A sensitive enzyme immunoassay for the measurement of low concentrations of IgA

Evaluation of particle gel immunoassays for the detection of severe immunoglobulin A deficiency and anti-human immunoglobulin A antibodies

BACKGROUND

Immunoglobulin A (IgA)-deficient patients with anti-IgA (Ab) require transfusions using blood components with less than 0.05 mg IgA/dL as they are known to be safe for these patients. Identification of severely IgA-deficient (IgA SD) donors involved preliminary screening by the Ouchterlony double immunodiffusion assay followed by confirmatory testing at the required level of sensitivity for IgA and Ab at an external reference laboratory. Two in vitro particle gel immunoassays (ID-PaGIA IgA deficiency test and anti-IgA test) were also evaluated for their suitability in identifying IgA SD individuals and determining their Ab status.

STUDY DESIGN AND METHODS

Samples from 198 donors and 36 patients, subjected to confirmatory testing for IgA SD and Ab over a 2-year period, were also evaluated using the ID-PaGIA kits.

RESULTS

DiaMed test sensitivity and specificity for detection of IgA SD in donors was 98% whereas for Ab, test sensitivity was 91% at a specificity of 94%. In patients, sensitivity was 94% for IgA SD and 67% for Ab, both tests at a specificity of 100%.

CONCLUSIONS

The ID-PaGIA IgA deficiency test was a sensitive and specific tool for identifying IgA SD donors or patients. Sensitivity of the Ab test was high for donors but reduced for patients and of high specificity in both groups. Further studies with patients are needed to confirm this latter observation. Implementation of these tests would make it possible to supply appropriate products from IgA SD donors to prevent anaphylactic transfusion reactions in patients.

Screening of Canadian Blood Services donors for severe immunoglobulin A deficiency

BACKGROUND

Immunoglobulin A (IgA)-deficient patients with antibodies to IgA require transfusions with IgA-deficient blood components to either avoid or reduce the frequency of serious adverse reactions. To supply compatible blood components for these individuals, the Canadian Blood Services (CBS) National Testing Laboratory must initially screen and subsequently identify, after confirmatory testing at the American Red Cross (ARC), donors severely deficient in IgA (<0.05 mg/dL).

STUDY DESIGN AND METHODS

The Ouchterlony double immunodiffusion assay was used as an initial screen at CBS to identify IgA-deficient donors (test sensitivity 2-4 mg/dL). Sample aliquots from these donors were then sent to the ARC for confirmatory testing using an enzyme-linked immunosorbent assay method for severe IgA deficiency (<0.05 mg/dL) and a passive hemagglutination assay to detect anti-IgA.

RESULTS

From November 2007 to December 2008, of 54,594 samples screened initially at CBS there were 137 samples (0.251%) identified as possibly IgA deficient. Of these 137, there were 100 reports returned from ARC confirming severe IgA deficiency in 65 donors (25 female, 40 male) without detectable anti-IgA and in 35 donors (18 female, 17 male) with anti-IgA. The remaining 37 donors had IgA levels of more than 0.05 mg/dL.

CONCLUSION

Results from the ARC confirmed a frequency of 1 in 546 in the CBS' blood donor population for severe IgA deficiency (<0.05 mg/dL), 1 in 840 for those without anti-IgA, and 1 in 1560 for those with antibody. Donors repeatedly confirmed as severely IgA deficient without anti-IgA were considered eligible for the CBS IgA-deficient donor registry program.

Establishment of an immunoglobulin�A?deficient blood donor registry with a simple in-house screening enzyme-linked immunosorbent assay

BACKGROUND

Transfusion of blood products to immunoglobulin A (IgA)-deficient patients who have developed IgA antibodies can result in serious adverse reactions. To prepare compatible blood components for these patients, blood centers usually maintain a list of IgA-deficient blood donors. An in-house enzyme-linked immunosorbent assay (ELISA) was used to identify new IgA-deficient blood donors.

STUDY DESIGN AND METHODS

An in-house ELISA was used to screen blood samples. IgA-deficient samples, defined as an IgA level below 0.05 mg per dL, were sent to the American Red Cross for confirmatory testing.

RESULTS

Seventy-three confirmed IgA-deficient blood donors were identified among 38,759 screened blood donor samples (frequency, 1:531). IgA antibodies were found in 39 of these 73 blood donors (53%), although only 9 donors had a history of adult IgA exposure (transfusion or pregnancy).

CONCLUSIONS

With a simple in-house ELISA, 73 blood donors were identified as IgA-deficient. From this number, 34 donors, without detectable anti-IgA in their plasma, were added to our IgA-deficient blood donor panel to maximize the management of our inventory of IgA-deficient frozen blood components.

A modified caprylic acid method for manufacturing immunoglobulin G from human plasma with high yield and efficient virus clearance

BACKGROUND AND OBJECTIVES

The increasing demand for intravenous immunoglobulin (IVIG) necessitates the development of improved plasma fractionation methods, providing higher immunoglobulin G (IgG) recovery. Here, we describe a new IVIG production process resulting in a high yield of IgG and effective reduction of physico-chemically resistant viruses.

MATERIALS AND METHODS

IgG was purified from Cohn fraction II+III by caprylic acid treatment, polyethylene glycol precipitation, anion-exchange chromatography, nanofiltration and ultrafiltration. Stability of the purified IgG was studied in different formulations. Virus reduction was studied with two viruses: bovine viral diarrhoea virus, assessed by an infectivity assay; and human parvovirus B19, assessed by polymerase chain reaction.

RESULTS

The combination of caprylic acid treatment with polyethylene glycol precipitation and a single anion-exchange chromatography yielded polymer-free, pure IgG. The purified IgG could be filtered through a small pore-size virus filter (Millipore V-NFP) with high throughput and excellent yield. The formulated product was stable as a 100 g/l IgG solution. Bovine viral diarrhoea virus was effectively inactivated by the caprylic acid treatment, and parvovirus B19 was effectively removed in the polyethylene glycol precipitation and nanofiltration stages, the total reduction of parvovirus being approximately 14 log10.

CONCLUSIONS

The new process gives pure and stable IgG solution with an average yield of 4.8 g of IgG per kg of recovered plasma and has a very high capacity to remove even physico-chemically resistant viruses.

Development of a pharmaceutical apotransferrin product for iron binding therapy

High-dose chemotherapy of patients with haematological malignancies results in extracellular iron accumulation and appearance of non-transferrin-bound iron, which is thought to predispose the patients to septic infections and contribute to organ toxicity. We describe the development of a human plasma-derived apotransferrin product for iron binding therapy. The product is purified from Cohn fraction IV of human plasma by two ion exchange chromatography steps and ultrafiltration. The process comprises solvent detergent treatment as the main virus inactivation step and 15 nm virus filtration and polyethylene glycol precipitation as removal steps for physico-chemically resistant infectious agents. Product characterization by electrospray and MALDI-TOF mass spectrometry indicated no other chemical modifications than N-linked glycan chains and disulphide bonds, except minor oxidation. The purity of the product was more than 98%, main impurities being IgG, IgA and hemopexin. The product had intact iron binding capacity and native conformation. A stable liquid formulation for the finished product was developed. The product has proved safe and well tolerated in early clinical trials in iron binding therapy.

The significance of IgG subclasses and mannan-binding lectin (MBL) for susceptibility to infection in apparently healthy adults with IgA deficiency

The aim of this study was to investigate the significance of IgG subclasses and MBL for susceptibility to infection in association with IgA deficiency. The study population consisted of 139 apparently healthy adult blood donors with IgA deficiency and normal serum levels of IgG and IgM, and an increased susceptibility to infection demonstrated at a population level. Additionally, 216 controls matched for age and sex were investigated. IgG4 deficiency was more common and the mean level of IgG4 lower in persons with IgA deficiency than in the controls. No significant associations could be demonstrated between overt IgG subclass deficiencies and increased susceptibility to infection. However, when the mean concentrations of IgG subclasses were analysed with regard to medical history, that of IgG1 was lower in persons who reported recurrent viral respiratory infections, that of IgG3 in persons who had episodes of severe infection in their history, and that of IgG4 in persons who had recurrent mild respiratory infections, compared with those who had no particular history of infections. In contrast, MBL deficiency-alone or combined with that of the IgG subclass-was not associated with increased susceptibility to infection in persons with IgA deficiency. The results indicate that the proneness to infections observed in a population of otherwise healthy persons with IgA deficiency can only for a small part be accounted for by concomitant deficiencies of IgG subclasses. Contrary to expectations, no synergism between the deficiencies of IgA and MBL could be demonstrated.

An enzyme-linked immunosorbent assay for the quantitative determination of anti-D in plasma samples and immunoglobulin preparations

Here we present an enzyme-linked immunosorbent assay (ELISA) on microtiter plates for the quantitative determination of anti-D. This method is based on the solubilization of red blood cells sensitized with anti-D and the subsequent measurement of immunoglobulin G by ELISA. The measuring range of the assay is 40-5,000 IU/ml and the lowest quantifiable concentration in plasma is 0.5 IU/ml. The interassay relative standard deviation for concentrations above 130 IU/ml ranges from 3.2 to 8.1% and below 50 IU/ml from 10.5 to 19.7%. Comparison of ELISA with automated hemagglutination shows that the results of the two assays correlate well: r = 0.992, n = 26. The assay was validated for donor plasma samples and anti-D immunoglobulin preparations and it can also be used in assessing the severity of Rh (D) hemolytic disease during pregnancy.

Long-term follow-up of anti-IgA antibodies in healthy IgA-deficient adults

A follow-up study of anti-IgA antibodies in 159 healthy blood donors with severe deficiency of serum IgA (< 0.05 mg/L) and in 45 donors with decreased serum IgA levels (0.05-799 mg/L), identified in 1971-1980, was carried out. Initially anti-IgA antibodies were determined by a hemagglutination (HA) method and two reexaminations were done in 1990-1992 by an enzyme immunoassay. The median follow-up period was 19 years, during which anti-IgA level was changed considerably in only four persons, increased in two, and high level antibodies (> 1/1000 by HA) appeared in two. In reexaminations anti-IgA antibodies were found in 30 (19%) subjects with severe IgA deficiency and the antibody levels remained relatively constant in those who had high and medium antibody levels. Anti-IgA antibodies were not found in subjects with decreased, but detectable serum IgA. Thus it seems that only those healthy adults who have severe IgA deficiency develop anti-IgA antibodies and their anti-IgA levels remain fairly constant. Of the 159 subjects with severe IgA deficiency, 66 had a history of IgA exposure, but no correlation to anti-IgA development was noted.

Quantitative determination of immunologic components of salivary gland secretion in long-term, event-free pediatric oncology patients

OBJECTIVES

Chemotherapy influences the human immune system. Salivary alterations occur during cancer treatment. In this article we examine the salivary immunoglobulin content in pediatric patients who were long-term event-free and correlate these findings with different oral factors.

STUDY DESIGN

Fifty-two children of a study group and 63 children of a control group were examined at our University Hospital. Caries prevalence and plaque index were scored. Whole saliva samples were taken for determination of slgA and IgG concentrations and Streptococcus mutans and Lactobacillus counts. For statistical analysis the Dental Survey Plus (Providence Software Services, Bristol, England) software package was used.

RESULTS

Concentrations of slgA and IgG were within normal limits in both groups; slgA level increased with age. A negative correlation between slgA concentration and caries experience was not found in all age groups. No correlation with other salivary parameters was found.

CONCLUSION

Salivary content of slgA and IgG can return to normal after cytotoxic therapy in these children. Salivary IgA seem to play a role in the development of dental caries in this population.

An enzyme immunoassay for the determination of anti-IgA antibodies using polyclonal human IgA

An enzyme immunoassay (EIA) for screening and quantitation of serum anti-IgA antibodies of IgG class is described. This method is based on the use of purified polyclonal human serum IgA as the coating antigen and a commercial alkaline phosphatase-conjugated anti-human IgG as the detecting antibody. Nonspecific reactions were minimized by blocking vacant protein binding sites with bovine serum albumin and by using individual sample blanks. The IgA specificity of a positive antibody finding was confirmed by testing inhibition: pooled normal human serum inhibited the binding of specific antibodies by over 80%. The same degree of inhibition could also be demonstrated by a commercial myeloma IgA preparation and by the IgA used for coating but not by IgA-deficient serum (< 0.05 mg/l). On the basis of the mean anti-IgA antibody titre in EIA, a value of 12,000 arbitrary units of anti-IgA per litre (AU/l) was assigned to a patient serum used as standard in the assay. Anti-IgA results obtained by EIA and haemagglutination correlated well, which makes it possible to compare earlier HA results with those obtained now by EIA. The measuring range of the assay was 0.6-27 AU/l and the lowest quantifiable concentration 7 AU/l. The dilution requirement for serum was 1/16. The interassay coefficients of variation for control sera with antibody levels from 35 AU/l to 3770 AU/l varied from 9 to 12%.

Long-term persistence of selective IgA deficiency in healthy adults

A follow-up study of 204 healthy blood donors with IgA deficiency, identified between 1971 and 1980, was carried out. Sera were initially screened by a double diffusion method and 182 were retested by a more sensitive haemagglutination inhibition method. A reexamination was performed in 1990 and, again, in 1991-1992 using an enzyme immunoassay (EIA) developed for the measurement of very low concentrations of IgA. The median follow-up period was 19 years, and in 159 (78%) subjects no serum IgA could be detected in any of the measurements. In 42 (21%) subjects, serum IgA was detectable (> 0.18 mg/L), but the level was below the lower limit of the reference range for adults (800 mg/L) and remained relatively constant. Three subjects showed minute amounts of IgA by EIA (0.2-3 mg/L) in one of the follow-up samples in 1990-1992, but the level was below the detection limit of the EIA (0.05 mg/L) in the other sample. Thus, not only does primary IgA deficiency appear to be permanent, but also lower than normal serum IgA levels remain the same in healthy adults.