IgA and IgA diphtheria antitoxin responses from human tonsil lymphocytes.

Human tonsil lymphocytes were stimulated with diphtheria toxoid and then cultured in a Marbrook culture system so that antibodies could be measured in the culture supernatant. Specific antibodies were measured with excess radiolabeled antigen and antisera specific for each immunoglobulin class. Good IgG and IgA diphtheria antitoxin responses have been obtained and responding culture supernatants were shown to neutralize toxin. The relationship between antitoxin response in vitro and immunization of donors with toxoid was investigated. It was found that at least two immunizations after the age of 6 months were necessary to prime the tonsils for an in vitro antibody response. The IgG and IgA in culture supernatants were demonstrated by immunodiffusion and were measured by radioimmunoassay. By sucrose density gradient ultracentrifugation, it was shown that 40% of the IgA produced in the cultures was greater than 7S. Evidence was obtained that neither the IgA nor the specific IgA antitoxin bears secretory piece. It appears that human lymphocytes from tonsils produce polymer IgA in vitro without secretory piece.     

Lymphadenopathy and selective IgA deficiency.

Four men presented with unexplained lymphadenopathy. Three had a history of recurrent respiratory infections for several years, and two had lymph node or hepatic granulomas. None was noted to have symptoms of immunodeficiency at the time of presentation. In one patient routine direct immunofluorescence study failed to detect IgA, and immunological investigations were therefore conducted in the rest. In all patients the findings were similar and characterised by a severe deficiency of IgA. In the absence of a more serious cause selective IgA deficiency may be enough to explain "idiopathic" lymphadenopathy.     

Regionalization in hereditary IgA nephropathy.

The genealogies of 80 patients with IgA nephropathy who were born in central or eastern Kentucky or whose parents were born in this region were researched. At a minimum, 48 of these patients were related to at least one other patient. On the basis of presence or absence of established kinships, the patients were divided into three groups. Twenty-nine patients in group 1 belonged to one large pedigree. Their birthplaces and those of their parents, grandparents, and great-grandparents clustered in the extreme eastern portion of the state. Seventeen other patients, group 2, were related to at least one other patient but not to a patient in group 1. Their birthplaces and those of their ancestors did not show significant clustering. With the exception of two siblings, the 34 patients of group 3 had no family members with IgA nephropathy. The birthplaces for these patients and ancestors were widely scattered. These data suggest that one or more genetically determined factors are important in the pathogenesis of IgA nephropathy in some patients. A founder effect, whereby a gene(s) conveying susceptibility to IgA nephropathy was carried into eastern Kentucky by one or more of the early settlers, would explain the geographic clustering of the birthplaces of the patients in group 1 and their ancestors. The characteristic immunopathology of IgA nephropathy may represent the histologic result of separate disease processes, one or more of which could be genetically influenced.     

IgA anti-dextran B1355 responses.

Injection of mice bearing the Ig-1a allotype with dextran B1355 results in an IgM antibody response that is generally regarded as thymus independent. Moreover, the antibody is directed to alpha[1,3] determinants on dextran B1355 and shares cross-reacting idiotypic determinants with a lambda 1 IgA (J558) myeloma protein as well as a lambda 1 IgM (MOPC 104E) myeloma protein. In this study, we show that BALB/c (Ig-1a) mice injected with dextran B1355 produced highly significant IgA anti-dextran responses with specificity directed to the alpha[1,3] epitope. Kinetics of the IgA anti-dextran response in BALB/c mice paralleled kinetics of the IgM response. However, the magnitude of the IgA response was markedly T cell dependent and age dependent.     

In vitro regulation of IgA subclass synthesis. II. The source of IgA2 plasma cells

In vitro regulation of IgA subclass synthesis was investigated in pokeweed mitogen (PWM)-stimulated cultures of peripheral blood lymphocytes. In past experiments we have demonstrated that 50% of the IgA plasma cells derived from PWM-stimulated cultures are positive for IgA1 and 50% are positive for IgA2. This observation is surprising because approximately 80% of the IgA B cells in the peripheral circulation bear IgA1 and 20% bear IgA2. To determine if the shift toward IgA2 predominance in PWM-stimulated cultures might be due to an enriched source for IgA2 plasma cells from a precursor pool of immature B cells, we used panning techniques to separate immature precursors that express surface IgM (sIgM+) from mature precursors that no longer express IgM (sIgM-). These separated B cells were cultured with equal numbers of T cells and PWM for 7 days. In all 10 experiments there was an enrichment for IgA2 in the sIgM+ cultures; 55 +/- 9.6% of the total IgA plasma cells were positive for IgA2 in the sIgM+ cultures vs 38 +/- 6.3% in the sIgM- cultures (p less than 0.001). These results indicate that both sIgM+ and sIgM- cells can give rise to IgA plasma cells in PWM-stimulated cultures and that there is an enrichment for IgA2 precursors in the sIgM+ population. Other possible regulatory mechanisms were also investigated. To determine if there was isotype switching from IgA1 to IgA2, monoclonal anti-IgA1 antibodies were added to PWM cultures. These antibodies resulted in a mean suppression of IgA1 plasma cell production of 82% with a concomitant 45% suppression of total IgA but only 4.6% suppression of IgA2. These results make it unlikely that IgA2 plasma cells in PWM-stimulated cultures are derived from cells that initially produced IgA1. To investigate the possibility that one IgA subclass might be more T cell dependent than the other, T and B cells were separated and B cells were reconstituted with T cells in ratios that varied from 1:10 to 10:1 or with irradiated T cells. These procedures did not alter the proportion of IgA plasma cells positive for IgA1 or IgA2, indicating that the two subclasses do not differ in their response to T cell signals in PWM-stimulated cultures.     

The wasted mutant mouse. I. An animal model of secretory IgA deficiency with normal serum IgA

The wasted (wst) mutation was recently described as a spontaneous, recessive mutation leading to pathologic changes affecting both the neurologic and the immune systems of wst/wst homozygotes, which presented symptoms analogous to those observed in patients with ataxia-telangiectasia (A.T.). We studied the IgA system of wst/wst mutants and their normal littermates to determine whether IgA deficiency commonly found in A.T. patients was also affecting these mutants. Interestingly, although IgA plasma cells were totally absent from their entire (small and large) intestine, their serum contained a normal level of IgA with a normal ratio of monomeric vs polymeric IgA. The absence of gut IgA plasma cells was not due to malnutrition and was not compensated by the appearance of cells secreting any other isotypes. Studies at the precursor cell level showed the absence of IgA-specific B cell precursors in the Peyer's patches, whereas sIgA B cells and IgA plasma cells were found in normal numbers in the spleen of wasted mice. These data suggest that secretory and serum IgA may comprise distinct systems and that the wasted mutant mouse is a potential model for the study of the physiology and regulation of IgA production.     

Isolated glomerulonephritis with mesangial IgA deposits.

Mesangial deposits of IgA, occurring in the absence of systemic disease known to be associated with nephritis, were detected by immunofluorescence microscopy in renal biopsy specimens from 25 patients (4% of 630 specimens studied). Associated deposits of C3 were always present, usually with IgG, but IgM deposits were less common and C1q was never seen. On light microscopy most of the biopsy specimens showed mesangial of focal nuclear proliferation though some were normal. Fifteen of the 25 patients presented with macroscopic haematuria, which was usually recurrent and preceded by a sore throat, whereas the remaining, and usually older, patients presented with persistent proteinuria and were more likely to have impaired renal function. This incidence of "mesangial IgA disease" is less than that reported by French workers. There was a significantly high incidence of familial renal disease among these patients. No abnormalities of serum complement or IgA concentration were found.     

Protein Rou. A human IgA hybrid

Protein Rou is a human IgA2 myeloma protein that carries the isoallotype marker n A2m(2). Partial amino acid sequence of its H chain (alpha) shows that the hinge region and the CH2 domain are homologous to alpha 2-chain and the CH1 and the CH3 domains homologous to alpha 1. Moreover, the CH1 domain contains the H-L disulfide bond identical to alpha 1. It is concluded that Rou H chain is a hybrid molecule caused by a recombination between alpha 1 and alpha 2 genes. The recombination event occurred between alpha 1-exon 1 and alpha 2-exon hinge and corresponds to position 222-223 of the alpha-chain.     

An abnormal human IgA1 half-molecule.

An IgA1 half-molecule, which is composed of a deleted alpha1 chain linked with a disulfide bond to an intact kappa chain, was detected in a patient (Cha). The molecular weights of the paraprotein and the isolated alpha1 chain were estimated to be 75 000 and 53 000, respectively. Identification of tyrosine as the C-terminal amino acid and the presence of idiotypic determinants in the abnormal alpha1 chain indicated that the molecule would have an intact N-terminal variable region and a C-terminal region. Furthermore, no cleavage of the abnormal protein into Fab and Fc by proteolytic enzyme isolated from Neisseria gonorrhoeae suggested the absence of a "hinge" region in the abnormal alpha1 chain.     

Difference in IgA1 O-glycosylation between IgA deposition donors and IgA nephropathy recipients

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis, and disease recurrence often occurs after transplantation. On the other hands, Asymptomatic IgA deposition (IgAD) is occasionally observed in donated kidney. It is recognized that IgAD does not progress to IgAN, but the mechanism has not demonstrated yet. In IgAN, aberrant IgA1 O-glycan structure in the hinge region (HR) of serum IgA is suggested as one of the most convincing key mediators. However, little is known about IgA1 O-glycan structure in IgAD patients. Herein, we investigated the prevalence of IgAD in living renal transplant donors in our cohort. IgAD was observed in 21(13.0%) among 161 renal transplant donors and have statistically significant blood relationship with IgAN recipients (28.6% in relatives vs. 9.8% in non-relatives, respectively; p?=?0.0073). Next, we evaluated the IgA1 O-glycan structure of serum IgA from IgAN recipients (n?=?26), IgAD donors (n?=?17), and non-IgAD helthy donors (n?=?27) using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI–TOF MS). The numbers of GalNAc and Gal and the Gal/GalNAc ratio in the HR of the IgAN recipients had significantly lower comparing to the IgAD and non-IgAD healthy donors. The decreased Gal/GalNAc ratio in IgAN recipients means the increased ratio of galactose-deficient IgA1. To the best of our knowledge, this is the first report to compare the O-glycan structures in IgAN recipients and IgAD donors using MALDI–TOF MS. We concluded that IgAD was more common in IgAN related donors. Overall, decreased GalNAc and Gal contents in HR could play a material pathogenic role in IgAN.     

In vitro regulation of IgA subclass production. III. Selective transformation of IgA1 producing cells by Epstein-Barr virus

In past experiments, using limited dilution analysis, we have demonstrated that a high percentage of immunoglobulin-secreting clones derived from Epstein-Barr virus- (EBV) stimulated lymphocytes secrete IgA. To further characterize the IgA produced by these clones, the IgA subclass of supernatants from clones stimulated 4 to 6 wk previously with EBV was determined by radioimmunoassay. All of 17 IgA-producing clones secreted IgA1; none secreted IgA2. Because we have shown that surface IgM+ (sIgM+) B cells are an enriched source of IgA2 plasma cell precursors, panning techniques were used to purify sIgM+ B cells from tonsils. Of 103 clones derived from these sIgM+ B cells, 102 secreted IgA1 and only one secreted IgA2. The relative absence of IgA2-producing clones could not be attributed to an absence of EBV receptors on IgA2 cells. A mean of 84 +/- 4% of freshly isolated IgA2 B cells and 78 +/- 6% of IgA1 B cells could be stained with a monoclonal antibody binding the EBV receptor; and there was no failure of EBV to infect IgA2 plasma cells precursors. Of IgA2 plasma cells derived from peripheral blood lymphocytes stimulated 7 days previously with EBV, 54 +/- 7% were positive for the EBV nuclear antigen, compared with 54 +/- 18% of IgA1 plasma cells from the same cultures. Seven days after EBV stimulation, a mean of 25% of the total IgA plasma cells were positive for cytoplasmic IgA2, whereas by 21 days after stimulation only 7% were positive for IgA2. This shift in the proportions of IgA1 and IgA2 plasma cells could be attributed to a failure of the IgA2 plasma cell number to increase after 10 days in culture. There was no evidence for selective suppression of IgA2 production by T cells or selective lysis of IgA2 plasma cells by infectious EBV particles. These results demonstrate that although precursors for both IgA1- and IgA2-producing cells can be stimulated to differentiate in response to EBV, there is preferential transformation of IgA1-producing cells.