Differential T cell-mediated regulation of CD23 (Fc epsilonRII) in B cells and follicular dendritic cells

CD4+ T-cell-dependent differentiation of CD23+ follicular B cells contributes to the pulmonary pathology in a primary Sjögren's syndrome mouse model

Introduction

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease that affects the function of exocrine glands, such as the lacrimal and the salivary glands. Extraglandular lesions and malignant lymphoma also occur during the progressive stage of pSS. We have, herein, focused on the pulmonary lesions of pSS and have aimed clarifying their pathophysiological mechanism by comparing the glandular with the extraglandular lesions observed in a mouse model of pSS.

Results

The histopathological analysis of lung tissues obtained from NFS/sld mice that have undergone neonatal thymectomy was performed. Moreover, in vivo and in vitro experiments were conducted along with immunological analyses in order to characterize the unique phenotypes of the pulmonary lesions identified in these pSS model mice. Inflammatory lesions with a bronchus-associated lymphoid tissue-like structure were identified in the lungs of pSS model mice. In addition, relative to salivary gland lesions, pulmonary lesions showed increased CD23⁺ follicular B (FB) cells. In vitro and pulmonary B cells were more readily driven to CD23⁺ FB cell phenotype than salivary gland B cells in pSS model mice. Furthermore, the CD23⁺ FB cell differentiation was found to be enhanced in a CD4⁺ T-cell-dependent manner under a Th2-type condition in the lungs of herein examined pSS model mice.

Discussion

A Th2-type response in the pSS lung may promote the progression of autoimmune lesions through an enhanced abnormal differentiation of B cells.

Bidirectional Transport of IgE by CD23 in the Inner Ear of Patients with Meniere's Disease

Meniere's disease (MD) is a disorder of the inner ear characterized by episodes of spontaneous vertigo, fluctuating hearing loss, and tinnitus. Recent studies have demonstrated that IgE may play a role in the pathogenesis of MD. Patients with MD (n = 103), acoustic neuroma (n = 5), and healthy subjects (n = 72) were recruited into the study. Serum from the participants was analyzed for IgE and type 2-related cytokines. IgE and CD23 expression levels in vestibular end organs of patients, C57BL/6 mice, or mouse HEI-OC1 cells were analyzed. Finally, the role of CD23 in IgE transcytosis was assessed using HEI-OC1 cells. Serum IgE was elevated in patients with MD and positively correlated with clinical symptoms. IL-4, IL-5, IL-10, IL-13, and CD23 levels were increased in patients with MD compared with the control group. In the transcytosis assay, mouse IgE was found to be bidirectionally transported across the HEI-OC1 cell monolayer. Additionally, CD23 downregulation using a small interfering RNA approach significantly reduced the efficiency of IgE transcytosis, suggesting that IgE is transported by CD23. Furthermore, exposure to IL-4 increased CD23 expression and enhanced IgE transcytosis in the HEI-OC1 cells and primary vestibular end organs. Our study indicated that IgE may play a role in the pathophysiology of MD. In addition, CD23-mediated IgE transcytosis in the hair cells may play a critical role in initiating inflammation in the inner ear. Thus, reducing the level of IgE may be a potentially effective approach for MD treatment.

Follicular dendritic cells

Follicular dendritic cells (FDCs) are unique accessory immune cells that contribute to the regulation of humoral immunity. They are multitasker cells essential for the organization and maintenance of the lymphoid architecture, induction of germinal center reaction, production of B memory cells, and protection from autoimmune disorders. They perform their activities through both antigen-driven and chemical signaling to B cells. FDCs play a crucial role in the physiological regulation of the immune response. Dis-regulation of this immune response results when FDCs retain antigens for years. This provides a constant antigenic stimulation for B cells resulting in the development of immune disorders. Antigen trapped on FDCs is resistant to therapeutic intervention causing chronicity and recurrences. Beyond their physiological immunoregulatory functions, FDCs are involved in the pathogenesis of several immune-related disorders including HIV/AIDS, prion diseases, chronic inflammatory, and autoimmune disorders. FDCs have also been recently implicated in rare neoplasms of lymphoid and hematopoietic tissues. Understanding FDC biology is essential for better control of humoral immunity and opens the gate for therapeutic management of FDC-mediated immune disorders. Thus, the biology of FDCs has become a hot research area in the last couple of decades. In this review, we aim to provide a comprehensive overview of FDCs and their role in physiological and pathological conditions.

Schistosome-induced pulmonary B cells inhibit allergic airway inflammation and display a reduced Th2-driving function

Chronic schistosome infections protect against allergic airway inflammation (AAI) via the induction of IL-10-producing splenic regulatory B (Breg) cells. Previous experiments have demonstrated that schistosome-induced pulmonary B cells can also reduce AAI, but act independently of IL-10. We have now further characterized the phenotype and inhibitory activity of these protective pulmonary B cells. We excluded a role for regulatory T (Treg) cell induction as putative AAI-protective mechanisms. Schistosome-induced B cells showed increased CD86 expression and reduced cytokine expression in response to Toll-like receptor (TLR) ligands compared with control B cells. To investigate the consequences for T cell activation we cultured ovalbumin (OVA)-pulsed, schistosome-induced B cells with OVA-specific transgenic T cells and observed less Th2 cytokine expression and T cell proliferation compared with control conditions. This suppressive effect was preserved even under optimal T cell stimulation by anti-CD3/28. Blocking of the inhibitory cytokines IL-10 or TGF-β only marginally restored Th2 cytokine induction. These data suggest that schistosome-induced pulmonary B cells are impaired in their capacity to produce cytokines to TLR ligands and to induce Th2 cytokine responses independent of their antigen-presenting function. These findings underline the presence of distinct B cell subsets with different stimulatory or inhibitory properties even if induced by the same type of helminth.

Triptolide-conditioned dendritic cells induce allospecific T-cell regulation and prolong renal graft survival

BACKGROUND

Previous studies show that triptolide (TPT), a diterpenoid isolated from the Chinese herb Tripterygium wilfordii Hook.f, inhibits dendritic cell (DCs) maturation. Whether TPT-conditioned DCs (TPT-DCs) may regulate allospecific immune responses remains unclear. In this study, we investigated the effects of TPT on allostimulatory function and phenotype of rat bone marrow-derived DCs (BMDCs).

METHODS

Brown Norway rats BMDCs were cultured with or without TPT and then stimulated with lipopolysaccharide (LPS). IL-10 in supernatants was quantitatively measured, and the cells were analyzed by flow cytometry and used as stimulators in mixed leukocyte reaction in which naive Lewis rat T lymphocytes were used as responders. The tolerogenic potential of TPT-BMDCs was evaluated in vivo in a rat model of MHC fully mismatched kidney transplantation.

RESULTS

After treatment with TPT, BMDCs remained immature with low expression of CD80 and CD86 in the presence of LPS. At low concentrations of TPT (1 and 2.5 nM), BMDCs produced higher levels of IL-10 than the untreated cells (431 and 205.4 pg/ml, respectively, vs. 122.9 pg/ml, p < .05). T cells cocultured with TPT-BMDCs were hyporesponsive in allogeneic mixed lymphocyte reaction. The CD25+foxp3+Treg cell populations increased from 19.9% to 29.7% in the coculture system. Without immunosuppressive therapy, infusion of TPT-BMDCs in recipients before transplantation prolonged rat kidney allograft survival (18.8 ± 1.30 days).

CONCLUSIONS

Our findings demonstrate that TPT inhibits the maturation and allogenicity of BMDCs and promotes the expansion of CD25+foxp3+ regulatory T cells. It suggests that TPT-DCs are potentially useful for preventing kidney transplant rejection.

Follicular dendritic cells in health and disease

Follicular dendritic cells (FDCs) are unique immune cells that contribute to the regulation of humoral immune responses. These cells are located in the B-cell follicles of secondary lymphoid tissues where they trap and retain antigens (Ags) in the form of highly immunogenic immune complexes (ICs) consisting of Ag plus specific antibody (Ab) and/or complement proteins. FDCs multimerize Ags and present them polyvalently to B-cells in periodically arranged arrays that extensively crosslink the B-cell receptors for Ag (BCRs). FDC-FcγRIIB mediates IC periodicity, and FDC-Ag presentation combined with other soluble and membrane bound signals contributed by FDCs, like FDC-BAFF, -IL-6, and -C4bBP, are essential for the induction of the germinal center (GC) reaction, the maintenance of serological memory, and the remarkable ability of FDC-Ags to induce specific Ab responses in the absence of cognate T-cell help. On the other hand, FDCs play a negative role in several disease conditions including chronic inflammatory diseases, autoimmune diseases, HIV/AIDS, prion diseases, and follicular lymphomas. Compared to other accessory immune cells, FDCs have received little attention, and their functions have not been fully elucidated. This review gives an overview of FDC structure, and recapitulates our current knowledge on the immunoregulatory functions of FDCs in health and disease. A better understanding of FDCs should permit better regulation of Ab responses to suit the therapeutic manipulation of regulated and dysregulated immune responses.

A disintegrin and metalloproteinase 10 regulates antibody production and maintenance of lymphoid architecture

A disintegrin and metalloproteinase 10 (ADAM10) is a zinc-dependent proteinase related to matrix metalloproteinases. ADAM10 has emerged as a key regulator of cellular processes by cleaving and shedding extracellular domains of multiple transmembrane receptors and ligands. We have developed B cell-specific ADAM10-deficient mice (ADAM10(B-/-)). In this study, we show that ADAM10 levels are significantly enhanced on germinal center B cells. Moreover, ADAM10(B-/-) mice had severely diminished primary and secondary responses after T-dependent immunization. ADAM10(B-/-) displayed impaired germinal center formation, had fewer follicular Th cells, decreased follicular dendritic cell networks, and altered chemokine expression in draining lymph nodes (LNs). Interestingly, when spleen and LN structures from immunized mice were analyzed for B and T cell localization, tissues structure was aberrant in ADAM10(B-/-) mice. Importantly, when ADAM10-deficient B cells were stimulated in vitro, they produced comparable Ab as wild type B cells. This result demonstrates that the defects in humoral responses in vivo result from inadequate B cell activation, likely because of the decrease in follicular Th cells and the changes in structure. Thus, ADAM10 is essential for the maintenance of lymphoid structure after Ag challenge.

In situ expression of CD23 in lymph nodes of patients with Kimura's disease

OBJECTIVE

The aim of this study was to investigate the expression of CD23 (Fcɛ RII) in the lymph nodes (LNs) of patients with Kimura's disease (KD).

METHODS

Expression of CD23 was examined immunohistochemically. The concentrations of soluble CD23 and titers of IgE in sera from patients with KD were studied by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In the germinal centers (GCs) of LNs from patients with KD, overexpression of CD23 on well-developed follicular dendritic cells (FDCs) was observed. GC lymphocytes in the LNs of KD patients were intensely positive for CD23, and positive cells were also observed in both the light and dark zones. In contrast, in the LNs of normal patients, CD23-positive cells were restricted to the light zone of the GCs. Although serum IgE titers were raised in all KD patients, serum concentrations of soluble CD23 were not elevated.

CONCLUSION

These results suggest that CD23 and FDCs play important roles in the pathogenesis of KD.

Arachidonate 5-lipoxygenase establishes adaptive humoral immunity by controlling primary B cells and their cognate T-cell help

In this study, we report the unique role of arachidonate 5-lipoxygenase (Alox5) in the regulation of specific humoral immune responses. We previously reported an L22 monoclonal antibody with which human primary resting B cells in the mantle zones of lymphoid follicles are well-defined. Proteomics analyses enabled identification of an L22 antigen as Alox5, which was highly expressed by naive and memory B cells surrounding germinal centers. Cellular growth of mantle cell lymphoma cells also seemed to depend on Alox5. Alox5(-/-) mice exhibited weak antibody responses specific to foreign antigens at the initial and recall phases. This was probably attributable to the low number of follicular and memory B cells and the functional loss of interleukin-21-mediated responses of follicular B cells. Moreover, Alox5(-/-) mice could not fully foster the development of follicular B helper T (Tfh) cells even after immunization with foreign antigens. Further experiments indicated that Alox5 affected mortality in experimentally induced enterocolitis in germ-prone circumstances, indicating that Alox5 would endow immunologic milieu. Our results illustrate the novel role of Alox5 in adaptive humoral immunity by managing primary B cells and Tfh cells in vivo.

Activation of B cells by antigens on follicular dendritic cells

A need for antigen-processing and presentation to B cells is not widely appreciated. However, cross-linking of multiple B cell receptors (BCRs) by T-independent antigens delivers a potent signal that induces antibody responses. Such BCR cross-linking also occurs in germinal centers where follicular dendritic cells (FDCs) present multimerized antigens as periodically arranged antigen-antibody complexes (ICs). Unlike T cells that recognize antigens as peptide-MHC complexes, optimal B cell-responses are induced by multimerized FDC-ICs that simultaneously engage multiple BCRs. FDC-FcgammaRIIB mediates IC-periodicity and FDC-BAFF, FDC-IL-6 and FDC-C4bBP are co-stimulators. Remarkably, specific antibody responses can be induced by FDC-ICs in the absence of T cells, opening up the exciting possibility that people with T cell insufficiencies may be immunized with T-dependent vaccines via FDC-ICs.

Deletion of putative intronic control sequences does not alter cell or stage specific expression of Cr2

The expression of the mouse Cr2 gene has been shown to be restricted to mature B cells, follicular dendritic cells and, in some reports, to a minor population of activated T cells. In this report, we demonstrate that the expression of antigen(s) recognized by the anti-CR2 antibody on the surface of T cells is co-incident with T cell apoptotic death. Two distinct regions of the Cr2 gene have been implicated as critical for specific expression, the promoter region at the transcription start site and a control region within the first intron of the gene, approximately 1500 bp from the transcription start site. We have created a mouse that is lacking this intronic control sequence which, in the wild type (WT) mouse, contains multiple known binding sites for RBP-jkappa, Oct, NFAT and YY1 proteins. The analysis of this mouse named Cr2iDelta (Cr2 intron deletion) demonstrated normal tissue specific expression of the Cr2 gene including a lack of expression in mouse T cells. B cell expression of the Cr2 gene products, CR1 and CR2, is normal compared to WT, and the FDC of these mice continue to express Cr2 gene products. Therefore the intronic control region of the Cr2 gene, defined in transfection-based reporter gene assays as instrumental in controlling the cell specific expression profile of Cr2, does not influence the expression of the Cr2 gene in vivo nor alter the relative production of the CR1 and CR2 proteins via alternative slicing of Cr2 gene products.

Selective targeting of B cells with agonistic anti-CD40 is an efficacious strategy for the generation of induced regulatory T2-like B cells and for the suppression of lupus in MRL/lpr mice

We have previously reported that IL-10(+) regulatory B cells, known to play an important role in controlling autoimmunity and inflammatory disorders, are contained within the transitional 2 immature (T2) B cell pool (T2 Bregs). Therapeutic strategies facilitating their enrichment or enhancing their suppressive activity are highly attractive. In this study, we report that agonistic anti-CD40 specifically targets T2 B cells and enriches Bregs upon short-term in vitro culture. Although transfer of unmanipulated T2 B cells, isolated from mice with established lupus, failed to confer protection to diseased mice, transfer of in vitro anti-CD40-generated T2 B cells (T2-like-Bregs) significantly improved renal disease and survival by an IL-10-dependent mechanism. T2-like-Bregs readily accumulated in the spleen after transfer, suppressed Th1 responses, induced the differentiation of IL-10(+)CD4(+)T cells, and conveyed a regulatory effect to CD4(+)T cells. In addition, in vivo administration of agonistic anti-CD40, currently on trial for the treatment of cancer, halted and reversed established lupus. Taken together, our results suggest a novel cellular approach for the amelioration of experimental lupus.

Molecular blocking of CD23 supports its role in the pathogenesis of arthritis

Background

CD23 is a differentiation/activation antigen expressed by a variety of hematopoietic and epithelial cells. It can also be detected in soluble forms in biological fluids. Initially known as the low-affinity receptor for immunoglobulin E (FcεRII), CD23 displays various other physiologic ligands such as CD21, CD11b/c, CD47-vitronectin, and mannose-containing proteins. CD23 mediates numerous immune responses by enhancing IgE-specific antigen presentation, regulating IgE synthesis, influencing cell differentiation and growth of both B- and T-cells. CD23-crosslinking promotes the secretion of pro-inflammatory mediators from human monocytes/macrophages, eosinophils and epithelial cells. Increased CD23 expression is found in patients during allergic reactions and rheumatoid arthritis while its physiopathologic role in these diseases remains to be clarified.

Methodology/Principal Findings

We previously generated heptapeptidic countrestructures of human CD23. Based on in vitro studies on healthy and arthritic patients' cells, we showed that CD23-specific peptide addition to human macrophages greatly diminished the transcription of genes encoding inflammatory cytokines. This was also confirmed by significant reduction of mediator levels in cell supernatants. We also show that CD23 peptide decreased IgE-mediated activation of both human and rat CD23⁺ macrophages. In vivo studies in rat model of arthritis showed that CD23-blocking peptide ameliorates clinical scores and prevent bone destruction in a dose dependent manner. Ex-vivo analysis of rat macrophages further confirmed the inhibitory effect of peptides on their activation. Taken together our results support the role of CD23 activation and subsequent inflammatory response in arthritis.

Conclusion

CD23-blocking peptide (p30A) prevents the activation of monocytes/macrophages without cell toxicity. Thus, targeting CD23 by antagonistic peptide decreases inflammatory markers and may have clinical value in the treatment of human arthritis and allergic reactions involving CD23.

Circulating CD23+ B cell subset correlates with the development of resistance to Schistosoma mansoni reinfection in occupationally exposed adults who have undergone multiple treatments

BACKGROUND

Elevated immunoglobulin E (IgE) levels are often associated with resistance to reinfection in human schistosomiasis. However, Although B cells are the source of schistosome-specific IgE, little is known about B cell subsets or their functions in this infection. We evaluated B cells and their expression of the low-affinity IgE receptor (CD23) in a unique cohort of men occupationally exposed to Schistosoma mansoni and longitudinally followed up through multiple treatments with praziquantel, cures, and reinfections.

METHODS

Resistance levels were calculated on the basis of documented water exposure and reinfection data over many years. The CD23(+) B cell subset was evaluated in whole blood by flow cytometry. Serum antibody isotype and soluble CD23 (sCD23) concentrations were measured by enzyme-linked immunosorbent assay.

RESULTS

Expression of membrane CD23 (mCD23) on B cells correlated with the development of resistance against S. mansoni. Higher levels of plasma sCD23, the cleaved form of mCD23, also correlated with resistance and other markers of resistance to reinfection, such as eosinophilia.

CONCLUSIONS

CD23 may be involved in the development of resistance to schistosome infection through its role in IgE regulation. Understanding these complex host-parasite interactions may lead to insights into the development, mechanisms, and regulation of resistance to reinfection with S. mansoni.

Evaluation of gene expression profiles of immature dendritic cells prepared from peripheral blood mononuclear cells

BACKGROUND

Dendritic cells (DCs) generated ex vivo from peripheral blood monocytes or mobilized CD34+ cells and intended for clinical immunotherapy are typically characterized by morphologic, phenotypic, and functional assays. Assay results are highly dependent on conditions used to prepare the cells, so there is no standard assay battery for clinical DC products. This study evaluated gene expression profiling for characterization of immature DCs prepared from monocytes that had been elutriated from normal donor peripheral blood mononuclear cells (PBMNCs) immediately after collection or after storage at 4 degrees C for 48 hours.

STUDY DESIGN AND METHODS

RNA was isolated from fresh and 48-hour-stored PBMNCs, elutriated monocytes, elutriated lymphocytes, and immature DCs from five healthy subjects and was analyzed with a cDNA gene expression microarray with 17,500 genes.

RESULTS

Unsupervised hierarchical clustering separated the 40 products into four groups: one with all 10 immature DCs, one with all 10 elutriated lymphocytes, one with 7 PBMNCs, and one with 10 elutriated monocytes and 3 PBMNCs. Within each of the four groups, however, fresh and stored products, or products derived from fresh or stored products, clustered together. Comparison of genes differentially expressed by fresh versus stored products (paired t tests, p < 0.005) found 273 genes that differed between fresh and stored PBMCs, 429 between lymphocytes elutriated from fresh versus stored PBMNCs, 711 between monocytes elutriated from fresh versus stored PBMNCs, and 3 between immature DCs prepared from monocytes elutriated from fresh versus stored PBMCs.

CONCLUSIONS

This study demonstrates the potential utility of gene expression profiling for characterization of cell therapy products.

Follicular dendritic cell networks of primary follicles and germinal centers: phenotype and function

Follicular dendritic cells (FDCs) were identified decades ago by their ability to retain immune complexes and more recent findings indicate that they are a source of B cell attractants and trophic factors. New imaging studies have shown that B cells closely associate with their dendritic processes during migration. Here we will review the properties of these specialized follicular stromal cells and provide an update on the requirements for their maturation into phenotypically distinct cells within germinal center light and dark zones. We will then discuss current understanding of how they help support the B cell immune response.

Ultrastructural study of highly enriched follicular dendritic cells reveals their morphology and the periodicity of immune complex binding

Follicular dendritic cells (FDCs) are immune accessory cells found in the follicles of secondary lymphoid organs where they promote B cell maturation in germinal centers (GCs) that develop following antigen exposure. Recently, we published a method for isolating functional murine FDCs in high purity. We reasoned that disruption of FDC reticula in vivo would alter FDC morphology. The present study was undertaken to determine the morphological features of isolated FDCs. FDC-M1 and immune complex (IC) labeling were used to identify FDCs in isolated preparations. Results at the light-microscopic level revealed that isolated FDCs trapped ICs, expressed FDC-M1 and cadherins, but generally appeared non-dendritic. However, at the ultrastructural level, the majority of FDCs exhibited dendrites and typical euchromatic nuclei that appeared as single, bilobed, or double nuclei. Based on morphology, four varieties of FDCs were distinguishable, possibly indicative of differences in maturity. Remarkably, ICs trapped by FDCs showed a distinctive periodic arrangement consistent with that known to induce immune responses by thymus independent-2 (TI-2) antigens that engage and cross-link multiple B cell receptors. The ability of FDCs to trap ICs and then display these T-cell-dependent antigens with repeating periodicity suggests that multiple B cell receptors are cross-linked by antigen on FDCs, thus promoting B cell stimulation and proliferation. Rapid proliferation is characteristic of the GC reaction, and the arrangement of T-dependent antigens in this periodic fashion may help to explain the profuse B cell proliferation in the GC microenvironment.

B cells amplify IFN-gamma production by T cells via a TNF-alpha-mediated mechanism

Aside from being the precursors of the Ab-secreting cells, B cells are engaged in other immune functions such as Ag presentation to T cells or cytokine production. These functions may contribute to the pathogenic role of B cells in a wide range of autoimmune diseases. We demonstrate that B cells acquire the capacity to amplify IFN-gamma production by CD4 and CD8 T cells during the course of the Th1 inflammatory response to Toxoplasma gondii infection. Using the two following different strategies, we observed that B cells from T. gondii-infected mice, but not from naive mice, induce higher IFN-gamma expression by splenic host T cells: 1) reconstitution of B cell-deficient mice with B cells expressing an alloantigen different from the recipients, and 2) adoptive transfer of B and T cells into RAG-/- mice. In vitro assays allowing the physical separation of T and B cells demonstrate that Ag-primed B cells enhance IFN-gamma production by T cells in a contact-dependent fashion. Using an OVA-transgenic strain of T. gondii and OVA-specific CD4 T cells, we observed that the proinflammatory effect of B cells is neither Ag specific nor requires MHCII expression. However, TNF-alpha expressed on the surface of B cells appears to mediate in part the up-regulation of IFN-gamma by the effector T cells.

CD23: an overlooked regulator of allergic disease

Given the importance of immunoglobulin (Ig) E in mediating type I hypersensitivity, inhibiting IgE production would be a general way of controlling allergic disease. The low-affinity IgE receptor (FceRII or CD23) has long been proposed to be a natural regulator of IgE synthesis. In vivo research supporting this concept includes the observation that mice lacking CD23 have increased IgE production whereas mice overexpressing CD23 show strongly suppressed IgE responses. In addition, the finding that mice injected with monoclonal antibody directed against the coiled-coil stalk of CD23 have enhanced soluble CD23 release and increased IgE production demonstrates that full-length, trimeric CD23 is responsible for initiating an IgE inhibitory signal. The recent identification of ADAM10 (a disintegrin and metalloprotease) as the CD23 metalloprotease provides an alternative approach for designing therapies to combat allergic disease. Current data suggest that stabilizing cell-surface CD23 would be a natural means to decrease IgE synthesis and thus control type I hypersensitivity.

IgE Enhances Specific Antibody and T-cell Responses in Mice Overexpressing CD23

IgE administered with its specific antigen in vivo induces enhanced proliferation of specific T cells as well as enhanced production of specific antibodies. Both effects are dependent on the low-affinity receptor for IgE (CD23) and the underlying mechanism is thought to be increased antigen presentation following uptake of IgE/antigen complexes via CD23(+) B cells. By contrast, CD23 negatively regulates antibody responses to antigens administered with alum, i.e. without IgE. This effect has been observed as low IgG1 and IgE responses in transgenic mice overexpressing CD23 (CD23Tg). The present study was designed to test whether IgE could enhance antibody and T-cell responses in CD23Tg animals or whether CD23's downregulatory effect precludes IgE-mediated enhancement. IgE-anti-TNP administered with OVA-TNP enhances the OVA-specific antibody responses in wild-type (wt) and CD23Tg mice equally well. Interestingly, the total magnitude of antibody responses to IgE + OVA-TNP and to uncomplexed OVA-TNP, as well as to sheep erythrocytes and keyhole limpet haemocyanine, were lower in the CD23Tg mice. IgE induced proliferation of OVA-specific CD4(+) T cells to the same degree in wt and CD23Tg mice. The effect on T cells was dependent on CD23(+) B cells as demonstrated in in vitro proliferation assays. In conclusion, CD23 does indeed have dual immunoregulatory effects in the same animal. The receptor mediates enhancement of antibody and T-cell responses to IgE-complexed antigen, most likely via increased presentation of complexed antigen, while it negatively regulates the total antibody response to a variety of antigens.

In vivo murine CD23 destabilization enhances CD23 shedding and IgE synthesis

To investigate the effects of in vivo CD23 destabilization on CD23 shedding and IgE production, an anti-CD23 stalk monoclonal (19G5), previously shown to enhance proteolysis of CD23 in vitro, was utilized. Compared to isotype control-treated mice, BALB/cJ mice injected with 19G5 displayed significantly enhanced serum soluble CD23 and IgE. Soluble CD23 and IgE levels were also increased in 19G5-treated C57BL/6J mice (intermediate IgE responders); however, the kinetics of the responses differed between the high (BALB/cJ) and intermediate responder mice, suggesting a potential role for CD23 in regulating IgE responder status. The 19G5-induced IgE response was dependent on IL-4 and independent of CD21 as demonstrated through use of IL-4Ralpha and CD21/35-deficient mice, respectively. Overall, the data provide a direct demonstration for CD23's role in regulating IgE production in vivo and suggest that therapies aimed at stabilizing cell surface CD23 would be beneficial in controlling allergic disease.

Isolation of functionally active murine follicular dendritic cells

Biochemical, genetic, and immunological studies of follicular dendritic cells (FDCs) have been hampered by difficulty in obtaining adequate numbers of purified cells in a functional state. To address this obstacle, we enriched FDCs by irradiating mice to destroy most lymphocytes, excised the lymph nodes, and gently digested the nodes with an enzyme cocktail to form single cell suspensions. The FDCs in suspension were selected using the specific mAb FDC-M1 with magnetic cell separation technology. We were able to get nearly a million viable lymph node FDCs per mouse at about 90% purity. When examined under light and transmission electron microscopy, the cytological features were characteristic of FDCs. Furthermore, the cells were able to trap and retain immune complexes and were positive for important phenotypic markers including FDC-M1, CD21/35, CD32, CD40, and CD54. Moreover, the purified FDCs exhibited classical FDC accessory activities including: the ability to co-stimulate B cell proliferation, augment antibody responses induced by mitogens or antigens, maintain B cell viability for weeks, and protect B lymphocytes from anti-FAS induced apoptosis. In short, this combination of methods made it possible to obtain a substantial number of highly enriched functional murine FDCs.