Human peritoneal B-1 cells and the influence of continuous ambulatory peritoneal dialysis on peritoneal and peripheral blood mononuclear cell (PBMC) composition and immunoglobulin levels

In mice, peritoneal B cells are composed of a unique B-1 cell population which can repopulate the intestinal lamina propria with IgA-producing cells, as well as contribute to the majority of serum IgM. In this study, peritoneal lymphocytes from patients starting continuous ambulatory peritoneal dialysis (CAPD) and from women undergoing bilateral tubal ligation (BTL) were analysed for the presence of a B-1 cell population as well as the expression of potential homing receptors. Up to 63% of the peritoneal B cells express surface antigen CD5, and most peritoneal lymphocytes express the mucosal homing receptors, α4β7 and αEβ7. When analysing serial samples collected from patients from the beginning of dialysis to 1 year, no marked changes were observed in serum or salivary immunoglobulin levels, although the peritoneal lymphocyte population was reduced by 50%. These data suggest that the phenotype of human peritoneal B-1 cells is similar to that of mice, but the contributions to the immune system may differ.     

Variations in immunoglobulins and IgA subclasses of human uterine cervical secretions around the time of ovulation

The quantity and subclass distribution of IgA produced by the human uterine cervix may have a significant impact on the defence against sexually transmitted diseases as well as the regulation of fertility. Cervical mucus was obtained from 15 normal ovulating women around the time of ovulation. The total amounts of secreted IgA (including IgA1 and IgA2), IgG, and IgM were determined by ELISA. IgA was detected at high levels in all samples of cervical mucus. When ovulation was ascertained by daily urinary luteinizing hormone testing, IgA production was maximal 2–3 days before ovulation. Equal proportions of IgA1 and IgA2 were detected in cervical mucus, and 80% of the IgA occurred in the polymeric forms. The increased levels of IgA, the ratios of IgA1 to IgA2, and the predominance of polymeric IgA indicate that much of the IgA in human uterine cervical fluid originates from local production.     

Structural heterogeneity of glycans in IgA molecules: Implications for IgA nephropathy

Summary: The carbohydrate moieties on glycoproteins, including immunoglobulins (Ig), are involved in a broad spectrum of biological functions. As revealed by enzymatic or chemical removal of carbohydrate moieties, inhibition of glycosylation, or site-directed mutagenesis of asparagine residues to prevent N-linked glycosylation, carbohydrates on Ig have been shown to participate in binding, internalization and catabolism by hepatocytes or other cells, binding to Fc receptors on phagocytic cells, activation of complement, and opsonization. the structure of human IgA1 is unique among all Ig. the heavy chain contains a hinge region with a characteristic primary structure not seen in any other Ig, and which contains five short O-linked oligosaccharide side-chains composed of serine-linked N-acetylgalactosamine (GalNAc) and βl-3-linked galactose (Gal). Both of these monosaccharides may be sialylated. In contrast to ubiquitous N-linked side-chains, O-linked carbohydrate moieties are found rarely among human serum glycoproteins. We have demonstrated that IgA1 proteins from the sera of patients with IgA nephropathy (IgAN) are galactosylated to a lesser extent than those from healthy controls. Decreased content of Gal and decreased reactivity of IgA from IgAN patients with lectins specific for GalNAc indicate that these structural changes occur on glycans located in the hinge region of IgA1. Thus, in addition to rheumatoid arthritis, systemic lupus erythmatosus, inflammatory bowel disease and other disorders, IgA nephropathy may represent another example of a chronic disease in which aberrancies of carbohydrates are observed and may participate in aetiopathogenesis.     

Properties of IgA-Binding Receptors on Murine T Cells: Relative Importance of FcαR, β-Galactosyltransferase and Anti-Secretory Component Reactive Proteins (ASCP)

Murine T cells and T-cell lines express receptors for the Fc of IgA (Fc alpha R); however, their molecular properties remain to be elucidated. In the present study, we examined three candidate molecules for IgA-binding receptors including Fc alpha R, beta-galactosyltransferase (beta-GT) and anti-secretory component (SC) reactive proteins (ASCP) expressed on T cells which might participate in the binding of different molecular forms of IgA. T-cell lines derived from CD4+ T cells of mouse Peyer's patches (PP) (designated PPT 4-6 and PPT 4-16) and from cloned PP T helper (Th) cell lines (ThHA1 #9 and #10) bound both monomeric and dimeric IgA (mIgA and dIgA), while the fusion partners (BW 5147 and R1.1) did not. In contrast, both Fc alpha R+ and Fc alpha R- cell lines bound to high molecular weight polymeric or aggregated IgA (pIgA). All cell lines reacted with a monoclonal anti-beta-GT (MoAb) and beta-GT enzyme activity was associated with the cell lysates and membrane fractions of all cells tested. The anti-beta-GT MoAb stained a 47-kDa band on immunoblots which was identical to that seen with native enzyme. mRNA analysis with beta-GT cDNA showed that all cell lines constitutively produced enzyme-specific mRNA. Both Fc alpha R+ T cells and Fc alpha R- control cell lines showed cell surface specific beta-GT activity. This is the first study which shows that mouse T cells produce beta-GT. However, Fc alpha R and beta-GT appear to be separate receptors, because Fc alpha R+ T cells bound mIgA and dIgA, and this treatment did not affect staining with biotinylated anti-beta-GT MoAb. Further, preincubation of the Fc alpha R+ cells with anti-beta-GT MoAb did not block mIgA binding. However, the anti-beta-GT MoAb partially blocked binding of pIgA to both Fc alpha R+ and Fc alpha R- T cells, suggesting that beta-GT may be a receptor for pIgA. Others have shown that T cells may bind IgA through a receptor serologically related to SC. We found that antibodies both to human SC and to rat SC specifically bound to both Fc alpha R+ and Fc alpha R- T cells. Further, a 72-kDa band was detected when cell membrane fractions were analysed with these antisera (ASCP) by solid phase immunoisolation technique and immunoblot analysis. The ASCP is not an IgA-binding receptor, since anti-SC did not block either mIgA or pIgA binding.(ABSTRACT TRUNCATED AT 400 WORDS)     

Heterogeneity of carbohydrate moieties of IgA1 molecules from IgA nephropathy patients and normal individuals

Summary: IgA nephropathy (IgAN) is characterized by the deposition of IgA1 in kidney mesangia and the presence of IgA1-containing immune complexes in the circulation. Structural studies of IgA1 isolated from sera of IgAN patients indicated a statistically significant decrease in the content of galactose (Gal). Using a combination of lectins specific for glycans in O- or N-linked glycan side chains, this Gal deficiency was restricted to O-linked glycans present in the hinge region of IgA1 molecules. Gal-deficient IgA1 displayed a significantly higher binding to mesangial cells through a putative non-internalizing receptor specific for N-acetyl galactosamine (GalNAc) in O-linked glycans. These data suggest that Gal deficiency results in diversion of IgA1 molecules from the usual degradative pathway and deposition of altered IgA1 in the mesangium.     

Site of Catabolism of Autologous and Heterologous IgA in Non-Human Primates

Because of similarities between the human and monkey immune systems, we considered the monkey a suitable model for studies on the catabolism of various molecular forms of IgA, for which little information is available. The residualizing label dilactitol-[125I]tyramine was coupled to monkey (Macaca fuscata) IgA and IgG, as well as to human monomeric and polymeric myeloma IgA1 and IgA2 proteins. When labelled proteins were injected intravenously into monkeys, the non-metabolizable radioiodinated tracer accumulated at the cellular site of protein degradation, allowing identification of the catabolic sites. To determine the uptake of injected proteins by various tissues, monkeys were sacrificed 6-7 days after injection of labelled proteins, when blood-associated radioactivity was less than or equal to 10% of the injected dose, as measured by plasma clearance. When monkey or human monomeric IgA, as well as human polymeric IgA, irrespective of subclass, was administered to monkeys, the liver showed the greatest tissue uptake relative to total dose injected and to organ weight, and the highest acid soluble radioactivity (degraded protein). Although both hepatocytes and non-parenchymal liver cells were involved in IgA uptake, the hepatocytes were more active. Therefore, it appears that the liver is the major site of uptake and catabolism of IgA in monkeys and possibly in humans.     

Normal Uterine Cervix: Characterization of Isolated Lymphocyte Phenotypes and Immunoglobulin Secretion

PROBLEM : Isolation of viable cervical lymphocyte populations and characterization of their function in healthy tissue is necessary to understand immunity in the genital tract. METHODS : Normal, cervical tissue was digested using a multi-enzymatic digestion procedure. Lymphocytes were characterized using FACS analysis and ELISPOT analysis for immunoglobulin secreting cells. RESULTS : Following the digestion procedure, 0.16 × 10⁶ ± 0.8 cells/g of tissue with a viability of 90–98% were isolated from normal cervical tissue. FACS analysis determined that B lymphocytes were the predominant cell type in normal cervical tissue representing a significantly higher percentage than that found in peripheral blood (P=0.015). T lymphocytes and NK cells represented a significantly lower percentage than that found in peripheral blood (P=0.0001 and 0.026, respectively). The largest percentage of immunoglobulin secreting cells isolated were secreting IgG followed by IgA. A limited number of IgM secreting cells were detected. IgA2 secreting cells represented 34.46 ± 4.6% of the total number of IgA plasma cells. CONCLUSION : These studies represent the first analysis of viable mononuclear cells isolated from normal cervical tissue. The results form a baseline from which it will now be possible to compare changes that occur at the cervical squamocolumnar junction in response to infection or neoplasia.     

Urinary Immunoglobulins in Healthy Individuals and Children with Acute Pyelonephritis

Urine samples obtained from children with acute pyelonephritis and from healthy children and adults were analysed with regard to the molecular form and specific antibody activity of urinary immunoglobulins. The urinary IgA and IgG levels were quantified in unconcentrated urine by radioimmunoassay. The children with urinary tract infection had significantly higher levels of IgG and IgA than age-matched controls but not higher than healthy adults. After tenfold concentration, the urine was fractionated on an Ultrogel AcA 22 column, and the IgA, secretory IgA, and IgG in the fractions were determined by radioimmunoassay. IgA in urine from healthy adults was predominantly represented by polymeric IgA linked to secretory component; small quantities of monomeric IgA were also present. IgG eluted in the position of the serum standard. Increased proportions of IgG and monomeric IgA were found in the infected patients. Specific antibody activity of the IgG and IgA classes to antigens of the infecting Escherichia coli strain was detected in whole and in fractionated urine from children with acute pyelonephritis. The specific antibody activity in healthy adults and children was low.     

Mucosal immunity and strategies for novel microbial vaccines

Infectious diseases continue to be the leading cause of morbidity and mortality worldwide. Increased awareness of the fact that mucosal membranes are the most frequent portals of entry of pathogenic microorganisms has prompted studies aimed at the development of vaccination protocols and antigen delivery systems that would lead to an increased protection of mucosae. Although systemic and strictly local immunizations are of limited effectiveness in the induction of mucosal protection, ingestion or inhalation of antigens results in a generalized immune response manifested by the appearance of specific antibodies of the secretory immunoglobulin (Ig) isotype in external secretions due to the dissemination of IgA precursor cells from IgA-inductive lymphoid tissues. Furthermore, additional inductive sites strategically positioned at the opening of the respiratory and digestive tracts may also be suitable targets for induction of immune responses at desired effector sites. To prevent degradation and the increase of ingested antigens absorption, novel strategies including enclosure of antigens into biodegradable microspheres, liposomes or their expression in viral and bacterial vectors and plants are currently being considered. Forthcoming technological advances in antigen preparation and routes of delivery will undoubtedly have a profound impact on immunization practices in the future.