Novel protein transfection of primary rat cortical neurons using an antibody that penetrates living cells.

An Ab-based system to deliver functional proteins into neurons was developed using the murine mAb, mAb 3E10. This was achieved by covalently conjugating catalase to the Ab so that the conjugate retained high activity for the degradation of hydrogen peroxide. Three-dimensional fluorescence microscopy was used to demonstrate penetration of the Ab into the nucleus of living primary cortical neurons. The Ab conjugate localized in both the cytoplasm and nucleus. Retention of catalase activity after penetration and distribution of conjugate was demonstrated by reduction in cell death following exposure of treated neurons to hydrogen peroxide. These studies illustrate the potential of this method for the intracellular delivery of therapeutic proteins.

Idiotypic vaccination with a murine anti-dsDNA antibody: phase I study in patients with nonactive systemic lupus erythematosus with nephritis.

OBJECTIVE: To determine the safety and immunogenicity of an idiotypic anti-dsDNA vaccine in patients with nonactive systemic lupus erythematosus (SLE) and stable lupus nephritis. METHODS: Patients with SLE with a history of nephritis were randomized for vaccination with the murine anti-dsDNA monoclonal antibody (Mab) 3E10 in a dose ranging, double blind, placebo controlled study (phase I). RESULTS: Of the 9 patients injected with Mab 3E10, 5 showed a human anti-mouse antibody (HAMA) response, in large part antiidiotypic, which developed within the first 3 months in 3 strong HAMA responders, and more than one year after immunization in an initially weak HAMA responder. All but one nonresponder were receiving low dose prednisone. No adverse events, in particular no evidence of lupus flares, and no untoward laboratory findings were reported over a followup of 2 years. CONCLUSION: In patients with stable lupus nephritis, immunization with Mab 3E10 appears safe and can generate a significant antiidiotypic response. Idiotypic vaccination may be an approach to specific immunotherapy of autoimmune lupus nephritis.

An autoantibody is modified for use as a delivery system to target the cell nucleus: therapeutic implications.

A murine monoclonal anti-dsDNA antibody was found to penetrate living cells and localize in the nucleus without pathologic effects. A single mutation in VH markedly enhanced cellular penetration. The mutant antibody was produced as recombinant Fab and single chain antibody fragments to investigate its use as a delivery system to target the cell nucleus. Complexes were made containing Fab fragments and alkaline phosphatase conjugated goat antibodies to mouse |gk chains. Fab fragments transported 305 kDa goat antibody-enzyme complexes into the nucleus in COS-7 and CHO cells. A single chain antibody cDNA was constructed by splice overlap extension PCR and expressed in COS-7 cells. Binding of the single chain antibody to dsDNA was shown by ELISA, and cellular penetration and nuclear localization were demonstrated in COS-7 and CHO cells. The single chain antibody cDNA was ligated into the expression vector, pEGFP, to produce a fusion protein with green fluorescent protein. The fusion protein penetrated COS-7 cells and localized in the cell nucleus. The single chain antibody produced during sustained expression in CHO cells re-entered antibody-producing cells and localized in the nucleus without affecting cell viability. Our results demonstrate the potential use of a modified autoantibody as a delivery system to target the cell nucleus.

Mechanisms of cellular penetration and nuclear localization of an anti-double strand DNA autoantibody.

An anti-dsDNA Ab, mAb 3E10, was identified that bound membranes of fixed human renal tubular cells, penetrated live murine renal tubular cells in vivo, and localized in the cell nucleus. mAb 3E10 binds both dsDNA and an extracellular matrix protein, HP8/HEVIN, expressed in high endothelial venules. Previous studies showed both shared and distinct binding determinants of mAb 3E10 VH for DNA and HP8/HEVIN. To independently assess the requirement of DNA and HP8/HEVIN in cellular penetration, site-directed mutants of mAb 3E10 VH and V kappa were studied for penetrating kidney cell lines. The results showed that residues required for binding DNA, but not HP8/HEVIN, were necessary for Ab penetration, indicating that cellular penetration required the presence of DNA or binding of Ab to a membrane determinant precisely resembling DNA. Ab Fab penetrated cells, indicating that neither the Fc nor multivalent Ab binding is necessary for cellular penetration. Ab synthesized in the cytoplasm as a result of deleting heavy and light chain signal peptides was not translocated to the nucleus, indicating a mechanism distinct from the usual protein nuclear localization signals and suggesting the need for a membrane-mediated pathway or for post-translational modification of the Ab.

Two kappa immunoglobulin light chains are secreted by an anti-DNA hybridoma: implications for isotypic exclusion.

An anti-DNA hybridoma derived from an MRL/lpr mouse secretes two different kappa light chains in combination with a single heavy chain. Multiple single cell clones express and secrete immunoglobulin containing both kappa light chains. The N-terminal protein sequences of the light chains correspond to sequences predicted from functionally rearranged mRNAs subjected to reverse transcription and amplified by polymerase chain reaction (PCR). Karyotype analysis of the hybridoma indicates a clonal line derived from the fusion of two cells. By amino acid sequence comparison and PCR analysis, both functional kappa light chains are derived from the MRL/lpr spleen. The two functional light chain cDNAs were cloned and co-transfected into COS-7 cells with the heavy chain cDNA. Only one of the light chains in combination with mAb 3E10 heavy chain confers anti-DNA reactivity. The presence of two separate kappa light chains and, therefore, two separate antigen receptors on a single B cell may have ramifications for both polyclonal activation and toleration of lupus B cells.

Localization of an Fc-binding reactivity to the constant region of human IgG4. Implications for the pathogenesis of rheumatoid arthritis.

The majority of plasma cells in rheumatoid arthritis (RA) synovium produce rheumatoid factors (RF). IgG RF predominate in the immune complexes found in RA synovial fluid and have been implicated in the pathogenesis of RA. IgG4 RF are a major component of IgG RF produced in serum and synovium of RA patients, even though this subclass comprises only 4% of the serum IgG. We produced an IgG4 mAb, hRF-1, with RF reactivity from the synovial tissue of a patient with RA. mAb hRF-1 had binding specificity for mammalian IgG similar to Staphylococcus aureus protein A, which is characteristic of RF from patients with RA. To determine the molecular basis of this particular RF reactivity, the heavy and light chain genes of mAb hRF-1 were amplified by PCR, cloned, and ligated into the pSG5 plasmid for expression in COS-7 cells. Chain recombination experiments localized the Fc-binding reactivity to the hRF-1 heavy chain. Using a series of chimeric Ab sequences, the Fc-binding reactivity was mapped to the constant region of IgG4 rather than the variable region involved in classic RF reactivity. Multiple domains, including Hinge, CH2, and CH3 of the IgG4 constant region were required for Fc binding. Our studies demonstrate an example of RF-like Fc-binding reactivity that is conferred by the gamma-4 constant region rather than the classic Ag binding site and suggest that increased production of IgG4 may contribute to the pathogenesis of RA.

DNA mimics a self-protein that may be a target for some anti-DNA antibodies in systemic lupus erythematosus.

Recent studies suggest that some anti-DNA Abs in systemic lupus erythematosus may actually be Abs to specific proteins and that binding to dsDNA is a nonspecific cross-reactive event. To identify such proteins that bind to anti-DNA Abs, a cDNA expression library from human placenta was screened with mAb 3E10, a pathogenic anti-dsDNA Ab. MAb 3E10 was shown to bind to a 44-amino-acid fragment of HP8, a newly identified protein with amino acid sequence homology to the family of SPARC extracellular matrix proteins. To determine if Ab binding to both dsDNA and HP8 protein occurs through a common binding site, and therefore represents molecular mimicry, the Ab binding domains for protein and DNA were mapped. Chain recombinations between mAb 3E10 and a non-anti-DNA mAb showed that both the heavy and the light chains of mAb 3E10 were essential for anti-dsDNA and anti-HP8 reactivity. Mutagenesis experiments demonstrated that dsDNA and HP8 shared several critical binding residues located in all three complementarity-determining regions of mAb 3E10 VH. Moreover, Abs to HP8 were demonstrated in the sera of a subset of lupus patients. These results indicate that DNA mimics the HP8 protein in binding a lupus Ab, and that this protein may be a target for a subpopulation of anti-dsDNA Abs in systemic lupus erythematosus.

Novel structural features of autoantibodies in murine lupus: a possible superantigen binding site?

The stimulus for the production of anti-DNA autoantibodies in lupus remains unknown. Since double-stranded DNA (dsDNA) is a weak immunogen, other stimuli such as B cell superantigens or anti-idiotypic antibodies may provide an alternative mechanism for their production. The presence of regulatory determinants on autoantibodies might be revealed through their structural characterization, but they have eluded detection, perhaps because they may be three-dimensional and require closer analysis. In this report we cloned and sequenced the heavy chain variable region (VH) of a monoclonal anti-dsDNA antibody, mAb 3E10, derived from MRL/lpr mice with lupus nephritis previously shown to express an idiotype associated with nephritis in murine and human lupus. We now show that mAb 3E10 VH contains novel structural features unrelated to DNA binding which are shared only by a subset of autoantibodies expressed in murine lupus. These lupus autoantibodies can be distinguished from antibodies of non-autoimmune strains by the presence of a specific sequence at the junction of the diversity and joining genes combined with the use of variable region genes with conserved sequences in framework 1 (FR1) and FR3. The location of the novel sequences indicates the possibility of a three-dimensional solvent-exposed determinant located distant from the classical antigen binding site that could regulate their production, possibly through binding B cell superantigens or other infectious agents.

An antibody that binds a neutrophil membrane protein, ERp72, primes human neutrophils for enhanced oxidative metabolism in response to formyl-methionyl-leucyl-phenylalanine. Implications for ERp72 in the signal transduction pathway for neutrophil priming.

Human neutrophils are primed by cytokines for enhanced oxidative metabolism in response to chemotactic factors, but the signal transduction pathways for cytokine activation and priming are unknown. Neutrophil priming may play an important role in mechanisms of host defense and inflammatory responses associated with autoimmune diseases. A rabbit antibody was produced that reacted with human neutrophils and induced priming in response to the chemoattractant, FMLP. The protein responsible for neutrophil priming in response to binding antibody was identified in a neutrophil cDNA library by expression cloning. The cloned protein absorbed the neutrophil-priming activity from rabbit serum. Furthermore, antibody priming activity was recovered by elution from the cloned protein. The gene for the protein associated with neutrophil priming was sequenced and identified as the endoplasmic reticulum protein, ERp72, which contains three copies of the active site sequences of protein disulfide isomerase. The antibody that primed neutrophils was shown to bind ERp72 in neutrophil membranes by immunoprecipitation of the same 72-kDa protein from neutrophils as a known antibody to ERp72. These studies implicate ERp72 in the signal transduction pathway for priming human neutrophils.

The rheumatoid factor reactivity of a human IgG monoclonal autoantibody is encoded by a variant V kappa II L chain gene.

To determine the genetic and molecular basis for rheumatoid factor (RF) autoantibody reactivity in patients with destructive, erosive arthritis, we established a human lymphoblastoid cell line (hRF-1) from a patient with polyarthritis that produced an IgG RF mAb, mAb hRF-1. Studies of isolated H and L chains showed that the specificity of RF reactivity is conferred by mAb hRF-1 L chains. The L chain gene was cloned from a cDNA library prepared from hRF-1 cells. The nucleotide sequence was similar to known V kappa II L chains except for a two nucleotide change corresponding to a change of two amino acids in an invariable region of FR3. A germ-line gene with one of the nucleotide changes was identified by polymerase chain reaction in multiple cell lines, including K562 that does not rearrange Ig genes, but the other nucleotide change appeared to be due to mutation. Either or both of these amino acid changes may contribute to the RF reactivity, because an antibody with the same V kappa II L chain except for these two amino acid changes in FR3 did not have RF reactivity. The RF reactivity of isolated L chains from mAb hRF-1 was confirmed by transfecting COS cells with an expression vector encoding the hRF-1 kappa-chain and showing that the secreted k-chains had RF reactivity. Expression of this variant V kappa II L chain gene may form the basis for RF autoantibody reactivity in some patients.

Apheresis enhances the selective removal of antinuclear antibodies in systemic lupus erythematosus.

Apheresis suppresses clinical manifestations of lupus and reduces levels of antinuclear antibodies implicated in the pathogenesis of systemic lupus erythematosus (SLE). It is not known, however, if reduced levels of antinuclear antibodies are due to nonspecific removal, or specific mechanisms associated with decreased production, or enhanced clearance from the circulation. In order to distinguish between specific and nonspecific effects of apheresis on antinuclear antibodies in SLE, we compared plasma levels of IgG antibodies to DNA and IgG antibodies to microbial antigens in 13 SLE patients before and after apheresis. Although apheresis lowered plasma levels of IgG (21% mean reduction), there was a disproportionate reduction in IgG antibodies to DNA (42% mean reduction, p less than 0.13). In marked contrast, reduction in antibodies to microbial antigens did not exceed those of plasma IgG. A rapid rebound of serum anti-DNA antibodies following apheresis in certain SLE patients suggests that the selective reduction in anti-DNA antibodies is due to enhanced clearance from the circulation rather than decreased production. These results indicate that apheresis enhances selective removal of antinuclear antibodies in some patients with SLE.

Rheumatoid factors specific for active rheumatoid arthritis.

To measure rheumatoid factors specific for patients with rheumatoid arthritis an enzyme linked immunosorbent assay (ELISA) was developed to measure rheumatoid factors in human serum that bind a cross-reactive determinant shared on human and other mammalian IgG. Rheumatoid factors that cross link human IgG and sheep IgG in a double binding ELISA were almost completely specific (greater than 99%) for rheumatoid arthritis in assays of 108 sera from patients with rheumatoid arthritis compared with 231 sera from patients with other connective tissue diseases and 365 sera from healthy subjects and patients without these diseases. Moreover, positive tests occurred primarily in patients with active arthritis (r = 0.68). In contrast, these rheumatoid factor autoantibodies were not detected in sera from most of the patients with other autoimmune diseases, including patients with systemic lupus erythematosus. These results show that rheumatoid factors identified in human sera by the double binding test are specific for active rheumatoid arthritis.

A conserved anti-DNA antibody idiotype associated with nephritis in murine and human systemic lupus erythematosus.

In order to identify unique structural features of pathogenic autoantibodies to DNA in SLE, a murine anti-anti-DNA (anti-Id) mAb (mAb 1C7) was produced in response to immunization of lupus mice with a syngeneic anti-DNA mAb (mAb 3E10). Immunization of lupus mice with mAb 3E10 inhibited production of native anti-DNA antibodies, suppressed development of lupus kidney disease (nephritis), and induced production of anti-anti-DNA (anti-Id) antibodies. mAb 1C7 bound F(ab')2 fragments of mAb 3E10, and it bound other murine anti-DNA mAb, but not murine mAb or polyclonal serum antibodies unreactive with DNA. Moreover, binding of mAb 1C7 anti-Id to mAb 3E10 was inhibited by DNA, suggesting anti-Id binding within or near the binding site for DNA. Furthermore, mAb 1C7 bound serum IgG immunoglobulins from 9/12 patients with lupus nephritis and serum anti-DNA antibodies compared to only 3/12 SLE patients with comparable serum levels of anti-DNA antibodies, but without nephritis (p = 0.04), and only 1/53 SLE patients without serum anti-DNA antibodies, 0/49 patients with rheumatoid arthritis, and 1/47 healthy subjects (p less than 0.001). These results provide evidence that mAb 1C7 identifies a conserved Id associated with anti-DNA antibodies in murine and human SLE and may be useful as a structural probe to characterize pathogenic anti-DNA antibodies in SLE.

Human granulocyte colony-stimulating factor: biologic activities and receptor characterization on hematopoietic cells and small cell lung cancer cell lines.

Human granulocyte colony-stimulating factor (G-CSF) is a regulatory glycoprotein that stimulates the production of neutrophilic granulocytes from committed hematopoietic progenitor cells both in vitro and in vivo. In this report, we show that biosynthetic (recombinant) human G-CSF enhances colony formation by normal human bone marrow and the human myeloid leukemic cell lines, HL-60 and KG-1, as well as nonhematopoietic small cell lung cancer lines, H128 and H69. G-CSF also modulates multiple differentiated functions of human neutrophils, including enhanced oxidative metabolism in response to f-Met-Leu-Phe (f-MLP), increased antibody-dependent cell-mediated cytotoxicity (ADCC), and augmented arachidonic acid release in response to ionophore and chemotactic agents. These effects are all maximal at a concentration of 100 to 500 pmol/L. Using 125I-labeled recombinant human G-CSF, high affinity binding sites were identified on human neutrophils, the myeloid leukemia cell lines KG-1 and HL-60, and the small cell carcinoma cell lines, H128 and H69. G-CSF receptor numbers ranged between 138 and 285 sites per cell with a kd of 77 to 140 pmol/L, consistent with the concentrations of G-CSF that elicit biologic responses in vitro. Decreased specific binding of 125l-G-CSF by human neutrophils was consistently observed in the presence of excess unlabeled human granulocyte-macrophage colony-stimulating factor (GM-CSF), suggesting competition or down modulation by GM-CSF of the G-CSF receptor.

Responses of neutrophils to myeloid growth factors.

Colony-stimulating factors (CSFs) have important effects on mature myeloid cells in addition to their regulatory role in haemopoiesis. Exposure of neutrophils to granulocyte macrophage-CSF (GM-CSF) increases chemotaxis, phagocytosis and cytotoxicity and primes the cells for enhanced oxidative metabolism in response to stimuli, such as formylated oligopeptides derived from bacteria (f-Met-Leu-Phe) and endogenous activated complement components (C5a). GM-CSF induces time-dependent changes in neutrophil f-Met-Leu-Phe receptor number and affinity that correspond to changes in functional activity. The neutrophil IgA Fc receptor is also modulated by GM-CSF such that it develops a high affinity state and transduces a phagocytic signal. The ability to regulate the number and activity of mature myeloid effector cells in vivo establishes unique therapeutic opportunities in the area of infectious disease, cancer treatment, bone marrow transplantation and augmentation of host defence in immunodeficient patients.

Physiology of granulocyte and macrophage colony-stimulating factors in host defense.

The colony-stimulating factors (CSF) are a family of glycoprotein hormones that regulate the proliferation and maturation of hematopoietic progenitor cells. In addition to their effects on hematopoiesis, CSFs modulate the function of fully mature cells and, therefore, play an important role in regulating inflammatory responses vital to host defense. Here we review recent information that describes the biological activity of the CSFs on mature cell function, including chemotaxis, adherence, motility, phagocytosis, oxidative metabolism, and cytotoxicity.

Colony-stimulating factors and host defense.

Colony-stimulating factors are growth factors responsible for the proliferation and the maturation of bone marrow stem cells to fully differentiated granulocytes and monocytes. In addition to their effects on hematopoiesis, some colony-stimulating factors prime mature cells for enhanced chemotaxis, phagocytosis, and killing in response to physiologic stimuli. The action of colony-stimulating factors is mediated by growth factor receptors on precursor and mature effector cells. The results of studies of granulocyte-macrophage colony-stimulating factors in patients with the acquired immunodeficiency syndrome (AIDS) suggest a possible therapeutic role for colony-stimulating factors in augmenting mechanism of host defense.

GM-CSF induces human neutrophil IgA-mediated phagocytosis by an IgA Fc receptor activation mechanism.

Immunoglobulin A is the primary immunoglobulin isotype in tears, saliva, breast milk and other mucosal secretions, constituting between 6% and 15% of the total serum immunoglobulins. Human peripheral blood neutrophils have IgA receptors, but these cells do not normally participate in IgA-mediated phagocytosis. The haematopoietic factors granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) prime neutrophils to be more responsive to a variety of stimuli. We therefore studied their effect on IgA-mediated phagocytosis. GM-CSF and G-CSF both induce a change from low to high-affinity neutrophil IgA Fc crystallizable fragment receptors within 30 min; a change which is associated with the development of IgA-mediated phagocytosis. Human IL-3, which does not affect neutrophil function, is inactive in this system. These results define a new mechanism for CSF-augmented host defence whereby neutrophil function can be modulated by CSF-mediated IgA Fc receptor activation.

Human monoclonal IgG rheumatoid factor has structural homology with bacterial Fc receptor proteins.

A cloned lymphoblast cell line, hRF-1, that secreted human monoclonal IgG4 rheumatoid factor autoantibody was produced by Epstein-Barr virus transformation of lymphocytes from rheumatoid arthritis synovium. The binding of hRF-1 rheumatoid factor to IgG globulins of different mammalian species was similar to the binding specificity of Staphylococcus aureus protein A (SpA) and to antibodies found in the sera from patients with rheumatoid arthritis. hRF-1 also had the same binding pattern to human IgG subclasses as SpA. Direct competition was observed between SpA and hRF-1 in binding IgG Fc. These results provide evidence for structural homology between a bacterial Fc receptor protein (SpA) and the monoclonal IgG rheumatoid factor.