Immunogenic and antigenic epitopes of immunoglobulins. X: Monoclonal antibodies specific for human IgA, the IgA1 and IgA2 subclasses and an nA2m(2) iso-allotypic epitope

Saliva antiviral antibody levels are detectable but correlate poorly with serum antibody levels following SARS-CoV-2 infection and/or vaccination

The importance of salivary SARS-CoV-2 antibodies, following infection and vaccination, has not been fully established. 875 healthcare workers were sampled during the first wave in 2020 and 66 longitudinally in response to Pfizer BioNTech 162b2 vaccination. We measured SARS-CoV-2 total IgGAM and individual IgG, IgA and IgM antibodies. IgGAM seroprevalence was 39.9%; however, only 34.1% of seropositive individuals also had salivary antibodies. Infection generated serum IgG antibodies in 51.4% and IgA antibodies in 34.1% of individuals. In contrast, the salivary antibody responses were dominated by IgA (30.9% and 12% generating IgA and IgG antibodies, respectively). Post 2nd vaccination dose, in serum, 100% of infection naïve individuals had IgG and 82.8% had IgA responses; in saliva, 65.5% exhibited IgG and 55.2% IgA antibodies. Prior infection enhanced the vaccine antibody response in serum but no such difference was observed in saliva. Strong neutralisation responses were seen for serum 6 months post 2nd-vaccination dose (median 87.1%) compared to low neutralisation responses in saliva (median 1%). Intramuscular vaccination induces significant serum antibodies and to a lesser extent, salivary antibodies; however, salivary antibodies are typically non-neutralising. This study provides further evidence for the need of mucosal vaccines to elicit nasopharyngeal/oral protection. Although saliva is an attractive non-invasive sero-surveillance tool, due to distinct differences between systemic and oral antibody responses, it cannot be used as a proxy for serum antibody measurement.

Development of a high-sensitivity ELISA detecting IgG, IgA and IgM antibodies to the SARS-CoV-2 spike glycoprotein in serum and saliva

Detecting antibody responses during and after SARS-CoV-2 infection is essential in determining the seroepidemiology of the virus and the potential role of antibody in disease. Scalable, sensitive and specific serological assays are essential to this process. The detection of antibody in hospitalized patients with severe disease has proven relatively straightforward; detecting responses in subjects with mild disease and asymptomatic infections has proven less reliable. We hypothesized that the suboptimal sensitivity of antibody assays and the compartmentalization of the antibody response may contribute to this effect. We systematically developed an ELISA, optimizing different antigens and amplification steps, in serum and saliva from non-hospitalized SARS-CoV-2-infected subjects. Using trimeric spike glycoprotein, rather than nucleocapsid, enabled detection of responses in individuals with low antibody responses. IgG1 and IgG3 predominate to both antigens, but more anti-spike IgG1 than IgG3 was detectable. All antigens were effective for detecting responses in hospitalized patients. Anti-spike IgG, IgA and IgM antibody responses were readily detectable in saliva from a minority of RT-PCR confirmed, non-hospitalized symptomatic individuals, and these were mostly subjects who had the highest levels of anti-spike serum antibodies. Therefore, detecting antibody responses in both saliva and serum can contribute to determining virus exposure and understanding immune responses after SARS-CoV-2 infection.

Intra-tumour IgA1 is common in cancer and is correlated with poor prognosis in bladder cancer

A high frequency of IgA1-positive tumour cells was found in tissue micro-arrays of oesophagus, colon, testis, lung, breast, bladder and ovarian cancer. IgA1 was observed in the cytoplasm and the plasma membrane. A correlation was found between intra-tumour IgA1 and poor overall survival in a large cohort of bladder cancer patients (n = 99, p = 0.011, log-rank test). The number of IgA1-positive tumour cells was also found to be higher in female than male bladder cancer patients. The presence of IgA1 was confirmed in formalin-fixed paraffin-embedded ovarian carcinoma samples using LC-MS/MS analysis. Uptake of IgA1 was also observed in breast cancer and melanoma cell lines when cultivated in the presence of serum from healthy individuals, indicating a possible origin of the IgA1 antibodies in cancer cells.

Large scale generation and characterization of anti-human IgA monoclonal antibody in ascitic fluid of BALB/c mice

PURPOSE

Monoclonal antibodies are potentially powerful tools used in biomedical research, diagnosis, and treatment of infectious diseases and cancers. The monoclonal antibody against Human IgA can be used as a diagnostic application to detect infectious diseases. The aim of this study was to improve an appropriate protocol for large-scale production of mAbs against IgA.

METHODS

For large-scale production of the monoclonal antibody, hybridoma cells that produce monoclonal antibodies against Human IgA were injected intraperitoneally into Balb/c mice that were previously primed with 0.5 ml Pristane. After ten days, ascitic fluid was harvested from the peritoneum of each mouse. The ELISA method was carried out for evaluation of the titration of produced mAbs. The ascitic fluid was investigated in terms of class and subclass by a mouse mAb isotyping kit. MAb was purified from the ascitic fluid by ion exchange chromatography. The purity of the monoclonal antibody was confirmed by SDS-PAGE, and the purified monoclonal antibody was conjugated with HRP.

RESULTS

Monoclonal antibodies with high specificity and sensitivity against Human IgA were prepared by hybridoma technology. The subclass of antibody was IgG1 and its light chain was the kappa type.

CONCLUSION

This conjugated monoclonal antibody could have applications in designing ELISA kits in order to diagnose different infectious diseases such as toxoplasmosis and H. Pylori.

Primary breast cancer tumours contain high amounts of IgA1 immunoglobulin: an immunohistochemical analysis of a possible carrier of the tumour-associated Tn antigen

The Tn antigen (GalNAc alpha-O-Ser/Thr) as defined by the binding of the lectin, helix pomatia agglutinin (HPA) or anti-Tn monoclonal antibodies, is known to be exposed in a majority of cancers, and it has also been shown to correlate positively with the metastatic capacity in breast carcinoma. The short O-glycan that forms the antigen is carried by a number of different proteins. One potential carrier of the Tn antigen is immunoglobulin A1 (IgA1), which we surprisingly found in tumour cells of the invasive parts of primary breast carcinoma. Conventional immunohistochemical analysis of paraffin-embedded sections from primary breast cancers showed IgA1 to be present in the cytoplasm and plasma membrane of 35 out of 36 individual primary tumours. The immunohistochemical staining of HPA and anti-Tn antibody (GOD3-2C4) did to some extent overlap with the presence of IgA1 in the tumours, but differences were seen in the percentage of stained cells and in the staining pattern in the different breast cancers analysed. Anti-Tn antibody and HPA were also shown to specifically bind to a number of possible constellations of the Tn antigen in the hinge region of IgA1. Both reagents could also detect the presence of Tn positive IgA in serum. On average 51% of the tumour cells in the individual breast cancer tumour sections showed staining for IgA1. The overall amount of staining in the invasive part of the tumour with the anti Tn antibody was 67%, and 93% with HPA. The intra-expression or uptake of IgA1 in breast cancer makes it a new potential carrier of the tumour associated and immunogenic Tn antigen.

Evaluation of monoclonal antibodies with specificity for human IgA, IgA subclasses and allotypes and secretory component. Results of an IUIS/WHO collaborative study

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.

Generation of monoclonal antibodies to Macaca mulatta (rhesus) IgA

One IgG1 and five IgM murine monoclonal antibodies (mAb) specific for rhesus (Rh) IgA were generated. These mAbs bound to Rh IgA but not IgG or IgM when tested by enzyme-linked immunosorbent assay. Immunoblotting revealed that the mAbs reacted with the alpha heavy chain of Rh but not human IgA. The IgG1 anti-Rh IgA mAb detected IgA-producing cells in sections of monkey gut examined by immunofluorescent staining. These mAbs should be useful for characterizing IgA responses in the Rh monkey.

Native epitopes of human IgA

We have studied the epitopes of the human IgA molecule by using 27 monoclonal antibodies in two simple gel diffusion methods. By testing pairs of monoclonal antibodies for coprecipitation of an IgA myeloma protein, we have clearly identified sterically independent epitopes on the molecule. By testing the non-coprecipitating monoclonal antibodies with soluble IgA-monoclonal antibody immune complexes, we have identified the overlapping epitopes. Eleven proto-epitopes were mapped on the IgA molecule. Since we have not used solid-phase methods, we have presumably identified native epitopes of the IgA molecule.

Lack of cleavage of immunoglobulin A (IgA) from rhesus monkeys by bacterial IgA1 proteases

Bacterial immunoglobulin A1 (IgA1) proteases cleaving IgA1 and secretory IgA1 molecules in the hinge region are believed to be important virulence factors. Previous studies have indicated that IgA of humans, gorillas, and chimpanzees are the exclusive substrates of these enzymes. In a recent study, IgA from the rhesus monkey was found to be susceptible to the IgA1 protease activity of Streptococcus pneumoniae. In an attempt to reproduce this observation, we found that neither five isolates of S. pneumoniae nor other IgA1 protease-producing bacteria representing different cleavage specificities caused cleavage of rhesus monkey IgA. Hence, the rhesus monkey does not appear to be a suitable animal model for studies of IgA1 proteases as virulence factors.

Specificity and association constants of 33 monoclonal antibodies to human IgA epitopes

We used an immunofluorescent sequential-saturation-of-antibody assay and an interactive computer program for Scatchard analysis to determine association constants (Ka) of 33 murine monoclonal antibodies (Mabs) specific for human IgA epitopes. Ka ranged from 0.37 to 690 x 10(7) liters per mole (an approximate 1900-fold difference). Specificity was validated with a panel of 18 highly purified IgA1 and IgA2 myeloma proteins and secretory IgA using an immunofluorometric assay. Western blots of bacterial IgA protease digests were used to locate the epitopes of IgA specific Mabs in either the Fab, Fc, or hinge region. Mabs specific for unique epitopes on secretory IgA or free secretory component (FSC) were produced and evaluated.

An enzyme-linked immunosorbent assay for the determination of the IgA subclass distribution of antigen-specific antibodies

An ELISA for the determination of the IgA subclass distribution of antigen-specific antibodies was developed using commercially available monoclonal anti-IgA1 anti-IgA2 subclass antibodies. Furthermore an anti-A2m allotype-specific antibody was included in the study. The specificity and sensitivity of the monoclonal anti-immunoglobulin antibodies used was analyzed using sera from normal and IgA class- or subclass-deficient individuals (with or without homozygous C alpha 1 subclass gene deletions). Human IgA1 and IgA2 hybridoma antibodies were also used. In this particular assay, only two out of four tested anti-IgA1 and two out of three tested anti-IgA2 antibodies proved to be specific for their corresponding IgA subclass. The anti-A2m(2) monoclonal antibody was shown to be specific for the corresponding allotype. These ELISA methods may facilitate further work on the regulation of IgA subclass production in man.

Comparison of the effector functions of human immunoglobulins using a matched set of chimeric antibodies

Cell lines have been established that secrete a matched set of human chimeric IgM, IgG1, IgG2, IgG3, IgG4, IgE, and IgA2 antibodies that are directed against the hapten 4-hydroxy-3-nitrophenacetyl. These chimeric antibodies secreted from mouse plasmacytoma cells behave exactly like their authentic human counterparts in SDS-PAGE analysis, binding to protein A and in a wide range of serological assays. The antibodies have been compared in their ability to bind human C1q as well as in their efficacy in mediating lysis of human erythrocytes in the presence of human complement. A major conclusion to emerge is that whereas IgG3 bound C1q better than did IgG1, the chimeric IgG1 was much more effective than all the other IgG subclasses in complement-dependent hemolysis. The IgG1 antibody was also the most effective in mediating antibody-dependent cell-mediated cytotoxicity using both human effector and human target cells. These results suggest that IgG1 might be the favoured IgG subclass for therapeutic applications.

Cells containing IgA subclasses in bronchi of subjects with and without chronic obstructive lung disease

Necropsy specimens were obtained from the lungs of 10 subjects who had no history of lung disease, 10 who had died with chronic bronchitis, and 10 with bronchiectasis. Tissue sections were stained for IgA1 or IgA2 using the immunoperoxidase technique, and the number of cells in the bronchi stained for these proteins was counted. The total number of IgA positive cells was increased in bronchitic and bronchiectatic lungs compared with those from control subjects. The number of IgA2 positive cells was similar in those with bronchitis and bronchiectasis and significantly higher than in controls. Similarly, cells containing IgA1 were increased in the lungs of subjects with chest disease but were higher in those with bronchitis than in those with bronchiectasis. The proportion of IgA2:total IgA containing cells was similar in sections from controls (mean (SD) 25 (5.0)%) and those with bronchiectasis (mean (SD) 24 (4)%), but lower in those with bronchitis (mean (SD) 19 (5.0)%). The results show that cells containing IgA1 predominate in the major bronchi but that the proportion of cells containing IgA2 is higher than in non-mucosal lymphoid tissues. Bronchitis and bronchiectasis are associated with greater numbers of cells producing IgA in the bronchi, and this is consistent with increased local production of IgA in the lung secretions of bronchitic subjects.

Monoclonal antibodies against different domains of human IgA: specificities determined by immunoblotting and haemagglutination-inhibition

The specificity of 14 monoclonal antibodies has been determined by immunoblotting (IB) and haemagglutination-inhibition (HAI) analysis using IgA1 and IgA2 myeloma proteins and eight different IgA1 fragments. Two antibodies probably recognized epitopes on the CH1 domain of IgA. They reacted with all Fab-containing fragments irrespective of whether these originated from the same or different IgA proteins. Seven antibodies were directed against epitopes on the CH2 domain. These antibodies were reactive with F(abc)2 fragments. They failed to react with Fab, Fab' and F(ab')2 fragments. Two out of these seven antibodies did not react with two-chain IgA half-molecules and Fabc fragments containing a single heavy and a single light chain. This suggests that these two antibodies recognized an epitope whose structure is dependent on disulfide linked heavy chains. Five other antibodies showed specificity for the CH3 domain. They were reactive with all CH3-containing molecules, irrespective of whether they comprised one or two alpha chains. Our study demonstrates that IB is an appropriate technique to determine domain specificity of monoclonal anti-immunoglobulin reagents. Although the IB tests were performed on denatured proteins the results agreed surprisingly well with those of the HAI analyses. Moreover, the IB technique could be used on fragments which could not be purified well enough for HAI analyses.

Monoclonal antibodies to distinct epitopes on human IgA and their use to IgA determination

Several monoclonal antibodies (MAbs) against human IgA have been obtained which specifically bind to human myeloma and polyclonal IgA. Three of these MAbs have been purified and studied further. They recognize both IgA subclasses and define three distinct epitopes on the IgA molecule. These MAbs were used to develop a solid-phase radioimmunoassay (RIA) in which one MAb was immobilized and the other two were labeled with 125I. The assay has a sensitivity in the nanogram range. A good correlation was found (r = 0.97, P less than 0.001) when the solid-phase RIA was compared with a commercially available immunodiffusion technique for the determination of IgA levels in serum samples.

Double precipitin arcs of IgA myeloma sera on immunoelectrophoresis. Origin and suggestion of IgA2m(2) allotype

The serum from two patients with IgA myeloma displayed double precipitin arcs upon immunoelectrophoresis with class-specific (light chain absorbed) anti-IgA antisera obtained by immunization with monoclonal IgA1, but not IgA2 proteins. Both sera contained large amounts of monoclonal IgA2m(2) together with some polyclonal IgA1. No incomplete IgA molecules were found. The double precipitin arcs resulted from the reaction of large amounts of monoclonal IgA2m(2) with class-specific antibodies, and of small amounts of polyclonal IgA1 with subclass-specific anti-IgA1 antibodies of the same antiserum. Such double arcs, if not due to incomplete IgA molecules, could indicate the IgA2m(2) nature of the monoclonal IgA in these rare sera.