The human secretory immunoglobulin system: immunohistoligical localization of gamma A, secretory "piece," and lactoferrin in normal human tissues

The secretory immune system and renal disease

An immunopathological analysis of renal tissue from 105 patients was undertaken: (1) to clarify the relationship of the secretory immune system to renal diseases in which glomerular deposits of immunoglobulin A, (alpha chain), occurred; (2) to determine the lower nephron localization of secretory component and alpha chain in renal disease. This study, which included twenty-four patients with glomerular deposits of alpha chain, failed to reveal glomerular localization of secretory IgA. Secretory component was not found in renal tubular cells in kidneys with normal or minimally abnormal renal histology. In contradistinction to these findings, significant amounts of secretory component were found in tubular epithelial cells and casts in tissue from fifty-one patients with morphological evidence of significant renal damage; this localization had no correlation with glomerular deposits of IgA, IgM or other immunoreactants. Alpha Chain was rarely found in the tubular epithelium or in interstitial round cells; fifteen patients had alpha chain in casts. We conclude that the glomerular localization of immunoglobulin in glomerulonephritis is not derived from the secretory immune system, and the IgA present in glomeruli is not secretory IgA. The finding of secretory component in tubular cells in diseased kidneys without alpha chain may support an hypothesis for an independent role for secretory component in renal disease, apart from its function in the transport and stabilization of secretory IgA.

Synthesis of immunoglobulins and 15 other proteins by diseased human kidneys

In an effort to determine the synthetic capacity of human kidneys for serum proteins, pieces of both kidneys removed at operation prior to transplantation were placed in organ culture. Incubation with 14C labelled amino acids and subsequent radioimmunoelectrophoresis with antisera to all five classes of immunoglobulins showed synthesis of IgG by all 5 pairs of kidneys of IgA and IgE by 4, and of IgM by 2. None synthesized IgD. Radioimmunoelectrophoresis with specific antisera to 15 non-immunoglobulin proteins revealed synthesis of lactoferrin and uromucoid while several other serum proteins, such as alpha1 antitrypsin and alpha2 macroglobulin, known for their binding properties, showed apparent synthesis. No evidence for secretory component synthesis was seen despite positive immunofluorescent localization in the tubular cells. Further, Zn alpha2 and beta2GP I also showed positive immunofluorescence but negative synthesis. It seems possible that these latter proteins may not be synthesized by the tubular cells but rather may be actively excreted or reabsorbed by them.

Structural composition of canine secretory component and immunoglobulin A

Dog serum and colostral immunoglobulin A (IgA) and free secretory component from colostrum were isolated using affinity chromatography. Both serum and colostral IgA showed similar susceptibility to reduction with dithiothreitol, but only colostral IgA released the additional subunit, bound secretory component. This released secretory component was identical with free secretory component with respect to electrophoretic migration, isoelectric focusing point, and molecular weight, but lacked some antigenic determinants. The amino acid composition and the N-terminal sequence of canine free secretory component was similar to that reported for the cow.

Localization of secretory IgA, secretory component, and alpha chain in the mammary gland of lactating rabbits by immunoelectron microscopy

The different steps in the processing of secretory IgA (sIgA) of the mammary gland of lactating rabbits have been investigated with immunoelectron microscopy. The method employed consists of an indirect localization sequence, in which the immunologic reagents are allowed to diffuse into the fixed tissue prior to embedding and thin sectioning. In the first step, goat F(ab')2 fragments directed against sIgA, secretory component (SC), or alpha chain were used. To visualize the location of these first-step antibody fragments, a second Fab fragment directed against goat F(ab')2 antibody was prepared and coupled to a small heme octapeptide that possessed peroxidatic activity, the reaction product of which is visible by electron microscopy. Both the epithelial cell and the local plasmacytes of the mammary gland contain alpha chain, whereas SC is exclusively located in the epithelial cells. In the plasmacytes, both the cisternae of the rough endoplasmic reticulum and the saccules and vesicles of the Golgi complex contain alpha chain. In the epithelial cells, the elements of the Golgi complex and large apical vacuoles situated in the apical region of the cell. Based on these results, a model for processing of sIgA is proposed and discussed.

Secretory immunoglobulin A in oral and respiratory passages in man

Secretory IgA (SIgA) is the predominant immunoglobulin in certain external secretions and may have an important role in immunological mucosal resistance. SIgA differs in chemical and immunological properties from serum IgA. The present study was undertaken to investigate the antigenic relationship between SIgA, free secretory component (FSC) and serum IgA and the localization of SIgA as well as other immunological classes in tissues of oral and respiratory passages by use of immunofluorescence technique. SIgA and FSC were highly purified from human colostrum and rabbit anti-SIgA and anti-SC antisera were prepared. On the basis of antigenic relationships between SIgA, FSC and serum IgA, it was emphasized that individual specific antisera for SC and IgA and/or SIgA should be used in immunochemical or immunohistological investigations for SIgA. The present study failed to detect SC determinants in palatine and lingual tonsils. However, it was evident that cells present in the pharyngeal tonsillar epithelium contain SC determinants. SC molecules may be synthesized in certain secretory cells of mucous membrane and glandular epithelium and the combining of SC with IgA could occur in the cytoplasm of epithelial cells, the intercellular spaces and/or in the lumens of glandular acini and ductules.

Immunopathology of bullous pemphigoid. Basement membrane deposition of IgE, alternate pathway components and fibrin

Sixteen patients with bullous pemphigoid were examined using direct and indirect immunofluorescent techniques with antisera specific for C1q, C4, C3, C5, C3 proactivator, properdin, fibrinogen, IgA, IgM, IgG and IgE. The results of these studies are consistent with the activation of complement via the classical (antibody–C1q) sequence as well as via the alternate pathway. Fibrinogen and/or fibrin derivatives were demonstrated on the basement membrane of ten of fifteen patients tested and IgE basement membrane staining was found in four individuals.

IgA nephropathy

From a series of 470 specimens of renal tissue examined by immunofluorescence microscopy, 20 specimens were identified and studied in detail from patients without evidence of systemic disease in which IgA was the predominant localizing immunoglobulin. All patients presented with hematuria which was recurrent or persistent, often being exacerbated by upper respiratory infection. Most of the group pursued a benign clinical course with little evidence of decline in renal function. Histopathologic changes in renal biopsy specimens of most of the group consisted of a proliferative glomerulonephritis of variable intensity. Characteristic alterations were seen by electron microscopy which included the presence of electron-dense deposits within the mesangium, the hilar regions of the glomerulus and the basement membrane of Bowman's capsule. Evidence for activation of complement by the alternate pathway at C3 was found with properdin localization in 14 of 15 specimens and with the absence of detectable Clq and C4 in 15 specimens studied for these early acting components. It is concluded that the combined clinical, morphologic and immunologic findings warrant consideration of IgA nephropathy as a distinct clinicopathologic entity.

Quantitative determination of secretory immunoglobulin A (SIgA) in middle ear effusions

For the purpose of investigating the nature of middle ear effusion, quantitative analysis of secretory immunoglobulin A (SIgA) by radioactive single radial diffusion (RSRD) technique was performed on specimens of middle ear effusion and serum from the corresponding patient. Specimens consisted of 61 serous effusions (32 acute and 29 chronic type) and 29 mucoid effusions (9 acute and 20 chronic). The mean value of SIgA concentration in the serous effusions was 212.7 ± 13.5 μg/ml and that in sera from these patients was 27.0 ± 3.0 μg/ml. In the mucoid type the mean value of SIgA in effusions was 357.7 ± 13.2 μg/ml and that in sera was 24.3 ± 2.8 μg/ml. The difference in the mean value of SIgA concentration between the serous and mucoid types of effusions was statistically significant. The mean value of SIgA concentration in serous effusions was eight times that in sera from these patients and in mucoid effusions the SIgA value was approximately 14 times that in sera. The calculated percentage of SIgA in the total IgA of middle ear effusions was 11–12% in both the serous and mucoid categories. The percentage in sera was about 1%. Results of this study indicate that all middle ear effusions contain appreciable amounts of the secretory element, although the transudate from serum is the major component of effusion, and support an hypothesis that while serous middle ear effusions are a mixture of normal ear secretions bathing the membrane surface and transudates from serum, mucoid effusions are the result of enhanced epithelial secretory activity and transudates.

Localization of free and bound secretory component in human intestinal epithelial cells. A model for the assembly of secretory IgA

Antibody reagents were made specific for each of the two forms of human SC, FSC and BSC, which is an integral part of the sIgA molecule. With the fluorescent antibody method the cytological and histological localization of FSC, BSC, and alpha-chains has been studied in various human mucous membranes. SC was present in columnar epithelial cells of the intestines and in the cells of serous acini of bronchial and salivary glands. In contrast, SC was not found in intestinal goblet cells or cells of mucous acini of bronchial and salivary glands. In the columnar epithelial cells of the small and large bowel, FSC was present most prominently in the Golgi zone, and much less prominently in the apical cytoplasm. On the other hand, BSC and alpha-chains were located only in the apical cytoplasm in an overlapping manner. The results favor a model in which sIgA is assembled inside epithelial cells from SC, which was synthesized in the same cell, and IgA, which entered the epithelial cell after synthesis in and secretion by a plasma cell.

Antibacterial mechanisms of the lower respiratory tract. I. Immunoglobulin synthesis and secretion

Immunoglobulin synthesis and secretion have been studied in the rabbit lower respiratory tract, both in the normal state and after infection with Diplococcus pneumoniae or Listeria monocytogenes. In vitro synthesis of immunoglobulin and specific antibody was assessed by incorporation of 14C-labeled amino acids into protein. Lower respiratory tract secretions and serum were analyzed for immunoglobulin and antibody against the infecting organism. Normal respiratory tract produced small quantities of immunoglobulin, most of which was IgG. After bacterial infection of the lower respiratory tract, there was a marked increase in local synthesis of immunoglobulin, especially IgG. Specific antibody of IgG class was produced in all lungs infected with listeria by the 11th day, and in lungs infected with pneumococcus by the 8th day. Secretions from all normal and infected lower respiratory tracts contained IgA and IgG. The IgA to IgG ratios in secretions of normal animals, and animals infected with listeria or pneumococcus, were 2.3, 2.5, and 2.6, respectively. Sera of animals infected with L. monocytogenes contained specific antibody of IgG class but lacked IgA antibody, whereas secretions had both IgA and IgG class antibody against listeria. Similarly, sera of animals infected with D. pneumoniae had IgG class antibody but no IgA antibody, whereas only IgA antibody was found in secretions. The evidence that locally synthesized immunoglobulin (especially IgA), including specific antibody, is secreted into the lower respiratory tract lumen is discussed. Further definition of the role of "local" antibacterial antibody in the respiratory tract is of considerable importance.

Secretory immunoglobulin A (SIgA) in middle ear effusions. A further report

Immunochemical and immunofluorescent studies of secretory immunoglobulin A (SIgA) in otitis media with effusion were carried out to investigate the local immunologic defense system and secretory activity in the middle ear. SIgA was isolated from pooled middle ear effusions by an immunoadsorbents technique and its antigenicity and subunit structure compared with SIgA derived from other external secretions, such as saliva, nasal discharge, and colostrum. The antigenicity and subunit structure of the isolated SIgA from middle ear effusions were identical or very similar to those of SIgA obtained from other external secretions. Radioimmunodiffusion analysis revealed that SIgA was present in 43 of 47 (91.5%) cases of serous middle ear effusion, whereas the sera from only 3 of 47 (6.4%) of these patients was found to have SIgA. Immunoelectrophoresis, using anti-SIgA antiserum, and radioimmunoelectrophoresis detected free SC (secretory component) in 1 of 47 (2%) serous and 6 of 30 (20%) mucoid effusions. Apices of epithelial cells and glandular acinar cells of the middle ear mucosa obtained from patients with otitis media with effusion were stained specifically with anti-SC antibodies. Findings of the study would suggest: 1) that the middle ear maintains the local immunologic defense system, as do respiratory tracts and salivary glands, and 2) that while serous middle ear effusions are a mixture of normal middle ear secretions bathing the membrane surface and transudates from serum, mucoid effusions are the result of enhanced epithelial secretory activity and transudates.

Local antibody response to experimental poliovirus infection in the central nervous system of rhesus monkeys

By employing the techniques of immunofluorescence and radioimmunodiffusion using (32)P-labeled poliovirus as the antigen, the immunoglobulin response to poliovirus in serum, nasopharynx, spinal fluid, and in different segments of the central nervous system (CNS) was studied after intramuscular, oral, intranasal, and intrathalamic administration of inactivated (Salk), live attenuated (Sabin), or live virulent (Mahoney) type I poliovirus. Spinal fluid gammaG antibody was detected after immunization with Sabin or Mahoney virus and intramuscular administration of Salk vaccine. The response in the CNS was characterized by the appearance of gammaG antibody after oral or intrathalamic administration of Mahoney virus and rarely after intrathalamic inoculation of Sabin vaccine. The antibody activity in CNS was limited to the areas of poliovirus replication. Intrathalamic immunization with Mahoney virus resulted in local gammaG antibody production in the CNS in the absence of any detectable response in serum. Discrete foci of gammaG-containing cells were observed in those areas of CNS which contained poliovirus antibody. No immunoglobulin-containing cells or poliovirus antibody was seen in the CNS of monkeys immunized with intramuscularly or orally administered Sabin or Salk vaccine and in sham-immunized control monkeys. It is suggested that the CNS, when stimulated locally with a potent replicating viral antigen, may manifest a specific local antibody response, which is independent of the response in serum.

Mucosal secretory IgA and secretory piece in adult coeliac disease

Immunofluorescence studies with specific antisera to secretory IgA (11S IgA) and secretory piece were carried out on the jejunal mucosa of nine patients with adult coeliac disease (treated and untreated). The results were compared with those obtained in four normal patients and in four patients with local and systemic IgA (7S) deficiency. 11S IgA and secretory piece were localized to the upper third of the epithelial cells of both surface and glandular epithelium in all groups of patients. However, in the untreated coeliac patients fluorescence was also demonstrated in the basement membrane and connective tissue of the mucosa (returning to normal on treatment). On the basis of our findings, a revised pathway for the normal production of 11S IgA is proposed as well as an additional pathway involving a ;backflow' of 11S IgA into the lamina propria in pathological states such as coeliac disease. This backflow is reversed by an adequate gluten-free diet. It is suggested that 7S IgA and 11S IgA may be involved in immune reactions in the mucosa with antigens such as gluten.

Nasal immunoglobulin responses in acute rubella determined by the immunofluorescent technique

The indirect immunofluorescent technique has been used to study the specific immunoglobulin responses in nasal secretions from ten adults with acute rubella. Titres of IgA antibody in nasal washings usually exceeded those of IgG, but both types of antibody were detected in all patients. They appeared a few days after the rash, reached maximum titres during the second week and then declined. IgA antibody was no longer detectable after 47 days and was not detected at all in nasal washings from adults who had experienced rubella in the past. Low titres of IgG antibody persisted in some patients for longer than IgA and traces of IgG were found in nasal washings from a minority of adults with a past history of rubella. Nasal antibodies in acute rubella are therefore transient and unlikely to take part in resistance to reinfection.In sucrose-density gradients nasal IgA antibody sedimented more rapidly than IgG and there was little overlap between these two types of antibody. IgA antibody in serum was more heterogeneous; it was found in nearly all the fractions which contained IgG antibody and in many of those which contained IgM.

Serum immunoglobulins, complement component levels and autoantibodies in liver disease

Serum immunoglobulins, complement component levels and autoantibodies were measured in patients presenting with acute and chronic liver disease. One-hundred and seventeen patients were studied and the results of the immunological estimations were found to be of value in the differential diagnosis of liver disease when considered in conjunction with clinical and other laboratory findings. The results of the study are of interest in discussing the possible pathogenesis of liver disease.

In vitro synthesis of immunoglobulins, secretory component and complement in normal and pathological skin and the adjacent mucous membranes

A study on the synthesis of immunoglobulins (IgG, IgA, IgM, IgD, and IgE), secretory component and complement in normal and pathological skin and in the adjacent mucous membranes (i.e. conjunctiva, nasal, oral and vaginal mucosa) is reported. The results are based on the culture of tissue samples in a medium with two radioactive amino acids and the detection of synthesized proteins by autoradiography of the immunoelectrophoretic pattern of the culture fluid, except in the case of IgE for which the Ouchterlony technique was used.

The results indicate that the normal skin does not synthesize immunoglobulins, whereas normal mucous membranes produce IgG and IgA. In the lesions of various skin diseases immunoglobulins are synthesized, mainly IgG but sometimes also IgA and IgE. The cells responsible for the production of immunoglobulins are plasma cells and lymphoid cells present in the skin lesions and mucous membranes.

Synthesis of the free secretory component could be demonstrated only in certain mucous membranes (i.e. conjunctiva, nasal mucosa, and oral mucosa).

Complement (C3) synthesis was found in normal skin, mucous membranes (i.e. conjunctiva, nasal and oral mucosa), and in the lesions of such skin diseases as discoid lupus erythematosus, (bullous) pemphigoid, dermatitis herpetiformis, malignant reticulosis, eczema and lichen planus. Complement production was also demonstrated in allergic skin reactions (i.e. tissue from allergic-positive patch tests, positive Mantoux tests and drug eruptions), but no immunoglobulin synthesis was detected in these lesions.

Evidence for complement activation via the alternate pathway in skin diseases, I. Herpes gestationis, systemic lupus erythematosus, and bullous pemphigoid

A patient with herpes gestationis, 6 of 6 patients with bullous pemphigoid, and 5 of 25 patients with systemic lupus erythematosus were found to have properdin deposited along the skin basement membrane.The patient with herpes gestationis demonstrated by immunofluorescence basement membrane deposition of C3 and C5 in the absence of C1q, immunoglobulins, and light chains. A second patient with herpes gestationis had C3 deposition with no demonstrable immunoglobulins or light chains. A thermolabile humoral factor(s) capable of depositing C3 (without C1q or C4) on normal skin basement membrane was found in the sera of both patients with herpes gestationis. No anti-basement membrane antibodies could be demonstrated in the sera of these patients.The patients with systemic lupus erythematosus and bullous pemphigoid who manifested properdin deposition also showed skin basement membrane deposits of C1q, C4, C3, C5, and immunoglobulins. C3 proactivator (C3PA) was also found deposited along the skin basement membrane of three patients with systemic lupus erythematosus and all six bullous pemphigoid patients. This study provides suggestive evidence that activation of complement is occurring via the alternate pathway in herpes gestationis. In systemic lupus erythematosus and bullous pemphigoid, both the classical (antibody) mediated activation of complement as well as the alternate pathway may be operative.

Secretory immunoglobulin A (SIgA) in middle ear effusions. Observation of 160 specimens

Immunochemical studies of secretory immunoglobulin A (SIgA) in middle ear effusions were attempted for the purpose of investigating the existence of the local immunologic defense mechanism and the local protein synthesis in the middle ear. SIgA was isolated from normal human parotid secretions by means of DEAE-cellulose column chromatography and G-200 Sephadex gel filtration. Antiserum against SIgA was made by immunizing a rabbit with the SIgA isolated from the parotid secretions. Antisecretory piece antiserum was made by absorbing the anti-SIgA antiserum with pooled normal human sera. Immunodiffusion analysis of SIgA was performed on 160 specimens of middle ear effusion from patients with otitis media with effusion. Seventy-five of 160 (46.9%) specimens were found to have SIgA. In the serous category 5 of 41 (12.2%) acute cases were positive while 24 of 59 (40.7%) chronic cases were positive. One of 2 acute cases of the seropurulent effusions showed the positive reaction and 2 of 3 cases of the purulent type were positive. In the mucopurulent type 2 of 4 acute cases were positive and all 3 chronic cases were positive. In the mucoid type 9 of 14 (64%) acute cases gave a positive precipitation line while 29 of 33 (87.9%) chronic cases gave the positive reaction. The appearance of precipitation line developed with effusions varies from very faint to distinct. However, as a rule the line of the mucoid, mucopurulent and purulent effusions was strong. Since SIgA is the predominant immunoglobulin in external secretions but is not present or is at very low concentration in normal sera, findings of this study suggested that the middle ear lining membrane possesses the secretory function similar to the epithelium of other external secretory tissues, and suggested the hypothesis that the middle ear epithelium shares the local immunologic defense system as that of respiratory epithelium.

Immunoglobulin A: site and sequence of expression in developing chicks

Synthesis of immunoglobulins A, G, and M (IgA, IgG, and IgM) is prevented in chickens by embryonic treatment with heterologous antibodies to IgM when combined with bursectomy at hatching. Cells that produce IgA are seeded from the bursa of Fabricius later than cells capable of IgM and IgG synthesis; the latter do not convert to IgA synthesis outside of the bursa.

Intestinal secretion of immunoglobulins in the preruminant calf

Intestinal immunoglobulins have been examined in secretions obtained from Thiry-Vella loops prepared in the mid-jejunum of six calves. Free secretory component and 11S IgA were demonstrated. Immunofluorescent studies of intestinal tissue confirmed the presence of a secretory IgA system similar to that described in other species. However quantitative assays showed that IgA was not at any time the predominant immunoglobulin in intestinal secretions. IgM consistently exceeded the level of IgA by approximately two-fold and its localization in lymphoid cells of the lamina propria and crypt epithelial cells suggested that IgM may normally play an important role in local intestinal defence in the calf.

IgG1 appeared in consistently low levels in intestinal secretions in spite of being the major serum immunoglobulin.

Nasal secretion protein responses in patients with wild-type adenovirus disease

Proteins were studied in nasal secretions obtained from Marine Corps trainees infected with wild adenovirus type 7 both during the acute phase of illness and after recovery. Illness was associated with a marked increase in the concentration of serum proteins in the secretions, and during inflammation there was no apparent barrier to the passage of large molecules (molecular weight 775,000) from the serum into the respiratory passages. At the time of virus isolation, trainees requiring hospitalization had less immunoglobulin A (IgA) in their secretions even though they had greater quantities of immunoglobin G (P < 0.05) and albumin than trainees followed in the field, whose secretions were also tested at the time of virus isolation. Base-line IgA and protein concentrations were lower (P < 0.05) in hospitalized trainees than in trainees followed prospectively in the field. The results suggest a nonspecific protective function for secretion protein, although we have not excluded the possibility that field study trainees were protected by specific neutralizing antibody present in the nasal secretion.

Immunoglobulin-containing cells in the intestinal mucosa and immunoglobulins in the intestinal juice in children

The numbers of immunoglobulin-containing cells in the mucosae of the small intestine and rectum were counted by a direct immunofluorescence technique in biopsy specimens from children. Immunoglobulins in the intestinal juice of the same patients were quantified by electroimmunodiffusion. In all biopsy specimens IgA-containing cells predominated. These cells were more numerous in the specimens from children over 2 years of age than in those of younger ones. The cells seemed to be fairly evenly distributed along the intestinal tract. The number of IgM-containing cells did not change with age in the group studied.

In the intestinal juice the mean content of IgA was higher than that of the other immunoglobulins. More IgM and less IgA were found in the juice of infants under 2 years of age than in that of older children.

The results suggest that quantitatively the IgA-producing system of the gut is not fully developed in infancy, whereas the reverse is true for the cells producing IgM.

Clinical, microbiological, and immunological studies in patients with immunoglobulin deficiencies and gastrointestinal disorders

Seven patients with gastrointestinal disorders and deficiencies of serum and secretory immunoglobulins were evaluated clinically, microbiologically, and immunologically. Five patients had generalized deficiencies of immunoglobulins; two were selectively deficient. Diarrhoea and malabsorption in six of the seven patients were at least partially explained. Four of the five patients with generalized hypogammaglobulinaemia had intestinal infestation with Giardia lamblia; in three of the five, excessive numbers of anaerobic bacteria were cultured from small bowel fluids. Despite much variability in relative severity of patients' respiratory and gastrointestinal tract symptoms, deficiencies of mucosal immunocytes and immunoglobulins in nasopharyngeal and gastrointestinal tract tissues and secretions were similar. Except for one selectively IgA-deficient patient, all patients were deficient in IgE. The study characterizes in greater detail than heretofore the gastrointestinal disorders associated with immunoglobulin deficiency states.

An immunofluorescent study of the distribution of immunoglobulin-containing cells in the normal and the inflamed human gall bladder

Immunoglobulin-containing cells are present in the normal human gall bladder but they are much less numerous in this site than in the normal intestine. IgA-containing cells predominate in the mucosa but in the muscle layer IgM cells are the more numerous. In both acute and chronic inflammation of the gall bladder there is a marked increase in the number of immunoglobulin-containing cells. In all but the most severe cases of inflammation it is those cells containing IgA which show the greatest increase in numbers, but in severe cases there is a disproportionate rise in the number of IgG- and IgM-containing cells, these latter being possibly derived from the blood. IgA cannot be demonstrated in the epithelial cells of the gall bladder and positive evidence of secretion into the bile of locally produced immunoglobulin is lacking. It is suggested that the concentration of IgA normally present in bile is such that, irrespective of local production, some is derived from the serum or the intestine.

Characterization of the J chain from polymeric immunoglobulins (IgA-IgM-immunological specificity-primary structure)

The J chains isolated from polymeric IgA and IgM were shown to be distinct from the other immunoglobulin subunits, including the secretory component, both on the basis of amino-acid content and antigenic determinants. By the same criteria, the J chains were found to be indistinguishable from each other whether they were derived from pentamer IgM, polydisperse myeloma IgA, or dimer colostral IgA. The only differences were observed in (a) the extent of disulfide bond cleavage required for J chain release from the different polymers, and (b) the three-dimensional arrangement of J chains in the different polymers. These data support the hypothesis that the same J chain joins the monomeric units of IgA and IgM to form their respective polymeric molecules.