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PubMed1984

Interaction of the fluorescence-labeled secretory component with human polymeric immunoglobulins.

The secretory component (SC) isolated from human milk was labeled with 2 mol of the fluorescent thiol reagent N-[7-(dimethylamino)-4-methylcoumarinyl]maleimide (DACM) per mol of SC through the reactive disulfide bond of SC. The binding of the labeled SC to polymeric immunoglobulins was examined by gel filtration by measuring the fluorescence of DACM at 478 nm. The labeled SC was bound to immunoglobulin M (IgM) and its (Fc)5 mu fragment and to dimeric immunoglobulin A (IgA). When the labeled SC was bound to IgM or the (Fc)5 mu fragment, the fluorescence of DACM increased about 30%. By use of this fluorescence change, quantitative studies were made on the equilibrium and kinetics of the reversible interactions of the labeled SC with two IgM proteins and their (Fc)5 mu fragments at pH 7.0 and 25 degrees C. All the IgM proteins and their (Fc)5 mu fragments had one binding site per mole of polymers. The affinity constant (6 X 10(8) M-1), the association rate constant (7 X 10(7) M-1 min-1), and the dissociation rate constant (0.1 min-1) of one IgM were different from those of the other IgM (1.7 X 10(9) M-1, 1.0 X 10(8) M-1 min-1, and 0.06 min-1, respectively). However, the values for the (Fc)5 mu fragments of the two proteins were the same (1.9 X 10(9) M-1, 1.1 X 10(8) M-1 min-1, and 0.06 min-1, respectively) and were very similar to those of the IgM with the higher affinity constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites, Antibody↗

PubMed1981

Sensitive solid phase enzyme immunoassay for human IgA, secretory IgA, and secretory component.

Highly sensitive solid-phase immunoassay systems for human immunoglobulin A (IgA), secretory component (SC), secretory immunoglobulin A (SIgA) were developed by use of antisera against the alpha-chain of IgA and SC, and beta-D-galactosidase from Escherichia coli as label. IgA and SC wee assayed with the respective solid-phase (silicone rubber)-immobilized F(ab')2 antibody fragments and the corresponding antibody Fab'-beta-D-galactosidase complex. More than 1 and 0.4 fmol (or 0.16 and 0.03 ng) of IgA, and SC, respectively, were determined, but the assay system for IgA and that for SC cross-reacted with SIgA about 90% and 2%, respectively. SIgA was specifically determined in an assay using silicone rubber with immobilized (anti-alpha-chain)F(ab')2 fragments and (anti-SC) Fab'-beta-D-galactosidase complex with a minimum detectable sensitivity of 2.5 fmol or 1 ng. IgA and SC values could be corrected by subtracting the amounts of cross-reacting SIgA in the same samples. Small amounts of SIgA, SC, and IgA in saliva, sweat, urine, and feces could be determined by the present method.

Child, Preschool↗

PubMed1987

High and low molecular weight rabbit secretory components. Evidence for the deletion of the second and third domains in the smaller polypeptide.

Rabbit secretory components exist in two forms which differ in apparent mass by about 25 kDa. Each of these two forms were reduced, carboxymethylated, and extensively digested with trypsin. The resulting peptides were purified by reverse-phase high performance liquid chromatography and characterized by NH2- and COOH-terminal sequence determination and/or amino acid analysis. They were aligned with the protein sequence predicted from the cDNA nucleotide sequence encoding the rabbit poly(Ig) receptor (Mostov, K. E., Friedlander, M., and Blobel, G. (1984) Nature 308, 37-43). All peptides belonging to the fourth and fifth domains except one (positions 488-496) were accounted for in both forms. In addition, limited tryptic proteolysis of the native low Mr secretory components produced the intact 18-kDa NH2-terminal domain (positions 1-117) and the 30-kDa fragment encompassing the fourth and fifth domains. These results suggest that the smaller polypeptide derives from the larger secretory component form by the deletion of the second and third domains.

Amino Acid Sequence↗

PubMed1988

Tumor necrosis factor-alpha up-regulates expression of secretory component, the epithelial receptor for polymeric Ig.

Secretory component (SC) is the receptor that facilitates transcytosis of polymeric IgA and polymeric IgM through secretory epithelial cells and into exocrine fluids. The present study showed that rTNF-alpha enhanced the cellular pool, membrane expression, and secretion of functionally SC in a human colonic carcinoma cell line (HT-29m2) which is known to express and process SC like normal glandular cells. TNF-alpha also up-regulated membrane expression of the constitutive HLA class I molecules, whereas the cells remained HLA class II-negative.

Cell Membrane↗

PubMed1984

[Demonstration of secretory component in membrane structures of the human thymus].

A large amount of secretory component (Sc) was demonstrated in human thymus by the immunofluorescence technique. The component was found to be contained by the membranes permeating the parenhuyma and surrounding numerous tubular formations in the cortical layer of the organ under discussion. It is suggested that like other heteroorgan antigens, secretory component is involved in the formation of natural immunological tolerance, informing organ lymphocytes of the structures of the host own antigens. It is possible that in addition Sc promotes the differentiation of lymphocytes which repopulate to the lymphoid organs where serum IgA is synthesized and secretory IgA is formed.

Adolescent↗

PubMed1993

Alpha-chain disease: analysis of alpha-chain protein and secretory component in jejunal fluid.

BACKGROUND: It is unclear why different forms of alpha-chain disease protein appear in intestinal fluid. This was studied in a 23-year-old Mauritanian man in whom alpha-chain disease was diagnosed localized to the duodenum and jejunum, nasopharynx, and bone marrow. METHODS: The duodenal infiltrate was studied by immunohistochemistry. Forms of alpha chain-containing proteins in serum and jejunal fluid were analyzed by ultracentrifugation and radioimmunoassays. RESULTS: The infiltrating cells contained alpha-1 chain but no light chains, and approximately 66% showed variable expression of J chain. Serum contained a large fraction of monomeric alpha-chain disease protein, whereas both monomeric and heavier forms appeared in jejunal fluid. Some of the latter were bound to secretory component, and the fluid contained virtually no free component. CONCLUSIONS: Linkage of polymeric alpha-chain disease protein to secretory component depends on balanced synthesis of alpha chains and J chain in the proliferating B cells, giving rise to polymers with binding site for secretory component expressed as an epithelial receptor. Insufficient receptor-mediated transport capacity (either relative and/or because of intestinal crypt reduction) results in passive external transfer of polymers without bound secretory component along with leakage of serum-derived or locally produced monomeric alpha-chain disease protein, the latter presumably originating from immunocytes with little or no J-chain synthesis.

Adult↗

PubMed1988

[Production and characterization of monoclonal antibodies to the secretory components of human IgA].

The monoclonal antibodies BL-HSC/1-3 are characterized by means of indirect radioimmunotechnique with regard to their binding pattern to a set of human proteins. The results suggest a binding specificity of the three monoclonals for A-determinants of the human secretory component. However, we could not point out a different binding pattern to the immunoglobulin-bound and the free molecule, respectively. By use of appropriate immunoassays, the monoclonal antibody BL-HSC/3 is the most suitable one for the detection of the secretory component and secretory IgA in body fluids. The protein band labeled by BL-HSC/3 in the immunoblotting analysis corresponds to a molar mass of 79,000 D according to the data known for the human secretory component.

Antibodies, Monoclonal↗

PubMed1980

Immunohistochemical localization of IgA and secretory component in rat liver.

IgA is transported from rat blood into bile. The localization of IgA and secretory component in rat liver was studied in order to facilitate understanding of this IgA transport. Both indirect immunofluorescence and unlabeled antibody enzyme histochemical techniques were used. Immunoglobulin A was found surrounding bile canaliculi, within bile duct epithelium, on or near the plasma membranes of hepatocytes, within the cytoplasm of a few intensely stained hepatocytes, within the cytoplasm of intensely reactive cells found in or adjacent to the sinusoids, and in sparsely distributed plasma cells. Reactivity for secretory component was present surrounding bile canaliculi, within bile duct epithelium, or or near the plasma membranes of hepatocytes and in the cytoplasm of hepatocytes. These findings are compatible with the hypothesis that immunoglobulin A is transported from blood to bile through hepatocytes by a process involving secretory component. Bile duct epithelium may also have a role in immunoglobulin A transport.

Animals↗

PubMed1978

Characterization and localization of secretory component in the chicken.

A component found free in intestinal contents and caecal contents of conventional and germ-free chickens (lacking IgA producing cells) was found to have similar characteristics to mammalian secretory component (SC). Free secretory component (FSC) showed a classic reaction of partial identity with secretory IgA (SIgA) from bile, intestinal contents and cystic oviduct fluid. Furthermore, there was demonstrable cross-reactivity between FSC and a low molecular weight component released from SIgA by mild reductive dissociation, confirming the presence of a disulphide-linked accessory polypeptide chain. Fractionation of serum IgA revealed two molecular classes of IgA, a high molecular weight 15S IgA which possessed SC and could not be differentiated antigenically from SIgA and a low molecular weight 7S IgA which showed a reaction of partial identity with 15S IgA and non-identity with FSC. Fluorescent localization of SC in young germ-free chicks demonstrated its presence in the supranuclear golgi zone, apical cytoplasm and basement membrane of crypt epithelial cells. It is concluded that the characteristics of chicken SIgA are closely aligned with those of its mammalian counterpart and are consistent with a system in which SIgA is the wynthetic product of two distinct cells, final assembly occurring in the crypt epithelium.

Animals↗

PubMed1975

Secretory component of the guinea-pig.

Free secretory component (FSC) was purified from guinea-pig milk by gel-filtration and immunoabsorption on anti-SC antibodies. Guinea-pig FSC cross-reacted with antisera to human FSC, and the reverse. Guinea-pig and human FSC resembled each other in molecular size, electrophoretic mobility and heterogeneity, as well as by the existence of antigenic determinants restricted to the unassociated form of the molecule. Guinea-pig FSC associates in vitro with guinea-pig IgM. Distribution of disulphide links is required to set free guinea-pig FSC from secretory IgA.

Animals↗

PubMed1983

Serum secretory component: a potential marker of biliary obstruction.

Secretory Component (SC) was measured in serum samples from patients with a variety of disorders using enzyme-linked immunosorbent assay (ELISA). The overall precision of the method at high and low concentrations of SC was 11% (CV). Serum concentrations of SC were significantly higher in patients with several forms of liver disease (means = 82.37 mg/l +/- SD 56.9) compared with normals (means = 6.0 +/- SD 4.2), patients with diseases of mucosal surfaces (means = 7.4 mg/l +/- SD 4.2) and patients with elevated alkaline phosphatase due to causes other than overt liver disease (means = 16.4 mg/l +/- SD 7.6). Serum SC levels correlated strongly with serum alkaline phosphatase activity (rs = 0.648) in the presence of liver disease. Raised serum SC in liver disease probably reflects reflumeans of biliary SC and secretory IgA into blood due to cholestasis. Estimation of serum SC could be clinically useful as an index of biliary obstruction, especially to distinguish a raised serum alkaline phosphatase activity of liver or bone origin.

Alkaline Phosphatase↗

PubMedDate not supplied

[Immunohistochemical identification of secretory component (SC) in activated mesothelial cells].

Twenty-two cytoblocks from serous effusions very rich in activated mesothelial cells were immunohistochemically tested to indicate about the presence of synthesis of Secretory Component and transport of IgA Antibodies across mesothelium; the tests were positive for S.C., while failed in order to demonstrate intracytoplasmic IgA. Authors hypothesize that association between Secretory Component synthesis and IgA transport may be not necessary absolute and that Secretory Component may play another unknown role related to glandular epithelial specialisation.

Antibodies, Monoclonal↗

PubMed1976

Synthesis of immunoglobulin and secretory component by gastrointestinal mucosa in patients with hypogammaglobulinaemia or IgA deficiency.

Biopsies of intestinal mucosa from patients with adult hypogammaglobulinaemia or selective IgA deficiency have been studied for the ability to synthesize immunoglobulins and secretory component. Tissue fragments were cultured in vitro in medium containing 14C-labelled amino acids and newly snythesized proteins were detected by radioimmunoelectrophoresis. Synthesis of IgA, and in some cases IgG and IgM, was found in intestinal mucosal biopsies from hypogammaglobulinaemics and IgA-deficient subjects. Biopsies from all the patients also synthesized secretory component, but evidence was obtained which indicated that secretory component does not combine normally with IgA. Tissue sections of these biopsies have also been studied by immunofluorescence and immunoglobulin bearing cells have been demonstrated. The present findings demonstrate that immunoglobulin synthesizing cells are present in the intestinal mucosa of immunoglobulin-deficient individuals. Local immunoglobulin synthesis may partially explain why these patients do not often have major problems with intestinal infections.

Adolescent↗

PubMed1983

A functional homologue of mammalian secretory component exists in chickens.

The existence of a molecule in chickens homologous to the secretory component of mammals has long been in dispute. An intravenous injection of [14C]fucose was given to chickens as a marker for newly synthesized glycoproteins and then unlabeled human IgA was injected intravenously half an hour later. It was shown that the human IgA subsequently appeared in the bile of the chickens combined with a [14C]fucose-labeled molecule; the chicken IgA in these bile samples was similarly labeled. Radiolabeled human secretory IgA was not transported in large amounts across the chicken liver in vivo and neither was purified chicken bile IgA. These results indicate that a molecule exists in chickens which behaves in a manner analogous to mammalian secretory component.

Animals↗

PubMed1988

High serum levels of secretory component in hepatocellular carcinoma.

PURPOSE: Elevated levels of secretory IgA (S-IgA) have been detected in serum samples from patients with liver diseases and neoplasia with liver metastasis. We undertook the current study in order to determine the concentrations of different forms of free secretory component (SC) in sera from patients with hepatocellular carcinoma. MATERIALS AND METHODS: The concentrations of SC, S-IgA, and secretory IgM (S-IgM) were quantified in the sera of 100 patients with hepatocellular carcinoma, and in 77 matched healthy control subjects by using an enzyme-linked immunosorbent assay. RESULTS: Free SC serum levels exceeded the upper limits of control values in 82 percent of patients with hepatocellular carcinoma, S-IgA levels in 88 percent of them, and S-IgM levels in 32 percent. Free SC levels were positively correlated with S-IgA and S-IgM levels. They were weakly correlated with gamma-glutamyl transpeptidase activity, but not with alpha-fetoprotein, beta 2-microglobulin, albumin, or IgA serum concentrations, nor with alkaline phosphatase activity. CONCLUSION: The data clearly demonstrate the elevation of serum free SC concentrations as a novel biologic alteration in hepatocellular carcinoma since free SC levels appear to be correlated neither with tumor markers (alpha-fetoprotein, beta 2-microglobulin) nor with biliary obstruction.

Adult↗

PubMed1995

Constitutive and cytokine induced expression of HLA molecules, secretory component, and intercellular adhesion molecule-1 is modulated by butyrate in the colonic epithelial cell line HT-29.

Normal colonic epithelial cells play an important part in the mucosal immune system and use butyrate, a bacterial fermentation product, as an important energy source. Butyrate deficiency has been associated with inflammatory bowel disease, diversion colitis, and pseudomembranous colitis. Butyrate effects on important molecules for epithelial immune functions were studied in a colonic epithelial cell line (HT-29): the constitutive and cytokine regulated expression of secretory component (poly-Ig receptor), HLA class I and II molecules, and intercellular adhesion molecule-1 (ICAM-1). Butyrate facilitated the constitutive expression of secretory component and HLA class I. Butyrate furthermore tended to enhance cytokine mediated stimulation of protein expression, although tumour necrosis factor alpha (TNF) and interleukin 4 (IL 4) responses on HLA class I and secretory component, respectively, were relatively inhibited by butyrate. Cytokine mediated accumulation in the various mRNAs usually increased even more in the presence of butyrate, with the exception of TNF response on HLA class I and secretory component mRNA concentrations. In conclusion, butyrate may substantially influence constitutive and cytokine mediated expression of molecules with immune functions in a complex and differentiated manner, and butyrate deficiencies, as seen in various clinical conditions, might influence mucosal immune responses.

Base Sequence↗

PubMed1984

Hormonal influence on the secretory immune system of the eye: androgen control of secretory component production by the rat exorbital gland.

Androgens are known to regulate the level of secretory component (SC) in tears of male rats. The purpose of the present study was to explore the underlying mechanism of this hormone action by (i) identifying the ocular tissue(s) involved in SC production; and (ii) determining whether androgens increase SC production by this tissue. We also examined whether androgen administration influenced the concentration of SC in tears of female rats. Ocular tissues from adult Sprague-Dawley rats were cultured in the presence or absence of cycloheximide in the incubation medium. Secretory component in the culture media was measured by an RIA which detects primarily free SC. Analysis of media obtained after incubation of exorbital (lacrimal) glands, 'lid' tissues, globes, and Harderian glands revealed that only exorbital glands released substantial amounts of SC. This exorbital gland production of SC, which was significantly greater in tissues from male rats, as compared to those of female rats, was reduced by approximately 50% when cycloheximide was present in the culture medium. To determine whether SC production by exorbital glands was influenced by androgens, orchiectomized glands was influenced by androgens, orchiectomized rats were administered either saline or testosterone (2.0 mg/day for 4 days), and exorbital glands were cultured 24 hr after the last injection. Testosterone treatment in vivo induced a significant, cycloheximide-sensitive increase in SC production in vitro, compared to the glandular SC output of saline-injected controls. It is interesting that similar androgen treatment of ovariectomized females also resulted in elevated tear SC concentrations and enhanced output of SC by their exorbital glands in vitro. These findings indicate that the exorbital gland is primarily responsible for SC production in the rat eye and that androgens may modulate the synthesis of SC in this gland.

Animals↗

PubMed1992

Rat secretory component binds poorly to rodent IgM.

Our previous studies and those of others indicated that human secretory component (SC), the five domain extracellular portion of the poly Ig receptor, binds avidly to both pIgA and IgM. In this study we report that in rodents, SC binds primarily to pIgA. Rat secretory component was isolated from bile and radiolabeled to known specific activity with 125I. Radiolabeled rat SC was incubated with rat and mouse monoclonal proteins for 1 h at room temperature and overnight at 4 degrees D. Binding of 125I-rat SC to Ig was determined in two ways: 1) immunoprecipitation of putative 125I-rat SC-Ig complexes with anti-L chain antibodies; 2) HPLC gel filtration on an analytical TSK 4000 column that separated free 125I-rat SC from 125I-rat SC bound to Ig. Both methods of analysis yielded similar results. Rat and mouse polymeric (p) IgA bound rat SC with high avidity, although the binding activity of the IgM from either species was virtually nil. The number of SC-binding sites on rat polymeric Ig was determined by immunoprecipitation of mixtures of rat pIg with saturating concentrations of 125I-rat SC and yielded values of 1.0 and 0.05 for rat pIgA and IgM, respectively. The significance of these findings with respect to the biologic function of the pIg R in rodents and the nature of the pIg R-binding site on pIg is discussed.

Animals↗