How do follicular dendritic cells interact intimately with B cells in the germinal centre?

Cellular composition of the tumor microenvironment

In addition to malignant cells, the tumor microenvironment also includes nonmalignant cells, secreted proteins, and blood vessels that surround and support the growth of the tumor. Interactions between the various components of the tumor microenvironment are significant; tumor cells can change the nature of the microenvironment, and conversely, the microenvironment can affect how a tumor grows and spreads. The structure and composition of the tumor microenvironment varies among different types of cancers and between patients. This paper focuses on the composition and function of the tumor microenvironment in hematologic malignancies with a specific focus on B-cell lymphomas.

Tertiary lymphoid organ development coincides with determinant spreading of the myelin-specific T cell response

While the role of T cells has been studied extensively in multiple sclerosis (MS), the pathogenic contribution of B cells has only recently attracted major attention, when it was shown that B cell aggregates can develop in the meninges of a subset of MS patients and were suggested to be correlates of late-stage and more aggressive disease in this patient population. However, whether these aggregates actually exist has subsequently been questioned and their functional significance has remained unclear. Here, we studied myelin basic protein (MBP)-proteolipid protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE), which is one of the few animal models for MS that is dependent on B cells. We provide evidence that B cell aggregation is reflective of lymphoid neogenesis in the central nervous system (CNS) in MBP-PLP-elicited EAE. B cell aggregation was present already few days after disease onset. With disease progression CNS B cell aggregates increasingly displayed the phenotype of tertiary lymphoid organs (TLOs). Our results further imply that these TLOs were not merely epiphenomena of the disease, but functionally active, supporting intrathecal determinant spreading of the myelin-specific T cell response. Our data suggest that the CNS is not a passive "immune-privileged" target organ, but rather a compartment, in which highly active immune responses can perpetuate and amplify the autoimmune pathology and thereby autonomously contribute to disease progression.

HSP90α deficiency does not affect immunoglobulin gene hypermutation and class switch but causes enhanced MHC class II antigen presentation

Heat shock protein 90 (HSP90) is a molecular chaperone required for efficient antigen presentation and cross-presentation. In addition, HSP90 was recently reported to interact with and stabilize the activation-induced cytidine deaminase (AID) and plays a critical role in immunoglobulin gene hypermutation and class switch recombination. In mice and humans, there are two HSP90 isoforms, HSP90α and HSP90β, but the in vivo role of each isoform remains largely unknown. Here we have analyzed humoral immune responses in HSP90α-deficient mice. We found that HSP90α deficiency did not affect AID protein expression. B cell development and maturation, as well as immunoglobulin gene hypermuation and class switch, occurred normally in HSP90α-deficient mice. However, antibody production to a T-dependent antigen was elevated in the mutant mice and this was associated with enhanced MHC class II antigen presentation to T helper cells by dendritic cells. Our results reveal a previously unidentified inhibitory role for HSP90α isoform in MHC class II antigen presentation and the humoral immune response. Along with our recent finding that HSP90α is required for antigen cross-presentation, these results suggest that HSP90α controls the balance of humoral and cellular immunity by dictating the fate of presentation of exogenous antigen.

Extranodal follicular dendritic cell sarcoma with rapid growth in parapharynx: a case report

Follicular dendritic cell sarcoma (FDCS) is a rare malignancy arising from the antigen-presenting cells in the lymph node and extranodal tissue. We describe a 31-year-old male patient who presented with a swelling of the left parapharynx. The radiologic findings showed a 4.7×4.5×1.9 cm-sized, ill-defined mass in the left parapharyngeal space. A fine-needle aspiration cytology was performed and it showed scattered, irregular, cohesive clusters of tumor cells with a spindle-to-ovoid shape with irregular contours in a background of lymphocytes. Based on these findings, a diagnosis of spindle cell neoplasm was made. The surgically resected tumor was composed of elongated, ovoid or polygonal cells showing positive immunohistochemistry for CD21, CD23, and CD35. Postoperatively, the residual tumor was observed to undergo a rapidly growth. There is an overlap in the cytologic and histologic findings between FDCS of the parapharynx and other tumors. Pathologists should therefore be aware of its characteristics not only to provide an accurate diagnosis but also to recommend the appropriate clinical management.

Human decidual stromal cells secrete C-X-C motif chemokine 13, express B cell-activating factor and rescue B lymphocytes from apoptosis: distinctive characteristics of follicular dendritic cells

BACKGROUND

Decidual stromal cells (DSCs) have classically been considered fibroblastic cells, although their function, cell lineage and origin are not fully understood. We previously demonstrated that human DSCs showed similarities with follicular dendritic cells (FDCs): DSCs expressed FDC-associated antigens, both types of cells are contractile and both are related to mesenchymal stem cells (MSCs). To further characterize DSCs, we investigated whether DSCs and FDCs share any distinctive phenotypical and functional characteristics.

METHODS

Human FDC lines were obtained from tonsillectomy samples, human DSC lines from elective termination of pregnancy samples and human MSC lines from bone marrow aspirates. We isolated DSC, FDC and MSC lines and compared their characteristics with flow cytometry and enzyme-linked immunosorbent assay. Cell lines were cultured with tumour necrosis factor (TNF) and lymphotoxin (LT)α(1)β(2), cytokines involved in FDC differentiation. Cell lines were also differentiated in culture after exposure to progesterone and cAMP, factors involved in the differentiation (decidualization) of DSC.

RESULTS

Like MSCs, DSCs and FDCs expressed MSC-associated antigens (CD10, CD29, CD54, CD73, CD106, α-smooth muscle actin and STRO-1) and lacked CD45 expression, and all three types of cell line showed increased expression of CD54 (ICAM-1) and CD106 (VCAM-1) when cultured TNF and LTα(1)β(2). DSCs and FDCs, however, exhibited characteristics not observed in MSCs: DSCs expressed FDC-associated antigens CD14, CD21 and CD23, B cell-activating factor and secreted C-X-C motif chemokine 13. Moreover, DSC lines but not MSC lines inhibited the spontaneous apoptosis of B lymphocytes, a typical functional attribute of FDC. During culture with progesterone and cAMP, FDCs, like DSCs but in contrast to MSCs, changed their morphology from a fibroblastic to a rounder shape, and cells secreted prolactin.

CONCLUSIONS

Our results suggest that DSCs and FDCs share a common precursor in MSCs but this precursor acquires new capacities when it homes to peripheral tissues. We discuss these shared properties in the context of immune-endocrine regulation during pregnancy.

STAT6 and JAK1 are essential for IL-4-mediated suppression of prostaglandin production in human follicular dendritic cells: opposing roles of phosphorylated and unphosphorylated STAT6

Prostaglandins (PGs) are emerging as important immune mediators. Since our first report on the expression of prostacyclin synthase in the germinal centers, we have investigated production mechanisms and biological functions of PG using human follicular dendritic cell (FDC)-like cells. In the previous report, we observed that TGF-β enhances PG production, and IL-4 prevents this upregulation. To elucidate the inhibitory mechanism of IL-4, its effects on the key enzyme leading to PG production were analyzed in this study. IL-4 but not IL-10 inhibited TGF-β-induced COX-2 expression at both mRNA and protein levels. Next the early signaling molecules of IL-4 were identified by siRNA technology. IL-4 induced tyrosine phosphorylation of STAT1, 3, and 6, but only JAK1-STAT6 pathway was responsible for the prevention of COX-2 augmentation and PG production. Phosphorylated STAT6 accumulated in the nucleus rapidly upon IL-4 addition, and the complete inhibition of COX-2 upregulation required 24 h of pretreatment with IL-4, implying that newly transcribed molecules mediate the inhibitory signals downstream of STAT6. Interestingly, unphosphorylated STAT6 proteins were constitutively expressed in the nucleus, and depletion of STAT6 impaired background level expression of COX-2 and PGs. Our results highlight the crucial roles of TGF-β and IL-4 in the regulation of PG production, which lead us to suggest that T cells play an important role in FDC production of PGs.

Early steps of follicular lymphoma pathogenesis

Follicular lymphoma (FL) pathogenesis is a complex and fascinating multi-hit process, escalating along successive derailments of the distinctive molecular and cellular mechanisms paving B-cell differentiation and activation. This progressive subversion of B-cell receptor diversification mechanisms and B-cell homeostasis likely occurs during a protracted preclinical phase of asymptomatic growth, in which premalignant clones already disseminate and establish "niches" in secondary lymphoid organs. Following FL diagnosis, a parallel indolent behavior is observed in most patients, slowly progressing over a period of many years, to eventually generate a highly refractory (and in some case transform into an aggressive subtype of) lymphoma. Novel insights in human germinal center B-cell biology recently allowed a more comprehensive understanding of the various illegitimate events sequentially involved in the premalignant progression phases. In this review, we will discuss how these new data have modified our perception of early FL pathogenesis, the new questions and challenges it opened up, and how this knowledge could impact on innovative programs of early detection, follow-up, and patient management.

Wnt5a is secreted by follicular dendritic cells to protect germinal center B cells via Wnt/Ca2+/NFAT/NF-κB-B cell lymphoma 6 signaling

Follicular dendritic cells (FDCs) protect germinal center (GC) B cells from rapid apoptosis to allow their survival and maturation. In this article, we show that FDCs normally produce and secrete Wnt5a to protect GC B cells. Wnt5a production is upregulated by polyI:C. Purified Wnt5a protects GC B cells from apoptosis in a dose-dependent manner. GC B cells are protected by FDC coculture or conditioned medium, and the protection is inhibited significantly by anti-Wnt5a Ab, suggesting a major role of Wnt5a in the FDC-mediated GC B cell protection. A calcium chelator BAPTA-AM blocks the Wnt5a-mediated GC B cell protection, implying a role of Wnt/Ca(2+) signaling in the GC B cell survival. Wnt5a and calcium ionophore activate NFATc1, NFATc2, NF-κB, and B cell lymphoma 6 (BCL-6) promptly and upregulate CD40 expression in GC B and Ramos cells, whereas p53 and JNK are not upregulated or activated. Cyclosporine A inhibits the Wnt5a and calcium-induced activation of NF-κB and BCL-6 in Ramos cells, supporting a role of β-catenin-independent Wnt/Ca(2+)/NFAT/NF-κB-BCL-6 signaling. Our data support that Wnt5a is a novel survival factor for GC B cells and might be a potential target for the regulation of B cell immunity.

HIV-1 and influenza antigens synthetically linked to IgG2a Fc elicit superior humoral responses compared to unmodified antigens in mice

Using murine IgG subclass molecules (IgG1 or IgG2a) synthetically fused to HIV-1 or influenza test antigens, we explored the potential for IgG Fc scaffolds to augment immunogenicity. Each antigen (Ag) was grafted onto a hinge-Fc scaffold containing all critical residues necessary for interaction with effector cells, thus retaining effector functions of the native IgG subclass. We hypothesized that the differential affinity of FcγRs for specific IgG subclasses would influence the magnitude of immune responses elicited by immunization with an Ag-IgG Fc fusion vaccine. We demonstrate here that the antigen-specific humoral response elicited by Ag-IgG2a fusion vaccines is at least tenfold greater than that elicited by native antigen, that this response is superior to that elicited by Ag-IgG1, and that the augmented antigen-specific humoral response elicited is Fcγ receptor-dependent.

The role of the lymphatic system in vaccine trafficking and immune response

The development and improvement of vaccines has been a significant endeavor on the part of the medical community for more than the last two centuries, and the success of these efforts is obvious when one considers the millions of lives that have been saved. Recent work in the field of vaccines, however, indicates that vaccines may be developed for even more challenging diseases than those previously addressed. It will be important in achieving this feat to account for the physical and chemical processes related to vaccine trafficking, rather than solely relying on our knowledge of the pathogen and our empirical experience. A thorough understanding of the lymphatic system is essential considering the role it plays in antigen trafficking and all immunological activity. This review describes the results of recent work that provides insight into the physiological processes of the lymphatic system and its various components with an emphasis on vaccine antigen trafficking from the administration site to secondary lymphoid tissues and the ensuing immune response. The review also discusses current challenges in designing vaccines and presents modern strategies for designing vaccines to better interface with the lymphatic system.

Activation-induced cytidine deaminase and aberrant germinal center selection in the development of humoral autoimmunities

Humoral immunity, which is the branch of the immune system governed by B cells, protects the body from extracellular pathogens through the secretion of immunoglobulins. Given the unpredictability of exogenous antigens, B cells must be accommodating to numerous genetic alterations to mold immunoglobulin specificity to recognize offending pathogens. Abnormalities in this process leave the host susceptible to permanent pathological modifications and in particular humoral autoimmunities in which secreted immunoglobulins mistake host proteins as pathogenic targets. Underlying the development of self-reactive immunoglobulins is activation-induced cytidine deaminase (AID), a mutagenic enzyme responsible for modifying the specificity of B cells by producing point mutations at the immunoglobulin gene locus. Ideally, these mutations result in an increased affinity for exogenous antigens. However, in pathological scenarios, these mutations produce or enhance a B cell's ability to target the host. AID-induced mutations occur in the germinal center microenvironment of peripheral lymphoid tissue, where pathogenic B-cell clones must evade overwhelming selection pressures to be released systemically. Recent research has revealed numerous genes and pathways responsible for eliminating self-reactive clones within the germinal center. On the basis of these studies, this review aims to clarify the link between AID and the generation of pathogenic immunoglobulins. Furthermore, it describes the selective pressures that pathogenic B cells must bypass within the germinal center to secrete immunoglobulins that ultimately result in disease.

Oxidative stress induces protein and DNA radical formation in follicular dendritic cells of the germinal center and modulates its cell death patterns in late sepsis

Profound depletion of follicular dendritic cells (FDCs) is a hallmark of sepsis-like syndrome, but the exact causes of the ensuing cell death are unknown. The cell death-driven depletion contributes to immunoparalysis and is responsible for most of the morbidity and mortality in sepsis. Here we have utilized immuno-spin trapping, a method for detection of free radical formation, to detect oxidative stress-induced protein and DNA radical adducts in FDCs isolated from the spleens of septic mice and from human tonsil-derived HK cells, a subtype of germinal center FDCs, to study their role in FDC depletion. At 24h post-lipopolysaccharide administration, protein radical formation and oxidation were significantly elevated in vivo and in HK cells as shown by ELISA and confocal microscopy. The xanthine oxidase inhibitor allopurinol and the iron chelator desferrioxamine significantly decreased the formation of protein radicals, suggesting the role of xanthine oxidase and Fenton-like chemistry in radical formation. Protein and DNA radical formation correlated mostly with apoptotic features at 24h and necrotic morphology of all the cell types studied at 48h with concomitant inhibition of caspase-3. The cytotoxicity of FDCs resulted in decreased CD45R/CD138-positive plasma cell numbers, indicating a possible defect in B cell differentiation. In one such mechanism, radical formation initiated by xanthine oxidase formed protein and DNA radicals, which may lead to cell death of germinal center FDCs.

Isolated lymphoid follicles in colon: switch points between inflammation and colorectal cancer?

Gut-associated lymphoid tissue is supposed to play a central role in both the organization of colonic repair mechanisms and colorectal carcinogenesis. In inflammatory conditions, the number, diameter and density of isolated lymphoid follicles (ILFs) increases. They are not only involved in immune surveillance, but their presence is also indispensable in normal mucosal regeneration of the colon. In carcinogenesis, ILFs may play a dual role. On the one hand they may support tumor growth and the metastatic process by vascular endothelial growth factor receptor signaling and producing a specific cytokine and cellular milieu, but on the other hand their presence is sometimes associated with a better prognosis. The relation of ILFs to bone marrow derived stem cells, follicular dendritic cells, subepithelial myofibroblasts or crypt formation, which are all involved in mucosal repair and carcinogenesis, has not been directly studied. Data about the putative organizer role of ILFs is scattered in scientific literature.

IL-4 and IL-13 suppress prostaglandins production in human follicular dendritic cells by repressing COX-2 and mPGES-1 expression through JAK1 and STAT6

Originally discovered as a B cell growth and differentiation factor, IL-4 displays a variety of functions in many different cell types. Germinal center T cells are abundant producers of IL-4. In a recent report, we demonstrated that IL-4 inhibits prostaglandins (PGs) production in follicular dendritic cell (FDC)-like cells, HK. To understand the inhibitory mechanisms of IL-4, its effects on the biosynthesis of enzymes in charge of PG production were assessed in this study. Although IL-4 did not affect COX-1 expression, it specifically inhibited LPS-induced COX-2 biosynthesis at mRNA and protein levels. Protein expression of mPGES-1, a downstream enzyme of COX-2, was also markedly diminished by IL-4 but not by IL-10, maximizing the inhibitory activity. Next, we attempted to identify the early signaling molecules that led to this inhibition of COX-2 expression. Although IL-4 induced tyrosine phosphorylation of JAK1 and TYK2, RNA interference experiments revealed that only JAK1 was responsible for the IL-4-stimulated STAT6 phosphorylation. Knocking down JAK1 and STAT6 ablated the inhibitory effect of IL-4 on COX-2 expression and significantly reduced production of PGE(2) and prostacyclin. Similar results were obtained with IL-13. Pharmacologic inhibitors of ERK and p38 mitogen-activated protein kinases inhibited the COX-2 upregulation. However, IL-4 did not affect LPS-induced phosphorylation of ERK and p38. These results stress the essential roles of JAK1 and STAT6 in the early signaling pathway of IL-4 and IL-13 leading to suppression of COX-2 expression and repression of PG production by HK cells. Our results suggest that T cells via IL-4 play a regulatory role in PG generation in FDC. IL-4 therapeutics may be applied to immune disorders where normal and ectopic expression of germinal center reactions needs to be regulated.

Vitamin A and retinoic acid in the regulation of B-cell development and antibody production

Signaling by vitamin A through its active metabolite retinoic acid (RA) is critical for the normal development and functions of the hematopoietic and immune systems. B cells, as both factories for antibody production and part of the immune regulatory system, are critical to a successful vaccination response. RA is a factor in the development and competence of mature B cells, in B cell proliferation, and in the regulation of transcription factors associated with B cell differentiation, class switch recombination, and the generation of antibody-secreting plasma cells. Emerging evidence suggests that RA can function alone and in combination with other immune system stimuli to augment the formation of germinal centers, leading to increased primary and secondary antibody responses. Taken together, RA could be a useful component in vaccine strategies and/or for immunotherapy.

Follicular dendritic cell-induced microRNA-mediated upregulation of PRDM1 and downregulation of BCL-6 in non-Hodgkin's B-cell lymphomas

B-cell lymphoma 6 (BCL6) and PR domain containing 1 (PRDM1) are considered as master regulators for germinal center (GC) formation and terminal B-cell differentiation. Dysregulation of BCL6 and PRDM1 has been associated with lymphomagenesis. Here, we show for the first time that direct cell-cell contact between follicular dendritic cells (FDC) and B-lymphocytes, by influencing the expression of a set of microRNAs (miRNAs), regulates the expression of BCL6 and PRDM1. We identify that, on cell adhesion to FDC, FDC induces upregulation of PRDM1 expression through downregulation of miR-9 and let-7 families and induces downregulation of BCL-6 through upregulation of miR-30 family in B-lymphocytes and lymphoma cells. We further demonstrate that the miR-30 family directly controls BCL-6 expression and miR-9-1 and let-7a directly control PRDM-1 expression through targeting their 3'UTR, mediating the FDC effect. Our studies define a novel regulatory mechanism in which the FDC, through induction of miRNAs in B-lymphocytes, orchestrates the regulation of transcription factors, promotes germinal center B-cell survival and differentiation. Dysregulation of miRNAs may interfere with B-cell survival and maturation, thus representing a novel molecular mechanism, as well as a potential therapeutic target in B-cell lymphomas.

The follicular lymphoma microenvironment: From tumor cell to host immunity

Follicular lymphoma (FL) is a neoplasm derived from follicular germinal center cells. Like the normal components of this lymphoid structure, FL cells interact with various immune cells, such as the follicular helper T cells, suppressor regulatory T cells, dendritic cells, and histiocytes, that define the tumor microenvironment. Gene expression studies have shown that the nature of the tumor microenvironment predicts survival in patients with FL and may influence the response to immunotherapy and risk of transformation. The immune system may either promote or constrain tumor cell development, depending on the relative distribution and activation status of various cell subpopulations. The prognostic value of germline genetic variants of some immune genes suggests that the host genetic background may also influence the biology of FL. Some efforts have been carried out to validate those findings and provide clinical tools that may be used at the time of diagnosis.

Progressive multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system, which starts in the majority of patients with a relapsing/remitting MS (RRMS) course , which after several years of disease duration converts into a progressive disease. Since anti-inflammatory therapies and immune modulation exert a beneficial effect at the relapsing/remitting stage of the disease, but not in the progressive stage, the question was raised whether inflammation drives tissue damage in progressive MS at all. We show here that also in progressive MS, inflammation is the driving force for brain injury and that the discrepancy between inflammation-driven tissue injury and response to immunomodulatory therapies can be explained by different pathomechanisms acting in RRMS and progressive MS.

Interleukin-15 enhances proliferation and chemokine secretion of human follicular dendritic cells

The germinal centre (GC) is a specialized microenvironment where high-affinity antibodies are produced through hypermutation and isotype switching. Follicular dendritic cells (FDCs) are the stromal cells of the GC. The timely expansion and establishment of an FDC network is essential for a protective GC reaction; however, only a few factors modulating FDC development have been recognized. In this study, we report that interleukin-15 (IL-15) enhances human primary FDC proliferation and regulates cytokine secretion. The FDCs express IL-15 receptor complexes for IL-15 signal transduction as well as for specific binding. Moreover, the secretion of chemokines CCL-2, CCL-5, CXCL-5 and CXCL-8 was reduced by blocking IL-15 signalling while the secretion of other cytokines, and the expression of CD14, CD44, CD54 (ICAM-1) and CD106 (VCAM-1) proteins remained unchanged. These results suggest that IL-15 plays a crucial role in the development of FDC networks during GC reaction, offering a new target for immune modulation.

The possible role of isolated lymphoid follicles in colonic mucosal repair

The continuous reformation and rapid repair of the colonic mucosa is essential for avoiding the aggregation of pernicious mutations induced by bacterial, toxic, or mitogenic factors. Gut-associated lymphoid tissue is supposed to play a central role in the organization of the repair mechanisms. In inflammatory conditions, the number, the diameter and the density of isolated lymphoid follicles (ILFs) are increasing. They are involved not just in immune surveillance, but their presence is also indispensable in normal mucosal regeneration of the colon. The relation of ILFs to the components of mucosal renewal such as bone marrow derived stem cells, follicular dendritic cells, subepithelial myofibroblasts or crypt formation has not been directly studied, and data about their putative organizer role are scattered in scientific literature. Whether they act as a regenerative pool containing stem cells in case of mucosal damage, or they are responsible only for the optimal cytokine milieu for the differentiation of immigrating stem cells is a question under debate. Our aim is to review the relation of ILFs to the different elements of colonic mucosal repair.

Class II beta-tubulin is a novel marker for human tonsillar M cells and follicular dendritic cells

OBJECTIVE

Membranous (M) cell of the human palatine tonsil is an antigen entry site for mucosal infection, but its location is obscure in histological sections. Recently, a microarray analysis has demonstrated that clusterin, annexin A5, CD44, MMP14, and beta-tubulin are candidate genes of M cell marker in mice. Among these genes, we here describe class II beta-tubulin as a new marker for human tonsillar M cells and follicular dendritic cells (FDCs), and present its usefulness for diagnosis of angioimmunoblastic T-cell lymphomas (AILTs).

MATERIALS AND METHODS

Immunohistochemistry and Western blotting for class II beta-tubulin were performed using 81 cases of lymphoid, gastrointestinal and thyroid tissues, and an FDC cell line, respectively. Double immunostaining with clusterin and class II beta-tubulin were carried out.

RESULTS

Class II beta-tubulin localized the M cells and FDCs in the palatine tonsils (10/10, 100%) and adenoids (10/10, 100%). It was colocalized with clusterin in the palatine tonsils. However, class II beta-tubulin staining did not identify intestinal M cells in the intestines. Immunoblot analysis revealed that class II beta-tubulin expression was upregulated in HK cells, a normal FDC cell line. Class II beta-tubulin immunostaining highlighted hyperplastic FDC meshworks in all AILTs (14/14, 100%).

CONCLUSION

Class II beta-tubulin is a specific histochemical marker for human tonsillar M cells and FDCs. Thus, class II beta-tubulin immunostaining may be useful to identify tonsillar M cells and to diagnose FDC proliferative lesions such as AILT.

IL-21 and IL-10 have redundant roles but differential capacities at different stages of Plasma Cell generation from human Germinal Center B cells

The GC is the anatomical site where antigen-activated B cells differentiate into PC, producing high-affinity antibodies in physiological and pathological states. PC differentiation is regulated by multiple factors within the GC microenvironment, including cytokines. IL-21, a recently identified type I cytokine produced by GC-Th cells, promotes differentiation of human B cells into ISC. In this study, we investigated in detail the functional role of IL-21 in the course of GC-B cell differentiation into terminally differentiated PC compared with that of IL-10, a well-known PC differentiation factor. IL-21 had a greater capacity to initiate PC differentiation from CD77(+) centroblasts than IL-10 by strongly inducing PC transcription factors through activation of STAT3; however, IL-10 was more potent than IL-21 in generating CD138(+) PC from CD20(-)CD38(++) plasmablasts in the terminal stage of GC-B cell differentiation. This differential effect of IL-21 and IL-10 was reflected in receptor expression on B cell subsets emerging in the course of differentiation. Our studies have revealed that IL-21 is a critical decision-maker for driving initial PC differentiation at the stage of CD77(+) centroblasts, yet IL-10 is more effective in producing IgG by generating terminally differentiated CD138(+) PC at the later stage of PC differentiation in the GC.

Mice deficient for CD137 ligand are predisposed to develop germinal center–derived B-cell lymphoma

In the germinal center (GC), B cells proliferate dramatically and diversify their immunoglobulin genes, which increases the risk of malignant transformation. The GC B-cell reaction relies on crosstalk with follicular dendritic cells (FDCs), to which the costimulatory receptor CD137 on FDCs and its ligand on GC B cells potentially contribute. We report that mice deficient for CD137 ligand (CD137L) are predisposed to develop B-cell lymphoma, with an incidence of approximately 60% at 12 months of age. Lymphoma membrane markers were characteristic of GC B cells. Longitudinal histologic analysis identified the GC as site of oncogenic transformation and classified 85% of the malignancies found in approximately 200 mice as GC-derived B-cell lymphoma. To delineate the mechanism underlying lymphomagenesis, gene expression profiles of wild-type and CD137L-deficient GC B cells were compared. CD137L deficiency was associated with enhanced expression of a limited gene set that included Bcl-10 and the GC response regulators Bcl-6, Spi-B, Elf-1, Bach2, and activation-induced cytidine deaminase. Among these are proto-oncogenes that mediate GC B-cell lymphoma development in humans. We conclude that CD137L ordinarily regulates the GC B-cell response and thereby acts as a tumor suppressor.

Toll-like receptor 3 ligand and retinoic acid enhance germinal center formation and increase the tetanus toxoid vaccine response

Immunizations with T-cell-dependent antigens induce the formation of germinal centers (GC), unique lymphoid microenvironments in which antigen-activated B cells undergo class switching, affinity maturation, and differentiation into memory B cells. Poly(I:C) (PIC), a double-stranded RNA, and retinoic acid (RA), a metabolite of vitamin A which induces cell differentiation, have been shown to augment both primary and memory anti-tetanus toxoid (anti-TT) IgG responses. However, their influence on the GC reaction is unknown. In the present study, 6-week-old C57BL/6 mice were immunized with TT and cotreated with PIC, RA, or both. The splenic GC reaction was evaluated using immunofluorescence staining 10 days after TT priming. Each treatment enhanced the TT-induced GC formation (number of GC/follicle and GC area) about two- to threefold, which correlated with the titers of plasma anti-TT immunoglobulin G (IgG). Isotype switching to IgG1 was dramatically stimulated, with the greatest increase in IgG1-positive GC B cells induced by RA-PIC (P < 0.001). Moreover, PIC alone and RA-PIC robustly promoted the formation of the follicular dendritic cell (FDC) network in the GC light zone. PIC and RA-PIC also increased IgG1-positive B cells in the periarterial lymphatic sheath regions, where most IgG1-positive cells were plasma cells (CD138/syndecan-1 positive), suggesting that plasma cell generation was also enhanced in non-GC regions. The stimulation of several processes, including antigen-induced GC formation, isotype switching, FDC network formation within GC, and plasma cell differentiation by RA and/or PIC, suggests that this nutritional-immunological combination could be an effective means of promoting a robust vaccine response.

Anti-PrP Mab 6D11 suppresses PrP(Sc) replication in prion infected myeloid precursor line FDC-P1/22L and in the lymphoreticular system in vivo

The pathogenesis of prion diseases is related to conformational transformation of cellular prion protein (PrP(C)) into a toxic, infectious, and self-replicating conformer termed PrP(Sc). Following extracerebral inoculation, the replication of PrP(Sc) is confined for months to years to the lymporeticular system (LRS) before the secondary CNS involvement results in occurrence of neurological symptoms. Therefore, replication of PrP(Sc), in the early stage of infection can be targeted by therapeutic approaches, which like passive immunization have limited blood-brain-barrier penetration. In this study, we show that 6D11 anti-PrP monoclonal antibody (Mab) prevents infection on a FDC-P1 myeloid precursor cell line stably infected with 22L mouse adapted scrapie strain. Passive immunization of extracerebrally infected CD-1 mice with Mab 6D11 resulted in effective suppression of PrP(Sc) replication in the LRS. Although, a rebound of PrP(Sc) presence occurred when the Mab 6D11 treatment was stopped, passively immunized mice showed a prolongation of the incubation period by 36.9% (pb0.0001) and a significant decrease in CNS pathology compared to control groups receiving vehicle or murine IgG. Our results indicate that antibody-based therapeutic strategies can be used, even on a short-term basis, to delay or prevent disease in subjects accidentally exposed to prions.

Enhanced humoral immune responses against T-independent antigens in Fc alpha/muR-deficient mice

IgM is an antibody class common to all vertebrates that plays a primary role in host defenses against infection. Binding of IgM with an antigen initiates the complement cascade, accelerating cellular and humoral immune responses. However, the functional role of the Fc receptor for IgM in such immune responses remains obscure. Here we show that mice deficient in Fc alpha/muR, an Fc receptor for IgM expressed on B cells and follicular dendritic cells (FDCs), have enhanced germinal center formation and affinity maturation and memory induction of IgG3(+) B cells after immunization with T-independent (TI) antigens. Moreover, Fc alpha/muR-deficient mice show prolonged antigen retention by marginal zone B (MZB) cells and FDCs. In vitro studies demonstrate that interaction of the IgM immune complex with Fc alpha/muR partly suppress TI antigen retention by MZB cells. We further show that downregulation of complement receptor (CR)1 and CR2 or complement deprivation by in vivo injection with anti-CR1/2 antibody or cobra venom factor attenuates antigen retention by MZB cells and germinal center formation after immunization with TI antigens in Fc alpha/muR(-/-) mice. Taken together, these results suggest that Fc alpha/muR negatively regulates TI antigen retention by MZB cells and FDCs, leading to suppression of humoral immune responses against T-independent antigens.

[Expression Fas and FasL antigen protein of lymphocytes T and B in hypertrophied adenoid in children with otitis media with effusion]

INTRODUCTION

Apoptosis of lymphocytes can be induced by different factors mainly however the activation of antigen Fas (CD95) and his ligand FasL (CD95L) route. Apoptosis induced by Fas-FasL has large significance in elimination of lymphocytes T in final phase immune response designate AICD (activation induced cell death). Lymphocytes B undergo apoptosis induced by Fas-FasL in germinal center, which has special meaning in elimination of cells about low specificity and weak affinity of receptor BCR ( B-cell antigen receptor).

AIM OF STUDY

The aim of this study was evaluation of percentage of apoptotic lymphocytes and expression of Fas and FasL in CD4+, CD8+, CD19+ lymphocytes in hypertrophied adenoid and hypertrophied adenoid and otitis media with effusion.

METHODS

CD4+Fas+, CD8+Fas+, CD19+Fas+CD4+FasL+, CD8+FasL+, CD19+FasL+ cells subpopulation were identified using monoclonal antibodies and flow cytometry method.

RESULTS

The percentage of lymphocytes CD4+ Fas+, CD8+Fas+, CD19+Fas+ was higher in hypertrophied adenoid and otitis media with effusion compored to the control group. Their was no significant difference the percentage CD4+ Fas+, CD8+Fas+, CD19+Fas+CD4+FasL+, CD8+FasL+, CD19+FasL+ in hypertrophied adenoid and otitis media with effusion then the control group. The percentage of apoptotic lymphocytes was higher in hypertrophied adenoid and otitis media with effusion compored to the control group.

CONCLUSIONS

The susceptibility the individual subpopulation of lymphocytes in hypertrophied adenoid seems to influence on change of relations of quantitative lymphocytes and upset the immunological function of tonsils which can influence on course otitis media with effusion at children.

Dendritic cells in Plasmodium infection

Infection with Plasmodium parasites (malaria) contributes greatly to morbidity and mortality in affected areas. Interaction of the protozoan with the immune system has a critical role in the pathogenesis of the disease, but may also hold a key to containing parasite numbers through specific immune responses, which vaccine development aims to harness. A central player in the generation of such immune responses is the dendritic cell. However, Plasmodium parasites appear to have profound activating and suppressing effects on dendritic cell function, which may enhance immunopathology or facilitate the parasite's survival by depressing beneficial immunity. Furthermore, immune responses to other infections and vaccines may be impaired. A greater understanding of the effects of the parasite on dendritic cells will contribute to insight and potential defeat of this infectious disease.

Isolation of chicken follicular dendritic cells

The aim of the present study was to isolate chicken follicular dendritic cells (FDC). A combination of methods involving panning, iodixanol density gradient centrifugation, and magnetic cell separation technology made it possible to obtain functional FDC from the cecal tonsils from chickens, which had been infected with Eimeria tenella. CD45- dendritic cells were selected using the specific monoclonal antibody against chicken CD45, which is a marker for chicken leukocytes, but is not expressed on chicken FDC. Isolated FDC were characterized morphologically, phenotypically and functionally. The phenotype of the selected cells was consistent with FDC in that they expressed IgG, IgM, complement factors C3 and B, ICAM-1, and VCAM-1, but lacked cell surface markers characteristic of macrophages, T-, and B cells. Transmission electron microscopy confirmed their characteristic dendritic morphology. In addition, the identity of the FDC was further confirmed by their ability to trap chicken immune complexes (ICs) on their surface, whereas they did not trap naive antigen (ovalbumin) or ICs generated with mammalian immunoglobulins. Co-culturing allogeneic or autologous isolated FDC with B cells resulted in enhanced B cell proliferation and immunoglobulin production. The lack of MHC restriction, a functional characteristic feature of FDC, further reinforces the identity of the isolated cells as chicken FDC.

Podoplanin (d2-40): a new immunohistochemical marker for reactive follicular dendritic cells and follicular dendritic cell sarcomas

The diagnosis of follicular dendritic cell (FDC) sarcoma can be challenging because of its morphologic overlaps with many other spindle cell neoplasms and, therefore, new phenotypic markers will be helpful in its differential diagnosis. Podoplanin is a mucin-type transmembrane glycoprotein that has recently been detected in reactive FDCs. In this study, we investigated the expression patterns of podoplanin using a new mouse monoclonal antibody D2-40, and compared them with CD21, a well-established FDC marker, in a comprehensive panel of cases. The panel included 4 FDC sarcomas, 38 spindle cell neoplasms of other types, 25 reactive lymphoid hyperplasia, and 117 lymphoid and 5 myeloid malignant hematopoietic neoplasms. Our study revealed that D2-40 strongly stained 3 of 4 FDC sarcomas. In contrast, D2-40 stained only 2/38 other spindle cell neoplasms tested. Furthermore, we observed that D2-40 highlighted more FDC meshworks than CD21 in Castleman's disease, follicular lymphoma, nodular lymphocyte predominance Hodgkin lymphoma, and residual reactive germinal centers in a variety of lymphoma types. D2-40 and CD21 stained an equal number of cases of reactive lymphoid hyperplasia, progressively transformed germinal centers and angioimmunoblastic T-cell lymphoma. No expression of podoplanin was detected in normal or neoplastic lymphoid and myeloid cells. We conclude that podoplanin (D2-40) is a sensitive and specific FDC marker, which is superior or equal to CD21 in evaluating both reactive and neoplastic FDCs. In addition, our results suggest that podoplanin (D2-40) can be used to support the diagnosis of FDC sarcoma.

Lymphoma microenvironment: culprit or innocent?

Studies are revealing that lymphoid neoplasms are characterized by well-defined chromosome translocations and by the accumulation of subsequent molecular alterations involving mainly the cell cycle and/or apoptotic pathways. However, survival of B and T tumor cells is also dependent on the interactions with the accompanying cells that comprise the lymphoma microenvironment. Although non-tumor cells can contribute both positive and negative signals to the lymphoma cells, in this review we present compelling evidence of the essential influence of the tumor microenvironment on the initiation and progression of specific lymphoma types, highlighting some new therapeutic approaches that target the lymphoma microenvironment.

Role for CD21 in the establishment of an extracellular HIV reservoir in lymphoid tissues

Follicular dendritic cells (FDC) represent a major extracellular reservoir for HIV. A better understanding of the mechanisms of virion attachment to FDC may offer new avenues for reducing viral burdens in infected individuals. We used a murine model to investigate the establishment of extracellular HIV reservoirs in lymph nodes (LN). Consistent with findings in human tissues, CD21 was required for trapping of HIV to LN cells, as evidenced by significantly reduced virion binding when mice were pretreated with a C3 ligand-blocking anti-CD21 mAb and absence of virion trapping in CD21 knockout mice. Also consistent with findings in human tissues, the majority of HIV virions were associated with the FDC-enriched fraction of LN cell preparations. Somewhat surprisingly, HIV-specific Abs were not essential for HIV binding to LN cells, indicating that seeding of the FDC reservoir may begin shortly after infection and before the development of HIV-specific Abs. Finally, the virion-displacing potential for anti-CD21 mAbs was investigated. Treatment of mice with anti-CD21 mAbs several days after injection of HIV significantly reduced HIV bound to LN cells. Our findings demonstrate a critical role for CD21 in HIV trapping by LN cells and suggest a new therapeutic avenue for reducing HIV reservoirs.

BNIP3 expression in follicular lymphoma

AIMS

To investigate the role of BNIP3, a 19-kDa interacting protein of the Bcl-2 family, alongside Bcl-2 in follicular lymphoma in comparison with reactive lymphoid hyperplasia. The results were compared with those from p53 and caspase-3 (apoptotic markers) and Ki67 (proliferation marker).

METHODS AND RESULTS

Immunohistochemistry using monoclonal antibodies showed BNIP3 to be strongly expressed in most follicular lymphomas but to be weak to negative in all of the reactive cases. There was also an inverse relationship with Bcl-2 expression. There was no correlation of BNIP3 immunoreactivity with proliferation and caspase and p53 were virtually negative in all follicular lymphomas and reactive lymphoid cases.

CONCLUSIONS

BNIP3 is strongly expressed in most follicular lymphomas, especially those that are Bcl-2 negative. BNIP3 may serve as a marker of more aggressive behaviour in follicular lymphoma and be useful diagnostically in the distinction from reactive lymphadenitis.

The dynamics of the B follicle: understanding the normal counterpart of B-cell-derived malignancies

The repertoire of B cells secreting antibodies with unique antigen-binding specificities is produced at two stages: a primary B-cell repertoire is formed in the bone marrow through immunoglobulin gene rearrangements, whereas a secondary B-cell repertoire is generated in the peripheral lymphoid organs (spleen, lymph nodes and mucosa-associated lymphoid tissue) through somatic hypermutation and class-switch recombination upon antigen encounter. The latter events take place within highly specialized histological structures, designated B follicles, which are composed of distinct microanatomical compartments namely the follicle centre, lymphocytic corona and marginal zone. Each compartment comprises a particular subset of B cells, characterized by unique properties, thereby reflecting the complexity and variability in the spectrum of defence mechanisms against invading pathogens. The past years have spawned an avalanche of new data and information that encompasses both the structure and function of each compartment and its B cells. This review incorporates up-to-date information on peripheral B-cell differentiation into a challenging working model, thereby pointing to the structural and functional imprint of both the T-cell-dependent and T-cell-independent immune response on the B follicle. As such, this article aims to form an excellent base for a better understanding of the normal counterpart of B-cell-derived haematological malignancies (leukemias and lymphomas).

Lymphotoxin-independent expression of TNF-related activation-induced cytokine by stromal cells in cryptopatches, isolated lymphoid follicles, and Peyer's patches

Stromal cells play a crucial role in the organogenesis of lymphoid tissues. We previously identified VCAM-1(+) stromal cells in cryptopatches (CP) and isolated lymphoid follicles (ILF) in the small intestine of C57BL/6 mice. Nonhemopoietic stromal cell networks in CP and ILF of adult mice also expressed FDC-M1, CD157 (BP-3), and TNF-related activation-induced cytokine (TRANCE). Individual stromal cells were heterogeneous in their expression of these markers, with not all stromal cells expressing the entire set of stromal cell markers. Expression of VCAM-1, FDC-M1, and CD157 on CP stromal cells was absent in alymphoplasia mice deficient in NF-kappaB-inducing kinase (NIK) and NIK knockout mice. Administration of lymphotoxin beta receptor (LTbetaR)-Ig to wild-type mice on day 13 resulted in the absence of CP on day 20; delaying administration of LTbetaR-Ig until day 18 resulted in an 80% decrease in the number of CP on day 22 and diminished expression of VCAM-1, FDC-M1, and CD157 on the remaining CP. In sharp contrast, TRANCE expression by stromal cells was completely independent of NIK and LTbetaR. In addition, expression of TRANCE in ILF was concentrated just beneath the follicle-associated epithelium, a pattern of polarization that was also observed in Peyer's patches. These findings suggest that TRANCE on stromal cells contributes to the differentiation and maintenance of organized lymphoid aggregates in the small intestine.

The role of cystatins in cells of the immune system

The cystatins constitute a large group of evolutionary related proteins with diverse biological activities. Initially, they were characterized as inhibitors of lysosomal cysteine proteases - cathepsins. Cathepsins are involved in processing and presentation of antigens, as well as several pathological conditions such as inflammation and cancer. Recently, alternative functions of cystatins have been proposed: they also induce tumour necrosis factor and interleukin 10 synthesis and stimulate nitric oxide production. The aim of the present review was the analysis of data on cystatins from NCBI GEO database and the literature, and obtained in microarray and serial analysis of gene expression (SAGE) experiments. The expression of cystatins A, B, C, and F in macrophages, dendritic cells and natural killer cells of the immune system, during differentiation and activation is discussed.

Establishment of Lymphotoxin β Receptor Signaling-Dependent Cell Lines with Follicular Dendritic Cell Phenotypes from Mouse Lymph Nodes

Follicular dendritic cells (FDCs) have been shown to play a crucial role in the positive selection of high-affinity B cells that are generated by somatic hypermutation in germinal center (GC). Because of technical difficulties in preparing and maintaining pure FDCs, a role for FDCs in this complicated process has not been fully elucidated. In this study, we established a cell line designated as pFL that retained major FDC phenotypes from a three-dimensional culture of mouse lymph node cells. pFL cells proliferated slowly in response to an agonistic anti-lymphotoxin beta receptor mAb and TNF-alpha. A more rapidly growing clone, named FL-Y, with similar requirements for growth was isolated from a long-term culture of pFL. Analysis of surface markers in these two cell lines by immunostaining, flow cytometry, and DNA microarray revealed the expression of genes, including those of CD21, FcgammaRIIB, lymphotoxin beta receptor, ICAM-1, VCAM-1, IL-6, and C4, which have been shown to be characteristic of FDCs. In addition, B cell-activating factor was expressed in these two cell lines. At the pFL or FL-Y:B cell ratio of 1:100, the cell lines markedly sustained B cell survival and Ab production during 2 wk of culture, while most B cells collapsed within 1 wk in the absence of the FDC-like cells. Interestingly, expression of typical GC markers, Fas and GL-7, was notably augmented in B cells that were cocultured with Th cells on these two cell lines. Thus, pFL and FL-Y cells may be useful for providing insight into the functional role for FDCs in GC.

Survival response to B-cell receptor ligation is restricted to progressive chronic lymphocytic leukemia cells irrespective of Zap70 expression

Despite very similar gene expression profiles, the clinical course of B-cell chronic lymphocytic leukemia (B-CLL) is heterogeneous. Immunoglobulin VH (IgVH) mutational status and expression of B-cell receptor (BCR) signaling mediators have been associated with disease progression. However, the consequences of BCR engagement on cell survival and evolution of the disease remain unclear. We show here that B-CLL cell survival is dependent on the threshold of BCR stimulation induced by immobilized antibody, in contrast to soluble anti-mu F(ab)'2 antibody, which leads to apoptosis. Measurement of metabolic activity and apoptotic response discriminated two subgroups. "Nonresponders" showed low metabolic activity and unmodified apoptotic response upon BCR stimulation. In contrast, "responders" exhibited increased metabolic activity and inhibition of spontaneous apoptosis. This survival advantage was associated to a BCR-dependent activation profile leading to induction of cyclin D2/cyclin-dependent kinase 4 (cdk4) expression and G1 cell cycle progression. The ability to respond to BCR ligation correlated with an unfavorable clinical course and allowed to define an additional group of patients among IgVH-mutated cases exhibiting a risk of progression. Remarkably, we show that Zap70 expression was neither mandatory nor sufficient to generate downstream survival signals and cyclin D2/cdk4 up-regulation. In conclusion, BCR engagement has a significant effect on B-CLL cell survival, activation, and G1 progression. Furthermore, our results provide new insights in the physiopathology of progressive IgVH-mutated cases.

Role of Dendritic Cells in Sjogren's Syndrome

Sjögren's syndrome (SS) is a chronic inflammatory and lymphoproliferative autoimmune disease of unknown aetiology. It is characterised by progressive mononuclear cell infiltration of the salivary and lacrimal glands and a decreased glandular secretion, resulting in dryness of the mouth and eyes (xerostomia and keratoconjunctivitis sicca, respectively). Dendritic cells (DC) are considered to be the most potent antigen-presenting cells. Because of their central role in initiating an immune response while maintaining tolerance, impaired function of these cells might lead to the break of peripheral tolerance and initiation of immune responses to self-antigens. This review will focus on the possible role of DC in SS.