Lectin histochemistry of the spleen: a new lectin visualizes the stromal architecture of white pulp and the sinuses of red pulp.

The subcompartmentalization of the white pulp in the spleen is the result of interactions of specific resident stromal cells and migrating subtypes of lymphocytes. Because carbohydrate residues of cell membranes and extracellular matrices are involved in cell-cell and cell-matrix interactions, they were investigated in rat spleen by a broad panel of lectins. Splenic macrophages, which were also demonstrated by Perls' Prussian blue reaction, were labeled selectively by most mannose-specific lectins and gave the characteristic distribution patterns in all splenic (sub)compartments. One recently isolated lectin, Chelidonium majus agglutinin (CMA), visualized predominantly central arterioles, the reticular meshwork (RM) in the periarteriolar lymphatic sheaths (PALS), the circumferential reticulum cells limiting PALS and follicles, and some follicular dendritic cells (FDCs) in white pulp. The endothelial cells of venous sinuses in red pulp were also labeled by CMA and, if frozen sections were used, CMA also labeled the macrophages of the red pulp. Compared to CMA, the monoclonal antibody CD11, which can be used only in frozen sections, stained almost solely the fibrous (extracellular) component of the RM. Because CMA stains the reticulum cells in particular, it is better suited to visualize the stromal architecture of splenic white pulp than the monoclonal antibody. Because CMA can be applied to paraffin-embedded material, it is a particularly useful tool to study the splenic stromal architecture in archival material.     

Immunoarchitecture of distinct reticular fibroblastic domains in the white pulp of mouse spleen.

The development of peripheral lymphoid tissues requires a series of cognate interactions between hemopoietic and stromal cell populations, including reticular fibroblasts, which form the mesenchymal scaffolding of distinct tissue compartments. Here we describe the formation of different fibroblastic domains in the mouse spleen white pulp by using two new rat monoclonal antibodies (MAbs). In the white pulp, MAb IBL-10 labels both T- and B-cell zone reticular elements at various intensities. The IBL-10hi subset was found primarily at the edge between the peripheral part of the PALS and follicles, and the IBL-10lo compartment was distributed evenly within the white pulp. The IBL-10hi subset appeared during the first 2 postnatal weeks and was absent in SCID mice. The white pulp fibroblast subset identified with MAb IBL-11 had a different tissue distribution and kinetics of ontogeny, with an appearance overwhelmingly restricted to the PALS and a narrow rim at the edge of the follicular border area toward the marginal zone. The appearance of IBL-11-positive reticular cells was delayed compared with that of the IBL-10lo-positive subset. The formation was independent of the influence of antigen receptor-bearing lymphocytes, as evidenced by the presence of IBL-11-positive fibroblasts in SCID mice. By transferring various lymphocyte subsets into SCID mice, partial compartmentalization of the white pulp fibroblasts could be induced, indicating that these mesenchymal fibroblast precursors retain their ability to differentiate upon encountering mature T- or B-cells.     

The three-dimensional structure of human splenic white pulp compartments.

The precise arrangement of B- and T-lymphocytes in the different compartments of the human splenic white pulp is still largely unknown. We therefore performed a 3D reconstruction of 150 serial sections of a representative adult human spleen alternately stained for CD3 and CD20. The results indicate that the T-cell regions of human spleens may be interrupted by B-cell follicles. Therefore, there is no continuous periarteriolar lymphatic T-cell sheath (PALS) around white pulp arterioles. An arteriole may be surrounded by T-lymphocytes at one level, then run across a follicle without any T-cells around, and finally re-enter a T-cell region. T- and B-cell compartments are intricately interdigitated in the human splenic white pulp. CD4(+) T-lymphocytes and the typical fibroblasts of the T-cell region may extend as a thin shell at the follicular surface within the marginal zone. On the other hand, IgD(++) B-cells continue from the follicular outer marginal zone along the surface of the T-cell region. Our findings indicate that the microanatomy of the splenic white pulp differs between humans and rodents. This may have consequences for the immigration of recirculating lymphocytes and for initial interactions among antigen-specific T- and B-lymphocytes.     

Regeneration of splenic tissue after autologous subcutaneous implantation: Homing of T- and B- and Ia-positive cells in the white pulp of the rat spleen

The localization of T- and B lymphocytes and interdigitating cells (IDC) was investigated during the regeneration process of splenic implants. For this purpose a two-step immunoperoxidase technique was used to visualize T-cell antigen, immunoglobulins and Ia-antigen on cryostat sections. The specific localization of the repopulating lymphocytes occurred simultaneously with the development of non-lymphoid elements characteristic for the different compartments of the white pulp, i.e., the periarteriolar lymphocyte sheaths (PALS) and follicles. The marginal zone (MZ) developed after the PALS and primary follicles, but before germinal center reactions were found. During ontogeny, however, the development of a broad MZ precedes the formation of follicles. This difference in sequence of events is discussed.     

Migration of B lymphocytes in lymphoid organs of lethally irradiated,thymocyte-reconstituted mice

Summary The migration of radiolabeled intravenously injected B lymphocytes through thymus-dependent areas was studied in lymphoid organs of mice with experimentally defined T cell domains (B cell-deprived mice or T mice). In the spleen, B cells were found to enter the peri-arteriolar lymphoid sheath (PALS) by two routes: (i) via the marginal zone, and (ii) via reticulin sheaths surrounding terminal arterioles. B cells migrated through the peripheral and central PALS and initiated the formation of primary follicles in the peripheral PALS 6 h after injection. Distinct primary follicles were noted at 18 h after injection of the labeled B cells. After 24 h small numbers of labeled cells were also noted in the efferent lymphatic vessels of the spleen.The reconstitution of B cell compartments in the mesenteric lymph node was delayed compared to the spleen. B cells entered the nodal stroma across the wall of high endothelial venules in the paracortex and by 6 h were found scattered throughout the paracortex. Isolated clusters of a few labeled cells were noted in the outer cortex at 18 h after cell transfer. Defined primary nodules were seen only 24 h after reconstitution. A minority of labeled cells was found at 24 h in the cortico-medullary junctions and in medullary cords.The present study shows that B lymphocytes traverse T cell domains on their way to their own specific B cell compartments. The immunological significance of this particular migration route is discussed in view of data on the cellular cooperation of B cells, T cells and macrophages during the humoral immune response.     

Postnatal development of the splenic white pulp in the golden hamster Mesocricetus auratus. I. The periarterial lymphoid sheath (PALS)

The histological organization of the periarterial lymphoid sheath (PALS) was studied during the postnatal life of the golden hamster Mesocricetus auratus with special interest in the cell components occurring in each of their regions. Our results suggest a role of the cell components defining the splenic microenvironment at each developmental stage in governing the developmental process. This process can be temporarily and histologically divide into three stages: 1. At birth, a few lymphocytes and lymphoblasts surrounding the central artery define primitive PALS. 2. A second period is determined on the 2nd day by the appearance of a marginal sinus which bounds the two splenic compartments, white and red pulp. The PALS increases circumferentially around the central artery defined by the pattern of reticular cells and fibres. 3. Between the 4th and 10th days, the PALS reaches its definitive organization, except for the absence of primary and secondary lymphoid follicles, defining an inner and outer region. The marginal zone appears on the 6th day.     

Neuritogenic effects of T cell-derived IL-3 on mouse splenic sympathetic neurons in vivo

To determine the role played by lymphocytes and cytokines in the growth of sympathetic neurons in vivo, the innervation and cytokine levels were examined in the spleens of SCID mice that lack T and B cells. Splenic noradrenaline, nerve growth factor (NGF), and IL-1beta levels were elevated in SCID mice. Immunohistochemical examination revealed that the density of tyrosine hydroxylase-positive (TH(+)) fibers of splenic central arteries in SCID mice was increased compared with wild-type C.B-17 mice, while SCID mice had significantly fewer TH(+) fibers in their periarteriolar lymphatic sheaths (PALS). Two weeks after SCID mice were injected with C.B-17 splenic T cells, their TH(+) fiber staining increased in the PALS. IL-3 levels increased significantly in SCID mice following T cell reconstitution, and the administration of anti-IL-3 Ab blocked the above T cell-induced increase in innervation in the PALS. Anti-IL-3 treatment also inhibited the regeneration of splenic sympathetic neurons in C.B-17 mice after they were chemically sympathetomized with 6-hydroxydopamine. Depletion of NK cells by anti-asialo GM1 promoted the splenic innervation in SCID mice, while there were no significant changes in the innervation between CD8(+) T cell-deficient beta(2)-microglobulin knockout mice and their wild type. Our results suggest that T cells (probably CD4(+) Th cells but not CD8(+) CTLs) play a role in regulating the sympathetic innervation of the spleen; this effect appeared to be mediated, at least in part, by IL-3. On the contrary, NK cells may exert an inhibitory effect on the sympathetic innervation.     

Pathways of lymphocyte migration within the periarterial lymphoid sheath of rat spleen

Summary Male Wistar rats were injected intravenously with 5-(³H)uridine-labeled lymphocytes isolated from lymph nodes of syngeneic donors and enriched in T cells. After short periods of time (3 to 120 min after injection), labeled lymphocytes were localized in spleen compartments using autoradiography to identify routes of lymphocyte movement from blood into splenic parenchyma and to follow migration pathways of recirculating lymphocytes within the periarterial lymphoid sheath (PALS). Topographical analysis of labeled lymphocytes was performed in specific planes of PALS characterized by the diameter of the arterial vessel and termed PALS large, PALS medium, and PALS small (PALS L, PALS M, PALS S, respectively). Attention was also paid to accumulations of labeled lymphocytes close to the arterial vessel wall. Initially, labeled lymphocytes were localized in PALS S and PALS M near the terminal branching of arterial vessels and in the marginal zone (MZ). We conclude that lymphocytes emigrate from blood into splenic parenchyma within two white pulp compartments: in MZ, and directly within PALS through the wall of capillary vessels. The sequential accumulation of labeled cells near arterial vessels of increasing diameter suggests that the recirculating pool of lymphocytes migrates into the central part of PALS L by two routes: from MZ, and along arterial vessels from PALS S and PALS M.R.B. was a fellow of the Alexander von Humboldt-Stiftung, on leave from the Department of Histology and Embryology, Institut of Biostructure, Academy of Medicine, ul. Swiecickiego 6, PL-60-781 Pozna, Poland.     

The development of IgM- and IgG-containing plasmablasts in the white pulp of the spleen after stimulation with a thymus-independent antigen (LPS) and a thymus-dependent antigen (SRBC)

Summary This study describes the development of IgM and IgG containing plasmablasts in splenic white pulp after a single intravenous injection of the thymus-independent antigen lipopolysaccharide (LPS) or the thymus-dependent antigen sheep erythrocytes (SRBC) using immunohistoperoxidase techniques.Attention has been paid especially to the sites where IgM and IgG blasts develop in the white pulp and their migration route, from the white pulp towards the red pulp. The distribution of IgM and IgG blasts in the different white pulp compartments, i.e. outer periarteriolar lymphocytic sheath (PALS), inner PALS, follicles and the area along the terminal arteriolar branches, has been studied. Our findings indicate that both the thymus-independent IgM response to LPS and the thymus-dependent IgM response to SRBC start in the outer PALS. During the course of the immune response against SRBC the early localization of IgG plasmablasts in the white pulp was dispersed through the whole PALS. Later in the immune response the IgG blasts in the white pulp were localized especially in and at the border of follicle centres. No significant development of IgG blasts was found after LPS administration. The results of the present study suggest that during the immune response the bulk of IgM blasts migrates via the outer PALS and along the terminal arteriolar branches into the red pulp.     

Deep splenic lymphatic vessels in the mouse: a route of splenic exit for recirculating lymphocytes

A study of pathways of lymphocyte migration through mouse spleen revealed lymphatic channels closely following arteries in trabeculae and white pulp. Because there is no detailed record of the layout of deep splenic lymphatics in the mouse, or other species, we present our observations in this paper, relating our findings to normal migratory pathways of lymphocytes through the spleen. Lymphatics draining the spleen are so inconspicuous that they often are not mentioned in anatomical discussions. The data presented clearly demonstrate 1) the existence and layout of deep lymphatic vessels in the mouse spleen, and 2) that migrating lymphocytes exit white pulp via these lymphatic vessels. CD4+ and CD8+ T cell subsets migrated proximally along the central artery from distal (dPALS) to proximal periarterial lymphatic sheaths (pPALS) and exited via deep lymphatic vessels that originate there. B cells migrated from dPALS to enter lymphatic nodules (NOD), thus segregated from T cells. B cells then migrated toward and exited via deep lymphatics. The appearance of labelled lymphocytes in lymph coincided with their disappearance from white pulp compartments. Labelled T cells were observed in splenic lymphatics as early as 1 hr after intravenous infusion but took, on average, about 6 hr. B cells took somewhat longer. Thus T and B cells entered and left white pulp through shared pathways, but took divergent intermediate routes through dedicated zones, pPALS for T cells, NOD for B cells.     

Ontogeny of reticular framework of white pulp and marginal zone in human spleen: immunohistochemical studies of fetal spleens from the 17th to 40th week of gestation

The antigenic heterogeneity of the reticular framework of the white pulp (WP) and marginal zone (MZ) is well documented in the human adult spleen. The ontogeny of the WP and MZ of human fetal spleens was examined with special reference to the heterogeneity of the reticular framework. In the spleen of the 17th gestational week (gw), α-smooth muscle actin (α-SMA)-positive reticulum cells were scattered around the arterioles. From the 20th to 23rd gw, α-SMA-positive reticulum cells increased in number and began to form a reticular framework. An accumulation of T and B lymphocytes occurred within the framework, and a primitive WP was observed around the arterioles. At the 24th gw, antigenic diversity of the reticular framework was observed, and T and B lymphocytes were segregated in the framework. T lymphocytes were sorted into the α-SMA-positive reticular framework, and the periarteriolar lymphoid sheath (PALS) was formed around the arteriole. B lymphocytes aggregated in eccentric portions to the PALS and formed the lymph follicle (LF). The reticular framework of the LF was α-SMA-negative. MZ appeared in the α-SMA-positive reticular framework around the WP at the 26th gw. The PALS, LF, and MZ developed with gestational time. The reticular framework of the PALS, LF, and MZ is thus heterogeneous in the fetal spleen, and the development of the heterogeneity is related to the ontogeny of the PALS, LF, and MZ. This work was supported, in part, by the Open Translational Research Project, Advanced Medical Science Center, Iwate Medical University.     

Fibroblastic reticular cells guide T lymphocyte entry into and migration within the splenic T cell zone

Although a great deal is known about T cell entry into lymph nodes, much less is understood about how T lymphocytes access the splenic white pulp (WP). We show in this study that, as recently described for lymph nodes, fibroblastic reticular cells (FRCs) form a network in the T cell zone (periarteriolar lymphoid sheath, PALS) of the WP on which T lymphocytes migrate. This network connects the PALS to the marginal zone (MZ), which is the initial site of lymphocyte entry from the blood. T cells do not enter the WP at random locations but instead traffic to that site using the FRC-rich MZ bridging channels (MZBCs). These data reveal that FRCs form a substrate for T cells in the spleen, guiding these lymphocytes from their site of entry in the MZ into the PALS, within which they continue to move on the same network.     

Specific localization of epidermal-type fatty acid binding protein in dendritic cells of splenic white pulp

Dendritic cells in the splenic white pulp of mice were intensely immunoreactive for epidermal-type fatty acid binding protein (E-FABP). This specific immunostaining revealed a clear difference in morphology between the dendritic cells in the periarterial lymphoid sheath (PALS) and follicular dendritic cells in the follicles in terms of cell sizes and process branching. No immunoreactivity was detected in dendritic cells in the marginal zones and the red pulp, although endothelial cells of almost all capillaries in the red pulp were immunoreactive for E-FABP. After peritoneal injection of lipopolysaccharide, the immunoreactive cells in PALS progressively enlarged and became rounded in shape with a peak in size at 24 h postinjection and they eventually resumed the dendritic form at 48 h postinjection. Within each of the enlarged immunoreactive cell perikarya were included small immunonegative apoptotic cells, presumptive lymphocytes. Taken together, E-FABP is useful as a marker for dendritic cells in the splenic white pulp, and may be involved through combination with fatty acids in antigen presentation and retention as well as in cytokine production.     

In vivo effects of toxic and detoxified endotoxin alone or in combination with muramyl dipeptide on lymphoid and non-lymphoid cells in the spleen of Meth A sarcoma-bearing mice

In this study we confirmed that combinations of toxic or detoxified endotoxin with muramyl dipeptide (MDP) induced much more necrosis of transplanted Meth A sarcoma in mice than toxic endotoxin alone. Detoxified endotoxin and MDP alone had little antitumor effects. We investigated whether these divergent antitumor effects could be related to histopathological changes in the white pulp of the spleen of Meth A sarcoma-bearing mice. Toxic endotoxin reduced the T:B cell compartment ratio in the splenic white pulp by increasing the size of the B-cell compartment while leaving the size of the T-cell dependent inner PALS unaffected. The number of the T-lymphocytes in this area, however, was reduced. The border of B-lymphocytes in the marginal zone was markedly narrowed and the number of marginal metallophils along the inner border of the marginal sinus was decreased. None of these changes were observed after treatment with detoxified endotoxin or MDP. Addition of MDP to either endotoxin did not change their effects. The histopathological changes in the lymphoid and non-lymphoid compartments of the splenic white pulp are apparently exclusively induced by toxic endotoxin. As the antitumor activity of both toxic and detoxified endotoxin combined with MDP are about equal and more powerful than the activity of toxic endotoxin alone, it is concluded that these antitumor effects cannot be related to changes in the white pulp of the spleen.     

White pulp compartments in the spleen of the turtle Mauremys caspica

Summary The aim of the present study was to analyze the nature of lymphoid and non-lymphoid cellular components occurring in distinct histological compartments of the splenic white pulp of the turtle, Mauremys caspica, in order to define their possible correlations with those of the spleen of higher vertebrates, principally mammals. The white pulp of M.caspica consisted of 3 clearly distinguishable regions: (1) the periateriolar lymphoid sheath, and (2) the inner and (3) the outer zones of the periellipsoidal lymphoid sheath. Reticular cells intimately associated with reticular fibres constituted an extensive meshwork in the periarteriolar lymphoid sheath which housed principally Ig-negative lyphoid cells, mature and immature plasma cells, and interdigitating cells. A few Ig-positive cells were also present in the peripheral region of the periarteriolar lymphoid sheath. The inner and outer zones of the periellipsoidal lymphoid sheath were separated by a discontinuous layer of reticular cell processes. In the inner zone, surface Ig-positive lymphoid cells predominated as well as dendritic cells, resembling ultrastructurally the mammalian follicular dendritic cells, although no germinal centres were found in the turtle spleen. Macrophages, some cytoplasmic Ig-positive cells, and Ig-negative lymphoid cells appeared in the outer zone of the periellipsoidal lymphoid sheath. These results allow us to speculate on a phylogenetic relationship between the periarteriolar lymphoid sheath and the inner and the outer zones of the periellipsoidal lymphoid sheath of the spleen of M. caspica and the periarteriolar lymphoid tissue, the lymphoid follicles and the marginal zone, respectively, of the mammalian splenic white pulp.     

Cellular events during the primary immune response in the spleen

Summary The cellular events during the primary immune response in T and B cell compartments in the splenic white pulp were analysed in germfree mice immunized with sheep erythrocytes. Light, fluorescence and electronmicroscopic studies revealed that the initial formation of lymphoid blast cells occurs in the thymus-dependent area, i.e. the central periarteriolar lymphatic sheath (central PALS), 2 days after immunization. Lymphoblasts were found in close relation with erythrocyte-containing macrophages and with interdigitating cells. With fluorescence microscopy these blast cells were Ig negative. Lymphoblasts in the central PALS showed many polyribosomes in the cytoplasm, but were virtually devoid of endoplasmic reticulum. The ultrastructure of lymphoblasts in the central PALS, and their relation with interdigitating cells, suggests that these cells are the progeny of antigen-activated T cells.Cells with a positive cytoplasmic fluorescence, plasmablasts, appeared 3 days after immunization in the peripheral part of the PALS. During the progress of the immune response these cells accumulated around branches of the central arteriole, and moved along marginal zone bridging channels towards the red pulp. In the electron microscope plasmablasts showed many polyribosomes, short strands of rough endoplasmic reticulum close to mitochondria, and a few electron-dense bodies. The cell organelles of plasmablasts were frequently gathered in a so called uropod, which is a morphological sign of active cell movement.Germinal center formation started within primary follicles, 4 days after immunization. Blast cells in germinal centers did not show cytoplasmic fluorescence. During the course of the immune response, germinal centers extended in diameter, and fluorescent dendritic cells appeared at the periphery of the germinal center.From the present observations we conclude that: (1) cellular cooperation between different lymphoid and non-lymphoid cell types during the immune response against SRBC takes place in the PALS, (2) the cellular cooperation in the PALS results in the differentiation of B cells into immunoglobulin-producing plasmablasts, (3) the cellular cooperation in the PALS preceeds the formation of germinal centers in primary follicles, hence germinal centers are not involved in early T-B cell cooperation.     

B lymphocyte differentiation in lethally irradiated and reconstituted mice

The recovery of the B lymphocyte compartments was investigated in lethally irradiated mice reconstituted with fetal liver cells. This was done by means of immunofluorescence on frozen sections of spleen, lymph nodes and Peyer's patches. The first B lymphocyte recovery in the spleen was observed on day 8, a few days earlier than in lymph nodes and Peyer's patches (day 13). These early B cells in the spleen were found in the central part of the periarteriolar lymphatic sheath (PALS). Later on, while increasing in number, the B cells formed growing follicles at the periphery of the PALS. Subsequently, brightly fluorescent B cells appeared in the marginal zone, which surrounded the follicles. Another two weeks later, around day 30, also germinal center formation was observed in the follicles of the spleen. B cell development in lymph nodes and Peyer's patches started somewhat later than in the spleen, but once started, the recovery of the different compartments was completed very fast. Germinal center reactions were found in lymph nodes and Peyer's patches already on day 25, and thus earlier than in the spleen, but later than the first occurrence of the strongly fluorescent cells in the marginal zone. Apparently, germinalcenter formation is not essential for the recovery of the population of brightly fluorescent B cells in the marginal zone after irradiation and reconstitution.     

The pathology and homing of a transplantable murine B cell leukemia (BCL1).

The pathology and homing characteristics of a murine B cell leukemia are described. Experiments utilizing autoradiography to determine the early homing pattern of the leukemic cells revealed a pronounced localization of the labeled cells to the spleen. The cells that were seen in the white pulp showed preferential localization to the follicles or B cell domains. Tissue section immunofluorescence with antibodies to kappa- and lambda-light chains was used to study the initial mouse with this disease as well as to study the mice that were injected with in vivo passaged cells. These mice also showed predominant involvement of the spleen. Although the initial mouse with this disease had 200,000 lambda-bearing B lymphocytes per mm3 in the peripheral blood and closely resembled a human chronic lymphocytic leukemia patient, the studies described suggest that this murine B cell neoplasm is a lymphoma with a striking predilection for splenic involvement. The other organs including the bone marrow as well as the peripheral blood appeared to be involved secondarily. This unusual spontaneously occurring murine B cell disease provides a useful model for the investigation of certain commonly occurring human lymphomas and leukemias.     

The cellular response of T and B dependent areas of the spleen after focal thermocoagulation of liver and kidney

Using 3H-thymidine autoradiography, the cellular response of the white splenic pulp after single or repeated thermolesions on liver and kidney was studied. Sham operations served as controls, and did not induce any significant changes in the splenic white pulp. After single or repeated thermolesions, the labeling index increased distinctly in the B and T cell areas. The central T-dependent periarteriolar lymphatic sheath (PALS) showed an earlier rise of radioactively labeled lymphocytes after repeated thermolesions than after a single lesion. After a single heat coagulation of liver and kidney a dissociation of the germinal centers occurred with consecutive hyperplasia. However, compared with the splenic reaction after other surgical injuries, especially after cryosurgical operations, the response of the B-dependent splenic areas was weaker. The distinct reaction of the central T-dependent PALS supports the conception of a more prominent cell mediated immune response of the peripheral lymphatic system with temporary T cell dysfunctions. Possibly the inflammatory complications of burned patients and the delayed wound healing of thermosurgical tissue lesions may be caused by the alteration of the lymphatic system with a disturbed cooperation of T and B lymphocytes with macrophages.