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

Bet v 1-specific IgA increases during the pollen season but not after a single allergen challenge in children with birch pollen-induced intermittent allergic rhinitis

Allergen-specific immunoglobulins of the Immunoglobulin A (IgA) type have been found in the nasal fluid of patients with allergic rhinitis. IgA may play a protective role, but there are also data which show that allergen-specific IgA can induce eosinophil degranulation. The aim of this study was to quantitate Bet v 1-specific IgA in relation to total IgA in the nasal fluid of children with birch pollen-induced intermittent allergic rhinitis and healthy controls, after allergen challenge and during the natural pollen season. Eosinophil cationic protein (ECP), Bet v 1-specific IgA and total IgA were analyzed in nasal fluids from 30 children with birch pollen-induced intermittent allergic rhinitis and 30 healthy controls. Samples were taken before the pollen season, after challenge with birch pollen and during the pollen season, before and after treatment with nasal steroids. During the pollen season, but not after nasal allergen challenge, Bet v 1-specific IgA increased in relation to total IgA in children with allergic rhinitis. No change was found in the healthy controls. The ratio of Bet v 1-specific IgA to total IgA increased from 0.1 x 10(-3) (median) to 0.5 x 10(-3) in the allergic children, p < 0.001. No change was seen after treatment with nasal steroids, although symptoms, ECP and eosinophils were reduced. In conclusion, allergen-specific IgA in relation to total IgA increases in nasal fluids during the pollen season in allergic children but not in healthy controls. These findings are compatible with the hypothesis that allergen-specific IgA plays a role in the allergic inflammation and further studies are needed to clarify the functional role of these allergen-specific antibodies.

Allergen-reactive antibodies are found in nasal fluids from patients with birch pollen-induced intermittent allergic rhinitis, but not in healthy controls

BACKGROUND

Increased levels of allergen-reactive immunoglobulins (Igs) have been reported in nasal fluids from patients with intermittent allergic rhinitis (IAR) sensitive to ragweed and grass. The aims of this study were to make a detailed characterization of nasal fluid Igs in birch pollen-induced IAR.

METHODS

Nasal fluids were obtained from 23 patients with birch pollen-induced IAR during and after the birch pollen season, and from 20 healthy controls. Nasal fluid total and Bet v 1-reactive (IgA), IgE and IgG as well as albumin were analyzed by immunoassays. The integrity of IgA and IgG, and the molecular form of IgA were assessed by Western blotting and column fractionation, respectively.

RESULTS

Nasal fluid total IgE and IgG, but not IgA, were higher in patients compared with controls. Western blotting indicated no significant degradation of IgA (including S-IgA) and IgG. Most of the IgA, including Bet v 1-reactive antibodies, was of the secretory form and of the IgA1 subclass. Bet v 1-reactive IgA and IgG were present in all patients, but was mostly nondetectable in controls. No significant differences in the levels of Bet v 1-reactive IgA and IgG were found in patients during the birch pollen season compared with off season. Both Bet v 1 and Bet v 2-reactive IgE were nondetectable in most samples.

CONCLUSIONS

Nasal fluid Bet v 1-reactive IgA and IgG were found in all patients with birch pollen-induced IAR, but not in controls. However, no significant differences were found between patients during and after the birch pollen season.

DNA microarrays to study gene expression in allergic airways

BACKGROUND

Allergic rhinitis results from interactions between a large number of cells and mediators in different compartments of the body. DNA microarrays allow simultaneous measurement of expression of thousands of genes in the same tissue sample.

OBJECTIVE

To study gene expression in nasal mucosal biopsies from patients with allergic rhinitis using DNA micro-arrays.

METHODS

Nasal biopsies were obtained from 14 patients with symptomatic birch pollen-induced allergic rhinitis and five healthy controls. RNA was extracted from the biopsies and pooled into one patient pool and one control pool. These were analysed in duplicate with DNA micro-arrays containing more than 12 000 known genes.

RESULTS

Approximately half of the genes were expressed in the patient and control samples. Guided by the current literature we chose 32 genes of possible relevance to allergic airway inflammation and investigated their relative expression. Among these, transcripts encoding immunoglobulins and their receptors were most abundant. The expression of cytokines and growth factors was low, whereas their corresponding receptors and cell surface markers displayed higher expression levels. IgA had the highest expression of all 12 626 genes. RT-PCR showed that IgA1 was the predominant subclass. This was confirmed by the protein level in nasal fluids. Allergen-specific IgA was significantly higher in patients than in controls and correlated significantly with eosinophil granulae proteins.

CONCLUSION

DNA micro-array analysis can be used to identify genes of possible relevance to allergic airway inflammation. In this study, the expression profile in the nasal mucosa was quantitatively dominated by immunoglobulins, particularly IgA. Protein analyses in nasal fluids indicated a role for allergen-specific IgA in eosinophil degranulation.

Increased intestinal intra-epithelial T lymphocytes in primary glomerulonephritis: a role of oral tolerance breakdown in the pathophysiology of human primary glomerulonephritides?

BACKGROUND

There is increasing evidence that some organ-specific and generalized autoimmune diseases in humans might be related to a breakdown of oral tolerance. We explored this hypothesis in human primary glomerulonephritides. We prospectively counted intraepithelial T lymphocytes in the duodenal mucosa (as a marker of rupture of oral tolerance), together with IgA1 and IgA2 mucosal plasma cells, in patients with primary glomerulonephritides.

METHODS

We investigated eight adults with immune-complex glomerulopathy (membranous nephropathy+membranoproliferative glomerulonephritis), 16 adults with an idiopathic nephrotic syndrome, and 25 adults with IgA nephropathy. Patients with glomerulonephritides were compared to two control groups: group 1 consisted of nine healthy adults; group 2 comprised five adults with coeliac disease before dietary gluten withdrawal or during a clinical relapse related to gluten ingestion. (The latter disease is associated with increased numbers of intraepithelial T lymphocytes, and a breakdown of oral tolerance to gliadins is involved in the pathogenesis of coeliac disease). Duodenal fibroscopy was performed under neuroleptanalgesia. Four to six endoscopic biopsy specimens were taken from the second duodenum. Intraepithelial T lymphocytes were blindly counted on paraffin sections stained with haematein-eosin-saffron (HES), within the epithelium of a villus in a zone with at least 100 cells. Mucosal IgA1 and IgA2 plasma cells were blindly counted in a mucosal tissue unit by using specific mouse monoclonal antibodies directed against IgA1 and IgA2, with alkaline phosphatase anti-alkaline phosphatase (APAAP) revelation. As values were not normally distributed, we used non-parametric analysis of variance with the Kruskal-Wallis test, and compared median values by using the non-parametric Mann-Whitney test.

RESULTS

Intraepithelial T lymphocytes were significantly more abundant in patients with primary glomerulonephritides and coeliac disease than in healthy controls (P < 0.0001 in the Kruskal-Wallis test): healthy controls, median 11 (range 4.65-16); immune complex glomerulopathy, 27.45*** (15-93); idiopathic nephrotic syndrome, 16.5** (9-26.5); IgA nephropathy, 26.10*** (11.3-47.5); coeliac disease, 55*** (20-80) (*P <0.05; **P <0.01; ***P < 0.005, Mann-Whitney test). No difference was found in the number of duodenal IgA1 and IgA2 plasma cells between controls and patients with primary glomerulonephritides. IgA1 and IgA2 plasma cells were increased in patients with coeliac disease.

CONCLUSION

The significant increase in intestinal intraepithelial T lymphocytes in primary glomerulonephritides suggests a pathophysiological role of oral tolerance breakdown.

Imbalances in serum proinflammatory cytokines and their soluble receptors: a putative role in the progression of idiopathic IgA nephropathy (IgAN) and Henoch-Schönlein purpura nephritis, and a potential target of immunoglobulin therapy?

Following recent experimental data suggesting an aggravating effect of circulating proinflammatory cytokines on the histological lesions of IgAN, we studied changes in serum proinflammatory cytokines and their soluble receptors and antagonists in patients treated with polyvalent immunoglobulins (15 with severe nephropathy who had indicators of poor prognosis: heavy proteinuria, hypertension, altered renal function and Lee's histological grade III or IV; and 14 with moderate forms of IgAN who had permanent albuminuria > 300 mg/day and < 2000 mg/day, Lee's histological grade II and a glomerular filtration rate > 70 ml/min) in comparison with healthy controls (n = 20) and patients with non-IgA nephritides (n = 50). These were measured by means of specific immunometric assays before and after 9 months of immunoglobulin therapy. Total tumour necrosis factor (TNF) serum and IL-6 levels were elevated in IgAN patients before therapy, relative to controls, and normalized after immunoglobulin therapy. Levels of soluble TNF receptor of type I (sR55) and type II (sR75) increased on immunoglobulin therapy. TNF index alpha-55,75 used to assess biologically available TNF-alpha (ratio of total TNF-alpha divided by levels of soluble TNF receptors sR55 and sR75) was elevated before therapy and was below healthy control values after 9 months of immunoglobulin administration. Levels of serum IL-1 receptor antagonist were low prior to immunoglobulin administration in patients with severe forms of IgAN, and normalized on therapy. Serum interferon-gamma was unmodified. The histological activity index correlated with serum total TNF-alpha, TNF index alpha-55,75 and serum IL-6 levels, whereas proteinuria correlated with serum total TNF-alpha and TNF index alpha-55,75 but not with serum IL-6. These data suggest that the overproduction of proinflammatory cytokine is unbalanced by their natural antagonists in IgAN and Henoch-Schönlein syndrome. This process may play a role in the progression of the disease and be one of the targets of immunoglobulin therapy.

Deficient IgA1 immune response to nasal cholera toxin subunit B in primary IgA nephropathy

Twelve IgA nephropathy (IgAN) patients and 18 controls were immunized with novel protein antigens, cholera toxin subunit B (CTB) via the nasal route and keyhole limpet hemocyanin (KLH) subcutaneously. Antibody secreting cells and antibody response in body fluids were determined by ELISPOT assay and ELISA, respectively. Analysis of variance showed, in contrast to controls (P < 0.001), no CTB-specific IgA response in the nasal washes of patients with IgAN. Significantly lower numbers of CTB-specific antibody-secreting cells in peripheral blood (P < 0.001) and CTB-specific antibodies in plasma (P < 0.005) were found in IgAN, both restricted to the IgA1 subclass. The proportions of CTB-specific IgA1-secreting cells in bone marrow aspirates correlated significantly with the corresponding ratios in plasma, with significantly lower values (P < 0.005) in IgAN as compared to controls. These results support the existence of a "mucosa-bone marrow axis" in humans, but no dysregulation of this axis was found in IgAN. The deficient mucosal IgA immune response to CTB observed in this study after primary mucosal immunization indicates that patients with IgAN have a defective immune response when challenged intranasally. These patients may depend on more frequent and/or prolonged antigen encounter at mucosal sites before efficient mucosal immunity is established. Repeated seeding of antigen-specific cells to secondary lympoid organs could result secondarily in the relative hyperresponsiveness found in IgAN upon reactivation by parenteral immunization.

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.

Immunoglobulin A subclass measurement in serum and saliva: sensitivity of detection of dimeric IgA2 in ELISA depends on the antibody used

The existence of two IgA subclasses in humans has been reliably shown by biochemical, immunochemical and genetic means. IgA is unique among immunoglobulins in the regular occurrence of both monomeric and polymeric forms. In order to be able to study the relationship between monomeric and polymeric IgA1 and IgA2 concentrations in the circulation and mucosal compartment i.e. secretions, it is essential that the methods used are not biased by the molecular size of the IgA under investigation. We validated IgA and IgA subclass measurements in serum and saliva by sandwich enzyme-linked immunosorbent assay (ELISA). Coating reagents were specific mAbs against IgA (clone 4E8), IgA1 (clone 69-11.4) or IgA2 (clone 16-512-H5 and clone IF8.58). Pooled normal human serum and purified dimeric IgA1 (d-IgA1) or IgA2 (d-IgA2) myeloma proteins were used to standardize the assays. Polymeric and monomeric forms of IgA in sera from volunteers and patients with myelomatosis were assayed in fractions separated by high performance liquid chromatography (HPLC). Dithioerythritol (DTE) was used to determine the influence of the quarternary structure of IgA on its detection by mAbs. We found that mAbs 4E8, 69-11.4 and 16-512-H5 reliably measured d-IgA, d-IgA1 and d-IgA2 respectively, independent of the standard employed. Clone IF8.58 underestimated the concentration of d-IgA2 (correction factor +/- 2) with increased sensitivity in the presence of DTE. This difference is probably explained by the composition of the immunogen against which the mAb was raised. We conclude that no reliable conclusions can be made concerning the subclass ratio in biological fluids unless the monoclonal antibodies used have been appropriately validated.

Quantitative analysis of IgA-subclass antibodies against tetanus toxoid

Sera were analysed for levels of IgA- and IgG-class and IgA-subclass antibodies against tetanus toxoid and synthesized, tetanus-toxoid, beta-chain peptides. Forty-five peptides, deduced from the amino-acid sequence of the tetanus-toxoid beta-chain, were synthesized, in order to analyse epitope-binding of antibodies. Monoclonal, human, anti-tetanus antibodies were used to evaluate the synthesized peptides. Five synthesized peptides, bound by high, medium or low levels of IgA antibodies, were selected for the quantification of IgA1 and IgA2 antibodies. A set of chimeric, IgA-subclass antibodies with NP-specificity were used to quantify the antigen-specific IgA-subclass antibodies in a novel assay. Antibodies against the synthesized peptides were predominantly of IgA1 subclass.

IgA, IgG and IgM quantification in bronchoalveolar lavage fluids from allergic rhinitics, allergic asthmatics, and normal subjects by monoclonal antibody-based immunoenzymetric assays

Recent reports have suggested that human secretory IgA (sIgA) may have a role in the mediation of atopic disease. We have studied the levels of sIgA, IgA, IgG and IgM in bronchoalveolar lavage (BAL) fluids collected from lungs of healthy non-allergic adults (n = 14), allergic subjects with rhinitis (n = 15), and allergic asthmatics (n = 13), using a panel of monoclonal antibody-based immunoenzymetric assays (IEMAs). In contrast to commercially available immunodiffusion and nephelometric assays, these IEMAs employ highly specific monoclonal antibodies and demonstrate required precision (intra-assay CVs < 17%), parallelism (inter-dilutional CVs < 20%) at minimal detectable immunoglobulin levels in the ng/ml range, and excellent specificity with < 0.1% crossreactivity for heterologous immunoglobulin isotypes. Using these assays, we have observed a significant correlation between sIgA levels and total IgA levels in BAL fluids from all the study patients (r = 0.94; p < 0.01). The percentage of sIgA to total IgA was 84.0 +/- 2.2%. sIgA in BAL fluids from allergic rhinitics (18.0 +/- 2.5 micrograms/ml) and allergic asthmatics (15.5 +/- 2.5 micrograms/ml) were higher than those from nonallergic subjects (10.2 +/- 1.9 micrograms/ml). The only statistically significant difference in sIgA levels was observed in BAL fluids from the rhinitics and nonallergic groups (p = 0.03). Similar differences among the groups were found for levels of total IgA in BAL fluid. There were no significant differences in the levels of IgM and IgG in BAL fluids among the three groups of subjects. We conclude from these results that IgA is the predominant immunoglobulin on the airway surface and that it appears to be produced locally.

Cross-reactivity of 75 monoclonal antibodies to human immunoglobulin with sera of non-human primates

We systematically analyzed a panel of 75 murine monoclonal antibodies (mAbs) reactive with human immunoglobulins IgG, IgA, IgM, IgD, and kappa and lambda light chains for reactivity with serum immunoglobulins of higher primates. In the great apes, and to a lesser extent in other primates, epitopes related to human light chains, IgM, IgA, IgD, and all 4 IgG subclasses were identified with many of the mAbs. Those mAbs identified as reactive with a given species may be useful for immunologic studies of these species. Cladistic analysis of antigenic relatedness generated a phylogenetic tree consistent with current anatomic or molecular taxonomies.

Secretory IgA are elevated in both saliva and serum of patients with various types of primary glomerulonephritis

Secretory immunoglobulin A (IgA) was determined by means of an enzyme-linked immunosorbent assay (using as capture antibody an MoAb specific for secretory component) in saliva and serum from 46 patients with IgA mesangial nephritis (IgAGN), 36 with an idiopathic nephrotic syndrome (INS), 30 with an idiopathic membranous nephropathy (MGN) and 40 healthy controls. Secretory IgA levels were elevated in both saliva and serum of patients with primary glomerulonephritis (P < 0.05; Mann-Whitney test) regardless of the histological type of the primary glomerulonephritis. Salivary IgA1 and IgA2 levels were increased in the saliva of patients with IgAGN, INS and MGN (P < 0.05; Mann-Whitney test). The monomeric/total IgA ratio, and interferon-gamma and soluble IL-2 receptor levels, in saliva did not differ between the patients and controls (P > 0.05; Mann-Whitney test). We conclude that the mucosal immune system is activated in forms of glomerulonephritis other than IgAGN.

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.

Both IgA subclasses are reduced in parotid saliva from patients with AIDS

Secretory IgA (SIgA), the isotypes IgA1 and IgA2, and IgM were measured by ELISA in stimulated parotid saliva from patients with AIDS (n = 16), subjects with asymptomatic HIV infection (n = 28), and HIV-seronegative healthy controls (n = 19). SIgA was significantly reduced in the AIDS group (10.4 micrograms/ml) compared with the asymptomatic HIV-infected subjects (17.1 micrograms/ml) and the controls (23.0 micrograms/ml). This decrease comprised both IgA1 and IgA2 to a similar extent on a relative basis. The SIgA decrease in AIDS patients was in striking contrast to their serum IgA level, which was significantly increased (6.9 g/l) compared with the asymptomatic HIV-infected subjects (2.9 g/l) as well as the controls (2.8 g/l). Low parotid output of SIgA in patients with HIV infection was associated with low numbers of CD4+ lymphocytes in peripheral blood as well as the presence of oral infections. The parotid output of IgM was similar in all groups. A low level of SIgA in the external secretions of patients with AIDS may well contribute to their frequent mucosal infections of opportunistic microorganisms.

Monoclonal antibody-based capture enzyme immunoassays for specific serum immunoglobulin G (IgG), IgA, and IgM antibodies to respiratory syncytial virus

Monoclonal antibodies (MAbs) to the fusion protein (F), attachment protein (G), and nucleoprotein (N) of respiratory syncytial (RS) virus were evaluated for use as detector antibodies in immunoglobulin G (IgG), IgA, and IgM capture enzyme immunoassays. MAb assays were tested against assays using polyclonal antibodies (PAbs) with serum specimens from patients with and without evidence of recent RS virus infection. Assays developed with N MAbs were comparable to or better than PAb assays for detecting specific IgG and IgM antibodies but were somewhat less sensitive for IgA. F MAb assays were less sensitive for IgG and IgM antibodies but identified specific IgA in some specimens negative by N MAb assay. G MAb assays were insensitive for IgG and IgM antibodies but did detect about 50% of the IgA antibodies identified by the PAb assay. The basis for the low sensitivity of the G MAb assays is unclear, since many of these specimens were positive for IgG antibodies to G by Western immunoblot. The sensitivity of MAb assays varied with patient age: N MAb assays detected specific antibody responses to RS virus in all immunoglobulin classes in both adults and infants less than 1 year of age, F MAb assays detected specific IgG responses in adults and IgA responses in both adults and infants, and G MAb assays only detected IgA responses in adults. A mixture of N and F MAbs was complementary overall, identifying 54 of 55 (IgG), 51 of 52 (IgA), and 16 of 17 (IgM) serum specimens positive by PAb assay. These MAb assays were also specific with specimens tested from persons without a history of recent RS virus infection. The availability of these MAb-based assays offers other laboratories the opportunity to have long-term, standardized reagents and tests for serological diagnosis of RS virus infection.

An immunoassay for the determination of total IgA subclass antibodies in human serum

An enzyme immunoassay capable of determining total IgA1 and IgA2 concentrations in human serum has been developed. Subclass-specific monoclonal antibodies are bound to polyacrylamide bead-conjugated anti-mouse immunoglobulin antibodies. Bound IgA is detected with an anti-IgA peroxidase conjugate and the standard curve is linear in the region 0.25 - 2.0 micrograms/ml. Coefficient of variation values range from 0.24 - 5.77% for the IgA1 standard curve and from 0.86 - 5.92% for the IgA2 standard curve. Inter-assay variation for the IgA1 and IgA2 control sample values were 8.2% and 13.4%, respectively.