Immunological studies in two children of a mother with IgA deficiency and anti-IgA antibodies

Genetic linkage of IgA deficiency to the major histocompatibility complex: evidence for allele segregation distortion, parent-of-origin penetrance differences, and the role of anti-IgA antibodies in disease predisposition

Immunoglobulin A (IgA) deficiency (IgAD) is characterized by a defect of terminal lymphocyte differentiation, leading to a lack of IgA in serum and mucosal secretions. Familial clustering, variable population prevalence in different ethnic groups, and a predominant inheritance pattern suggest a strong genetic predisposition to IgAD. The genetic susceptibility to IgAD is shared with a less prevalent, but more profound, defect called "common variable immunodeficiency" (CVID). Here we show an increased allele sharing at 6p21 in affected members of 83 multiplex IgAD/CVID pedigrees and demonstrate, using transmission/diseqilibrium tests, family-based associations indicating the presence of a predisposing locus, designated "IGAD1," in the proximal part of the major histocompatibility complex (MHC). The recurrence risk of IgAD was found to depend on the sex of parents transmitting the defect: affected mothers were more likely to produce offspring with IgAD than were affected fathers. Carrier mothers but not carrier fathers transmitted IGAD1 alleles more frequently to the affected offspring than would be expected under random segregation. The differential parent-of-origin penetrance is proposed to reflect a maternal effect mediated by the production of anti-IgA antibodies tentatively linked to IGAD1. This is supported by higher frequency of anti-IgA-positive females transmitting the disorder to children, in comparison with female IgAD nontransmitters, and by linkage data in the former group. Such pathogenic mechanisms may be shared by other MHC-linked complex traits associated with the production of specific autoantibodies, parental effects, and a particular MHC haplotype.

Clinical manifestations in selective IgA deficiency in childhood. A follow-up report

Clinical manifestations in 40 children with selective IgA deficiency were studied during a follow-up period of 2-10 years. The patients were divided into two groups: group I consisted of 25 children with "sporadic" IgA deficiency and group II of 15 children with "familial" IgA deficiency. Respiratory tract infections including otitis media were frequent in both groups. Concomitant IgG2-IgG4 deficiency was found in two patients in group I. Longitudinal serum IgG levels were elevated significantly in both groups. Atopic complaints were observed in 10 children of the "sporadic" group, but only in two of the "familial" group. However, elevated serum IgE levels were more often found in group II. Two children of group I were mentally retarded and chromosomal examination showed abnormalities in both. Anti-IgA antibodies were detected in one child in group I and three children in group II. These three patients had an IgA deficient mother with class-specific anti-IgA antibodies. Concomitant IgG4-IgE deficiency was found in all four.

Familial selective IgA deficiency with circulating anti-IgA antibodies: a distinct group of patients?

Two families were investigated in which the mothers had selective IgA deficiency and circulating class-specific anti-IgA antibodies. Both gave birth to two children who were found to be IgA deficient. Three of these children developed anti-IgA antibodies before puberty. In vitro immunoglobulin production studies performed in the children of both families revealed an IgA B cell defect combined with IgA-specific excessive T suppressor function in all four. The mechanisms by which transplacental passage of maternal anti-IgA antibodies could have interfered with the developing IgA system in the offspring are discussed.

Anti-IgA antibodies in IgA-deficient children

IgG and IgM isotype antibodies to polyclonal human IgA, myeloma IgA1, and myeloma IgA2 were estimated in 38 IgA-deficient children aged between 0.9 and 15 years. All children had IgM anti-IgA antibodies. IgG antibodies against either polyclonal IgA, IgA1, or IgA2 were present in 63% of the IgA-deficient children. IgG anti-IgA antibodies were detected against all three antigens in 8 of 11 severely IgA-deficient children and in 7 of 27 partially IgA-deficient children, but in only 1 of 23 healthy adult controls. The proportion of children with IgG anti-IgA antibodies was significantly greater in the severely IgA-deficient group in comparison with the partially IgA-deficient group and the adult controls (chi-square test, P less than 0.01 and P less than 0.005, respectively). There was a strong correlation within each IgG subclass between antibody responses toward each of the three IgA antigens. Twenty-four children were followed over a period ranging from 0.9 to 11 years (mean, 2.3 years). Three children who were initially IgG anti-IgA antibody negative became antibody positive and three who were antibody positive became antibody negative. Five children with severe IgA deficiency remained severely IgA deficient and IgG antibodies to IgA persisted in all five at follow-up. The presence of IgG anti-IgA antibodies did not influence the normalization of serum IgA at follow-up in 14 of 19 children who were initially partially IgA deficient.

[Immunoglobulin A and its significance for mucosa immunity--a contribution to the understanding of microbial interactions]

The secretory immunoglobulin A is still dominating with regard to knowledges and further investigations of the causes of mucosal immunity. Origin, formation, structure and mode of action of s-IgA are extensively explored. In the clinical range results of researches on symptoms and consequences of selective IgA deficiency are gaining importance, increasingly. Patients with IgA defect suffer up to 40 times more frequently from allergies and autoimmunopathies. In the induction of the immune response cellular components of mucosa immunity attaining the Lamina propria and the epithelium with the effector cells of Peyer's patches play a particular role.

Selective IgA deficiency in Japanese blood donors: frequency and statistical analysis

The incidence of selective IgA deficiency (SIgAD) was determined in a healthy adult population of 222,597 Japanese volunteer blood donors. Of the blood donors screened, only 0.007% (1:14,840) were found to be IgA-deficient (less than 10 mg/dl) by means of the double diffusion method, while 0.005% (1:18,500) were less than 5 mg/dl, and 0.003% (1:31,800) were less than 1 mg/dl by means of the single radial immunodiffusion method. Statistical analysis of the results clearly showed that the incidence of SIgAD in Japanese blood donors is very much lower than that in blood donors of European ancestry. The Japanese population may occupy a unique position in the ethnical peculiarities. Anti-IgA antibodies were found in 3 (25.0%) of 12 IgA-deficient blood donors whose IgA levels were less than 5 mg/dl, a prevalence rate comparable to that in donors of European ancestry. Although it is difficult to develop a suitable file of IgA-deficient donors in Japan, the establishment of a Rare Donor Registry System on IgA deficiency is a matter of urgency.

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.

Anti-IgA in selective IgA deficiency. In vitro effects and Ig subclass pattern of human anti-IgA

Anti-IgA antibodies were found in 14 of 33 (42%) IgA-deficient donors. In healthy IgA-deficient blood donors anti-IgA appeared associated with the presence of HLA DR3. The antibodies were mainly of the IgG1 and, in high-titred sera, IgG4 subclasses. Sera containing high-titred anti-IgA selectively impaired IgA synthesis in vitro as induced by direct and indirect polyclonal B-cell activators. These antibodies may play a role in the pathogenesis and/or the maintenance of IgA deficiency.

Allotypic and isotypic aspects of human immunoglobulin A

The location of isotypic, isoallotypic and allotypic determinants is reviewed in the light of data obtained when specific antisera are tested with proteolytic fragments of IgA molecules or mutants of IgA obtained from patients with alpha-heavy chain disease. Isotypic determinants are distributed throughout the alpha chain constant regions although when intact IgA proteins are used as immunogens the CH3 domain is immunodominant. Alpha 1 subclass specific isotypic determinants are present in both Fab and Fc fragments. Amino acid sequence analysis suggest that alpha 1 subclass isotypic determinants depend on substitution in the CH1, hinge and/or CH2 domain. The isoallotypic determinants nA2m(2) appears to be located on the CH1 domain and appears to require disulphide-linked alpha chains for its expression. The allotypic determinant A2m(2) appears to be located in the CH3 domain involving residues 428, 458 and/or 467. The latter residues are present in both A2m(1) and A1 proteins which indicates that for A2m(1) to be the antithetical determinant of A2m(2), the determinant formed by residues 428, 458 and/or 467 in these proteins must be influenced by subclass differences which allows its expression in A2m(1) proteins and not in A1 proteins.