Pathogenicity of catalytic antibodies: catalytic activity of Bence Jones proteins from myeloma patients with renal impairment can elicit cytotoxic effects

Diagnostic and Prognostic Value of PACAP in Multiple Myeloma

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide with well-known anti-inflammatory, antioxidant, antitumor, and immunomodulatory effects. PACAP regulates the production of various proinflammatory factors and may influence the complex cytokine network of the bone marrow microenvironment altered by plasma cells, affecting the progression of multiple myeloma (MM) and the development of end-organ damage. The aim of our study was to investigate the changes in PACAP-38 levels in patients with MM to explore its value as a potential biomarker in this disease. We compared the plasma PACAP-38 levels of MM patients with healthy individuals by ELISA method and examined its relationship with various MM-related clinical and laboratory parameters. Lower PACAP-38 levels were measured in MM patients compared with the healthy controls, however, this difference vanished if the patient achieved any response better than partial response. In addition, lower peptide levels were found in elderly patients. Significantly higher PACAP-38 levels were seen in patients with lower stage, lower plasma cell infiltration in bone marrow, lower markers of tumor burden in serum, lower total urinary and Bence-Jones protein levels, and in patients after lenalidomide therapy. Higher PACAP-38 levels in newly diagnosed MM patients predicted longer survival and a higher probability of complete response to treatment. Our findings confirm the hypothesis that PACAP plays an important role in the pathomechanism of MM. Furthermore, our results suggest that PACAP might be used as a valuable, non-invasive, complementary biomarker in diagnosis, and may be utilized for prognosis prediction and response monitoring.

Catalytic Antibodies: Design, Expression, and Their Applications in Medicine

Catalytic antibodies made it feasible to develop new catalysts, which had previously been the subject of research. Scientists have discovered natural antibodies that can hydrolyze substrates such as nucleic acids, proteins, and polysaccharides during decades of research, as well as several ways of producing antibodies with specialized characteristics and catalytic functions. These antibodies are widely used in chemistry, biology, and medicine. Catalytic antibodies can continue to play a role and even fully prevent the emergence of autoimmune disorders, especially in the field of infection and immunity, where the process of its occurrence and development often takes a long time. In this work, the development, design and evolution methodologies, and the expression systems and applications of catalytic antibodies, are discussed. Trial registration: not applicable.

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.

A Monoclonal Antibody to Cryptococcus neoformans Glucuronoxylomannan Manifests Hydrolytic Activity for Both Peptides and Polysaccharides

Studies in the 1980s first showed that some natural antibodies were "catalytic" and able to hydrolyze peptide or phosphodiester bonds in antigens. Many naturally occurring catalytic antibodies have since been isolated from human sera and associated with positive and negative outcomes in autoimmune disease and infection. The function and prevalence of these antibodies, however, remain unclear. A previous study suggested that the 18B7 monoclonal antibody against glucuronoxylomannan (GXM), the major component of the Cryptococcus neoformans polysaccharide capsule, hydrolyzed a peptide antigen mimetic. Using mass spectrometry and Förster resonance energy transfer techniques, we confirm and characterize the hydrolytic activity of 18B7 against peptide mimetics and show that 18B7 is able to hydrolyze an oligosaccharide substrate, providing the first example of a naturally occurring catalytic antibody for polysaccharides. Additionally, we show that the catalytic 18B7 antibody increases release of capsular polysaccharide from fungal cells. A serine protease inhibitor blocked peptide and oligosaccharide hydrolysis by 18B7, and a putative serine protease-like active site was identified in the light chain variable region of the antibody. An algorithm was developed to detect similar sites present in unique antibody structures in the Protein Data Bank. The putative site was found in 14 of 63 (22.2%) catalytic antibody structures and 119 of 1602 (7.4%) antibodies with no annotation of catalytic activity. The ability of many antibodies to cleave antigen, albeit slowly, supports the notion that this activity is an important immunoglobulin function in host defense. The discovery of GXM hydrolytic activity suggests new therapeutic possibilities for polysaccharide-binding antibodies.

Nature and nurture of catalytic antibodies

Immunoglobulins (antibodies) frequently express constitutive functions. Two such functions are nucleophilic catalysis and the reversible binding to B-cell superantigens. Constitutive or "naturally-occurring" antibodies are produced spontaneously from germline genetic information. The antibody structural elements mediating the constitutive functions have originated over millions of years of phylogenic evolution, contrasting with antigen-driven, somatic sequence diversification of the complementarity determining regions (CDR) that underlies the better-known high affinity antigen binding function of antibodies. Often, the framework regions (FRs) play a dominant role in antibody constitutive functions. Catalytic antibody subsets with promiscuous, autoantigen-directed and microbe-directed specificities have been identified. Mucosal antibodies may be specialized to express high-level catalytic activity against microbes transmitted by the mucosal route, exemplified by constitutive production of IgA class antibodies in mucosal secretions that catalyze the cleavage of HIV gp120. Catalytic specificity can be gained by constitutive noncovalent superantigen binding at the FRs and by adaptive development of noncovalent classical antigen or superantigen binding, respectively, at the CDRs and FRs. Growing evidence suggests important functional roles for catalytic antibodies in homeostasis, autoimmune disease and protection against infection. Adaptive antibody responses to microbial superantigens are proscribed underphysiological circumstances. Covalent electrophilic immunogen binding to constitutively expressed nucleophilic sites in B-cell receptors bypasses the restriction on adaptive antibody production, and simultaneous occupancy of the CDR binding site by a stimulatory antigenic epitope can also overcome the downregulatory effect of superantigen binding at the FRs. These concepts may be useful for developing novel vaccines that capitalize and improve on constitutive antibody functions for protection against microbes.

Anti-histone H1 IgGs from blood serum of systemic lupus erythematosus patients are capable of hydrolyzing histone H1 and myelin basic protein

Novel hydrolytic activity of the anti-histone H1 antibodies (Ab) toward histone H1 and myelin basic protein (MBP) was shown. Blood serum of ten patients with clinically diagnosed systemic lupus erythematosus (SLE), and nine healthy donors (control) were screened for the anti-histone H1 antibody- and anti-MBP antibody-mediated specific proteolytic activity. IgGs were isolated by chromatography on Protein G-Sepharose, and four of ten SLE patients appeared to possess IgGs that were capable of cleaving both histone H1 and MBP. Such activity was confirmed to be an intrinsic property of the IgG molecule, since it was preserved at gel filtration at alkaline and acidic pH. At the same time, proteolytic activity was absent in the sera-derived Ab of all healthy donors under control. Anti-histone IgGs were purified by the affinity chromatography on histone H1-Sepharose. Their cross-reactivity toward cationic proteins (histones, lysozyme, and MBP) and their capability of hydrolyzing histone H1 and MBP were detected. However, these IgGs were not cleaving core histones, lysozyme, or albumin. Capability of cleaving histone H1 and MBP was preserved after additional purification of anti-histone H1 IgGs by the HPLC gel filtration. The protease activity of anti-histone H1 IgG Ab was inhibited by serine protease inhibitors.

Antibody-mediated sialidase activity in blood serum of patients with multiple myeloma

Cell surface sialylation is known to be tightly connected with tumorigenicity, invasiveness, metastatic potential, clearance of aged cells, while the sialylation of IgG molecules determines their anti-inflammatory properties. Four sialidases - hydrolytic enzymes responsible for cleavage of sialic residues - were described in different cellular compartments. However, sialidases activity in body fluids, and specifically in blood serum, remains poorly studied. Here, we characterize first known IgG antibodies possessing sialidase-like activity in blood serum of multiple myeloma (MM) patients. Ig fractions were precipitated with ammonium sulfate (50% of saturation) from blood serum of 12 healthy donors and 14 MM patients, and screened for the presence of sialidase activity by using 4-MUNA (2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid) as substrate. High level of sialidase activity was detected in the MM patients, but not in healthy donors. Subsequent antibody purification by protein-G affinity chromatography and HPLC size exclusion chromatography at acidic conditions demonstrated that sialidase activity was attributable to IgG molecules. Sialidase activity was also specific for (Fab)(2) fragment of IgG and blocked by sialidase inhibitor DANA. Sialidase activity of IgG molecule was also confirmed by in gel assay for cleavage of sialidase substrate. Kinetic parameters of the catalysis reaction were described by Michaelis-Menten equation with K(m)  = 44.4-108 µM and k(cat) = 2.7-23.1 min(-1). The action of IgG possessing sialidase-like activity towards human red blood cells resulted in a subsequent increase in their agglutination by the peanut agglutinin, that confirms their desialylation by the studied IgG. This is the first demonstration of the intrinsic sialidase activity of IgG isolated from blood serum of MM patients.

A human germ line antibody light chain with hydrolytic properties associated with multimerization status

Antibodies with nucleophilic or catalytic properties often have these characteristics encoded in their germ line genes. Because hydrolytic activity has been reported to be associated with light chain V regions, we have begun an analysis of germ line light chain proteins that could be the basis for affinity maturation into hydrolytic or other reactive antibodies. We produced the germ line A18b light chain and characterized its hydrolytic, nucleophilic, and tertiary structural activities. This light chain was purified to >99% purity and found to hydrolyze aminomethylcoumarin-peptide and larger protein substrates and bind a fluorophosphonate probe. Mutation of putative catalytic residues only resulted in loss of activity of a tetrameric but not dimeric form of the light chain. These biochemical properties provide a framework for understanding the structure-function relationships of germ line antibodies.