Promotion of long-term heart allograft survival by combination of mobilized donor plasmacytoid dendritic cells and anti-CD154 monoclonal antibody.

Infusion of donor immature dendritic cells (DC) can significantly prolong survival of organ allografts, and this is believed to be due to antigen recognition by T cells in the absence of co-stimulation. In this study we report that a single pre-operative infusion of donor-mobilized immature plasmacytoid dendritic cells (pDCs) is superior to that of other DC sub-sets in suppressing allograft rejection. The combination of pDC infusion with injection of anti-CD154 monoclonal antibody further inhibited graft rejection and, in 50% of the mice, led to indefinite graft survival. This finding suggests a role for the plasmacytoid DC sub-set in facilitating organ transplant survival and also in the treatment of autoimmune disorders.

Isolation and characterization of plasmacytoid dendritic cells from Flt3 ligand and granulocyte-macrophage colony-stimulating factor-treated mice.

Interferon alpha/beta plays an important role in the first-line defense against viral infections and can modulate cytokine responses by T-helper cells. Type 1 interferons (IFNs) are clinically important in infectious diseases and in the treatment of leukemia and lymphomas. Many different cell types have the capacity to produce IFN-alpha after encounter with virus and bacteria. The major, natural type 1 IFN-producing cell in humans was recently described as the plasmacytoid T cell, or pDC2, and it can differentiate into dendritic cells (DCs) on culture. This study describes the murine natural IFN-alpha-producing cell, or pDC2, that shares morphologic features with its human counterpart but has some distinct phenotypical characteristics. Murine plasmacytoid DCs can be differentially isolated based on their expression of CD11c, B220 (CD45R), and Thy1.2 (CD90). They lack expression of myeloid (eg, CD11b) antigens and CD8 alpha, a marker used to isolate lymphoid DCs. Like human pDC2, murine plasmacytoid DCs exhibit their maximal type 1 IFN-producing capacity at a precursor stage; pDCs isolated from bone marrow responded to viral stimulation with higher IFN-alpha production than cells of the same phenotype isolated from spleen. Mobilization of mice with Flt3 ligand (Flt3L) or Flt3L and granulocyte-macrophage colony-stimulating factor, hematopoietic factors that specifically enhance DC growth, resulted in strikingly increased numbers of pDC in bone marrow and spleen. The isolation of this novel murine DC subset may serve as a useful tool in the study of viral immunobiology and for the design of treatments for murine malignancies.

Human interdigitating dendritic cells induce isotype switching and IL-13-dependent IgM production in CD40-activated naive B cells.

Interdigitating dendritic cells (IDC) represent a mature progeny of dendritic cells (DC) in vivo and are exhibiting a strong lymphocyte stimulatory potential. Because of the restricted localization to secondary lymphoid organs where decisive cellular interactions take place in the initial events of immunity, IDC regulatory function was addressed in relation to naive B cells. In this study, we demonstrate that human tonsillar IDC induce a dual response from CD40-activated IgD+/CD38- naive B lymphocytes. IDC direct naive B cells toward either isotype switching or an IL-13-dependent IgM secretion. IDC-dependent proliferation, isotype switching, and Ig production are all strictly mediated by soluble factors, suggesting that such skewing in B cell activation is the result of differential cytokine expression. Moreover, IDC-expressed IL-13 represents a novel source of a cytokine with recently established effects in Th2 induction as well as in immunological disorders resulting in allergic reactions.

CD19+ pro-B cells can give rise to dendritic cells in vitro.

Dendritic cells (DC) have the specific capacity of initiating primary T cell responses and ultimately derive from precursors in bone marrow. DC were originally thought to be only of myeloid origin, and myeloid precursor cells could be induced to differentiate into functional DC in response to granulocyte-macrophage (GM)-CSF. However, early CD4low precursor cells from the thymus can also develop into DC when cultured in IL-1beta, IL-3, IL-7, TNF-alpha, stem cell factor, and Flt-3L. In that case, GM-CSF was not required. We now show that CD19+ pro-B cells develop into DC with T cell stimulatory properties when cultured under similar conditions. These pro-B cells acquired the DC-related markers CD11c and NLDC145/DEC205, along with CD80/B7-1, CD86/B7-2, and a high density of MHC class II Ags. The marrow-derived DC did not express CD4 or CD8alpha, which are markers related to thymic DC. These findings are consistent with a new pathway through which DC are generated from B lymphoid precursors.

Stimulation of CD40 in human bladder carcinoma cells inhibits anti-Fas/APO-1 (CD95)-induced apoptosis.

CD40 and the CD95 (Fas/APO-1 antigen) are both members of the tumor necrosis factor receptor family. Whereas CD40 mediates a strong growth stimulatory signal in B cells, engagement of the CD95 receptor leads to growth inhibition and induction of apoptosis. As it has been reported that CD40 activation may rescue B cells from undergoing apoptosis, we were interested to see whether it had a similar effect in other cells expressing the CD40 receptor. We used epithelial tumor cells from the urinary bladder, a cell type that frequently expresses CD40 but for which no clear function of the molecule has been assigned. We found that the ligation of CD95 with the antibody anti-APO-1 induced apoptosis in most of the cell lines tested. Stimulation of CD40 with antibodies or a soluble construct of the CD40 ligand was shown to protect cells from apoptosis, as demonstrated by their ability to suppress the growth inhibition exerted by the anti-APO-1 antibody. Our results show that CD40 stimulation make cells less vulnerable to apoptosis induced via CD95 and suggest that CD40 expression on epithelial tumors may be associated with cell survival.

IL-6 antisense oligonucleotides inhibit IgE production in IL-4 and anti-CD40-stimulated human B-lymphocytes.

Stimulation of tonsillar B-lymphocytes with CD40 antibodies and IL-4 leads to homotypic adhesion, proliferation, and differentiation into Ig-producing cells. It also leads to the production of IL-6, a pleiotropic cytokine involved in B-cell maturation and differentiation. To assess the importance of IL-6 in the differentiation process, an antisense oligonucleotide to IL-6 was added to tonsillar B-cells together with CD40 antibodies and IL-4. This led to clearly reduced levels of IL-6 as well as to a specific inhibition of IgE production. Also, IgG secretion was somewhat reduced while IgM appeared to be unaffected. The effects were not due to toxicity of the oligonucleotide since proliferation proceeded normally or was slightly enhanced in the presence of the antisense. The findings show that endogenous IL-6 is an important co-factor for the generation of B-cells secreting IgE and IgG but that it is not required for IgM production. They further indicate that IL-6 may not be necessary as a co-factor in CD40/IL-4 induced proliferation.

Human interdigitating dendritic cells directly stimulate CD40-activated naive B cells.

Human interdigitating dendritic cells (IDC) were isolated from tonsils based on their CD40+ lineage-negative expression in situ. Isolated IDC displayed a phenotypic profile similar to that of IDC in tonsils and spleen in situ, characterized by high-level expression of major histocompatibility complex class II, the co-stimulatory molecules B7.1 (CD80) and B7.2 (CD86), expression of the late DC maturation marker CD83, and no expression of CD1a, CD13, or CD33. IDC also showed weak nonspecific esterase staining and had the ability to induce an allogeneic mixed lymphocyte reaction. In this study, we further show that in the presence of surrogate activated T cells in the form of CD40 ligation and IL-2, IDC enhance the proliferation of naive B cells and induce their differentiation into plasma cells producing IgM. Evidence for the anatomical co-localization of naive B cells and IDC in the T cell area together with the data obtained in vitro implies a role for IDC in the initiation of the extrafollicular reaction.

CD40 ligation counteracts Fas-induced apoptosis of human dendritic cells.

Dendritic cells (DC) are cells of the hematopoletic system specialized in capturing antigens and initiating T cell-mediated immune responses. We show here that human DC generated in vitro by culturing CD34+ cord blood progenitor cells in granulocyte macrophage colony stimulating factor plus tumor necrosis factor-alpha express the Fas antigen (APO-1, CD95) and undergo apoptosis upon triggering of Fas by mAb. However, only a proportion of the cells die in response to Fas ligation, an observation that may be related to the virtual absence of the bcl-2 protein in about half of the cells. Ligation of DC CD40 by culture on CD40L-transfected fibroblastic cells up-regulates the expression of bcl-2 and, concomitantly, renders DC virtually resistant to Fas-induced apoptosis. Parallel experiments with mature, interdigitating dendritic cells (IDC) isolated from tonsils revealed that IDC express Fas but do not enter into apoptosis following Fas ligation, a finding that may be explained by their high levels of bcl-2. Thus, upon encountering antigen-specific T cells, DC become resistant to Fas-induced apoptosis, as a consequence of CD40 ligation and possibly by mechanisms associated to the up-regulation of bcl-2 protein expression.

CD40 ligation on human cord blood CD34+ hematopoietic progenitors induces their proliferation and differentiation into functional dendritic cells.

Human CD34+ multilineage progenitor cells (CD34HPC) from cord blood and bone marrow express CD40, a member of the tumor necrosis factor-receptor family present on various hematopoietic and nonhematopoietic cells. As hyper-IgM patients with mutated CD40 ligand (CD40L) exhibit neutropenia, no B cell memory, and altered T cell functions leading to severe infections, we investigated the potential role of CD40 on CD34HPC development. CD40-activated cord blood CD34HPC were found to proliferate and differentiate independently of granulocyte/macrophage colony-stimulating factor, into a cell population with prominent dendritic cell (DC) attributes including priming of allogeneic naive T cells. DC generated via the CD40 pathway displayed strong major histocompatibility complex class II DR but lacked detectable CD1a and CD40 expression. These features were shared by a dendritic population identified in situ in tonsillar T cell areas. Taken together, the present data demonstrate that CD40 is functional on CD34HPC and its cross-linking by CD40L+ cells results in the generation of DC that may prime immune reactions during antigen-driven responses to pathogenic invasion, thus providing a link between hematopoiesis, innate, and adaptive immunity.

CD40 antibodies defining distinct epitopes display qualitative differences in their induction of B-cell differentiation.

IgE production can be obtained in vitro by stimulating B lymphocytes with CD40 antibodies and interleukin-4 (IL-4). This stimulation also results in homotypic aggregation and cell proliferation. We have shown previously that IgE synthesis may be dependent on additional signals provided by the close cellular contact. Thus inhibition of the aggregation by lymphocyte function-associated antigen-1 (LFA-1) antibodies leads to a decrease in IgE production. In the present study we show that the inhibitory effect of LFA-1 antibodies is critically dependent on the CD40 antibody used for stimulation. Thus, while previously using the monoclonal antibody (mAb) S2C6, IgE production induced by the CD40 antibody mAb89 was generally higher and could be enhanced more than fivefold in the presence of LFA-1 antibodies. Similarly, the addition of the CD23 mAb MHM6, which blocked aggregation to a similar degree as the LFA-1 antibodies, inhibited S2C6-induced IgE production but enhanced that induced by mAb89. In contrast to these opposing effects on IgE synthesis, proliferation induced by the two CD40 antibodies was affected similarly by the blocking antibodies. As the interaction between CD23 and CD21 has been suggested to involve recognition of carbohydrate structures on CD21 by the lectin-like domain on CD23, we also tested the effect of some different sugars on IgE synthesis and proliferation. Addition of fucose-1-phosphate to anti-CD40 and IL-4-stimulated B cells completely inhibited IgE synthesis and proliferation. Inhibition was also seen with mannose-6-phosphate but not with glucose-1-phosphate. In contrast to the MHM6 antibody, the effect of the sugars was similar irrespective of the CD40 antibody used for stimulation. The study shows that different antibodies to CD40 may give rise to qualitatively distinct signals depending on the epitope recognized.

Antibodies to distinct epitopes on the CD40 molecule co-operate in stimulation and can be used for the detection of soluble CD40.

The B-cell surface protein, CD40, belongs to the tumour necrosis factor/nerve growth factor (TNF/NGF) receptor family and plays a crucial role in T cell-dependent B-cell activation. Ligation of this receptor with antibodies or its recently defined ligand, gp39, generates an intracellular signal that, when combined with triggering of surface immunoglobulin or the interleukin-4 (IL-4) receptor, induces a variety of stimulatory effects in B cells. In this study we provide further evidence for the importance of receptor cross-linking in generating this signal and we also report on the presence of a soluble form of CD40. A new CD40 monoclonal antibody (mAb), 17:40, was found to synergize with other CD40 antibodies (mAb89 and S2C6) in inducing proliferation as well as IgE synthesis in IL-4-treated tonsillar B cells. However, both this mAb and mAb89 failed to co-operate with a soluble construct of the CD40 ligand, whereas such co-operation was seen with the S2C6 antibody. Cross-inhibition experiments showed that the 17:40 mAb recognized an epitope that was clearly distinct from that seen by S2C6 and mAb89. Although directed to separate epitopes, both 17:40 and mAb89 completely blocked binding of gp39 to its receptor, while the S2C6 mAb only partially interfered with this binding. The findings suggest a close relationship between the degree of receptor clustering and the strength of the delivered signal. With the access to antibodies recognizing distinct structures on CD40 we also established a sandwich enzyme-linked immunosorbent assay for quantitative determinations of the antigen. With this assay we could demonstrate the presence of a soluble form of CD40 (sCD40) in culture supernatants. The fact that sCD40 also retained its ligand-binding capacity indicates that it may have an important regulatory role and modulate the T cell-dependent stimulation via CD40. Both the finding of soluble receptors and the need for receptor clustering are features that CD40 share with other members of the TNF/NGF receptor family.

Interleukin-10 inhibits motility in murine and human B lymphocytes.

We here report the finding that the anti-inflammatory cytokine interleukin-10 (IL-10) inhibits motility of B lymphocytes. B cells were induced to display motile morphology and active migration by IL-4. IL-10 inhibited locomotor responses to IL-4, when B cells of both murine and human origin were used. The inhibitory effect of IL-10 was reversible, since washing of B cells preincubated in IL-10 restored the ability to respond to IL-4. Time-course experiments showed that IL-10 did not have to be present from the very onset of culture, but could be added as late as 5 hr after initiation. In addition, murine B cells stimulated with lipopolysaccharide (LPS) showed motile morphology, as well as cellular aggregation and proliferation. All these parameters were suppressed by IL-10. However, viability of B cells was not adversely affected by IL-10. Exposure to IL-10 did not result in any changes in the surface expression of molecules involved in adhesion, such as CD2, CD11a/CD18, CD44, CD54 or L-selectin, on B lymphocytes.

CD23 and CD21 function as adhesion molecules in homotypic aggregation of human B lymphocytes.

We have previously found that interleukin-4 and CD40 monoclonal antibodies (mAb) are strong potentiators of homotypic B cell aggregation which is dependent on LFA-1. We show here that CD23 mAb were also able to inhibit aggregation to a similar extent as LFA-1 antibodies. This inhibition was restricted to the MHM6 epitope of CD23 and antibodies to other epitopes [Epstein-Barr virus (EBV) CS-1, EBV CS-2, EBV CS-5 and mAb 25] or occupation of the Fc-binding site by IgE had no or a slightly enhancing effect on aggregation. When testing two antibodies to CD21, the recently defined ligand for CD23, one of these (BU32) was found to be inhibitory whereas the other (THB5) had no effect. By combining antibodies to LFA-1 and CD23, aggregation was often completely inhibited. These data suggest that LFA-1/ICAM-1 and CD23/CD21 are the major molecules involved in homotypic aggregation of human B cells.

Inhibition of LFA-1-dependent human B-cell aggregation induced by CD40 antibodies and interleukin-4 leads to decreased IgE synthesis.

Antibodies to CD40 have been shown to induce homotypic aggregation of human resting B cells and B-cell lines via an LFA-1-dependent mechanism. We show here that interleukin-4 (IL-4) is a strong potentiator of this process and stimulation of tonsillar B cells for 4 days with IL-4 and CD40 antibodies resulted in the formation of large, dense aggregates. Also in this case, aggregation appeared to be chiefly dependent on the activation of LFA-1, although the small clusters of cells remaining after blocking with LFA-1 antibodies suggest the involvement of another adhesion system(s). When testing the relationship between aggregation and IgE synthesis, a known consequences of IL-4/CD40 stimulation, IgE levels were found to be significantly decreased in the presence of LFA-1 antibodies. In contrast to these observations, proliferation occurring in response to the IL-4/CD40 stimulation was not inhibitable by LFA-1 antibodies. Rather, in most cases, this was slightly enhanced, suggesting that aggregation may have a limiting effect on cell growth. Isolated aggregates, each of which could comprise more than 10(5) cells, were also examined by electron microscopy. This revealed a tissue-like structure of the aggregates with large contact areas and with minimal intercellular space between the adjacent cells. As the apparent inhibitory effect of aggregation on proliferation may reflect a negative autocrine signalling, which is enhanced by the close cell contact, we also tested the effect of neutralizing antibodies to IL-6, one of the factors known to be produced in the system. Such treatment did not affect aggregation but in most experiments enhanced proliferation. The results suggest that a possible effect of aggregation may be to enhance differentiation of cells and that this may also be associated with the difficulties in growing B cells in vitro.

Interleukin-4-mediated aggregation of anti-IgM-stimulated human B cells: inhibition of aggregation but enhancement of proliferation by antibodies to LFA-1.

Direct cellular interactions, involving adhesion structures like lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1), play a critical role in the initial stages of T-cell-dependent B-cell activation. However, the relevance of cellular contact in later, lymphokine driven stages of B-cell stimulation is less well understood. We have here studied the ability of different lymphokines [interleukin (IL)-1 alpha, IL-1 beta, IL-2, IL-3, IL-4, IL-6 and interferon-gamma (IFN-gamma)] to stimulate adhesion processes as well as proliferation of highly purified tonsillar B lymphocytes. None of the lymphokines were by themselves able to induce aggregation in resting B cells but, when added together with anti-IgM, IL-4 and to a lesser extent IL-2, promoted the formation of large, dense aggregates which were macroscopically visible after 3-4 days in culture. Addition of anti-LFA-1 antibodies (anti-CD11a or CD18) completely inhibited the lymphokine-promoted aggregation, indicating that cluster formation was mediated by LFA-1. Fluorescence-activated cell sorter (FACS) analysis showed that the expression of both LFA-1 and ICAM-1 increased after stimulation with IL-4 as well as with IFN-gamma. However, in contrast to IL-4, IFN-gamma did not enhance cellular aggregation, suggesting that qualitative rather than quantitative changes in LFA-1/ICAM-1 promote aggregation. Although anti-LFA-1 antibodies inhibited aggregation of both IL-2- and IL-4-stimulated cells they did not inhibit proliferation. In contrast, in IL-4-stimulated cultures inhibition of cell contact resulted in a significantly increased proliferation. Furthermore, IFN-gamma-stimulated cells responded with proliferation in the absence of aggregation. Taken together, the findings suggest that LFA-1-dependent cellular contact plays a minor role in lymphokine driven B-cell proliferation. The possible importance of aggregation in B-cell differentiation is discussed.

Expression of CD40 and CD43 during activation of human B lymphocytes.

CD40 and CD43 are two cell-surface glycoproteins that appear to be functionally involved in the growth stimulation of human B cells. Whereas CD40 is structurally similar to the NGF receptor and is present on all resting B cells, CD43 displays no homology to other known proteins and is expressed only on a subpopulation of these cells. To further understand the extra- and intracellular signals regulating these molecules and in which stage of activation they may play a role, we used various activation strategies and studied their expression on tonsillar B cells. As expected, activation of protein kinase C by TPA increased both CD40 and CD43. In contrast, a rise in intracellular Ca2+, e.g. by ionomycin, did not influence the expression of these antigens. However, in the presence of TPA, ionomycin further up-regulated CD43 but not CD40. Anti-IgM behaved similarly to ionomycin suggesting that the effect of this reagent was due primarily to its ability to increase intracellular Ca2+. Of three interleukins (IL-2, IL-4 and IL-6) only IL-4 had a significant effect when used alone in that it up-regulated CD40 but not CD43. However, in the presence of anti-IgM, both IL-2 and IL-4 synergistically up-regulated the two antigens. Complementation of antigen receptor stimulation with TPA or IL-4 increased CD40 during the first 24 h, whereas up-regulation of CD43 did not occur until 24 to 48 h after stimulation. With regard both to up-regulation in response to different stimuli and to kinetics, CD40 expression paralleled that of the early activation antigen CD23, whereas CD43 was induced in parallel with the transferrin receptor (CD71). Taken together, our results suggests that the expression of CD40 and CD43 is regulated by different intracellular signals and that CD40 may be important during early activation, whereas CD43 may have its major function during later stages of B-cell differentiation. These assumptions are in line with the observations that CD40 antibodies can directly activate resting B cells and that CD43 are retained on plasma cells.

Studies on the role of CD43 in human B-cell activation and differentiation.

The monoclonal antibody (MoAb) B1B6 to human leucocyte sialoglycoprotein, CD43, induces aggregation of T cells and delivers progression signals early during activation of both T and B cells in the presence of primary activators of protein kinase C. In this report we further studied the role of CD43 in human B-cell activation and differentiation. About 5-10% of resting tonsillar B cells are CD43+. In the presence of TPA or antibodies to CDw40, the proportions of CD43+ cells drastically increased. The expression was optimal on day 3 of culture, when up to 80% and 50%, respectively, were CD43+. Whereas MoAb B1B6 together with TPA induced a three- to fivefold higher proliferative response as compared to TPA alone, antibodies to CDw40 did not synergize with MoAb B1B6 in B-cell proliferation. Tonsillar populations depleted of CD43+ B cells responded with lower proliferation to TPA alone or to TPA and B1B6 or anti-CDw40 antibodies. MoAb B1B6 did not affect the production of IgM or IgG as induced by pokeweed mitogen in the presence of autologous T cells, from either peripheral blood or tonsillar B cells. Neither did it affect the IgG production from the CD43+ BSF-2 sensitive Epstein-Barr virus-transformed lymphoblastoid cell line CESS. The results show that CD43 is upregulated on B cells during activation. Furthermore, CD43+ B cells are included in the population which responds to signals delivered by TPA, anti-CD43 or anti-CDw40 antibodies, and the proliferation of this population is not merely due to an expansion of the small population of CD43+ cells present among these cells. Moreover, the epitopes recognized by MoAb B1B6 are not involved in the differentiation of and ultimate Ig-secretion from activated B cells.

Enhancement of human B-cell proliferation by a monoclonal antibody to CD43.

Monoclonal antibodies (MoAb) to human leucocyte sialoglycoprotein, CD43, have been shown to deliver mitogenic signals to human T cells or to enhance T-cell proliferation induced by concanavalin A, anti-CD3 antibodies or phorbol ester. In this paper, we studied the effects of anti-CD43 MoAb B1B6 on the activation of human B cells. Anti-CD43 MoAb B1B6 was not mitogenic by itself for human B cells. However, when added together with TPA, both resting and in vivo activated tonsillar B cells, containing 5-10% and about 35% CD43+ respectively, responded with three- to fivefold higher proliferation compared to that obtained with TPA alone. A peak in the proliferative response was reached on day 3. Optimal proliferation was obtained when the antibody was present from the start of culturing. Addition of MoAb B1B6 together with a calcium ionophore, ionomycin, did not induce B-cell proliferation. Neither did mAb B1B6 sustain the growth of B cells that were already in the cell cycle, i.e. precultured with phorbol ester (PDB) and ionomycin for 3 days. The results are similar to those obtained with antibodies to CD22 and CD23 and show that early progression signals are delivered to resting B cells through CD43 in the presence of primary activators of protein kinase C.

Induction of CD43 expression during activation and terminal differentiation of human B cells.

Only a small population (25-30%) of human peripheral blood B lymphocytes expresses large sialoglycoprotein (LSGP) (CD43). However, in the presence of autologous T cells and pokeweed mitogen (PWM) a majority (50-90%) of the immunoglobulin-producing cells (cIg+ cells) that develop from these B cells express CD43 is detected with anti-CD43 monoclonal antibodies (MoAb) B1B6, and the proportion of CD43+cIg+ cells increases with time of culture. Furthermore, a relatively larger proportion (60-80%) of the IgG-producing cIg+ cells are CD43+ compared with IgM-containing cIg+ cells (30-50%). In human tonsils, significantly more CD43+ cells (35%) are found in the in vivo-activated fraction of B cells than in the fraction of resting B cells (5%). A majority of the cIg+ cells that develop from the resting or the in vivo-activated tonsillar B cells in a PWM-induced B-cell differentiation system are CD43+ (80-100%). Furthermore, tonsillar B cells depleted of CD43+ cells give rise to cIg+ cells, of which the majority are CD43+, and the proportion of such cells increases with time of culture (60-90%). Taken together, these results indicate that LSGP belongs to a group of B-cell membrane molecules that are induced and upregulated upon activation and differentiation.