Human dendritic reticulum cells of lymphoid follicles: their antigenic profile and their identification as multinucleated giant cells

Immunohistochemical analysis for CD21, CD35, Caldesmon and S100 protein on dendritic cells types in oral lymphomas

Objective:

Follicular dendritic cells (FDCs) and interdigitating dendritic cells (IDCs) are dendritic cells found in lymphoid follicles, reactive follicles and in lymphomas. The goal of this study was to evaluate the presence and distribution of FDCs and IDCs in oral lymphomas.

Material and Methods:

Immunohistochemistry reactions were applied to 50 oral lymphomas using the antibodies anti-CD21, anti-CD35 and anti-caldesmon to FDCs, and anti-S100 protein to IDCs. Caldesmon+/FDCs and S100+/IDCs were quantified in Imagelab® software.

Results:

FDCs revealed by CD21 and CD35 were positively stained in two cases of diffuse large B-cell lymphoma, one MALT lymphoma, and in one case of mantle cell lymphoma. FDCs were immunopositive to caldesmon in all cases, as well as IDCs to S100 protein. Burkitt lymphoma presented a lower amount of caldesmon+/FDCs and S100+/IDCs than diffuse large B-cell lymphoma and plasmablastic lymphoma of the oral mucosa type.

Conclusions:

The microenvironment determined by neoplastic lymphoid cells in oral lymphomas is responsible by the development and expression of dendritic cells types.

Dendritic cell neoplasms: an overview

Dendritic cell neoplasms are rare tumors that are being recognized with increasing frequency. They were previously classified as lymphomas, sarcomas, or histiocytic neoplasms. The World Health Organization (WHO) classifies dendritic cell neoplasms into five groups: Langerhans' cell histiocytosis, Langerhans' cell sarcoma, Interdigitating dendritic cell sarcoma/tumor, Follicular dendritic cell sarcoma/tumor, and Dendritic cell sarcoma, not specified otherwise (Jaffe, World Health Organization classification of tumors 2001; 273-289). Recently, Pileri et al. provided a comprehensive immunohistochemical classification of histiocytic and dendritic cell tumors (Pileri et al., Histopathology 2002;59:161-167). In this article, a concise overview regarding the pathological, clinical, and therapeutic aspects of follicular dendritic, interdigitating dendritic, and Langerhans' cell tumors is presented.

Follicular Dendritic Cell Sarcoma of the Tonsil: A Case Report and Literature Review

We describe a case of follicular dendritic cell sarcoma (FDCS) of the tonsil in a 59-year-old woman. She was successfully treated with excision of the mass and postoperative radiation therapy. According to our review of the literature, only 25 cases of extranodal FDCS in the head and neck have been previously reported, including only 10 cases that involved a tonsil. We briefly review these earlier reports, and we discuss the diagnosis and management of FDCS.

Follicular dendritic cells are related to bone marrow stromal cell progenitors and to myofibroblasts

Follicular dendritic cells (FDC) are involved in the presentation of native Ags to B cells during the secondary immune response. Some authors consider FDC to be hemopoietic cells, whereas others believe them to be mesenchymal cells. The low proportion of FDC in the lymphoid follicle, together with technical difficulties in their isolation, make these cells difficult to study. We show that Fibroblast Medium can be used successfully to isolate and maintain FDC lines. In this culture medium, we obtained 18 FDC lines from human tonsils, which proliferated for as long as 18 wk and showed a stable Ag phenotype as detected by flow cytometry and RT-PCR. FDC lines were CD45-negative and expressed Ags associated to FDC (CD21, CD23, CD35, CD40, CD73, BAFF, ICAM-1, and VCAM-1) and Ags specific for FDC (DRC-1, CNA.42, and HJ2). These cell lines were also able to bind B cells and secrete CXCL13, functional activities characteristic of FDC. Nevertheless, the additional expression of STRO-1, together with CD10, CD13, CD29, CD34, CD63, CD73, CD90, ICAM-1, VCAM-1, HLA-DR, alkaline phosphatase, and alpha-smooth muscle actin (alpha-SM actin) indicated that FDC are closely related to bone marrow stromal cell progenitors. The expression of alpha-SM actin also relates FDC with myofibroblasts. Like myofibroblasts, FDC lines expressed stress fibers containing alpha-SM actin and were able to contract collagen gels under the effect of TGFbeta1 and platelet-derived growth factor. These findings suggest that FDC are a specialized form of myofibroblast and derive from bone marrow stromal cell progenitors.

Follicular Dendritic Cell Immunohistochemical Markers in Angioimmunoblastic T-Cell Lymphoma

Angioimmunoblastic T-cell lymphoma is characterized by a paracortical proliferation of medium to large neoplastic T cells, often with clear cytoplasm, in a background of arborizing high endothelial venules, many surrounded by follicular dendritic cells (FDCs). IHC staining may be applied to highlight these extrafollicular FDCs, traditionally using CD21, or CD23. Several alternative FDC markers have been described, including CNA.42, cystatin A/acid cysteine proteinase inhibitor (ACPI, involved in antigen presentation), and fascin (an actin binding protein). The authors stained a collection of 45 angioimmunoblastic T-cell lymphomas with CD21, CD23, CNA.42, cystatin A, and fascin for direct comparison of FDC staining characteristics in this setting. CD21 highlighted the expected dendritic network of cell processes, within residual follicles and outside of follicles, often adjacent to proliferating vessels. CD23 exhibited similar staining quality but was less sensitive than CD21. CNA.42 showed only diffuse weak labeling of FDCs. Cystatin A stained the cytoplasm of follicular dendritic cells within and outside of follicles; however, staining was often not sharply localized to dendritic cell processes, and scoring was further complicated by reactivity with other cell types in over half of the cases. Likewise, fascin stained a variety of cell types, including strong staining of interdigitating dendritic-like cells, moderate staining of endothelial cells, and only weak staining of follicular dendritic cells within and outside of follicles. Thus, CD21 remains the most reliable marker of follicular dendritic cells in angioimmunoblastic T-cell lymphoma.

Sarcoma of follicular dendritic cells in the dorsal mediastinum

Follicular dendritic cell sarcomas (FDCSs) are very rare and usually originate in lymph nodes. We report an exceedingly rare case with localization in the dorsal mediastinum and, for the first time, provide positron emission tomography (PET) data for this tumor. This report describes the case of a 76-year-old man with a clinically aggressive tumor in the dorsal mediastinum. Computed tomography scan revealed displacement of soft tissue and lymph nodes. PET showed that the tumor had a high proliferation rate. Investigation of the successfully removed tumor mass revealed reactivity of the tumor cells for follicular dendritic cell markers and desmosomes linking adjacent tumor cells at the ultrastructural level. Marked atypia, a high mitotic rate, and areas of coagulative necrosis were found. The tumor in our case revealed the typical features and thus was classified as FDCS. In contrast to previous reports in the literature, preoperative imaging, histology, and immunohistochemistry studies indicated at least an intermediate degree of malignancy. Nevertheless, the patient made a good postoperative recovery and remained apparently disease-free 2 years later.

Estrogen receptor alpha is a novel marker expressed by follicular dendritic cells in lymph nodes and tumor-associated lymphoid infiltrates

During routine assessment of the hormonal phenotype of breast carcinomas, we detected expression of the estrogen receptor (ER) in the germinal centers of reactive lymphoid follicles surrounding malignant foci. To confirm and extend this finding, we compared ER-alpha, progesterone receptor (PR), and androgen receptor (AR) immunostaining in hyperplastic or metastatic lymph nodes obtained from patients with various pathology, disease location, gender and age. Irrespective of these parameters, we found that: 1) ER-alpha-positive cells were located prevalently in germinal centers, 2) the PR was weakly expressed by cells within and surrounding germinal centers, and 3) the androgen receptor was undetectable. Transcripts for ER-alpha and PR were also detected by reverse transcription-polymerase chain reaction on laser-microdissected lymph node germinal centers. Morphologically, the ER-positive cells resemble dendritic cells and by double immunostaining were found to express both CD21 and CD23, which is characteristic of follicular dendritic cells. Finally, we assessed the effects of Tamoxifen treatment by comparing the numbers of ER-positive follicular dendritic cells in lymph nodes obtained from breast cancer patients before and after treatment. The results show that Tamoxifen treatment generated larger germinal centers with more abundant ER(+)/CD21(+)/CD23(+) cells. Taken together, these results open new perspectives on the effects of sex steroids and their antagonists on the human response in cancer and inflammation.

Follicular Dendritic Cell Sarcoma of the Tonsil: Report of a Rare Case

Follicular dendritic cell tumors are extremely rare. Only 17 cases have been previously described in the literature, and only three of them involved primary tumors of the oral cavity. We describe a new case of the latter, which occurred in a 51-year-old man who sought evaluation for a painless enlargement of his left palatine tonsil. The tonsil was excised, and histologic examination revealed that the tumor was a primary sarcoma that had arisen from the dendritic reticulum cells of the palatine tonsil. Postoperatively, the tumor site was treated with percutaneous irradiation (total dose: 70 Gy). After more than 5 years of follow-up, the patient showed no evidence of recurrence. We also discuss the salient features of the immunohistochemical examination.

Immunohistochemical recognition of human follicular dendritic cells (FDCs) in routinely processed paraffin sections

A number of monoclonal antibodies (MAbs) that recognize human follicular dendritic cells (FDCs) have been identified. Although some of them have already been applied individually in routine immunolabeling using formalin-fixed paraffin sections for diagnostic and experimental purposes, many antibodies are still employed only for immunolabeling using cryostat sections or particularly processed sections because they have been thought unsuitable for routine sections. A comprehensive examination re-evaluating their suitability in paraffin sections has not been reported. Accordingly, there is limited ability to examine the immunopathological contribution or diagnostic value of FDCs using routinely processed specimens or archived materials. In this study a broad panel of antibodies was systematically applied to the immunolabeling of paraffin sections of reactive tonsils or lymph nodes, in combination with advanced antigen retrieval (AR) techniques. Several antibodies, including Ki-M4p, X-11, 12B1, CNA.42, 1F8/BU32 (anti-CD21), BU38/1B12 (anti-CD23), Ber-MAC-DRC/To5 (anti-CD35), 1.4C3 (anti-CD106), NGFR5 (anti-nerve growth factor receptor p75), IIH6 (anti-CD55), 55K-2 (anti-fascin), and anti-S100 protein alpha-chain, were found to label FDCs in routine sections when combined with suitable AR techniques. Our results are easily adaptable for routine practice and provided useful suggestions concerning the immunopathological behavior and diversity of the particular cells.

Accessory cell tumour: a clinicopathological study of 16 aggressive tumours containing EBV-positive Hodgkin and Reed-Sternberg-like giant cells

AIMS

Lymph nodes contain non-lymphoid accessory cells including follicular dendritic cells and interdigitating dendritic cells. Functionally, these cells belong to the category of immune accessory cells involved in antigen presentation to B or T-lymphocytes. Neoplastic proliferation of these cells is very uncommon. We present here the clinicopathological features of 16 cases of accessory cell tumour.

METHODS AND RESULTS

We performed electron microscopic and immunohistochemical examinations, and used in-situ hybridization for EBV-encoded RNA (ISH-EBV) to detect the EBV genome in 11 cases, and Southern blot analysis to assess EBV clonality in two cases. Tumour cells were composed of oval-to-spindle cells arranged in diffuse, vague storiform, fascicular and sometimes whorled patterns in a background of small lymphocytes. In all cases, binucleated or multinucleated Hodgkin and Reed-Sternberg-like giant cells were encountered. Staining for CD68 was positive in all cases. CD21, CD35, Ki-M4p, Ki-FDC1p, and S100 exhibited variable reactivity. ISH-EBV yielded positive labelling in seven of 11 cases, of which five exhibited EBV only in Hodgkin and Reed-Sternberg-like giant cells. Southern blot analysis showed clonality of EBV terminal repeats (EBV-TR) in the two cases examined. Electron microscopic examination showed that many of the tumour cells had numerous interwoven long villous cell processes connected by occasional desmosomes. Many tumours were very refractory to chemotherapy and radiation, with a few exceptions, and half of the cases classified initially as stage IV. A short survival time, of 10 months or less, was observed in seven of 16 patients.

CONCLUSIONS

Our study identified more aggressive behaviour of accessory cell tumours. Our results suggest that EBV may potentially induce activation of accessory cells to form Hodgkin and Reed-Sternberg-like giant cells, which correspond with poor prognosis.

Extranodal follicular dendritic cell sarcoma of the head and neck region: three new cases, with a review of the literature

Extranodal follicular dendritic cell (FDC) sarcoma of the head and neck region is uncommon, with 16 well-documented cases previously reported (four in the tonsil, four in the pharynx, two in the palate, five in the soft tissue, and one in the thyroid). We here report an additional three cases of extranodal FDC sarcoma in the tonsil (two cases) and pharynx (one case). In these new cases, the neoplastic cells were arranged in diffuse, fascicular, and vaguely whorled growth patterns. A background lymphocytic infiltrate was sprinkled throughout the neoplasms, with focal prominent perivascular cuffing. Scattered multinucleated giant cells were present. Immunohistochemically, tumor cells were strongly and diffusely positive for follicular dendritic cell markers CD21 and CD35. Tumor cells were diffusely positive for fascin and negative for leukocyte common antigen, S-100 protein, cytokeratin, and Epstein-Barr virus (EBV) latent membrane protein-1 (EBV-LMP). EBV was also not detected in the tumor cells by in situ hybridization for EBV-encoded RNAs. FDC sarcomas are probably an underrecognized neoplasm, especially when they occur in extranodal sites in the head and neck region. Two of the three new cases we report were initially misdiagnosed, and five cases of extranodal FDC sarcoma in the head and neck region reported in the recent literature were initially misdiagnosed. Our aim is to complement the current understanding of this neoplasm and alert pathologists to this rare entity in this region to avoid misdiagnosis. Recognition of extranodal FDC sarcoma requires a high index of suspicion, but this tumor has numerous distinctive histological features that should bring the neoplasm into the differential diagnosis. Confirmatory immunohistochemical staining with follicular dendritic cell markers such as CD21 and/or CD35 is essential for the diagnosis. Correct characterization of this neoplasm is imperative given its potential for recurrence and metastasis.

Follicular dendritic cells in reactive and neoplastic lymphoid tissues: a reevaluation of staining patterns of CD21, CD23, and CD35 antibodies in paraffin sections after wet heat-induced epitope retrieval

Structural alterations in the meshwork of follicular dendritic cells (FDCs) are frequently found in malignant lymphomas. Formaldehyde fixation and paraffin embedding, however, have long prevented consistent detection of FDCs. Wet heat-induced epitope retrieval in Dako Target Retrieval Solution (TRS) (pH 6.0) enabled the reliable detection of FDCs through CD21, CD23, and CD35 antigens in routinely processed tissues from 11 reactive and 69 neoplastic lymphoproliferations, thus allowing the distribution of the FDCs to be reevaluated. Germinal center FDCs in lymphoid hyperplasias and expanded FDC meshworks in the 8 mantle cell lymphomas, 7 low-grade MALT lymphomas, and 6 low-grade follicular lymphomas were intensely stained with all these markers. In 6 cases of B cell chronic lymphocytic leukemia, tumor cells were CD23+. In four cases of nodular lymphocyte predominance Hodgkin's disease (HD), expanded FDC meshwork's sharply delineating negative tumor cells and their rosetting T cell, were revealed mainly with the CD21 and CD35 antibodies. Follicular dendritic cells were also demonstrated in 11 cases of grade I nodular sclerosing HD, including follicular HD. Striking dendritic cell clusters were revealed with all 3 antibodies in 9 angioimmunoblastic T cell lymphomas. Sparse or no FDC meshworks were detected in the 4 cases of grade II nodular sclerosing HD, 5 follicular lymphomas with high-grade transformation, and 5 T cell-rich B cell lymphomas. CD35 immunostaining showed the most consistent labeling in the four FDC sarcomas studied in the current article. Reproducible demonstration of FDCs in routinely processed paraffin sections with CD21, CD23, and CD35 antibodies, as presented here, provides invaluable pieces of information in the diagnosis of lymphoproliferative disorders.

Follicular dendritic cells share a membrane-bound protein with fibroblasts

The expression of a fibroblast antigen (AS02) on a proportion of CD21+ follicular dendritic cells (FDCs) provides evidence in support of their fibroblastic reticular origin. This antigen is expressed on the membrane of tissue fibroblasts but is absent from lymphocytes, macrophages or granulocytes. The distribution of AS02 in conjunction with other FDC markers (DRC-1, RFD3, CD23, IgM, and vitronectin) showed six types of FDCs. AS02 is present in the outer layers of primary and secondary follicles, but gradually decreases and disappears in the centre of germinal centres. In contrast, there is a progressive up-regulation of the other FDC markers. AS02 is re-expressed in involuting FDCs. Intermediate forms from fibroblastic to dendritic appearance are also apparent and occasionally FDC processes contain collagen type I and IV fibres, a characteristic feature of fibroblasts. In pathological follicles the normal differentiation pattern is disrupted, with persistence of the fibroblast marker, possibly due to altered interactions between FDCs and disrupted lymphocytic patterns. These findings provide new evidence for a local differentiation pathway of fibroblasts to mature FDCs.

Immune complexes containing human immunodeficiency virus type 1 primary isolates bind to lymphoid tissue B lymphocytes and are infectious for T lymphocytes

This study investigated the interaction of tonsil B lymphocytes with immune complexes containing human immunodeficiency virus (HIV IC) primary isolates and the infectivity of the B cell-bound HIV IC. Treatment of virus with a source of antibody and complement increased HIV IC binding to B cells by 5.6-fold. Most of the HIV IC that bound to B cells were not internalized but remained on the cell surface and were gradually released over 72 h. Cell-bound HIV IC were highly infectious for T cells while virus released by cultured B cells was only slightly infectious. Removal of HIV IC from the B-cell surface by protease treatment reduced the infection of T cells to near-background levels, indicating that infectious virus remained on the B-cell surface. These studies show that B lymphocytes can carry and transfer infectious HIV IC to T cells and thus suggest a novel mode of infection of T cells in lymphoid tissue that could be important for pathogenesis during HIV infection.

Hodgkin's disease expressing follicular dendritic cell marker CD21 without any other B-cell marker: a clinicopathologic study of nine cases

Reed-Sternberg (RS) and Hodgkin's (H) cells are considered to be the neoplastic cells in Hodgkin's disease (HD). Although most data suggest their lymphoid origin, the nature of these cells still remains a subject of controversy. Recently, a number of RS cells have been found to express an antigen that is also present on follicular dendritic cells (FDCs), asserting FDCs as the possible progenitor cells of H-RS cells. This prompted us to investigate whether these CD21-positive cases had distinct clinicopathologic characteristics. In a series of 94 examined cases of HD, we identified 9 CD21-positive ones (4 of 37 cases of nodular sclerosis, 1 of 41 mixed cellularity, and 4 of 12 lymphocyte depletion HD) without any other B-cell marker on paraffin sections. The patients varied in age from 16 to 82 years (median, 50 years) and included six men and three women. They had superficial or mesenteric lymphadenopathy without hepatosplenomegaly. Peripheral blood leukocytosis was seen in three patients. The clinical course was indolent, and all patients but one achieved an initial complete response with HD-based treatment regimens, although three of them relapsed. Morphologically, two subgroups could be delineated. Six of the cases were characterized, besides by the classic RS cells, by a varying number of the cells with the distinctive walnutlike or cerebrumlike nuclei and cytologically with cytoplasmic processes. Their fine structural examination also revealed villous processes, but no desmosomes. The other three cases had multinucleated RS cells often with triangular nuclei, but not cytoplasmic processes. The percentage of CD21-positive tumor cells ranged from less than 10% to 60% among the H-RS cells. These RS cells were positive for CD30 (9 of 9), CD15 (7 of 9), CD68 (1 of 8), fascin (8 of 8), S-100 protein (1 of 7), and epithelial membrane antigen (2 of 8) on paraffin sections. Notably, of eight cases examined on frozen sections, two showed immunostaining for DRC1, CD35, R4/23, and Ki-M4p. Only CD35 was also detected in the other two cases. Genotypic investigation showed germline configuration of the T-cell receptor beta and gamma chain genes and the immunoglobulin heavy chain gene in all eight cases examined. In situ hybridization showed Epstein-Barr virus sequences in four cases, three of which were examined by the terminal region analysis and showed the Epstein-Barr virus to be monoclonal. We concluded that in a small proportion (9.6%) of HD, H-RS cells might be derived from FDCs and that they appear to represent a distinct pathologic variant based on morphologic and phenotypic traits within the framework of HD.

Follicular dendritic cell tumor of the mesentery

Follicular dendritic cell (FDC) tumor is an exceedingly rare malignant neoplasm and occurs mainly in the cervical lymph nodes. We report a mesenteric FDC tumor occurring in a 66-year-old female, that manifested with intraabdominal multifocal recurrence 7 years after resection of the primary tumor. Histologically, both primary and recurrent tumors were composed of oval to spindle cells with paley eosinophilic cytoplasms, indistinct cell borders, round to elongated nuclei with clear or finely dispersed chromatin, and medium to large nucleoli. Characteristically, the tumor cells were growing in sheets, fascicles, and sometimes in whorls and a storiform pattern. In addition, focal necrosis, nuclear pleomorphism and abnormal mitoses were also observed. The neoplastic cells were intimately admixed with small lymphocytes. The diagnosis was confirmed by positive immunoreactivity with CD21 and CD35 antibodies and by ultrastructural demonstration of convoluted interdigitating cell processes connected by scattered desmosome-like junctions. Although our case showed a low proliferative activity evaluated by MIB-1, multifocal recurrence has occurred. The clinicopathologic features and differential diagnosis of FDC tumors are discussed with the review of the literature.

Follicular dendritic cell sarcoma mimicking diffuse large cell lymphoma: a case report

Follicular dendritic cell sarcomas (FDCSs) are rare tumors arising from follicular dendritic cells in lymphoid tissue. Fewer than 20 cases have been described in the English-language literature. We describe the second case of an FDCS with primary liver involvement. The initial diagnosis was lymphoma, and appropriate treatment was prescribed. After the initial treatment failed, additional biopsy samples were obtained. Standard pathologic analysis and immunophenotyping for a panel of monoclonal antibodies were performed on formalin-fixed paraffin-embedded tissue and frozen sections. The pathologic findings were consistent with FDCS, and the specimens showed some of the characteristic pathologic features suggestive of this tumor, including multinucleation and a spindle pleomorphic morphology. The tumor cells were positive for S-100 protein, CD45, CD14, and vimentin. Because of its morphological characteristics, FDCS can be confused with other neoplastic entities, such as lymphomas and other solid tumors.

Production of a monoclonal antibody (59.4) against canine lymphocyte surface antigen and its immunohistochemical application

A monoclonal antibody was produced by immunizing BALB/c mice with freshly prepared canine thymocytes and peripheral blood leukocytes. The antibody, designated 59.4, was of the IgG1 subclass type and mainly reacted with lymphocytes. In single-color flow cytometric analysis, lymphocytes from the peripheral blood, thymus and spleen were graded into three categories according to their fluorescence intensity labeling by antibody 59.4: weakly, moderately and intensely positive cells. Two-color analysis revealed that a major population of CD8-positive cells were intensely labeled by antibody 59.4, but less than 50% of CD4-positive cells were moderately reacted with antibody 59.4. Immunohistochemically, thymocytes in the medulla showed moderately intense immunoreactivity to 59.4, but most lymphocytes in the cortex were negative in reaction. Immunostaining using antibody 59.4 demonstrated characteristic aggregations of 59.4-positive lymphocytes in the reticulum cell-free region of the thymic medulla. In the spleen, scattered lymphocytes in the outer layer of the marginal zone and in the red pulp were intensely labeled by antibody 59.4, while lymphocytes gathering in the mantle zone and periarterial lymphatic sheath (PALS) were moderately stained. Antibody 59.4 appears to recognize an antigen which is expressed by a more-differentiated T cell-lineage but not by immature T cells in the thymic cortex.

Follicular dendritic cell tumor: report of 13 additional cases of a distinctive entity

Follicular dendritic cell (FDC) tumor is an extremely rare malignant neoplasm with approximately 17 well-documented cases in the literature. We report 13 additional cases of this distinctive neoplasm. There were seven men and six women, with a mean age of 46.5 years (range, 27-62 years). There was involvement of cervical lymph nodes (six cases), mediastinum (three cases), axilla, tonsil, spleen, and peripancreatic soft tissues (one case each). The neoplasms were grey to tan, ranging in size from 1 to 13 cm. They were formed by oval to spindle cells with eosinophilic cytoplasm growing in sheets and fascicles, with a focal storiform pattern and whorls reminiscent of those seen in meningioma. The nuclei were oval or elongated with thin nuclear membranes, inconspicuous or small eosinophilic nucleoli, and clear or dispersed chromatin. Typically, the tumor cells were intimately admixed with small lymphocytes, with a prominent perivascular cuffing. Multinucleated tumor cells were present in seven cases. Necrosis, marked cellular atypia, high mitotic rate, and/or abnormal mitoses were present in seven cases. The tumor cells were positive for CD21 (10 of 11), CD35 (10 of 11), Ki-M4p (seven of eight) Ki-FDRC1p (six of seven), vimentin (five of nine), and S100 protein (five of nine). One case stained with actin. In situ hybridization, done in six cases, did not show Epstein-Barr virus RNA sequences. Ultrastructural examination of eight cases showed long, complex, occasionally interdigitating cytoplasmic processes joined by desmosomes. The behavior of these tumors is more akin to that of a low-grade soft tissue sarcoma than a malignant lymphoma and is characterized by local recurrences and occasional metastases. Two patients died of tumor, two were alive with recurrent or metastatic disease, eight were alive with no disease, and one was lost to follow-up.

SIV infection of monkey spleen cells including follicular dendritic cells in different stages of disease

Immunoaffinity enriched spleen follicular dendritic cells (FDCs), lymphocytes, and macrophages from SIVsm-inoculated cynomolgus monkeys (Macaca fascicularis) at different stages of disease were compared for latent and productive SIV infection. Analysis of FDCs by in situ hybridization, electron microscopy, and coculture assays indicated that comparatively high levels of virus were associated with the FDC fraction. Polymerase chain reaction (PCR) and RT-PCR results revealed that the levels for SIVpol DNA did not correlate with the level of env mRNA in the various cell subsets, suggesting differences in latency. Limiting dilution assays for spliced env mRNA showed a 10-100-fold higher amount of env mRNA in FDCs than in other spleen cell subsets early during SIV infection. At late stages of disease, the number of productively infected FDCs significantly decreased in parallel with a marked reduction of the FDC network and follicular involution. Our findings indicate that destruction of FDCs probably reflects a cytopathic effect of SIV and/or the activity of specific antiviral cytotoxic T lymphocytes.

Follicular dendritic cells and germinal centers

Follicular dendritic cells (FDCs) are stromal cells unique to primary and secondary lymphoid follicles. Recirculating resting B cells migrate through the FDC networks, whereas antigen-activated B cells undergo clonal expansion within the FDC networks in a T cell-dependent fashion, thereby generating germinal centers. Here, B cells undergo somatic mutation, positive and negative selection, isotype switching and differentiation into high-affinity plasma cells and memory B cells. Since the discovery of FDCs by electron microscopy as long-term antigen-retaining cells 30 years ago isolation of FDCs and generation of FDC-like cells lines and of FDC-specific monoclonal antibodies have been achieved. FDCs express all three types of complement receptors as well as Ig-Fc receptors, through which antigen-antibody immune complexes are retained. However, the mechanism that prevents FDCs from internalizing the antigens and retaining them in native form for long periods of time remains obscure. Substantial evidence derived from cultures in vitro indicates that FDCs contribute directly to the survival and activation of peripheral B cells. The adhesion between FDCs and B cells is mediated by ICAM-1 (CD54)-LFA-1(CD11a) and VCAM-VLA-4. T cells may interact with FDCs in a CD40/CD40-ligand-dependent fashion. Whether FDCs originate from hematopoietic progenitors or from stromal elements is still a controversy. New evidence suggests the presence of two types of dendritic cells within human germinal centers: (i) the classic FDCs that express DRC-1, KiM4, and 7D6 antigens represent stromal cells; and (ii) the newly identified CD3-CD4-CD11c- germinal center dendritic cells (GCDC) represent hematopoietic cells that may be analogous to the antigen-transporting cells described in mice. Finally, FDCs appear to be involved in the growth of follicular lymphomas and in the pathogenesis of HIV infection.

An immortalized cell line with features of human follicular dendritic cells. Antigen and cytokine expression analysis

Follicular dendritic cells (FDC) are specialized cells residing primarily within lymphoid follicles. They bind immunocomplexes and play an important role in the presentation of antigen to follicular B cells. Isolation of FDC for in vitro studies, however, is difficult because they constitute only about 1% of the cells in lymphoid tissue and form tight clusters entrapping lymphocytes within their dendritic processes. The monoclonal antibody (mAb) Ki-M4, which is highly restricted in its binding to FDC, is used to identify these cells. In order to establish a new immortalized cell line with features of FDC, we applied a modified procedure to isolate and enrich FDC from human tonsils and fused them with the myeloma cell line SP2/0-Ag14. The new hybrid cell line, designated FDC-H1, is of both mouse lymphoid and human FDC origin. FDC-H1 was found to have unlimited growth potential and to consistently express the Ki-M4 antigen and other surface antigens of human FDC. Semiquantitative reverse-transcribed polymerase chain reaction (RT-PCR) of enriched FDC and FDC-H1 revealed the same highly restricted cytokine/mRNA profile for both, with detectable levels of interleukin (IL)-1 alpha and surface CD23 and a lack of mRNA for IL-1 beta, IL-2, IL-3, IL-4, IL-7, IL-9, IL-10, interferon-gamma, tumor necrosis factor-alpha, transforming growth factor-beta and granulocyte/macrophage-colony-stimulating factor. Additionally a weak but constant IL-6 mRNA expression was found in the cell line FDC-H1 by RT-PCR. In situ hybridization experiments in tonsils revealed IL-6 transcripts in cells with a staining pattern characteristic of a dendritic cell only in a few germinal centers. To our knowledge, FDC-H1 is the first cell line that constantly expresses surface antigens and a cytokine profile characteristic of FDC. It is, therefore, well suited for studying the biology of FDC and the functional relationship between FDC and normal or neoplastic lymphatic cells.

Moabs MAS516 and 5B5, two fibroblast markers, recognize human follicular dendritic cells

Follicular dendritic cells (FDC) are only located within follicles of secondary lymphoid tissues. The origin of this peculiar cell type is not clearly defined. To contribute to this study, we applied two monoclonal antibodies (MAS516 and 5B5) considered as specific for fibroblasts to tonsil cryosections and to isolated follicular dendritic cells. On the basis of an enzyme cocktail digestion of human tonsils and a fractionation procedure on albumin gradients, FDC can be prepared in the form of cell aggregates with associated lymphoid cells. MAS516 reacts with surface membrane molecules expressed by human fibroblasts, tissue macrophages and peripheral blood monocytes. With immunoperoxidase assays on tonsil cryosections connective tissue cells and macrophages are stained. Inside germinal centres, heavy labelling of the light zone was found. The MAS516 staining pattern is very similar to that of specific FDC markers DRC-1 or BU10. All isolated FDC reacted with MAS516 antibody. 5B5, considered as a typical fibroblast marker, reacts with human prolyl-4-hydroxylase which is an intracellular enzyme related to collagen biosynthesis. In cryosections, interfollicular and capsular areas showed 5B5 positive connective tissue fibroblasts. In germinal centres, some cells presenting features of FDC were 5B5 positive. After cell separation, 25%-50% of the isolated FDC were labelled with this antibody. This positivity of some FDC for 5B5 antibody may support the idea of their fibroblastic origin. The combination of observations realized in situ and after cell purification ensured an unequivocal recognition and identification of FDC.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular dendritic cells in non-Hodgkin's lymphomas

Follicular dendritic cells (FDC) are restricted to the B-cell regions of secondary lymphoid tissue and to non-Hodgkin's lymphomas derived from the follicular center or the mantle zone. With their cytoplasmic ramifications they form a dense network which contains the B-lymphocytes. In situ, FDC are only detectable at the ultrastructural level or when stained with anti FDC-reagents. On the surface of their dendritic extensions they express transferrin receptors (CD71), the B-cell epitope CD20, class II antigens, the myelomonocytic molecule CD14, the glycoprotein gp50 (CD40), and several receptors for components of the complement system (CD11b, CD21, CD35). Subsequent to an antigen challenge, FDC trap and retain immune-complexes for a long period of time. In vitro FDC and neoplastic lymphocytes spontaneously form small cellular aggregates. This adhesion is mediated by the LFA-1-alpha/beta = ICAM-1, the VLA-4 = VCAM-1, and the ICAM-1 = C3bi- receptor ligand pathways on B-cells and on FDC, respectively. The loss of LFA-1- alpha/beta and ICAM-1 molecules may enable neoplastic lymphocytes to detach from FDC. The monoclonal B-cells now invade new compartments. In vitro, FDC have the capacity to activate resting B-cells and to save them from dying by apoptosis. Signals involved in this activation include cell-surface immunoglobulin and CD40. Immunocytochemistry and autoradiography with single cell suspensions of neoplastic B cells suggest that FDC also provide signals leading to the continued stimulation of lymphoma lymphocytes. During the early stage of HIV infection lymph nodes show an immense follicular hyperplasia, with a massive increase of the dendritic network of FDC. In the later stage of the disease, the continuous involution of the germinal centers is associated with a progressive destruction of FDC.

Follicular dendritic cells: whose children?

At the recent Germinal Centre Conference in Spa*, over 200 immunologists gathered to study the fate of lymph follicles, B- and T-cell selection, cell migration, accessory cells, and pathological conditions such as lymphoproliferative diseases and AIDS. Here, Ernst Heinen and Alain Bosseloir report on this fascinating field.

Castleman's disease. Differences in follicular dendritic network in the hyaline vascular and plasma cell variants

Twenty-seven cases of the hyaline vascular variant and 10 cases of the plasma cell variant of Castleman's disease were studied with the paraffin resistant monoclonal antibodies Ki-FDC1p and/or Ki-M4p against follicular dendritic cells. Studies with the monoclonal antibody Ki-M9, for the detection of sinus lining cells, were also performed on the available frozen tissue in four cases of the hyaline vascular variant. In nine of the 10 plasma cell variant cases, the predominant type of follicular dendritic cell network was similar to that seen in normal or reactive germinal centres. In contrast, the hyaline vascular variant demonstrated either an expanded, disrupted, follicular dendritic cell network (10 cases) or multiple tight collections of follicular dendritic cells (16 cases). Sinus lining cells were not detected in the four cases studied. The difference in the predominant type of dendritic meshwork is an additional distinguishing feature to separate the plasma cell and hyaline vascular variants of Castleman's disease. The patterns of dendritic network seen in the hyaline vascular type, together with the absence of sinus lining cells, appear to favour the hamartoma theory proposed for this variant.

Functionally active Epstein-Barr virus-transformed follicular dendritic cell-like cell lines

Follicular dendritic cells (FDC) are unique nonlymphoid cells found only in germinal centers. FDC can be distinguished from other accessory cells based on a characteristic set of cell surface markers. It is known that FDC are able to rescue germinal center B cells from apoptosis. To investigate the role of FDC in the process of selection and maturation of B cells during germinal center reactions, we tried to establish factor-independent immortalized FDC-like cell lines. Because freshly isolated FDC express the Epstein-Barr Virus (EBV) receptor CD21, we attempted EBV transformation on isolated FDC. After incubation of FDC-enriched cell populations with EBV, cell lines were obtained consisting of slowly duplicating very large cells. These cell lines have a fibroblast-like morphology but could be clearly distinguished from several human fibroblast cell lines by displaying a different phenotype including intercellular adhesion molecule 1, CD40, and CD75 expression. Detection of the EBV-encoded proteins latent membrane protein 1 and Epstein-Barr virus nuclear antigen 2 in our FDC-like cell lines implicated successful EBV transformation. FDC-like cells are able to bind nonautologous B cells and preserve the latter from apoptosis. The binding of B cells to FDC-like cells is dependent on adhesion via lymphocyte function-associated antigen 1/intercellular adhesion molecule 1 and closely resembles the pattern of emperipolesis as described by others. These data demonstrate that FDC can be successfully infected by EBV, and that the cell lines obtained share phenotypic and functional characteristics with freshly isolated FDC.

Optimizing follicular dendritic cell isolation by discontinuous gradient centrifugation and use of the magnetic cell sorter (MACS)

Follicular dendritic cells (FDC) contribute minimally to the total cell population of lymphatic tissue. In order to obtain higher numbers of viable FDC with only a small fraction of contaminating cells the following procedure was developed. Subsequent to the usual mechanical and enzymatical digestion of human tonsils, single cells were layered on top of a discontinuous bovine albumin gradient and centrifuged at 8500 x g. The suspension collected from the 1.052-1.030 interphase contained an average of 10.5% FDC. Next, the preparation was subjected to a new step involving separation of FDC previously treated with biotin-labelled KiM4 monoclonal antibody, raised against FDC, and attached via biotin-streptavidin bonding to streptavidin-conjugated paramagnetic beads. Purification on a magnetic cell sorter (MACS) yielded 3.3-10.1 x 10(6) cells with an average FDC content of 78.4%. The viability and morphology of the resulting FDC population was examined using trypan blue staining or electron microscopy. This technique will permit in vitro studies and long term cultures with FDC isolated from human lymphatic tissue.

Infection of accessory dendritic cells by human immunodeficiency virus type 1

Many details of the pathogenesis of the human immunodeficiency virus type 1 remain to be elucidated. Details of how the virus gains entry via the mucosal surface upon sexual contact or during breast feeding remain obscure. The means by which the infection travels throughout the body as well as the nature of the major reservoirs of virus infection remains, for the most part, unknown. Recent studies raise the possibility that cells of the Langerhans/dendritic lineage play a central role in human immunodeficiency virus (HIV-1) infection and pathogenesis. It has been known for several years that veiled dendritic cells in the circulation as well as skin Langerhans are infected in people with prolonged HIV-1 infections. More recently it has been found that a large burden of viral DNA sequences is found, not only in the circulating T-cell population, but also in a population that is defined as a non-T, non-B, non-monocyte/macrophage population rich in T-helper dendritic cells. Detailed analysis of infection of primary blood-derived T-helper dendritic cells by HIV-1 shows that such cells are the most susceptible cells in the blood to infection by this virus. The cells also produce much more virus per cell than do purified populations of other blood mononuclear cells. Moreover, primary blood-derived T-helper dendritic cells are not killed by infection by HIV-1. These cells are susceptible to lymphotropic, monocyte tropic, and primary isolates of HIV-1. The sensitivity of primary blood-derived T-helper dendritic cells to infection by HIV-1 has been shown to be attributable to rapid uptake of virus particles as well as rapid synthesis of viral DNA. Subsequent steps of virus replication also occur more rapidly and more efficiently in populations of primary blood-derived T-helper dendritic cells than they do in purified preparations of blood-derived T cells and monocyte/macrophages. Studies with primates using the simian immunodeficiency virus (SIV) show that dendritic cells at the surface of sexual mucosa are rapidly infected upon exposure to high concentrations of the virus. SIV is also produced in abundance in Langerhans cells located at the surface of the sexual mucosa in animals infected for prolonged periods of time.

Isolation of normal human follicular dendritic cells and CD4-independent in vitro infection by human immunodeficiency virus (HIV-1)

Immunohistological and electron microscopy studies of lymph nodes from patients infected with the human immunodeficiency virus 1 (HIV-1) demonstrated that follicular dendritic cells (FDC), the antigen-presenting cells of the B cell system, contain and may produce the virus. To elucidate the mode of infection of FDC with HIV-1 in vitro we developed an improved method for the preparation of single-cell suspensions of viable FDC with high purity (greater than 90% FDC). These isolated FDC were subjected to human T cell leukemia virus IIIB infection, which was monitored after 4 days in culture using the polymerase chain reaction. We were able to demonstrate that normal human FDC are highly susceptible to infection by HIV-1. Inhibition experiments with the monoclonal antibody OKT4a demonstrate that this infection is independent of the CD4 molecule.

Nerve growth factor receptor expression on dendritic reticulum cells in follicular lymphoid proliferations

Using an antibody to the nerve growth factor receptor (NGFR), we examined dendritic reticulum cells (DRCs) immunohistochemically in 62 formalin-fixed, paraffin-embedded lymph nodes from patients with reactive follicular hyperplasia or with various types of lymphoma. A dendritic staining pattern within germinal centers was present in 25 of 26 routinely processed lymph nodes with reactive follicular hyperplasia. In contrast, dendritic staining with anti-NGFR was present within neoplastic follicles in only three of 28 follicular lymphomas. Staining of benign, residual germinal centers with anti-NGFR was present in mantle zone lymphoma and Hodgkin's disease. These findings suggest a possible role for the NGFR in the maturation and/or activation of normal DRCs. The loss of NGFR expression in most follicular lymphomas indicates that DRCs are altered as part of the neoplastic process. The possibility that DRCs may play a role in the pathogenesis of follicular lymphoma is suggested.

Human follicular dendritic cells: isolation and characteristics in situ and in suspension

Follicular dendritic cells (FDC) in human tonsils, either in situ in follicular germinal centres or isolated from tissue, were characterized by immunohistochemical, enzyme cytochemical and electron microscopical methods. Using polyclonal and monoclonal antibodies, expression of DRC-1, Ki-M4, HLA-DR, CR1, C1q antigens, a macrophage marker, and surface IgG and IgM were found on isolated FDC and on FDC in situ. None of these reagents proved to be specific for FDC, e.g. the FDC-directed antibodies DRC-1 and Ki-M4 labelled B lymphocytes in cytofluorography. Enzyme cytochemical staining revealed activities of non-specific esterase, acid alpha-naphthylacetate esterase and ATPase in germinal centres and in freshly isolated FDC. Immunohistochemistry demonstrated a weak expression of CD4 by a fraction of isolated FDC, which was confirmed by two-colour immuno-staining and immuno-electron microscopy.

Sarcomatoid tumours of lymph nodes showing follicular dendritic cell differentiation

Putative sarcomas of follicular dendritic cells are extremely uncommon and only small case numbers have been clearly documented. A major difficulty in their delineation has been the persistent controversy over the phenotype and ontogeny of normal follicular dendritic cells. Two new cases arising in adult females are presented herein, both of which had initially been mistaken for metastases from a true soft tissue sarcoma. Their morphology, immunophenotype, and ultrastructure (in one case) are described in order to aid their wider recognition. In the light of these findings, the nature and origin of follicular dendritic cells are discussed.

Isolation and long-term cultivation of human tonsil follicular dendritic cells

Highly purified follicular dendritic cells (FDC) were isolated from human tonsils and cultivated for up to 150 days. The cell separation method employed produced pure aggregates (FDC-clusters) composed of FDC and germinal center lymphoid cells, useful for the analysis of the relationship between these two cell types and of the behavior of FDC in culture. During the first few days of culture, lymphoid cells located between FDC extensions survived better than those which were free or partly covered by FDC. After 6 days, the lymphoid population degenerated and only the FDC survived. The unique antigenic pattern of FDC (positive for HLA-DR. DRC-1, CD14b, CD21, CD23, CD35) disappeared within a few days of culture. Recombinant interferon-gamma exerted a positive effect either on retaining HLA-DR expression or on the reexpression of these antigens by FDC. HLA-ABC antigens were traced until the 10th day and desmosomal junctions until the 14th day. Subsequently, FDC presented peculiar features, including oval and rhomboid shapes, one to ten nuclei, fine amoeboid extensions, stress fibers and a radical dense zone in their cytoplasm. FDC possessed actin, tubulin and vimentin, but neither desmin nor cytokeratin. After 40 days of culture, FDC enlarged and were covered with abundant membrane extensions. Even when kept as long as 150 days in vitro. FDC did not proliferate in any of the culture conditions employed.

Vimentin immunostaining in fibroblastic reticulum cells within human reactive and neoplastic lymphoid follicles

We analyzed the distribution of fibroblastic reticulum cells (FRCs), stationary cells of lymphoid tissues, as visualized by the anti-vimentin (V9) monoclonal antibody in human reactive and neoplastic lymphoid follicles, by using immunoenzymatic and immunofluorescence methods on fixed and paraffin-embedded tissue sections from 37 lymphoid specimens with reactive disorders and 10 specimens with nodular/follicular non-Hodgkin's lymphomas (NHLs). The pattern of distribution of the vimentin-positive (VIM+) FRCs was compared with that of follicular dendritic reticulum cells (DRCs) as visualized by anti-S-100 protein antibody. Elongate VIM+ FRCs intimately attached to reticulum fibers were randomly distributed in the paracortical and interfollicular areas of lymph nodes, whereas they were recognized specifically in the mantle zones of the secondary follicles, mostly in the outer margins. Germinal centers were consistently devoid of VIM+ FRCs. Comparative analysis on serial sections as well as paired immunoperoxidase and double immunofluorescence studies demonstrated that there was a sharp difference between the patterns of intrafollicular distribution of VIM+ FRCs and S-100 protein-positive (S-100+) DRCs without juxtaposition, the FRCs being confined to the mantle zones. In the 10 nodular/follicular NHLs VIM+ FRCs could be observed in the thinned mantles of neoplastic nodules displaying a corona-like pattern that accentuated the boundaries of the nodules. The results of this study support the view that the intrafollicular distribution of VIM+ FRCs is specific for the mantle zone. The different microenvironmental organization within the follicles of VIM+ FRCs and S-100+ DRCs suggests that FRCs or at least VIM+ FRCs are stationary cells strictly related to the mantle zone microenvironment, where they may play a role in supposed sustentacular and immunologic functions similar to that of DRCs in the germinal center microenvironment.

Induction of antigen expression of follicular dendritic cells in a monoblastic cell line. A contribution to its cellular origin

Experiments were carried out to elucidate the cellular origin of the dendritic reticulum cell (DRC). The monoblastic cell line THP-1, the histiocytic cell line U-937, and the mononuclear cell fraction from peripheral blood (PMC) were stimulated with supernatants from lectin-stimulated peripheral blood lymphocytes and from stimulated T- and B-cell lines. Differentiation towards DRC was assessed by immunocytochemical demonstration of the DRC-specific antigen Ki-M4. Supernatants from isolated peripheral T lymphocytes and from T- and B-cell lines were capable of stimulating THP-1 to Ki-M4 antigen expression, whereas U-937 and the PMC fraction remained negative for this antigen throughout the experiments. These results provide further evidence for a relationship of DRCs with the mononuclear-phagocytic cell system and hence for their bone marrow origin. Furthermore, the data suggest that soluble factors of T and/or B cells are involved in mediating the differentiation process of precursor cells to DRC.