The immunoglobulin alpha (Ig-alpha)-Ig-beta heterodimer is the signaling component of the antigen receptor complex on B cells (BCR) and B cell progenitors (pre-BCR). A mouse mutant that lacks most of the Ig-alpha cytoplasmic tail exhibits only a small impairment in early B cell development but a severe block in the generation of the peripheral B cell pool, revealing a checkpoint in B cell maturation that ensures the expression of a functional BCR on mature B cells. B cells that do develop demonstrate a differential dependence on Ig-alpha signaling in antibody responses such that a signaling-competent Ig-alpha appears to be critical for the response to T-independent, but not T-dependent, antigens.

Nucleotide sequences of the human alpha 1 and two allelic alpha 2 immunoglobulin heavy chain constant region genes are presented. The genes contain three exons, each encoding a single constant region protein domain. The protein hinge region is encoded at the 5' end of the second exon, and the rapid evolutionary changes in length of the hinge correspond to duplications or deletions within the hinge-coding region, probably facilitated by repeats in the DNA sequence. Alignment of the alpha 1 and alpha 2 gene sequences reveals an unusual coupled deletion-duplication in the 5'-flanking region, which can be explained in terms of a slipped-strand mispairing model. Comparison of nucleotide sequences of the alpha 1 gene and two alleles of the alpha 2 gene indicates a localized transfer of genetic information from the 3' end of the alpha 1 gene to one of the alpha 2 alleles, probably by a gene conversion. At one end of the region within which conversion apparently occurred, there is a 40 bp sequence of the type that can form Z-DNA.

In order study patterns of local antibody responses following mucosal immunization of mice via different routes, a method for collection of secretions directly from mucosal surfaces was developed. Mice were immunized on days 0, 10, 17, and 24 by administration of cholera toxin into the oral cavity, stomach, colon-rectum, or vagina. At sacrifice on day 32, absorbent wicks were placed in the oral cavity and, via an applicator tube, into the vagina and distal colon-rectum and along the entire small intestine after flushing of luminal contents. Protein was quantitatively extracted from wicks, and specific anti-cholera toxin immunoglobulin A (IgA) and IgG were measured by enzyme-linked immunosorbent assay. Concentrations of specific IgA in secretions at various mucosal sites were dramatically influenced by the route of immunization. Oral immunization effectively induced IgA in saliva, and the intragastric route was optimal for induction of IgA in the small intestine. High levels of specific IgA appeared on the colonic-rectal mucosal surface only after rectal delivery of antigen. Oral, gastric, and rectal immunizations also produced distant responses in the vagina. Following vaginal immunization, however, neither local nor distant IgA responses were detected. These results suggest that vaccines intended for protection of colonic-rectal and vaginal mucosal surfaces might best be administered by the rectal route.

We have used a 175-nucleotide-long primer extension product corresponding to the 5' end of HLA-DR alpha-chain mRNA to isolate a genomic clone from a human DNA library. The entire HLA-DR alpha gene is contained in two contiguous EcoRI fragments spanning about 7.5 kilobases (kb); most of the sequence has been determined. The 5' end of the gene is contained in a 4.4-kb fragment, and the coding segments and the 3' untranslated region are contained in a 3.1-kb fragment. The gene is split into five exons. The 5' untranslated region, the leader peptide, and the first two NH2-terminal amino acids are fused into the first exon. Exons 2 and 3 represent two extracellular coding domains of mature p34. The transmembrane domain, cytoplasmic domain, and part of the 3' untranslated region are merged into a fourth exon. The rest of the 3' untranslated region is in exon 5. The predicted amino acid sequence of mature p34, as deduced from its gene structure, has 229 residues and reveals a single potential disulfide loop (between cysteine residues 107 and 163) as well as a 22-amino acid residue membrane integrated segment (residues 193-214). Fifteen amino acids (residues 215-229) reside on the cytoplasmic side of the plasma membrane. There is considerable amino acid sequence homology between the second external domains of p34 and p29, as well as the immunoglobulin-like third domain of HLA-B7, and beta 2-microglobulin and the homologous constant region domains of the light and heavy chains of immunoglobulins.

OBJECTIVE

To develop and validate a dual-targeted ultrasonographic (US) imaging agent with microbubbles (MBs) that attaches to both vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and alpha(v)beta(3) integrin and to compare the US imaging signal obtained from dual-targeted MBs (MB(D)) with that from single-targeted MBs (MB(S)) in a murine model of tumor angiogenesis.

METHODS

Animal protocols were approved by the institutional Administrative Panel on Laboratory Animal Care. Single- and dual-targeted US imaging agents were prepared by attaching anti-VEGFR2, anti-alpha(v)beta(3) integrin, or both antibodies to the shell of perfluorocarbon-filled MBs. Binding specificities of targeted MBs compared with isotype-matched immunoglobulin G-labeled control MBs (MB(C)) and nontargeted nonlabeled MBs (MB(N)) were tested with VEGFR2-positive and alpha(v)beta(3) integrin-positive cells (mouse SVR cells) and control cells (mouse 4T1 cells). In vivo imaging signals of contrast material-enhanced US by using anti-VEGFR2-targeted MBs (MB(V)), anti-alpha(v)beta(3) integrin-targeted MBs (MB(I)), MB(D), and MB(C) were quantified in 49 mice bearing SK-OV-3 tumors (human ovarian cancer). Tumor tissue was stained for VEGFR2, alpha(v)beta(3) integrin, and CD31.

RESULTS

Attachment of MB(D) to SVR cells (mean, 0.74 MBs per cell +/- 0.05 [standard deviation]) was significantly higher than attachment to 4T1 cells (mean, 0.04 +/- 0.03), and attachment to SVR cells was higher for MB(D) than for MB(V) (mean, 0.58 +/- 0.09), MB(I) (mean, 0.42 +/- 0.21), MB(C) (mean, 0.11 +/- 0.13), and MB(N) (mean, 0.01 +/- 0.01) (P < .05). Imaging signal in the murine tumor angiogenesis model was significantly higher (P < .001) for MB(D) (mean, 16.7 +/- 7.2) than for MB(V) (mean, 11.3 +/- 5.7), MB(I) (mean, 7.8 +/- 5.3), MB(C) (mean, 2.8 +/- 0.9), and MB(N) (mean, 1.1 +/- 0.4). Immunofluorescence confirmed expression of VEGFR2 and alpha(v)beta(3) integrin on tumor vasculature.

CONCLUSIONS

Dual-targeted contrast-enhanced US directed at both VEGFR2 and alpha(v)beta(3) integrin improves in vivo visualization of tumor angiogenesis in a human ovarian cancer xenograft tumor model in mice.

BACKGROUND

http://radiology.rsnajnls.org/cgi/content/full/248/3/936/DC1.

Forty-five volunteers were vaccinated twice intranasally with 10, 100, or 1,000 microg of cholera toxin B subunit (CTB). Blood and nasal and vaginal secretions were collected before and 1 week after the second vaccination from all volunteers, and the specific and total immunoglobulin A (IgA) and IgG titers were determined by enzyme-linked immunosorbent assay. Samples were also taken 6 months (n = 16) and 1 year (n = 14) after the vaccination. The 10- and 100-microg doses were well tolerated by the volunteers, but the 1,000-microg dose induced increased secretions from the nose and repetitive sneezings for several hours. The CTB-specific serum IgA and IgG increased 21- and 7-fold, respectively, 1 week after vaccination with the medium dose and increased 61- and 37-fold, respectively, after the high dose. In nasal secretions the specific IgA and IgG increased 2- and 6-fold after the medium dose and 2- and 20-fold after the high dose, respectively. In vaginal secretions the specific IgA and IgG increased 3- and 5-fold after the medium dose and 56- and 74-fold after the high dose, respectively. The lowest dose did not induce any significant antibody titer increases in serum or in secretions. The specific IgA and IgG levels in secretions were still elevated after 6 months but were decreasing 1 year after the vaccination. These results show that intranasal vaccination of humans with CTB induces strong systemic and mucosal antibody responses and suggest that CTB may be used as a carrier for antigens that induce protective immunity against systemic as well as respiratory and genital infections.

Trifluoroethanol (TFE) is known to stabilize the alpha-helical structure in proteins and their fragments. However, the relationship between the TFE-induced structures and the native structure is not clear. Here we show that beta-lactoglobulin, which consists predominantly of beta-sheets, exhibited a markedly high propensity to form an alpha-helical structure in the presence of TFE, as measured by far-UV circular dichroism. A cooperative transformation from the beta-sheet structure to an alpha-helical structure occurred at a TFE concentration between 10% and 20%. These results were in contrast to a gradual beta-sheet to alpha-helix transition of the constant fragment of the immunoglobulin light chain, which is also a beta-sheet protein. To understand the significance of the high helical propensity of beta-lactoglobulin, we measured the TFE-induced conformational transition of more than 20 proteins of various secondary structural types. Whereas the alpha-helical proteins showed a propensity to form an extensive helical structure in TFE, the helical propensity of proteins with a low helical content in the native state varied. The helical content in TFE was correlated more with the helical content predicted by a secondary structure prediction than with the helical content of the native structure, suggesting that the stability of the helical structure in TFE is determined by local interactions between nearby amino acid residues. Our results suggest that an alpha-helical intermediate can accumulate during the refolding process of beta-lactoglobulin and that a hierarchical model of protein folding is not necessarily true for some beta-sheet proteins including beta-lactoglobulin.

Ingestion of capsules which contained killed Streptococcus mutans by four healthy human subjects led to the appearance of specific antibodies in external secretions. Salivary and lacrymal antibodies were detected within 1 wk of ingestion and continued to increase throughout a 14-day immunization period, with a gradual decline during the 2 ensuing months. A second period of immunization resulted in a pronounced increase of specific antibody levels which occurred earlier than in the primary immunization period and reached peak levels by day 10. No change was detected in serum antibody levels throughout either immunization period. The antibody activity in all secretions was associated with the immunoglobulin A class, as determined by immunochemical analyses. These data indicate that ingestion of bacterial antigens selectively stimulates the immune response in secretions.

BACKGROUND

Serologic measurement of antibodies to Epstein-Barr virus (EBV) immunoglobulin A/viral capsid antigen (IgA/VCA) and early antigen (IgA/EA) has been used widely to screen for nasopharyngeal carcinoma (NPC) in China. Recently, it was found that plasma EBV DNA concentration is an indicator for the staging and prognosis of patients with NPC. To determine whether there is a correlation between plasma EBV DNA levels and serum levels of IgA/VCA, the authors measured both in patients with NPC and in a control group.

METHODS

Real-time polymerase chain reaction was used for quantitative analysis of plasma EBV DNA concentration, and enzyme-linked immunoadsorbent assay was used to measure EBV VCA/IgA in patients with primary NPC (n = 120 patients), locally recurrent NPC (n = 8 patients), and distant metastatic NPC (n = 21 patients) among 76 patients with NPC after the completion of radiotherapy, in 60 patients with NPC in clinical remission, in 38 patients with non-NPC tumors, and in 47 control individuals.

RESULTS

The median plasma EBV DNA levels were 6200 copies/mL, 9200 copies/mL, and 2050 copies/mL in patients with primary, locally recurrent, and distant metastatic NPC, respectively, but declined to 0 copies/mL in patients with clinically remissive NPC, in patients who completed radiotherapy, in patients with non-NPC tumors, and in the control group. In contrast, EBV VCA/IgA titers and detection rates remained high in all NPC groups. Plasma EBV DNA levels were significantly higher in patients who had serum VCA/IgA titers>> or = 1:640 (median, 83,450 copies/mL) compared with the levels in patients who had titers < or = 1:320 (median, 17,200 copies/mL). Patients with NPC who had advanced TNM stage (Stages III and IV; median, 8530 copies/mL) and T classification (T3 and T4 tumors; median, 8530 copies/mL) had significantly higher plasma EBV DNA levels compared with patients who had early TNM stage (Stages I and II; median, 930 copies/mL) and T classification (T1 and T2 tumors; median, 3700 copies). Patients who had advanced TNM stage NPC had significantly higher mean VCA/IgA titers (1:424) compared with patients who had early TNM stage NPC (1:246), but there was no correlation between IgA/VCA titer and T or N classification of NPC.

CONCLUSIONS

The results suggest that plasma EBV DNA detection is a more sensitive and specific marker than the serum IgA/VCA titer for the diagnosis and monitoring of patients with NPC. These findings provide convincing evidence for the use of plasma EBV DNA measurements for the early diagnosis and staging of NPC as well as for monitoring recurrence and metastasis of this tumor.

Saliva contains a large number of proteins that participate in the protection of oral tissue. We found, for the first time, small vesicles (30-130 nm in diameter) in human whole saliva. Vesicles from saliva were identified by electron microscopy after isolation by gel-filtration on Sepharose CL-4B. They resemble exosomes, which are vesicles with an endosome-derived limiting membrane that are secreted by a diverse range of cell types. We performed a biochemical characterization of these vesicles by amino acid sequence analysis and Western blot analysis. We found that they contain dipeptidyl peptidase IV (DPP IV), galectin-3 and immunoglobulin A, which have potential to influence immune response. The DPP IV in the vesicles was metabolically active in cleaving substance P and glucose-dependent insulinotropic polypeptide to release N-terminal dipeptides. Our results demonstrate that human whole saliva contains exosome-like vesicles; they might participate in the catabolism of bioactive peptides and play a regulatory role in local immune defense in the oral cavity.

The developmental origin of type I interferon (IFN)-producing plasmacytoid dendritic cells (PDCs) is controversial. In particular, the rearrangement of immunoglobulin heavy chain (IgH) genes in murine PDCs and the expression of pre-T cell receptor alpha (pTalpha) gene by human PDCs were proposed as evidence for their "lymphoid" origin. Here we demonstrate that PDCs capable of IFN production develop efficiently from both myeloid- and lymphoid-committed progenitors. Rearranged IgH genes as well as RAG transcripts were found in both myeloid- and lymphoid-derived PDCs. The human pTalpha transgenic reporter was activated in both myeloid- and lymphoid-derived PDCs at a level comparable to pre-T cells. PDCs were the only cell population that activated murine RAG1 knockin and human pTalpha transgenic reporters outside the lymphoid lineage. These results highlight a unique developmental program of PDCs that distinguishes them from other cell types including conventional dendritic cells.

Several proteins associate with surface IgM to form the antigen receptor. We show that just two, the alpha and beta associated chains, are sufficient to reconstitute an IgM surface receptor in fibroblasts. Contrary to expectation, a common alpha chain associates with all five immunoglobulin classes. We propose that B-cell antigen receptors consist of a common alpha/beta heterodimer associated with each immunoglobulin class. But the classes differ both in the glycosylation of their associated alpha chain and in their dependence on alpha/beta for surface transport.

Secretory immunoglobulin A (sIgA) plays a role in defense against Vibrio cholerae and other microorganisms that infect mucosal surfaces, but it is not established whether sIgA alone can prevent disease. We report here a strategy for identifying the antigen specificities of monoclonal sIgA antibodies that are capable of providing such protection. IgA hybridomas were generated from Peyer's patch lymphocytes after oral immunization with V. cholerae Ogawa 395. A clone was selected that produced dimeric monoclonal IgA antibodies directed against an Ogawa-specific lipopolysaccharide carbohydrate antigen exposed on the bacterial surface. Hybridoma cells were used to produce subcutaneous "backpack" tumors in syngeneic mice, resulting in secretion of monoclonal sIgA onto mucosal surfaces. Neonatal mice bearing anti-lipopolysaccharide hybridoma backpack tumors were specifically protected against oral challenge with 100 50% lethal doses of virulent Ogawa 395 organisms. Thus, the IgA hybridoma backpack tumor method identifies protective epitopes in the mucosal system and demonstrates that a single monoclonal sIgA can be sufficient to protect against intestinal disease.

Amebiasis is a major cause of morbidity and mortality throughout the tropical world. Entamoeba histolytica is now recognized as a separate species from the morphologically identical E. dispar, which cannot invade. Cysteine proteinases are a key virulence factor of E. histolytica and play a role in intestinal invasion by degrading the extracellular matrix and circumventing the host immune response through cleavage of secretory immunoglobulin A (sIgA), IgG, and activation of complement. Cysteine proteinases are encoded by at least seven genes, several of which are found in E. histolytica but not E. dispar. A number of new animal models, including the formation of liver abscesses in SCID mice and intestinal infection in human intestinal xenografts, have proven useful to confirm the critical role of cysteine proteinases in invasion. Detailed structural analysis of cysteine proteinases should provide further insights into their biochemical function and may facilitate the design of specific inhibitors which could be used as potential chemotherapeutic agents in the future.

In order to discover novel protein markers indicative of disease processes or drug effects, the proteomics technology platform most commonly used consists of high resolution protein separation by two-dimensional electrophoresis (2-DE), mass spectrometric identification of proteins from stained gel spots and a bioinformatic data analysis process supported by statistics. This approach has been more successful in profiling proteins and their disease- or treatment-related quantitative changes in tissue homogenates than in plasma samples. Plasma protein display and quantitation suffer from several disadvantages: very high abundance of a few proteins; high heterogeneity of many proteins resulting in long charge trains; crowding of 2-DE separated protein spots in the molecular mass range between 45-80 kD and in the isoelectric point range between 4.5 and 6. Therefore, proteomic technologies are needed that address these problems and particularly allow accurate quantitation of a larger number of less abundant proteins in plasma and other body fluids. The immunoaffinity-based protein subtraction chromatography (IASC) described here removes multiple proteins present in plasma and serum in high concentrations effectively and reproducibly. Applying IASC as an upfront plasma sample preparation process for 2-DE, the protein spot pattern observed in gels changes dramatically and at least 350 additional lower abundance proteins are visualized. Affinity-purified polyclonal antibodies (pAbs) are the immunoaffinity reagents used to specifically remove the abundant proteins such as albumin, immunoglobulin G, immunoglobulin A, transferrin, haptoglobin, alpha-1-antitrypsin, hemopexin, transthyretin, alpha-2-HS glycoprotein, alpha-1-acid glycoprotein, alpha-2-macroglobulin and fibrinogen from human plasma samples. To render the immunoaffinity subtraction procedure recyclable, the pAbs are immobilized and cross-linked on chromatographic matrices. Antibody-coupled matrices specific for one protein each can be pooled to form mixed-bed IASC columns. We show that up to ten affinity-bound plasma proteins with similar solubility characteristics are eluted from a mixed-bed column in one step. This facilitates automated chromatographic processing of plasma samples in high throughput, which is desirable in proteomic disease marker discovery projects.

The display of repertoires of antibody fragments on the surface of filamentous bacteriophage offers a new way of making antibodies with predefined binding specificities. Here we explored the use of this technology to make immunochemical reagents to a range of antigens by selection from a repertoire of>> 10(8) clones made in vitro from human V gene segments. From the same 'single pot' repertoire, phage were isolated with binding activities to each of 18 antigens, including the intracellular proteins p53, elongation factor EF-1 alpha, immunoglobulin binding protein, rhombotin-2 oncogene protein and sex determining region Y protein. Both phage and scFv fragments secreted from infected bacteria were used as monoclonal and polyclonal reagents in Western blots. Furthermore the monoclonal reagents were used for epitope mapping (a new epitope of p53 was identified) and for staining of cells. This shows that antibody reagents for research can be readily derived from 'single pot' phage display libraries.

Interleukin (IL)-13 has recently been shown to play important and unique roles in asthma, parasite immunity, and tumor recurrence. At least two distinct receptor components, IL-4 receptor (R)<em>alpha</em> and IL-13R<em>alpha</em>1, mediate the diverse actions of IL-13. We have recently described an additional high affinity receptor for IL-13, IL-13R<em>alpha</em>2, whose function in IL-13 signaling is unknown. To better appreciate the functional importance of IL-13R<em>alpha</em>2, mice deficient in IL-13R<em>alpha</em>2 were generated by gene targeting. Serum <em>immunoglobulin</em> E levels were increased in IL-13R<em>alpha</em>2-/- mice despite the fact that serum IL-13 was absent and immune interferon gamma production increased compared with wild-type mice. IL-13R<em>alpha</em>2-deficient mice display increased bone marrow macrophage progenitor frequency and decreased tissue macrophage nitric oxide and IL-12 production in response to lipopolysaccharide. These results are consistent with a phenotype of enhanced IL-13 responsiveness and demonstrate a role for endogenous IL-13 and IL-13R<em>alpha</em>2 in regulating immune responses in wild-type mice.

The detection of a monoclonal immunoglobulin in serum or urine usually raises concerns about the size of the underlying B-cell-derived clone and possible systemic effects caused by its expansion. However, a small clone can synthesize a very toxic protein, producing devastating systemic damage and protean clinical presentations. The resulting "monoclonal component-related diseases," although difficult to diagnose, may be progressive and even fatal. The monoclonal protein can aggregate and deposit systemically as occurs in light-chain amyloidosis, monoclonal immunoglobulin deposition disease, crystal-storing histiocytosis, and monoclonal cryoglobulinemia. Alternatively, some monoclonal proteins possess antibody activity toward autogenous antigens and cause chronic cold agglutinin disease, mixed cryoglobulinemia, and peripheral neuropathies. Other humoral mediators may contribute to neuropathy in variant disorders such as the POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) syndrome. The clone synthesizing the noxious monoclonal proteins is often small, and sensitive techniques may be required to detect these immunoglobulins. A delay in diagnosis can allow irreversible organ damage and dramatically shorten survival. Prompt recognition of suggestive signs and symptoms should trigger a thorough diagnostic approach to reach the correct diagnosis quickly, because this is the key to effective therapy. Although the treatment of these conditions is not optimal, significant advances have been made, improving the duration and quality of life.

Prevention of infections by vaccination remains a compelling goal to improve public health. Mucosal vaccines would make immunization procedures easier, be better suited for mass administration, and most efficiently induce immune exclusion - a term coined for non-inflammatory antibody shielding of internal body surfaces, mediated principally by secretory immunoglobulin A (SIgA). The exported antibodies are polymeric, mainly IgA dimers (pIgA), produced by local plasma cells (PCs) stimulated by antigens that target the mucose. SIgA was early shown to be complexed with an epithelial glycoprotein - the secretory component (SC). A common SC-dependent transport mechanism for pIgA and pentameric IgM was then proposed, implying that membrane SC acts as a receptor, now usually called the polymeric Ig receptor (pIgR). From the basolateral surface, pIg-pIgR complexes are taken up by endocytosis and then extruded into the lumen after apical cleavage of the receptor - bound SC having stabilizing and innate functions in the secretory antibodies. Mice deficient for pIgR show that this is the only receptor responsible for epithelial export of IgA and IgM. These knockout mice show a variety of defects in their mucosal defense and changes in their intestinal microbiota. In the gut, induction of B-cells occurs in gut-associated lymphoid tissue, particularly the Peyer's patches and isolated lymphoid follicles, but also in mesenteric lymph nodes. PC differentiation is accomplished in the lamina propria to which the activated memory/effector B-cells home. The airways also receive such cells from nasopharynx-associated lymphoid tissue but by different homing receptors. This compartmentalization is a challenge for mucosal vaccination, as are the mechanisms used by the mucosal immune system to discriminate between commensal symbionts (mutualism), pathobionts, and overt pathogens (elimination).

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common form of glomerulonephritis, and a substantial number of patients succumb to end-stage renal disease (ESRD). However, prediction of the renal outcome in individual patients remains difficult. We have already published a scoring system using the data in a prospective cohort of IgAN patients followed up from 1995 to 2002.

METHODS

The cohort was further followed up until 2005 in 97 clinical units in Japan. The data from 2283 patients were analysed by Cox regression to determine the predictors of ESRD in IgAN, and their beta-coefficients were converted into scores to estimate ESRD risk within 10 years.

RESULTS

During the follow-up (median, 87 months), 252 patients developed ESRD. Male sex, age less than 30 years, family histories of chronic renal failure and chronic glomerulonephritis, hypertension, proteinuria, mild haematuria, hypoalbuminaemia, low glomerular filtration rate and a high histological grade at initial renal biopsy were associated with the risk of ESRD in the multivariable analysis. A scoring system was framed to estimate the 10-year ESRD risk using eight variables significant in both univariable and multivariable models. This prognostic score accurately classified patients by risk: patients with estimates of 0-4.9, 5.0-19.9, 20.0-49.9 and 50.0-100% had an observed incidence of 1.7, 8.3, 36.7 and 85.5%, respectively. The corresponding area under the receiver-operating characteristic curve was 0.942 (95% confidence interval, 0.925-0.958).

CONCLUSIONS

This validated scoring system to quantitatively estimate ESRD risk during the 10-year follow-up of IgAN patients will serve as a useful prognostic tool in clinical practice.

Although secretory immunoglobulin A (IgA) is important in mucosal immunity. selective IgA deficiency is the most common primary immunodeficiency of humans. In most cases this defect is not associated with any illness. The reasons for this are unknown, but other immunological compensations might provide sufficient or complete restitution. Alternatively, it is possible that IgA deficiency alone may not predispose to disease, but additional immunological abnormalities might be present in symptomatic individuals. Some IgA-deficient individuals have a reduced antibody response to immunizations (even with normal IgG and IgM levels) and others have deficient responses to bacterial polysaccharides when IgG subclass levels are normal. The physiological role of IgA, the frequency and causes of IgA deficiency, the diseases associated with its absence, and current limited understanding of the pathogenesis of selective IgA deficiency will be reviewed.

Chromaffin cells of the adrenal medulla synthesize, store and secrete catecholamines. These cells contain numerous electron-dense secretory granules which discharge their contents into the extracellular space by exocytosis. The subplasmalemmal area of the chromaffin cell is characterized by the presence of a highly organized cytoskeletal network. F-Actin seems to be exclusively localized in this area and together with specific actin-binding proteins forms a dense viscoelastic gel; fodrin, vinculin and caldesmon, three actin cross-linking proteins, and gelsolin, an actin-severing protein, are found in this subplasmalemmal region. Since fodrin-, caldesmon- and alpha-actinin-binding sites exist on secretory granule membranes, actin filaments can also link secretory granules. Chromaffin granules can be entrapped in this subplasmalemmal lattice and thus the cytoskeleton acts as a barrier preventing exocytosis. When cells are stimulated, molecular rearrangements of the subplasmalemmal cytoskeleton take place: F-actin depolymerizes and fodrin reorganizes into patches. In addition, introduction of monospecific antifodrin immunoglobulins into digitonin-permeabilized cells blocks exocytosis, demonstrating the crucial role of this actin-binding protein. In bacterial toxin-permeabilized chromaffin cells, experiments using actin-perturbing agents such as cytochalasin D and DNAase I suggest that exocytosis is in part controlled by the cytoskeleton. The intracellular signal governing the cytoskeletal reorganization (associated with exocytosis) is calcium. Calcium inhibits some and activates other actin-binding proteins and consequently causes dissolution of the subplasmalemmal cytoskeleton. This dissolution of cytoskeletal filaments should result in granule detachment and permit granules free access to exocytotic sites on the plasma membrane.

Ingestion of killed cells of a highly cariogenic strain of Streptococcus mutans induced specific antibodies in both saliva and milk but not in serum of gnotobiotic rats. These antibodies were associated with the immunoglobulin A class. When infected with Streptococcus mutans, orally immunized animals developed significantly fewer carious lesions than nonimmunized infected controls.

BACKGROUND

Selective immunoglobulin A (IgA) deficiency (SIgAD) is associated with coeliac disease (CD).

OBJECTIVE

To make a retrospective study of the association of SIgAD with CD in Italy.

METHODS

Hospital medical records of 2098 patients consecutively diagnosed as having CD were reviewed.

RESULTS

Of 2098 patients with CD, 54 (2.6%) had SIgAD, representing a 10-16-fold increase over that in the population in general. This increase was not influenced by age or geographical factors. Patients with SIgAD had a higher incidence of silent forms (7/54, 13%), recurrent infections (16/54, 29.6%), and atopic diseases (7/54, 13%) than those without. The association with autoimmune and malignant diseases and the outcome after eating a gluten free diet were similar in patients with or without SIgAD. In all patients with SIgAD, antibodies for IgA gliadin and endomysium were absent, but serum levels of IgG anti-gliadin antibodies were high in almost all of them (51/54).

CONCLUSIONS

Serum IgA should be measured in order to be able to interpret negative results for IgA anti-gliadin antibodies and anti-endomysial antibodies in patients being screened for CD. Since some patients with CD and SIgAD may be negative for IgG anti-gliadin antibodies, an intestinal biopsy should be performed in all suspected cases.