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PubMed1982

IgA nephropathy: characterization of the polymeric nature of mesangial deposits by in vitro binding of free secretory component.

IgA nephropathy, as Berger defined it, is characterized by mesangial deposits of IgA, which are easily visualized by immunofluorescence on kidney biopsies. The structure (mono- or dimeric) of these IgA has not been clearly defined so far. Fifteen renal biopsies were studied to find out whether these IgA are serum monomers, or are polymers from a different origin. This was done by tissue fixation in vitro of free secretory component, which was then visualized by immunofluorescence (IF). In all 15 cases, the IgA deposits were shown to lack bound secretory component, but were able to bind, specifically, with the free secretory component. The presence of J chain in these deposits was also evidenced by indirect IF. These findings favour the hypothesis that these immunoglobulins are polymeric.

Fluorescent Antibody Technique↗
PubMed1987

Circulating secretory component in breast neoplasms.

The serum concentrations of IgAp and IgMr associated secretory component (SIgA and SIgM) of 98 patients with neoplasms of the breast were measured. Of the 56 patients with carcinomas, 11 had increased concentrations of circulating SIgM, which was almost twice as sensitive as SIgA as a marker for carcinoma. Concentrations of circulating SIgA and SIgM were independent of expression of secretory component, IgA, and carcinoembryonic antigen (CEA); histological tumour grade; and tumour cell DNA ploidy, whereas a weak correlation between SIgA and SIgM and circulating CEA was seen. The three patients who had liver metastases indicated had particularly high concentrations of circulating SIgA and SIgM, whereas no difference was generally seen between patients with malignancy and those with benign tumours.

Adult↗
PubMed1979

Identification of secretory component as an IgA receptor on rat hepatocytes.

Secretory component (SC) was found to be synthesized by isolated rat hepatocytes. SC was detected by radioimmunoassay and cultured hepatocytes were found to synthesize 0.078 microgram SC/10(6) hepatocytes in a 48-h period. SC was also present on the surface of hepatocytes as detected by the specific binding of radiolabeled anti-SC antibodies as well as by the detection of specific membrane staining in indirect immunofluorescence tests using specifically purified anti-SC antibodies. Rat SC was detected on hepatocytes and intestinal epithelial cells but not on peripheral blood lymphocytes, unfractionated spleen cells, or erythrocytes. Specific binding of radiolabeled rat dimeric IgA to rat hepatocytes was also observed and evidence was obtained to indicate that such binding was mediated by SC. Thus, prior incubation of hepatocytes with anti-SC prevented binding of radiolabeled IgA. Moreover, prior incubation of radiolabeled IgA with rat SC prevented binding of the IgA to isolated hepatocytes. Cells treated with 0.25% trypsin lost their ability to bind to radiolabeled dimeric IgA.

Animals↗
PubMed2002

Gains and losses of glycoprotein CD44 and secretory component expression in endometrial hyperplasia and neoplasia.

CD44 is an adhesion molecule, which binds hyaluronic acid and participates in a number of cell-cell interactions, including lymphocyte homing. The CD44 antigen is expressed on approximately 90% of lymphocytes, monocytes, granulocytes, and, in lower amounts on thymocytes, fibroblasts, and erythrocytes. Platelets lack CD44. In non-haematopoietic tissues, CD44 is widely distributed. The secretory component is isolated from human colostrum and is of help in more precise grading of endometrial carcinoma. In this study we examined CD44 and secretory component expression in adenomatous hyperplasia, atypical adenomatous hyperplasia and well-differentiated adenocarcinoma (cribriform pattern). The results showed decreased expression of CD44 and increased expression of secretory component as the lesion progressed to malignancy.

Adenocarcinoma↗
PubMed1979

Biliary transport of IgA: role of secretory component.

Biliary transport of rat immunoglobulin was studied by perfusion of isolated rat liver with blood containing radiolabeled immunoglobulin. Transport to bile was selective for polymeric IgA. Between 15 and 27% of polymeric IgA was transported from blood to bile during a 210-min perfusion period, and approximately 60% of the IgA transported to bile bore secretory component. Small quantities of IgM (0.12%) were transported; transport of IgG2 alpha, IgE, or monomeric IgA was not detected. Purification of radiolabeled polymeric IgA by affinity chromatography on human secretory component-Sepharose yielded a fraction that was transported more efficiently (i.e., up to 40% transported). In contrast, secretory IgA (colostral or biliary) was transported 1/25th to 1/12th as well as polymeric IgA myeloma protein. Complexes of 125I-labeled secretory component and polymeric IgA formed in vitro were transported poorly (0.1%) compared to polymeric IgA (26%). It was concluded that biliary transport of polymeric IgA requires combination of it with secretory component in the liver. In support of this hypothesis, rabbit IgG anti-rat secretory component antibodies were also transported to bile but normal rabbit IgG was not.

Animals↗
PubMed2002

Immunohistochemical expression of vimentin and secretory component antigens in endometrial hyperplasia and neoplasia.

Vimentin is an intermediate filament protein normally expressed in mesenchymal cells, but evidence is accumulating in the literature which suggests that the aberrant expression of vimentin in epithelial cancer cells might be related to local invasiveness and metastatic potential. Previous studies strongly support the implication of vimentin in the metastatic progression of breast and cervical lesions. The secretory component is isolated from human colostrum and is of help in more precise grading of endometrial carcinoma. In this study we examined vimentin and secretory component (SC) expression in adenomatous hyperplasia, atypical adenomatous hyperplasia and well-differentiated adenocarcinoma (cribriform pattern). The results showed decreased expression of vimentin and increased expression of the secretory component as the lesion progressed to malignancy.

Adenocarcinoma↗
PubMed1975

Identification and some properties of rat secretory component.

An antiserum, prepared against partially reduced and alkylated rat milk SIgA, was shown to contain antibodies reacting with a rat milk protein of alpha-2 mobility, which possessed antigenic determinants common with SIaA, eluted from Sephadex G-200 at the same position as mammalian secretory components, and could be released from rat SIgA by mild reduction and alkylation. This protein, called rat secretory component, was also detected in saliva, tears and urine. Rat free secretory component (FSC) possessed antigenic determinants which were inaccessible in rat SIgA, as found in other species. In vitro, ra FSC combined with rat serum polymeric IgA or IgM, but not with monomeric IgA or IgG. These data emphasize the many similarities between the human and rat SIgA systems.

Adsorption↗
PubMed2001

Reduced epithelial expression of secretory component in small airways correlates with airflow obstruction in chronic obstructive pulmonary disease.

The epithelial polymeric immunoglobulin receptor/transmembrane secretory component (pIgR/SC) transports into secretions polymeric immunoglobulin A (pIgA), which is considered the first line of defense of the respiratory tract. The present study, done with quantitative immunohistochemistry, evaluated epithelial expression of secretory component (SC) and Clara cell protein (CC16) and neutrophil infiltration into the airways of eight patients with severe chronic obstructive pulmonary disease (COPD) who were undergoing lung transplantation, as compared with these processes in six nonsmoking patients with pulmonary hypertension who were used as controls and in lung specimens from five smokers without chronic bronchitis. Staining for SC was significantly decreased in the COPD patients as compared with the controls, both in large (mean optical density [MOD]: 23.4 [range: 21.1 to 27.8] versus 42.2 [range: 28.2 to 49.3], p = 0.003) and in small airways (MOD: 30.8 [range: 20.3 to 39.4] versus 41.5 [range: 39.2 to 46.2], p = 0.003). SC expression in small airways correlated strongly with functional parameters such as FEV1 (Kendall's tau (K) = 0.76, p = 0.008), FVC (K = 0.64, p = 0.03), and midexpiratory flow at 50% of VC (MEF50) (K = 0.74, p = 0.01). The reduced expression of SC in large airways correlated with neutrophil infiltration in submucosal glands (K = -0.47, p = 0.03). Expression of CC16 in the bronchial epithelium of COPD patients was also significantly decreased as compared with that of controls, especially in small airways (MOD: 28.3 [range: 26.8 to 32.4] versus 45.8 [range: 40.7 to 56.0], p = 0.002), but no correlation was observed with lung function tests. In conclusion, this study shows that reduced expression of SC in airway epithelium is associated with airflow obstruction and neutrophil infiltration in severe COPD.

Adolescent↗
PubMed1988

Expression of IgA and secretory component in the normal and in adenocarcinomas of Fallopian tube, endometrium and endocervix.

The occurrence and localization of IgA and secretory components (SC) were examined in the normal and in adenocarcinomas of Fallopian tube, endometrium and endocervix. IgA-containing immunocytes were identified in the stroma of 90% of normal Fallopian tubes. It is suggested that the Fallopian tube may have an immunological function and may, together with the endocervix, constitute the local secretory immune system of the female genital tract. IgA and SC were frequently demonstrated in the cytoplasm and luminal secretion of adenocarcinomas of the endocervix, endometrium and Fallopian tube. This study has shown a decrease in immunoreactivity of SC among poorly differentiated adenocarcinomas but has failed to demonstrate any correlation between the expression of IgA and the degree of differentiation of the tumours. Secretory component appears, therefore, to be more useful than IgA as an indicator of secretory activity and differentiation of adenocarcinomas of the female genital tract.

Adenocarcinoma↗
PubMed1985

Secretory IgA, secretory component and pathogen specific antibodies in the middle ear effusion during an attack of acute and secretory otitis media.

The total concentration of secretory IgA (SIgA) and secretory component (SC) as well as the occurrence of pathogen specific serum type (IgG, IgA and IgM) and secretory type antibodies against Streptococcus pneumoniae and Haemophilus influenzae in the middle ear effusion during an attack of otitis media were studied by using the ELISA method. The middle ear effusion samples were taken at 2 to 4 weeks' intervals from patients with recurrent acute otitis media (RAOM) or secretory otitis media (SOM). In the samples of the RAOM patients the SC/SIgA ratio was 2.2, while in the SOM samples the ratio was 13.6. Both serum and secretory type antibodies to the infecting bacteria could be detected in the middle ear effusions in both of the patient groups. The results of this study show that the middle ear can develop antigenic specific antibodies against the infecting bacteria. The increased production of SC seems to be related to the pathogenesis of SOM.

Acute Disease↗
PubMed1994

Up-regulated epithelial expression of HLA-DR and secretory component in salivary glands: reflection of mucosal immunostimulation in sudden infant death syndrome.

Human parotid glands from 55 forensic autopsy subjects, 1-12 mo of age, were examined by immunohistochemistry without knowledge about the cause of death. Various combinations of monoclonal or polyclonal antibody reagents of the following specificities were applied in two-color immunofluorescence analyses: HLA class I or II (DR, DP, or DQ); pan-T cell (CD3); leukocyte common antigen (CD45); and secretory component (poly-Ig receptor). Sudden infant death syndrome victims (n = 17) were shown to have significantly increased numbers of CD45+ stromal leukocytes and intensified epithelial expression of HLA-DR and secretory component as well as increased endothelial expression of both HLA class I and II (DR, DP, and DQ) determinants compared with controls (n = 31) who had died from noninfectious causes. Seven overtly infectious subjects (bronchopneumonia) showed still more up-regulated expression. This result suggested that enhanced stimulation of the local immune system exists in sudden infant death syndrome, with release of certain cytokines that are known to up-regulate epithelial expression of HLA-DR and secretory component.

Epithelium↗
PubMedDate not supplied

Failure to use measurement of megalin secretory components complexed with serum thyroglobulin as a tool to identify metastases after surgery in papillary thyroid cancer.

When thyroid follicles are intact, some colloidal thyroglobulin (Tg) reaches the circulation by megalin-mediated transcytosis and is to various extents complexed with megalin secretory components. In contrast, in papillary thyroid cancer (PTC), serum Tg is not complexed with megalin because it is directly secreted by tumor cells. Here we attempted to use measurement of megalin secretory components to distinguish PTC patients with thyroid remnant plus metastases from those with thyroid remnant only, after thyroidectomy and before 131I ablation. Tg values in anti-Tg antibodies (TgAb)-free sera from 5 PTC patients with thyroid remnant plus metastases and 12 PTC patients with thyroid remnant only were measured following pre-adsorption with uncoupled protein A beads or with protein A beads coupled with antimegalin antibodies. The degree of Tg pre-adsorption with antimegalin antibodies was minimal, with no substantial differences between the two groups. Thus, we concluded that measurement of megalin secretory components is unlikely to be useful to identify the origin of serum Tg in PTC patients after thyroidectomy.

Adsorption↗
PubMed1991

Sustained production of secretory component by human tracheal epithelial cells in primary culture.

Secretory immunoglobulin A (sIgA) is an important initial defense against environmental agents in the airway. The purposes of our study were to determine whether human tracheal epithelial (HTE) cells produce secretory component (SC), the receptor for dimeric IgA (dIgA), to determine whether HTE cells in primary culture continue to produce SC, and if so, to develop a model for studying SC metabolism in the airway. Immunoperoxidase staining of the human trachea using antibody raised against human SC reveals that many surface epithelial cells and the cells of the submucosal glands express SC but basal cells do not. HTE cells, obtained from tracheal specimens at necropsy, contain 10-51 ng of SC/10(5) cells, at the time of isolation. However, when these cells are placed in culture on plastic, SC release diminishes with time (from 19.6 ng/10(5) cells on day 2 to 6.4 on day 8) despite continued cell proliferation. In contrast, HTE cells cultured on floating collagen gels increase SC release over the same period (26.2 ng/10(5) cells on day 2 and 193.9 on day 8). HTE cells cultured on collagen-coated and uncoated nitrocellulose filters also produced SC at least through day 8 (collagen coated, 21.5 ng/10(5); uncoated, 6.3). Furthermore, SC was released preferentially to the apical surface (4:1 ratio) under both conditions. This system will allow us to study the production, processing, and release of SC by HTE cells and further understand the transport and function of secretory IgA in the airway.

Biological Transport↗
PubMed1999

Different regulatory pathways employed in cytokine-enhanced expression of secretory component and epithelial HLA class I genes.

The transmembrane secretory component (SC, or pIg receptor) plays a crucial role in mucosal immunity by translocating dimeric IgA and pentameric IgM through exocrine epithelia. This receptor is up-regulated by cytokines in parallel with increased epithelial HLA expression. By use of the human epithelial cell line HT-29m3, we show that IFN-gamma, TNF-alpha and IL-4 activate transcription of the SC gene. This activation was slow, suggesting mediation via newly synthesized protein factors. IFN-gamma and TNF-alpha, but not IL-4, also up-regulated expression of HLA class I genes. However, this gene induction was rapid and did not depend on new protein synthesis. Nuclear run-on experiments showed that the transcription rate of HLA class I genes nearly peaked after only 30 min of IFN-gamma or TNF-alpha stimulation, whereas the SC transcription rate did not peak until after 20-36 h of IFN-gamma, TNF-alpha or IL-4 stimulation. Gel electrophoresis mobility shift assays demonstrated binding of nuclear proteins from cytokine-stimulated HT-29 cells to consensus elements in the promoter of the SC gene, involving the binding site for the nuclear factor-kappaB p50 subunit after TNF-alpha stimulation, and IFN-stimulated response element after IFN-gamma stimulation (and weakly after TNF-alpha. Our observations in vitro likely parallel events in vivo by which activated mucosal T cells and macrophages enhance pIg receptor-mediated external transport of secretory IgA and IgM and up-regulate epithelial HLA expression.

Base Sequence↗
PubMed1982

A transmembrane precursor of secretory component. The receptor for transcellular transport of polymeric immunoglobulins.

Secretory component (SC), a glycoprotein associated with polymeric IgA and IgM in external secretions, is produced by certain epithelial cells and is thought to be the receptor mediating the transepithelial transport of these immunoglobulins. We studied the biosynthesis of human SC in a cloned cell line (HT29.E10) derived from a colon adenocarcinoma. In both cell-free translations and pulse labeling of cells, SC is made as a larger precursor (Mr = 95,000). This precursor is a transmembrane protein, as a large fragment (Mr = 80,000), is protected by the membrane from proteolytic digestion. Both this membrane-protected fragment and the undigested precursor have the same NH2-terminal sequence as mature SC. These data indicate that SC is proteolytically cleaved from the NH2-terminal, ectoplasmic (noncytoplasmic) domain of the precursor. This conclusion is supported by pulse-chase experiments. The Mr = 95,000 form is first converted to a Mr = 100,000 form by addition of peripheral sugars. The Mr = 100,000 form is then slowly cleaved to a Mr = 80,000 form which is gradually released into the medium. We propose that the transmembrane precursor of SC is the receptor involved in transepithelial transport of polymeric immunoglobulins.

Adenocarcinoma↗
PubMed1990

Urinary IgA, secretory IgA and secretory component in women with recurrent urinary tract infections.

Urinary secretory IgA (sIgA), consisting of free secretory component (FSC) and dimeric IgA, is involved in the defense against urinary tract infections (UTI). Recurrent UTIs (rUTI) have been suggested to be associated with a defective excretion of sIgA. Therefore urinary sIgA, FSC and serum-type IgA concentrations were measured by ELISA in 68 normal women, 10 asymptomatic women with rUTIs and no urological abnormality (group A), 8 asymptomatic women with rUTIs and a urological abnormality (B), 4 women with acute UTI (C) and 5 women with a selective serum IgA deficiency (D). Annual UTI rates were increased in groups A, B and C, but normal in group D. In no patient group urinary FSC concentration was different from the normals, while sIgA concentrations were increased in group C, markedly reduced in group D, but normal in groups A and B. Urinary serum-type IgA concentrations were significantly increased in group A and C, markedly reduced in group D and normal in group B. These results demonstrate that the urinary sIgA system participates in the immune response to bacterial infections, but that even a complete failure of the sIgA system does not lead to an increased UTI rate. Furthermore, no association of recurrent UTIs with disturbances of the urinary sIgA excretion could be demonstrated.

Adolescent↗
PubMed1999

Expression, purification and biochemical characterization of recombinant murine secretory component: a novel tool in mucosal immunology.

Reconstitution of secretory IgA (S-IgA) by the association in vitro of secretory component (SC) and polymeric IgA (pIgA) obtained from hybridomas is a valuable tool in the study of the structure-function relationship in this particular class of antibody. Although dimeric IgA (dIgA) can be obtained and purified from hybridoma clones, SC remains tedious to isolate in sufficient amounts from colostral milk. Several murine models for the study of mucosal immunity are available, which could potentially benefit from the use of cognate IgA antibodies in various molecular forms, including dIgA and S-IgA. We report here on the establishment of two expression systems allowing the production of milligram amounts of pure recombinant murine SC (rmSC) with preserved murine pIgA-binding capability. The first system relies on the use of recombinant vaccinia virus to prompt infected HeLa cells to express the murine SC protein, whereas the second system is based on a stably transfected cell clone exhibiting murine glycosylation. The second source of rmSC will permit the study of the role of its sugar moieties in pathogen-host interactions, and the evaluation of its function in passive protection without risking adverse immune responses. The extensive biochemical characterization conducted in this study demonstrates that rmSC is a dependable and convenient alternative to the natural product, and indicates that the J chain is dispensable in the recognition of pIgA and SC in vitro, whereas it is required for proper pIgA-polymeric Ig receptor interaction in vivo.

Animals↗