Serum levels of IgA1 and IgA2 in children and in patients with IgA deficiency

Age-specific pediatric reference ranges for immunoglobulins and complement proteins on the Optilite™ automated turbidimetric analyzer

BACKGROUND

Measurement of immunoglobulins and complement proteins are frontline tests used in the assessment of immune system integrity, and reference values can vary with age. Their measurement provides an insight into the function of the innate and adaptive immune systems.

METHODS

We generated pediatric reference ranges for IgG, IgA, IgM, IgD, the IgG and IgA subclasses, and C3 and C4 using the Optilite™ turbidimetric analyzer.

RESULTS

The concentrations of IgG, IgA, and IgD showed an increase with age, as expected, while IgM remained stable between the age groups. For the IgG subclasses, no significant differences were observed in IgG1 or IgG3, while IgG2 and IgG4 concentrations increased steadily with age. The concentration of IgG2 plateaued at 15-18 years, while IgG4 plateaued at 10-14 years. The trend of concentrations across all groups was IgG1 > IgG2 > IgG3 > IgG4. For both IgA1 and IgA2, concentrations increased significantly with age, plateauing at 15-18 years. The median IgA1 concentration was greater than IgA2 across all groups. There was a good correlation between the total IgG or IgA concentration and summation of their subclasses (R²  = 0.89, P < .0001, slope y = 0.98x + 14.51 mg/dL and R²  = 0.91, P < .0001, slope y = 1.35x-3.28 mg/dL, respectively). The concentration of C3 and C4 remained stable across the groups, with no significant differences observed.

CONCLUSION

We have generated age-specific reference ranges in healthy children for C3, C4, IgG, IgA, IgM, IgD and the IgG and IgA subclasses using the Optilite^™ turbidimetric analyzer. These ranges will help identify individuals with abnormal concentrations, thus will aid in the diagnosis of both primary and secondary immunological disorders.

The gastrointestinal frontier: IgA and viruses

Viral gastroenteritis is one of the leading causes of diseases that kill ~2.2 million people worldwide each year. IgA is one of the major immune effector products present in the gastrointestinal tract yet its importance in protection against gastrointestinal viral infections has been difficult to prove. In part this has been due to a lack of small and large animal models in which pathogenesis of and immunity to gastrointestinal viral infections is similar to that in humans. Much of what we have learned about the role of IgA in the intestinal immune response has been obtained from experimental animal models of rotavirus infection. Rotavirus-specific intestinal IgA appears to be one of the principle effectors of long term protection against rotavirus infection. Thus, there has been a focus on understanding the immunological pathways through which this virus-specific IgA is induced during infection. In addition, the experimental animal models of rotavirus infection provide excellent systems in which new areas of research on viral-specific intestinal IgA including the long term maintenance of viral-specific IgA.

Human Male Genital Tract Secretions: Both Mucosal and Systemic Immune Compartments Contribute to the Humoral Immunity

In contrast to numerous studies of female genital tract secretions, the molecular properties of Abs and the magnitude of humoral responses in human male genital tract secretions to naturally occurring Ags and to mucosal and systemic immunizations have not been extensively investigated. Therefore, seminal plasma (SP) collected from healthy individuals was analyzed with respect to Ig levels, their isotypes, molecular forms of IgA, and for the presence of Abs to naturally occurring Ags, or induced by systemic or mucosal immunizations with viral and bacterial vaccines. The results indicated that in SP, IgG and not IgA, is the dominant Ig isotype, and that IgM is present at low levels. IgA is represented by secretory IgA, polymeric IgA, and monomeric IgA. In contrast to the female genital tract secretions in which IgA2 occurs in slight excess, the distribution of IgA subclasses in SP resembles that in plasma with a pronounced preponderance of IgA1. The IgG subclass profiles in SP are also similar to those in serum. Thus, SP is an external secretion that shares common features with both typical external secretions and plasma. Specifically, SP contains naturally occurring secretory IgA Abs to environmental Ags of microbial origin and to an orally administered bacterial vaccine, and plasma-derived IgG Abs to systemically injected vaccines. Therefore, both mucosal and systemic immunization with various types of Ags can induce humoral responses in SP. These findings should be considered in immunization strategies to induce humoral responses against sexually transmitted infections, including HIV-1.

Establishment of age-dependent reference values for IgA subclasses

BACKGROUND

Recently, subclass-specific antisera have been introduced for application in a nephelometric assay. The aim of this study was to establish age-dependent reference values for serum concentrations of the two IgA subclasses in children and adults.

METHODS

Serum levels of IgA1 and IgA2 were measured by automated immunonephelometry in samples from 235 clinically healthy children between 6 months and 18 years of age and 36 healthy adults.

RESULTS

Both IgA1 and IgA2 were detectable in all samples, and both IgA1 and IgA2 increased with increasing age. In adults, the mean value for IgA1 is 1.46 g/l for IgA2 0.21 g/l and for total IgA 1.94 g/l. Individual IgA2 values correlate significantly (p < 0.0001) with IgA1 values (r(2) = 0.5433). In addition, there was a highly significant (p < 0.0001) correlation (r(2) = 0.9530) between the measured total IgA and the sum of the two IgA subclasses indicating that immunonephelometry using highly specific polyclonal antisera might be superior to other methods.

CONCLUSIONS

These results and the availability of age-dependent reference values make it worthwhile to reassess the role of IgA subclasses in immunodeficiency and autoimmune diseases where conventional methods have led to conflicting results.

Increases of IgA milk concentrations correlate with IgA2 increment

IgA, IgA1, and IgA2 concentrations were determined in 81 defatted human milk samples: colostrum (days 1-5, n = 42), transitional milk (days 6-14, n = 18) and mature milk (days 15-75, n = 21) by immunonephelometry. Correlations were found between total IgA levels and the concentrations of both IgA subclasses (P < 0.0001). The levels of the three molecules decreased over lactation with significant differences (P < 0.05) between colostrum and transitional milk levels and between colostrum and mature milk. Colostral IgA1 and IgA2 mean concentrations dropped respectively from 10.89 +/- 2.12 g/L, and 15.41 +/- 2.10 g/L to 1.83 +/- 0.73 g/L and 3.40 +/- 1.25 g/L in transitional milk reaching finally to 0.36 +/- 0.07 g/L and 0.27 +/- 0.06 g/L in mature milk. IgA2 concentrations were higher than those of IgA1 when the total IgA level was high. The IgA2 levels in colostrum could be an adaptation resistance of IgA to potentially harmful pathogens able to secrete IgA proteases and also a way to regulate colonization of the microflora in the newborn.

Allotype-associated differences in concentrations of human IgA2

Concentrations of immunoglobulin (Ig)A2 were determined in 176 Finnish blood donor sera. Their IgA, IgM, IgE, IgG1, IgG2, IgG3 and IgG4 concentrations and Gm allotypes had been determined earlier. The mean concentration of IgA2 was higher in individuals carrying the Gm(ax) allele (0.15 g/l) than in those negative for Gm(x) (0.103 g/l). The difference was statistically significant (P = 0.006). As > or = 70% of IgA was usually IgA1, its concentration could be calculated fairly reliably by subtracting the IgA2 value from the IgA value. The mean IgA1 concentration (2.03 g/l) seemed to be independent of the Gm allotypes.

Method for the isolation of biologically active monomeric immunoglobulin A from a plasma fraction

A purification method for immunoglobulin A (IgA) yielding monomeric IgA with a purity of over 97% has been developed. This procedure uses ethanol-precipitated plasma (Cohn fraction III precipitate) as the starting material and includes heparin-Sepharose adsorption, dextran sulfate and ammonium sulfate precipitation, hydroxyapatite chromatography, batch adsorption by an anion-exchange matrix and gel permeation. Additional protein G Sepharose treatment leads to an IgA preparation of greater than 99% purity. The isolated IgA presented with an IgA subclass distribution, equivalent to IgA in unfractionated plasma, and was biologically active, as was shown by its ability to down-modulate Haemophilus influenzae-b-induced IL-6 secretion of human monocytes.

Increase in density of jejunal IgA2 cells during infancy without change in IgA1 cells

To determine any association between densities of cells containing IgA, IgA1, IgA2, IgG, and IgM in the lamina propria of the jejunum and the age of the individual, we restudied 65 specimens from 65 patients in the age range 66 days to 4 years. Indications for jejunal biopsy were minor symptoms; none of the patients had any gastrointestinal disease, and the specimens showed normal morphology. We used murine anti-human monoclonal antibodies to IgA, IgA1, IgA2, IgG, and IgM and an indirect immunoperoxidase method and found a significant increase with advancing age in the densities of cells containing IgA, IgA2, and IgG, whereas the densities of IgA1- and IgM-positive cells did not change with age. Densities of IgA2 and IgG cells in children over 1 year were significantly greater than in infants under 9 months (upper vs. lower quartile of the study group, p < 0.05 in both comparisons). In the jejunum, an increase in IgA2 cells was responsible for the increase in total IgA production for the age range studied.

Delineation of producing ability of IgG and IgA subclasses by naive B cells in newborn infants and adult individuals

Neonatal B cells with the naive (sIgD+) phenotype are able to generate IgG- and IgA-producing cells as well as IgM production in the presence of memory CD4+ T cells expressing L-selectin (CD62L) in pokeweed mitogen-stimulated cultures. We used this system to examine comparatively the ability of naive B cells to produce IgG and IgA subclasses in newborn infants and adult individuals. Naive B cells were enriched from both donors on the basis of sIgD positivity, and memory (CD45RO+) CD4+ T cells with CD62L expression were isolated from adults. We here demonstrate some differences in profiles of IgG and IgA subclass production between neonatal and adult naive B cells. In neonatal B cells, IgG1 and IgG3 were predominantly produced, but IgG2 and IgG4 production was virtually absent. Similar to neonatal B cells, adult naive B cells produced mainly IgG1 and IgG3, although memory (sIgD-) B cells from adults secreted all of the IgG subclasses. It should be noted that low but detectable levels of IgG2 and IgG4 were found in adults' naive B cell cultures. Although IgA produced by neonatal B cells was exclusively IgA1, IgA2-secreting cells were identifiable in adult naive B cells. The results suggest that further class switch of naive B cells to IgG2, IgG4 and IgA2 in addition to IgG1 and IgG3 may be controlled by their own age-dependent maturation process.

Chronic bullous disease of childhood and linear IgA disease of adults are IgA1-mediated diseases

Linear IgA disease is characterized by the presence of linear IgA deposits at the basement membrane zone of the skin, and in some cases by circulating basement membrane zone antibodies. The disease occurs in both adults and children, and is designated adult linear IgA disease in the former and chronic bullous disease of childhood in the latter. The subclass distribution of the circulating and bound basement membrane zone antibodies was studied in 32 children and eight adults. The results were compared with five dermatitis herpetiformis patients and five normal controls. The circulating antibodies (39 patients) and the cutaneous deposits (39 patients) were IgA1 in all 40 patients with linear IgA disease. The cutaneous deposits in dermatitis herpetiformis were also all IgA1, and no circulating antibodies were detected. The controls were all negative. This large series of children and adults with linear IgA disease demonstrates that the circulating and cutaneous basement membrane zone deposits are all IgA1, and suggests that linear IgA disease is an IgA1-mediated disease.

Secretory IgA in cervical mucus

PURPOSE

Sexually active adolescent girls are uniquely vulnerable to sexually transmitted disease, including cervical cancer and AIDS. Little is known about the development of genital immunity in adolescents. Secretory IgA (sIgA) in cervical mucus is an important component of genital immunity. We studied sIgA levels in cervical mucus samples for both adolescent and adult females.

METHODS

Samples were collected in a university-based adolescent medicine clinic and a university student health center. Participants consisted of 13 sexually active adolescent girls and fourteen adult controls. Samples were collected in the course of routine pelvic exams. All subjects were at least two years post menarche. Mucus was aspirated directly from the cervical os. Diluted samples were liquefied with a proteolytic enzyme (bromelain). Secretory IgA levels were measured by radial immunodiffusion using IgA2 from pooled human plasma as a standard.

RESULTS

Secretory IgA levels for the adolescent group (mean 0.157 g/L SD 0.080) were slightly lower than for the adult group mean (0.199 g/L SD 0.130) although not statistically significant.

CONCLUSIONS

Cervical sIgA levels were comparable between sexually active adolescents and adults.

Is there IgA of gut mucosal origin in the serum of HIV1 infected patients?

This study was performed in 77 HIV1 seropositive adult patients to characterise the IgA hyperglobulinaemia seen in the serum during the course of HIV infection. It was shown that both IgA1 and IgA2 subclass concentrations were simultaneously increased but the IgA1 increase was predominant. Secretory IgA (SIgA) concentration was significantly increased and IgA activity to gliadin, bovine serum albumin, and casein could be detected and was correlated with SIgA concentration. In contrast, IgA activity to cytomegalovirus and to tetanus toxoid did not correlate with total IgA concentration. These data suggest the presence of IgA from gut mucosal origin in the serum of these patients. Hyper IgA was inversely correlated with the CD4+ cell number. The increase of all parameters studied varied according to the total IgA concentration in the serum but was also directly related to the stage of immune deficiency in patients with hyper IgA.

Molecular heterogeneity of human IgA antibodies during an immune response

Human IgA occurs in multiple molecular forms (polymeric and monomeric) and two subclasses which show differential distribution between the mucosal and circulatory compartments of the immune system. However, the molecular form and subclass of specific IgA antibodies are influenced, especially during an immune response, by the type of antigen and duration of the response as well as by the route of exposure. These considerations question previously held notions that polymeric IgA and an increased representation of the IgA2 subclass among circulating antibodies or antibody-secreting cells signify their mucosal origin. Although the functional properties of different molecular forms and subclasses of IgA antibodies are incompletely understood, it appears that there is physiological benefit in the diversity of the IgA immune system.

Immunohistochemical evidence for IgA1 involvement in Graves ophthalmopathy

Orbital muscle, adipose tissues, and periorbital muscle from 11 patients with Graves ophthalmopathy were studied with in situ assays using monoclonal antibodies for IgA1, IgA2, IgM, and IgG. Tissue biopsies were taken from varied extraocular muscles and orbital sites. All cases were from patients with severe disease or disease of long duration. Control specimens of extraocular muscle tissues were obtained from nine patients treated for unrelated orbital disorders. Only connective tissue associated with the extraorbital muscles and periorbital muscles showed any reactivity. Of the muscle tissue obtained from patients with Graves disease all exhibited IgA1 positive staining of the endomysium and perimysium, without staining of the muscle fibers themselves. Parallel sections of orbital muscles reacted with anti-IgA2 or anti-IgM antibody failed to demonstrate staining. Control extraocular muscle tissue did not stain with anti-IgM and one control muscle of seven reacted minimally with anti-IgA2. Some reactivity with anti-IgA1 was seen in four of the seven control muscles but this was qualitatively much less than that of muscle tissue from patients with Graves disease. Monoclonal anti-IgG did not stain tissue from the six Graves specimens and three control specimens tested.

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.

Genetic aspects of immunoglobulin A deficiency

IgA deficiency is one of the most common of all immune defects. While it is often not associated with clinical illness, presumably due to compensation from other sectors of the immune system, IgA-deficient individuals are distinctly more likely to become ill and have one or more of specific groups of diseases. While the unifying immunologic perturbation in IgA deficiency is a lack of mature IgA-secreting B cells, a host of other, usually minor, immunologic abnormalities have been reported in such patients. IgA deficiency can be inherited in an autosomal dominant or autosomal recessive fashion, but most individuals who are IgA deficient have no other affected family members. From a genetic point of view, IgA deficiency has been associated with three chromosomes, 18, 14, and 6. Many IgA-deficient individuals who have cytogenically detectable abnormalities of chromosome 18 have been reported, but all the individuals with these defects have severe congenital defects of other kinds. Obscuring the relationship between chromosome 18 and IgA deficiency is the fact that both short- and long-arm deletions have been reported in IgA deficiency. The chromosome deletions in the individuals who are IgA deficient thus appear to have no common pattern. While a rare individual can be IgA1 deficient on the basis of heavy-chain deletions of alpha 1 genes in concert with other heavy-chain genes on chromosome 14, such individuals are quite rare, and from a clinical point of view, those reported have usually been healthy. Absence of both IgA1 and IgA2 genes (presumably in concert with other heavy-chain genes) has never been reported. For chromosome 6, a more complex puzzle emerges. IgA-deficient individuals have been reported to have one of a few specific HLA haplotypes. While many individuals with these supratypes are not IgA deficient, these findings encourage the notion that the secretion of IgA could be at least partly controlled by genes residing in the major histocompatibility locus.

Mucosal IgA elaboration

Secretory IgA is the main immunoglobulin present along mucosal surfaces. It is elicited best by oral rather than parenteral administration of specific antigens. The role of antigen form on the development of a secretory IgA response is still unclear. IgA protects by preventing attachment of microorganisms or their toxic products to the surface epithelium. A wide variety of regulatory T cells are now known to be of considerable importance in optimizing the secretory IgA response. This regulation is at least partly due to the elaboration of small polypeptide products (lymphokines). These lymphokines have been shown to be key signals during the maturation of IgA precursor B cells to IgA-secreting plasma cells. By studying models of the mucosal immune system which closely approximate the natural mucosal immune response, it should be possible to develop vaccines against many pathogenic microorganisms, their toxic products, and to toxicants and carcinogens within the environment.

IgA deficiency in shar-pei dogs

Two shar-pei puppies examined because of signs of sinopulmonary disease, one of which also had skin disease, had deficient IgA concentrations. Deficient serum IgA concentrations also were confirmed in 30 of 39 (76.9%) clinically normal adult dogs in two colonies of shar-peis. Both courses of disease--sinopulmonary signs and chronic skin disease and a benign clinical course--have been reported in human patients with IgA deficiency. Thus, the shar-pei might be an appropriate model for studying the immunopathology of IgA deficiency in man.

Anti-IgA antibodies in pregnancy

A survey of 28,000 pregnant women revealed an incidence of IgA deficiency (serum IgA less than 1 mg per deciliter) of 1 in 450, which is identical to that in a normal blood-donor population of both sexes. Using an enzyme-linked immunosorbent assay (ELISA) in a study of 61 serum samples from IgA-deficient pregnant women, we observed antibodies to IgA2 alone in 20 per cent, as compared with 7.5 per cent of pregnant women not deficient in IgA and no IgA-deficient blood donors. Antibodies reacting with IgA1 alone were present in occasional serum samples (2 to 7 per cent) from all groups studied, and class-specific anti-IgA antibodies were present in 17 per cent of IgA-deficient blood donors and in 16 per cent of IgA-deficient pregnant women. Blocking experiments showed that some serum samples contained an antibody that reacted with both IgA1 and IgA2, whereas others contained two antibodies, one reacting with IgA1 and the other with IgA2. The anti-IgA2 antibodies tended to diminish in titer after delivery. The ELISA was, as expected, more sensitive than the hemagglutination assay. The offspring of IgA-deficient mothers (but not of IgA-deficient fathers) had levels of serum IgA below the normal mean (21 of 27); 12 had levels more than 1 S.D., and seven had levels more than 2 S.D., below the normal mean. Of the seven infants with serum IgA levels more than 2 S.D. below the normal age-related mean, five had mothers with anti-IgA antibodies during gestation. It is possible that maternal anti-IgA exerts a transplacental effect on the fetal immune system, causing IgA deficiency in some instances.

Subclass distribution and molecular form of immunoglobulin A hemagglutinin antibodies in sera and nasal secretions after experimental secondary infection with influenza A virus in humans

Serum and nasal wash specimens from 13 human volunteers undergoing experimental secondary infection with influenza A/Peking/2/79 (H3N2) wild-type virus were examined for the molecular form and subclass distribution of immunoglobulin A (IgA) antibodies to the viral hemagglutinin (HA). Nasal IgA antibodies were polymeric and did not bind radiolabeled secretory component, indicating that they were secretory IgA antibodies. Both IgA1 and IgA2 antibodies were detected; however, IgA1 accounted for most of the rise in IgA anti-HA levels seen after infection. In serum virtually all of the IgA HA antibodies were of the IgA1 subclass. Furthermore, the serum antibodies were predominantly polymeric and were capable of binding radiolabeled secretory component. These results suggested that the serum IgA antibodies to HA were of mucosal origin and that influenza A virus HA preferentially stimulates an IgA1 response.