Biomedical subjects

Jonathan C Poe

Publications and source records attributed to Jonathan C Poe.

14 recordsLinked to original sources

PubMed2005

Immunotherapy using unconjugated CD19 monoclonal antibodies in animal models for B lymphocyte malignancies and autoimmune disease.

Immunotherapy with unconjugated CD20 monoclonal antibodies has proven effective for treating non-Hodgkin's lymphoma and autoimmune disease. CD20 immunotherapy depletes mature B cells but does not effectively deplete pre-B or immature B cells, some B cell subpopulations, antibody-producing cells, or their malignant counterparts. Because CD19 is expressed earlier during B cell development, a therapeutic strategy for the treatment of early lymphoblastic leukemias/lymphomas was developed by using CD19-specific monoclonal antibodies in a transgenic mouse expressing human CD19. Pre-B cells and their malignant counterparts were depleted as well as antibody- and autoantibody-producing cells. These results demonstrate clinical utility for the treatment of diverse B cell malignancies, autoimmune disease, and humoral transplant rejection.

Animals↗

PubMed2005

The peritoneal cavity provides a protective niche for B1 and conventional B lymphocytes during anti-CD20 immunotherapy in mice.

Although anti-CD20 immunotherapy effectively treats human lymphoma and autoimmune disease, the in vivo effect of immunotherapy on tissue B cells and their subsets is generally unknown. To address this, anti-mouse CD20 mAbs were used in a mouse model in which the extent and kinetics of tissue B cell depletion could be assessed in vivo. CD20 mAb treatment depleted most mature B cells within 2 days, with 95-98% of B cells in the bone marrow, blood, spleen, lymph nodes, and gut-associated lymphoid tissues depleted by day 7, including marginal zone and follicular B cells. The few spleen B cells remaining after CD20 mAb treatment included pre-B, immature, transitional, and some B1 B cells that expressed CD20 at low levels. By contrast, peritoneal cavity B cells expressed normal CD20 densities and were coated with CD20 mAb, but only 30-43% of B1 cells and 43-78% of B2 cells were depleted by day 7. Spleen B cells adoptively transferred into the peritoneal cavity were similarly resistant to mAb-induced depletion, while transferred B cells that had migrated to the spleen were depleted. However, peritoneal B1 and B2 cells were effectively depleted in mAb-treated wild-type and C3-deficient mice by thioglycolate-induced monocyte migration into this otherwise privileged niche. Inflammation-elicited effector cells did not promote peritoneal cavity B cell depletion in FcR-deficient mice treated with CD20 mAb. Thus, the majority of CD20(+) cells and B cell subsets within lymphoid tissues and the peritoneum could be depleted efficiently in vivo through Fc-dependent, but C-independent pathways during anti-CD20 immunotherapy.

Animals↗

PubMed2005

B-1a and B-1b cells exhibit distinct developmental requirements and have unique functional roles in innate and adaptive immunity to S. pneumoniae.

B-1a and B-1b lymphocytes were found to exhibit specialized roles in providing immunity to Streptococcus pneumoniae and differ dramatically in their developmental requirements. Transgenic mice overexpressing CD19 (hCD19Tg) generated B-1a cells and natural antibodies that provided protection during infection, while CD19-deficient (CD19(-/-)) mice lacked B-1a cells, lacked natural antibodies, and were more susceptible to infection. By contrast, pneumococcal polysaccharide (PPS) immunization protected CD19(-/-) mice during lethal challenge, whereas hCD19Tg mice remained unprotected. This resulted from differences in the B-1b subset: the key population found to produce protective PPS-specific antibody in both wild-type and CD19(-/-) mice. Thus, CD19(-/-) mice generated B-1b cells and protective adaptive PPS-specific antibody responses, whereas hCD19Tg mice lacked B-1b cells and adaptive PPS-specific antibody responses. This reciprocal contribution of B-1a and B-1b subsets to innate and acquired immunity reveals an unexpected division of labor within the B-1 compartment that is normally balanced by their coordinated development.

Animals↗

PubMed2005

CD22: a multifunctional receptor that regulates B lymphocyte survival and signal transduction.

Recent advances in the study of CD22 indicate a complex role for this transmembrane glycoprotein member of the immunoglobulin superfamily in the regulation of B lymphocyte survival and proliferation. CD22 has been previously recognized as a potential lectin-like adhesion molecule that binds alpha2,6-linked sialic acid-bearing ligands and as an important regulator of B-cell antigen receptor (BCR) signaling. However, genetic studies in mice reveal that some CD22 functions are regulated by ligand binding, whereas other functions are ligand-independent and may only require expression of an intact CD22 cytoplasmic domain at the B-cell surface. Until recently, most of the functional activity of CD22 has been widely attributed to CD22's ability to recruit potent intracellular phosphatases and limit the intensity of BCR-generated signals. However, a more complex role for CD22 has recently emerged, including a central role in a novel regulatory loop controlling the CD19/CD21-Src-family protein tyrosine kinase (PTK) amplification pathway that regulates basal signaling thresholds and intensifies Src-family kinase activation after BCR ligation. CD22 is also central to the regulation of peripheral B-cell homeostasis and survival, the promotion of BCR-induced cell cycle progression, and is a potent regulator of CD40 signaling. Herein we discuss our current understanding of how CD22 governs these complex and overlapping processes, how alterations in these tightly controlled regulatory activities may influence autoimmune disease, and the current and future applications of CD22-directed therapies in oncology and autoimmunity.

Animals↗

PubMed2005

The CD19-CD21 signal transduction complex of B lymphocytes regulates the balance between health and autoimmune disease: systemic sclerosis as a model system.

Cell-surface CD19 functions as a general rheostat for defining intrinsic and antigen receptor-induced signaling thresholds critical for clonal expansion of the B cell pool and humoral immunity. CD19 also governs B cell responses initiated through the CD21 receptor, where complement C3d binding to CD21 links humoral immune responses with the innate immune system. Alterations in this signaling pathway can predispose mice and humans to autoantibody production and systemic autoimmunity. Transgenic mice that overexpress CD19 by 20-170% lose tolerance and generate autoantibodies. Likewise, B cells from CD21-deficient mice overexpress CD19 by approximately 50%, which leads to autoantibody production. Autoimmune patients with systemic sclerosis also overexpress CD19 by approximately 20%, which may contribute to their intrinsic B cell abnormalities and autoantibody production. Thus, chronic B cell activation resulting from augmented CD19 expression or signaling through the CD19 pathway may reveal a prototype autoimmune disease susceptibility pathway in mice and humans.

Animals↗

PubMed2004

CD22 regulates B lymphocyte function in vivo through both ligand-dependent and ligand-independent mechanisms.

The interaction of CD22 with alpha2,6-linked sialic acid ligands has been widely proposed to regulate B lymphocyte function and migration. Here, we generated gene-targeted mice that express mutant CD22 molecules that do not interact with these ligands. CD22 ligand binding regulated the expression of cell surface CD22, immunoglobulin M and major histocompatibility complex class II on mature B cells, maintenance of the marginal zone B cell population, optimal B cell antigen receptor-induced proliferation, and B cell turnover rates. However, CD22 negative regulation of calcium mobilization after B cell antigen receptor ligation, CD22 phosphorylation, recruitment of SHP-1 to CD22 and B cell migration did not require CD22 ligand engagement. These observations resolve longstanding questions regarding the physiological importance of CD22 ligand binding in the regulation of B cell function in vivo.

Animals↗

PubMed2004

The innate mononuclear phagocyte network depletes B lymphocytes through Fc receptor-dependent mechanisms during anti-CD20 antibody immunotherapy.

Anti-CD20 antibody immunotherapy effectively treats non-Hodgkin's lymphoma and autoimmune disease. However, the cellular and molecular pathways for B cell depletion remain undefined because human mechanistic studies are limited. Proposed mechanisms include antibody-, effector cell-, and complement-dependent cytotoxicity, the disruption of CD20 signaling pathways, and the induction of apoptosis. To identify the mechanisms for B cell depletion in vivo, a new mouse model for anti-CD20 immunotherapy was developed using a panel of twelve mouse anti-mouse CD20 monoclonal antibodies representing all four immunoglobulin G isotypes. Anti-CD20 antibodies rapidly depleted the vast majority of circulating and tissue B cells in an isotype-restricted manner that was completely dependent on effector cell Fc receptor expression. B cell depletion used both FcgammaRI- and FcgammaRIII-dependent pathways, whereas B cells were not eliminated in FcR common gamma chain-deficient mice. Monocytes were the dominant effector cells for B cell depletion, with no demonstrable role for T or natural killer cells. Although most anti-CD20 antibodies activated complement in vitro, B cell depletion was completely effective in mice with genetic deficiencies in C3, C4, or C1q complement components. That the innate monocyte network depletes B cells through FcgammaR-dependent pathways during anti-CD20 immunotherapy has important clinical implications for anti-CD20 and other antibody-based therapies.

Animals↗

PubMed2004

Cutting edge: C3d functions as a molecular adjuvant in the absence of CD21/35 expression.

Complement component C3 covalently attaches to Ags following activation, where the C3d cleavage fragment can function as a molecular adjuvant to augment humoral immune responses. C3d is proposed to exert its adjuvant-like activities by targeting Ags to the C3d receptor (CD21/35) expressed by B cells and follicular dendritic cells. To directly assess the importance of CD21/35 in mediating the immunostimulatory effects of C3d, CD21/35-deficient (CD21/35(-/-)) mice were immunized with streptavidin (SA), SA-C3dg tetramers, recombinant HIV gp120 (gp120), or gp120 fused with linear multimers of C3d. Remarkably, SA- and gp120-specific Ab responses were significantly augmented in CD21/35(-/-) mice when these Ags were complexed with C3d in comparison to Ag alone. In fact, primary and secondary Ab responses and Ab-forming cell responses of CD21/35(-/-) mice approached those of wild-type mice immunized with SA-C3dg and gp120-C3d. Thus, C3d can function as a molecular adjuvant in the absence of CD21/35 expression.

Adjuvants, Immunologic↗

PubMed2004

Severely impaired B lymphocyte proliferation, survival, and induction of the c-Myc:Cullin 1 ubiquitin ligase pathway resulting from CD22 deficiency on the C57BL/6 genetic background.

Understanding the molecular mechanisms through which CD22 regulates B lymphocyte homeostasis, signal transduction, and tolerance is critical to defining normal B cell function and understanding the role of CD22 in autoimmunity. Therefore, CD22 function was examined in vivo and in vitro using B cells from CD22-deficient (CD22(-/-)) mice. Backcrossing of founder CD22(-/-) mice onto the C57BL/6 (B6) genetic background from a B6/129 mixed background resulted in a dramatically reduced B cell proliferative response following IgM ligation, characterized by a paucity of lymphoblasts and augmented apoptosis. Also, the phenotype of splenic B6 CD22(-/-) B cells was uniquely HSA(high) and IgD(low)/CD21(low) with intermediate levels of CD5 expression, although the percentages of mature and transitional B cells were normal. That B6 CD22(-/-) B cells predominantly underwent apoptosis following IgM ligation correlated with this unique tolerant phenotype, as well as defective induction of the c-Myc:Cullin 1 (CUL1) ubiquitin ligase pathway that is necessary for progression to the S phase of cell cycle. CD40 ligation compensated for CD22 deficiency by restoring lymphoblast development, proliferation, c-Myc and CUL1 expression, and protein ubiquitination/degradation in IgM-stimulated B6 CD22(-/-) B cell cultures. Thereby, this study expands our current understanding of the complex role of CD22 during B cell homeostasis and Ag responsiveness, and reveals that the impact of CD22 deficiency is dictated by the genetic background on which it is rendered. Moreover, this study defines CD22 and CD40 as the first examples of lymphocyte coreceptors that influence induction of the c-Myc:CUL1 ubiquitin ligase pathway.

Adjuvants, Immunologic↗

PubMed2004

Mouse CD20 expression and function.

CD20 plays a role in human B cell proliferation and is an effective target for immunotherapy. In this study, mouse CD20 expression and biochemistry were assessed for the first time using a new panel of CD20-specific mAb, with CD20 function assessed using CD20-deficient (CD20(-/-)) mice. CD20 expression was B cell restricted and was initiated during late pre-B cell development. The frequency and density of CD20 expression increased during B cell maturation in the bone marrow, with a subpopulation of transitional IgM(hi) B cells expressing higher CD20 levels than the majority of mature recirculating B cells. Transitional T1 B cells in the spleen also expressed high CD20 levels, providing a useful new marker for this B cell subset. In CD20(-/-) mice, immature and mature B cell IgM expression was approximately 20-30% lower relative to B cells from wild-type littermates. In addition, CD19-induced intracellular calcium responses were significantly reduced in CD20(-/-) B cells, with a less dramatic effect on IgM-induced responses. These results reveal a role for CD20 in transmembrane Ca(2+) movement in mouse primary B cells that complements previous results obtained using human CD20 cDNA-transfected cell lines. Otherwise, B cell development, tissue localization, signal transduction, proliferation, T cell-dependent antibody responses and affinity maturation were normal in CD20(-/-) mice. Thus, mouse and human CD20 share similar patterns of expression and function. These studies thereby provide an animal model for studying CD20 function in vivo and the molecular mechanisms that influence anti-CD20 immunotherapy.

Animals↗

PubMed2003

The tetraspanin CD81 regulates the expression of CD19 during B cell development in a postendoplasmic reticulum compartment.

CD81 is a widely expressed tetraspanin that associates in B cells with CD19 in the CD19-CD21-CD81 signaling complex. CD81 is necessary for normal CD19 expression; cd81(-/-) B cells express lower levels of CD19, especially cd81(-/-) small pre-BII cells, which are almost devoid of surface CD19. The dependence of CD19 expression on CD81 is specific to this particular tetraspanin since cd9(-/-) B cells express normal levels of CD19. Furthermore, expression of human CD81 in mouse cd81(-/-) B cells restored surface CD19 to normal levels. Quantitative analysis of CD19 mRNA demonstrated normal levels, even in cd81(-/-) pre-BII cells. Analysis of CD19 at the protein level identified two CD19 glycoforms in both wild-type and cd81(-/-) B cells. The higher M(r) glycoform is significantly reduced in cd81(-/-) B cells and is endoglycosidase H (endo-H) resistant. In contrast, the low M(r) glycoform is comparably expressed in cd81(-/-) and in wild-type B cells and is endo-H sensitive. Because endo-H sensitivity is tightly correlated with endoplasmic reticulum localization, we suggest that the dependency of CD19 expression on CD81 occurs in a postendoplasmic reticulum compartment where CD81 is necessary for normal trafficking or for surface membrane stability of CD19.

Animals↗

PubMed2002

A functional role for circulating mouse L-selectin in regulating leukocyte/endothelial cell interactions in vivo.

L-selectin mediates the initial capture and subsequent rolling of leukocytes along inflamed vascular endothelium and mediates lymphocyte migration to peripheral lymphoid tissues. Leukocyte activation induces rapid endoproteolytic cleavage of L-selectin from the cell surface, generating soluble L-selectin (sL-selectin). Because human sL-selectin retains ligand-binding activity in vitro, mouse sL-selectin and its in vivo relevance were characterized. Comparable with humans, sL-selectin was present in adult C57BL/6 mouse sera at approximately 1.7 micro g/ml. Similar levels of sL-selectin were present in sera from multiple mouse strains, despite their pronounced differences in cell surface L-selectin expression levels. Adhesion molecule-deficient mice prone to spontaneous chronic inflammation and mice suffering from leukemia/lymphoma had 2.5- and 20-fold increased serum sL-selectin levels, respectively. By contrast, serum sL-selectin levels were reduced by 70% in Rag-deficient mice lacking mature lymphocytes. The majority of serum sL-selectin had a molecular mass of 65-75 kDa, consistent with its lymphocyte origin. Slow turnover may explain the relatively high levels of sL-selectin in vivo. The t(1/2) of sL-selectin, assessed by transferring sera from wild-type mice into L-selectin-deficient mice and monitoring serum sL-selectin levels by ELISA, was >20 h, and it remained detectable for longer than 1 wk. Short-term in vivo lymphocyte migration assays demonstrated that near physiologic levels ( approximately 0.9 micro g/ml) of sL-selectin decreased lymphocyte migration to peripheral lymph nodes by >30%, with dose-dependent inhibition occurring with increasing sL-selectin concentrations. These results suggest that sL-selectin influences lymphocyte migration in vivo and that the increased sL-selectin levels present in certain pathologic conditions may adversely affect leukocyte migration.

Adoptive Transfer↗

PubMed2002

Complementary roles for CD19 and Bruton's tyrosine kinase in B lymphocyte signal transduction.

CD19 and Bruton's tyrosine kinase (Btk) may function along common signaling pathways in regulating intrinsic and B cell Ag receptor (BCR)-induced signals. To identify physical and functional interactions between CD19 and Btk, a CD19-negative variant of the A20 B cell line was isolated, and CD19-deficient (CD19(-/-)) and CD19-overexpressing mice with the X-linked immunodeficient (Xid; Btk) mutation were generated. In A20 cells, Btk physically associated with CD19 following BCR engagement. CD19 and Btk interactions were not required for initial Btk phosphorylation, but CD19 expression maintained Btk in an activated state following BCR engagement. In primary B cells, CD19 signaling also required downstream Btk function since CD19-induced intracellular Ca(2+) ([Ca(2+)](i)) responses were modest in Xid B cells. In addition, CD19 overexpression did not normalize the Xid phenotype and most phenotypic and functional hallmarks of CD19 overexpression were not evident in these mice. However, CD19 and Btk also regulate independent signaling pathways since their combined loss had additive inhibitory effects on BCR-induced [Ca(2+)](i) responses and CD19 deficiency induced a severe immunodeficiency in Xid mice. Thus, CD19 expression amplifies or prolongs Btk-mediated signaling, rather than serving as a required agent for Btk activation. Consistent with this, phosphatidylinositol 3-monophosphate kinase and Akt activation were normal in CD19(-/-) B cells following IgM engagement, although their kinetics of activation was altered. Thus, these biochemical and compound gene dosage studies indicate that Btk activation and [Ca(2+)](i) responses following BCR engagement are regulated through multiple pathways, including a CD19/Src family kinase-dependent pathway that promotes the longevity of Btk signaling.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed2002

Complement receptors CD21/35 link innate and protective immunity during Streptococcus pneumoniae infection by regulating IgG3 antibody responses.

The CD21/35 receptor provides an important link between innate and adaptive immunity. Its importance during protective immune responses to encapsulated extracellular bacteria was assessed using a new line of mice completely deficient in CD21/35 expression (CD21/35(-/-)). CD21/35 expression was essential for the rapid trapping of C3dg-antigen complexes by B cells in vivo, especially in splenic marginal zones. Despite normal B cell development in CD21/35(-/-) mice, T cell-independent and -dependent antibody responses to low-dose antigens were significantly decreased, with a striking impairment in IgG3 responses. Accordingly, CD21/35(-/-) mice were more susceptible to acute lethal Streptococcus pneumoniae infection. Thus, CD21/35 expression is critical for early protective antibody responses to lethal pathogens that rapidly multiply and quickly overwhelm the immune system.

Animals↗