Characterization of dendritic cells,isolated from normal and stimulated lymph nodes of the rat

Summary Non-lymphoid dendritic cells were isolated from normal and paratyphoid vaccine-stimulated lymph nodes draining the rat skin. They were studied using enzymecytochemical, immunocytochemical and electron-microscopical methods. These cells had an irregular outline and an eccentrically situated nucleus. All showed acid phosphatase activity in a central area and expressed Ia antigen on the plasma membrane. Birbeck granules were exclusively present in dendritic cells isolated from lymph nodes in the induction phase of the immune response. This observation concurs with the presence of Birbeck granules in interdigitating cells in situ during the same period of the immune response. It is concluded that the dendritic cells are the in-vitro equivalents of the non-actively phagocytizing population of interdigitating cells.     

人肠系膜淋巴结内树突细胞免疫细胞化学研究

本文用免疫细胞化学的方法检测了胎儿（胎龄２７～３８周）和成人肠系膜淋巴结内树突细胞的分布及对Ｓ－１００蛋白抗体和ＨＬＡ－ＤＲ抗体的反应。结果显示胎儿淋巴结内Ｓ－１００蛋白阳性树突细胞分布在外周区,中央区较少;这些细胞对ＨＬＡ－ＤＲ抗体亦呈阳性反应。成人淋巴结的树突细胞有两种,一种是位于初级和次级淋巴小结生发中心的小结树突细胞,另一种是位于小结间和副皮质区的交错突细胞。小结树突细胞与ＨＬＡ－ＤＲ抗体呈阴性反应,而交错突细胞则呈强阳性,提示这两种细胞不仅在分布上不同,而且对ＨＬＡ－ＤＲ抗体反应也不同。进一步证实了小结树突细胞和交错实细胞在细胞来源和免疫功能方面是不同的两种辅助性细胞。     

The function and origin of follicular dendritic cells

Follicular dendritic cells (dendritic reticular cells) in germinal centres bind antigen-antibody complexes via C3 receptors and retain the complexes at their surface for long periods of time. The follicular dendritic cells (FDC) are distinct from macrophages and from dendritic cells found in T-dependent areas, and are not derived from bone marrow stem cells. On histological evidence it has been proposed that they are derived from reticulum cells. Complexes are probably transported to FDC by a subpopulation of B cells in the marginal zone. Binding of complexes to FDC causes germinal centre enlargement and is a very efficient, and possibly essential stimulus to the generation of B memory cells which recognize epitopes on antigen or antibody in the complexes. An hypothesis is discussed which draws together these observations and suggests that antigen on FDC plays a central role in control of humoral immunity.     

Emperipolesis of lymphoid cells by human follicular dendritic cells in vitro.

Isolated follicular dendritic cells (FDCs) showed true and pseudoemperipolesis of fresh tonsillar lymphocytes, even after long-term (50-day) cultivation. Emperipolesis by FDCs was not restricted by allotype specificity, nor was it inhibited by the addition of antibodies against MHC-I & II antigens. Follicular dendritic cells predominantly engulfed B-cells; monocytes and macrophages were not found between FDC cytoplasmic extensions. When highly purified T-cell populations were added to FDC cultures emperipolesis of T-cells occurred, particularly those of the CD4-positive phenotype. Mitoses appeared within 6 h in the emperipolesed lymphocytes and, after an additional 18 h, some lymphocytes exhibited apoptosis.     

Isolated follicular dendritic cells: cytochemical antigen localization, Nomarski, SEM, and TEM morphology

The objectives of the present study were to determine the cytological features of isolated follicular dendritic cells (FDC), which distinguish them from other leukocytes or dendritic cell types. Consequently, we have developed methods for the fixation, peroxidase cytochemistry, and visualization of FDC, which are applicable to cytological evaluations by Nomarski optics, scanning, and transmission electron microscopy. A functionally supported identification of FDC in vitro was made possible by utilizing, in conjunction with the dendritic morphology, the cytochemically identifiable antigen, horseradish peroxidase (HRP), and the known capacity of FDC to sequester immune complexes (i.e. HRP-anti-HRP) on their plasma membranes. The observations showed that FDC constitute a relatively pleomorphic, nonphagocytic group, distinct from other dendritic type cells such as lymphoid dendritic cells, Langerhans cells, and interdigitating cells (LDC, LC, and IDC), as well as typical leukocytes. Morphologically distinct FDC were identified as cells either with filiform dendrites or with "beaded" dendrites. FDC possessed a single or sometimes a double, lymphocyte-size cell body, which contained an irregular, lobated nucleus, Golgi apparatus, numerous small vesicles, and some mitochondria. Mitochondria were not abundant in the dendritic processes. Filiform dendrites tended to branch and anastomose near the cell body and form a radiating "sunburst"-like pattern. On the average, dendrites measured 15-20 microns in length and 0.1-0.3 micron in diameter. Occasional dendrites were extremely elongated, reached several hundred microns in length, and terminated in an enlargement measuring nearly a micron in diameter. Other filiform dendrites usually had a club-shaped terminal enlargement. The microspheres of "beaded" dendrites ranged between 0.3 and 0.6 micron in diameter. The dendritic processes were also shown to have a highly ordered pattern of immune complex attachment on their surface, suggestive of a periodic arrangement of receptor sites.     

Induction of interdigitating reticulum cell-like differentiation in human monocytic leukemia cells by conditioned medium from IL-2-stimulated helper T-cells

Monocytic leukemia (MoL) cells were obtained from the peripheral blood of a patient in whom the leukemic cells infiltrating various lymphoreticular organs exhibited features intermediate between interdigitating reticulum cells (IDC) and ordinary phagocytic macrophages, whereas the leukemic cells in the peripheral blood were essentially monocytic and lacked such features. Peripheral blood CD4+ T-cells were established as an interleukin-2-dependent T-cell line. When the MoL cells were exposed for a few days to conditioned medium from the T-cell line, they extended several dendritic cytoplasmic projections and became intensely positive for HLA-DR antigen, cytoplasmic S-100β protein, and CD1 antigen. Functionally, the conditioned medium significantly down-regulated Fc-mediated and Fc-independent phagocytic activities, and the levels of lysosomal enzymes such as lysozyme and nonspecific esterase in the MoL cells. Moreover, the conditioned medium significantly up-regulated the accessory cell function of the MoL cells as measured by the primary allogenic mixed leukocyte reaction (MLR). Furthermore, the conditioned medium significantly down-regulated the expression of CD14 antigen. Biochemical analysis indicated that the factor responsible for these changes is a protein which is distinct from known human cytokines and whose molecular weight is approximately 31 kDa. These findings suggest that IDC are closely related the monocytic lineage and that helper T-cells play an important role in constructing the microenvironment of T-lymphoid tissues which is necessary for the differentiation and maturation of IDC.     

Origin of follicular dendritic cell in the chicken spleen

The ellipsoid-associated cell (EAC) is a blood-borne phagocytic cell, residing in the antigen trapping zone of the chicken spleen. Binding and endocytosis of βGalactosidase (βGal) are independent from the Fc and complement receptors, because sulfated polysaccharides, in a concentration manner, inhibit the bacterial antigen uptake. The βGal-positive cells migrate to the periarterial lymphatic sheath (PALS), the preexisting germinal centers (GC), and form clusters with B- and T-cells. βGal, E5G12 double positive cells on the surface of the ellipsoid and in the PALS, GC and clusters prove that the EACs carry the enzyme. The EAC and the follicular dendritic cell (FDC) express, 68.2 and E5G12 and, 74.3 and E5G12, antigens, respectively. During migration the cessation of 68.2 and expression of 74.3 indicate the differentiation of EAC to FDC. By day 14 the clusters had disappeared, and in several GC the presence of double positive cells (74.3 and βGal; E5G12 and βGal) showed that the clusters had developed to GC. The presence of βGal⁺ cells in the PALS, where interdigitating dendritic cells (IDC) cooperate with the T-cells, suggests that in the spleen alternate routes exist for the EAC differentiation to FDC: EAC to FDC: βGal-loaded cells in the preexisting GC; and EAC through IDC to FDC: βGal⁺ EAC in the PALS and clusters. The EAC-FDC axis works exclusively inside the spleen; therefore; this system may be operated in pneumococcus infection.This work was supported by OTKA Grant number: T-042558.     

Induction of interdigitating reticulum cell-like differentiation in human monocytic leukemia cells by conditioned medium from IL-2-stimulated helper T-cells.

Monocytic leukemia (MoL) cells were obtained from the peripheral blood of a patient in whom the leukemic cells infiltrating various lymphoreticular organs exhibited features intermediate between interdigitating reticulum cells (IDC) and ordinary phagocytic macrophages, whereas the leukemic cells in the peripheral blood were essentially monocytic and lacked such features. Peripheral blood CD4+ T-cells were established as an interleukin-2-dependent T-cell line. When the MoL cells were exposed for a few days to conditioned medium from the T-cell line, they extended several dendritic cytoplasmic projections and became intensely positive for HLA-DR antigen, cytoplasmic S-100 beta protein, and CD1 antigen. Functionally, the conditioned medium significantly down-regulated Fc-mediated and Fc-independent phagocytic activities, and the levels of lysosomal enzymes such as lysozyme and nonspecific esterase in the MoL cells. Moreover, the conditioned medium significantly up-regulated the accessory cell function of the MoL cells as measured by the primary allogenic mixed leukocyte reaction (MLR). Furthermore, the conditioned medium significantly down-regulated the expression of CD14 antigen. Biochemical analysis indicated that the factor responsible for these changes is a protein which is distinct from known human cytokines and whose molecular weight is approximately 31 kDa. These findings suggest that IDC are closely related the monocytic lineage and that helper T-cells play an important role in constructing the microenvironment of T-lymphoid tissues which is necessary for the differentiation and maturation of IDC.     

Development of follicular dendritic cells in lymph nodes of B-cell-depleted mice

Summary We have studied follicular dendritic cells (FDC) in lymph nodes of normal and thymus dysgeneic nude mice depleted of B-cells by chronic treatment with anti-IgM antibodies. We found that B cell depletion was accompanied by the absence of mature FDC as defined morphologically at the ultrastructural level. Only precursor FDC (p-FDC) could be demonstrated. Upon release of B-cell suppression, the repopulation of lymph nodes with B-cells was associated with the reappearance of fully differentiated FDC in primary follicles of nude mice and in secondary follicles of T-cell competent mice. We conclude that mature B-cells and/or B-cell products are required for the development of mature follicular dendritic cells in the mouse lymph node.     

Interdigitating reticulum cells in lymph nodes of Sézary syndrome. Freeze-fracture and ultrathin-section morphology

Lymph nodes with extensive leukemic infiltration from three patients with the Sézary syndrome were examined in ultrathin sections and in freeze-fracture replicas. Sézary cells (SC) and interdigitating reticulum cells (IDC) were the predominant cell types in the lymph nodes. Both were closely connected with each other by apparently interdigitating cytoplasmic processes. The projections between these cells were, in the main, processes from the IDC. In freeze-fracture replicas these cellular processes did not appear as interdigitations but were more bubble-like, and for this reason these cells are imprecisely described by the term "interdigitating." The SC were seen to possess only short cytoplasmic processes. The frequent polar grouping of cell organelles in SC in the region of the contact zone with IDC and the high organelle content of IDC ('activated IDC') could be the morphologic expression of intense interaction between IDC and SC. IDC displayed three features in freeze-fracture which are not specific to the Sézary syndrome, but should be applicable to IDC in general: (1) they exhibited an approximately equal density of intramembrane particles in both the E-face and the P-face, (2) some of the intramembrane particles in the P-face were assembled in clusters and (3) the surface showed bubble-like formations of the cytoplasmic processes. On the basis of these properties it was possible to distinguish IDC from macrophages and lymphocytes in freeze-fracture replicas.     

Characterization of non-lymphoid cells in the white pulp of the mouse spleen: An in vivo and in vitro study

Summary Non-lymphoid cells (marginal metallophils, follicular immunecomplex-retaining cells, interdigitating cells), which are present in certain areas of the white pulp in the mouse spleen were characterized by means of (immuno)enzyme histochemical techniques, carbon uptake and experiments with lethal X-irradiation. Marginal metallophils are clearly present at the inner border of the marginal zone and show a very strong, E-600 sensitive, non-specific esterase (NSE) activity. Follicular immune-complex-retaining cells show a weak and diffuse NSE activity and no carbon uptake as shown by the combined application of an immunohistoperoxidase technique (for the demonstration of immune complexes), enzyme histochemistry (for NSE activity) and carbon uptake (for phagocytosis). Interdigitating cells show a distinct focus of NSE activity in the cytoplasm, weak carbon uptake and high radiation sensitivity. Demonstration of NSE activity is useful for the identification of the different non-lymphoid cells in the white pulp of the mouse spleen. It is suggested that the in vitro observed dendritic cells of Steinman and Cohn (1973) belong to the mononuclear phagocyte system, as transitional cells are encountered with cytological features of both dendritic cells and macrophages. These in vitro dendritic cells (or a portion of them) are probably similar to the interdigitating cells.Abbreviations HRP horseradish peroxidase - IDC interdigitating cells - PALS periarteriolar lymphocytic sheath - NSE non-specific esterase     

Expression of the intercellular adhesion molecule-1 on high endothelial venules and on non-lymphoid antigen handling cells: interdigitating cells,antigen transporting cells and follicular dendritic cells

Intercellular adhesion molecule-1 (ICAM-1)¹ has been implicated in the development of germinal center reactions in vitro, and the present study was undertaken to determine the distribution of ICAM-1 in active germinal centers in vivo and in murine secondary lymphoid tissues in general. Anti-ICAM-1-specific monoclonal antibodies were used in conjunction with immunohistochemistry at both the light and ultrastructural levels of resolution. Examination of cryostat sections of lymph nodes, spleens, and Peyer's patches revealed that anti-ICAM-1 distinctly labeled cells in the light zones of germinal centers, a few cells in the T cell zones (e.g. paracortex of lymph nodes), cells in the sinus floor of the subcapsular sinuses of lymph nodes, and high endothelial venules (HEV). Ultrastructural studies revealed that the cells labeling with anti-ICAM-1 in germinal centers were follicular dendritic cells (FDC) which appeared to have more ICAM-1 than any other cell type. The surfaces of well-developed, intricate, convoluted FDC processes were intensely labeled even under conditions where B cells appeared negative. Interdigitating cells (IDC) were also labeled as were certain endothelial cells in the HEV. The cells in the subcapsular sinus floor labeling with anti-ICAM-1 were the antigen transporting cells (ATC) that carry antigen-antibody complexes into lymph node follicles. We suspect ATC are FDC precursors which mature into FDC in the follicles. Interestingly, FDC, IDC, and ATC are 3 important accessory cells known to handle antigens in specific compartments of lymphoid tissues. The marked localization of this adhesion molecule on these critical antigen handling cells supports the concept that ICAM-1 is important in providing the intercellular adhesion necessary for optimal initiation of immune responses in vivo.Abbreviations ICAM-1 Intercellular adhesion molecule-1 - LFA-1 leukocyte functional antigen-1 - IDC interdigitating cells - ATC antigen transporting cells - FDC follicular dendritic cells - HEV high endothelial venules - DC dendritic cells - PBS phosphate-buffered saline - PLP periodate-lysine-4% paraformaldehyde - GPLP periodate-lysine-0.1% glutaraldehyde-2% paraformaldehyde - EM electron microscopy - HRP horseradish peroxidase - DAB diaminobenzidine tetrahydrochloride - HSA human serum albumin     

人胎脾交错突细胞对T,B淋巴细胞发育影响的免疫组织化学研究

用免疫酶单重和双重染色研究人胎儿脾连续切片中交错突细胞（ＩＤＣ）与Ｔ,Ｂ淋巴细胞的定位关系及ＨＬＡ－ＤＲ表达。结果表明,Ｓ－１００阳性树突状细胞为ＩＤＣ,多数表达ＨＬＡ－ＤＲ。９－１２周的胎脾中就可见到散在分布的ＩＤＣ。１３－１６周胎脾中ＩＤＣ开始定位于白髓的Ｔ细胞集落内和周缘,及Ｂ细胞集落的周边。在上述区域ＩＤＣ常与Ｔ细胞形成ＩＤＣ－Ｔ细胞聚合体。在脾的发育过程中,ＩＤＣ不仅与Ｔ,Ｂ淋巴细胞在分布上关系密切,而且可与这两类细胞形成突起－胞体、胞体－胞体的连接。提示,胎儿脾中ＩＤＣ与Ｔ,Ｂ细胞的迁移,定位及功能成熟过程有密切联系。     

The early postnatal development of the primary immune response in TNP-KLH-stimulated popliteal lymph node in the rat

Summary The popliteal lymph nodes were removed from young rats of various ages five days after a single immunization with TNP-KLH in the hind footpads. Cryostat sections of the lymph nodes were investigated by means of enzyme and immunohistochemical techniques at the light-microscopical level.The presence and localization of anti-TNP antibody-containing cells were examined using a new technique to visualize specific antibodies. Moreover, the development of the lymph nodes following exogenous antigenic stimulation was compared with that of unstimulated lymph nodes.Specific antibody-containing cells could not be found before day 15 after birth, in rats immunized at day 10. From that time these lymphoid cells were located primarily at the border between cortex and medulla. Younger popliteal lymph nodes showed only aspecific immunoglobulin-containing lymphoid cells. With age, the number of specific antibody-containing cells tended to increase. These cells were more mature, according to morphological criteria and were located nearer the medulla.The first primary follicles were seen at day 19, as was the case in unstimulated animals. The first secondary follicles, containing germinal centers, were detected at day 23, whereas in unstimulated popliteal lymph nodes they were never found.Trapping of immune complexes could not be demonstrated before day 33 after birth. The later appearance of this phenomenon might be a consequence of the techniques applied to demonstrate specific antibody-containing cells.Abbreviations PLN popliteal lymph node - FDC follicular dendritic cell - IDC interdigitating cell - HEV high endothelial venule - TNP trinitrophenyl - KLH keyhole limpet hemocyanin - PBS phosphate-buffered saline - GCPC germinal center precursor cell - sIg surface immunoglobulin - cIg cytoplasmic immunoglobulin     

Effect of cytokines on thymic hematopoietic precursors

Summary We have previously shown that the interaction of thymocytes with thymic accessory cells (macrophages and/or interdigitating cells) is one of the factors required for thymocyte activation. Precursors of both thymic accessory cell and thymocytes are included in the CD4^- CD8^- Mac-1^- Ia^- subpopulation, and their respective maturation and/or activation may be modulated by granulocyte-macrophage colony-stimulating factor, interleukin 1 and interleukin 2. When CD4^- CD8^- thymic cells are activated with granulocyte-macrophage colony-stimulating factor plus interleukin 2, both macrophages and interdigitating-like cells are present, as shown by electron microscopy. When activated with interleukin 1 plus interleukin 2, the interdigitating-like cells is the only accessory cell present. In both culture conditions, large clusters are formed between interdigitating cells and lymphoid cells. These results have led us to propose two-step signals for thymocyte proliferation: first, the maturation of macrophages under granulocyte-macrophage colony-stimulating factor control and the production of interleukin 1, and secondly, the maturation of interdigitating cells under interleukin 1 control, their clustering with thymocytes which are then activated.Abbreviations CFU-S colony-forming units in the spleen - CSF colony-stimulating factor - DC dendritic cells - DN double negative cells (CD4^- CD8^-) - EC epithelial cells - GM-CFC granulocyte/macrophage colony-forming cells - GM-CSF granulocytemacrophage CSF - IDC interdigitating cell - IL-1 interleukin 1 - IL-2 interleukin 2 - MØ macrophage - P-TR phagocytic cell of the thymic reticulum     

Characterization of the population of phagocytic cells in thymic cell suspensions

Rat thymic phagocytic cells were characterized in vitro using various light- and electron-microscopical techniques. Thymic cell suspensions were mechanically prepared and enriched for non-lymphoid cells, which were predominantly phagocytic and of three types. Type I showed acid phosphatase (APh) activity in small granules dispersed throughout the cytoplasm and were mostly Ia antigen-positive, although the Ia membrane label varied in intensity and distribution among individual cells. Only a few cells had endogenous peroxidase activity. The type-I cells could not be clearly distinguished morphologically from type-II or -III cells, and most likely comprise precursors of both these cell types. Type-II were large pale cells with many slender cell processes. These cells had APh activity centrally positioned, were strongly positive for Ia on the cell membrane and were negative for endogenous peroxidase. The cytoplasm frequently contained Birbeck granules, which unequivocally classifies these cells as the in vitro equivalent of the interdigitating cells present in the medullary area of the thymus in situ. Type-III cells were rounded with a smooth or ruffled cell membrane and contained vacuoles and many phagolysosomes. They were strongly positive for APh which was present throughout the cytoplasm. About 50% of these cells were positive for endogenous peroxidase in a pattern resembling resident macrophages. The cells were negative for Ia antigens. Type-III cells mostly likely represent the macrophages found in the cortical area of the thymus.     

Organization of lymphoid tissue in the tonsilla lingualis

Summary Lymphoid organs are highly organized structures made up of different tissue compartments, each with its own specific cell populations. However, the cellular elements of the lingual tonsil, which forms a significant part of Waldeyer's pharyngeal ring, are not yet documented. This study, therefore, describes the fine structure and tissue organization of tonsilla lingualis in Macaca fascicularis. Ten selected crypto-lymphatic units originating from five perfusion-fixed animals were analysed ultrastructurally. Based on the fine-structural elements contained within, the lymphoid tissue of tonsillar units could be subdivided into follicular (germinal centre) and parafollicular areas. The latter contained predominantly small lymphocytes, lymphoblasts resembling T-blasts, plasma cells, macrophages, occasional neutrophils and many reticular cells resembling fibroblasts. A distinct feature of the parafollicular area was the presence of numerous high endothelial (HEV)or postcapillary venules (PCV). The follicular areas contained many small and large lymphoid cells, mitotic cells, plasmablasts, macrophages and specialised reticular cells resembling follicular dendritic cells (FDC) with distinct desmosomal junctions. These observations show that the crypto-lymphatic units of the lingual tonsil are, in fact, organised into distinct B- and T-cell compartments with their own specific lymphoid and accessory cells.     

Lymph node macrophages and reticulum cells in the immune response

Summary The morphology and kinetics of macrophages and reticulum cells of rat lymph nodes have been studied in relation to the immune response to a second exposure to antigen. During the first 24 h after stimulation monocyte-like exudate macrophages, including some scattered interdigitating cells (IDC), contain granules similar to those present in epidermal Langerhans cells and lymph-borne veiled cells. In this induction phase these macrophages migrate from the marginal sinus into the paracortex and during the migration they gradually transform into IDC. In the proliferation phase the paracortex is mainly populated by transitional macrophages and there are almost no typical IDC present between the lymphoblasts. In the memory phase the relative number of IDC again rapidly increases. During this period in the paracortex there are often typical IDC which contain partially digested necrotic lymphocytes, thus resembling tingible body macrophages (TBM) of the germinal centre in this respect.It is suggested that the newly arrived macrophages induce the lymphoblast reaction, while mature IDC may have an inhibitory function in the memory phase of the immune response. In this phase the phagocytic potential of IDC is clearly shown.     

The development of the human lymph node

Summary Lymph nodes of human fetuses from the 11th to the 20th gestational week (g.w.) were investigated by light- and electron microscopy under particular consideration of the development of the T-cell and the B-cell regions and their specific reticulum cells. Lymph node development begins as a mesenchymal condensation, containing capillaries and mesenchymal cells; this primordium bulges into a lymph sac. Within the primordium of the lymph node granulopoiesis and erythropoiesis occur temporarily from the 12th to the 14th g.w. The first lymphoid cells and undifferentiated blast cells are seen in the 12th g.w.; monocytes and macrophages can be found from the 13th g.w. onward.The development of the T-cell regions begins during the 13th g.w., before differentiation into cortex and medulla becomes obvious in the 14th g.w. Near the marginal sinus, cells displaying features of interdigitating reticulum cells (IDC) show similarities to monocytes. The morphological differentiation of the IDC is complete in the 17th g.w. when they are found in the paracortical region. Among the IDC, lymphoid cells with features of thymocytes are arranged in small groups.The first indication of the development of B-cell regions can be recognized in the 14th g.w. when precursors of dendritic reticulum cells (DRC) are seen near the marginal sinus; this area also displays lymphoblasts, immunoblasts, and plasmoblasts. During the 20th g.w. small primary follicles are discernible in the outer cortex; in addition to blast cells they contain small lymphocytes, none of which show features of thymocytes. The morphological development of DRCs is not entirely complete until the 20th g.w.; however, some cells already show a characteristic network of interwoven processes.The probable origin of (i) the IDC from monocytes, and (ii) the DRC and fibroblastic reticulum cells from a common type of mesenchymal precursor cells, as well as their significance for a specific micromilieu in the T-cell and the B-cell regions, are discussed.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft and the Sonderforschungsbereich 111 of the Deutsche ForschungsgemeinschaftThe authors appreciate the contribution of human fetal material from Dr. J. von Hollweg and Dr. J. Körner, Hospital Heidberg, Hamburg, and the excellent technical assistance of Mrs. O.M. Bracker, Mrs. H. Hansen, Mrs. R. Köpke, Mrs. I. Knauer, Mrs. F. Müller, Mrs. H. Siebke, and Mrs. H. Waluk     

Precise localization of antigens on follicular dendritic cells

Summary Horse-spleen ferritin or bovine serum albumin conjugated to colloidal gold (BSA-gold) were injected subcutaneously in preimmunized mice. In draining lymph nodes both antigens were located in macrophages or between the cytoplasmic processes of follicular dendritic cells (FDC). Some of the antigens remained trapped on FDC until day 31 after injection. Simultaneous injection of both antigens showed that they were located between the infoldings of the same FDC. These cells are thus able to retain at least two different antigens on their surface. The peculiar arrangement of ferritin between the cytoplasmic infoldings suggests that this antigen is fixed on both cell membranes by specific antibodies. The trapped immune complexes could thus stabilize the FDC membrane system.The antigen retention requires the presence of specific antibodies since BSA-gold or ferritin injected without preimmunization were not found between FDC processes. Nonantigenic materials, such as colloidal gold or carbon particles, are not trapped by FDC, except when injected in large amounts.The antigens were trapped on the surface of FDC, however unfrequently in close contact with lymphocytes. FDC might protect lymphocytes against an excess of immune complexes and act as regulators of contacts between lymphocytes and immune complexes.Abbreviations BSA bovine serum albumin - BSA-gold BSA conjugated to colloidal gold particles - FDC follicular dendritic cells