Cell-penetrating autoantibody induces caspase-mediated apoptosis through catalytic hydrolysis of DNA

Nanobodies as molecular imaging probes

Camelidae derived single-domain antibodies (sdAbs), commonly known as nanobodies (Nbs), are the smallest antibody fragments with full antigen-binding capacity. Owing to their desirable properties such as small size, high specificity, strong affinity, excellent stability, and modularity, nanobodies are on their way to overtake conventional antibodies in terms of popularity. To date, a broad range of nanobodies have been generated against different molecular targets with applications spanning basic research, diagnostics, and therapeutics. In the field of molecular imaging, nanobody-based probes have emerged as a powerful tool. Radioactive or fluorescently labeled nanobodies are now used to detect and track many targets in different biological systems using imaging techniques. In this review, we provide an overview of the use of nanobodies as molecular probes. Additionally, we discuss current techniques for the generation, conjugation, and intracellular delivery of nanobodies.

Immunoglobulins with Non-Canonical Functions in Inflammatory and Autoimmune Disease States

Immunoglobulins are known to combine various effector mechanisms of the adaptive and the innate immune system. Classical immunoglobulin functions are associated with antigen recognition and the initiation of innate immune responses. However, in addition to classical functions, antibodies exhibit a variety of non-canonical functions related to the destruction of various pathogens due to catalytic activity and cofactor effects, the action of antibodies as agonists/antagonists of various receptors, the control of bacterial diversity of the intestine, etc. Canonical and non-canonical functions reflect the extreme human antibody repertoire and the variety of antibody types generated in the organism: antigen-specific, natural, polyreactive, broadly neutralizing, homophilic, bispecific and catalytic. The therapeutic effects of intravenous immunoglobulins (IVIg) are associated with both the canonical and non-canonical functions of antibodies. In this review, catalytic antibodies will be considered in more detail, since their formation is associated with inflammatory and autoimmune diseases. We will systematically summarize the diversity of catalytic antibodies in normal and pathological conditions. Translational perspectives of knowledge about natural antibodies for IVIg therapy will be also discussed.

Autoantibodies from SLE patients induce programmed cell death in murine fibroblast cells through interaction with TNFR1 receptor

Various pathological processes are known to be associated with the production of IgG autoantibodies, which have high affinity for self-antigens and often cause tissue injury and the development of autoimmune diseases. However, the mechanism of their cytotoxic activity is not clearly understood yet. Here, we have shown that the action of these autoantibodies on cells expressing TNFR1 (the cell surface receptor for TNFα) can cause both caspase-dependent apoptosis and necroptosis of these cells, with suppression of apoptosis resulting in switching to RIP1-dependent necroptosis. Analysis of necroptotic mechanisms has shown that a critical point of necroptosis is phosphorylation of RIP1 and RIP3 kinases, which is followed by the involvement of lysosomes and mitochondria in this process. The induction of cytotoxicity is initiated by the interaction of autoantibodies with TNFR1, and autoantibodies can therefore be regarded as a new functional ligand for this receptor. The innate immunity protein Tag7 (PGLYRP1) described in our recent studies is also a ligand for TNFR1 and competes with autoantibodies for binding with it. Supposedly, the cytotoxic effect of autoantibodies is one of the factors responsible for autoimmune diseases that lead to tissue injury.

Cytosolic Internalization of Anti-DNA Antibodies by Human Monocytes Induces Production of Pro-inflammatory Cytokines Independently of the Tripartite Motif-Containing 21 (TRIM21)-Mediated Pathway

Anti-DNA autoantibodies are a hallmark of systemic lupus erythematosus (SLE). A subset of anti-DNA IgG autoantibodies is cell-internalizable; thus they can enter living cells in the form of free IgG. However, the contribution made by the Fc region of internalized free-form IgG to the cytokine response has not been studied, despite the recent discovery of tripartite motif-containing 21 (TRIM21), a cytosolic Fc receptor involved in immune signaling. This study used an internalizable IgG anti-DNA antibody (3D8) to examine the cytokine responses of human monocytes to the Fc region of cytosolic free IgG. Internalization of 3D8 IgG and a 3D8 single-chain variable fragment-Fc (scFv-Fc) induced production of IL-8 and TNF-α via activation of NF-κB. By contrast, a 3D8 scFv (comprising variable domains alone) did not. This suggests Fc-dependent cytokine signaling. A 3D8 IgG-N434D mutant that is not recognized by TRIM21 induced greater production of cytokines than 3D8 IgG. Moreover the amounts of cytokines induced by 3D8 IgG in TRIM21-knockdown THP-1 cells were higher than those in control cells, indicating that cytokine signaling is not mediated by TRIM21. The results suggest the existence of a novel Fc-dependent signaling pathway that is activated upon internalization of IgG antibodies by human monocytes.

Heparan sulfate proteoglycans (HSPGs) and chondroitin sulfate proteoglycans (CSPGs) function as endocytic receptors for an internalizing anti-nucleic acid antibody

A subset of monoclonal anti-DNA autoantibodies enters a variety of living cells. Here, we aimed to identify the endocytic receptors recognized by an internalizing anti-nucleic acid autoantibody, the 3D8 single-chain variable fragment (scFv). We found that cell surface binding and internalization of 3D8 scFv were inhibited markedly in soluble heparan sulfate (HS)/chondroitin sulfate (CS)-deficient or -removed cells and in the presence of soluble HS and CS. 3D8 scFv colocalized intracellularly with either HS proteoglycans (HSPGs) or CSPGs in HeLa cells. 3D8 scFv was co-endocytosed and co-precipitated with representative individual HSPG and CSPG molecules: syndecan-2 (a transmembrane HSPG), glypican-3 (a glycosylphosphatidylinositol (GPI)-anchored HSPG); CD44 (a transmembrane CSPG); and brevican (a GPI-anchored CSPG). Collected data indicate that 3D8 scFv binds to the negatively charged sugar chains of both HSPGs and CSPGs and is then internalized along with these molecules, irrespective of how these proteoglycans are associated with the cell membrane. This is the first study to show that anti-DNA antibodies enter cells via both HSPGs and CSPGs simultaneously. The data may aid understanding of endocytic receptors that bind anti-DNA autoantibodies. The study also provides insight into potential cell membrane targets for macromolecular delivery.

Antibody-Mediated Catalysis in Infection and Immunity

The existence of catalytic antibodies has been known for decades. Natural antibodies capable of cleaving nucleic acid, protein, and polysaccharide substrates have been described. Although the discovery of catalytic antibodies initially aroused great interest because of their promise for the development of new catalysts, their enzymatic performance has been disappointing due to low reaction rates. However, in the areas of infection and immunity, where processes often occur over much longer times and involve high antibody concentrations, even low catalytic rates have the potential to influence biological outcomes. In this regard, the presence of catalytic antibodies recognizing host antigens has been associated with several autoimmune diseases. Furthermore, naturally occurring catalytic antibodies to microbial determinants have been correlated with resistance to infection. Recently, there has been substantial interest in harnessing the power of antibody-mediated catalysis against microbial antigens for host defense. Additional work is needed, however, to better understand the prevalence, function, and structural basis of catalytic activity in antibodies. Here we review the available information and suggest that antibody-mediated catalysis is a fertile area for study with broad applications in infection and immunity.

Anti-ribosomal-phosphoprotein autoantibodies penetrate to neuronal cells via neuronal growth associated protein, affecting neuronal cells in vitro

OBJECTIVE

Anti-ribosomal-phosphoprotein antibodies (anti-Ribos.P Abs) are detected in 10-45% of NPSLE patients. Intracerebroventricular administration of anti-ribosomal-P Abs induces depression-like behaviour in mice. We aimed to discern the mechanism by which anti-Ribos.P Abs induce behavioural changes in mice.

METHODS

Anti-Ribos.P Abs were exposed to human and rat neuronal cell cultures, as well as to human umbilical vein endothelial cell cultures for a control. The cellular localization of anti-Ribo.P Abs was found by an immunofluorescent technique using a confocal microscope. Identification of the target molecules was undertaken using a cDNA library. Immunohistochemistry and an inhibition assay were carried out to confirm the identity of the target molecules. Neuronal cell proliferation was measured by bromodeoxyuridine, and Akt and Erk expression by immunoblot.

RESULTS

Human anti-Ribos.P Abs penetrated into human neuronal cells and rat hippocampal cell cultures in vitro, but not to endothelial cells as examined. Screening a high-content human cDNA-library with anti-Ribos.P Abs identified neuronal growth-associated protein (GAP43) as a target for anti-Ribos.P Abs. Ex vivo anti-Ribos.P Abs bind to mouse brain sections of hippocampus, dentate and amygdala. Anti-Ribos.P Abs brain-binding was prevented by GAP43 protein. Interestingly, GAP43 inhibited in a dose-dependent manner the anti-Ribos.P Abs binding to recombinant-ribosomal-P0, indicating mimicry between the ribosomal-P0 protein and GAP43. Furthermore, anti-Ribos.P Abs reduced neuronal cell proliferation activity in vitro (P < 0.001), whereas GAP43 decreased this inhibitory activity by a factor of 7.6. The last was related to Akt and Erk dephosphorylation.

CONCLUSION

Anti-Ribos.P Abs penetrate neuronal cells in vitro by targeting GAP43. Anti -Ribos.P Abs inhibit neuronal-cell proliferation via inhibition of Akt and Erk. Our data contribute to deciphering the mechanism for anti-Ribos.P Abs' pathogenic activity in NPSLE.

A nucleolytic lupus autoantibody is toxic to BRCA2-deficient cancer cells

Cancer cells with defects in DNA repair are highly susceptible to DNA-damaging agents, but delivery of therapeutic agents into cell nuclei can be challenging. A subset of lupus autoantibodies is associated with nucleolytic activity, and some of these antibodies are capable of nuclear penetration. We hypothesized that such antibodies might have potential as therapeutic agents targeted towards DNA repair-deficient malignancies. We identified the lupus autoantibody 5C6 as a cell-penetrating nucleolytic antibody and found that 5C6 has a differential effect on a matched pair of BRCA2-proficient and deficient DLD1 colon cancer cells. 5C6 selectively induced γH2AX in, and suppressed the growth of, the BRCA2-deficient cells. These findings demonstrate the potential utility of 5C6 in targeted therapy for DNA repair-deficient malignancies and strengthen the rationale for studies of additional lupus autoantibodies in order to identify the best candidates for development as therapeutic agents. In addition, the toxic effect of 5C6 on BRCA2-deficient cells provides further support for the hypothesis that some lupus autoantibodies contribute to the lower risk of specific cancers associated with systemic lupus erythematosus.

Deoxyribonuclease activity of polyclonal IgGs: a putative serological marker in patients with spondyloarthritides

Antibodies executing catalytic activity are referred to as antibody enzymes or short "abzymes" and may have diagnostic relevance. Abzymes with deoxyribonuclease (DNase) activity have been demonstrated in patients with autoimmune and infectious diseases. Despite several reports on the occurrence of DNase abzymes in systemic autoimmune rheumatic diseases, conclusive data about DNase activity of antibodies in patients with spondyloarthritides (SpAs) are lacking. In recent cross-sectional studies evaluating levels of IgG DNase activity in patients with psoriatic arthritis (PsA), reactive arthritis (ReA), and ankylosing spondylitis (AS), DNase activity of IgG has been assessed by the rivanol clot method and confirmed by agarose gel electrophoresis. Remarkably, levels of IgG DNase activity were significantly higher in sera of SpA patients than those in control subjects. In patients with PsA, ReA, and AS, a positive correlation of DNase IgG activity with synovitis, disease activity, and stage of spondylitis was observed, respectively. Given the involvement of autoimmune reactions in cytolysis and connective tissue degradation in PsA, ReA, and to a lesser extent in AS, abzymes might have an impact on the pathophysiology of SpAs. Detection of IgG DNase activity in patients suffering from SpA represents an exciting new research field and may assist in the differential diagnosis of SpA.

Functional consequences of complementarity-determining region deactivation in a multifunctional anti-nucleic acid antibody

Many murine monoclonal anti-DNA antibodies (Abs) derived from mice models for systemic lupus erythematosus have additional cell-penetration and/or nucleic acid-hydrolysis properties. Here, we examined the influence of deactivating each complementarity-determining region (CDR) within a multifunctional anti-nucleic acid antibody (Ab) that possesses these activities, the catalytic 3D8 single chain variable fragment (scFv). CDR-deactivated 3D8 scFv variants were generated by replacing all of the amino acids within each CDR with Gly/Ser residues. The structure of 3D8 scFv accommodated single complete CDR deactivations. Different functional activities of 3D8 scFv were affected differently depending on which CDR was deactivated. The only exception was CDR1, located within the light chain (LCDR1); deactivation of LCDR1 abolished all of the functional activities of 3D8 scFv. A hybrid Ab, HW6/3D8L1, in which the LCDR1 from an unrelated Ab (HW6) was replaced with the LCDR1 from 3D8, acquired all activities associated with the 3D8 scFv. These results suggest that the activity of a multifunctional 3D8 scFv Ab can be modulated by single complete CDR deactivation and that the LCDR1 plays a crucial role in maintaining Ab properties. This study presents a new approach for determining the role of individual CDRs in multifunctional Abs with important implications for the future of Ab engineering.

An anti-nucleic acid antibody delivers antigen to the cross-presentation pathway in dendritic cells and potentiates therapeutic antitumor effects

Cross-presentation is important for initiating CTL responses against tumors. Delivery of exogenous Ags to the cross-presentation pathway in dendritic cells (DCs), using a number of different carriers, has been attempted to further understand the mechanisms underlying cross-presentation and to develop therapeutic tumor vaccines. The present study reports a new antigenic carrier molecule: a single-chain V region fragment (scFv) of a nucleic acid-hydrolyzing Ab, 3D8. A fusion protein comprising 3D8 scFv and the CTL epitope OVA(250-264) (chicken OVA aa 250-264) was internalized by DC2.4 DCs and processed via a proteasome-dependent, brefeldin- and cycloheximide-sensitive, chloroquine- and primaquine-insensitive pathway, resulting in loading of the CTL epitope onto H-2K(b). In vivo cross-presentation and cross-priming were efficient, even without adjuvant; injection of mice with 3D8 scFv-OVA(250-264) induced cross-presentation of the CTL epitope by draining lymph node CD11c(+) B7.1(+) MHC class II(high) DCs, elicited a CTL response, and suppressed the growth of tumors expressing the OVA epitope. This report shows that an anti-nucleic acid Ab is used to deliver exogenous Ag to the cross-presentation pathway and inhibit in vivo tumor growth.

Autoantibodies with enzymatic properties in human autoimmune diseases

Immunoglobulins (Ig) or antibodies are heavy plasma proteins, with sugar chains added to amino acid residues by N-linked glycosylation and occasionally by O-linked glycosylation. The versatility of antibodies is demonstrated by the various functions that they mediate such as neutralization, agglutination, fixation with activation of complement and activation of effector cells. In addition to this plethora of functions, some antibodies express enzymatic activity. Antibodies endowed with enzymatic properties have been described in human autoimmune manifestations in a variety of disorders such as autoimmune thyroiditis, systemic erythematosus (SLE), scleroderma, rheumatoid arthritis (RA), multiple sclerosis (MS) and acquired hemophilia (AH). Antibodies isolated from these conditions were able to specifically hydrolyze thyroglobulin, DNA, RNA, myelin basic protein (MBP), and factor VIII (FVIII) or factor IX (FIX), respectively. The therapeutic relevance of these findings is discussed.

Immune maintenance of self in morphostasis of distinct tissues, tumour growth and regenerative medicine

Morphostasis (tissue homeostasis) is a complex process consisting of three circumstances: (1) tissue renewal from stem cells, (2) preservation of tissue cells in a proper differentiated state and (3) maintenance of tissue quantity. This can be executed by a tissue control system (TCS) consisting of vascular pericytes, immune system-related components--monocyte-derived cells (MDC), T cells and immunoglobulins and autonomic innervation. Morphostasis is established epigenetically, during the critical developmental period corresponding to the morphogenetic immune adaptation. Subsequently, the tissues are maintained in a state of differentiation reached during the adaptation by a 'stop effect' of MDC influencing markers of differentiating tissue cells and presenting self-antigens to T cells. Retardation or acceleration of certain tissue differentiation during adaptation results in its persistent functional immaturity or premature ageing. The tissues being absent during adaptation, like ovarian corpus luteum, are handled as a 'graft.' Morphostasis is altered with age advancement, because of the degenerative changes of the immune system. That is why the ageing of individuals and increased incidence of neoplasia and degenerative diseases occur. Hybridization of tumour stem cells with normal tissue cells causes an augmentation of neoplasia by host pericytes and MDC stimulating a 'regeneration' of depleted functional cells. Degenerative diseases are associated with apoptosis. If we are able to change morphostasis in particular tissue, we may disrupt apoptotic process of the cell. An ability to manage the 'stop effect' of MDC may provide treatment for early post-natal tissue disorders, improve regenerative medicine and delay physical, mental and hormonal ageing.

Antibody-dependent cell-mediated cytotoxicity- and complement-dependent cytotoxicity-independent bactericidal activity of an IgG against Pseudomonas aeruginosa O6ad

In addition to Ag recognition, some Abs are capable of killing target organisms in the absence of phagocytes and complement. In this study, we report that an anti-Pseudomonas aeruginosa O6ad LPS IgG(1), tobacco-expressed human S20 IgG(1) (te-hS20), as well as its recombinant Fab and single-chain variable fragment (scFv) fragments have cellular- and complement-independent bactericidal activity. te-hS20 and its Fab and scFv significantly reduced viability of P. aeruginosa O6ad in dose- and time-dependent manners in vitro and also showed lower levels of bactericidal activity against P. aeruginosa PAO1, but had no activity against P. aeruginosa O10, Escherichia coli TG1, and Streptococcus agalactiae. The H chain and its Fd fragment both had significant Ag-binding and bactericidal activities against P. aeruginosa O6ad. Bactericidal activity was completely inhibited with specific LPS Ag, suggesting that Ag binding is involved in the bactericidal mechanism. Live/dead cell staining and electron microscopic observations indicate that the bactericidal effect was due to disruption of the cell wall and suggest inhibition of cell division. In addition to te-hS20, the Fab and scFv were also protective in vivo, as leukopenic mice had prolonged and improved survival after administration of these Ab fragments followed by challenge with P. aeruginosa O6ad cells at 80-90% lethal dose, supporting a bactericidal mechanism independent of phagocytes and complement. Understanding of the bactericidal mechanism will allow assessment of the potential for therapeutic application of these Abs.

Catalytic antibodies: balancing between Dr. Jekyll and Mr. Hyde

The immunoglobulin molecule is a perfect template for the de novo generation of biocatalytic functions. Catalytic antibodies, or abzymes, obtained by the structural mimicking of enzyme active sites have been shown to catalyze numerous chemical reactions. Natural enzyme analogs for some of these reactions have not yet been found or possibly do not exist at all. Nowadays, the dramatic breakthrough in antibody engineering and expression technologies has promoted a considerable expansion of immunoglobulin's medical applications and is offering abzymes a unique chance to become a promising source of high-precision "catalytic vaccines." At the same time, the discovery of natural abzymes on the background of autoimmune disease revealed their beneficial and pathogenic roles in the disease progression. Thus, the conflicting Dr. Jekyll and Mr. Hyde protective and destructive essences of catalytic antibodies should be carefully considered in the development of therapeutic abzyme applications.