Distribution and processing of the polymeric immunoglobulin receptor in the rat hepatocyte: morphological and biochemical characterization of subcellular fractions

The transepithelial transport of polymeric immunoglobulins is an essential process in the mucosal immune system. Transport across the epithelial cells of mucous or exocrine glands is affected by an integral membrane glycoprotein receptor known as membrane secretory component (SCm) or as polymeric immunoglobulin receptor (pIgR). This receptor binds polymeric immunoglobulins at the basolateral cell surface and mediates their transcellular translocation and their release from the apical plasma membrane into external secretions. Release depends on cleavage of the membrane-anchoring domain of the receptor, resulting in liberation of polymeric immunoglobulin bound to the ectoplasmic domain of the receptor (secreted SC or SCs) into extracellular secretions. Using a monoclonal antibody directed against the cytoplasmic tail of the receptor and a polyclonal antibody directed against the secreted ectoplasmic domain, we have combined cell fractionation and Western blotting techniques to examine the fate of these receptor domains in the hepatocyte. In this study, we characterize biochemically and morphologically the various subcellular components separated by our fractionation scheme, and correlate this with biochemical analysis of the receptor in each fraction.

Bacterial immunoglobulin A proteases monitored by continuous spectrophotometry

IgA proteases were estimated in a turbid aqueous two-phase system with 10% polyethylene glycol-Tris buffer, where IgA spontaneously concentrates in microscopic spherical particles (less than 1 micron). After enzymatic cleavage of IgA into Fab alpha and Fc alpha fragments, these fragments are soluble and decreasing turbidity is observed. The reaction may be followed by conventional spectrophotometry. In this manner, IgA proteases may be estimated in 10 min. Examples of the utility of the method are given with results from inhibitor studies, estimation of Km and purification of IgA protease from Haemophilus influenzae.

Secretory IgA and secretory component in women affected by recidivant vaginal candidiasis

Local immunity was evaluated in 47 patients affected by recidivant vaginal candidiasis and 33 control women. IgG, IgA, IgM and secretory component (SC) were determined by single radial immunodiffusion in samples of cervicovaginal secretion. IgG in dosable levels was detected in 17/47 samples (36.2%) and IgA in 15/47 patients (31.9%) whereas in the controls, the incidence was 31/33 (93.9%) for IgG and 24/33 (72.7%) for IgA. The difference was significative (P less than 0.001) for both immunoglobulins. Significant differences were not obtained for IgM. The SC was detected in 4/47 cervicovaginal secretions of patients affected by candidiasis (8.5%) whereas in the control samples the incidence was 21/33 (63.6%) (P less than 0.001). In only 2/15 patients with dosable levels of IgA (13%) the secretory nature of this immunoglobulin could be shown by its reaction with anti-SC serum. In the control group, secretory IgA was detected in 19/24 cases (79%) (P less than 0.001). Serum immunoglobulins levels were normal. The lack of secretory IgA and SC in the secretion could be related to the adherence capacity of the Candida albicans to epithelial cells.

Effect of age, malnutrition and renutrition on free secretory component and IgA in secretions

The development of free secretory component (FSC) was studied in the tears of normal infants, children and adults. The level of FSC in tears was higher in older adults than in children. Free secretory component was also measured in the tears of normal, moderately and severely malnourished Colombian children. Children suffering from kwashiorkor, combined protein-calorie malnutrition or marasmus were studied before and after renutrition. No change was detected in the concentration of FSC in tears of moderately malnourished (Grade I and II) children. There was a significant difference between normal and severely malnourished children which improved with renutrition. The levels of tear IgA were decreased in the moderately malnourished children. These results indicate that reduction in secretory IgA levels in moderate malnutrition may not be explained by a lack of available free secretory component in tears, but that severe malnutrition may impair the S-IgA system by significantly reducing the availability of free secretory component.

[Clinico-immunological evaluation of T cells bearing IgG Fc receptors in brain tumor patients]

T cells bearing IgG Fc receptors (Tr cells) were determined in 40 cases of brain tumor using the double rosette method, and compared with the changes of PHA reaction, immunoglobulin (IgG A M), performance status, and mass effect on CT in 20 pre-and post-operative and/or radio-clinico-immunotherapeutic patients. The proportion of control Tr cells was 8-19% in 20 healthy adults. Values of Tr cells over 20% were correlated with a poor grade of performance status, and large mass effects on CT. Post-therapeutic change in the value was well correlated with change in performance status, mass effects, and IgG. Our results suggest a correlation between the value of Tr cells and clinico-radiological findings. Immunological analysis of Tr cells serves as a parameter of tumor expansion or prognosis, and could be of significant importance clinically.

Preparation and biologic characterization of fragments containing dimeric and monomeric C gamma 2 domain of rabbit IgG

A number of fragments derived from acid-treated rabbit IgG by digestion with plasmin have been separated by high-resolution gel filtration. Fragments isolated included a dimer and monomer Facb, named F(acb)2 and Facb, respectively and a heterodimer composed of Facb and Fab subunits, named F(acb)(ab). A C gamma 2 fragment was obtained by papain digestion of Facb. A heterodimer composed of Facb and Fab', named F(acb)(ab'), was also prepared by oxidizing a reduced mixture of these fragments. Fragments thus obtained are classified into two groups--those carrying paired C gamma 2 domains, i.e. F(acb)2, and the disulfide-linked dimeric C gamma 2 fragment; and those having a single C gamma 2 domain, i.e. reduced, alkylated Facb and C gamma 2 fragment, F(acb)(ab) and F(acb)(ab'). These fragments exhibited marked differences in their capacity to activate complement in assay systems of hemolysis and complement consumption by immune complexes or aggregates on polystyrene latex. Fragments of the former group could activate complement but with a definitely reduced efficiency (50%) compared to intact IgG, whereas fragments of the latter group were practically inactive. Although it was not determined whether the C1-binding capacity itself is changed by monomerization of the C gamma 2 domain, the results suggested that the intact paired C gamma 2 module is required at least for the activation process of complement.

The clinical relevance of classes of immunoglobulins on spermatozoa from infertile and vasovasostomized males

Following reversal of vasectomy, conceptions occur even when antisperm antibodies are present in the seminal plasma, but this is most unusual in men with similar titers of such antibodies who are spontaneously infertile. To clarify the differences between antisperm antibodies occurring in infertile men and those associated with vasectomy reversal, we have studied 23 spontaneously infertile men and 22 men who underwent vasectomy reversal, all of whom had antisperm antibodies detected in seminal plasma by the same tray agglutination test. The class of antibody on spermatozoa was defined by a double-antibody technique using diluted rabbit anti-human IgG, IgM, or IgA or secretory component, followed, after washing, by 125I-labeled donkey anti-rabbit Ig. The results have shown that similar amounts of IgG and IgM were present on the spermatozoa, but infertile men had significantly more IgA and especially more secretory component than men who underwent vasectomy reversal. This was associated with significantly greater impairment of penetration of cervical mucus in the former group. It appears that the type of antibody on the spermatozoa may vary according to the stimulus for its production.

Biogenesis of the polymeric IgA receptor in rat hepatocytes. II. Localization of its intracellular forms by cell fractionation studies

In the companion paper (Sztul, E. S., K. E. Howell, and G. E. Palade, J. Cell Biol., 100:1248-1254), we have shown that pulse labeling of hepatic proteins with [35S]cysteine can be obtained in vivo in intact rats. Soluble label clears the plasma in approximately 5 min, and incorporated label reaches peak values in the liver approximately 20 min after injection. In the present study, we show that the 105,000-mol-wt protein (105K), kinetically the earliest intracellular form of secretory component (SC), is the predominant form found, between 5 and 20 min postinjection, in homogeneous rough microsomal fractions. The second kinetically defined form, i.e., 116K, is the predominant species present in relatively homogeneous, light Golgi fractions in which it appears at approximately 15 min, and peaks at approximately 25 min, postinjection. The third kinetically defined form, 120K, is found 30 min after injection as the major SC species (albeit still accompanied by its immediate precursor, 116K), in a sinusoidal plasmalemmal fraction isolated by immunoadsorption to anti-SC-coated Sepharose beads. These findings lead to the following conclusions: (a) SC is synthesized on polysomes attached to the rough endoplasmic reticulum (ER) membrane; (b) it is partially translocated across the ER membrane and core glycosylated co-translationally to give a 105K peptide; (c) 105K moves from the ER to the Golgi complex where it is terminally glycosylated to give the 116K form; (d) the latter moves to the sinusoidal plasmalemma where it appears together with the final mature form, 120K. Kinetic evidence indicates that the vesicular carriers involved in the transport of SC from the Golgi complex to the sinusoidal plasmalemma, and from the latter to the biliary front of the hepatocytes, are present in a Golgi heavy fraction and a crude carrier vesicle fraction from which they remain to be isolated, purified, and characterized.

Biogenesis of the polymeric IgA receptor in rat hepatocytes. I. Kinetic studies of its intracellular forms

The polymeric IgA receptor (or secretory component [SC]) is a major biliary secretory protein in the rat. It was identified as an 80,000-mol-wt (80 K) glycoprotein by coprecipitation (with IgA) by anti-IgA antibodies (Sztul, E. S., K. E. Howell, and G. E. Palade, 1983, J. Cell Biol., 97:1582-1591) and was used as antigen to raise anti-SC antibodies in rabbits. Pulse labeling with [35S]cysteine in vivo, followed by the immunoprecipitation of solubilized total microsomal fractions with anti-SC sera, made possible the identification of three intracellular forms of SC (all apparently membrane proteins) and the definition of their kinetic and structural interrelations. At 5 min postinjection of [35S]cysteine, a major band of Mr 105,000 was maximally labeled. This peptide lost radioactivity concomitantly with the appearance of a radioactive doublet of Mr 116,000 and 120,000 at 15-30 min postinjection. Loss of radioactivity from 116K paralleled increased labeling of the 120K peptide which appears to be the mature form of the receptor. The 105K form was sensitive to endoglycosidase H which converted it to a 96K peptide. The 116K and 120K forms were resistant to endoglycosidase H but sensitive to endoglycosidase F which converts them to 96K and 100K forms, respectively. Taken together, these findings support the following conclusions: (a) All rat hepatic SC forms are the products of a single gene; (b) all SC forms are N-glycosylated; (c) the 116K form is the result of the terminal glycosylation of the 105K form; and (d) the 120K peptide is probably produced by modifications at other sites than its complex oligosaccharide chains.

[Immunohistochemical localization of keratin and secretory component in carcinoma of the uterine cervix]

Carcinoma of the uterine cervix is said to frequently show a combination of squamous epithelial and glandular epithelial characteristics. In the present study, immunohistochemical localization of keratin and secretory component (SC) was studied to clarify these characteristics of cancers of the cervix, and the following results were obtained. Demonstration of the localization of keratin and SC was useful in providing functional markers of the squamous and glandular epithelium of the cervix. In epidermoid carcinomas, the squamous epithelial character of the keratinizing carcinomas was strongest and decreased in the large cell non-keratinizing, followed by the small cell non-keratinizing carcinomas. The glandular character of these lesions decreased in the same order. Subclassification of CIS did not reveal any major changes with either kind of staining. So-called bipotential differentiation was found in 21% of the epidermoid, 53% of the adenocarcinomas and 13% of the CIS. In the clinical stages of epidermoid carcinomas, the stage I and II cases more frequently showed squamous characteristics than did the stage 0 cases.

Immunohistochemical demonstration of IgA and secretory component in relation to epithelial cell differentiation in normal colorectal mucosa and metaplastic polyp: a semiquantitative study

The metaplastic polyp is a non-neoplastic epithelial lesion found within the human colorectum. Although not regarded as precancerous, recent studies have demonstrated the expression of multiple cancer-associated phenotypes. This might indicate a possible indirect relationship between metaplastic polyps and colorectal cancer. Epithelial secretory component and IgA were demonstrated by the immunoperoxidase technique and staining intensities were assessed semiquantitatively. The findings were related to cellular differentiation in normal colorectal epithelium as compared to the metaplastic polyp. The crypt base cells and also the surface epithelial cells stained with similar intensity in both types of epithelium. However, the expected increase in staining characterizing normal lower and upper crypt columnar cells and reduction in staining associated with the switch from crypt to surface columnar cell was not observed in the metaplastic polyp. Metaplastic crypt columnar cells showed significantly reduced staining for both IgA and secretory component as compared to their normal counterparts. There was also a significant reduction in the number of IgA-secreting plasma cells in the lamina propria of the metaplastic polyp. These findings are consistent with the concept of a premature switch to mature surface cell characteristics within the metaplastic polyp. They are discussed in the light of other changes in phenotype associated with this lesion.

Nasopharyngeal carcinoma: immunohistochemical study for keratin, secretory component and leukocyte common antigen

Immunohistochemical studies using antisera to keratin and secretory component (SC) and monoclonal antibody against leukocyte common antigen (LCA) were performed on 92 biopsy and autopsy specimens taken from 65 patients with nasopharyngeal carcinoma. Five biopsy specimens from malignant lymphoma of the nasopharynx and tonsil, and 20 biopsy specimens of nasopharyngeal epithelium were also included in the study. Keratin was positively stained in all squamous cell carcinomas and nonkeratinizing carcinomas, and 38 of 46 undifferentiated carcinomas (82.6%), but in no malignant lymphomas. LCA was intensely stained in all malignant lymphoma, but in no nasopharyngeal carcinomas. SC was positively stained in two of the 46 undifferentiated carcinomas (4.3%). Nasopharyngeal carcinoma is a definite malignant epithelial neoplasm and can be distinguished from malignant lymphoma by immunostaining for keratin and LCA. Some undifferentiated carcinoma may show cellular differentiation toward ciliated epithelium.

The ocular secretory immune system of the rat

Ocular tissues and tears of adult male rats were examined for the presence of immunoglobulins (Ig) and secretory component (SC). By immunofluorescent analysis, we found the highest density of Ig-containing cells in the exorbital (lacrimal) gland. In contrast, few if any Ig-containing cells were observed in the conjunctiva or Harder's gland. IgA was the most frequent cell-associated isotype identified in the exorbital gland, and the number of IgA-containing cells was much greater than that of IgM- or IgG-containing cells. With respect to IgG, cell counts were fairly evenly distributed among the various subclasses. No IgE-containing cells were detected in ocular tissues. SC was identified exclusively within the acinar cells of the exorbital gland. In tears, IgA was the predominant isotype and occurred almost entirely in the polymeric form. Of the IgG subclasses, IgG 2a was present in the greatest concentration. Only trace amounts of IgG 2b were found, and IgG 1, IgG 2c and IgM could not be detected. The level of free SC in tears was relatively high, compared to the concentration of free SC reported in other mucosal secretions. These results suggest that the exorbital gland is the primary tissue associated with the ocular secretory immune system of the rat. Furthermore, our findings indicate that rat tears contain components that may provide immune defense for the ocular surface.

[Study on the local immune system of the human pancreas and liver--ultrastructural localization of IgA and secretory component]

The localization of IgA and secretory component (SC) in human pancreas and liver was studied by the peroxidase-labeled antibody method. Ultrastructurally, SC was found in perinuclear spaces, in endoplasmic reticulum, in saccules associated with Golgi complexes, on basolateral membranes, in endocytic invaginations and in cytoplasmic vesicles of the pancreatic epithelial cells and the biliary epithelial cells. IgA was found in subepithelial connective tissues, in basement membrane and on basolateral membranes, in endocytic invaginations and in cytoplasmic vesicles of the cells in which SC was visualized. From the above findings, we concluded that IgA was transported into pancreatic juice and bile by SC-mediated vesicular transport mechanism across the pancreatic epithelial cells and the biliary epithelial cells. The presence of local immune system in human pancreas and liver is assumed to be one of the principal factors that prevent severe infection after surgical operation for the organs.

Immunological abnormalities in healthy relatives of patients with IgA nephropathy

Patients with IgA nephropathy have elevated serum levels of polymeric IgA, probably due to an increase in their synthesis by peripheral blood mononuclear cells, and specific abnormalities in the immunoregulation of IgA. The existence of familial cases of IgA nephropathy, as well as the published association of this nephropathy with some antigens of the HLA system, decided us to test the hypothesis that some of these alterations might be genetically controlled. For this reason we studied some of these immunological assays in 25 first-degree relatives of 7 patients with IgA nephropathy and 22 control subjects matched for age and sex. An abnormal immunological assay was found in at least 1 relative of all families examined. Thus, 16 of 25 relatives had a significant increase in the percentage of polymeric IgA-producing cells after 7 days of culture in the presence of pokeweed mitogen. Some derangement in the concanavalin A generation of specific IgA suppressor cells was found in 11 out of 25 relatives. These results are, though in lower frequency, similar to those seen in patients and suggest that the IgA-immunological abnormalities observed are genetic markers, even if they cannot by themselves explain the pathogenesis of the IgA nephropathy. The absence of IgA immune complexes seen in relatives as well as their high prevalence in patients suggest that in predisposed subjects other factors (genetic or not) are required for the development of IgA nephropathy.

[Cellular histamine liberation and mediators of anaphylaxis]

A study of the release of histamine from basophils and mast cells is clearly important to understand the mechanisms of activation of these cells and the anti-allergic mechanisms of the drugs in use. Important information has been gained through the study of highly purified rodent mast cells as well as human mast cells and basophils of low purity, in many fields: morphology, triggering mechanisms, degranulation and mediator release. Recent findings obtained with purified human mast cells and basophils could better identify the specific potential mediators of these two cells. Many biochemical events have been associated with anaphylactic mediator release: recent evidence suggested that an elevation of intracellular calcium level was an essential event in the processes by which mediators are released.

Distribution of secretory component and immunoglobulins in the developing lung

The distribution of secretory component and immunoglobulins, IgA, IgG, and IgM in developing human lungs, ranging in age from 12 gestational weeks to 8 yr, was studied using the indirect peroxidase-labeled antibody method. Secretory component appeared first in the serous bronchial epithelium near the duct openings at the sixteenth gestational week, in goblet cells at the twentieth gestational week, and in bronchiolar epithelium at the twenty-second gestational week. The number of secretory component-positive cells (Y) in bronchial epithelium increased with age in weeks (X) according to the formula Y = 15.328 + 0.094 log X (p less than 0.001). Secretory component was almost absent in bronchiolar epithelium in atelectatic lungs with or without hyaline membrane. Secretory component-positive cells were never observed below the levels of respiratory bronchioles. Immunocompetent cells appeared in the bronchial walls after birth in normal lungs, but they appeared at the thirty-ninth gestational week in cases of pulmonary infection. The IgA- and IgM-containing cells were present around the bronchial glands in normal lungs, whereas IgG-containing cells were not associated with the glands. In normal lungs, IgA-containing cells were most prominent, followed by IgM-containing cells and IgG-containing cells. The apical portions of serous epithelial cells of bronchi and bronchial glands were positive for IgA and IgM. In bacterial and viral pulmonary infections, IgA-containing cells increased in number in the bronchial glands. The appearance of secretory component-positive cells long before immunoglobulin-containing cells in fetal lungs suggests that secretory component may play some role in the formation of the mucociliary blanket, instead of selective transport of IgA or IgM.

Secretory component in breast cancer. Analysis of the levels in primary and metastatic disease

Levels of secretory component (SC) were measured in breast tumors from 95 patients with primary or metastatic cancer. Tumor cytosols were prepared by polytron disruption and high speed centrifugation (105,000 g X 30 min) and SC was measured using a sensitive radioimmunoassay which detects primarily free SC. In frozen samples stored for up to 5 months SC resisted degradation and could be measured quantitatively without interference. In primary tumors from patients between ages 28 and 97, SC positive samples ranged from 4 ng/mg protein to 600 ng/mg protein. In metastatic lesions, SC positive samples ranged no higher than 46 ng/mg protein. The studies indicate that SC can be measured quantitatively in both primary and metastatic tumors and that prolonged storage does not interfere with measurements of SC. The wide variation in SC levels in primary tumor samples may be related to a susceptibility to metastasis. Further, the low levels of SC in metastatic lesions could indicate a potential for SC involvement in immune regulation of tumor growth.

The concentrations of IgA and free secretory piece in the nasal secretions of patients with recurrent respiratory infections

The concentrations of total IgA, 11S IgA, total and free secretory piece (SP) were measured in the nasal secretions of 39 patients with recurrent upper and lower respiratory tract infections during an infection free period. In all of eight patients who had selective serum IgA deficiency (less than 0.05 g/l) IgA was also undetectable in their nasal secretions and the mean concentration of free SP was significantly raised. However, the mean concentrations of 11S IgA, SP and free SP in nasal secretions of patients with normal or low (greater than 0.05 g/l but below the normal range) serum IgA were not significantly different from those of 10 healthy normal subjects. In patients with detectable nasal secretory IgA, 11S IgA concentrations correlated significantly (r = 0.57; P less than 0.001) with concentrations of free SP. One patient with normal serum IgA was found to have a large excess of free SP and therefore may have had a relative defect in local IgA production.

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.

A comparison of the amino acid sequences of the extracellular domains of the immunoglobulin superfamily. Possible correlations between conservancy and conformation

Amino acid sequences of immunoglobulins, histocompatibility antigens, Thy-1 antigens, polyimmunoglobulin receptor and T-lymphocyte receptor have been compared and conserved residues correlated with features on the atomic models of immunoglobulin fragments. The peptide chains are apparently folded into globular domains closely related in three-dimensional structure to immunoglobulin V or C domains. Exceptions are histocompatibility class I alpha 2 and class II beta 1 domains, distantly related, and class I and II alpha 1 domains, no apparent relationship to immunoglobulin domains.