Biomedical subjects

Falk Nimmerjahn

Publications and source records attributed to Falk Nimmerjahn.

17 recordsLinked to original sources

PubMed2007

The antiinflammatory activity of IgG: the intravenous IgG paradox.

How high doses of intravenous IgG (IVIG) suppress autoimmune diseases remains unresolved. We have recently shown that the antiinflammatory activity of IVIG can be attributed to a minor species of IgGs that is modified with terminal sialic acids on their Fc-linked glycans. Here we propose that these Fc-sialylated IgGs engage a unique receptor on macrophages that, in turn, leads to the upregulation of an inhibitory Fcgamma receptor (FcgammaR), thereby protecting against autoantibody-mediated pathology.

Animals↗

PubMed2006

Activating and inhibitory FcgammaRs in autoimmune disorders.

Autoimmune disorders are characterized by the destruction of self-tissues by the immune system. Multiple checkpoints are in place to prevent autoreactivity under normal circumstances. Coexpression of activating and inhibitory Fc receptors (FcR) represents such a checkpoint by establishing a threshold for immune cell activation. In many human autoimmune diseases, however, balanced FcR expression is disturbed. Analysis of murine model systems provides strong evidence that aberrant FcR expression can result in uncontrolled immune responses and the initiation of autoimmune disease. This review will summarize this data and explain how this information might be used to better understand human autoimmune diseases and to develop novel therapeutic strategies.

Animals↗

PubMed2006

Impaired clearance of apoptotic cardiocytes is linked to anti-SSA/Ro and -SSB/La antibodies in the pathogenesis of congenital heart block.

The role of cardiocytes in physiologic removal of apoptotic cells and the subsequent effect of surface binding by anti-SSA/Ro and -SSB/La antibodies was addressed. Initial experiments evaluated induction of apoptosis by extrinsic and intrinsic pathways. Nuclear injury and the translocation of SSA/Ro and SSB/La antigens to the fetal cardiocyte plasma membrane were common downstream events of Fas and TNF receptor ligation, requiring caspase activation. As assessed by phase-contrast and confirmed by confocal microscopy, coculturing of healthy cardiocytes with cardiocytes rendered apoptotic via extrinsic pathways revealed a clearance mechanism that to our knowledge has not previously been described. Cultured fetal cardiocytes expressed phosphatidylserine receptors (PSRs), as did cardiac tissue from a fetus with congenital heart block (CHB) and an age-matched control. Phagocytic uptake was blocked by anti-PSR antibodies and was significantly inhibited following preincubation of apoptotic cardiocytes with chicken and murine anti-SSA/Ro and -SSB/La antibodies, with IgG from an anti-SSA/Ro- and -SSB/La-positive mother of a CHB child, but not with anti-HLA class I antibody. In a murine model, anti-Ro60 bound and inhibited uptake of apoptotic cardiocytes from wild-type but not Ro60-knockout mice. Our results suggest that resident cardiocytes participate in physiologic clearance of apoptotic cardiocytes but that clearance is inhibited by opsonization via maternal autoantibodies, resulting in accumulation of apoptotic cells, promoting inflammation and subsequent scarring.

Animals↗

PubMed2006

Anti-inflammatory activity of immunoglobulin G resulting from Fc sialylation.

Immunoglobulin G (IgG) mediates pro- and anti-inflammatory activities through the engagement of its Fc fragment (Fc) with distinct Fcg receptors (FcgRs). One class of Fc-FcgR interactions generates pro-inflammatory effects of immune complexes and cytotoxic antibodies. In contrast, therapeutic intravenous gamma globulin and its Fc fragments are anti-inflammatory. We show here that these distinct properties of the IgG Fc result from differential sialylation of the Fc core polysaccharide. IgG acquires anti-inflammatory properties upon Fc sialylation, which is reduced upon the induction of an antigen-specific immune response. This differential sialylation may provide a switch from innate anti-inflammatory activity in the steady state to generating adaptive pro-inflammatory effects upon antigenic challenge.

Animals↗

PubMed2006

Pathology and protection in nephrotoxic nephritis is determined by selective engagement of specific Fc receptors.

Introduction of heterologous anti-glomerular basement membrane antiserum (nephrotoxic serum, NTS) into presensitized mice triggers the production of IgG anti-NTS antibodies that are predominantly IgG2b and the glomerular deposition of pathogenic immune complexes, leading to accelerated renal disease. The pathology observed in this model is determined by the effector cell activation threshold that is established by the coexpression on infiltrating macrophages of the IgG2a/2b restricted activation receptor FcgammaRIV and its inhibitory receptor counterpart, FcgammaRIIB. Blocking FcgammaRIV with a specific monoclonal antibody thereby preventing IgG2b engagement or treatment with high dose intravenous gamma-globulin (IVIG) to down-regulate FcgammaRIV while up-regulating FcgammaRIIB, protects mice from fatal disease. In the absence of FcgammaRIIB, IVIG is not protective; this indicates that reduced FcgammaRIV expression alone is insufficient to protect animals from pathogenic IgG2b immune complexes. These results establish the significance of specific IgG subclasses and their cognate FcgammaRs in renal disease.

Animals↗

PubMed2006

Antibody isotype-specific engagement of Fcgamma receptors regulates B lymphocyte depletion during CD20 immunotherapy.

CD20 monoclonal antibody (mAb) immunotherapy is effective for lymphoma and autoimmune disease. In a mouse model of immunotherapy using mouse anti-mouse CD20 mAbs, the innate monocyte network depletes B cells through immunoglobulin (Ig)G Fc receptor (FcgammaR)-dependent pathways with a hierarchy of IgG2a/c>IgG1/IgG2b>IgG3. To understand the molecular basis for these CD20 mAb subclass differences, B cell depletion was assessed in mice deficient or blocked for stimulatory FcgammaRI, FcgammaRIII, FcgammaRIV, or FcR common gamma chain, or inhibitory FcgammaRIIB. IgG1 CD20 mAbs induced B cell depletion through preferential, if not exclusive, interactions with low-affinity FcgammaRIII. IgG2b CD20 mAbs interacted preferentially with intermediate affinity FcgammaRIV. The potency of IgG2a/c CD20 mAbs resulted from FcgammaRIV interactions, with potential contributions from high-affinity FcgammaRI. Regardless, FcgammaRIV could mediate IgG2a/b/c CD20 mAb-induced depletion in the absence of FcgammaRI and FcgammaRIII. In contrast, inhibitory FcgammaRIIB deficiency significantly increased CD20 mAb-induced B cell depletion by enhancing monocyte function. Although FcgammaR-dependent pathways regulated B cell depletion from lymphoid tissues, both FcgammaR-dependent and -independent pathways contributed to mature bone marrow and circulating B cell clearance by CD20 mAbs. Thus, isotype-specific mAb interactions with distinct FcgammaRs contribute significantly to the effectiveness of CD20 mAbs in vivo, which may have important clinical implications for CD20 and other mAb-based therapies.

Animals↗

PubMed2006

Fcgamma receptors: old friends and new family members.

Although cellular receptors for immunoglobulins were first identified nearly 40 years ago, their central role in the immune response was discovered only in the last decade. They are key players in both the afferent and efferent phase of an immune response, setting thresholds for B cell activation, regulating the maturation of dendritic cells, and coupling the exquisite specificity of the antibody response to innate effector pathways, such as phagocytosis, antibody-dependent cellular cytotoxicity, and the recruitment and activation of inflammatory cells. Moreover, because of their general presence as receptor pairs consisting of activating and inhibitory molecules on the same cell, they have become a paradigm for studying the balance of positive and negative signals that ultimately determine the outcome of an immune response. This review will summarize recent results in Fc-receptor biology with an emphasis on data obtained in in vivo model systems.

Amino Acid Sequence↗

PubMed2005

Divergent immunoglobulin g subclass activity through selective Fc receptor binding.

Subclasses of immunoglobulin G (IgG) display substantial differences in their ability to mediate effector responses, contributing to variable activity of antibodies against microbes and tumors. We demonstrate that the mechanism underlying this long-standing observation of subclass dominance in function is provided by the differential affinities of IgG subclasses for specific activating IgG Fc receptors compared with their affinities for the inhibitory IgG Fc receptor. The significant differences in the ratios of activating-to-inhibitory receptor binding predicted the in vivo activity. We suggest that these highly predictable functions assigned by Fc binding will be an important consideration in the design of therapeutic antibodies and vaccines.

Animals↗

PubMed2005

Stringent doxycycline-dependent control of gene activities using an episomal one-vector system.

Conditional expression systems are of pivotal importance for the dissection of complex biological phenomena. Here, we describe a novel EBV-derived episomally replicating plasmid (pRTS-1) that carries all the elements for conditional expression of a gene of interest via Tet regulation. The vector is characterized by (i) low background activity, (ii) high inducibility in the presence of doxycycline (Dox) and (iii) graded response to increasing concentrations of the inducer. The chicken beta actin promoter and an element of the murine immunoglobin heavy chain intron enhancer drive constitutive expression of a bicistronic expression cassette that encodes the highly Dox-sensitive reverse tetracycline controlled transactivator rtTA2(S)-M2 and a Tet repressor-KRAB fusion protein (tTS(KRAB)) (silencer) placed downstream of an internal ribosomal entry site. The gene of interest is expressed from the bidirectional promoter P(tet)bi-1 that allows simultaneous expression of two genes, of which one may be used as surrogate marker for the expression of the gene of interest. Tight down regulation is achieved through binding of the silencer tTS(KRAB) to P(tet)bi-1 in the absence of Dox. Addition of Dox releases repression and via binding of rtTA2(S)-M2 activates P(tet)bi-1.

Animals↗

PubMed2005

Alternative splicing generates putative soluble CD83 proteins that inhibit T cell proliferation.

CD83 is expressed on mature dendritic cells and activated lymphocytes and has been implicated to play an important role during T cell development in the thymus. In contrast, not much is known about the function of CD83 in the periphery. Soluble forms of CD83 have been detected in the serum, but neither the function nor the mechanism of how these soluble forms of CD83 are generated are fully understood. In this study, we report the identification of four different transcripts of CD83 in unstimulated PBMCs. Sequence analysis demonstrated that the longest form codes for transmembrane CD83 (CD83-TM), whereas the smaller transcripts are splice variants of full-length CD83, coding for putative soluble CD83 proteins. Stimulation of PBMCs with PHA, TNF-alpha, or LPS leads to the up-regulation of the full-length CD83 transcript and to a strong down-regulation of two of the three smaller transcripts. The smallest CD83 splice product can be translated efficiently into protein, and recombinant soluble CD83 shows a strong inhibitory effect on T cell proliferation in MLRs. Our results suggest that the constitutive production of soluble forms of CD83 under steady-state conditions may have an important function in regulating immune homeostasis.

Alternative Splicing↗

PubMed2005

FcgammaRIV: a novel FcR with distinct IgG subclass specificity.

Mouse IgG subclasses display a hierarchy of in vivo activities, with IgG2a and IgG2b showing the greatest protective and pathogenic properties. These enhanced activities result, in part, from their ability to bind to a novel, gamma chain-dependent, activating IgG Fc receptor, FcgammaRIV. FcgammaRIV maps in the 75 kb genomic interval between FcgammaRII and FcgammaRIII; its expression is restricted to myeloid lineage cells, and it binds to IgG2a and IgG2b with intermediate affinity. No binding to IgG1 or IgG3 was observed. Blocking FcgammaRIV binding to pathogenic anti-platelet antibodies is sufficient to protect mice from antibody-induced thrombocytopenia. Thus, the FcgammaR system has evolved distinct activation receptors displaying selectivity for IgG subclasses, with IgG1 antibodies exclusively dependent on FcgammaRIII, whereas IgG2a and IgG2b show preferential dependence on FcgammaRIV activation. These distinct binding affinities for the IgG subclasses to FcgammaRs account for their differential protective and pathogenic activities in vivo.

Animals↗

PubMed2004

The inhibitory Fcgamma receptor modulates autoimmunity by limiting the accumulation of immunoglobulin G+ anti-DNA plasma cells.

Deletion of the gene encoding the Fc immunoglobulin G receptor IIB (FcgammaRIIB) results in a fulminant, lupus-like disease in C57BL/6 but not BALB/c mice. Here we have investigated this strain-specific, epistatic loss of tolerance using gene-targeted immunoglobulin variable heavy-chain (V(H)) alleles 3H9 or 56R, which encode DNA-specific heavy chains, expressed on the C57BL/6 or BALB/c background. The combination of C57BL/6 and V(H) 56R (B6.56R) resulted in a loss of tolerance; hybridoma and single-cell analysis indicated an FcgammaRIIB-independent difference in immunoglobulin light-chain usage, consistent with an alteration in receptor editing. FcgammaRIIB deficiency resulted in an increase in immunoglobulin G (IgG) antibodies to DNA in the serum, an increased frequency of anti-DNA-reactive IgG(+) B cells with a plasma cell phenotype and immune complex deposition in the glomeruli and renal disease in B6.56R mice. Thus, FcgammaRIIB provides a distal peripheral checkpoint to limit the accumulation of autoreactive plasma cells, thereby maintaining tolerance.

Animals↗

PubMed2004

Epstein-Barr virus nuclear antigen 1 evades direct immune recognition by CD4+ T helper cells.

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is the only viral protein regularly expressed in EBV-associated malignancies. Immune recognition of EBNA1 by CD8+ T cells is prevented by an internal glycine-alanine repeat (GAr) which blocks proteasomal degradation. To test whether EBV-infected cells could be recognized by T helper cells, human CD4+ T cell clones specific for EBNA1 were isolated from latently EBV-infected individuals. These T cells, however, failed to recognize EBV-positive target cells. To investigate whether endogenous presentation of EBNA1 epitopes on MHC class II was prevented by the GAr domain, a mutant EBV strain with an EBNA1 lacking the GAr (EBNA1DeltaGA) was generated and used to establish an Epstein-Barr virus-immortalized lymphoblastoid B cell line (LCL). The EBNA1DeltaGA LCL were not recognized by the EBNA1-specific T cell clones either, indicating that the GAr domain does not mediate this effect. Immune recognition could be restored by overexpression of EBNA1, for which at least 60-fold higher levels of both EBNA1 or EBNA1DeltaGAr protein were required. These results demonstrate that EBNA1 evades direct recognition by CD4+ T helper cells, since its steady state level is below the threshold required for efficient presentation on MHC class II. These findings have important implications for the design of immunotherapeutic approaches to target EBV-positive malignancies.

Antigen Presentation↗

PubMed2004

Active NF-kappaB signalling is a prerequisite for influenza virus infection.

Influenza virus still poses a major threat to human health. Despite widespread vaccination programmes and the development of drugs targeting essential viral proteins, the extremely high mutation rate of influenza virus still leads to the emergence of new pathogenic virus strains. Therefore, it has been suggested that cellular cofactors that are essential for influenza virus infection might be better targets for antiviral therapy. It has previously been reported that influenza virus efficiently infects Epstein-Barr virus-immortalized B cells, whereas Burkitt's lymphoma cells are virtually resistant to infection. Using this cellular system, it has been shown here that an active NF-kappaB signalling pathway is a general prerequisite for influenza virus infection of human cells. Cells with low NF-kappaB activity were resistant to influenza virus infection, but became susceptible upon activation of NF-kappaB. In addition, blocking of NF-kappaB activation severely impaired influenza virus infection of otherwise highly susceptible cells, including the human lung carcinoma cell lines A549 and U1752 and primary human cells. On the other hand, infection with vaccinia virus was not dependent on an active NF-kappaB signalling pathway, demonstrating the specificity of this pathway for influenza virus infection. These results might be of major importance for both the development of new antiviral therapies and the understanding of influenza virus biology.

B-Lymphocytes↗

PubMed2003

Major histocompatibility complex class II-restricted presentation of a cytosolic antigen by autophagy.

Biochemical and functional studies have demonstrated major histocompatibility complex (MHC) class II-restricted presentation of peptides derived from cytosolic proteins, but the underlying processing and presentation pathways have remained elusive. Here we show that endogenous presentation of an epitope derived from the cytosolic protein neomycin phosphotransferase II (NeoR) on MHC class II is mediated by autophagy. This presentation pathway involves the sequestration of NeoR into autophagosomes, and subsequent delivery into the lytic compartment. These results identify endosomes/lysosomes as the processing compartment for cytosolic antigens and furthermore link endogenous antigen presentation on MHC class II with the process of cellular protein turnover by autophagy.

Antigen Presentation↗

PubMed2003

Efficient generation and expansion of antigen-specific CD4+ T cells by recombinant influenza viruses.

Adoptive transfer of in vitro generated antigen-specific T cells has been successfully used to treat viral infections in immunodeficient patients. Therefore, methods for the rapid in vitro expansion of antigen-specific T cells are needed. Influenza virus efficiently infects dendritic cells, and peptides derived from viral proteins are processed and presented to CD8(+) cytotoxic T cells. However, both, CD4(+) and CD8(+) T cells are necessary for the efficient control of viral infections, and it is becoming increasingly clear that a T helper cell response is very important for the maintenance and strength of the immune response. Here we show that recombinant influenza virus efficiently infects a wide range of professional antigen-presenting cells and does not interfere with antigen presentation pathways. Using T cell clones for three different MHC class II-restricted antigens we demonstrate that peptides derived from these antigens are efficiently presented on MHC class II molecules. Importantly, it was possible to generate and expand antigen-specific CD4(+) T cells following in vitro infection of professional antigen-presenting cells with recombinant influenza virus. These findings support the notion that recombinant influenza virus is a valuable tool for the expansion of antigen-specific CD4(+) T cells in vitro.

Animals↗

PubMed2003

Latent membrane protein 1 of Epstein-Barr virus induces CD83 by the NF-kappaB signaling pathway.

Epstein-Barr virus (EBV) infects human resting B cells and transforms them in vitro into continuously growing lymphoblastoid cell lines (LCLs). EBV nuclear antigen 2 (EBNA2) is one of the first viral proteins expressed after infection. It is able to transactivate viral as well as cellular target genes by interaction with cellular transcription factors. EBNA2 target genes can be studied easily by using an LCL (ER/EB2-5) in which wild-type EBNA2 is replaced by an estrogen-inducible EBNA2. Since the cell surface molecule CD83, a member of the immunoglobulin superfamily and a marker for mature dendritic cells, appeared on the surface of ER/EB2-5 cells within 3 h after the addition of estrogen, we analyzed the regulation of CD83 induction by EBV in more detail. Despite its rapid induction, CD83 turned out to be an indirect target gene of EBNA2. We could show that the viral latent membrane protein 1 (LMP1) is responsible for the induction of CD83 by using an LCL expressing a ligand- or antibody-inducible recombinant nerve growth factor receptor-LMP1 fusion protein. The inducibility of the CD83 promoter by LMP1 was mediated by the activation of NF-kappaB, as seen by use of luciferase reporter assays using the CD83 promoter and LMP1 mutants. Additionally, fusion constructs of the transmembrane domain of LMP1 and the intracellular signaling domain of CD40, TNF-R1, and TNF-R2 likewise transactivated the CD83 promoter via NF-kappaB. Our studies show that CD83 is also a target of the NF-kappaB signaling pathway in B cells.

Antigens, CD↗