Factor VIII-Specific Memory B-Cells in Patients with Hemophilia A.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1020-1020 ◽  
Author(s):  
Pauline M.W. van Helden ◽  
Paul H.P. Kaijen ◽  
H. Marijke van den Berg ◽  
Jan Voorberg
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Hemophilia A ◽  
Low Frequency ◽  
Memory B Cells ◽  
The Past ◽  
Specific Memory ◽  
Specific Igg ◽  
Inhibitory Antibodies

Abstract The quick anamnestic antibody response seen after recurrent exposure to antigen involves memory B- cells that, helped by T-cells, undergo rigid proliferation and subsequent differentiation into antibody producing cells. The presence of a pool of memory B-cells allows for a rapid response to antigens which quickly eliminates incoming pathogens. In the context of immune responses to therapeutic agents such as blood coagulation factor VIII (FVIII), antigenic re-stimulation of specific memory B-cells is undesirable. In approximately 25% of hemophilia A patients replacement therapy is hampered by inhibitory antibodies that bind to FVIII. Currently, the FVIII-specific memory B-cell compartment in patients with hemophilia A has remained poorly characterized. We have developed a protocol that allows for identification and quantification of circulating memory B-cells in patients with hemophilia A. CD19+ B-cells were sorted on a layer of irradiated EL4B5 thymoma cells expressing CD40L in the presence of the supernatant of mitogen-stimulated T-cells. These experimental conditions, that mimic the interaction of B-cells with an activating helper CD4+ T-cell, induce proliferation of memory B-cells and allow them to differentiate into antibody secreting cells (ASC) in an antigen-independent manner. After 9–10 days of culture, total IgG and FVIII-specific IgG was determined by ELISA and number of ASC was determined by ELISpot. We analyzed blood samples of five multi-transfused patients (>50 FVIII administrations) who never experienced any inhibitor episode, five patients who experienced inhibitory antibodies in the past but were successfully treated with immune tolerance induction and 6 patients with an inhibitor at the time of blood sampling. The ELISA set-up appeared to be more sensitive than ELISpot showing ASC producing anti-FVIII antibodies varying from 0.2–50 ng/ml. In contrast, ELISpot analysis only allowed for detection of B-cell clones producing over ~4 ng/ml of FVIII-specific IgG. Frequencies of FVIII-specific memory B-cells varied from 0–0.027% of total number of circulating peripheral B-cells. The relative amount of circulating memory B-cells did not correspond to inhibitor titers as measured in a Bethesda assay. The highest frequencies were observed in patients suffering from anamnestic response to FVIII suggesting the importance of antigenic stimulation for maintenance of memory B-cell levels. This is further supported by the low frequency that was observed in a high-titer inhibitor patient who had not been treated with FVIII for several months prior to blood sampling. Surprisingly, we detected FVIII-specific memory B-cells in two multi-transfused patients who did not experience any inhibitor episode in the past. These B-cells were present in a low frequency however and developed into ASC producing only limited amounts of anti-FVIII antibodies. These observations suggest that peripheral blood memory B-cells can develop in the absence of clinically relevant inhibitors.

Inhibition of Factor VIII-Specific Memory B Cell Responses by Supra-Physiological Concentrations of Factor VIII.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 38-38
Author(s):  
Christina Hausl ◽  
Rafi U. Ahmad ◽  
Maria Sasgary ◽  
Christopher B. Doering ◽  
Pete S. Lollar ◽  
...  
Keyword(s):  
T Cells ◽  
B Cells ◽  
Factor Viii ◽  
B Cell ◽  
Immune Tolerance ◽  
Hemophilia A ◽  
Memory B Cells ◽  
Memory B Cell ◽  
Specific Memory ◽  
Stimulation Of

Abstract Inhibitory antibodies against factor VIII (FVIII) are the major complication experienced by hemophilia A patients treated with FVIII products. The most effective therapy to eradicate these antibodies is elevated doses of FVIII over a prolonged period. Despite clinical practice in using such protocols, nothing is known about the immunological mechanisms that cause the down-modulation of FVIII-specific immune responses and the induction of long-lasting immune tolerance against FVIII. Understanding the underlying mechanisms, however, would facilitate designing new therapeutic strategies. The re-stimulation of FVIII-specific memory responses after each dose of FVIII is probably the most important event in the maintenance of FVIII inhibitors in patients. Therefore, the eradication of these memory responses should be an essential step in the down-modulation of inhibitory antibodies and the induction of immune tolerance. We used a murine model of hemophilia A to answer the question whether FVIII-specific memory responses are sensitive to increasing doses of FVIII. In particular, we were interested in the differential effects of FVIII on memory-B-cell and memory-T-cell responses. For the analysis of FVIII-specific memory responses, we re-stimulated FVIII-specific memory B- and T-cells obtained from spleens of hemophilic mice treated with four doses of human FVIII or eight doses of murine FVIII as described (Sasgary et al.: Thromb Haemost2002; 87:266–72; Hausl et al.: Blood2004; 104:115–22). Our results show dose-dependent effects of FVIII on the re-stimulation of FVIII-specific memory B cells in vitro. Physiological concentrations of FVIII below 100 ng/ml re-stimulate memory B cells and induce their differentiation into anti-FVIII antibody-secreting plasma cells. Supra-physiological concentrations above 100 ng/ml, however, inhibit memory-B-cell re-stimulation. The inhibition of memory-B-cell re-stimulation is irreversible and seems to be due to an induction of apoptosis that is at least partly mediated by Fas-dependent mechanisms. Furthermore, the inhibition appears to be initiated by triggering the B-cell receptor (BCR) without the requirement of an excessive cross-linking of the BCR. The activation of FVIII-specific T cells is not affected by increasing doses of FVIII. We conclude that the induction of apoptosis in FVIII-specific memory B cells might be the first step in the induction of immune tolerance in hemophilia A patients with FVIII inhibitors who receive high doses of FVIII. The eradication of memory B cells would prevent their differentiation into antibody-secreting plasma cells and, moreover, might lead to a deficiency of effective antigen-presenting cells required for the re-stimulation of FVIII-specific memory T cells. The induction of regulatory T cells rather than effector T cells could be the consequence of this deficiency.

scholarly journals Memory B Cell Responses to Vibrio cholerae O1 Lipopolysaccharide Are Associated with Protection against Infection from Household Contacts of Patients with Cholera in Bangladesh

2012 ◽  
Vol 19 (6) ◽  
pp. 842-848 ◽  
Author(s):  
Sweta M. Patel ◽  
Mohammad Arif Rahman ◽  
M. Mohasin ◽  
M. Asrafuzzaman Riyadh ◽  
Daniel T. Leung ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Vibrio Cholerae ◽  
Memory B Cells ◽  
Content Type ◽  
Cell Responses ◽  
Household Contacts ◽  
Specific Memory ◽  
Specific Igg ◽  
Protection Against Infection

ABSTRACTVibrio choleraeO1 causes cholera, a dehydrating diarrheal disease. We have previously shown thatV. cholerae-specific memory B cell responses develop after cholera infection, and we hypothesize that these mediate long-term protective immunity against cholera. We prospectively followed household contacts of cholera patients to determine whether the presence of circulatingV. choleraeO1 antigen-specific memory B cells on enrollment was associated with protection againstV. choleraeinfection over a 30-day period. Two hundred thirty-six household contacts of 122 index patients with cholera were enrolled. The presence of lipopolysaccharide (LPS)-specific IgG memory B cells in peripheral blood on study entry was associated with a 68% decrease in the risk of infection in household contacts (P= 0.032). No protection was associated with cholera toxin B subunit (CtxB)-specific memory B cells or IgA memory B cells specific to LPS. These results suggest that LPS-specific IgG memory B cells may be important in protection against infection withV. choleraeO1.

Preventing restimulation of memory B cells in hemophilia A: a potential new strategy for the treatment of antibody-dependent immune disorders

Blood ◽  
2004 ◽  
Vol 104 (1) ◽  
pp. 115-122 ◽  
Author(s):  
Christina Hausl ◽  
Rafi U. Ahmad ◽  
Hans Peter Schwarz ◽  
Eva M. Muchitsch ◽  
Peter L. Turecek ◽  
...  
Keyword(s):  
T Cells ◽  
B Cells ◽  
Hemophilia A ◽  
Memory B Cells ◽  
Third Party ◽  
Activated T Cells ◽  
Specific Memory ◽  
Inducible Costimulator

Abstract Memory B cells are responsible for the rapidly emerging antibody response after antigen reexposure. The signals required for the restimulation of memory B cells have not been fully explained. We used a murine model of anti–factor VIII (FVIII) antibody responses in hemophilia A to study the requirements for the restimulation of FVIII-specific memory B cells and their differentiation into anti-FVIII antibody-producing cells. We were particularly interested in the significance of activated T cells and costimulatory interactions. Our results indicate that the restimulation of FVIII-specific memory B cells is strictly dependent on interactions with activated T cells. These activated T cells can be specific for either FVIII or third-party antigens. Restimulation by T cells specific for third-party antigens requires the presence of FVIII, indicating that signals induced by B-cell receptor (BCR) triggering and by interactions with activated T cells are important. The blockade of B7-1 or B7-2 as well as the blockade of CD40L inhibits the restimulation and differentiation of FVIII-specific memory B cells in vitro and in vivo. The interference with inducible costimulator–inducible costimulator ligand (ICOS-ICOSL) interactions, however, does not cause any modulation. As expected, the production of anti-FVIII antibodies by plasma cells is not dependent on any of the costimulatory interactions tested.

scholarly journals SARS-CoV-2 spike-specific memory B cells express higher levels of T-bet and FcRL5 after non-severe COVID-19 as compared to severe disease

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0261656
Author(s):  
Raphael A. Reyes ◽  
Kathleen Clarke ◽  
S. Jake Gonzales ◽  
Angelene M. Cantwell ◽  
Rolando Garza ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Symptom Onset ◽  
Cell Response ◽  
Severe Disease ◽  
Memory B Cells ◽  
Memory B Cell ◽  
Specific Memory ◽  
Specific Igg ◽  
B Cell Response

SARS-CoV-2 infection elicits a robust B cell response, resulting in the generation of long-lived plasma cells and memory B cells. Here, we aimed to determine the effect of COVID-19 severity on the memory B cell response and characterize changes in the memory B cell compartment between recovery and five months post-symptom onset. Using high-parameter spectral flow cytometry, we analyzed the phenotype of memory B cells with reactivity against the SARS-CoV-2 spike protein or the spike receptor binding domain (RBD) in recovered individuals who had been hospitalized with non-severe (n = 8) or severe (n = 5) COVID-19. One month after symptom onset, a substantial proportion of spike-specific IgG+ B cells showed an activated phenotype. In individuals who experienced non-severe disease, spike-specific IgG+ B cells showed increased expression of markers associated with durable B cell memory, including T-bet and FcRL5, as compared to individuals who experienced severe disease. While the frequency of T-bet+ spike-specific IgG+ B cells differed between the two groups, these cells predominantly showed an activated switched memory B cell phenotype in both groups. Five months post-symptom onset, the majority of spike-specific memory B cells had a resting phenotype and the percentage of spike-specific T-bet+ IgG+ memory B cells decreased to baseline levels. Collectively, our results highlight subtle differences in the B cells response after non-severe and severe COVID-19 and suggest that the memory B cell response elicited during non-severe COVID-19 may be of higher quality than the response after severe disease.

Single-Cell Analysis of FVIII-Specific Memory B Cells in Murine Hemophilia A.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1157-1157 ◽  
Author(s):  
Christina Hausl ◽  
Rafi U. Ahmad ◽  
Bernhard Baumgartner ◽  
Hans Peter Schwarz ◽  
Hartmut Ehrlich ◽  
...  
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Single Cell ◽  
Cd4 T Cells ◽  
Single Cell Analysis ◽  
Memory B Cells ◽  
Cell Analysis ◽  
Memory B Cell ◽  
Specific Memory

Abstract The elimination of FVIII-specific memory B cells is an essential step in the design of new therapeutic strategies for the induction of immune tolerance in hemophilia A with FVIII inhibitors. Using a mouse model of hemophilia A we recently reported that low dose FVIII stimulates the differentiation of FVIII-specific memory B cells into antibody-secreting plasma cells whereas high dose FVIII inhibits this process. The inhibition of memory-B-cell re-stimulation is irreversible and seems to be due to an induction of apoptosis. Further understanding of the complex interactions that lead to either re-stimulation and differentiation of memory B cells or inhibition and eradication of these cells requires appropriate technologies for single-cell analysis and functional studies. We established a new technology for single-cell analysis and cell sorting of FVIII-specific murine memory B cells. A combination of magnetic bead separation and multi-color flow cytometry enabled us to analyze and purify FVIII-specific memory B cells obtained from hemophilic mice treated with FVIII. In a first step, we depleted undesirable cell populations (IgM+, IgD+, CD11c+, F4/80+, Gr1+ and CD49b+ cells) from total spleen cells by magnetic bead separation. In a second step, we used multicolor flow cytometry to exclude CD4+ T cells and analyze the FVIII-specific memory B cell compartment. This compartment was specified by staining the specific B-cell receptor with FVIII and anti-IgG antibodies. Frequencies of cells in this compartment ranged from 0.1–0.5% of total spleen cells in animals treated with 4 intravenous doses of FVIII, given at weekly intervals. We could not detect any FVIII-specific memory B cells in naïve mice. By means of single cell sorting we isolated FVIII-specific memory B cells for further functional studies. We were able to cultivate FVIII-specific memory B cells in microwell cultures in vitro and differentiate them into antibody-secreting plasma cells. The re-stimulation and differentiation of single-cell sorted memory B cells was strictly dependent on the presence of activated CD4+ T cells. CD4+ T cells obtained from naïve mice did not support the memory response. Furthermore, the re-stimulation and differentiation of memory B cells in the presence of activated CD4+ T cells did not require additional dendritic cells for antigen presentation. Obviously, memory B cells provide sufficient antigen presentation to CD4+ T cells to enable them to trigger the memory response. Our approach for single-cell analysis and purification of FVIII-specific memory B cells provides a new tool for tracking memory B cell populations in vivo and for directly analyzing the regulation of memory B cell function. It opens the field for future studies which should elucidate signals and molecules involved in activation or inhibition and eradication of FVIII-specific memory B cells. These activities will eventually lead to the identification of targets for the design of new treatment strategies for patients with FVIII inhibitors.

Deletion or Inhibition of Fc Gamma Receptor IIb (CD32) Prevents the Memory B Cell Response to Factor VIII in a Hemophilia A Mouse Model

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 204-204 ◽  
Author(s):  
Sonja Werwitzke ◽  
Marcus von Hornung ◽  
Katy Kalippke ◽  
Arne Trummer ◽  
Arnold Ganser ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Knockout Mice ◽  
Cell Response ◽  
Hemophilia A ◽  
Memory B Cells ◽  
Double Knockout ◽  
Memory B Cell ◽  
Specific Memory ◽  
Antibody Secreting Cells

Abstract Abstract 204 The formation of inhibitory antibodies to factor VIII (FVIII) is the foremost complication of replacement therapy in hemophilia A. Patients with inhibitors are treated with very high doses of FVIII, over prolonged periods of time, to induce immune tolerance. Studies in a hemophilia A mouse model demonstrated that very high doses of FVIII can induce apoptosis in FVIII-specific memory B cells and prevent their differentiation into antibody-secreting cells. The Fc gamma receptor IIb (FcgRIIb) is expressed on B cells and mediates inhibitory signals after crosslinking with the B cell receptor. Here, we studied the potential role of this receptor in the regulation of memory B cell response to FVIII. FVIII knockout mice (B6;129S4-F8tm2Kaz/J) were crossed with FcgRIIb knockout mice (B6;129S4-Fcgr2btm1Ttk/J). Comparing F8−/− mice and F8−/−/FcgR2b−/− double knockout mice, the initial anti-FVIII antibody formation was similar after intravenous exposure to 4 weekly doses of 80 or 400 IU/kg. Similar numbers of FVIII-specific antibody-secreting cells were detected in the spleen and bone marrow by ELISPOT. As previously shown, in vitro re-stimulation of memory B cells from spleens of immunized F8−/− mice at doses of 1 to 200 ng/ml induced their differentiation into antibody-secreting cells. Higher doses of 400 to 800 ng/ml prevented differentiation. In F8−/−/FcgR2b−/− double knockout mice, however, formation of antibody-secreting cells was completely inhibited across all FVIII doses tested. Addition of B220-depleted splenocytes from F8−/− mice did not restore memory B cell function in F8−/−/FcgR2b−/− double knockout mice, indicating that the observed effect was not due to dysfunction of follicular dendritic cells or other antigen-presenting cells. Inhibition of FcgRIIb using a monoclonal antibody prevented the FVIII-specific memory B cell response in splenocytes from immunized F8−/− mice. Staining with propidium iodide, annexin V, or anti-caspase 3 indicated increased rates of apoptosis when FcgRIIb was blocked during re-stimulation. In summary, FcgRIIb plays a crucial role for the differentiation of FVIII-specific splenic memory B cells into antibody-secreting cells. Inhibition of FcgRIIb appears to sensitize B cells for apoptosis during re-stimulation with FVIII. This mechanism could potentially facilitate the eradication of FVIII-specific memory B cells during ITI. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Regulation of IgG memory responses by helper and suppressor T cells activated by the type 2 antigen, polyvinylpyrrolidone.

1985 ◽  
Vol 161 (6) ◽  
pp. 1357-1367 ◽  
Author(s):  
H Braley-Mullen
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
Suppressor Cells ◽  
Memory B Cells ◽  
High Dose ◽  
Suppressor T Cells ◽  
Specific Memory ◽  
Specific Igg

T cells from CAF1 mice immunized with various amounts of the type 2 antigen polyvinylpyrrolidone (PVP) were assessed for their ability to provide help to PVP-specific memory B cells for the production of IgG. Low doses (0.0025 micrograms) of PVP consistently activated helper T cells (Th), which were required for the production of IgG by primed B cells. In contrast, T cells from mice primed with higher amounts (0.25 or 25 micrograms) of PVP did not provide significant help to the same B cells for IgG production. Moreover, when mixed with B cells and low-dose PVP-primed Th, T cells from mice primed with 0.25 or 25 micrograms PVP suppressed PVP-specific IgG, but not IgM antibody responses. The suppressor cells induced by higher amounts of PVP were eliminated either by injecting cyclophosphamide (CY) before priming with PVP, or by treating the primed T cells with anti-Lyt-2.2 and C before transfer. Pretreatment of suppressor T cell (Ts) donors with CY or removal of Lyt-2+ T cells not only eliminated Ts activity, but also unmasked significant Th activity in the T cells from high-dose PVP-primed mice. Thus, both low and high amounts of PVP can activate Th, although high amounts of PVP also induce Ts, the activity of which predominates in a normal unfractionated T cell population. The amount of PVP (0.0025 micrograms) that induces dominant help for IgG memory responses was only marginally immunogenic for induction of primary PVP-specific IgM responses, while 0.25 and 25 micrograms PVP, which induce dominant suppression for IgG memory responses, are optimally immunogenic for primary IgM responses. These results are discussed in the context of the inability of most type 2 antigens to elicit primary IgG responses or to prime memory B cells for production of IgG, responses which are dependent on the function of antigen-specific Th.

Toll-Like Receptor Triggering Modulates Factor VIII-Specific Immune Memory in Murine Hemophilia A with Factor VIII Inhibitors.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 214-214 ◽  
Author(s):  
Peter Allacher ◽  
Christina Hausl ◽  
Rafi U. Ahmad ◽  
Hans Peter Schwarz ◽  
Peter L. Turecek ◽  
...  
Keyword(s):  
B Cells ◽  
Factor Viii ◽  
B Cell ◽  
Hemophilia A ◽  
Memory B Cells ◽  
Immune Memory ◽  
Low Doses ◽  
Specific Memory ◽  
High Doses ◽  
Stimulation Of

Abstract The development of inhibitory antibodies against factor VIII (FVIII) is the major complication in the treatment of hemophilia A patients with FVIII products. Immune Tolerance Induction (ITI) therapy using long-term application of high doses of FVIII has evolved as an effective therapy to eradicate the antibodies and induce long-lasting immune tolerance. It is a common observation that infections, particularly central venous catheter infections during ITI cause a rise in anti-FVIII antibody titers that can prolong the course of ITI or possibly even lead to failure of ITI. Based on this observation, we asked the question whether microbial components derived from viruses or bacteria modulate the re-stimulation of FVIII-specific immune memory and disturb the recently described inhibition of memory-B-cell-re-stimulation by high doses of FVIII (Hausl et al.: Blood2005; in press). Microbial components are recognized by toll-like receptors (TLRs) that serve as an important link between innate and adaptive immunity. TLRs can discriminate various microbial components such as lipopeptides derived from bacteria or zymosan derived from yeast (recognized by TLR1/2 or TLR2/6), double-stranded RNA derived from viruses (recognized by TLR3), lipopolysaccharide (LPS) derived from gram-negative bacteria (recognized by TLR4), flagellin derived from bacterial flagella (recognized by TLR5), single-stranded RNA derived from viruses (recognized by TLR7/8) or bacterial DNA containing the unmethylated CpG motif (recognized by TLR9). We analyzed the re-stimulation of FVIII-specific memory-B cells using a murine model of hemophilia A as described previously (Hausl et al.: Blood2004; 104:115–22; Hausl et al.: Blood2005, in press). The following TLR ligands were tested: zymosan for TLR2 (0.1–10,000 ng/ml), poly I:C for TLR3 (1.0–50,000 ng/ml), LPS for TLR4 (0.1–10,000 ng/ml), Flagellin for TLR5 (0.01–1,000 ng/ml), Loxoribine for TLR7 (1.0–50,000 ng/ml) and CpG oligonucleotides for TLR9 (0.1–10,000 ng/ml). Our results indicate that none of the TLR ligands at the concentrations tested induced a significant re-stimulation of FVIII-specific memory B cells in the complete absence of either FVIII or T cells. However, ligands for TLR3, TLR4, TLR7 and TLR9 were able to disturb the inhibition of memory-B-cell-re-stimulation by high doses of FVIII and amplified the re-stimulation induced by low doses of FVIII substantially. We conclude that triggering of TLRs by microbial components that are present during infections amplify the re-stimulation of FVIII-specific memory B-cells induced by low doses of FVIII and disturb the inhibition induced by high doses of FVIII.

scholarly journals Activation of Virus-specific Memory B Cells in the Absence of T Cell Help

2004 ◽  
Vol 199 (4) ◽  
pp. 593-602 ◽  
Author(s):  
Barbara J. Hebeis ◽  
Karin Klenovsek ◽  
Peter Rohwer ◽  
Uwe Ritter ◽  
Andrea Schneider ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cd4 T Cells ◽  
Plasma Cells ◽  
Human Herpesvirus ◽  
Memory B Cells ◽  
Specific Memory ◽  
T Cell Help

Humoral immunity is maintained by long-lived plasma cells, constitutively secreting antibodies, and nonsecreting resting memory B cells that are rapidly reactivated upon antigen encounter. The activation requirements for resting memory B cells, particularly the role of T helper cells, are unclear. To analyze the activation of memory B cells, mice were immunized with human cytomegalovirus, a complex human herpesvirus, and tick-born encephalitis virus, and a simple flavivirus. B cell populations devoid of Ig-secreting plasma cells were adoptively transferred into T and B cell–deficient RAG-1−/− mice. Antigenic stimulation 4–6 d after transfer of B cells resulted in rapid IgG production. The response was long lasting and strictly antigen specific, excluding polyclonal B cell activation. CD4+ T cells were not involved since (a) further depletion of CD4+ T cells in the recipient mice did not alter the antibody response and (b) recipient mice contained no detectable CD4+ T cells 90 d posttransfer. Memory B cells could not be activated by a soluble viral protein without T cell help. Transfer of memory B cells into immunocompetent animals indicated that presence of helper T cells did not enhance the memory B cell response. Therefore, our results indicate that activation of virus-specific memory B cells to secrete IgG is independent of cognate or bystander T cell help.

FVIII Specific Memory B Lymphocytes in Hemophilia A with Inhibitors Treated by Immune Tolerance Induction.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3162-3162 ◽  
Author(s):  
Isabelle Diaz ◽  
Karine Bollore ◽  
Chantal Rothschild ◽  
Hervé Chambost ◽  
Ségolène Claeyssens ◽  
...  
Keyword(s):  
B Cells ◽  
Immune Tolerance ◽  
Hemophilia A ◽  
Conflicts Of Interest ◽  
Tolerance Induction ◽  
Memory B Cells ◽  
Immune Memory ◽  
Immune Tolerance Induction ◽  
Specific Memory ◽  
Specific Igg

Abstract Abstract 3162 Poster Board III-99 Background and objectives Hemophilia A (HA) is a life-threatening hemorrhagic bleeding disorder caused by deficiency of Factor VIII (FVIII). Twenty to thirty percent of HA patients treated by FVIII develop inhibitors. The presence of these inhibitors in high titer (>5 Bethesda Units (BU)/ml) requires modification of the treatment regimen: use of products that by-pass the action of FVIII for haemorrhagic accidents and treatment protocols by immune tolerance induction (ITI) to eradicate inhibitors. The aim of our study was to enumerate and characterize FVIII-specific memory B-cells in peripheral blood by using polyclonal activation of enriched B-cells and an ELISpot assay in hemophilia patients with inhibitors. Methods Two groups of patients were prospectively included. First group included six severe HA patients treated by ITI; three with inhibitors (mean 3.04 ± 0.67 BU/ml; mean 14.6±4.2 years old) while the three others had a past of inhibitors, successfully treated by ITI (<0.6BU/ml; mean 18.6 ±6.3 years old). Second group were six severe HA who never developed inhibitors (mean 19.5±1.7 years old). Circulating FVIII specific memory B-cells were enumerated in each cohort and 13 controls using the ELISpot system as previously described. The results were expressed as the number of FVIII specific Secreting Cells (SCs) (IgG, IgA or IgM)/106 B-cells. Results In the first group,circulating FVIII-specific IgM-SCs were detected in 5 patients (1.07-45/106 B-cells), FVIII-specific IgA-SCs in 6 patients ( 2.9-7.5/106 B-cells).Only in patients with detectable inhibitors, FVIII-specific IgG-SCs (4-5.2/106 B-cells) were detected. In the second group FVIII-specific IgM-SCs (between 5 and 52 per 106 B-cells) were found, one patient had FVIII-specific IgA-SCs (2/106 B-cells). Conclusion We were able to detect FVIII specific memory B-cells. Before the treatment by ITI, the FVIII-specific immune memory seems to be characterized by the presence of circulating FVIII-specific memory B-cells belonging to the three isotype classes whereas FVIII-specific IgG-memory B-cells could not be found after a successful treatment. These results suggest an evolution of the pool of FVIII-specific circulating memory B-cells during the period of ITI. It would be interesting to study the FVIII-specific memory B-cells at the different periods of ITI (before, during and at the end of the protocol).The significance of FVIII specific memory B-cells in HA patients without inhibitor deserve to be study. Disclosures No relevant conflicts of interest to declare.

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