HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by van Eijk, M. Articles by de Groot, C. Search for Related Content PubMed PubMed Citation Articles by van Eijk, M. Articles by de Groot, C.

Cutting Edge: Cellular Fas-Associated Death Domain-Like IL-1-Converting Enzyme-Inhibitory Protein Protects Germinal Center B Cells from Apoptosis During Germinal Center Reactions

Marco van Eijk^1,*, Jan Paul Medema and Cornelis de Groot^2,*

^* Department of Cell Biology and Histology, Cellular Immunology Group, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; and Department of Immunohematology and Bloodbank, Leiden University Medical Center, Leiden, The Netherlands

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
During germinal center (GC) reactions, follicular dendritic cells are believed to select memory B lymphocytes by switching off apoptosis in the successfully binding B cells. The cellular signals involved in this process are largely unknown. Here, we show that GC B lymphocytes have a long isoform of the cellular homologue of the viral Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein (cFLIP_L), which is capable of inhibiting death receptor-induced caspase activation. In isolated GC B cells, cFLIP_L decays rapidly even without Fas ligation, and this results in activation of caspase activity and apoptosis. Contact with follicular dendritic cells prevents cFLIP_L degradation and blocks all signs of apoptosis, even in the presence of anti-Fas Abs. cFLIP_L expression is sustained by CD40 ligation as well, suggesting that at least at some stage of the GC reaction activated T cells may help selected B cells to leave the follicular dendritic cell network without becoming apoptotic.

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
During germinal center (GC)³ reactions, memory B cells are generated with increased affinity of their B cell receptors (1, 2, 3). In this complicated process, Ag specificity and affinity of the B cell receptor is repeatedly checked to warrant high affinity without autoreactivity (4). Follicular dendritic cells (FDCs) are crucial, because they are believed to select the high affinity B cells by binding and switching off the trigger-prone apoptotic machinery of these cells.

Interestingly, GC B lymphocytes have an endonuclease in their nuclei that is readily activated when the B cell is detached from its microenvironment but is effectively silenced as soon as the contact with FDCs is restored in vitro (5, 6). Recently, we have shown that, in addition to and downstream of their caspase cascade, GC B lymphocytes have a thus far unidentified cathepsin activity that controls DNA fragmentation (7).

The mechanism by which FDCs silence apoptosis in adhering B cells is not clear. Freshly isolated single GC B cells have little caspase-3 activity, but this increases dramatically within a few hours at 37°C (7). Activation of caspases can be induced by signals derived from death receptors (DR) that belong to the TNFR1 family (8). GC B lymphocytes express Fas/APO-1/CD95, and this receptor is part of a well-studied DR pathway (9). Ligation of this DR results in the formation of an internal death-inducing signaling complex (DISC). When Fas is activated, the adapter molecule Fas-associated death domain will bind with its C-terminal death domain to Fas. The N-terminal death effector domain of the adapter molecule binds to the death effector domain of caspase-8, resulting in activation of this enzyme, followed by activation of caspase-3 (8). Fas ligation can induce cell death by two different routes. The type I cell death route implies the rapid formation of the DISC with high levels of active caspase-8. Alternatively, a type II cell death route involves low levels of DISC formation and caspase-8 activation. In this situation, amplification of the apoptotic signal involves loss of mitochondrial integrity, leading to cytochrome c release and consequent activation of caspase-9 (10).

Fas-associated death domain-like IL-1-converting enzyme-like inhibitory proteins (FLIPs) can inhibit both death routes. FLIPs were first identified as viral products that interfere with DR-mediated elimination of infected cells (11). Cellular homologues of viral FLIPs (cFLIPs) have been found as well (12). At least two splice variants have been described, a short and a long isoform (FLIP_L), which are both capable of inhibiting DR-induced apoptosis. Both cFLIP variants can block caspase-8 activation, but cFLIP_L is more potent (13).

Here, we show that cFLIP_L is highly expressed in GC B cells and is associated with survival of the cells. Its expression is critically dependent on physical interaction of these B cells with FDCs. In addition, cFLIP_L expression is sustained by CD40 ligation as well, thereby giving a clue as to how selected GC B lymphocytes might be able to escape the FDC network without undergoing apoptosis (i.e., by interaction with a proper T cell).

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
Isolation and culture of GC B lymphocytes and FDCs

B lymphocytes and FDCs were isolated from human tonsils as described previously (7). A total of 1 x 10⁶/ml purified GC B cells were incubated in IMDM with 10% FCS (HyClone Laboratories, Logan, UT) for 5 h at 37°C. GC B cells were incubated with or without the cathepsin inhibitor E64d (Scientific Marketing Associates, Barnet, U.K.). Fas ligation was done with the anti-Fas Ab CH11 (Immunotech, Luminy, France). CD40 ligation was done with a CD40 ligand (L)-transfected L cell line (the kind gift of Dr. C. van Kooten, Leiden University Medical Center, Leiden, The Netherlands). FDC-enriched fractions were incubated for 16 h at 37°C, and the resultant FDC-B cell clusters were purified by 1 x g sedimentation on 30% FCS (HyClone) in IMDM. These clusters were monitored under a microscope to ensure that no single cells were present. Clusters were incubated at 37°C for 5 h with or without anti-Fas Abs.

Detection of apoptotic parameters

Phosphatidyl serine (PS) exposure was assessed after annexin V and propidium iodide (PI) double staining using the Apo Target annexin V FITC apoptosis kit (Biosource Europe, Fleurus, Belgium). DNA strand breaks were analyzed by dUTP-fluorescein labeling using the in situ cell death detection method (Roche Diagnostics, Mannheim, Germany) according to the instructions of the manufacturer. PS exposure and DNA strand breaks were analyzed by FACS. Caspase-8 activity was determined using a caspase-8 fluorometric kit (R&D Systems, Minneapolis, MN) using IETD-7-amino-4-trifluoromethyl coumarin (AFC) as a substrate. AFC release was measured using a Wallac Vitor 1420 multilabel counter (EG & G Wallac, Turku, Finland).

Western blotting of cFLIP was done with 30 µg protein/lane, and expression of cFLIP was assessed using the FLIP-specific mAb Nf6. For caspase-8, 100 µg protein was applied per lane, and caspase-8 was detected using the mAb c1 (both Nf6 and c1 mAbs were kind gifts of P. H. Krammer, German Cancer Research Center, Heidelberg, Germany). Blots were stained with the peroxidase-conjugated rabbit anti-mouse Ig (Dako, Glostrup, Denmark), and Lumi-Light PLUS Western blotting substrate (Roche Diagnostics).

	Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
Apoptosis in GC B lymphocytes is a spontaneous process

GC B cells undergo rapid apoptosis upon in vitro culture. This process is autonomous (i.e., it does not require an inducing death receptor signal). Typically, 40–50% of the cells express PS within 5 h (Fig. 1A). This is definitely accelerated after ligation of Fas with the CH11 mAb, indicating that the Fas route is functional in these cells. Ligation of CD40 profoundly inhibits PS expression.

View larger version (31K): [in this window] [in a new window]   FIGURE 1. Activation of apoptosis in GC B cells is inhibited by CD40 ligation and by interaction with FDCs. A, PS exposure of GC B cells, either freshly isolated (t0) or after 2 or 5 h at 37°C (t2 and t5, repectively), with anti-Fas (t2 + anti-Fas; t5 + anti-Fas), with CD40L (t2 + CD40L; t5 + CD40L), in FDC-B cell clusters (cluster) or anti-Fas treated clusters (cluster t5 + anti-Fas). Data are expressed as mean ± SD (n = 3). B, Caspase-8 expression analyzed by Western blotting. Treatments were similar to those in A. A total of 100 µg of protein was used in each lane. One representative example of three experiments is shown. C, Caspase-8 activity using IETD-AFC as a substrate. AFC release correlates with caspase-8 activity. Treatments similar to those in A. Data are presented as mean ± SD (n = 3).

GC B lymphocytes contain cFLIP_L, that decays rapidly in single cells

Freshly isolated GC B cells express cFLIP_L, as shown by Western blotting (Fig. 2). Upon incubation at 37°C, this protein rapidly decays and is virtually gone after 5 h. Remarkably, ligation of CD40 with a CD40L leads to sustained expression of the cFLIP_L (Fig. 2A). Also, if GC B lymphocytes are cultured with FDCs and the B cells are recovered from these clusters, the expression of cFLIP_L is maintained (Fig. 2B). These data imply that CD40 ligation (presumably by T cells) and physical contact with FDCs are powerful signals to maintain cFLIP_L expression in GC B cells and, hence, may prevent DR-induced caspase activation.

View larger version (29K): [in this window] [in a new window]   FIGURE 2. cFLIPL rapidly disappears from isolated GC B cells upon culture, but cFLIPL expression is maintained by CD40 ligation and contact with FDCs. Western blotting of cFLIPL from GC B cells either directly after isolation (t0) or after 5 h incubation at 37°C (t5). Data are compared with 5 h incubation of single GC B cells with CD40L (A) or with GC B cells recovered from FDC-B cell clusters (B). A total of 30 µg of protein were loaded in each lane. Data are representative examples of at least three different experiments in both A and B.

As we recently published, GC B lymphocytes have a cathepsin-like activity that is instrumental in their rapid DNA fragmentation (7). To find out whether this cathepsin may be responsible for the disappearance of cFLIP_L, the general cathepsin inhibitor E64d was added, and cFLIP_L expression was followed. As seen in Fig. 3, E64d effectively blocks the formation of DNA strand breaks (Fig. 3B) but leaves PS exposure unhampered (Fig. 3A). Also, addition of E64d to isolated GC B lymphocytes did not prevent the disappearance of cFLIP_L from these cells. These data indicate that cFLIP_L decay is independent of cathepsin activity. Similar results were obtained when isolated GC B cells were incubated with the caspase inhibitors z-VAD-fmk or z-DEVD-fmk (data not shown). Altogether, these data indicate that the disappearance of cFLIP_L is an initial event in the triggering of apoptosis in GC B cells and not a result of apoptosis-associated proteolysis in these cells.

View larger version (44K): [in this window] [in a new window]   FIGURE 3. cFLIPL decay is independent of cathepsin activity. FACS data showing PI uptake vs PS exposure (A) and DNA strand breaks (B), showing that the cathepsin inhibitor E64d inhibits DNA fragmentation but not PS exposure. In the presence of E64d cFLIPL, disappearance is uninhibited. Western blotting was done with 30 µg protein in each lane. Data are representative of three different experiments.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

A role for Fas in the selection of high affinity B cells has recently been strengthened, because lpr mice (who lack functional Fas) show impaired selection of high affinity B lymphocytes in GC reactions (14). It remains unclear whether Fas must be ligated by FasL or, alternatively, Fas is activated spontaneously. In GCs, an obvious FasL source is lacking, as only few cells express this L. FasL expression has been demonstrated on scattered nonlymphoid cells, but in tonsils, the FasL is mainly expressed on plasma cells (15). Caspase-8 activation is strongly inhibited by cFLIP (13). We have shown here that freshly isolated GC B cells contain the 55-kDa isoform of cFLIP, cFLIP_L. Naive and memory B cells express much lower amounts (data not shown). None of these B cell fractions expressed the short isoform of cFLIP.

Upon incubation of isolated GC B lymphocytes in vitro, cFLIP_L is rapidly degraded and is virtually absent after 5 h. Several experiments argue in favor of the idea that this decay of cFLIP_L is a triggering event for caspase activation rather than a result of general proteolysis during apoptosis. For instance, inhibition of cathepsin activity by the general cathepsin inhibitor E64d did not prevent cFLIP_L degradation (Fig. 3C). Similar results were found when caspases were blocked by the caspase inhibitors z-VAD-fmk or z-DEVD-fmk (not shown). In addition, Hennino et al. (16) have recently studied the composition of the DISC in GC B lymphocytes at different time points. They demonstrated that cFLIP_L disappearance from the DISC is virtually complete within 10 min after Fas ligation, indicating that it must be an initial step rather than a result of apoptosis.

Our data suggest an important role of early cFLIP_L decay and caspase-8 activation typical of a type I route of cell death in GC B lymphocytes. However, as we showed earlier, GC B cell apoptosis also includes reduction of mitochondrial membrane potential (7). Mitochondria are involved in both the type I and II routes of cell death, but their inactivation is not strictly necessary for the type I route (8). Transgenic overexpression of Bcl-2 or Bcl-x_L, proteins involved in inhibition of mitochondrial cytochrome c release, inhibits GC B cell apoptosis, indicating an important role for the type II cell death route as well (17, 18). In tonsillar B lymphocytes, it has been shown that especially Bcl-x_L expression is associated with survival, arguing in favor of a mitochondrial involvement in GC B cell apoptosis (19).

By contrast, the recent data of Defrance and coworkers using selective inhibitors of either caspase-8 or caspase-9 strongly suggest that apoptosis of human tonsillar GC B cells in vitro predominantly depends on caspase-8 activity, not on caspase-9 activity (16). This is in line with their earlier data showing that, in CD40L-activated virgin B cells, Fas-induced cell death bypasses the mitochondrial pathway (20).

In our experiments, cFLIP_L decay is profoundly inhibited when GC B lymphocytes are either in contact with FDCs or with a CD40L-transfected cell line. The CD40-mediated signal requires some time because simultaneous CD40 ligation and anti-Fas treatment does not inhibit apoptosis, whereas CD40 ligation for 4 h followed by anti-Fas treatment results in inhibition of apoptosis (data not shown). The contact with FDCs effectively protects GC B lymphocytes against Fas-mediated cell death. The signaling conditions for this anti-Fas insensitivity are not clear, but cell to cell contact between FDCs and B cells is important (21). The FDC-derived signal acts independently of CD40 signals, Ig receptors, or adhesion molecules (5, 22). Bcl-2 seems not to be involved because this protein is only present at low levels in GC B lymphocytes and is down-regulated on B cells in contact with FDCs (23, 24).

The data presented here may provide a clue as to how selected GC B cells are kept alive in the FDC network. Moreover, because cFLIP_L expression is maintained by CD40 ligation as well, it may be hypothesized that activated T cells in the GC that can rapidly express large amounts of the L (25) are the permissive factor that help the putative memory B cells to leave the GC for further differentiation.

	Acknowledgments

 
We thank Dr. P. H. Krammer for the Nf6 and c1 Abs, Dr. C. van Kooten for the CD40L-transfected cell line, R. Bleijswijk for technical assistance, and the Onze Lieve Vrouwe Gasthuis hospital for providing us with tonsils.

	Footnotes

 
¹ Current address: Tanox Pharma bv., Kruislaan 318, 1098 SM, Amsterdam, The Netherlands.

² Address correspondence and reprint requests to Dr. Cornelis de Groot, Department of Cell Biology and Histology, Cellular Immunology Group, Academic Medical Center, University of Amsterdam, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands. E-mail address: c.degroot{at}amc.uva.nl

³ Abbreviations used in this paper: GC, germinal center; FDC, follicular dendritic cell; DR, death receptor; DISC, death-inducing signaling complex; FLIP, Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein; cFLIP, cellular homologue of viral FLIP; FLIP_L, long isoform of FLIP; PS, phosphatidyl serine; L, ligand; AFC, 7-amino-4-trifluoromethyl coumarin: PI, propidium iodide.

Received for publication February 22, 2001. Accepted for publication April 4, 2001.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

1. MacLennan, I. C.. 1994. Germinal centers. Annu. Rev. Immunol. 12:117.[Medline]
2. Tsiagbe, V. K., G. Inghirami, G. J. Thorbecke. 1996. The physiology of germinal centers. Crit. Rev. Immunol. 16:381.[Medline]
3. Liu, Y. J., C. Arpin. 1997. Germinal center development. Immunol. Rev. 156:111.[Medline]
4. Lindhout, E., G. Koopman, S. T. Pals, C. de Groot. 1997. Triple check for antigen specificity of B-lymphocytes during germinal centre reactions. Immunol. Today 18:573.[Medline]
5. Lindhout, E., A. Lakeman, C. de Groot. 1995. Follicular dendritic cells inhibit apoptosis in human B-lymphocytes by rapid and irreversible blockade of preexisting endonuclease. J. Exp. Med. 181:1985.[Abstract/Free Full Text]
6. Lindhout, E., M. L. Mevissen, J. Kwekkeboom, J. M. Tager, C. de Groot. 1993. Direct evidence that human follicular dendritic cells (FDC) rescue germinal center B cells from death by apoptosis. Clin. Exp. Immunol. 91:330.[Medline]
7. Van Eijk, M., C. de Groot. 1999. Germinal center B cell apoptosis requires both caspase and cathepsin activity. J. Immunol. 163:2478.[Abstract/Free Full Text]
8. Krammer, P. H.. 2000. CD95’s deadly mission in the immune system. Nature 407:789.[Medline]
9. Lagresle, C., C. Bella, P. T. Daniel, P. H. Krammer, T. Defrance. 1995. Regulation of germinal center B cell differentiation: role of the human APO-1/Fas (CD95)molecule. J. Immunol. 154:5746.[Abstract]
10. Scaffidi, C., S. Fulda, A. Srinivasan, C. Friesen, F. Li, K. J. Tomaselli, K. M. Debatin, P. H. Krammer, M. E. Peter. 1998. Two CD95 (APO-1/Fas) signaling pathways. EMBO J. 17:1675.[Medline]
11. Thome, M., P. Schneider, K. Hofmann, H. Fickenscher, E. Meinl, F. Neipel, C. Mattmann, K. Burns, J. L. Bodmer, M. Schroter, et al 1997. Viral FLICE-inhibitory proteins (FLIPs) prevent apoptosis induced by death receptors. Nature 386:517.[Medline]
12. Irmler, M., M. Thome, M. Hahne, P. Schneider, K. Hofmann, V. Steiner, J. L. Bodmer, M. Schroter, K. Burns, C. Mattmann, et al 1997. Inhibition of death receptor signals by cellular FLIP. Nature 388:190.[Medline]
13. Tschopp, J., M. Irmler, M. Thome. 1998. Inhibition of Fas death signals by FLIPs. Curr. Opin. Immunol. 10:552.[Medline]
14. Takahashi, Y., H. Ohta, T. Takemori. 2001. Fas is required for clonal selection in germinal centers and the subsequent establishment of the memory B cell repertoire. Immunity 14:181.[Medline]
15. Sträter, J., S. M. Mariani, H. Walczak, F. G. Rücker, F. Leithäuser, P. H. Krammer, P. Möller. 1999. CD95 Ligand (CD95L) in normal human lymphoid tissues: a subset of plasma cells are prominent producers of CD95L. Am. J. Pathol. 154:193.[Abstract/Free Full Text]
16. Hennino, A., M. Berard, P. H. Krammer, T. Defrance. 2001. FLICE-inhibitory protein is a key regulator of germinal center B cell apoptosis. J. Exp. Med. 193:447.[Abstract/Free Full Text]
17. Takahashi, Y., D. M. Cerasoli, J. M. Dal Porto, M. Simoda, R. Freund, W. Fang, D. G. Telander, E.-N. Malvey, D. L. Mueller, T. W. Behrens, G. Kelsoe. 1999. Relaxed negative selection in germinal centers and impaired affinity maturation in bcl-x_L transgenic mice. J. Exp. Med. 190:399.[Abstract/Free Full Text]
18. Smith, K. G. C., A. Light, L. A. O’Reilly, S.-M. Ang, A. Strasser, D. Tarlinton. 2000. Bcl-2 transgene expression inhibits apoptosis in the germinal center and reveals differences in the selection of memory B cells and bone marrow antibody-forming cells. J. Exp. Med. 191:475.[Abstract/Free Full Text]
19. Tuscano, J. M., K. M. Druey, A. Riva, J. Pena, C. B. Thompson, J. H. Kehrl. 1996. Bcl-x rather than Bcl-2 mediates CD40-dependent centrocyte survival in the germinal center. Blood 88:1359.[Abstract/Free Full Text]
20. Hennino, A., M. Berard, M. Casamayor-Pallejà, P. H. Krammer, T. Defrance. 2000. Regulation of the Fas death pathway by FLICE-inhibitory protein in primary human B cells. J. Immunol. 165:3023.[Abstract/Free Full Text]
21. Koopman, G., H. K. Parmentier, H. J. Schuurman, W. Newman, C. J. L. M. Meijer, S. T. Pals. 1991. Adhesion of human B cells to follicular dendritic cells involves both the lymphocyte function-associated antigen 1/intercellular adhesion molecule 1 and very late antigen 4/vascular cell adhesion molecule 1 pathways. J. Exp. Med. 173:1297.[Abstract/Free Full Text]
22. Koopman, G., R. M. Keehnen, E. Lindhout, D. F. Zhou, C. de Groot, S. T. Pals. 1997. Germinal center B cells rescued from apoptosis by CD40 ligation or attachment to follicular dendritic cells, but not by engagement of surface immunoglobulin or adhesion receptors, become resistant to CD95-induced apoptosis. Eur. J. Immunol. 27:1.[Medline]
23. Martinez-Valdez, H., C. Guret, O. de Bouteiller, I. Fugier, J. Banchereau, Y. J. Liu. 1996. Human germinal center B cells express the apoptosis-inducing genes Fas, c-myc, P53, and Bax but not the survival gene bcl-2. J. Exp. Med. 183:971.[Abstract/Free Full Text]
24. Lindhout, E., C. de Groot. 1995. Follicular dendritic cells and apoptosis: life and death in the germinal centre. Histochem. J. 27:167.[Medline]
25. Casamayor-Palleja, M., M. Khan, I. C. M. MacLennan. 1995. A subset of CD4⁺ memory T cells contains preformed CD40 ligand that is rapidly but transiently expressed on their surface after activation through the T cell receptor complex. J. Exp. Med. 181:1293.[Abstract/Free Full Text]

This article has been cited by other articles:

				B. Alabyev, R. Vuyyuru, and T. Manser Influence of Fas on the regulation of the response of an anti-nuclear antigen B cell clonotype to foreign antigen Int. Immunol., October 1, 2008; 20(10): 1279 - 1287. [Abstract] [Full Text] [PDF]

				J.-J. Goval, C. Thielen, C. Bourguignon, R. Greimers, E. Dejardin, Y. S. Choi, J. Boniver, and L. de Leval The prevention of spontaneous apoptosis of follicular lymphoma B cells by a follicular dendritic cell line: involvement of caspase-3, caspase-8 and c-FLIP Haematologica, August 1, 2008; 93(8): 1169 - 1177. [Abstract] [Full Text] [PDF]

				K. van Nierop, F. J.M. Muller, J. Stap, C. J.F. Van Noorden, M. van Eijk, and C. de Groot Lysosomal Destabilization Contributes to Apoptosis of Germinal Center B-lymphocytes J. Histochem. Cytochem., December 1, 2006; 54(12): 1425 - 1435. [Abstract] [Full Text] [PDF]

				R. A. Barrington, M. Zhang, X. Zhong, H. Jonsson, N. Holodick, A. Cherukuri, S. K. Pierce, T. L. Rothstein, and M. C. Carroll CD21/CD19 Coreceptor Signaling Promotes B Cell Survival during Primary Immune Responses J. Immunol., September 1, 2005; 175(5): 2859 - 2867. [Abstract] [Full Text] [PDF]

				J. J. F. Muris, S. A. G. M. Cillessen, W. Vos, I. S. van Houdt, J. A. Kummer, J. H. J. M. van Krieken, N. M. Jiwa, P. M. Jansen, H. C. Kluin-Nelemans, G. J. Ossenkoppele, et al. Immunohistochemical profiling of caspase signaling pathways predicts clinical response to chemotherapy in primary nodal diffuse large B-cell lymphomas Blood, April 1, 2005; 105(7): 2916 - 2923. [Abstract] [Full Text] [PDF]

				R. Sacedon, B. Diez, V. Nunez, C. Hernandez-Lopez, C. Gutierrez-Frias, T. Cejalvo, S. V. Outram, T. Crompton, A. G. Zapata, A. Vicente, et al. Sonic Hedgehog Is Produced by Follicular Dendritic Cells and Protects Germinal Center B Cells from Apoptosis J. Immunol., February 1, 2005; 174(3): 1456 - 1461. [Abstract] [Full Text] [PDF]

				A. Dutton, J. D. O'Neil, A. E. Milner, G. M. Reynolds, J. Starczynski, J. Crocker, L. S. Young, and P. G. Murray Expression of the cellular FLICE-inhibitory protein (c-FLIP) protects Hodgkin's lymphoma cells from autonomous Fas-mediated death PNAS, April 27, 2004; 101(17): 6611 - 6616. [Abstract] [Full Text] [PDF]

				V. S. Raman, R. S. Akondy, S. Rath, V. Bal, and A. George Ligation of CD27 on B Cells In Vivo during Primary Immunization Enhances Commitment to Memory B Cell Responses J. Immunol., December 1, 2003; 171(11): 5876 - 5881. [Abstract] [Full Text] [PDF]

				I. Schmitz, A. Krueger, S. Baumann, H. Schulze-Bergkamen, P. H. Krammer, and S. Kirchhoff An IL-2-Dependent Switch Between CD95 Signaling Pathways Sensitizes Primary Human T Cells Toward CD95-Mediated Activation-Induced Cell Death J. Immunol., September 15, 2003; 171(6): 2930 - 2936. [Abstract] [Full Text] [PDF]

				T. Jinquan, H. H. Jacobi, C. Jing, A. Millner, E. Sten, L. Hviid, L. Anting, L. P. Ryder, C. Glue, P. S. Skov, et al. CCR3 Expression Induced by IL-2 and IL-4 Functioning as a Death Receptor for B Cells J. Immunol., August 15, 2003; 171(4): 1722 - 1731. [Abstract] [Full Text] [PDF]

				D. E. Muscarella and S. E. Bloom Cross-linking of Surface IgM in the Burkitt's Lymphoma Cell Line ST486 Provides Protection against Arsenite- and Stress-induced Apoptosis That Is Mediated by ERK and Phosphoinositide 3-Kinase Signaling Pathways J. Biol. Chem., January 31, 2003; 278(6): 4358 - 4367. [Abstract] [Full Text] [PDF]

				E. Flano, I.-J. Kim, D. L. Woodland, and M. A. Blackman {gamma}-Herpesvirus Latency Is Preferentially Maintained in Splenic Germinal Center and Memory B Cells J. Exp. Med., November 18, 2002; 196(10): 1363 - 1372. [Abstract] [Full Text] [PDF]

				R. K. Thomas, A. Kallenborn, C. Wickenhauser, J. L. Schultze, A. Draube, M. Vockerodt, D. Re, V. Diehl, and J. Wolf Constitutive Expression of c-FLIP in Hodgkin and Reed-Sternberg Cells Am. J. Pathol., April 1, 2002; 160(4): 1521 - 1528. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by van Eijk, M. Articles by de Groot, C. Search for Related Content PubMed PubMed Citation Articles by van Eijk, M. Articles by de Groot, C.