Rat IgG subclasses: differences in affinity to protein A-sepharose

High-throughput rat immunoglobulin G N-glycosylation profiling revealed subclass-specific changes associated with chronic stress

Immunoglobulin G (IgG) glycosylation corresponds well with immune system changes, so it can potentially be used as a biomarker for the consequences of chronic stress such as low-grade inflammation and enhanced immunosenescence in older animals. Here we present a high-throughput glycoproteomic workflow, including IgG enrichment, HILIC glycopeptide purification, and nano-LC-MS analysis of tryptic glycopeptides applied for the analysis of rat IgG. A cohort of 80 animals was exposed to seven stressors in a customized chronic stress protocol with blood and tissue sampling in three timepoints. Young female rats experienced an increase in agalactosylated glycoforms on IgG2a and IgG2c accompanied by a decrease in monogalactosylation. Among old females, increased galactosylation was observed in the IgG2b subclass, pointing to an anti-inflammatory activity of IgG. Additionally, IgG Fc N-glycosylation patterns in Sprague Dawley rats were analyzed, quantified, and reported for the first time. Our findings emphasize age-, sex- and subclass-dependent differences in IgG glycosylation related to chronic stress exposure, confirming the relevance of newly developed methods for further research in glycobiology of rodent immune response. SIGNIFICANCE: In this study, we showed that a high-throughput streamlined methodology based on protein L 96-well monolithic plates for efficient rat IgG immunoaffinity enrichment from blood plasma, paired with appropriate tryptic glycopeptide preparation, HILIC-SPE enrichment, and nano-LC-MS methods was suitable for quick processing of large sample sets. We report a subclass-specific profiling and changes in rat IgG Fc galactosylation and adrenal gland immunohistochemistry of male and female animals exposed to a customized chronic stress protocol.

Protein A superantigen: structure, engineering and molecular basis of antibody recognition

Staphylococcus aureus interacts with the human immune system through the production of secreted factors. Key among these is protein A, a B-cell superantigen capable of interacting with both antibody Fc and VH regions. Here, we review structural and molecular features of this important example of naturally occurring bacterial superantigens, as well as engineered variants and their application in biotechnology.

Optimization of Enzymatic Antibody Fragmentation for Yield, Efficiency, and Binding Affinity

Enzymatic antibody fragmentation has been well studied for various hosts and isotypes, but fragmentation patterns also vary unpredictably by clone, and optimizing Fab or F(ab')₂ production by trial and error consumes large quantities of antibodies. Here, we report a systematic strategy for optimizing functional F(ab')₂ production via pepsin digestion from small quantities of IgG. We tested three key parameters that affect fragmentation, pH, enzyme concentration (% pepsin w/w), and reaction time, and found that pH had the greatest impact on fragmentation yield and efficiency. We then developed a systematic approach to obtaining acceptable yields, digestion efficiency, and binding affinity. Three case studies are described to illustrate the approach. We anticipate that this work will provide a quick and cost-effective method for researchers to produce antibody fragments from whole IgG, avoiding haphazard trial and error.

Optimization of photoactive protein Z for fast and efficient site-specific conjugation of native IgG

Antibody conjugates have been used in a variety of applications from immunoassays to drug conjugates. However, it is becoming increasingly clear that in order to maximize an antibody's antigen binding ability and to produce homogeneous antibody-conjugates, the conjugated molecule should be attached onto IgG site-specifically. We previously developed a facile method for the site-specific modification of full length, native IgGs by engineering a recombinant Protein Z that forms a covalent link to the Fc domain of IgG upon exposure to long wavelength UV light. To further improve the efficiency of Protein Z production and IgG conjugation, we constructed a panel of 13 different Protein Z variants with the UV-active amino acid benzoylphenylalanine (BPA) in different locations. By using this panel of Protein Z to cross-link a range of IgGs from different hosts, including human, mouse, and rat, we discovered two previously unknown Protein Z variants, L17BPA and K35BPA, that are capable of cross-linking many commonly used IgG isotypes with efficiencies ranging from 60% to 95% after only 1 h of UV exposure. When compared to existing site-specific methods, which often require cloning or enzymatic reactions, the Protein Z-based method described here, utilizing the L17BPA, K35BPA, and the previously described Q32BPA variants, represents a vastly more accessible and efficient approach that is compatible with nearly all native IgGs, thus making site-specific conjugation more accessible to the general research community.

Stochastic sensing of proteins with receptor-modified solid-state nanopores

Solid-state nanopores are capable of the label-free analysis of single molecules. It is possible to add biochemical selectivity by anchoring a molecular receptor inside the nanopore, but it is difficult to maintain single-molecule sensitivity in these modified nanopores. Here, we show that metallized silicon nitride nanopores chemically modified with nitrilotriacetic acid receptors can be used for the stochastic sensing of proteins. The reversible binding and unbinding of the proteins to the receptors is observed in real time, and the interaction parameters are statistically analysed from single-molecule binding events. To demonstrate the versatile nature of this approach, we detect His-tagged proteins and discriminate between the subclasses of rodent IgG antibodies.

Selective suppression of IgG2a subclass in LEC rats during development

The LEC rat is a mutant strain that has been established as a model of hepatitis and hepatoma. In addition to hepatic disorders, it has been found that this strain has a defect in T cell maturation, and has low levels of serum IgG. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis showed that low levels of serum IgG were largely due to reduction of the IgG2a subclass. Quantitative determination of IgG subclasses by enzyme-linked immunosorbent assay (ELISA) using subclass-specific antibodies indicated that IgG2b and IgG2c subclasses were increased during development in this strain, whereas the IgG2a subclass was markedly decreased. These results suggest that dysfunction of some helper T cells in LEC rats selectively suppress synthesis of the IgG2a subclass during development but not affect production of IgG2b and IgG2c.

Cathepsin L proteinase secreted by Fasciola hepatica in vitro prevents antibody-mediated eosinophil attachment to newly excysted juveniles

Cathepsin L-like activity was demonstrated in the excretory/secretory (E/S) products of Fasciola hepatica newly excysted juveniles (NEJ), 3-week-old, 5-week-old and mature flukes using the fluorogenic substituted 7-amino-4-methylcoumarin substrates Z-phe-arg-AMC, Z-arg-arg-AMC and Z-arg-AMC. Gelatin-substrate polyacrylamide gel analysis revealed that the E/S from each of these stages contained multiple proteolytic enzymes; however, the pattern of proteinases obtained for NEJ E/S differed markedly from that of all other stages examined. The four NEJ proteinases identified were inhibited by leupeptin and Z-phe-ala-diazomethyl ketone indicating that each had cathepsin L-like activity. The E/S products of all four developmental stages contain an enzyme capable of cleaving immunoglobulin at the hinge region, the activity of which is also inhibited by Z-phe-ala-diazomethyl ketone. Using in vitro cell attachment assays we show that the cathepsin L-like proteinase purified from the E/S products of adult F. hepatica can prevent the antibody-mediated attachment of eosinophil to NEJ. These experiments indicate that this proteinase has an important biological function in immune evasion.

Interaction of aglycosyl immunoglobulins with the IgG Fc transport receptor from neonatal rat gut: comparison of deglycosylation by tunicamycin treatment and genetic engineering

The role of carbohydrate in the structure and function of immuno-globulin Fc regions has been studied using the interaction of a monoclonal mouse IgG2b anti-NIP antibody with the IgG Fc transport receptor from neonatal rat gut. An aglycosyl variant of this immunoglobulin, in which site-directed mutagenesis had been used to eliminate the carbohydrate attachment site in the CH2 domain by changing Asn297 to Ala, was compared in this system to aglycosyl immunoglobulin prepared from immunoglobulin-secreting cells treated with tunicamycin to inhibit N-linked glycosylation. Loss of carbohydrate from the heavy chain was confirmed for both methods by Western blotting of the separated chains with Concanavalin A, and no significant differences in circular dichroism spectra were found between glycosylated and non-glycosylated mutants. Removal of carbohydrate by site-directed mutagenesis had no effect on binding of the immunoglobulin to the Fc transport receptor (FcTR) in vitro or transport from the gut to blood in vivo. Short-term clearance from circulation and degradation by gut contents in vitro were similarly unaffected. Mutation of Glu235 to Leu, an alteration that allows binding to human monocyte Fc gamma RI, did not alter the interaction with FcTR. However, treatment of wild-type or aglycosyl mutant cells with tunicamycin resulted in immunoglobulin which was less stable, cleared more rapidly and was transported slightly less efficiently. These findings indicate that the binding site for the FcTR may be unique among Fc-binding ligands, and that tunicamycin treatment may cause alterations in the immunoglobulin molecule in addition to loss of N-linked carbohydrate.

Immune response to Acanthocheilonema viteae infection in multimammate rats (Mastomys natalensis)

The multimammate rat Mastomys natalensis, when infected with the filarial parasite Acanthocheilonema viteae, develops amicrofilaraemia. Worm recovery and the duration and intensity of microfilaraemia were analysed and related to the humoral and cellular immune responses of the host by using an antibody-dependent cell-mediated cytotoxicity (ADCC) assay towards microfilariae (Mf). Mf were detected in the peripheral blood at 7 weeks post-infection (p.i.), reaching maximum levels by 20 weeks p.i., and then gradually decreasing to undetectable levels during the next 36 weeks. The cytotoxic antibodies appeared around 15-18 weeks p.i., and the serum at 36 weeks p.i. induced 70% cytotoxicity to the Mf in vitro in the presence of host cells. The IgM fraction of the immune serum from amicrofilaraemic Mastomys promoted ADCC to Mf both in vitro and in vivo. Macrophages were more potent in inducing cytotoxic effect than eosinophils and neutrophils. Platelets were ineffective in killing the Mf in the presence of immune serum. IgM antibody cleared the circulating Mf from the blood when given passively to infected Mastomys. The average recovery of adult worms was about 20% of the inoculated larvae. No live females could be recovered 56 weeks p.i. Thus protective immune responses built up over an extended period of time are elicited against the Mf and perhaps even to adults in Mastomys infected with A. viteae.

A rat monoclonal antibody which interacts with mammalian ornithine decarboxylase at an epitope involved in phosphorylation

Ornithine decarboxylase was purified from androgen-treated mouse kidney to homogeneity and high specific activity. The purified enzyme was utilized for production and screening of rat monoclonal and polyclonal antibodies. A rat monoclonal antibody was isolated which was capable of immunoprecipitation of native mouse kidney ornithine decarboxylase activity or the [3H]difluoromethylornithine-inactivated enzyme. Phosphorylation of mouse ornithine decarboxylase by casein kinase-II prior to immunoprecipitation led to complete loss of the epitope recognized by the monoclonal antibody but did not alter recognition by polyclonal antibody. Mammalian ornithine decarboxylase activity obtained from several species, in crude or partially purified extracts, was subjected to quantitative immunoprecipitation with monoclonal and polyclonal antibody. Polyclonal antibody immunoprecipitated all of the ornithine decarboxylase activity from every extract tested, while monoclonal antibody was capable of only limited immunoprecipitation (60-80%). Due to the inability of the monoclonal antibody to recognize ornithine decarboxylase phosphorylated in vitro by casein kinase-II and the partial immunoprecipitation of ornithine decarboxylase activity from cell extracts, a portion of the ornithine decarboxylase molecule population must exist in a phosphorylated state. This immunological evidence further confirms existing data that the enzyme exists in at least two distinct forms.

A surface glycoprotein of Trypanosoma lewisi binds immunoglobulin G from the serum of uninfected rats

Detergent extracts of whole Trypanosoma lewisi were fractionated by polyacrylamide gel electrophoresis and transferred to nitrocellulose for immunoblotting analysis. Antibody probes to rat immunoglobulin G (IgG) and IgM detected intact gamma chains, mu chains, and light chains in extracts. The amount of immunoglobulin detected increased as the infection progressed. Transfers were also incubated in serum from conventionally reared (CRS), specific-pathogen-free (SPFS), or germ-free rats before being probed with anti-rat IgG or anti-rat IgM. Components of 200, 175, and 120 kilodaltons (kDa) bound IgM from all sera tested and were present in extracts of trypanosomes isolated from lethally irradiated or intact rats on different days during infection. No parasite components bound IgG from serum of germ-free rats. However, 145-, 175-, and 200-kDa components bound IgG from CRS and SPFS. A 74-kDa protein was the major IgG-binding component in extracts of reproducing parasites. This component bound much more IgG from CRS than it bound from SPFS. The 74-kDa protein was removed from parasites by mild trypsinization and corresponded to a major surface glycoprotein detected when intact cells were radioiodinated. These results indicate that natural antibodies to T. lewisi exist in rats or that these parasites have surface proteins that bind immunoglobulins without regard to antigenic specificity.

Suppression of terminal axonal sprouting at the neuromuscular junction by monoclonal antibodies against a muscle-derived antigen of 56,000 daltons

After the partial denervation or paralysis of a muscle, the remaining motor axon terminals may sprout fine, neuritic processes (terminal sprouts) which escape the endplate region of the neuromuscular junction. We previously identified a muscle-derived, protein antigen of 56,000 daltons (56 kD) which plays a necessary role in terminal sprouting. A panel of monoclonal antibodies have been produced against the 56-kD antigen, some of which also partially suppress motor axon terminal sprouting. These monoclonal antibodies define at least two different epitopes upon the surface of the antigen, one of which is necessary for it to effect its biological role in vivo.

Modulation of IgG effector functions by a monovalent fragment of staphylococcal protein A

The monovalent V-1 fragment of protein A (fSpA) with a mol. wt of 13,000 obtained from an u.v. mutant of Staphylococcus aureus Cowan I strain was proved to be able to modulate significantly some of the effector functions of IgG, such as complement fixation, catabolism, attachment to Fc receptors and antibody-dependent cell-mediated cytotoxicity. Moreover fSpA-like protein A obtained from the A676 strain is mitogenic and enhances NK activity of human peripheral lymphocytes. The efficiency of fSpA was found to be lower than that of protein A with regard to its ability to inhibit complement fixation, EA rosette formation and antibody-dependent cell-mediated cytotoxicity. Both protein A and fSpA had the same efficiency in activation of the complement system after reaction with human or guinea pig IgG, and in increasing the IgG catabolism. Unlike fSpA the monovalent B fragment of protein A (with mol. wt of 7000) was not able to inhibit EA rosette formation and antibody-dependent cell-mediated cytotoxicity. The results recommend fSpA, substituting for protein A, as a molecular probe for the investigation of IgG antibody and lymphocyte effector functions.

Isolation of porcine, canine and feline IgG by affinity chromatography using protein A

Isolation of porcine, canine and feline IgG has hitherto been achieved usually by DEAE-ion exchange chromatography and gel filtration. These procedures, however, are rather time-consuming, as they involve purification of IgG. Isolation of IgG by affinity chromatography on a column of protein A-Sepharose was attempted. IgG of all three animal species was very easily isolated with a high yield. In the absence of any other method that allows isolation of IgG of three animal species from a single column, the procedure proposed would be very useful.

Mouse IgG1 heterogeneity: variable binding of monoclonal IgG1 antibodies to protein A-sepharose

Binding strength to protein A discriminates three definitive types of mouse monoclonal IgG1. Each of these types of IgG1 elutes from protein A-Sepharose as a coherent peak representing the great majority of IgG1 protein. One type of IgG1 is not present to any significant extent in polyclonal mouse IgG preparations, and to our knowledge has not been reported previously. This type of IgG1 does not bind firmly to protein A at pH 8.0, but is retarded sufficiently that it can be purified by protein A-Sepharose chromatography in high yields.

Heterogeneity of human polyclonal IgE reacting with staphylococcal protein A

A small part of polyclonal IgE (6%) was bound to protein A-Sepharose from the serum of M.P., containing a high concentration of IgE. No monoclonal IgE isolated from the serum of V.L. was bound to this sorbent. This binding of polyclonal IgE appears to be heterogeneous since a multiphasic pattern was observed with discontinuous pH gradient elution from protein A-Sepharose. Also, like IgE from the whole serum, monomeric IgE isolated from the serum of M.P. on Sepharose 6B showed this binding heterogeneity. It is suggested that IgE molecules with different affinities for protein A could belong to different isotypic or allotypic variants.

Proteolysis of rat IgG subclasses by Staphylococcus aureus V8 proteinase

Monoclonal IgG belonging to the four rat IgG subclasses (IgG1, IgG2a, IgG2b, IgG2c) and some IgG subclasses from normal rat serum were subjected to enzymatic degradation with Staphylococcus aureus V8 proteinase. The results show that only one subclass, IgG2b, is significantly cleaved by the enzyme, with the release of two main products identified as F(ab)2 and Fc-like fragments. This unique susceptibility of the IgG2b subclass represents therefore an easy means of identification and also offers a simple procedure for a preparation of F(ab)2 fragments from monoclonal IgG2b antibodies.

Subclass restriction of the antiidiotypic antibody response in the rat

Antiidiotypic antibodies were induced in LOU/M rats by immunization with two myeloma proteins of LOU origin: IR-162 (IgE) and IR-418 (IgG2a). Antibodies to IR-162 were easily obtained after a limited number of immunizations with protein in soluble form; polymerization with glutaraldehyde did not enhance immunogenicity. Antibodies to IR-418 appeared only after a large number of immunizations with protein in polymerized form or with protein copolymerized with rabbit IgG. All of the antibodies, either to IR-162 or to IR-418, were found to be idiotype-specific. In every case for which significant levels of antiidiotypic antibodies were produced, most or all of the antibodies belonged to rat IgG1 subclass. Since, in mice, antiidiotypic antibodies are restricted to the IgG1 subclass, our results indicate a functional analogy between rat and mouse IgG1. Our studies also suggest that the rat IgG1 subclass may be predominantly expressed in T-cell-dependent antibody responses, such as production of antiidiotypic antibodies.

Binding of immunoglobulins to protein A and immunoglobulin levels in mammalian sera

The use of protein A from S. aureus (SpA) as an anti-IgG reagent in immunological techniques has extended in recent years, together with knowledge about its interaction with immunoglobulins of different species. Current data with respect to the binding of protein A to immunoglobulins and to the levels of immunoglobulins in the sera of some mammalian species are reviewed.

Use of protein A to remove immunoglobulins from serum in hybridoma culture media

The levels of protein A-reactive immunoglobulin (PA-Ig) in foetal bovine serum were measured in commercial batches. For tissue culture media incorporating 10% foetal bovine serum, the levels of bovine PA-Ig were of a similar order to those of mouse monoclonal antibodies produced by hybridomas grown in such media. The equilibrium constants were calculated for the binding to protein A-Sepharose of a number of mouse monoclonal antibodies, and of PA-Ig in foetal bovine serum and normal mouse serum. The average affinity of the mouse PA-Ig was 10 times higher than that of the bovine PA-Ig, suggesting that the two could be separated by affinity chromatography on protein A-Sepharose. The mouse monoclonal antibodies, however, displayed a range of affinity 1.5-100 times that of the bovine PA-Ig, indicating that such separation could not be generally applied. The optimal technique involved removing PA-Ig from bovine serum before its inclusion in the culture medium and then purifying the monoclonal antibody on a second protein A-Sepharose column.

Mouse IgG antibodies have subclass associated affinity differences

Subclasses of IgG were separated from pools of mouse sera by letting immunoglobulins absorb on protein A-Sepharose and by eluting with buffers of decreasing pH. Most donor mice were immunized with a conjugate of a hapten (NIP) and chicken gamma globulin 20 days previously. The results indicate that concentrations of IgG varied from 5.1 to 8.6 mg/ml in the pools of immune sera and was 3.0 mg/ml in one normal serum tested. One half of this was IgG1, ca. 20% of IgG2a and IgG2b each, and 10% IgG3 in the pools of BALB/c sera. IgG2a and IgG3 could not be separated from C57BL sera (due to allotype b), but their combined share of IgG appears to be higher than in BALB/c. Immune sera contained 0.5-1.6 mg/ml of anti-NIP antibodies. Of this 90-98% was IgG1 and the remainder was split between the other subclasses. Up to one half of the protein in the IgG1 fraction was anti-NIP antibody. This surprising finding was confirmed by demonstrating that nearly 50% of the u.v.-light absorption was specifically removed by a NIP-immunosorbent. Subclass-associated affinity-differences were observed. IgG1 anti-NIP had a greater average affinity than IgG2a anti-NIP antibodies. The difference was ca. 1.5-fold when the equilibrium dialysis was focusing on the high-affinity bracket of the total population (concentration of free hapten 16-200 nM). At higher hapten concentrations the trend was the same but the data are fewer. Antibodies in subclasses IgG2b and IgG3 appear to share the lower affinity of IgG2a.

Separation of guinea pig IgG subclasses by affinity chromatography on protein A-sepharose

Guinea pig serum was chromatographed on a column of protein A-Sepharose equilibrated in citrate-phosphate buffer at pH 7.3. The bulk of serum proteins eluted in the starting buffer. Two peaks of protein A-bound serum proteins were eluted by a decreasing pH gradient, a smaller peak centered at pH 4.7 and a larger peak centered at pH 4.3. IgG contained in the peak eluted at pH 4.7 had fast gamma immunoelectrophoretic mobility and IgG in the peak eluted at pH 4.3 had slow gamma mobility. Antiserum to guinea pig IgG, when absorbed with the pH 4.7 peak, reacted only with the pH 4.3 peak. Antiserum to guinea pig IgG1, when absorbed with the pH 4.3 peak, reacted only with the pH 4.7 peak. The IgG in the pH 4.7 peak had the immunoelectrophoretic and antigenic characteristics of IgG1 and the IgG in the pH 4.3 peak had the characteristics of IgG2. The two subclasses were efficiently separated by pH-dependent affinity chromatography on protein A-Sepharose. The IgG1 in the pH 4.7 peak was contaminated with 10.8% IgG2, and the IgG2 in the pH 4.3 peak was contaminated with 2.7% IgG1.

Comparative study of the conformational features of rat immunoglobulin G subclasses by circular dichroism

Four subclasses of rat immunoglobulin G and some of their fragments were studied by circular dichroism. These studies were carried out in different conditions in order to determine whether conformational differences exist between each subclass. The results showed that in their native state the subclasses cannot be distinguished by characteristic differences. Moreover, differences between monoclonal immunoglobulins G of the same subclass were found, particularly in the 200-250 nm region, and their relationship to aromatic side chain contributions (especially those of tyrosine) has been investigated. However, the conformations of the immunoglobulin G were found to be differently affected by denaturing treatments and a relation to subclass has been demonstrated.