Proliferation of non-Hodgkin-lymphoma lymphocytes in vitro is dependent upon follicular dendritic cell interactions

Dual time-point FDG PET/CT and FDG uptake and related enzymes in lymphadenopathies: preliminary results

PURPOSE

The purpose of this study was to determine the ability of dual time-point (DTP) PET/CT with (18)F-FDG to discriminate between malignant and benign lymphadenopathies. The relationship between DTP FDG uptake and glucose metabolism/hypoxia markers in lymphadenopathies was also assessed.

METHODS

Patients with suspected lymphoma or recently diagnosed treatment-naive lymphoma were prospectively enrolled for DTP FDG PET/CT (scans 60 min and 180 min after FDG administration). FDG-avid nodal lesions were segmented to yield volume and standardized uptake values (SUV), including SUVmax, SUVmean, cSUVmean (with partial volume correction), total lesion glycolysis (TLG) and cTLG (with partial volume correction). Expression of glucose transporter-1 (GLUT-1), hexokinase-II (HK-II), glucose-6-phosphatase (G6Pase) and hypoxia-inducible factor-1alpha (HIF-1alpha) were assessed with immunohistochemistry and enzyme activity was determined for HK and G6Pase.

RESULTS

FDG uptake was assessed in 203 lesions (146 malignant and 57 benign). Besides volume, there were significant increases over time for all parameters, with generally higher levels in the malignant lesions. The retention index (RI) was not able to discriminate between malignant and benign lesions. Volume, SUVmax, TLG and cTLG for both scans were able to discriminate between the two groups statistically, but without complete separation. Glucose metabolism/hypoxia markers were assessed in 15 lesions. TLG and cTLG were correlated with GLUT-1 expression on the 60-min scan. RI-max and RI-mean and SUVmax, SUVmean and cSUVmean on the 60-min scan were significantly correlated with HK-II expression.

CONCLUSION

RI was not able to discriminate between malignant and benign lesions, but some of the SUVs were able to discriminate on the 60-min and 180-min scans. Furthermore, FDG uptake was correlated with GLUT-1 and HK-II expression.

Connexin 43 communication channels in follicular dendritic cell development and in follicular lymphomas

Follicular dendritic cells (FDC) show homo- and heterocellular metabolic coupling through connexin 43 (Cx43) gap junctions and support B cell selection and maturation in germinal centers. In follicular lymphomas B cells escape apoptosis while FDC develop abnormally. Here we tested Cx43 channels in reactive FDC development and follicular lymphomas. In culture, the treatment of FDC-B cell clusters (resembling to “ex vivo” germinal centers) with Gap27 peptide, mimicking the 2nd extracellular loop of Cx43 protein, significantly impaired FDC-B cell cluster formation and cell survival. In untreated cultures of intact clusters, cell proliferation showed a moderate reduction. In tissues, Cx43 protein levels run parallel with the density of FDC both in reactive germinal centers and in malformed follicles of follicular lymphomas and showed strong upregulation in newly generated and/or degrading bi-/multinuclear FDC of rudimentary processes. However, the inverse correlation between Cx43 expression and B cell proliferation seen in reactive germinal centers was not detected in follicular lymphomas. Furthermore, Cx43 levels were not associated with either lymphoma grade or bone marrow involvement. Our results suggest that Cx43 channels are critical in FDC and “ex vivo” germinal center development and in the persistence of FDC in follicular lymphomas but do not affect tumor progression.

Impact of the reactive microenvironment on the bone marrow involvement of follicular lymphoma

AIMS

  Follicular lymphoma (FL) is associated with bone marrow (BM) involvement in approximately 40-70% of cases. Previous studies have suggested that the immune-microenvironment of FL plays an important role in the clinical behaviour of the disease. To investigate the role of the microenvironment in BM involvement of FL, we performed immunophenotypical analysis of the reactive cell populations in lymph nodes (LN) and corresponding BM of 35 patients with FL. Microenvironment patterns of BM infiltrates were compared to the corresponding features of the LN in cases with BM manifestation, and the LN microenvironment was compared in FL cases with and without BM involvement.

METHODS AND RESULTS

  Automated image-segmentation-based quantitation was performed in whole digital slides of tissue microarrays of formalin-fixed paraffin-embedded tissue biopsies. We found significantly more CD8(+) T lymphocytes, forkhead box protein 3 (FoxP3)(+) T lymphocytes and CD68(+) macrophages and fewer PD1(+) T lymphocytes in the BM than in the matching LN samples. Furthermore, we observed significantly fewer CD8(+) T cells and CD68(+) macrophages in cases involving the BM compared to those localized only to the LNs.

CONCLUSIONS

  Our study showed that different tumour cell growth in the LN and BM may generate different microenvironments, and suggested that the reduced number of cytotoxic T lymphocytes and macrophages in LNs favours BM infiltration of neoplastic cells in FL.

Entourage: the immune microenvironment following follicular lymphoma

In follicular lymphoma, nonmalignant immune cells are important. Follicular lymphoma depends on CD4+ cells, but CD8+ cells counteract it. We hypothesized that the presence of follicular lymphoma is associated with higher CD4+ than CD8+ cell numbers in the tumor microenvironment but not in the immune system. Using flow cytometry, pre-treatment and follow-up CD4/CD8 ratios were estimated in the bone marrow, blood and lymph nodes of untreated follicular lymphoma patients in two independent data sets (N₁=121; N₂=166). The ratios were analyzed for their relation with bone marrow lymphoma involvement. Bone marrows were also investigated with immunohistochemistry. In either data set, the bone marrow CD4/CD8 ratios were higher in bone marrows involved with lymphoma (P=0.043 and 0.0002, respectively). The mean CD4/CD8 ratio was 1.0 in uninvolved and 1.4 in involved bone marrows. Also higher in involved bone marrows were CD4/CD56 and CD3CD25/CD3 ratios. No blood or lymph node ratios differed between bone marrow-negative and -positive patients. Sequential samples showed increased bone marrow CD4/CD8 ratios in all cases of progression to bone marrow involvement. Immunohistochemistry showed CD4+, CD57+, programmed death-1+, forkhead box protein 3+ and CD21+ cells accumulated inside the lymphoma infiltrates, whereas CD8+, CD56+ and CD68+ cells were outside the infiltrates. This study provides evidence in vivo that the microenvironment changes upon follicular lymphoma involvement.

The immunoglobulin heavy chain gene 3' enhancers induce Bcl2 deregulation and lymphomagenesis in murine B cells

Human follicular B-cell lymphoma is associated with the t(14;18) chromosomal translocation that juxtaposes the Bcl2 proto-oncogene with the immunoglobulin heavy chain (Igh) locus, resulting in the deregulated expression of Bcl2. Our previous studies have shown that the Igh 3' enhancers deregulate the Bcl2 expression in vitro. However, the effects of the Igh 3' enhancer elements on Bcl2 expression in vivo are not known. To investigate the role of the Igh 3' enhancers in Bcl2 deregulation, we used gene targeting to generate knock-in mice in which four DNase I-hypersensitive regions from the murine Igh 3' region were integrated 3' of the Bcl2 locus. Increased levels of Bcl2 mRNA and protein were observed in the B cells of Igh-3'E-bcl2 mice. B cells from Igh-3'E-bcl2 mice showed an extended survival in vitro compared with B cells from wild-type (Wt) mice. The Bcl2 promoter shift from P1 (the 5' promoter) to P2 (the 3' promoter) was observed in B cells from Igh-3'E-bcl2 mice, similar to human t(14;18) lymphomas. The IgH-3'E-bcl2 mice developed monoclonal B-cell follicular lymphomas, which were slowly progressive. These studies show that the Igh 3' enhancers have an important role in the deregulation of Bcl2 and B-cell lymphomagenesis in vivo.

Down-regulation of CD9 expression and its correlation to tumor progression in B lymphomas

Histological transformation, a pivotal event in the natural history of cancers including lymphomas, is typically associated with more aggressive clinical behavior. L3055, a B lymphoma cell line of germinal center (GC) origin, is dependent on follicular dendritic cells (FDCs) for survival and proliferation, similar to GC-B cells. However, L3055 cells become less FDC-dependent after prolonged culture, which is analogous to transformation in vivo. Comparison of two L3055 subclones (i.e., the FDC-dependent indolent clone 12 and the FDC-independent aggressive clone 33) by DNA microarray revealed that CD9 was the most differentially expressed gene (P = 0.05). L3055-12 expresses high levels of CD9 while L3055-33 does not. Reduced levels or loss of CD9 expression is also observed in other CD9-positive B lymphoma cell lines. The resultant CD9-negative cells grow faster than CD9-positive cells due to their greater resistance to apoptosis. Furthermore, CD9-negative cells are less dependent on FDCs for their survival and growth compared with CD9-positive cells. CD9 down-regulation in B lymphomas appears to be controlled epigenetically, mainly through histone modifications. These findings imply that CD9 is inversely correlated with B lymphoma progression, and CD9 inactivation may play an important role in B lymphoma transformation.

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.

Glut1 and Glut3 expression in lymphoma and their association with tumor intensity on 18F-fluorodeoxyglucose positron emission tomography

OBJECTIVE

To evaluate the expression of glucose transporters (Gluts) 1 and 3 in Hodgkin and nonHodgkin lymphoma and to assess the association between their expression and the tumor intensity on 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET).

METHODS

All 31 lymphoma patients in whom the histologic diagnosis was made and who had also undergone a prechemotherapy PET scan at our institution between June 2001 and December 2005 were included in this retrospective study. The percentage of tumor cells in the various lymphoma subtypes was estimated by comparison of hematoxylin and eosin stain with a lineage-associated immunohistochemical stain on the same block of tissue. Tissue specimens were stained with Glut1 and Glut3 antibodies. The percentages of Glut1+ and Glut3+ cells in the entire cell population (lymphoma cells and nonlymphomatous cells) and among the lymphoma cells were estimated. FDG PET images were reviewed and the tumor intensity was assessed by calculating the maximum standard uptake value (SUVmax). Correlation coefficients between SUVmax and the percentage of Glut1+ and Glut3+ cells in the entire cell population were calculated.

RESULTS

In all 31 cases, tumors were visible on FDG PET and positive for Glut1 and Glut3. The correlation between the percentage of Glut1+ cells and SUVmax was statistically significant across all 31 cases (r = 0.73, P<0.0001, 95% confidence interval: 0.50-0.86) and across the 25 cases of nonHodgkin lymphoma (r = 0.71, P<0.0001, 95% confidence interval: 0.44-0.87). There was no statistically significant correlation between the percentage of Glut3+ cells and SUVmax. More importantly, in 16 of 31 cases (52%), only nonlymphomatous, benign cells expressed Glut1 or Glut3.

CONCLUSION

Intensity of lymphoma on FDG PET is likely associated with Glut1 expression. The nonlymphomatous, benign cells may play an important role in visualization of lymphoma on FDG PET.

Exploration of factors affecting the onset and maturation course of follicular lymphoma through simulations of the germinal center

Genetic mutations frequently observed in human follicular lymphoma (FL) B-cells result in aberrant expression of the anti-apoptotic protein bcl-2 and surface immunoglobulins (Igs) which display one or more novel variable (V) region N-glycosylation motifs. In the present study, we develop a simulation model of the germinal center (GC) to explore how these mutations might influence the emergence and clonal expansion of key mutants which provoke FL development. The simulations employ a stochastic method for calculating the cellular dynamics, which incorporates actual IgV region sequences and a simplified hypermutation scheme. We first bring our simulations into agreement with experimental data for well-characterized normal and bcl-2(+) anti-hapten GC responses in mice to provide a model for understanding how bcl-2 expression leads to permissive selection and memory cell differentiation of weakly competitive B-cells. However, as bcl-2 expression in the GC alone is thought to be insufficient for FL development, we next monitor simulated IgV region mutations to determine the emergence times of key mutants displaying aberrant N-glycosylation motifs recurrently observed in human FL IgV regions. Simulations of 26 germline V(H) gene segments indicate that particular IgV regions have a dynamical selective advantage by virtue of the speed with which one or more of their key sites can generate N-glycosylation motifs upon hypermutation. Separate calculations attribute the high occurrence frequency of such IgV regions in FL to an ability to produce key mutants at a fast enough rate to overcome stochastic processes in the GC that hinder clonal expansion. Altogether, these simulations characterize three pathways for FL maturation through positively selected N-glycosylations, namely, via one of two key sites within germline V(H) region gene segments, or via a site in the third heavy chain complementarity-determining region (CDR-H3) that is generated from VDJ recombination.

Targeting the follicular lymphoma microenvironment through blockade of TNFalpha with etanercept

Follicular dendritic cells (FDCs) support the survival of follicular lymphoma (FL). Tumor necrosis factor alpha (TNFalpha) is overexpressed by FL cells and is critical in the development and maintenance of FDCs. We hypothesised that TNFalpha might be an ideal therapeutic target. We treated seven patients with relapsed/refractory FL with 8 weeks of etanercept, 25 mg SC on day 1 and 4 of each week. Patients without progression received 16 additional weeks of etanercept. All patients completed at least 8 weeks of etanercept and two patients completed 24 weeks. At the 8 week evaluation five patients had SD. Of the five with SD, two progressed at 9 and 12 weeks on therapy and the remaining three progressed between 12 and 24 weeks after initiating therapy. Minimal toxicity was observed. FDG-PET imaging demonstrated decreases in standardized uptake value (SUV) following treatment with etanercept in five patients. Further studies in FL targeting the microenvironment in conjunction with standard cytotoxic therapy are warranted.

Growth pattern and distribution of follicular dendritic cells in mantle cell lymphoma: a clinicopathological study of 96 patients

Mantle cell lymphoma (MCL) is an aggressive lymphoma with accepted risk factors such as proliferation markers. To date, the different follicular dendritic cell (FDC) patterns have never been analyzed in comparison with the overall survival time. Lymph node biopsy specimens from 96 patients were analyzed by conventional morphology and immunohistochemistry with antibodies against cluster differentiation (CD)20, CD5, CD23, cyclin D1, and FDC (Ki-M4P). Two groups can be distinguished with different FDC patterns: a nodular pattern in 79 cases and a diffuse pattern in 17 cases. A Kaplan-Meier analysis revealed significantly better survival for the nodular group (p=0.0312). This group was subdivided into a group with a nodular FDC pattern similar to the FDC distribution in primary follicles (PF-nodular in 72 cases) and one with a nodular FDC pattern resembling the colonization of germinal centers (GCs) by tumor cells (GC-nodular in seven cases). A Kaplan-Meier analysis showed that patients with MCL with a PF-nodular FDC pattern had a significantly better clinical outcome than patients with the other two patterns (p=0.0033). If only cases with classical cytology (n=79) were analyzed (blastoid types excluded), patients with a PF-nodular FDC pattern had a better clinical outcome (p=0.0008). The distribution of FDC in MCL is a diagnostic tool for identifying patients with a better clinical prognosis.

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

The germinal centre is a dynamic microenvironment where antigen-activated B cells rapidly expand and differentiate, generating plasma cells and memory B cells. These cellular events are accompanied by dramatic changes in the antibody molecules that undergo somatic hypermutation and isotype switching. Follicular dendritic cells (FDCs) are the stromal cells located in the germinal centre. Although the capacity of FDCs to present antigen to B cells through antigen-antibody complexes has been recognized for many years, additional critical functions of FDCs have only recently been recognized. FDCs prevent apoptosis of germinal centre B cells and stimulate cellular interaction and proliferation. Here, we review the FDC signalling molecules that have recently been identified, some of which offer potential therapeutic targets for autoimmune diseases and B-cell lymphomas.

The stromal composition of malignant lymphoid aggregates in bone marrow: variations in architecture and phenotype in different B-cell tumours

We present evidence that different B-cell tumours, in bone marrow, have different relationships to stroma. Marrow core biopsies from 46 patients with B-cell tumours were immunostained with antibodies for distinct stromal cells. Cases included follicular lymphoma (FL), chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma (MCL), lymphoplasmacytic lymphoma (LPL), and nodal, extranodal and splenic marginal zone lymphoma (NMZL, MALT, SMZL). In normal marrow, low-affinity nerve growth factor receptor (LNGFR) highlighted a fine network of adventitial reticular cells (ARC). The nodular aggregates of CLL/SLL, NMZL, MALT and SMZL were characterized by distortion of the ARC network and downregulation of LNGFR. In contrast, the aggregates of FL, LPL and MCL were composed of linear arrays of ARC in tight association with individual tumour cells. LNFGR+ was upregulated in ARC associated with the aggregates in FL, LPL and focally in MCL. Upregulation of CD35, vascular cell adhesion molecule (VCAM-1) and CD40 on ARC was noted exclusively in FL. Marrow lymphoid aggregates in CLL/SLL, NMZL, MALT and SMZL probably grow by displacing the pre-existing marrow stroma, while FL and LPL maintain a close association with the ARC network. In FL, expression of follicular dendritic cell-associated markers is modulated in pre-existing marrow stromal cells.

Establishment of a follicular lymphoma cell line (FLK-1) dependent on follicular dendritic cell-like cell line HK

A novel cell line, FLK-1, was established from bone marrow cells of a patient with follicular lymphoma by means of co-culture with follicular dendritic cell (FDC)-like cell line HK. Immunophenotypic analysis showed that FLK-1 expressed CD10, CD19, CD20, CD38, IgG and HLA-DR, which is a typical feature of germinal center B cells. Cytogenetic analysis of FLK-1 demonstrated t(14;18)(q32;q21) translocation involving BCL2 and immunoglobulin heavy chain genes. Especially noteworthy is that the growth of FLK-1 was found to be dependent on a FDC line, HK. When HK cells were removed from the culture, FLK-1 cells stopped growing and eventually died. An apoptotic mechanism appeared to be involved as indicated by the presence of chromosome condensation and DNA ladder formation. The culture experiment using micropore membranes showed that soluble factor(s) of HK cells supported the growth, while direct cell-to-cell contact appeared to be necessary for longterm cell proliferation. These findings suggest the importance of the micro-environment for follicular lymphoma cells to grow. The FLK-1 cell line may thus prove to be useful for studying the growth mechanism of follicular lymphoma and provide new insights into the pathogenesis of follicular lymphoma.

Expression of beta-catenins and cadherins by follicular dendritic cells in human lymph nodes

In lymph nodes, dendritic cells form a complex meshwork and are linked by intercellular junctions. Intercellular junctions contribute to the integrity of lymphatic follicles and can potentially be affected by malignant processes in neighbouring B cells. We examined whether transmembrane molecules that constitute "adherens junctions" are present in follicular dendritic cells of normal human lymph nodes. We found that follicular dendritic cells but not interdigitating dendritic cells or sinus lining cells expressed cadherin molecules. Follicular dendritic cells also expressed beta-catenin but not vinculin. The cadherin molecules, which were identified in situ with the use of a monoclonal pan-cadherin antibody, were not recognized by antibodies to E-cadherin, N-cadherin or P-cadherin. Intrafollicularly, cadherins were clearly colocalized with beta-catenins, in a dot-like fashion. We also detected intrafollicular expression of desmogleins and desmosomal plaque proteins. These findings indicate the presence of desmosomes within the dendritic meshwork. However, pan-cadherin reactivity was not only colocalized with desmoglein immunoreactivity that was abundantly present. Immunoprecipitation showed that pan-cadherin reactivity was absent in fractions of desmosomal plaque proteins or pan-desmogleins. We speculate that complexes of cadherins of an unknown subclass and beta-catenins form non-desmosomal intercellular junctions in the intrafollicular dendritic meshwork.

The indispensable role of microenvironment in the natural history of low-grade B-cell neoplasms

Follicular lymphoma (FL) and B-cell chronic lymphocytic leukemia (B-CLL) are paradigmatic examples of lymphoid malignancies in which the relevant biological mechanisms are alterations in the control of apoptosis rather than an exaggerated proliferation. This explains why low-grade B-cell neoplasms still fail to be cured with current approaches. It is becoming increasingly clear that the defective apoptosis of FL and B-CLL has to be ascribed not only to intrinsic defects of the neoplastic cells, but also to extrinsic factors that influence their behavior. Malignant B cells retain the capacity to respond to microenvironmental signals, but have devised a monothematic responsiveness. They have a specific sensitivity to anti-apoptotic signals that favor their survival, whereas they seem to have become insensitive to pro-apoptotic signals. Bystander, nontumoral cells play a fundamental (though not sufficient) role both in the onset and in the progression of these diseases. The survival of leukemic cells appears to be dependent on direct cell-cell contacts. The localization of malignant B cells in bone marrow or neoplastic follicles is not a passive adhesion phenomenon but a crucial step for their survival. Bidirectional malignant lymphocyte-nontumoral cell interactions may lead to the amplification of a microenvironment able to inhibit the apoptosis of neoplastic B cells. The pressure of antigenic selection and the role of the tumor necrosis factor receptor family through the functional survival signal provided by CD40 together with the crippled death signal exerted by CD95 are new prominent characters on the stage.

Functional effects of TNF and lymphotoxin alpha1beta2 on FDC-like cells

Recent studies suggest that tumor necrosis factor (TNF) family members such as TNFalpha and lymphotoxin alphabeta (LTalpha1beta2) are important in the development of follicular dendritic cells (FDCs) and maintenance of FDC function. In this study we used FDC-like cells (FDC-LC) cultured from normal human tonsil and investigated the effects of TNF and LTalpha1beta2 on expression of adhesion molecules and the production of cytokines and chemokines. TNF and LTalpha1beta2 both increased the expression of VCAM-1 and ICAM-1 on FDC-LC. In addition, IL-4 with LTalpha1beta2 synergistically increased the expression of VCAM-1, but not ICAM-1. Cytokine IL-6 and IL-15 mRNAs were induced following stimulation with TNF and LTalpha1beta2. These two cytokines were present in FDC-LC supernatants by ELISA and increased following TNF and LTalpha1beta2 stimulation. We also examined FDC-LC for chemokines, which affect B cells, including IL-8, SDF-1, MIP3beta/ELC, and BCA-1/BLC. SDF-1 mRNA and protein were expressed by FDC-LC, and following stimulation with TNF and LTalpha1beta2, decreases in both were observed. Therefore, TNF and LTalpha1beta2, which are produced by activated B cells, increased the expression of adhesion molecules and cytokines from FDC-LC, potentially providing key signals to support germinal center B cell survival and differentiation.

Identification of a human follicular dendritic cell molecule that stimulates germinal center B cell growth

The initial interaction between B cells and follicular dendritic cells (FDCs) appears to be essential for germinal center (GC) formation. To identify molecules regulating this interaction, we generated FDC-staining monoclonal antibodies (mAbs) and screened them for their ability to block FDC-mediated costimulation of growth and differentiation of CD40-stimulated B cells. Using one of the inhibitory mAbs, 8D6, we expression cloned the cDNA encoding the 8D6 antigen (Ag) from a human FDC line, HK. The 8D6 Ag is a novel protein of 282 amino acids that is expressed abundantly on FDCs. Monolayers of COS cells transiently transfected with the 8D6 Ag cDNA stimulate B cell growth. The mAb 8D6 blocks the costimulatory function completely. The inhibitory activity of the mAb 8D6 was demonstrated to be due to an inhibition of cell cycle progression of CD40 ligand-stimulated GC B cells. In addition, the mAb 8D6 inhibits the growth of a lymphoma of GC origin, L3055, which depends on FDCs or HK cells for its growth. These findings suggest that the primary function of FDCs in the GC is to stimulate B cell growth. An FDC signal molecule, 8D6 Ag, may be an important molecule to mediate this function.

Unbalanced Expression of Bcl-2 Family Proteins in Follicular Lymphoma: Contribution of CD40 Signaling in Promoting Survival

Although highly responsive, advanced stage follicular lymphoma (FL) is not curable with conventional treatment. This relative resistance is thought to be due to the t(14;18) that results in the constitutive overexpression of the death-inhibiting protein bcl-2. However, the observation that FL cells are sensitive to treatment in vivo and prone to apoptosis on in vitro culture questions whether bcl-2 alone is responsible for the pathogenesis and clinical behavior of this disease. Therefore, multiple genes are likely to be involved in both the lymphomagenesis and the clinical course of FL. We examined whether expression of other bcl-2 family genes might also be operative. Here, we show that FL cells display a different pattern of expression of bcl-2 family proteins from normal germinal center (GC) B cells that are thought to be their normal counterpart. FL cells express the death-suppressor proteins bcl-2, bcl-xL, and mcl-1; whereas GC B cells express bcl-xL and mcl-1 but also the proapoptotic proteins bax-α and bad. Although maintaining constitutive levels of bcl-2 and mcl-1, FL cells are not protected from apoptosis when cultured in vitro. Their propensity to undergo apoptosis is temporally associated with downregulation of bcl-xL. More importantly, activation of FL cells via CD40 not only prevents downregulation but increases the level of bcl-xL expression and results in promotion of survival. These results support the hypothesis that the overexpression of bcl-2 is not the only antiapoptotic mechanism responsible for the pathogenesis of FL. Survival of FL cells is determined by a number of death-inhibiting proteins, among which bcl-xL appears to have the most critical role. Moreover, these findings are consistent with the hypothesis that, although FL cells are malignant, they respond to microenvironmental signals such as CD40L that appear to contribute to their survival through the upregulation of death-inhibiting proteins.

Unbalanced Expression of Bcl-2 Family Proteins in Follicular Lymphoma: Contribution of CD40 Signaling in Promoting Survival

Although highly responsive, advanced stage follicular lymphoma (FL) is not curable with conventional treatment. This relative resistance is thought to be due to the t(14;18) that results in the constitutive overexpression of the death-inhibiting protein bcl-2. However, the observation that FL cells are sensitive to treatment in vivo and prone to apoptosis on in vitro culture questions whether bcl-2 alone is responsible for the pathogenesis and clinical behavior of this disease. Therefore, multiple genes are likely to be involved in both the lymphomagenesis and the clinical course of FL. We examined whether expression of other bcl-2 family genes might also be operative. Here, we show that FL cells display a different pattern of expression of bcl-2 family proteins from normal germinal center (GC) B cells that are thought to be their normal counterpart. FL cells express the death-suppressor proteins bcl-2, bcl-xL, and mcl-1; whereas GC B cells express bcl-xL and mcl-1 but also the proapoptotic proteins bax-α and bad. Although maintaining constitutive levels of bcl-2 and mcl-1, FL cells are not protected from apoptosis when cultured in vitro. Their propensity to undergo apoptosis is temporally associated with downregulation of bcl-xL. More importantly, activation of FL cells via CD40 not only prevents downregulation but increases the level of bcl-xL expression and results in promotion of survival. These results support the hypothesis that the overexpression of bcl-2 is not the only antiapoptotic mechanism responsible for the pathogenesis of FL. Survival of FL cells is determined by a number of death-inhibiting proteins, among which bcl-xL appears to have the most critical role. Moreover, these findings are consistent with the hypothesis that, although FL cells are malignant, they respond to microenvironmental signals such as CD40L that appear to contribute to their survival through the upregulation of death-inhibiting proteins.

Extracellular matrix and beta 1 integrin expression in nodal and extranodal T-cell lymphomas

Since non-Hodgkin's lymphoma (NHL) cells interact with surrounding structures similarly to their normal counterparts, micro-environmental changes and the aberrant expression of adhesion molecules are considered to be of importance in lymphomagenesis. In this immunohistochemical study, the composition of several extracellular matrix (ECM) components and the expression of their beta 1 integrin receptors were examined in nodal and extranodal T-cell NHLs. Except for the T-lymphoblastic NHLs, almost all T-NHLs displayed abundant deposition of matrix and considerable expression of the alpha 4 and beta 1 integrin chains. This is in contrast to B-cell NHLs, which show ECM patterns comparable to those in reactive lymphoid tissue or, in cases of high-grade malignancy, active matrix degradation and very low expression or absence of beta 1 integrins, as previously described. This difference is probably based on distinct cytokine production in B- and T-cell malignancies. As in B-NHL, nodal and extranodal T-NHLs of the same morphological subtype exhibit identical ECM patterns, which suggests that malignant lymphoid cells of both B and T origin create at least part of their own specific micro-environment.

Expression of the intercellular adhesion molecule-1 on high endothelial venules and on non-lymphoid antigen handling cells: interdigitating cells, antigen transporting cells and follicular dendritic cells

Intercellular adhesion molecule-1 (ICAM-1) has been implicated in the development of germinal center reactions in vitro, and the present study was undertaken to determine the distribution of ICAM-1 in active germinal centers in vivo and in murine secondary lymphoid tissues in general. Anti-ICAM-1-specific monoclonal antibodies were used in conjunction with immunohistochemistry at both the light and ultrastructural levels of resolution. Examination of cryostat sections of lymph nodes, spleens, and Peyer's patches revealed that anti-ICAM-1 distinctly labeled cells in the light zones of germinal centers, a few cells in the T cell zones (e.g. paracortex of lymph nodes), cells in the sinus floor of the subcapsular sinuses of lymph nodes, and high endothelial venules (HEV). Ultrastructural studies revealed that the cells labeling with anti-ICAM-1 in germinal centers were follicular dendritic cells (FDC) which appeared to have more ICAM-1 than any other cell type. The surfaces of well-developed, intricate, convoluted FDC processes were intensely labeled even under conditions where B cells appeared negative. Interdigitating cells (IDC) were also labeled as were certain endothelial cells in the HEV. The cells in the subcapsular sinus floor labeling with anti-ICAM-1 were the "antigen transporting cells" (ATC) that carry antigen-antibody complexes into lymph node follicles. We suspect ATC are FDC precursors which mature into FDC in the follicles. Interestingly, FDC, IDC, and ATC are 3 important accessory cells known to handle antigens in specific compartments of lymphoid tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular dendritic cells in non-Hodgkin's lymphomas

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

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

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

Follicular dendritic cells in non-Hodgkin-lymphoma express adhesion molecules complementary to ligands on neoplastic B-cells

In non-Hodgkin-lymphoma (NHL) with nodular growth patterns, follicular dendritic cells (FDC) form a spherical network which contains neoplastic B-cells. In order to dissect the basis of this close FDC/B cell association, the antigenic profile of adhesion molecules expressed by individual FDC and NHL-B-lymphocytes was evaluated. FDC isolated from NHL were found to express C3bi receptors (CD11b), the very late antigen (VLA) alpha-5- and alpha-6-chain (CD49e, CD49f), and the intercellular adhesion molecule-1 (ICAM-1; CD54). Only a percentage of the FDC population was positive for the VLA beta-1- and alpha-3-chain (CD29, CD49c), the vitronectin receptor (CD51) and the vascular cell adhesion molecule-1 (VCAM-1). B-cells obtained from the lymph nodes of patients with centroblastic-centrocytic lymphoma expressed several ligands complementary to the adhesion molecules detected on FDC. These include LFA-1 alpha- and beta-chains (CD11a, CD18), and ICAM-1 (CD54). Surprisingly, monoclonal lymphocytes in the peripheral blood of patients with a leukaemic course of this lymphoma entity were devoid of these antigens. It seems likely then that neoplastic B-cells without CD11a, CD18 and CD54 surface molecules are unable to associate with FDC and now invade other compartments. Thus, the adhesive interactions which do occur between FDC and NHL-B-cells may directly influence the peculiar growth pattern and spread of centroblastic-centrocytic lymphoma.