Marginal Zone B Cells Mediate a CD4 T Cell Dependent Extrafollicular Antibody Response Following RBC Transfusion in Mice

Blood ◽  
2021 ◽  
Author(s):  
Patricia E Zerra ◽  
Seema R Patel ◽  
Ryan Philip Jajosky ◽  
Connie M Arthur ◽  
James W McCoy ◽  
...  
Keyword(s):  
T Cell ◽  
B Cells ◽  
Antibody Response ◽  
B Cell ◽  
T Cell Activation ◽  
Antibody Formation ◽  
Marginal Zone ◽  
Cd4 T Cell ◽  
Marginal Zone B Cells ◽  
Rbc Transfusion

Red blood cell (RBC) transfusions can result in alloimmunization toward RBC alloantigens that can increase the probability of complications following subsequent transfusion. An improved understanding of the immune mechanisms that underlie RBC alloimmunization is critical if future strategies capable of preventing or even reducing this process are to be realized. Using the HOD (hen egg lysozyme and ovalbumin fused to human Duffy) model system, we aimed to identify initiating immune factors that may govern early anti-HOD alloantibody formation. Our findings demonstrate that HOD RBCs continuously localize to the marginal sinus following transfusion, where they co-localize with marginal zone (MZ) B cells. Depletion of MZ B cells inhibited IgM and IgG anti-HOD antibody formation, while CD4 T cell depletion only prevented IgG anti-HOD antibody development. HOD-specific CD4 T cells displayed similar proliferation and activation following transfusion of HOD RBCs into wild type or MZ B cell deficient recipients, suggesting that IgG formation is not dependent on MZ B cell-mediated CD4 T cell activation. Moreover, depletion of follicular B cells failed to substantially impact the anti-HOD antibody response and no increase in antigen specific germinal center B cells was detected following HOD RBC transfusion, suggesting that antibody formation is not dependent on the splenic follicle. Despite this, anti-HOD antibodies persisted for several months following HOD RBC transfusion. Overall, these data suggest MZ B cells can initiate and then contribute to RBC alloantibody formation, highlighting a unique immune pathway that can be engaged following RBC transfusion.

scholarly journals Marginal Zone B Cells Regulate RBC Alloimmunization Toward Distinct RBC Alloantigens

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3847-3847
Author(s):  
Patricia E. Zerra ◽  
Seema R. Patel ◽  
Connie M. Arthur ◽  
Kathryn R. Girard-Pierce ◽  
Ashley Bennett ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cd4 T Cells ◽  
Antibody Formation ◽  
Marginal Zone ◽  
Cd4 T Cell ◽  
Rbc Transfusion

Abstract Background: While red blood cell (RBC) transfusion can be beneficial, exposure to allogeneic RBCs can result in the development of RBC alloantibodies that can make it difficult to obtain compatible RBCs for future transfusions. Aside from phenotype matching protocols, no strategy currently exists that is capable of preventing RBC alloimmunization following therapeutic transfusion. As RBC alloantigens represent diverse determinants capable of driving distinct immune pathways, common immunological nodes must be identified in order to successfully prevent RBC alloimmunization against a variety of different alloantigens. Recent results demonstrate that marginal zone (MZ) B cells mediate anti-KEL antibody formation in the complete absence of CD4 T cells. However, whether MZ B cells similarly regulate RBC alloantibody formation against other RBC alloantigens remains unknown. As a result, we examined the role of MZ B cells and CD4 T cells in the development of RBC alloantibodies following exposure to the HOD (hen egg lysozyme, ovalbumin and duffy) antigen. Methods: Each recipient was transfused with HOD or KEL RBCs following either MZ B cell or CD4 T cell depletion using a cocktail of MZ B cell (anti-CD11a and anti-CD49d) or anti-CD4 depleting antibody, 4 and 2 days prior to transfusion. Control groups received isotype control injections in parallel. MZ B cell deficient (CD19cre/+ X Notch2flx/flx) and CD4 T cell deficient (MHC class II knockout) recipients were also used to examine the role of MZ B cells and CD4 T cells, respectively. Serum collected on days 5 and 14 post-transfusion was evaluated for anti-HOD or anti-KEL antibodies by incubating HOD or KEL RBCs with serum, followed by detection of bound antibodies using anti-IgM and anti-IgG and subsequent flow cytometric analysis. Evaluation of antibody engagement and overall survival of HOD or KEL RBCs was accomplished by labeling RBCs with the lipophilic dye, DiI, prior to transfusion, followed by examination for bound antibody and RBC clearance on days 5 and 14 post-transfusion by flow cytometry. Results: Similar to the ability of MZ B cell depletion to reduce anti-KEL antibody formation following KEL RBC exposure, depletion of MZ B cells significantly reduced anti-HOD IgM and IgG antibodies following HOD RBC transfusion. In contrast, injection of recipients with isotype control antibodies in parallel failed to prevent alloantibody formation following HOD or KEL RBC transfusion. Similar results were obtained following HOD or KEL RBC transfusion into recipients genetically deficient in MZ B cells. In contrast, although MZ B cells were required for HOD and KEL RBC-alloantibody formation, manipulation of CD4 T cells differentially impacted the ability of each antigen to induce alloantibodies. While transfusion of HOD or KEL RBCs resulted in robust IgM alloantibodies in the absence of CD4 T cells, depletion or genetic elimination of CD4 T cells significantly inhibited anti-HOD IgG antibody formation, while failing to impact IgG anti-KEL antibody formation. Consistent with this, while manipulation of CD4 T cells protected HOD RBCs from antibody deposition and subsequent RBC clearance, this same approach failed to similarly protect KEL RBCs following transfusion. In contrast, depletion of MZ B cells not only prevented detectable alloantibody production, but also completely protected HOD or KEL RBCs from antibody deposition and subsequent RBC clearance. Conclusion: These results suggest that while MZ B cells mediate a robust IgM antibody response following either KEL or HOD antigen exposure, MZ B cells appear to possess the capacity to orchestrate unique downstream IgG responses through CD4 T cell dependent and independent pathways contingent on target alloantigen. As a result, while manipulation of CD4 T cells may prevent alloantibody formation against some antigens, targeting this immune population inadequately prevents RBC alloantibody formation against all RBC antigens. As chronic transfusion therapy exposes recipients to a wide variety of alloantigens, these results suggest that MZ B cells may represent a central initiating node that governs RBC alloimmunization against a variety of RBC alloantigens, and may therefore serve as a useful target in preventing alloantibody formation in chronically transfused individuals. Disclosures No relevant conflicts of interest to declare.

scholarly journals Autoreactive marginal zone B cells are spontaneously activated but lymph node B cells require T cell help

2006 ◽  
Vol 203 (8) ◽  
pp. 1985-1998 ◽  
Author(s):  
Laura Mandik-Nayak ◽  
Jennifer Racz ◽  
Barry P. Sleckman ◽  
Paul M. Allen
Keyword(s):  
Lymph Node ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
B Cell Tolerance ◽  
Marginal Zone B Cells ◽  
T Cell Help

In K/BxN mice, arthritis is induced by autoantibodies against glucose-6-phosphate-isomerase (GPI). To investigate B cell tolerance to GPI in nonautoimmune mice, we increased the GPI-reactive B cell frequency using a low affinity anti-GPI H chain transgene. Surprisingly, anti-GPI B cells were not tolerant to this ubiquitously expressed and circulating autoantigen. Instead, they were found in two functionally distinct compartments: an activated population in the splenic marginal zone (MZ) and an antigenically ignorant one in the recirculating follicular/lymph node (LN) pool. This difference in activation was due to increased autoantigen availability in the MZ. Importantly, the LN anti-GPI B cells remained functionally competent and could be induced to secrete autoantibodies in response to cognate T cell help in vitro and in vivo. Therefore, our study of low affinity autoreactive B cells reveals two distinct but potentially concurrent mechanisms for their activation, of which one is T cell dependent and the other is T cell independent.

scholarly journals CD4+ T cell activation and tolerance induction in B cell knockout mice.

1996 ◽  
Vol 183 (4) ◽  
pp. 1339-1344 ◽  
Author(s):  
J A Phillips ◽  
C G Romball ◽  
M V Hobbs ◽  
D N Ernst ◽  
L Shultz ◽  
...  
Keyword(s):  
T Cell ◽  
B Cells ◽  
B Cell ◽  
T Cell Activation ◽  
Knockout Mice ◽  
Cell Activation ◽  
Peripheral Tolerance ◽  
Cd4 T Cell ◽  
T Cell Tolerance ◽  
Cell Tolerance

B cell knockout mice microMT/microMT were used to examine the requirement for B cell antigen (Ag) presentation in the establishment of CD4+ T cell tolerance. CD4+T cells from microMT mice injected with exogenous protein Ag in adjuvant responded to in vitro challenge by transcription of cytokine mRNA, cytokine secretion, and proliferation. Peripheral tolerance could be established in microMT mice with a single dose of deaggragated protein. This tolerance was manifested by a loss of T cell proliferation and cytokine production (including both T helper cell type 1 [Th1]- and Th2-related cytokines), indicating that B cells are not required for the induction of peripheral T cell tolerance and suggesting that the dual zone tolerance theory is not applicable to all protein Ags and is not mediated through Ag presentation by B cells.

Impaired T- and B-cell development in Tcl1-deficient mice

Blood ◽  
2005 ◽  
Vol 105 (3) ◽  
pp. 1288-1294 ◽  
Author(s):  
Sang-Moo Kang ◽  
Maria Grazia Narducci ◽  
Cristina Lazzeri ◽  
Adriana M. Mongiovì ◽  
Elisabetta Caprini ◽  
...  
Keyword(s):  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
Cell Development ◽  
B Cell Development ◽  
Cell Stage ◽  
Marginal Zone B Cells ◽  
Induced Apoptosis ◽  
Deficient Mice

AbstractTCL1, the overexpression of which may result in T-cell leukemia, is normally expressed in early embryonic tissues, the ovary, and lymphoid lineage cells. Our analysis of mouse B-lineage cells indicates that Tcl1 expression is initiated in pro-B cells and persists in splenic marginal zone and follicular B cells. T-lineage Tcl1 expression begins in thymocyte progenitors, continues in CD4+CD8+ thymocytes, and is extinguished in mature T cells. In Tcl1-deficient mice, we found B lymphopoiesis to be compromised at the pre-B cell stage and T-cell lymphopoiesis to be impaired at the CD4+CD8+ thymocyte stage. A corresponding increase was observed in thymocyte susceptibility to anti-CD3ϵ–induced apoptosis. Reduced numbers of splenic follicular and germinal center B cells were accompanied by impaired production of immunoglobulin G1 (IgG1) and IgG2b antibodies in response to a T-dependent antigen. The marginal zone B cells and T-cell–independent antibody responses were also diminished in Tcl1-/- mice. This analysis indicates a significant role for Tcl1, a coactivator of Akt signaling, in normal T- and B-cell development and function.

scholarly journals Development of Notch1 Positive T-Lineage Lymphomas or Splenic Marginal Zone Lymphomas with Pan-Hematopoietic or Pro-B Cell Specific Deletion of Trp53 with Distinct Differentially Dysregulated Pathways

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 2229-2229
Author(s):  
Jayanth Kumar Palanichamy ◽  
Tiffany Tran ◽  
Jennifer King ◽  
Sol Katzman ◽  
Gunjan Sharma ◽  
...  
Keyword(s):  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Signaling Pathways ◽  
Marginal Zone ◽  
B Cell Lymphoma ◽  
Gene Set Enrichment Analysis ◽  
Marginal Zone B Cells ◽  
Flow Cytometric ◽  
Specific Deletion

Abstract Deletion of the tumor suppressor gene TP53 (Trp53 in mice) has been associated with the development of numerous human malignancies. TP53 acts as a central coordinator of the DNA damage response. In mice, pan-Trp53 deletion leads predominantly to the development of T-cell lymphomas, followed by B-cell lymphomas, sarcomas and teratomas. In order to dissect the role of Trp53 in the hematopoietic system, we created two different loss of function mouse models: Pan-hematopoietic Trp53 deletion using Vav1-Cre based deletion; and a B-cell-specific deletion was created using CD19-Cre. Vav1-p53CKO mice developed hematolymphoid malignancies with 100% penetrance by 12 months. Most malignancies observed were CD3e+ T-lineage lymphomas involving the thymus or spleen (37/45). Beyond 200 days, these mice predominantly developed mixed myeloid malignancies. The shift away from T-lineage malignancies in older mice may reflect aging-related decline of pre-malignant lymphoid progenitors and skewing to myeloid progenitors. Flow cytometric characterization of the T-lineage lymphomas identified a mix of tumors, including double-negative (CD4-CD8-), double-positive (CD4+CD8+), or single positive (CD4/CD8). In pre-malignant mice, Vav1-p53CKO thymocytes showed accelerated maturation with most of the cells in the DN4 stage, suggesting a bypass of the p53-dependent DN3 β-selection checkpoint. All T-lineage lymphomas showed overexpression of surface Notch1 as well as overexpression of Notch1 targets Hes1 and p21 at the transcript level. Consistent with prior data, normal murine thymocyte subsets showed high levels of expression of Notch1 target genes at the DN3 stage of development, which appears dysregulated in these T-lineage lymphomas. This Notch1 activation was found to be multifactorial with increased Mdm2 and decreased Numb levels seen in tumors. Overall, we demonstrate Notch1 activation and subsequent acceleration through the T-cell developmental stages in this model of pan-hematopoietic Trp53 deletion. The B-cell specific Trp53 knockout mice (CD19-P53CKO) (n=54) were followed up for up to 2 years. The majority (47/54) developed splenomegaly in an age-dependent manner. Histologic examination showed marginal zone expansion (6/54), frank low-grade marginal zone lymphoma (16/54) or diffuse splenic lymphoma (25/54). The disease was confined to the spleen in the case of lower-grade histology while higher grades correlated with liver and kidney involvement. Flow cytometric analysis of tumors showed B220+ CD19+ IgM+ cells. Interestingly, these tumors demonstrated low levels of Notch2 expression, which normally is highly expressed in marginal zone B-cells. In order to characterize pathogenesis, we sorted follicular and marginal zone B-cells from floxed P53 and pre-malignant CD19-P53CKO mice. RNA was isolated from all these fractions and the spleens of 5 CD19-P53KO mice with diffuse lymphoma and subjected to RNA-Seq. A comparison of the floxed p53 with the CD19-P53CKO fractions (follicular and marginal zone) revealed a highly similar transcriptome. On the other hand, p53-deficient lymphomas showed >10,000 genes significantly differentially expressed demonstrating the unique transcriptome which developed during malignant transformation. Pathway analysis of these genes using Gene Set Enrichment Analysis (GSEA) identified enrichment of PI3K, Rap1 and MAPK signaling pathways, which are associated with cellular proliferation. Overexpression of the PI3K pathway genes Ccne1, Sgk1, Mapk13 and Pik3cb were validated by qPCR in 10 independent tumor samples when compared to the splenic marginal zone fractions. In the B-cell lineage, Trp53 deficiency leads to the dysregulation of multiple genes involved in key cellular signaling pathways, including the PI3K/MAPK pathway. In summary, pan hematopoietic deletion of Trp53 led to T-lineage lymphoma in young mice and myeloid tumors in older mice; with activation of Notch1 signaling in the former. B-cell specific deletion of Trp53 led to splenic marginal zone and diffuse B-cell lymphoma with transcriptional dysregulation of key signaling molecules. Hence, tumorigenesis by Trp53 deletion is tightly linked to lineage and appears to dysregulate key signaling pathways that are operant in those lineages, potentially identifying novel strategies for therapeutic interventions in P53 dependent human hematolymphoid malignancies. Disclosures No relevant conflicts of interest to declare.

scholarly journals Marginal Zone B Cells in Neonatal Rats Express Intermediate Levels of CD90 (Thy-1)

2002 ◽  
Vol 9 (4) ◽  
pp. 187-195 ◽  
Author(s):  
Peter M. Dammers ◽  
Monique E. Lodewijk ◽  
André Zandvoort ◽  
Frans G. M. Kroese
Keyword(s):  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
Cell Lineage ◽  
Neonatal Rats ◽  
Adult Rats ◽  
Marginal Zone B Cells ◽  
Immature B Cells

Here we show that marginal zone (MZ)-B cells in rats can already be detected in neonatal spleen from two days after birth. At this time point, morphologically distinct MZs are not present yet and the vast majority of B cells in spleen are located in a concentric area surrounding the T cell zones (PALS). Before MZs are obviously detectable in spleen (14 days after birth), MZ-B cells seem to be enriched at the outer zones of the concentric B cell areas. Similar to adult rats, neonatal MZ-B cells are intermediate-sized cells that express high levels of surface (s)IgM and HIS57 antigen, and low levels of sIgD and CD45R (HIS24). We show here, however, that in contrast to adult MZ-B cells, MZ-B cells (and also recirculating follicular (RF)-B cells) in neonatal rats express higher levels of CD90 (Thy-1). In adult rats, expression of CD90 on the B cell lineage is confined to immature B cells. We speculate that the expression of CD90 on neonatal MZ-B cells may have implications for their responsiveness to polysaccharide (T cell-independent type 2) antigens.

The MAML1 Transcriptional Co-Activator Is Required for the Development of Marginal Zone B Cells.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 777-777
Author(s):  
Lizi Wu ◽  
Ivan Maillard ◽  
Makoto Nakamura ◽  
Warren S. Pear ◽  
James D. Griffin
Keyword(s):  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
T Cell Development ◽  
Cell Development ◽  
Notch Receptor ◽  
Lymphoid Cells ◽  
Marginal Zone B Cells ◽  
Notch Receptors

Abstract Notch1 and Notch2 receptor-mediated signaling appear to have important and unique roles in lymphoid lineage commitment. Notch1 is required for T cell development, while Notch2 is essential for marginal zone B cell development. This specificity is not completely explained by differential expression patterns of Notch1 and 2 or Notch ligands, suggesting that there are other genes that contribute to specifying Notch receptor functions. We have previously shown that the MAML family of transcriptional co-activators is essential for Notch-induced transcriptional events, and functions by forming ternary complexes with Notch and the transcription factor CSL in the nucleus. This MAML family currently consists of three members, MAML1-3, all of which can function as co-activators for Notch receptors in vitro . In this study, we investigated the possibility that MAML1 co-activator contributes to determining Notch receptor function by generating mice deficient in the Maml1 gene. Maml1 -deficient mice fail to thrive and die within 10 days of birth. The morphology of marrow, nodes, and spleen was grossly intact. The ability of Maml1-deficient stem cells to generate different T and B lineages of lymphoid cells was determined by transplanting fetal liver cells isolated from E14.5 embryos into lethally irradiated wild-type recipient mice and analyzing donor-derived lymphoid cells 12 weeks post-transplantation. We found that the deletion of Maml1 results in complete loss of marginal zone B cell lineage (MZB, defined by B220+CD21hiCD23lo). Moreover, the number of MZB cells was reduced to about 50% in Maml1 -heterozygous fetal liver chimeras as compared to wild type controls. However, T cell development was largely unaffected, with only a modest but significant increase in the number of γδ T cells (about 2 fold) in both the thymus and the spleen. Therefore, these results suggest the unexpected finding that targeted deletion of Maml1 in hematopoietic cells is similar to the targeted deletion of either Notch2 or the Notch ligand, Delta-like 1 (Dll1) resulting in the loss of marginal zone B cells and minimal effects on T cell development. Moreover, the number of marginal zone B cells is correlated with Maml1 gene dosage, indicating haploinsufficiency. These data suggest that the Notch ligand Dll1 activates Notch2 signaling resulting in a Notch2/MAML1/CSL complex that is essential for marginal zone B cell development. Further studies with respect to relative expression levels of various MAML genes and interactions of MAML co-activators and Notch receptors may shed additional light into understanding how different Notch receptors regulate cell fate decisions in hematopoiesis.

RhoH-Deficient Mice Show Altered B Cell Populations In Vivo.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 2307-2307
Author(s):  
Abel Sanchez-Aguilera ◽  
Jose Cancelas ◽  
David A. Williams
Keyword(s):  
Bone Marrow ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
Cell Receptor ◽  
Wild Type ◽  
Marginal Zone B Cells

Abstract RhoH is a GTPase-deficient, hematopoietic-specific member of the family of Rho GTPases (Li et al, 2002). RhoH has been described as regulating proliferation and engraftment of hematopoietic progenitor cells (Gu et al, 2005) and integrin-mediated adhesion in T cells (Cherry et al, 2004). Additionally, RhoH plays a critical role in T-cell development and T-cell receptor signaling (Gu et al, 2006; Dorn et al, 2007). However, the potential role of RhoH in the differentiation and biological functions of B cells are unknown. To answer these questions, we analyzed the B-cell phenotype of RhoH−/− mice and the in vitro properties of RhoH-deficient splenic B cells compared to their wild-type counterparts. RhoH−/− mice showed increased B-cell numbers in the bone marrow, mainly due to an increase in the number of pro-B, pre-B and immature B cells. In the spleen, lymph nodes and peripheral blood, RhoH−/− mice showed a significant decrease in the number of follicular (B-2) cells (B220+ CD93– IgDhigh CD21low). The number of splenic marginal zone B cells (B220+ CD93– IgDlow CD21high), plasma cells (CD93– CD38+ CD138+) in bone marrow and spleen, and B-1 cells (IgM+ CD5+) in peritoneal cavity were not significantly different from those in wild-type animals. These alterations have functional significance, since the serum concentrations of IgM and IgG1 were significantly lower in RhoH−/− mice. However, splenic B cells isolated from RhoH−/− mice did not show any significant differences in their in vitro activation by anti-IgM, CD40 ligation or IL-4 stimulation, nor did they differ in their proliferative response to lipopolysaccharide. In vitro migration of RhoH-deficient B cells in response to CXCL12 or CXCL13 was similar to that of wild-type B cells. Given the important role of RhoH in signal transduction downstream the T cell receptor, we investigated the possible role of RhoH in B cell receptor signaling. Although total splenic B cells from RhoH−/− mice showed markedly increased phosphorylation of SYK and ERK after anti-IgM stimulation compared to wild-type B cells, sorted populations of splenic B-2 and marginal zone B cells from RhoH−/− and wild-type animals did not differ in the activation of these kinases, suggesting that the observed difference can be attributed to the different cellular composition of the B cell compartment (i.e. B-2 vs marginal zone B cells) in RhoH−/− mice. These data imply that the phenotype observed in RhoH−/− mice may not reflect an intrinsic defect in B cells but may be attributed to crosstalk between B cells and other hematopoietic cell populations. Composition of B cell subsets in wild-type and RhoH−/− mice (total cell number ×106, ± standard deviation, N=9) Bone marrow Spleen (*) indicates p<0.05; (**), p<0.01; (***), p<0.005 RhoH+/+ RhoH−/− RhoH+/+ RhoH−/− total B cells 7.8±1.8 11.0±2.4 (**) total B cells 31.7±10.1 25.4±8.8 pro-B 0.12±0.03 0.15±0.04 (*) transitional 8.7±1.2 8.6±2.8 pre-B 2.6±0.6 3.8±0.8 (***) B-2 11.6±4.1 7.6±2.5 (*) immature 1.5±0.4 2.1±0.5 (*) marginal 3.2±1.1 3.9±1.6 mature 1.4±0.7 1.7±0.9

Ligation of tumour-produced mucins to CD22 dramatically impairs splenic marginal zone B-cells

2009 ◽  
Vol 417 (3) ◽  
pp. 673-683 ◽  
Author(s):  
Munetoyo Toda ◽  
Risa Hisano ◽  
Hajime Yurugi ◽  
Kaoru Akita ◽  
Kouji Maruyama ◽  
...  
Keyword(s):  
Sialic Acid ◽  
B Cells ◽  
B Cell ◽  
Marginal Zone ◽  
Cell Signalling ◽  
Negative Regulator ◽  
Mammary Adenocarcinoma ◽  
Marginal Zone B Cells ◽  
Tumour Bearing

CD22 [Siglec-2 (sialic acid-binding, immunoglobulin-like lectin-2)], a negative regulator of B-cell signalling, binds to α2,6- sialic acid-linked glycoconjugates, including a sialyl-Tn antigen that is one of the typical tumour-associated carbohydrate antigens expressed on various mucins. Many epithelial tumours secrete mucins into tissues and/or the bloodstream. Mouse mammary adenocarcinoma cells, TA3-Ha, produce a mucin named epiglycanin, but a subline of them, TA3-St, does not. Epiglycanin binds to CD22 and inhibits B-cell signalling in vitro. The in vivo effect of mucins in the tumour-bearing state was investigated using these cell lines. It should be noted that splenic MZ (marginal zone) B-cells were dramatically reduced in the mice bearing TA3-Ha cells but not in those bearing TA3-St cells, this being consistent with the finding that the thymus-independent response was reduced in these mice. When the mucins were administered to normal mice, a portion of them was detected in the splenic MZ associated with the MZ B-cells. Furthermore, administration of mucins to normal mice clearly reduced the splenic MZ B-cells, similar to tumour-bearing mice. These results indicate that mucins in the bloodstream interacted with CD22, which led to impairment of the splenic MZ B-cells in the tumour-bearing state.

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