Induced Polyspecificity of Human Secretory Immunoglobulin A Antibodies: Is It Possible to Improve Their Ability to Bind Pathogens?

INTRODUCTION

As has been shown previously, various protein-modifying agents can change the antigen-binding properties of immunoglobulins. However, induced polyspecificity of human secretory immunoglobulin A (sIgA) has not been previously characterized in detail.

METHODS

In the present study, human secretory immunoglobulin A (IgA) was exposed to buffers with acidic pH, to free heme, or to pro-oxidative ferrous ions, and the antigen-binding behavior of the native and modified IgA to viral and bacterial antigens was compared using Western blotting and enzyme-linked immunosorbent assay. The ability of these agents to modulate the antigen-binding properties of human sIgA toward a wide range of pathogen peptides was investigated using an epitope microarray.

RESULTS

We have shown that acidic pH, heme, and pro-oxidative ferrous ions influenced the binding of secretory IgA in opposite directions (either increasing or decreasing); however, the strongest effect was observed when using buffers with low pH. This fraction had the highest number of affected reactivities; most of them were increased and most of the new ones were toward common pathogens.

CONCLUSIONS

Thus, it was shown that all investigated treatments can alter to some degree the antigen-binding of secretory IgA, but acidic pH has the most potentially beneficial effect by increasing binding to a largest number of common pathogens' antigens.

Suppression of dsDNA-specific B lymphocytes reduces disease symptoms in SCID model of mouse lupus

Self-specific B cells play a main role in the pathogenesis of lupus. This autoimmune disease is characterized by the generation of autoantibodies against self antigens, and the elimination of B and T cells involved in the pathological immune response is a logical approach for effective therapy. We have previously constructed a chimeric molecule by coupling a DNA-mimotope peptides to an anti-CD32 antibody. Using this protein molecule for the treatment of lupus-prone MRL/lpr mice, we suppressed selectively the autoreactive B-lymphocytes by cross-linking B cell receptors with the inhibitory FcγRIIb receptors. This approach was limited by the development of anti-chimeric antibodies in MRL mice. In order to avoid this problem, we established a murine severe combined immunodeficiency lupus model, allowing a long-term chimera therapy. Elimination of the double-stranded DNA-specific B cells by chimera therapy in MRL-transferred immunodeficient mice resulted in inhibition of T cell proliferation and prevented the appearance of IgG anti-DNA antibodies and of proteinuria.

Targeted silencing of DNA-specific B cells combined with partial plasma cell depletion displays additive effects on delaying disease onset in lupus-prone mice

Targeting autoreactive B lymphocytes at any stage of their differentiation could yield viable therapeutic strategies for treating autoimmunity. All currently used drugs, including the most recently introduced biological agents, lack target specificity. Selective silencing of double-stranded DNA-specific B cells in animals with spontaneous lupus has been achieved previously by the administration of a chimeric antibody molecule that cross-links their DNA-reactive B cell immunoglobulin receptors with inhibitory FcγIIb (CD32) receptors. However, long-lived plasmacytes are resistant to this chimeric antibody as well as to all conventional treatments. Bortezomib (a proteasome inhibitor) depletes most plasma cells and has been shown recently to suppress disease activity in lupus mice. We hypothesized that the co-administration of non-toxic doses of bortezomib, that partially purge long-lived plasma cells, together with an agent that selectively silences DNA-specific B cells, should have additive effects in an autoantibody-mediated disease. Indeed, our data show that the simultaneous treatment of lupus-prone MRL/lpr mice with suboptimal doses of bortezomib plus the chimeric antibody resulted in the prevention or the delayed appearance of the disease manifestations as well as in a prolonged survival. The effect of the combination therapy was significantly stronger than that of the respective monotherapies and was comparable to that observed after cyclophosphamide administration.

Generation of gene-engineered chimeric DNA molecules for specific therapy of autoimmune diseases

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the development of self-reactive B and T cells and autoantibody production. In particular, double-stranded DNA-specific B cells play an important role in lupus progression, and their selective elimination is a reasonable approach for effective therapy of SLE. DNA-based vaccines aim at the induction of immune response against the vector-encoded antigen. Here, we are exploring, as a new DNA-based therapy of SLE, a chimeric DNA molecule encoding a DNA-mimotope peptide, and the Fv but not the immunogenic Fc fragment of an FcγRIIb-specific monoclonal antibody. This DNA construct was inserted in the expression vector pNut and used as a naked DNA vaccine in a mouse model of lupus. The chimeric DNA molecule can be expressed in eukaryotic cells and cross-links cell surface receptors on DNA-specific B cells, delivering an inhibitory intracellular signal. Intramuscular administration of the recombinant DNA molecule to lupus-prone MRL/lpr mice prevented increase in IgG anti-DNA antibodies and was associated with a low degree of proteinuria, modulation of cytokine profile, and suppression of lupus nephritis.

Peptide-based approaches to treat lupus and other autoimmune diseases

After a long period where the potential of therapeutic peptides was let into oblivion and even dismissed, there is a revival of interest in peptides as potential drug candidates. Novel strategies for limiting metabolism and improve their bioavailability, and alternative routes of administration have emerged. This resulted in a large number of peptide-based drugs that are now being marketed in different indications. Regarding autoimmunity, successful data have been reported in numerous mouse models of autoimmune inflammation, yet relatively few clinical trials based on synthetic peptides are currently underway. This review reports on peptides that show much promises in appropriate mouse models of autoimmunity and describes in more detail clinical trials based on peptides for treating autoimmune patients. A particular emphasis is given to the 21-mer peptide P140/Lupuzor that has completed successfully phase I, phase IIa and phase IIb clinical trials for systemic lupus erythematosus.

B Cell in Autoimmune Diseases

The role of B cells in autoimmune diseases involves different cellular functions, including the well-established secretion of autoantibodies, autoantigen presentation and ensuing reciprocal interactions with T cells, secretion of inflammatory cytokines, and the generation of ectopic germinal centers. Through these mechanisms B cells are involved both in autoimmune diseases that are traditionally viewed as antibody mediated and also in autoimmune diseases that are commonly classified as T cell mediated. This new understanding of the role of B cells opened up novel therapeutic options for the treatment of autoimmune diseases. This paper includes an overview of the different functions of B cells in autoimmunity; the involvement of B cells in systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes; and current B-cell-based therapeutic treatments. We conclude with a discussion of novel therapies aimed at the selective targeting of pathogenic B cells.

Selective recognition and elimination of nicotinic acetylcholine receptor-reactive B cells by a recombinant fusion protein AChR-Fc in myasthenia gravis in vitro

AChR-reactive B cells play a key role in the pathogenesis of myasthenia gravis (MG) by producing autoantibodies. Selective elimination of AChR-reactive B cells will be a promising way to treat MG. Thus, we generated a fusion protein (referred to as AChR-Fc) composed of the human extracellular domain of AChR α1 subunit and the Fc domain of the human IgG1 heavy chain, which could bind both to AChR-reactive BCR and FcγRIIB on the surface of AChR-reactive B cells. Our results showed that AChR-Fc inhibited the proliferation of AChR-specific hybridoma cells, promoted their apoptosis, and mediated cytotoxicity by cross-linking effector cells and complement. Likewise, AChR-Fc significantly reduced the number of AChR-reactive B cells from spleen of Lewis rats immunized with AChR ex vivo.