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PubMed1979

Study of secretory component in patients with metastatic breast cancer.

A radioimmunoassay was developed for secretory component, a glandular epithelial cell product secreted as an accessory protein with dimeric immunoglobulins A and M. Forty-four normal women between the ages of 40 and 70 had plasma concentrations of secretory component of 7.195 microgram/ml +/- 3.590 (+/-2 SD). Of the patients with metastic breast cancer of epithelial origin, 34 (91.9%) had plasma concentrations greater than 8.990 microgram/ml; 29 (78.1%) had plasma concentrations greater than 10.785 microgram/ml; 10 (27%) had concentrations greater than 15.000 microgram/ml; and 3 (8.1%) had concentrations greater than 22.710 microgram/ml. Serial plasma concentrations (averaging 3.48 per patient) of 35 (94.6%) of these patients reflected the clinical course of the disease. All patients had some combination of surgery, radiation therapy, and chemotherapy. No direct correlation was noted between the type of therapy and concentration of secretory component. However, plasma secretory component served as a marker in the systemic circulation of a change in the status of the metastatic breast cancer. The impact of this research may lie in its incorporation into clinical management.

Adenocarcinoma↗
PubMed1995

Serum secretory IgA and IgM and free secretory component in IgA nephropathy.

IgA nephropathy (IgAN) is characterized by the presence of IgA and C3 deposits in the mesangium. Mesangial IgA is mostly dimeric IgA1 with a J chain, lacking a secretory component. In view of the recent demonstration of elevated serum levels of secretory component and secretory IgA in liver disease and HIV infection associated with hyper-IgA, we measured the serum secretory component in 50 IgAN patients and 45 controls. Free secretory component and secretory IgA and IgM levels were determined by enzyme-linked immunosorbent assay. Normal or low levels were found patients. These data support previous work suggesting that in IgAN circulating and probably mesangial IgA do not originate from the epithelial compartment of the mucosal immunoglobulins as it is the case in other hyper-IgA diseases.

Adolescent↗
PubMed1985

Differences in fragmentation between bound and unbound bovine secretory component suggest a model for its interaction with polymeric immunoglobulin.

Unbound bovine secretory component was cleaved into two-domain and one-domain fragments by trypsin within 1 h. Bovine secretory component covalently bound to bovine IgA dimer, as in secretory IgA, was much more resistant to fragmentation, which did not proceed beyond the three-domain stage even after 5 h. Bovine secretory component non-covalently bound to bovine IgM or to human IgM or IgA polymer was also relatively resistant to fragmentation, which again was largely arrested at the three-domain stage. A model for the binding of secretory component to polymeric immunoglobulin is proposed.

Animals↗
PubMed1988

Absence of secretory component expression by epithelial cells overlying rabbit gut-associated lymphoid tissue.

The expression of secretory component by epithelial cells overlying intestinal lymphoid aggregates was examined immunocytochemically in rabbits. Intensely labeled epithelial cells were distributed along surfaces of villi surrounding follicles in jejunal and ileal Peyer's patches and along interdomal epithelium in sacculus rotundus and appendix. Secretory component labeling extended from within crypts and appendiceal crevices to the tips of villi and interdomal regions. In contrast, no immunologically detectable secretory component sites were observed in follicle-associated epithelial cells. In crypts and crevices supplying follicles, epithelial cells facing the lamina propria of villi and interdomal epithelium expressed secretory component, but cells flanking the follicle domes lacked secretory component immunostaining, with a clear demarcation between positive and negative zones at the base of the stem cell regions. These findings demonstrate a unique difference in the expression of the receptor for immunoglobulin A antibody between follicle-associated and non-follicle-associated epithelium.

Animals↗
PubMed1975

Reactive half-cystine peptides of the secretory component of human exocrine immunoglobulin A.

On the basis of previous work the two forms of human secretory component, namely that which is covalently bound as a part of the exocrine immunoglobulin A molecule and the free form, are probably different states of the same protein. From autoradiographs of trypic peptide maps of bound and free secretory components which were radioactively alkylated after partial reduction, it was concluded that the same half-cystines in each are sensitive to reduction. in the present work the easily reduced half-cystines of the bound and free secretory components have been studies in more detail. In each form there are two such half-cystines. In the case of bound secretory component they provide the linkage to the remainder of the exocrine immunoglobulin A molecule. Peptides from the sensitive half-cystines were isolated from tryptic-peptic digests of free secretory component and sequenced. By diagonal electrophoresis these two peptides were shown to be joined in an intrachain disulfide bridge. Therefore, it is proposed that the exocrine immunoglobulin A molecule becomes fully assembled when a single, reactive intrachain disulfide bridge in free secretory component rearranges to yeild two interchain bridges with dimeric serum-type immunoglobulin A. This process is thought to occur within the epithelial lining cells of mucous membranes.

Amino Acids↗
PubMed1977

The finding that secretory component is not associated with gamma-glutamyltranspeptidase activity.

The gamma-glutamyltranspeptidase activity of human milk was concentrated by ammonium sulphate precipitation. On gel chromatography of the dissolved precipitate, the activity was eluted in the high-molecular-weight fraction containing secretory IgA, while no activity appeared in the eluate at the position of free secretory component. Various antisera were added to portions of the pool of active fractions. No change of gamma-glutamyltranspeptidase activity appearedse activity was obtained with antisera against either IgA, secretory IgA or secretory component, while a large reduction of activity was seen with anti-human colostrum. Finally, purified free secretory component, secretory IgA and in vitro complexes between secretory component and IgA dimers were shown to be inactive in the gamma-glutamltranspeptidase assay, both in the absence and presence of zinc ions. Thus secretory component, either when free or bound to IgA, does not exhibit gamma-glutamyltranspeptidase activity, and therefore cannot function as such an enzyme in the transport of IgA across mucous membranes, as has been suggested previously.

Animals↗
PubMed1976

Two immunochemically and physicochemically distinct secretory components from rat exocrine secretion.

Two proteins were isolated from rat milk by using ion-exchange and gel filtration chromatography and shown to be secretory components by the criteria of: a) occurrence as free proteins in exocrine secretions, as well as bound to exocrine IgA while absent from serum and serum IgA, b) immunohistochemical localization in the epithelial cells of the gut, c) dissociability from and in vitro binding to 11 S SIgA, d) cross-reactivity with antisera to mouse and bovine secretory components, and e) significant peptide homology with bovine secretory component. The secretory components were immunochemically and physicochemically distinct as shown by: a) the lack of cross-reactivity between their specific antisera and differential reactivity with anti-bovine FSC and anti-mouse SC, b) different electrophoretic mobilities, c) DEAE elution profiles, d) carbohydrate contents, e) molecular weights, and f) apparent polypeptide chain constitution. Another interesting difference in the two is that only one of the components dissociates spontaneously from SIgA. Possible functions of two secretory components are discussed.

Animals↗
PubMed1976

Binding of secretory component to dimers of immunoglobulin A in vitro. Mechanism of the covalent bond formation.

A complex between secretory component and an immunoglobulin A (IgA) myeloma dimer has been studied in vitro as a model to elucidate the mechanism of the formation of disulfide bonds during assembly in vivo of secretory immunoglobin A. A small amount of free thiol groups, totally about 0.4 groups per mole of protein, were shown to be present on both the heavy and light chains of the IgA dimer, but not on its J-chain, while no such groups could be demonstrated on free secretory component. The SH-groups on IgA most likely exist as a result of incomplete oxidation of some intra-or interchain disulfide bonds of the molecule, analogous to what has been suggested for IgG. Several types of evidence indicated that the disulfide bonds between secretory component and IgA are formed after the noncovalent association of the two proteins by a sulfhydryl group-disulfide bond exchange reaction, in which the small amount of free sulfhydryl groups on the IgA dimer initiate the reaction by reducing a reactive disulfide bond on secretory component. This exchange reaction, which thus proceeds by the mechanism of so-called disulfide interchange reactions, requires certain conformational features of one or both of the proteins and leads to the formation of presumably two new interchain disulfide bonds between secretory component and IgA. The reaction does not progress to completion, however, but ends in an equilibrium so that a small proportion of the secretory component molecules always are unattached by disulfide bonds.

Binding Sites↗
PubMed1980

Secretory component in human ocular tissues.

Lacrimal tissue and accessory lacrimal tissue from seven autopsy cases, lacrimal tissue from three patients undergoing orbital exploration, and biopsy specimens from conjunctiva of 14 subjects were examined for the presence and distribution of secretory component by three anti-secretory-component antisera. Secretory component was present in all lacrimal and accessory lacrimal tissues but in no other ocular tissues. Over 60% of acinar cells stained for secretory component; about 5% of acinar cells stained brightly; about 30% of tubular cells stained brightly. Main and accessory lacrimal tissues appeared identical in their staining patterns. We concluded that the main sites of synthesis of secretory IgA in human ocular tissues are the lacrimal and accessory lacrimal tissues.

Adult↗
PubMed1984

Specific and nonspecific humoral defense factors in the epithelium of normal and inflamed gastric mucosa. Immunohistochemical localization of immunoglobulins, secretory component, lysozyme, and lactoferrin.

Epithelial distributions of immunoglobulin A, secretory component, lysozyme, and lactoferrin were studied by paired immunofluorescence staining in ethanol-fixed biopsy specimens from gastric antral and body mucosa. Fluorescence scores were assigned semiquantitatively for the epithelium in three mucosal zones (foveolar, isthmus, and glandular). In each case, degree of inflammation was graded blindly after conventional histologic staining of serial sections. The results showed that the overall epithelial expression of local defense factors was significantly enhanced in association with gastritis, both with regard to nonspecific antimicrobial substances (lysozyme and lactoferrin) and the external transfer of immunoglobulin A (mediated by secretory component) as a potential carrier of protective antibodies. The antral isthmus and glandular zones were most active in both respects. Despite the expression of relatively large amounts of epithelial immunoglobulin A and secretory component in metaplastic glands, these elements lacked the nonspecific defense factors (except for lysozyme in Paneth cells)--even when they occurred in the antral mucosa--and may, therefore, represent particularly vulnerable areas.

Adult↗
PubMed2001

Cigarette smoke decreases the expression of secretory component in human bronchial epithelial cells, in vitro.

Epithelial secretory component (SC) is thought to be essential for immunologic protection of the respiratory tract from viral and bacterial infection, since it transports polymeric IgA from the basolateral to the luminal surface of epithelial cells. We have hypothesized that recurrent infection in airways of cigarette smokers is at least partly a consequence of cigarette smoke-induced downregulation of the expression and/or release of SC from airway epithelial cells, subsequently resulting in decreased transcytosis of secretory IgA to the airway lumen. To test this hypothesis, we have cultured human bronchial epithelial cells (HBEC) from surgical tissues and exposed these for 20 minutes to either air or cigarette smoke. Following exposure to cigarette smoke the HBEC cultures were incubated for a further period of up to 24 h, during which time separate cultures were processed by immunocytochemistry for the presence of SC, in a time-dependent manner. The stained HBEC cultures were evaluated by colour image analysis for the percentage of total cells staining for SC. Exposure to cigarette smoke significantly decreased the percentage of total HBEC staining for secretory component from a baseline value (median and interquartile[IQ]1, IQ3) of 35.9% (26.5, 41.6) to 15.7% (8.2, 25.4; p < 0.05) 1 h after exposure, compared with exposure to air. The percentage of cells staining for secretory component were further reduced to 5.3% (3.3, 6.4; p < 0.01), 6 h after exposure, compared to exposure to air. After incubation for 24 h following exposure to cigarette smoke, there was gross cell damage and the cells were not suitable for immunocytochemical analysis. These results suggest that short-term exposure to cigarette smoke may compromise the immune barrier function of the airway mucosa by decreasing the expression and/or release of epithelial SC, thereby decreasing the transcytosis of IgA necessary for inactivating the microbial pathogens in the airway lumen.

Bronchi↗
PubMed1995

Recognition of type 1 chain oligosaccharides and lacto-series glycolipids by an antibody to human secretory component.

Binding of the mouse IgM antibody 6C4 is lost after treatment of human free secretory component with peptide N-glycosidase F (Bakos et al. (1991) J. Immunol. 146, 162-168) or periodate, suggesting that asparagine-linked oligosaccharides contain the epitope recognized by this antibody. Inhibition of antibody binding to free secretory component by milk oligosaccharides established that lacto-N-tetraose is the minimum structure recognized by the antibody, but larger oligosaccharides with terminal Gal beta 1-3GlcNAc sequences bind with much higher affinity. Antibody binding is enhanced by substitution with the Lewis Fuc alpha 1-4 and is inhibited by Fuc alpha 1-2Gal substitution. Free secretory component, however, does not bind other antibodies that recognize Le(a) or Leb oligosaccharides, and binding is lost after digestion with a beta-galactosidase that cleaves Gal beta 1-3 linkages but not after digestion with alpha-L-fucosidase. Therefore, the major epitope recognized by 6C4 on free secretory component is probably not an asparagine-linked Le(a) oligosaccharide. The antibody also binds to human milk lactoferrin, some human mucins, and lacto-series glycolipids including III4 alpha Fuc-lactotetraosyl ceramide and lactotetraosyl ceramide. Based on affinity chromatography of oligosaccharides released from free secretory component, the epitope recognized by antibody 6C4 is present on approximately 3.5% of the asparagine-linked oligosaccharides.

Animals↗
PubMed1990

Effects of smokeless tobacco on the ability of secretory component to bind to the IgA/J chain complex.

Previously, we reported that smokeless tobacco users have significantly higher levels of immunoglobulin A and J chain in whole saliva than non-tobacco users. Because there was no difference in levels of secretory component between the two groups, the proportion of secretory component/immunoglobulin A was significantly lower in users than non-users. There was no significant difference in antibody function. In the present study, we examined immunoglobulin A from whole saliva of users and non-users to determine the effect of smokeless tobacco on the ability of secretory component to bind to immunoglobulin A containing J chain. Whole saliva was passed over an affinity chromatography filter unit coupled with anti-alpha heavy chain-specific antibody followed by passage over a molecular sieve high-performance liquid chromatography column. Peaks were collected and examined for immunoglobulin A, J chain and secretory component by enzyme-linked immunosorbent assay. Saliva from users had three significantly larger peaks (3-4 fold) at 280 nm than non-users, confirming the presence of a higher concentration of immunoglobulin A in users. The secretory component/J chain and secretory component/immunoglobulin A ratios for the largest peak were significantly less in users. This indicates that smokeless tobacco has an effect on the ability of secretory component to bind to immunoglobulin A without a loss in antibody function. This may occur either prior to immunoglobulin A/J chain binding to secretory component receptors on secretory epithelial cells or internal to the epithelial cells. These studies provide further evidence for the role of secretory component in mucosal immunity.

Adolescent↗
PubMed1987

Differential expression carcinoembryonic antigen and secretory component during colonic epithelial cell differentiation and in colonic carcinomas.

The cellular and ultrastructural distribution of carcinoembryonic antigen and secretory component during differentiation of normal colonic epithelium and in colonic carcinomas was evaluated by peroxidase-labeled antibody immunocytochemistry. Carcinoembryonic antigen and secretory component were found to be markers of distinctly different stages of normal colonocyte differentiation. Whereas secretory component was expressed principally by proliferating absorptive cells in the midcrypt, carcinoembryonic antigen expression was diminished in this crypt zone and was associated principally with mature columnar cells at the luminal surface and with undifferentiated cells at the crypt base. Carcinoembryonic antigen was preferentially expressed on the microvillar plasma membrane and secretory component on the basolateral plasma membrane in the normal colon. In 13 colon cancers studied, carcinoembryonic antigen was expressed on the entire surface of all the colon cancers except one anaplastic tumor, whereas secretory component was only expressed on five well or moderately differentiated cancers. These observations suggest that differentiation of colon cancers as assessed by morphology and phenotypic markers is not totally analogous to that found in the normal colon.

Carcinoembryonic Antigen↗
PubMed1979

Interaction of rabbit secretory component with rabbit IgA dimer.

Secretory component (SC), a glycoprotein with an apparent molecular weight of approximately 80,000, has been isolated from rabbit milk and found to be heterogenous in size and charge. Functionally intact IgA dimer has been dissociated from milk secretory IgA using a chaotropic agent and further purified to homogeneity. The interaction between SC and IgA dimer is a reversible time- and temperature-dependent process. At 23 degrees C, the association rate constant (2.4 x 10(5) M-1 min-1) and the dissociation rate constant (1.8 x 10(-3) min-1) have been measured independently and the affinity constant based on these rates (1.3 x 10(8) M-1) is similar to that calculated from Scatchard plots (1.9 x 10(8) M-1). One class of binding sites has been estimated from Scatchard plots in spite of the observed heterogeneity of SC. The interaction is tighter at low temperatures because the decrease in dissociation rate is greater than the decrease in association rate. The thermodynamic calculations reveal a delta G of -11.0 kcal . mol-1, a delta H of -8.9 kcal . mol-1 and a delta S of +7.0 cal. mol-1 degree-1. The pH range over which interaction occurs is rather large (5 to 8) with no significant differences in apparent Ka.

Animals↗
PubMed1991

Characterization of secretory component in amniotic fluid. Identification of new forms of secretory IgA.

Amniotic fluid (AmF) contains low levels of IgA of fetal origin. Western blot analysis revealed that the major forms of IgA in human AmF contain secretory component (SC), but ranged in size between 170 and 200 kDa, unlike the 380-kDa size typical of previously described secretory (s)IgA. Preliminary characterization of these novel forms of sIgA suggests they may arise by reduction of selected disulfide bonds, rather than proteolytic cleavage, of 380-kDa sIgA. This study also shows that AmF contains SC in its free form. Free SC measured by ELISA in 30 AmF samples increased with gestational age of the fetus from 26 to 40 wk postconception. Late in gestation, the concentrations of free SC levels reached those of other external secretions. Both the fetal urogenital system and the amniotic membrane appear to contribute to both the free SC and sIgA in AmF. This report presents the initial description of a new form of sIgA and provides evidence that the AmF may be an early expression of the mucosal immune system in the developing fetus.

Amniotic Fluid↗
PubMed1986

Posttranslational processing of secretory component in the rat jejunum by a brush border metalloprotease.

Secretory component (SC) is a glycoprotein that mediates the transcellular transport of polymeric immunoglobulins into external secretions. SC is synthesized and inserted into the plasma membrane of epithelial cells and hepatocytes as a transmembrane protein, where it serves as a receptor for polymeric immunoglobulins. SC is posttranslationally cleaved to a soluble protein before secretion into external fluids. In the rat jejunum, we observed that the molecular weights of both the major membrane and soluble forms of SC were 10,000-20,000 smaller than the comparable hepatic forms of the glycoprotein. We therefore set out to determine the reason for the differences in size of SC between these two tissues. The smaller size of jejunal SC was not due to the action of pancreatic proteases or differential glycosylation but was due to proteolysis by a jejunal brush border protease. The protease was characterized as a metalloprotease, with a pH optimum of approximately 5. It is present in jejunal, ileal, and renal tubular brush borders as an integral membrane constituent. When the protease was inhibited in vivo, conversion of jejunal secretory component to the smaller size was partially prevented. Thus, in the rat jejunum, SC undergoes two posttranslational proteolytic events: conversion of membrane secretory component to the soluble form and conversion of soluble SC to a smaller size by a previously undescribed brush border protease.

Animals↗
PubMed1978

Immunoglobulins and secretory component in endometrium and cervix. Influence of inflammation and carcinoma.

The synthesis of immunoglobulins and secretory component in the cervix and the endometrium was studied by tissue culture and immunofluorescence. Out of the 75 cervical biopsies studied, 17 were epidermoid carcinomas, 8 were carcinomas in situ and 23 tissues had inflammatory or metaplastic lesions. A total of 49 samples from endometrium were studied, out of which 22 were in the proliferative phase, 17 were in the secretory phase and 4 were carcinomas. In the cervical tissues without lesions, there were very few plasmacytes, the synthesis of immunoglobulins was low and in 66% of the tissues the synthesis of IgG was equal to or higher than that of IgA. With local modifications, the IgG synthesis was even more preponderant and was very important in epidermoid carcinomas which were infiltrated with numerous IgG plasmacytes. Secretory component was synthesized by almost all the tissues except the epidermoid carcinomas. The endometrium did not synthesize immunoglobulins; secretory component was synthesized only by endometrial tissue in the secretory phase and by 2 of the 4 carcinomas studied. It seems that in the cervix and the endometrium there is no relationship between the production of secretory component and the presence of IgA plasmacytes which probably localise as a result of other influences. The conditions in which the local secretory immunological system would react preferentially remain to be determined.

Autoradiography↗