Evaluation of production and characterization of monoclonal antibodies to human IgG of four subclasses

Production and properties of monoclonal antibodies against human IgG isotypes

Several monoclonal antibodies (MAbs) against human IgG isotypes were obtained by the fusion of myeloma cells with splenocytes from mice immunized with IgG fractions extracted from human plasma. Four MAbs (F7H7, D4F8, B12A8, and E7E10) were selected by an ELISA technique on the basis of their ability to detect one of the four IgG subclasses. Their specificity was checked using a panel of pure myeloma proteins representative of the main allotypes present on IgG isotypes. In addition, two other MAbs (F3E12 and E6D6) were found able to detect specifically kappa or lambda light chains. The immunochemical properties of these MAbs were analyzed mainly in respect to their capacity to detect and to purify the different human IgG isotypes. The following data were obtained: (1) The ability of the MAbs F7H7, D4F8, B12A8, and E7E10 to measure the concentration of each IgG subclass in serum was estimated by an immunocapture ELISA. Results obtained with the new antibodies were compared with several other MAbs recommended by the IUIS/WHO human Immunoglobulins subcommittee. Similar or better results were obtained with the new anti-IgG1, anti-IgG3, and anti-IgG4, MAbs. (2) The same MAbs were tested for their ability to purify a single IgG subclass from IgG preparations and from normal and pathological sera. Fractions containing about 80% of purified IgG1, IgG3, and IgG4 were obtained after one-step immunoaffinity purification. Consequently, these MAbs proved to be useful to detect, to measure and to purify IgG subclasses.

Production and characterization of murine monoclonal antibodies specific for baboon IgG heavy and light chain epitopes

We have generated a panel of murine monoclonal antibodies (MAbs) that recognize baboon IgG epitopes. The reactivity of the MAbs with IgG from other primate species was also examined. Specificity for IgG heavy (H) or light (L) chain epitopes was determined by Western blot analysis. The H chain-specific MAbs were analyzed for IgG subclass specificity and the L chain-specific MAbs for reactivity with baboon IgM and polymeric sIgA. Finally, an ELISA was developed to demonstrate the utility of the MAbs in analysis of humoral immune responses in baboons.

Relationship between antigens and IgG subclasses in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized in part by the presence of tissue-bound and circulating antibodies (mostly of IgG) to the basement membrane zone (BMZ). We previously reported that IgG subclasses of BP antibodies were IgG1, IgG2 and IgG4, and that only BP IgG1 fixed complements. In this study, we examined whether BP IgG sub-classes bound to the same epitope of BP antigen or a different epitope. In an inhibition immunofluorescence studies, the complement fixing capability of IgG1 was inhibited by the pretreatment with IgG4 and partially inhibited by IgG2. On immunoblot analysis, IgG1 and IgG4 were bound to the same MW of BP antigen. In enzyme-linked immunosorbent assay (ELISA), the binding capability of IgG subclass fractions from patients with BP to synthetic peptide P1-2, exceeding normal IgG subclass fractions was seen in five IgG1, one IgG2 and two IgG4, from eight BP patients. The binding capability of IgG subclass fractions from the patients with BP to P1-1, exceeding the normal IgG fractions was seen in two IgG1, three IgG2 and one IgG4 from ten BP patients. On inhibition ELISA, the binding activity to P1-2 of IgG4 was partially inhibited by the pretreatment of IgG1 and IgG2. These findings suggest that BP IgG1, IgG2 and IgG4 could bind to the same epitope though considerable variation occurred between patients.

Anti-human IgE monoclonal antibodies recognizing epitopes related to the binding sites of high and low affinity IgE receptors

Anti-human IgE monoclonal antibodies (mAbs) were produced and eight clones recognizing epitopes on native IgE were selected. Epitopes were mapped by a competitive inhibition enzyme-linked immunosorbent assay, Western blotting and a multi-pin peptide technology. Four sites (one each in the C epsilon 1, C epsilon 2, C epsilon 2/C epsilon 3 junction and C epsilon 3) were recognized by the mAbs. The relationship between the four epitopes and the binding sites of high and low affinity IgE receptors (Fc epsilon RI and Fc epsilon RII, respectively) was studied using a monovalent Fab fragment of each mAb as a binding inhibitor. The IgE-Fc epsilon RII binding was clearly inhibited by the mAb recognizing the C epsilon 2/C epsilon 3 junction, suggesting that Fc epsilon RII binds to a rather limited area around the C epsilon 2/C epsilon 3 junction. The IgE-Fc epsilon RI binding, on the other hand, was scarcely inhibited by any single mAb. However, the binding was inhibited when the epitope in C epsilon 2 was blocked simultaneously with that at the C epsilon 2/C epsilon 3 junction or with that in C epsilon 3, indicating that these three distinct epitopes are related to the Fc epsilon RI binding sites. When these three epitopes were shown in the stereograph of human IgE, the Fc epsilon RI binding area was spread largely on the groove side between C epsilon 2 and C epsilon 3 domains. These results suggest that Fc epsilon RI acquires the high affinity through multiple bindings.

Monoclonal antibodies against heavy and light chains of domestic mink IgG

A panel of 26 monoclonal antibodies (MAbs) specific to mink IgG was produced and analyzed by ELISA, immunodiffusion assay (IDA) and immunoblotting assay. All the raised MAbs were directed against the isotypic IgG epitopes. Immunoblotting assay demonstrated that 11 MAbs reacted only with the Fc-fragments of IgG and 7 only with the light chains. Four antibodies bound to the Fab-containing fragments and failed to react with the Fc-fragments or isolated L-chains. Three MAbs did not react with IgG in IDA. Based on the results of IDA and cross-blocking assays, the MAbs were divided into 10 groups, with the MAbs of each group recognizing the same epitope. In IDA some MAbs were able to react with the epitopes which are common to the IgGs of some other representatives of Mustelidae family and also to some mammalian species remote from mink (dog, horse, pig, fox and rabbit).

Evaluation of monoclonal antibodies having specificity for human IgG subclasses: results of the 2nd IUIS/WHO collaborative study

Following the 1st IUIS/WHO Collaborative Study of monoclonal anti-IgG subclass antibodies, a panel of WHO Specificity Reference Reagents (SRR) was established [Jefferis, R., et al. (1985) Immunol. Lett., 10, 223]. At the time, the hope was expressed that further reagents particularly for IgG2, and other allotypic specificities would become available which could be applied in a wide range of assay protocols. The 2nd study reports the evaluation of nineteen anti-subclass and seven anti-allotype monoclonal antibodies. The anti-IgG1 antibody HP6187 was equivalent in performance to the SRR. Others, that were not of the mouse IgG1 isotype, may be useful for particular applications. The anti-IgG2 antibody HP6200 could be a valuable addition to the WHO SRR; it is specific for an epitope in the Fab region but does not have the light chain bias of HP6014. Antibodies of putative allotype specificity exhibited the claimed specificity when used within protocols similar to those employed by the originating laboratory. It appears to be inherent in the nature of the epitopes (allotopes) recognized that it will take several years before reagents applicable to a wide range of techniques will become available.

Hinge region of human IgG2 protein: Conformational studies with monoclonal antibodies

We previously produced three anti-human IgG2 mAbs with high specificity and found that they recognize distinct epitopes in the hinge region and neighboring residues in human IgG2: HG2-6A was reactive with the hinge region (Glu216-Pro230); HG2-56F with the Pro234 residue and HG2-30F with the Val235 residue. In this study, we evaluated the reactivities of those three mAbs with human IgG2 protein under various conditions. The results obtained using HG2-6A mAb indicated that the hinge region was concealed in the native form, but exposed after heat treatment at 63 degrees C, or chemical treatment with 3 M KSCN, 3 M guanidine, 30% CH3CN, 8 M urea or acid at pH 2.0 as well as by adsorption onto polystyrene beads. The IgG2 hinge region was also exposed after binding to specific antigens. The Pro234 residue recognized by HG2-56F mAb was exposed under all conditions studied. The neighboring Val235 residue recognized by HG2-30F, however, was completely concealed in the native and antigen-bound states. Only treatment with 3 M guanidine and acid at pH 2.0, or physical adsorption induced conformational changes to partially expose the Val235 residue.

Clinical significance of IgG subclasses of Anti-Sm and U1 ribonucleoprotein antibodies in patients with systemic lupus erythematosus and mixed connective tissue disease

IgG subclasses of anti-Sm and anti-U1 ribonucleoprotein (U1 RNP) antibodies were determined using a new clone of the anti-IgG2 antibody (HG2-56F). Although the predominance of IgG1 coincided with previous reports, IgG2 anti-Sm and U1 RNP antibodies were detected in numerous patients. IgG3 anti-Sm antibody significantly correlates with joint involvement and a high titer of anti-DNA antibody. On the other hand, IgG4 anti-U1 RNP antibody significantly correlated with esophageal dilation and muscular involvement. These results may suggest that some IgG subclasses are related to a specific clinical feature or manifestation.

Identification of epitopes recognized by a panel of six anti-human IgG2 monoclonal antibodies

Human IgG2 contains several subclass specific amino acid residues or deletions in the CH1 and CH2 domains and also in the hinge region. These substituted residues are the structural correlates for IgG2 specific epitopes. Since human IgG2 has different biological properties from other subclasses, some IgG2 epitopes may be located in regions correlating with sites determining the biological functions. Previously, we produced three anti-IgG2 monoclonal antibodies (mAbs) with highly specific and interesting reactivities using improved immunization protocols. However, it has been almost impossible to identify epitopes conventionally, because human IgG2 is so resistant to proteolysis that various proteolytic fragments could not be isolated. In this study, we identified the epitopes recognized by anti-IgG2 mAbs by SDS-PAGE, Western blotting, amino acid sequence analysis and peptide/mAb binding ELISA, thus overcoming the need for fragment isolation. A panel of six anti-human IgG2 mAbs, including the current WHO/IUIS specificity standards (HP6002, HP6008, HP6014) and our own (HG2-6A, HG2-30F, HG2-56F), reacted with distinct epitopes. The residues essential to expression of the epitopes recognized by the mAbs were: Pro234, Val235 and Val309 for HG2-56F, HG2-30F and HP6008, respectively. HP6014 reacted with the epitope expressed by Thr214 and its neighboring residues. HG2-6A was reactive with the hinge region, and HP6002 was assumed to be directed against discontinuous epitopes requiring intact Fc for expression. Through these studies, the pepsin and papain cleavage sites of human IgG2 were also clarified.

Nerve growth factor specifically induces human IgG4 production

The effect of nerve growth factor (NGF) on human IgG4 production was studied. NGF specifically enhanced IgG4 production in cultures of human tonsillar mononuclear cells without affecting production of other isotypes or other IgG subclasses. Optimal enhancement of IgG4 production by NGF required the presence of T cells. However, NGF induced significant IgG4 production by small resting B cells in the absence of T cells, and this production was enhanced by stimulation with Staphylococcus aureus Cowan strain I (SAC). In contrast to small B cells, large activated B cells produced IgG4 spontaneously; this production was enhanced by NGF. NGF also enhanced IgM and IgA production by large B cells, while production of IgG1, IgG2, IgG3 and IgE was not affected. The enhancement of IgG4 production was blocked by anti-NGF serum but not by control serum. NGF, T cells and SAC, separately or together, failed to induce IgG4 production by surface (sIgG4+)-depleted B cells. In contrast to NGF, other recombinant human cytokines including interleukin (IL) 1 beta, IL 2, IL 4, IL 5, IL 6, granulocyte-macrophage colony-stimulating factor, interferon alpha and gamma failed to induce IgG4 production. These results suggest that NGF directly and preferentially stimulates activated sIgG4+ B cells to produce IgG4.