Macrophage-lymphocyte clusters in lymph nodes: a possible substrate for cellular interactions in the immune response

Role of the monocyte-macrophage in influenza virus infection of lymphocytes: implications for HIV infection

Knowledge of the pathogenesis of viruses which are less virulent than human immunodeficiency virus (HIV) may provide valuable insights into the pathogenesis of HIV infection. Influenza virus, an enveloped RNA virus, infects monocyte-macrophages, although the infection is brief and abortive. Isolated purified lymphocytes are completely resistant to infection. In contrast, mixtures of lymphocytes and macrophages can synthesize all virus proteins. Infection requires physical association of monocyte-macrophages and lymphocytes in "clusters." These studies with influenza virus suggest that the pathogenesis of virus infections in mixed cell cultures may be very different from that observed in purified cell populations, and they suggest that similar studies should be performed with HIV.

An electron microscopic study of cells with steroid-secreting morphology in the paraaortic lymph node of the hamster

Clustered cells with steroid-secreting morphology (SH), located within the paraaortic lymph node (PLN) capsules of normal and pregnant female golden hamsters, were examined by light and electron microscopy. Hydroxysteroid dehydrogenase (HD) activity of the SH cell cluster also was examined by histochemical techniques. The cluster was composed of mostly packed SH cells and surrounding mesenchymal cells. Individual SH cells possessed prominent smooth endoplasmic reticulum, well-developed Golgi complexes, some lipid droplets, and numerous mitochondria containing tubulovesicular cristae common to mammalian SH cells. Intermediate-type junctions were often observed between SH cells. The same SH cells were rarely detected in the subcapsular sinus and in the cortical parenchyma of the PLN. Early oophorectomy of the hamster resulted in cytoplasmic degeneration of the SH cell at day 5 after the operation. On the other hand, normal adult male hamsters possessed similar PLNs, but no SH cells were recognized in the nodes. The present histochemical preparation of normal female PLNs revealed moderate-to-strong HD activity, probably associated with SH cell clusters, in the limited regions of the capsules. Based on the present ultrastructural and histochemical findings, it is proposed that the SH cell cluster consists of steroid hormone producing cells.

Characterization of two clones isolated from the TC-1 murine marrow stromal cell line: growth factor and retrovirus production and physical support of hemopoiesis

We previously reported the isolation of an adherent murine marrow cell line termed TC-1, and the initial characterization of two subclones derived from this line. In this study we report a further characterization of two subclones from the non-cloned TC-1 cell line. One subclone, TC-1-C-3, consisted of large, slow-growing syncytial polypoid cells that grew to relatively low saturation densities, did not form colonies in soft agar and showed desmosome-like junctions. The other subclone, TC-1-C-11, consisted of smaller, rapidly growing fibroblast-like diploid cells which showed anchorage-independent growth in soft agar. Both these subclones produced growth factors which stimulated giant macrophage colonies in soft agar culture in vitro, but only the TC-1-C-3 subclone produced a retrovirus, whose source was most likely the endogenous ecotropic Emv-2 provirus present in chromosomal DNA in C57BL mice. This retrovirus from the TC-1-C-3 subclone did not appear capable of transforming TC-1-C-11 cells. Together, these data suggest that TC-1-C-3 cells have a special capacity for supporting hemopoiesis. The question of whether the mechanism of this support relates to an intrinsic property of the cell or is possibly related to retrovirus production remains unanswered.

Lamina propria of intestinal mucosa as a typical reticular tissue. A scanning electron-microscopic study of the rat jejunum

The three-dimensional architecture of the lamina propria in the jejunal mucosa of the rat was studied by scanning electron microscopy. The lamina propria is a typical reticular tissue with fine nets of reticular fibers and free and fixed cells lying among them. However, the lamina propria in the core of villi displayed structural features closer to other reticular or lymphoid tissues than that among the crypts. In the villi, the tissue was supported by a spongy framework of interconnecting fibroblasts, and densely infiltrated by free cells. Among the crypts, cellular elements were rather sparsely dispersed in a complex network of reticular fibers. A thin layer of reticular fibers lined the basal lamina of the epithelium. This layer contained a network of flattened cells which anastomosed with each other via slender processes. The basal lamina and the fibrous layer were perforated with round pores, through which free cells or basal processes of the epithelial cells passed. Many macrophages were found resting on the reticular framework of the lamina propria, frequently in close association with immunoblast-like cells. This paper further includes scanning electron-microscopic observations on the central lacteal with special reference to its luminal projections and trabeculae.

Evidence for the existence of a subsinus layer of the peripheral cortex in the lymph node of the rat

The peripheral cortex of a lymph node consists of folliculo-nodules (follicles with a nodule or germinal center) and an extrafollicular zone. In the course of an analysis of the nodes in rats under various experimental or abnormal conditions, our attention became focused on the particularities of a thin layer of peripheral cortex underlying the subcapsular sinus. The present paper reports on observations which led to the identification of the "subsinus layer" of the peripheral cortex. The observations suggest that this layer complements the activity of the inner wall of the subcapsular sinus. The layer probably contributes to the selection of certain elements from the afferent lymph and guides them towards the node area where they can join the cell population involved in the immunological activity in which they are to participate.

Vacuoles in macrophages and reticular cells of regional lymph nodes of the rat after injection of large doses of steroids

The ultrastructure of macrophages and reticular cells of regional lymph nodes of the rat after administration of large doses of cortisone acetate, estrone, progesterone, and cholesterol in aqueous suspensions was investigated. A large number of vacuoles, most of which were surrounded by unit membrane, and lipid droplets not surrounded by unit membrane were observed in the cytoplasm of both macrophages and reticular cells. They were not seen in these cells of control animals and in experimental animals that had received smaller doses of these steroid hormones. After cholesterol injection, many lipid droplets were observed in the cytoplasm of macrophages. These observations suggest that steroids injected in suspension accumulate in macrophages and reticular cells of the regional lymph nodes. Electron-dense material was often present in vacuoles of macrophages but not in those of reticular cells.

Postnatal development of the non-lymphoid elements in the rat lymph node. Connective reticulum cells, macrophages and postcapillary venules

The present study analyzes ultrastructurally the non-lymphoid elements occurring in the diffuse deep cortex and medulla of the postnatal developing lymph nodes of the rat. The supporting meshwork of the organ consist of connective reticulum cells joined together themselves by intercellular junctions. Two morphologically different macrophage cell types can be described in the developing lymph nodes. The first one consists of free-migrating macrophages homing the cortical parenchyma, apparently related with phagocytosis of necrotic cells. In contrast, macrophages located in the lumen of the medullary lymphatic sinuses are anchored to connective reticulum cell processes. They form lymphocyte-macrophage clusters and are involved also in erythrophagocytosis phenomena. Postcapillary venules lined by a low cuboidal endothelium, which allow lymphocyte diapedesis, appear in the diffuse deep cortex of the neonatal lymph nodes. The possible significance of all these cellular elements is discussed with respect to their role as constituents of the local lymph node microenvironments.

[Functional significance of reactive histologic changes in lymph nodes (author's transl)]

Being a reservoir of lymphocytes and plasma cells the lymph nodes are an integral part of the immune system. B and T lymphocytes in the lymph nodes show a distinct topographical distribution. The follicular outer cortex and the medullary cords are predominantly populated by B cells. The paracortical zone between cortex and medulla, is again subdivided in T cell areas and regions with heterogeneous populations of T and B lymphocytes. Even in the normal state nodal lymphocytes maintain a permanent exchange with blood lymphocytes via the mechanism of lymphocyte recirculation. Reactive structural changes of immunologic origin result in an increased immigration of blood lymphocytes into, as well as in local clonal proliferation within the lymph nodes. Four different morphologic patterns of nodal reaction can be determined in terms of functional impact: (1) cortical plasma cell reactions, (2) paracortical plasma cell reactions, (3) germinal center reactions, all three associated with humoral immune responses, and (4) hyperplastic changes of the paracortex associated with cell-mediated immune reactions. In both humoral and cell-mediated immune responses there may be an additional sinus histiocytosis, or mast cell hyperplasia.

Lymphoid organs of teleost fish. III. Splenic lymphoid tissue of Rutilus rutilus and Gobio gobio

The ultrastructure of splenic lymphoid tissue of two teleost fish, Rutilus rutilus and Gobio gobio, constitutes discrete foci around the small arteries and "melano-macrophage" centres. It contains small and medium lymphocytes, lymphoblasts, macrophages and plasma cells. Plasmacytopoiesis and macrophage-lymphocyte clusters have been described and the significance of "melano-macrophage" centres and macrophage-lymphocyte clusters is discussed.

An ultrastructural study of the primary follicle in the lymph node

The present authors have studied the cellular composition of the primary follicle (PF) in the germ-free rat lymph nodes and the development of PF in the human lymph node anlages by using the light- and the electron microscopy. According to the ultrastructural study, the cellular composition of PF in the germ-free rat lymph nodes and classified into five cell types, 1) lymphocytic cells (small and medium-sized lymphocytes), 2) large lymphocytes (= large germinal center cells), 3) reticulum cells with desmosomes (RED), 4) desmodendric cells (DDC), and 5) histiocytes. The interstitial cells with desmosome are classified into DDC and RED based on the relationship to collagenous fibers and the morphological differences. There are amorphous electron-dense intercellular materials among the cytoplasmic processes of DDC, which are distinguished from histiocytes based on the morphological differences. PF emerges as a spherical aggregation of young DDC straight underneath the marginal sinus in the outer cortex of the human embryonal lymph node anlages on the 16th fetal week.

The ultrastructure of medullary carcinoma of the breast

Three cases of medullary carcinoma complying with strictly defined criteria have been examined by electron microscopy. These carcinomas are characterised by the presence of light and dark tumour cells which exhibit prominent organelles and well-developed Golgi complexes but lack secretory activity. The essential stromal cellular infiltrate of macrophages, lymphocytes and plasma cells contains macrophage-lymphocyte clusters suggesting the existence of an immune response. Also present in the stroma are blood vessels lined by high-endothelial cells of the type said to facilitate lymphocyte migration. It is suggested that light and dark tumour cells with well-developed organelles but absent secretory activity, macrophage-lymphocyte clusters and stromal high-endothelial venules represent specific ultrastructure features of typical medullary carcinoma associated with good prognosis.

The structure of the sinus wall of the lymph node relative to its endocytic properties and transmural cell passage

The internal structure of cells lining the lymphatic sinus of the lymph node includes the presence of large bristle-coated vesicles, transfer tubules, and vesicular organelles for the uptake and intracellular disposition of endocytosed material. The lining cells of the sinuses phagocytose particulate material from the lymph in the same manner as the sinusoidal endothelium of the bone marrow takes up particulates from the blood and, thus, are similar in this respect to the endothelial lining of the bone marrow sinusoids. Transmission and scanning electron microscopic examination of the lymphatic sinus wall in rat lymph nodes show that the walls of the lymphatic sinuses are continuous and do not have permanent apertures allowing free communication between the extrasinusoidal and intrasinusoidal compartments in the lymph node. Migrating lymphocytes cross the lymphatic sinus wall intracellularly, i.e., through the body of the lining cell, by making a temporary migration pore, which closes after the cell has reached the lumen of the sinus. In addition there are sporadic aggregations of macrophages in transmural positions. The direction of their movement is unknown.

Contact sites between lymphoid cells of the bursa of Fabricius, in vivo and in vitro

Contact sites between lymphocytes and between lymphocytes and macrophages were demonstrated by electron microscopy in the lymphoid follicles of the bursa of Fabricius. When compared with nonspecialized regions of the cell membranes, these contact sites were characterized by a decreased intercellular distance, subplasmalemmal densities and coated pits. Microfilaments, microtubules and coated vesicles of the subjacent cytoplasm were frequently associated with these contact sites. When the same cells were isolated and introduced into culture, they formed cluster-like assemblies in which cells were closely approximated along broadly contacting surfaces. The morphology of the sites appeared to involve primarily the plasma membrane (including coated pits) and the cell coat. These observations indicated that the same cells of a given lymphoid tissue can form one type of contact site in vivo and another, dissimilar type of contact site, in vitro.

Macrophage-lymphocyte cluster formation in the medullary sinus of lymph node after immunization with sheep red blood cells (SRBC)

Normally the lymphatic sinuses of the lymph node are loosely packed with lymphocytes and free macrophages as well as with macrophages adhering to the fibrocellular trabeculae. After immunization with SRBC cluster formation occurs in the medullary sinuses of rats between a central macrophage and peripherally located lymphocytes. These rosette-like clusters are nearly identical with the clusters found during primary and secondary immune response against SRBC in vitro and seem to be the in vivo equivalent for the same immune response.

Restoration of defective cellular immunity by levamisole in a patient with immunoblastic lymphadenopathy

A 71-year-old woman presented with acutely developed symptoms of generalized lymphadenopathy, intermittent maculo-papular skin rash, pruritus, weight loss, hepato-splenomegaly, pleural exsudate and alternating breast swellings. The histopathological picture of biopsies from a lymph node and from the skin was diagnostic for immunoblastic lymphadenopathy, and the serum concentrations of IgG and IgA were increased. Delayed cutaneous hypersensitivity reactions to various antigens were totally extinguished and the number of T-lymphocytes in the peripheral blood was consistently very low. The number of both T- and B-lymphocytes further decreased during cytostatic treatment and the patient contracted numerous infections. During intermittent treatment with Levamisole the infectious episodes ceased, the cellular immune response was reestablished and the pathological hyperimmuneglobulinaemia suppressed. It is suggested that the primary immunological defect in this disease could be a failing cellular immunity, and that the hyperplasia and hyper-reactivity of the B-cell system are a secondary phenomenon.