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J Kwekkeboom

Publications and source records attributed to J Kwekkeboom.

At least 19 recordsLinked to original sources
PubMed2006

Prednisolone suppresses the function and promotes apoptosis of plasmacytoid dendritic cells.

Organ transplant recipients are highly susceptible to viral infections early after transplantation. Plasmacytoid dendritic cells (PDC) play a major role in antiviral immunity. Therefore, we determined the numbers of circulating PDC after liver transplantation (LTX) and established the effects of immunosuppressive drugs on PDC survival and function. PDC were determined longitudinally in 13 LTX recipients treated with prednisone and cyclosporin or tacrolimus. Purified PDC were cultured with or without clinically relevant concentrations of cyclosporin, tacrolimus or prednisolone. Apoptosis induction was monitored by determination of active caspase-3, nuclear condensation and annexin-V/7AAD staining. After LTX, a 4-fold reduction in the number of circulating PDC was observed (p < 0.01), which recovered partially after discontinuation of prednisone treatment. In vitro, prednisolone induced apoptosis in PDC, while cyclosporin and tacrolimus did not. Higher doses of prednisolone were needed to induce apoptosis in Toll-like receptor (TLR)-stimulated PDC. However, non-apoptosis inducing concentrations of prednisolone suppressed interferon-alpha production, upregulation of co-stimulatory molecules and allo-stimulatory capacity of TLR-stimulated PDC. In conclusion, prednisolone induces apoptosis in PDC, which explains the decline in circulating PDC numbers after transplantation. Moreover, prednisolone suppresses the functions of TLR-stimulated PDC. Therefore, corticosteroid-free immunosuppressive therapy may reduce the number and severity of viral infections after transplantation.

Adult↗
PubMed2005

Polymorphisms in the T cell regulatory gene cytotoxic T lymphocyte antigen 4 influence the rate of acute rejection after liver transplantation.

BACKGROUND: The cytotoxic T lymphocyte antigen 4 (CTLA-4) gene encodes for a membrane bound (mCTLA-4) and a soluble (sCTLA-4) isoform, which are both involved in regulation of T cell function. The CTLA-4 +49A/G single nucleotide polymorphism (SNP) influences expression of mCTLA-4; +6230G/A SNP affects the production of sCTLA-4. AIM: To examine whether these functional SNPs influence the rate of rejection after liver transplantation. PATIENTS AND METHODS: Liver graft recipients (n = 483) were genotyped for both SNPs, and haplotypes were reconstructed. Association with rejection was tested by the log rank test using the Kaplan-Meier method with time to the first acute rejection episode as outcome. Multiple analysis of SNPs together with demographic factors was performed by Cox regression. RESULTS: Three haplotypes were observed in the cohort: +49A/+6230A, +49A/+6230G, and +49G/+6230G. The +49A/+6230G haplotype was significantly and dose dependently associated with acute rejection (p = 0.01). Of the demographic factors tested, only underlying liver disease was significantly associated with rejection. Adjusted for underlying liver disease, each additional +49A/+6230G haplotype allele resulted in a significantly higher risk of acute rejection (risk ratio 1.34 (95% confidence interval 1.04-1.72); p = 0.02). Patients who lacked this haplotype had the lowest, carriers an intermediate, and homozygotes the highest risk of acute rejection. CONCLUSION: The CTLA-4 +49A/+6230G haplotype, which encodes for normal mCTLA-4 expression but reduced sCTLA-4 production, is a co-dominant risk allele for acute rejection after clinical liver transplantation. This implies that even under immunosuppression, CTLA-4 is critically involved in the regulation of the human immune response to allogeneic grafts.

Acute Disease↗
PubMed2005

Decrease of CD4+CD25+ T cells in peripheral blood after liver transplantation: association with immunosuppression.

CD25 (IL-2 receptor alpha-chain) marks a population of CD4-positive T cells with a suppressor phenotype. These CD4+CD25+ regulatory T cells can suppress both effector T cells and antigen-presenting cells and have been identified as a principle regulator of tolerance in experimental transplantation models. In the setting of human liver transplantation, however, little is known about the dynamics of these cells in relation to rejection, tolerance, and immunosuppression. In the current study we determined CD4+CD25+ T cell in blood of liver transplant recipients using flow cytometry and investigated a possible link with immunosuppressive therapies. Peripheral blood mononuclear cells (PBMC) of 27 liver transplant patients (pretransplantation and 12 months posttransplantation) and 16 healthy controls were included. We found that the percentages of CD25+ cells within the CD4 T-cell population was significantly reduced in more than two-thirds of patients 1 year after transplantation. Also the total percentage of CD4-positive T cells declined significantly within this period, making the absolute reduction of regulatory T cells after transplantation even more profound. Comparing PBMC samples of patients and healthy controls revealed an increased percentage of CD4+ T cells in the patients before transplantation, probably related to the chronic liver illness. The reduction in CD4+CD25+ T cells after transplantation was similar for different immunosuppression regiments. All patients, however, received calcineurin inhibitors, suggesting a possible suppressive effect of this therapy on regulatory T-cell levels in peripheral blood. Currently, assays for regulatory T-cell activity are used to further support this hypothesis.

Adrenal Cortex Hormones↗
PubMed2005

Flow cytometry of fine-needle-aspiration biopsies: a new method to monitor the intrahepatic immunological environment in chronic viral hepatitis.

SUMMARY: Information about the character and grade of the intrahepatic immune response in viral hepatitis is important for the evaluation of disease stage and effect of therapy. Complications like haemorrhage limit the frequent performance of tissue-needle biopsies (TB), and the cells of peripheral blood have to be used as surrogate markers instead. Fine-needle-aspiration biopsy (FNAB) of the liver represents a safe and atraumatic method that allows frequent cytological sampling. Our aim was to investigate whether flow cytometry of FNAB specimens allows co-analysis of phenotype, function and specificity of key populations of liver-infiltrating lymphocytes (LIL). In 20 consecutive patients with chronic viral hepatitis [10 hepatitis B virus (HBV), 10 hepatitis C virus (HCV)], flow cytometry was performed on FNAB cytology, and simultaneously on lymphocytes isolated from a TB and peripheral blood mononuclear cells (PBMC). The ratio of CD8+/CD4+ lymphocytes in FNAB correlated well with LIL from TB (r =0.78, P < 0.05) but differed from PBMC (mean ratio: 2.6, 2.1 and 0.7, respectively). Similarly, a correlation was observed for percentage CD56+ natural killer (NK) cells (mean %: 29.9, 32.3 and 14.5, respectively; r = 0.69, P < 0.05). The percentage of interferon (IFN)-gamma-producing CD3+ lymphocytes in both FNAB and TB was higher than in PBMC (mean %: 41, 44 and 22, respectively; P < 0.05). Furthermore, tetrameric complexes allowed analysis of HBV-specific T cells in FNAB specimens. In conclusion, flow cytometry of FNAB allows easy, atraumatic and reliable analysis of lymphocytes obtained from the intrahepatic compartment. Therefore, the FNAB is a valuable tool in the study of the immunopathology of viral hepatitis, and it may contribute to the improved clinical evaluation of chronic viral liver disease.

Biopsy, Fine-Needle↗
PubMed2005

Hepatitis B immunoglobulins inhibit dendritic cells and T cells and protect against acute rejection after liver transplantation.

The efficacy of anti-viral intravenous immunogobulins (anti-HBs Ig and anti-CMV Ig) in preventing acute rejection after liver transplantation was assessed in a retrospective analysis, and correlated to their effects on immune cells in vitro. HBs Ag-positive liver graft recipients (n = 40) treated prophylactically with anti-HBs Ig had a significantly lower incidence of acute rejection compared with recipients without viral hepatitis (n = 147) (12% vs. 34%; p = 0.012), while the incidence of rejection in HCV-positive recipients (n = 29) was similar to that in the control group. Treatment with anti-CMV Ig (n = 18) did not protect against rejection. In vitro, anti-HBs Ig suppressed functional maturation of and cytokine production by human blood-derived dendritic cells (DC) at concentrations similar to the serum concentrations reached during anti-HBs Ig treatment of liver graft recipients. In addition, anti-HBs Ig inhibited allo-antigen- and lectin-stimulated proliferation of peripheral T cells. Anti-CMV Ig suppressed functional DC-maturation and alloantigen-stimulated T-cell proliferation, but not lectin-driven T-cell proliferation. In conclusion, anti-HBs Ig protects against acute rejection after liver transplantation, probably by functional inhibition of the two principal immune cells involved in allograft rejection, DC and T cells.

Adult↗
PubMed2004

Human hepatic lymph nodes contain normal numbers of mature myeloid dendritic cells but few plasmacytoid dendritic cells.

We investigated whether the hyporesponsiveness of the adaptive arm of the liver immune system is related to the composition of the dendritic cell (DC) population in hepatic lymph nodes. Noninflamed human hepatic lymph nodes (LN) were obtained from multiorgan donors, inflamed hepatic LN from liver transplant recipients with autoimmune cholestatic liver diseases, and inguinal LN from kidney transplant recipients. Quantitative immunohistochemistry showed that all three types of LN contained comparable numbers of mature and immature myeloid DC, but that noninflamed and inflamed hepatic LN contained significantly fewer plasmacytoid DC as compared to inguinal LN. Likewise, DC-enriched cell preparations from hepatic LN contained relatively few plasmacytoid DC. The difference in numbers of plasmacytoid DC was confirmed in comparisons of hepatic LN and ileacal LN from the same organ-donors. Myeloid DC from hepatic LN showed similar expressions of HLA-DR, CD83, and CD86, and higher expression of CD80 compared to myeloid DC from inguinal LN. In conclusion, hepatic LN contain similar numbers of myeloid DC as muscle/skin lymph-draining LN, with no signs of immaturity, but relatively few plasmacytoid DC.

Antigens, CD↗
PubMed2004

Monitoring intrahepatic CD8+ T cells by fine-needle aspiration cytology in chronic hepatitis C infection.

Infection of the liver with hepatitis C virus (HCV) causes compartmentalization of CD8+ cytotoxic T cells to the site of disease. These cells are thought to be involved in viral clearance during interferon therapy. The repetitive analysis of the intrahepatic immune response is hampered by the difficulty to obtain the intrahepatic T cells. The fine-needle aspiration biopsy (FNAB) technique was evaluated for its use to obtain liver-derived CD8+ T cells in a minimally invasive way. In 26 chronic HCV patients who were evaluated for Peg-interferon and ribavirin combination therapy, pre-treatment FNABs and peripheral blood specimens were obtained simultaneously with liver tissue biopsies, and CD3+ and CD8+ T cells were quantified by immunocytochemistry. The CD8+/CD3+ ratio was significantly higher in the FNABs than in peripheral blood (P < 0.01), and similar to those in portal areas in the tissue biopsies. A significant correlation was observed between numbers of CD3+CD8+ T lymphocytes in the FNABs and the numbers of CD8+ cells in the lobular fields or in the portal tracts of the liver tissue biopsies, but not with CD3+CD8+ T lymphocytes in peripheral blood. Finally, the ratio of CD8+/CD3+ T lymphocytes in FNABs was significantly higher in those patients who responded rapidly to therapy when compared with slow responders at 4 weeks of treatment (P = 0.02). These findings demonstrate that the intrahepatic T-cell composition is reflected in FNABs, and that the FNAB technique can be used for predicting early virological response to therapy of patients chronically infected with HCV.

Biopsy, Fine-Needle↗
PubMed2003

Expression of CD80 on Kupffer cells is enhanced in cadaveric liver transplants.

In experimental animals inhibition of T cell co-stimulation immediately after organ transplantation effectively prevents rejection. We investigated whether the expression of co-stimulatory molecules is enhanced in cadaveric liver transplants, whether their expression is influenced by the transplantation procedure, and whether variation in expression between liver transplants is related to the occurrence of acute rejection. Expression of CD80, CD86 and the macrophage marker CD68 were determined by immunohistochemistry in biopsies from 40 clinical liver transplants obtained at different time-points during the transplantation procedure, and in normal liver tissue obtained from 10 human livers. Expression of CD80 and CD86 on Kupffer cells was graded by comparison with CD68-staining. In a subgroup CD80 and CD86 mRNA was quantified by real-time detection polymerase chain reaction. CD86 was expressed in all liver transplants and normal livers on the majority of Kupffer cells. CD80 was absent or sporadically expressed in normal liver tissue, but in 18 of 40 liver transplants at least one-quarter of Kupffer cells expressed CD80. CD80- and CD86-mRNA and protein expression in liver transplants did not change during the warm ischaemic and reperfusion phases of the transplantation procedure. CD80-expression on Kupffer cells varied strongly between individual donor livers; this variation was, however, not significantly related to the occurrence of acute rejection after transplantation. In conclusion, in nearly half of cold-preserved cadaveric liver transplants an increased proportion of Kupffer cells express CD80 at the time of transplantation in comparison with normal liver tissue. The expression was not further induced by warm ischaemia and reperfusion. However, the observed variation in CD80-expression between liver transplants is not a accurate predictive measure for acute rejection.

Adult↗
PubMed2003

In vivo immunization following virus suppression: a novel approach for inducing immune control in chronic hepatitis B.

summary. Antiviral treatment of patients with active chronic hepatitis B may lead to significant reduction in morbidity and mortality. However, after stopping nucleoside therapy, relapse rates are high in those without acquired specific immunity. We have treated two chronic hepatitis B patients with in vivo immunization. In vivo immunization aims to optimize conditions for an effective immune response: following rapid and profound virus suppression by interferon-lamivudine combination therapy, lamivudine is withdrawn intermittently for 4 weeks during continued interferon therapy. In both patients with profound virus suppression a rapid rebound in viral replication was observed after lamivudine withdrawal; despite continued interferon. These periods of renewed viral replication were followed by rises in hepatitis activity. After re-introduction of lamivudine HBV DNA became undetectable by PCR followed by normalization of serum ALT. These observations are a stimulus to further explore the concept of in vivo immunization as a novel therapeutic approach for chronic hepatitis B.

Adult↗
PubMed2003

The role of intrahepatic immune effector cells in inflammatory liver injury and viral control during chronic hepatitis B infection.

Cytotoxic T lymphocytes (CTL) and Kupffer cells play an important role in the immune control of hepatitis B virus (HBV), but may also induce liver injury during infection. We investigated the intrahepatic immune response in liver biopsies of chronic HBV patients in relation to inflammatory liver injury and viral control. Forty-seven liver biopsies from patients with chronic HBV with varying degrees of inflammation (ALT values) were selected. Acute hepatitis and normal liver specimens served as controls. Immune effector cells, cytotoxic effector molecules and cytokine producing cells were quantified after immunohistochemical staining in lobular and portal areas of the biopsies. The intralobular number of CD8+ T-lymphocytes was significantly decreased in biopsies of patients with high ALT (r = -0.54; P < 0.001). Higher ALT-values were correlated with increased numbers of granzyme+ cells in portal areas (r = 0.65; P < 0.001) and higher numbers of intralobular Fas-L+ cells (r = 0.32; P = 0.05). Fas-L was expressed on Kupffer and lymphoid cells. More intralobular CD8+ T-lymphocytes were found in HBeAg- than in HBeAg+ patients (P = 0.002). But IFN-gamma and TNF-alpha producing cells were observed sporadically in chronic HBV patients. Hence, in chronic HBV infection, low viral replication and HBeAg negativity is related to increased presence of intralobular CD8+ T-lymphocytes. Persistence of the virus may be caused by the absence of cells producing anti-viral cytokines in the liver. Inflammatory liver injury during chronic HBV infection is probably not the result of increased numbers of infiltrating CD8+ T-lymphocytes, but of Fas-L expression by Kupffer cells and increased cytolytic activity of cells in portal areas.

Adolescent↗
PubMed2001

In vitro cytokine production of TNFalpha and IL-13 correlates with acute liver transplant rejection.

Individuals may differ in their capacity to produce cytokines. Since cytokines play a key role in allograft rejection, we investigated whether inter-individual differences in cytokine production by in vitro stimulated PBMC are related to the occurrence of acute liver transplant rejection. Our study group comprised 49 liver transplant recipients and 30 healthy individuals. Rejection, which occurred within one month after liver transplantation, was defined in 22 patients ("rejectors") as biopsy-proven rejection, treated with high dose prednisolone. Patients who never experienced rejection episodes were termed as "nonrejectors" (n=27). PBMC of healthy individuals and of liver transplant recipients, collected late after transplantation (mean 3.5 years), were cultured in the presence and absence of Concanavalin A. The production of TNF-alpha, IFN-gamma, IL-10, and IL-13 was measured in supernatant after 1, 2, 3, 4, and 7 days of cell culture. In cell culture, stimulated PBMC of rejectors were found to produce significantly higher levels of TNF-alpha, while there was a trend towards higher production of IFN-gamma and IL-10 as compared to nonrejectors. After grouping patients into high or low cytokine producers based upon reference levels of the healthy individuals using multivariate analysis it was found that occurrence of acute liver transplant rejection correlated to high production of TNF-alpha and low production of IL-13. After stimulated cell culture PBMC of liver transplant recipients show a differential production of TNF-alpha and IL-13 which is correlated with the occurrence of acute liver transplant rejection.

Acute Disease↗
PubMed1998

A nylon wool filter coated with human immunoglobulin for rapid depletion of monocytes and myeloid cells from peripheral blood stem cell transplants.

The aim of this study was to develop an inexpensive method for reducing the number of differentiated cells from granulocyte colony-stimulating factor-mobilized leukocytapheresis products (LPs) containing peripheral blood stem cells. Analysis of LPs showed the presence of significant numbers of monocytes and myeloid cells. The myeloid cells represented largely immature stages of the granulocyte lineage (myelocytes and metamyelocytes). We investigated whether these cells could be selectively depleted by filtration over nylon wool. Filtration of LP samples over nylon wool in a medium containing fetal calf serum resulted in variable but on average low yields of CD34+ cells (48 +/- 30%; n=13) and strongly variable depletions of myeloid cells. The adherence of CD34+ cells to the polyamide fiber was partially mediated by activated platelets that were present in the LPs. Removal of platelets by counterflow centrifugal elutriation before filtration resulted in increased yields of CD34+ cells in the filtrates (65 +/- 13%; n=10). The yield of progenitor cells was similarly enhanced when trisodium citrate, a chelating substance, was added to the filtration medium. Adherence of the myeloid cells to the nylon fiber was promoted by preincubation of the columns with human immunoglobulin (Ig) (2 mg/mL). Small-scale filtrations of LP samples in the presence of trisodium citrate over columns with Ig-coated nylon wool resulted in removal of 96 +/- 4% of the monocytes and 74 +/- 18% of the myeloid cells, with a yield of 71 +/- 15% CD34+ cells and 67 +/- 10% granulocyte-monocyte colony-forming units (CFU-GM) (n=23). There was no loss of primitive stem cells during the procedure: the yield of late-appearing cobblestone area-forming cells (CAFCs, week 6) was 110 +/- 30% (n=4). CFU-GM production per CAFC-derived clone was unchanged upon filtration, indicating that the quality of stem cells was not affected. Moreover, the proportions of CD34+ cells expressing a primitive immunophenotype (CD38low or Thy-1+) were unchanged after filtration. Further enrichment of progenitor cells was obtained by separation of LP samples by elutriation before filtration. The combination of these two techniques resulted in complete removal of platelets, 89 +/- 7% depletion of erythrocytes, and 91 +/- 6% reduction of leukocytes, with a 50% yield of CD34+ cells (n=14). In conclusion, we have developed a rapid filtration technique by which monocytes and myeloid cells can be depleted from LP samples, with only minor loss of colony-forming cells and complete recovery of primitive stem cells.

Animals↗
PubMed1997

Separation of G-CSF-mobilized PBSC transplants by counterflow centrifugal elutriation: modest enrichment of CD34+ cells but no loss of primitive haemopoietic progenitors.

The suitability of counterflow centrifugal elutriation (CCE) for reduction of the number of non-stem cells in autologous G-CSF-mobilized peripheral blood stem cell (PBSC) transplants was investigated. By cell size-monitored CCE, small cells could be rapidly separated from the haemopoietic progenitor cells present in leukapheresis product (LP) samples. The large cell fraction contained an average 86 +/- 25% of the CD34+ cells and 76 +/- 20% of the granulocyte-macrophage progenitors (CFU-GM) loaded into the separation chamber, and was depleted of 75 +/- 18% of the lymphocytes, 89 +/- 7% of the erythrocytes and 98 +/- 2% of the platelets (n = 21). Due to the presence of high numbers of large immature myeloid cells, which co-elutriated with progenitor cells, enrichment of CD34+ cells in the large cell fraction was only modest (average 1.8 times). No indication of preferential co-elutriation of primitive stem cells with the small cells was obtained. There was no difference in expression of CD38 or Thy-1 on CD34+ cells between the two elutriation fractions. Frequencies of cobblestone-area-forming cells (CAFC) week 6, which are considered to represent cells with long-term repopulating ability, were reduced in the small cell fractions as compared to those in the unseparated samples and the large cell fractions. On average, 100% of CAFC week 6 were recovered in the large cell fractions (n = 5). In conclusion erythrocytes, platelets and 40-50% of leucocytes can be depleted from G-CSF-mobilized PBSC samples by CCE with an almost complete recovery of both clonogenic and primitive stem cells.

Antigens, CD34↗
PubMed1994

Helper effector function of human T cells stimulated by anti-CD3 mAb can be enhanced by co-stimulatory signals and is partially dependent on CD40-CD40 ligand interaction.

In this study we have investigated whether anti-CD3-induced human T cell help for immunoglobulin production could be enhanced by co-stimulation of the T cells via other T cell surface molecules, and the contribution of CD40-CD40 ligand interaction to the execution of T helper effector function induced by these different stimulatory signals. In a system in which irradiated tonsillar T cells were stimulated with immobilized anti-CD3 monoclonal antibody (mAb), it was found that ligation of CD2 with a mitogenic pair of mAb considerably enhanced anti-CD3-induced T cell help for immunoglobulin production. Likewise, ligation of CD28 with mAb enhanced T helper activity, although to a lesser extent. Upon addition of anti-CD28 and anti-CD2 mAb together, an even higher immunoglobulin production was observed. This combination resulted in a four- to fivefold increase in immunoglobulin production as compared to cultures in which T cells were stimulated with anti-CD3 mAb alone. The effect of ligation with B7, the natural ligand of CD28, was studied in a system which utilizes the presentation of anti-CD3 mAb on human Fc gamma RII-expressing mouse fibroblasts which were co-transfected with human B7. It appeared that B7 could stimulate help for immunoglobulin production much more efficiently than ligation of CD28 with mAb did. Physical separation of B cells from T cells led to complete abrogation of immunoglobulin production. Blocking of CD40 with specific mAb, which have no intrinsic B cell stimulatory properties, or the CD40 ligand with a soluble CD40-human IgM fusion protein, resulted in dose-dependent, but only partial, inhibition of T cell-dependent immunoglobulin production with all modes of T cell activation tested. A clear correlation was found between the induction of CD40 ligand expression on the T cells by the different modes of co-stimulation and subsequent immunoglobulin production by the B cells. It is concluded that ligation of CD28 and/or CTLA-4, and of CD2 can generate co-stimulatory signals for T cell help for immunoglobulin production, which was found to be only partially dependent on the CD40-CD40 ligand interaction.

Animals↗
PubMed1993

An efficient procedure for the generation of human monoclonal antibodies based on activation of human B lymphocytes by a murine thymoma cell line.

A new, efficient procedure for the generation of human monoclonal antibodies has been developed. The procedure is based on the activation of human B cells in microwells by murine thymoma EL4B5 cells. This mode of B cell stimulation leads to proliferation of at least one per eight of human B cells and to a high rate of antibody production. Subsequently, supernatants of the microwells are screened by ELISA for the presence of antibody of the desired specificity and B cells from selected wells are hybridized by electroporation. To optimize the procedure, the kinetics of the B cell expansion induced by EL4B5 cells were analysed. Counting and phenotyping of cultured cells at different time points indicated that the peak of B cell expansion occurred at day 5 for tonsil B cells (16-fold increase) and at day 7 for peripheral blood B cells (20-fold increase). The B cells did not merely proliferate but also differentiated, as indicated by loss of CD20 expression and increase of CD38 expression. At the peak of B cell expansion, B cells could be hybridized efficiently with myeloma cells. The majority of the resultant hybridomas secreted human immunoglobulin. The efficiency of the procedure is exemplified by the generation of hybridomas secreting human IgG against Haemophilus influenzae from limited numbers of either human tonsil B lymphocytes or peripheral blood B lymphocytes.

Animals↗
PubMed1993

Ligation of B7 with CD28/CTLA-4 on T cells results in CD40 ligand expression, interleukin-4 secretion and efficient help for antibody production by B cells.

It has been extensively shown that when T cells are co-stimulated with B7-CD28 interaction, a strong proliferative as well as cytolytic T cell response can be induced. In contrast, there exists only indirect evidence that the B7-CD28 interaction is of importance for the induction of T cell helper functions in B cell responses. Here we have used mouse fibroblasts transfected with the human Fc gamma receptor type II and human B7 to address this issue. We found that T cells, when activated through the T cell receptor (TcR)/CD3 complex with monoclonal antibodies and co-stimulated by B7-CD28 interaction, can provide efficient help for the induction of both IgM and IgG production by resting B cells. This helper activity is, at least in part, mediated by the interaction between the CD40 ligand on the T cells and CD40 on the B cells. We also demonstrate that more than one signal to the T cell is required for the induction of the CD40 ligand, one being delivered through the TcR/CD3 complex and the second by ligation of CD28 with the B7 molecule. In addition to the induction of cognate T helper function, we provide evidence that co-stimulation of T cells with B7-CD28 interaction can result in the secretion of both Th1- and Th2-type lymphokines.

Adult↗
PubMed1993

Direct evidence that human follicular dendritic cells (FDC) rescue germinal centre B cells from death by apoptosis.

It is supposed that FDC have a pivotal role in the rescue of germinal centre (GC) B lymphocytes from apoptosis. However, formal proof for this hypothesis has not as yet been presented. In the present study FDC and GC B cells were isolated from human tonsils and cultured. When brought into culture FDC and B cells rapidly formed spherical clusters. T cells were not observed inside these clusters. At different time points cultures of FDC and B cells were supravitally stained with Hoechst 33258 or acridine orange and examined by direct observation using fluorescence microscopy. Viable B cells appeared to be profoundly restricted to clusters, whereas cells not taking part in clusters all had an apoptotic appearance. The formation of clusters could be prevented by addition of MoAbs against CD11a (LFA-1 alpha) or CD49d (VLA-4 alpha), resulting in an apoptotic appearance of virtually all B lymphocytes. The present data demonstrate that a physical interaction between FDC and germinal centre B lymphocytes is able to rescue the latter from apoptotic cell death.

Apoptosis↗