‐containing livers as revealed by a panel of monoclonal antibodies

Mallory bodies (MBs) are characteristics morphologic features of alcoholic hepatitis and can be produced in mouse hepatocytes by chronic griseofulvin (GF) intoxication. The formation of MBs, which share some immunological, biochemical, and ultrastructural features with cytokeratin (CK) filaments of normal liver, is accompanied by derangement and even loss of the CK cytoskeleton of hepatocytes ("empty cells") as revealed by immunofluorescence microscopy. To clarify whether this diminution or lack of CK-related staining of MB-containing hepatocytes was due to loss of CK filaments or changes in antigenicity or accessibility of antigenic determinants immunohistochemical studies using a battery of monoclonal and polyclonal CK antibodies were performed. It could be shown that all these antibodies directed against different CK polypeptide components and antigenic determinants of CKs revealed a highly reduced or even undetectable cytoplasmic CK meshwork in most cells with fully developed large MBs. In the light of our present knowledge of the organization of CK intermediate filaments, these results indicate that the phenomenon of the "empty cells" reflects a diminution of CK meshwork rather than altered antigenic determinants.

Ontogeny, distribution and structure of aggregated lymphoid follicles in the large intestine of sheep

Aggregates of lymphocytes were demonstrated from 70 days gestation (term 150 days in sheep) in the proximal colon and rectum. Immunoperoxidase staining for 5′-bromo-2′-deoxyuridine incorporation and IgM, indicated that the lymphocyte population of lymphoid follicles in fetal sheep colon was actively dividing and surface IgM positive. Enzyme histochemistry for 5′-nucleotidase showed that the lymphocytes developed in a meshwork of positive reticular cells, suggestive of developing follicles. Follicle aggregates were distributed in a characteristic pattern in lambs, with major accumulations in the ascending colon and in the rectum. In adult sheep a partial atrophy of follicle aggregates was observed. The microscopic structure of large intestinal aggregates showed similarities to the jejunal Peyer's patch (PP), with broad follicles containing a prominent corona and wide interfollicular areas in older lambs. The apparent deep penetration of crypts into the lymphoid tissue proper, which is a frequently reported phenomenon for colon follicles, was dependent on the contractile state of the mucosa, as judged from its absence in specimens where the intestinal wall had been stretched before fixation.

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The adamantinoid basal cell epithelioma is a clinically uncharacteristic but histologically typical variant of basal cell epithelioma characterized by a meshwork of stellate tumor cells.

Lymphocytes in the Lung: Should We Continue to Exalt Only BALT?

Few lymphocytes are found in the normal human lung. Those cells that are present are found in four locations: (1) the pulmonary and hilar lymph nodes; (2) lymphoreticular aggregates in the parenchymal interstitium; (3) in the airway mucosa; and (4) within the airways (1). In certain disease states, such as influenza virus infection, sarcoidosis, or transplantation rejection, the number of lymphocytes in airways and lung increases dramatically. This influx of cells may be partly mediated by clonal expansion of resident lymphocytes, but it may also result from recruitment of lymphocytes from the blood. The mode of entry oflymphocytes into the lung has not been established, but it is thought to be similar to other tissues, involving the adherence of blood lymphocytes to specialized endothelium known as high endothelial venules (HEV). HEV express defined adhesion molecules known as addressins which bind to complementary adhesion molecules on lymphocytes. HEV are found only in defined sites in organized lymphoid tissue such as the lymph nodes and Peyer's patches in the gut (reviewed in reference 2). Bronchus-associated lymphoid tissue, or BALT, is a term coined by Bienenstock and associates (reviewed in references 3 and 4) to describe organized lymphoid tissue found in the submucosal region of large airways, which appeared analogous to that seen in other mucosal tissues, especially Peyer's patches (gut-associated lymphoid tissue, GALT). Like GALT, BALT contains HEV and is the site of homing for IgA-committed B cells, though both T and B cells have been found in BALT. In addition to containing a meshwork of lymphocytes and antigen-presenting cells, BALT is covered with a specialized epithelium which facilitates transport and processing of antigen from the airway lumen. Because of the presence of HEV, and because of studies showing translocation of blood lymphocytes into BALT (3), BALT is assumed to be important in the immune response to inhaled antigens and has been proposed to be the normal pathway for lymphocyte movement from blood to lung. BALThas been found in many mammalian species. BALT has been observed in normal human airways (1) and has been reported to be hyperplastic in patients with chronic respira-

Immunohistology of T cell differentiation in the thymus of H‐Y‐specific T cell receptor α/β transgenic mice

We examined the immunohistological aspects of the H-Y specific T cell receptor (TcR) alpha/beta transgene expression in the thymus of male and female transgenic (Tg) mice. Virtually all thymocytes expressed the beta transgene in both the male and female thymus. Expression of accessory molecules (co-receptors) in Tg mice deviated from control mice. In the male Tg thymus, CD8 expression was either low or absent on both cortical and medullary thymocytes. In contrast, in the thymus of female mice, CD8+ cells were found both in the cortex and in the medulla. The majority of medullary thymocytes was bright CD8+. This is in clear contrast to the CD8 distribution in control B6 mice, where only a few percent of medullary cells are CD8+. Similarly, the proportion of cells expressing CD4 antigens was reduced in the cortex and medulla of the thymus from male Tg mice, as compared to the thymus of female Tg mice and B6 control mice. Comparative analysis of the stromal cell types of the thymic microenvironments in the three groups of mice revealed that the cortical thymic microenvironment of male Tg mice differed, compared to that of female Tg mice. In particular, the deep cortex showed a closely packed meshwork of epithelial reticular cells. Moreover, H-2Db molecules (which are the restricting elements for the Tg TcR alpha/beta) were abnormally expressed in the thymic cortex of male mice. The cortical microenvironment in female mice, on the other hand, appeared normal. Together, the data indicate that TcR alpha/beta transgene expression in male mice leads to an aberrant co-receptor expression in both cortical and medullary lymphoid cells as well as an abnormal composition of the cortical microenvironment. Both phenomena may be the consequence of "negative selection" of developing H-Y-specific T cells, as it occurs only in the male Tg thymus. The absence of the H-Y antigen, but presence of the restricting element H-2Db in the thymic cortex of female mice, leads to accumulation of CD8+ in the medulla, a phenomenon interpreted as "positive selection".

Immunohistochemical and ultrastructural observations on Homer Wright (neuroblastic) rosettes and the "pale islands" of human cerebellar medulloblastomas.

A combined immunohistochemical and ultrastructural study of 20 cerebellar medulloblastomas has demonstrated features of early neuronal differentiation. The differentiation features are primarily encountered in the Homer Wright rosettes and in the reticulin-free "pale islands," or "follicles," of the desmoplastic variant. They consist of parallel arrays of aggregated neurite-like processes containing longitudinally oriented microtubules (immunoreactive for polyvalent antisera to tubulin and gamma-enolase, but nonreactive for a monoclonal antibody to the 150/200 kD subunits of neurofilament protein) and junctional adhesion plaques. We consider the inherent property of self-aggregation of the neurite-like processes with adhesion plaques a significant mechanism in the formation of Homer Wright rosettes. Further differentiation and elongation of these cell processes may lead to the formation of "pale islands" in the desmoplastic medulloblastoma. A meshwork of astroglial cells, coexpressing glial fibrillary acidic protein and S-100 protein immunoreactivity, forms an integral part of the "pale island." The histogenetic significance of these astrocytes and their relationship to tumor cells expressing early neuronal differentiation remains to be defined.

Ultrastructural study on the meninx of the goldfish brain.

The cranial meninges of the goldfish were studied by means of transmission electron microscopy combined with the freeze-fracturing technique. The goldfish has three cranial meninges. The outer layer consists of flattened cells, which are stratified in 3 to 7 layers and are packed densely with many interdigitations of cell processes. The constituent cells in the outer layer have copious smooth endoplasmic reticulum and are joined by gap junctions but have no desmosomes. The intermediate layer is thin, continuous, and single cell. In the replicas, both the upper and the lower surfaces of the intermediate layer cells have numerous openings of pinocytotic vesicles, but the upper surface is characterized by round gap junctions, whereas the lower surface is identified by a linear continuation of a combination of tight junctions and gap junctions and by desmosomes. The lateral surface has a hexagonal network of tight junctions and gap junctions with internally located desmosomes, which functions as a barrier to intercellular movement of lanthanum. The inner layer consists of a meshwork of reticular cells and large intercellular spaces, in which fine granular material, capillaries, and different types of blood-derived free cells can be found. Cells in the inner layer contain rough endoplasmic reticulum stacked in lamellae and have irregular processes joined by desmosomes. The goldfish meninges are compared with the meninges of mammals.

In vitro behavior of thymic nurse cell-like complexes from mechanically and enzymatically dissociated frog tadpole thymuses.

Cellular complexes, analogous by virtue of their external appearance, size, and number of seemingly internalized thymocytes to thymic nurse cells (TNCs) of endothermic vertebrates, were seen in short-term cultures (6-8 days) of mechanically and enzymatically dissociated thymuses of leopard frog tadpoles. Most TNC-like complexes from mechanically disrupted thymuses were covered with many thymocytes that morphologically resembled the "internalized" thymocytes. With time in culture, most complexes remained spherical and lost their externally adherent and "internalized" thymocytes. Some complexes, however, adhered to the glass substratum by means of macrophage-like cells. After one typically appearing TNC from a mechanically dissociated thymus had released its "internalized" thymocytes and spread completely over the glass substratum, it could be seen to consist actually of 9-10 stromal cells with the appearance of epithelial cells, macrophages, and dendritic cells. TNC-like structures from enzymatically dissociated thymuses had few, if any, attached thymocytes. Although these structures closely resembled murine TNCs initially, they displayed abnormal transformations within a few days of culture. Our observations led us to question the assumption that all TNCs from mechanically as well as enzymatically isolated TNCs from vertebrate thymuses are single cells. Rather, some if not all of the so-called TNC may actually be entities composed of several stromal cell types that enclose thymocytes. We suggest that this configuration seen in vitro may reflect the architecture of the compartmentalized reticular stromal cell meshwork that characterizes the intact thymus.

Scanning electron microscopic study of Warthin's tumor.

Three cases of Warthin's tumors were studied with a scanning electron microscope. The free surface of the epithelium was composed mainly of round or ovoid dome-like structures bearing microvilli and apocrine protrusions. Ciliated epithelial cells were detected in 2 of the tumors. The tumor epithelium encircled various amounts of cellular debris resembling degenerate lymphoid cells. A few tiny cystic spaces were also found. Within the lymphoid stroma, tightly packed lymphocytes, a meshwork of reticulum cells and medullary cord-like structures were observed. Our findings support the concept that Warthin's tumors develop from heterotopic salivary gland ducts within pre-existing lymph nodes.

In vitro behavior of thymic nurse cell-like complexes from mechanically and enzymatically dissociated frog ([formula omitted]. [formula omitted]) tadpole thymuses

Cellular complexes, analogous by virtue of their external appearance, size, and number of seemingly thymocytes to thymic nurse cells (TNCs) of endothermic vertebrates, were seen in short-term cultures (6-8 days) of mechanically and enzymatically dissociated thymuses of leopard frog tadpoles. Most TNC-like complexes from mechanically disrupted thymuses were covered with many thymocytes that morphologically resembled the internalized thymocytes. With time in culture, most complexes remained spherical and lost their externally adherent and internalized thymocytes. Some complexes, however, adhered to the glass substratum by means of macrophage-like cells. After one typically appearing TNC from a mechanically dissociated thymus had released its internalized thymocytes and spread completely over the glass substratum, it could be seen to consist actually of 9-10 stromal cells with the appearance of epithelial cells, macrophages, and dendritic cells. TNC-like structures from enzymatically dissociated thymuses had few, if any, attached thymocytes. Although these structures closely resembled murine TNCs initially, they displayed abnormal transformations within a few days of culture. Our observations led us to question the assumption that all TNCs from mechanically as well as enzymatically isolated TNCs from vertebrate thymuses are single cells. Rather, some if not all of the so-called TNC may actually be entities composed of several stromal cell types that enclose thymocytes. We suggest that this configuration seen in vitro may reflect the architecture of the compartmentalized reticular stromal cell meshwork that characterizes the intact thymus.

Mantle Zone Lymphoma

Using in-situ immuno- and enzymehistochemical techniques, the phenotype of the neoplastic cells in seven cases of mantle zone lymphoma (MZL) was compared to that in seven cases of nodular poorly-differentiated lymphocytic lymphoma (NPDLL). The neoplastic nodules in MZL consisted of medium-sized lymphoid cells with slightly irregular nuclei and finely dispersed chromatin, expressing monoclonal surface IgM or IgM plus IgD, and displaying membranous alkaline phosphatase (ALP) activity. These cells proliferated around follicular centers that demonstrated a polyclonal pattern of reactivity for both types of light chains and a distorted meshwork of dendritic reticulum cells. The neoplastic nodules in NPDLL consisted of small lymphoid cells with markedly irregular nuclei and coarsely granulated chromatin, expressing monoclonal surface IgM and lacking ALP-activity. These tumor cells also frequently expressed transferrin receptor and common acute lymphoblastic leukemia-antigen (CALLA). The neoplastic nodules showed an undistorted meshwork of dendritic reticulum cells, and were occasionally bordered by remnants of polyclonal lymphocytic coronas. These results confirm the previous suggestion that NPDLL arises from a cell type that is a normal constituent of follicular centers, whereas MZL arises from the lymphocytic corona. The morphological, enzyme- and immunohistochemical features of MZL cells strongly suggest that MZL arises from marginal zone lymphocytes, a subset of corona lymphocytes that expresses ALP-activity, high IgM and low IgD-levels.

The differential diagnosis of hairy cell leukemia with a panel of monoclonal antibodies.

A panel of monoclonal antibodies reactive with normal human lymphoid cells and with hairy cells has been applied to the immunocytochemical analysis of hairy cell leukemia. Staining was performed by immunoenzymatic methods on frozen sections of bone marrow trephines and extramedullary tissues and on cell smears. Hairy cells reacted with antibodies against HLA-DR, leukocyte common antigen, B-cell antigens (antibodies To15 and B1) and with three anti-hairy cell monoclonal antibodies (S-HCL3, HC1, and HC2). Neoplastic cells in other B-cell lymphoproliferative disorders also expressed HLA-DR, leukocyte common, and B-cell antigens but were consistently negative for the antigen detected by monoclonal antibody S-HCL3. Furthermore, hairy cells differed from other neoplastic B-cells in that they were unreactive with monoclonal antibodies against C3b receptors, anti-Leu-1, Tü1, Tü33, and lacked a meshwork of dendritic reticulum cells. These findings establish a distinctive antigenic phenotype for hairy cell leukemia and indicate that it may be diagnosed reliably by immunoenzymatic labeling of tissue sections or cell smears.

An immunohistological study of the cellular constituents of Hodgkin's disease using a monoclonal antibody panel

Cryostat sections of lymphoid tissue from 44 cases of Hodgkin's disease were analysed by immunoperoxidase staining using a panel of monoclonal antibodies which included reagents reactive with T cells and their subsets, B cells, HLA-DR, Ig, dendritic reticulum cells and C3b receptor. A wide spectrum of immunohistological patterns was observed ranging from cases in which T cells were numerous (B cells being absent or present in only small numbers) to cases in which very prominent B cell follicles were present. These follicles contained a meshwork of dendritic reticulum cells and were composed of polyclonal B cells (as assessed by light chain expression). T cells were present in small numbers within these B cell follicles, often clustered in a thin rim around individual Reed-Sternberg and Hodgkin's cells. All B cell-rich cases were examples of lymphocyte predominant Hodgkin's disease. Assessment of the T cell helper/suppressor ratios was hindered by the fact that both anti-helper antibodies (OKT4 and anti-Leu 3a) reacted with macrophages. However the majority of cases appeared to contain a normal excess of T helper cells. HLA-DR was strongly expressed in T cell rich areas, on Reed-Sternberg and Hodgkin's cells, on vascular endothelium and on numerous infiltrating cells in the fibrous tissue areas in cases of nodular sclerosing disease. Reed-Sternberg and Hodgkin's cells were not labelled by either anti-fibronectin or by antibodies reactive with dendritic reticulum cells (anti-C3b receptor and antibody R4/23).

A scanning electron microscopic study of the boundary zone of the human spleen.

The structural characteristics and cellular elements of the boundary zone between the white and red pulp of the human spleen were studied by SEM and TEM. The boundary zone consisted of both the perifollicular region and the region surrounding the periarterial lymphoid sheath. The perifollicular region was further subdivided into two, equally thick layers. The inner half layer of the perifollicular region outside the mantle zone of the lymph follicle was composed of tightly packed medium-sized lymphocytes, interspersed by a small number of reticular cells. The outer half layer was composed of a reticular cell meshwork containing blood cells in vessels, which communicated with the splenic cords of the red pulp. Intermittent rows of reticular cells distinguished the outer from the inner half layer. The region surrounding the periarterial lymphoid sheath revealed the same type of reticular cell meshwork as the outer half layer of the perifollicular region. Capillary ends opened into the reticular cell meshwork, which suggested the presence of an open circulation in the human spleen. A deep lymphatic vessel which communicated with the periarterial lymphoid sheath was noted.