An enzyme-linked immunosorbent assay for differential quantitation of secretory immunoglobulins of the A and M isotypes in human serum

An overview of autoantibodies in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic auto-immune disease principally effecting synovial joints. RA is characterized by immune cell infiltration in the joint. The presence of autoantibodies is a hallmark for the disease, among these are rheumatoid factor and antibodies against post-translational modified proteins like citrullination (ACPA) and carbamylation (anti-CarP antibodies). These autoantibodies may form immune complexes in the joint, leading to the attraction of immune cells. Based on the presence of these autoantibodies, RA patients can be subdivided in autoantibody positive and negative disease. Both subsets can be associated with genetic and environmental risk factors for RA, like the human leukocyte antigen (HLA) allele and smoking. Autoantibodies can already be detected years before disease onset in a subgroup of patients and at symptom onset a broad isotype spectrum is observed. This suggests that various events occur prior to the development of RA in which the first autoantibodies develop in predisposed individuals. Therefore, the presence of these autoantibodies can be useful in predicting future RA patients. Research on the characteristics and effector function of these autoantibodies is ongoing and will give more knowledge in the inflammatory responses underlying RA. This will give insight in the pathogenic role of autoantibodies in RA. Recent data are suggestive of a role for mucosal surfaces in the development of auto-immune responses associated with (the development of) RA. In conclusion, investigating the potential pathogenic effector functions of autoantibody isotypes and their molecular- and physicochemical-compositions might improve understanding of the disease origin and its underlying immunological processes. This may lead to the development of new therapeutic targets and strategies.

Higher Levels of Secretory IgA Are Associated with Low Disease Activity Index in Patients with Reactive Arthritis and Undifferentiated Spondyloarthritis

Introduction

Both reactive arthritis (ReA) and undifferentiated spondyloarthritis (uSpA) belong to the group of autoinflammatory diseases called spondyloarthritis (SpA). Hypotheses have been proposed about a relationship between the intestinal mucosa and inflammation of joint tissues. The role of immunoglobulin IgA or secretory immunoglobulin A (SIgA) in the inflammatory and/or clinical activity of patients with SpA remains poorly understood.

Objective

To evaluate the status of total IgA and SIgA, and the association among the levels of SIgA, IgA, IgA anti-Chlamydia trachomatis, and anti-Shigella spp. with the disease activity measures, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, was compared in a cohort of patients with ReA and uSpA and healthy subjects.

Methods

This was a cross-sectional study. The serum concentrations of SIgA, IgA anti-C. trachomatis, anti-Shigella spp., and total IgA were measured. Disease activity was measured in each patient by means of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). Statistical analysis did include as bivariate evaluation, comparisons by Student’s t-test, Kruskal–Wallis test, and U Mann–Whitney test, with a multivariate evaluation by principal components analysis (PCA). A correlation analysis was carried out using the Pearson correlation coefficient and a linear regression models. All analysis were made using Stata version 11.2^® for Windows, R V3.3.21. Statistical significance was defined a p-value <0.05.

Results

In all, 46 patients (78.2% men; mean age, 34.8 ± 12.3 years) and 53 controls (41% men; mean age, 32 ± 11.4 years) were included in the study. The mean serum levels of SIgA were higher in SpA patients than in healthy subjects (p < 0.001). Only SIgA levels correlated with disease activity: BASDAI (r = −0.42, p = 0.0046), ASDAS-CRP (r = −0.37, p = 0.014), and ASDAS-ESR (r = −0.45, p = 0.0021). The negative correlation between SIgA and all activity indices was higher in HLA-B27-positive patients (BASDAI r = −0.70, p = 0.0009, ASDAS-CRP r = −0.58, p = 0.0093, and ASDAS-ESR r = −0.57, p = 0.0083). The PCA showed three factors: the first component was constituted by variables referred as clinical activity measures, the second did include the serological activity markers, and the last component was compounded by age and symptoms time.

Conclusion

Elevated serum levels of SIgA were found to be related with low disease activity in patients with ReA and uSpA.

Rotavirus specific plasma secretory immunoglobulin in children with acute gastroenteritis and children vaccinated with an attenuated human rotavirus vaccine

Rotavirus (RV)-specific secretory immunoglobulin (RV-SIg) has been previously detected in serum of naturally RV infected children and shown to reflect the intestinal Ig immune response. Total plasma SIgA and plasma RV-SIg were evaluated by ELISA in children with gastroenteritis due or not due to RV infection and in 50 children vaccinated with the attenuated RIX4414 human RV vaccine and 62 placebo recipients. RV-SIg was only detected in children with evidence of previous RV infection or with acute RV gastroenteritis. Vaccinees had higher RV-SIg titers than placebo recipients and RV-SIg titers increased after the second vaccine dose. RV-SIg measured after the second dose correlated with protection when vaccinees and placebo recipients were analyzed jointly. RV-SIg may serve as a valuable correlate of protection for RV vaccines.

Social support and salivary secretory immunoglobulin A response in women to stress of making a public speech

Acute experimental stressors transiently increase volume of secretory immunoglobulin A (s-IgA) in saliva. The present study examined buffering effects of social support on response of s-IgA to a brief psychological stress (giving a public speech). 24 women were divided at random into three groups, an emotional support group, an informational support group and a no-support group (control). For each group, s-IgA measures were obtained from each person under baseline conditions, during preparation of a speech when social support or no support was given, immediately after the speech and during a 'recovery' period. Level of s-IgA in the control group significantly elevated during preparation for the speech and just after the speech compared to baseline, suggesting that the speech task stimulated secretory immune function. On the other hand, the subjects in the emotional support group showed increased s-IgA during the preparation period but secretion of s-IgA rapidly returned to the baseline after the speech task. Secretion of s-IgA in the informational social support group was unchanged at any measurement point. These results suggest that social support attenuates the affect of a stressor on somatic state.

The type A behavior pattern and immune reactivity to brief stress: change of volume of secretory immunoglobulin A in saliva

This article presents findings of a laboratory experiment on the association of the Type A behavior pattern with reactivity of secretory immune functioning to brief stress. 38 female undergraduate students classified as Type A (n = 19) or as Type B (n = 19) on the basis of their scores on the Kwansei Gakuin Type A scale performed a continuous arithmetic task in a situation in which they were exposed to aversive loud noise. Secretory immunoglobulin A (s-IgA) in saliva and autonomic measures (heart rate and frequency of eyeblink) were evaluated before and after the manipulation of stress. The volume of s-IgA at baseline was significantly higher for the Type A group than for the Type B group, suggesting that the former relative to the latter might be chronically higher in mucosal immune functioning. Also, the volume of s-IgA significantly increased after exposure to a brief stress for the Type B group but did not change for the Type A group, a finding which might indicate that the Type A group may have less immune reactivity to a brief stress.

Domain deletions in the human polymeric Ig receptor disclose differences between its dimeric IgA and pentameric IgM interaction

The human polymeric Ig receptor (pIgR), or transmembrane secretory component, is basolaterally expressed on secretory epithelial cells; its function is to transport externally J chain-containing dimeric IgA and pentameric IgM. The ligand-binding extracellular part of this receptor contains five disulfide-stabilized domains which show considerable homology with the variable domains of Ig chains. The N-terminal domain 1 (D1) mediates the initial noncovalent ligand interaction. In this study we made deletions of the human pIgR D2 and D3 (pIgRDelta2,3), or D4 and D5 (pIgRDelta4,5), to investigate the influence of these domains in receptor binding and transport of dimeric IgA and pentameric IgM across MDCK cells transfected with the truncated receptors. Both mutants were found to bind pentameric IgM, but only pIgRDelta4,5 bound dimeric IgA. These results showed that the two ligands interact differently with human pIgR; binding of pentameric IgM apparently depends fully on strong interactions with D1, while binding of dimeric IgA in addition depends on elements within D2 and / or D3 to support the initial noncovalent binding to D1. Moreover, our studies imply that dimeric human IgA binds differently to pIgR from various species. This observation cautions against interpretation of functional studies performed with non-homologous receptor-ligand pairs.

Induction of Mucosal Immunity by Inactivated Poliovirus Vaccine Is Dependent on Previous Mucosal Contact with Live Virus

The inactivated poliovirus vaccine (IPV) is used for protection against poliomyelitis in The Netherlands. It is not clear, however, whether IPV vaccination can lead to priming of the mucosal immune system and the induction of IgA. It has been demonstrated that IPV vaccination is able to induce strong memory IgA responses in the serum of persons who have been naturally exposed to wild-type poliovirus. This has led to the hypothesis that IPV vaccination is able to induce poliovirus-specific IgA at mucosal sites in persons who have been previously primed with live poliovirus at mucosal sites. To test this hypothesis, the kinetics of the IgA response in serum and saliva after IPV vaccination were examined in persons previously vaccinated with oral poliovirus vaccine (OPV) or IPV. ELISA and enzyme-linked immunospot assays were used for the detection of poliovirus-specific IgA responses. In addition, B cell populations were separated on the basis of the expression of mucosal (α4β7 integrin) and peripheral homing receptors (L-selectin). Parenteral IPV vaccination was able to boost systemic and mucosal IgA responses in previously OPV-vaccinated persons only. None of the previously vaccinated IPV recipients responded with the production of IgA in saliva. In agreement with this finding, a large percentage of the poliovirus-specific IgA-producing lymphocytes detected in previous OPV recipients expressed the α4β7 integrin. It is concluded that IPV vaccination alone is insufficient to induce a mucosal IgA response against poliovirus. In mucosally (OPV-) primed individuals, however, booster vaccination with IPV leads to a strong mucosal IgA response.

Intranasally administered immunoglobulin for the prevention of rhinitis in children

OBJECTIVE

To determine the efficacy of intranasally administered immunoglobulin in preventing symptoms of rhinitis in children.

METHODS

Forty children ages 1 to 4 years who attended day-care centers in Turku, Finland, were enrolled in the double blind, placebo-controlled study. The children were randomly assigned to receive treatment with immunoglobulin, composed mainly of immunoglobulin A, or placebo, both administered as nasal sprays twice daily for 8 weeks. During this medication period and an additional 8-week follow-up period, the parents recorded the symptoms of the children daily in the diaries provided. One child who met an exclusion criterion was withdrawn from the study after a few days of medication.

RESULTS

During the 8-week medication period the 19 children in the immunoglobulin group had 42% fewer days with rhinitis than the 20 children receiving placebo (mean, 10.8 vs. 18.7 days; P=0.004). The total numbers of episodes of rhinitis in the immunoglobulin and placebo groups were 33 and 51, respectively. No significant differences were observed between the groups during the postmedication follow-up period.

CONCLUSIONS

Intranasal administration of immunoglobulin appears to be an effective method to prevent symptoms of rhinitis in children, and further studies of this approach are needed.

Secretory component of immunoglobulin A in maternal serum and the prediction of preterm delivery

OBJECTIVE

Our purpose was to determine whether the secretory component of immunoglobulin A in maternal serum predicts delivery before 34 weeks' gestation.

STUDY DESIGN

Primigravid women of an urban population in New Zealand were recruited at booking into a prospective longitudinal nested case control study (n = 1651; after exclusions and withdrawals, n = 1511). Serum was collected at 8 to 12 weeks, 15 to 18 weeks, 21 to 24 weeks, 28 to 30 weeks, and 36 to 38 weeks of gestation and 6 weeks post partum. Concentrations of the secretory component of immunoglobulin A were determined by enzyme-linked immunosorbent assay in all women who were delivered preterm (n = 53) and in controls randomly selected from women delivered at > or =37 weeks' gestation (n = 178).

RESULTS

Serum concentrations of the secretory component of immunoglobulin A were similar in women delivered at term or preterm throughout pregnancy (n = 21 delivered at <34 weeks and n = 32 at 34 to 36.9 weeks, incidence 3.5%). Receiver-operator characteristic curves showed no discriminating ability of the secretory component of immunoglobulin A. Smokers had 50% higher concentrations than nonsmokers did (p < 0.0001 by analysis of variance).

CONCLUSION

The secretory component of immunoglobulin A in maternal serum does not predict preterm delivery in a low-risk population.

Determination of human immunoglobulin A and secretory immunoglobulin A in bronchoalveolar lavage fluids by solid phase enzyme immunoassay

Solid phase enzyme immunoassay methods for the determination of secretory immunoglobulin A (IgA) and the total amount of serum and secretory IgA in bronchoalveolar lavage fluids (BALF) were developed. The solid phase was prepared by immobilizing rabbit anti-human IgA. Horseradish peroxidase-conjugated goat anti-secretory component or horseradish peroxidase-conjugated goat anti-human IgA (Fc) were used as labeled antibodies. The minimum detectable amounts of secretory IgA and total IgA were 2 and 0.5 ng/well, respectively. These assay methods were successfully applied to the determination of secretory and total IgA levels in BALF samples obtained from 44 subjects including healthy non-smokers, smokers and patients with the following lung diseases: idiopathic pulmonary fibrosis, sarcoidosis and hypersensitivity pneumonitis. The secretory and total IgA levels in BALF collected from healthy non-smokers (n = 9) were 10.5 +/- 3.6 and 25.4 +/- 15.5 (S.D.) micrograms/ml, respectively. In healthy smokers, the secretory IgA concentration was significantly decreased and in idiopathic pulmonary fibrosis, the total IgA was increased. These results indicate that the quantitation of secretory and total IgA may be useful for the investigation of lung disease.

Secretory immunoglobulins in serum from human immunodeficiency virus (HIV)-infected patients

Infection by the human immunodeficiency virus is associated with polyclonal B cell activation and increased levels of serum IgA. In order to characterize the molecular species of serum IgA, we have measured total IgA, IgA1, and IgA2 in sera from 60 HIV-1-infected patients and 40 healthy controls. In addition, secretory IgA (S-IgA), secretory IgM (S-IgM), free immunoreactive secretory component (SC), and the distribution of monomeric and polymeric IgA were determined. The data confirm the elevation of total serum IgA levels in HIV-1-infected patients, and both IgA1 and IgA2 concentrations are elevated. Furthermore, the data show a substantial increase in serum levels of both monomeric and polymeric IgA. Serum S-IgA levels were significantly increased in CDC group II patients versus controls and more frequently elevated in CDC group IV patients. The highest S-IgA levels were found among patients with the lowest blood CD4+ cell counts. Serum S-IgA levels were not correlated with serum levels of either total IgA or polymeric IgA. Serum S-IgM levels were also increased in HIV-1-infected patients and positively correlated with serum S-IgA levels. Conversely, serum levels of free SC were not altered. An increase in serum S-IgA was not related to human hepatitis B virus infection and/or to hepatic dysfunction or to diarrhea or overt intestinal infection. The data indicate that secretory Ig (S-IgM and S-IgA), which are likely to be produced at mucosal sites, increase in the serum of HIV-1-infected patients.

Serum concentrations of secretory IgA in pregnancies delivering at term or preterm

Secretory component (SC) is a phospholipase A2 inhibitor possibly associated with pregnancy maintenance and in serum is bound either to IgA (sIgA) or IgM (sIgM). To determine if serum secretory component levels a) increase during pregnancy, b) fall as term approaches, c) are low in women who will deliver prematurely, serum sIgA was measured at "booking in" and related to weeks of gestation and length of gestation at subsequent noninduced delivery. Levels of sIgA increased during pregnancy; sIgA increased from a non-pregnant value of 1.6 nM +/- 0.2 (mean +/- SEM) to 2.8 nM +/- 0.3 at the end of the second trimester, then fell significantly between 31-34 weeks. Delivery before 37 weeks was associated with significantly reduced serum sIgA levels, particularly in women who delivered before 32 weeks and in whom sIgA concentrations were similar to those of nonpregnant women.

Circulating secretory component in relation to early diagnosis and treatment of liver metastasis from colorectal carcinomas

AIMS

To evaluate serum secretory component in relation to early detection and clinical management of liver metastasis in patients with colorectal cancer.

METHODS

Secretory component and carcinoembryonic antigen (CEA) were analysed in serial serum samples from 23 patients who had liver metastases as the only apparent recurrence, and in sera from 54 matched controls. Results of surgical treatment of recurrences were classified peroperatively as radical when no residual tumour was apparent and resection margins were free of disease.

RESULTS

In total, 18 (78%) patients had increased secretory component during the whole follow up period (median 16 months); 12 (52%) had raised secretory component concentrations before clinical recurrence (median lead time 5.2 months). There was no difference before recurrence between circulating secretory component and CEA in sensitivity and lead times. Seventeen patients underwent surgery for hepatic metastasis; seven had radical hepatic resection of which only two (29%) showed increased secretory component concentrations before clinical recurrence; both had concurrent raised CEA values. By contrast, secretory component was raised in 83% of those cases considered inoperable.

CONCLUSIONS

Although serum secretory component clearly increases in most patients with liver metastases, its clinical value seems questionable because secretory component apparently indicates mainly inoperable hepatic metastases.

Increased levels of serum IgA as IgA1 monomers in ankylosing spondylitis

The various subsets of serum IgA were determined in 43 patients with ankylosing spondylitis to investigate the putative mucosal origin of increased IgA concentrations in this disease. Total IgA was shown to be increased and weakly correlated with the erythrocyte sedimentation rate (ESR). In contrast, although the mean concentration (but not the median) of secretory IgA (SIgA) was slightly increased, no correlation was found with total IgA nor the ESR. Moreover, molecular sieving of nine serum samples selected for their high concentrations of total IgA, and absorption with insoluble jacalin showed these immunoglobulins to be essentially monomers of the IgA1 subclass. These results are consistent with a non-secretory origin of the increase of serum IgA, which must be ascribed to the central immune system.

Secretory component is bound to the paraproteins in sera of IgA and IgM gammopathies

Secretory immunoglobulins A (SIgA) and M (SIgM) were investigated in 20 sera containing high levels of monoclonal polymeric IgM or IgA. In the sera of patients suffering from Waldenström's macroglobulinemia (WM), the level of SIgA was found to be low, whereas that of SIgM was extremely high. Reciprocally, in the multiple myeloma (MM) patients, SIgA were increased and SIgM were dramatically decreased. Electrophoretic analysis showed these SIgA and SIgM to have the same monoclonal pattern as the corresponding paraprotein. Hence these molecules must originate from the malignant clone. The most likely mechanism involved is an intravascular formation of the secretory-like immunoglobulins. Free secretory component (SC) could diffuse passively from the digestive lumen and bind the circulating myeloma polymeric immunoglobulins. Such a possibility of in vivo binding of free SC to IgM and IgA polymers leads to a reconsideration of the secretory origin of SIgM and SIgA in normal human serum.

Alterations in polymeric immunoglobulin receptor expression and secretory component levels in bladder carcinoma

To assess the capacity of transitional cells to synthesize the release polymeric immunoglobulin receptor (pIg-R) in bladder carcinoma, we studied the localization of pIg-R in normal and tumor tissues and measured the levels of secretory component (SC) either in the free form or bound to Ig (S-IgA, S-IgM) in the serum and urine of 56 patients with transitional-cell carcinoma (TCC) of the bladder. In the normal bladder mucosa, pIg-R was localized in the cytoplasm and plasma membranes of the superficial cells and on all epithelial cell membranes. In TCC cases, 65% of those studied expressed pIg-R. A marked heterogeneity in pIg-R staining was observed in some tumors. Although a better expression of pIg-R in tumors with a well-preserved epithelial architecture was observed, no correlation was found between pIg-R expression and the grade or stage of the tumors in the patients under study. Three groups were established: (1) in TCC with no complications, serum levels of free SC and S-IgA were significantly increased; (2) in TCC with urinary infections (UI), serum levels of free SC and S-IgA were significantly higher than control values but lay within the same range observed in TCC with no complications and rates of urinary excretion of SC were significantly higher than those in normal subjects; (3) in TCC without UI but with hepatic disorders [high gamma-glutamyl transferase (GGT) activity], there was a correlation between serum S-IgA levels and GGT activity (r = 0.5, P less than 0.005) and serum SC levels were significantly higher than those observed in the other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The presence and measurement of secretory component in human bile and blood

Five monoclonal antibodies which recognized three separate epitopes on the free secretory component molecule were produced using free secretory component obtained from human colostrum. Two-site immunoradiometric assays were developed to measure free secretory component and secretory IgA. Monoclonal antibody M9 was used on coated plates as the capture antibody. Monoclonal antibody M7 was used as the labelled signal antibody for the assay of free secretory component and a commercially available monoclonal anti-IgA antibody was used as the labelled signal antibody for the assay of secretory IgA. Free secretory component was found in human serum and bile. In serum, its concentration was raised in patients with high serum alkaline phosphatase due to liver disorders but not in patients with high serum alkaline phosphatase due to non-liver disorders. In bile from bile duct drains collected during the first week after liver transplantation, free secretory component was found in concentrations of up to 33 mg/l, in vast excess of that found in bile from gallstone patients (up to 0.3 mg/l). Bile from gallstone patients but not from liver transplant patients produced proteolytic degradation of free secretory component when incubated in vitro. The finding of large amounts of free secretory component, the free cleaved fragment of the polymeric IgA receptor in human bile, further supports the existence of the blood to bile transhepatocytic pathway in humans.

Secretory component-binding properties of normal serum IgM

Our aim was to investigate why serum IgM is poorly transferred into secretions in normal subjects. Indeed, the low IgM level in secretions contrasts with the capacity of monoclonal IgM to bind to secretory component (SC), but it is not well established to what extent normal serum IgM can do so. The mean SC affinity was studied with a polyclonal IgM preparation from 250 normal subjects and with a representative pool of 100 different monoclonal IgM. The SC-binding percentages varied as a function of the IgM/SC molar ratio according to a common hyperbolic curve, with similar association constants: Ka = 4.19 +/- 2.61 x 10(7) M-1 (polyclonal pool) and Ka = 5.80 +/- 2.73 x 10(7) (monoclonal pool). It thus appears that the large difference in IgM concentrations between blood and secretions cannot be due to an SC-binding defect of serum IgM, but is probably explained by its low diffusion from blood to the extravascular compartment.

Secretory immunoglobulin A in urinary tract infection, chronic glomerulonephritis, and renal transplantation

An enzyme-linked immunoassay (ELISA) for the quantitation of secretory IgA (S-IgA) in the urine is described. The assay is sensitive (linear down to 0.02 microgram/ml), specific, and reproducible (intraassay variation 7.8%, interassay variation 18.9%). The assay was used to determine the urinary excretion rates of S-IgA in patients with bladder catheter (n = 12), cystotomy and urinary tract infection (n = 13), urosepsis (n = 5), chronic glomerulonephritis, including IgA-nephritis (n = 31), in renal allograft recipients (n = 30), and in healthy controls (n = 46). An elevated S-IgA urinary excretion (P less than 0.01) was found in all patient groups studied. The highest values were observed in urosepsis. No significant differences between S-IgA levels in IgA-nephritis and other forms of chronic glomerulonephritis were detected. The elevated S-IgA excretion in renal allograft recipients indicates that immunosuppressive therapy does not influence the local S-IgA production in the urinary tract. The susceptibility of these patients to urinary tract infections is therefore not due to a S-IgA deficiency.

An 'antigen capture' ELISA for secretory immunoglobulin A antibodies to hepatitis B surface antigen in human saliva

An enzyme-linked immunosorbent assay (ELISA) was developed which permits the assay of specific secretory immunoglobulin A (sIgA) antibodies against hepatitis B surface antigen (HBsAg) in saliva. The assay is based on the binding of sIgA antibodies present in saliva to microtitre plates coated with excess of F(ab')2 anti-secretory component antibodies, followed by the addition of specific antigen, HBsAg and finally peroxidase-labelled anti-HBsAg. The assay is fast, simple, reproducible and antigen specific as shown by total absence of inhibition of specific antigen by unrelated antigens but significant inhibition of labelled anti-HBsAg by unlabelled anti-HBsAg. The values obtained for hospital personnel exposed to hepatitis infections (0.068 +/- 0.083 U/ml) and for post-icteric hepatitis B patients (0.062 +/- 0.033 U/ml) were significantly higher than values in control subjects (0.013 +/- 0.006 U/ml).

Rapid selection of cultured cells with increased expression of a membrane marker (secretory component)

This study showed how immunomagnetic monodisperse microspheres (Dynabeads) can be used for rapid selection of stable and homogeneous sublines of cancer cells. The beads were activated with antibody to a specific surface membrane marker. We used a monoclonal antibody (MAb) to human secretory component (SC), the epithelial receptor for polymeric immunoglobulins (pIg). A relatively low number of particles favored rosetting of strongly positive cells. SC-expressing cells were isolated within 30 min from a colonic carcinoma cell line (HT-29.E10). After 13 months of continuous culture the selected cells had a 15 times higher cellular content and a 10 times higher secretory rate of SC than parallel cultures of the original cell line. Immunomagnetic microspheres can be recommended in experimental cancer research, e.g., in order to minimize cellular heterogeneity and to isolate cells with particular surface membrane phenotypes in differentiation studies. The selection method is rapid and simple, and eliminates laborious test systems for conventional subclone screening.

Up-regulation of the expression of secretory component and HLA molecules in a human colonic cell line by tumour necrosis factor-alpha and gamma interferon

Secretory component (SC) acts as a receptor for polymeric IgA (pIgA) and pIgM on the basolateral face of secretory epithelia. This study showed that both the production and surface membrane expression of SC were additively up-regulated by tumour necrosis factor-alpha (TNF) and gamma interferon (IFN-gamma) in a human colonic cell line (HT-29m2). TNF likewise enhanced membrane expression of HLA class I determinants. Moreover, TNF augmented synergistically the IFN-induced de novo synthesis of HLA class II (DR) molecules. These data suggest that there are different regulatory mechanisms for the action of TNF and IFN and for the expression of HLA-DR and SC/HLA class I. Addition of actinomycin D abolished the cytokine-mediated increase of SC synthesis and expression. This observation suggested that transcriptional events are required for the cytokine-mediated up-regulation of SC.

Sandwich-type ELISA for free and bound secretory component in human biological fluids

Three sandwich-type enzyme-linked immunosorbent assays (ELISA) are described for the measurement of free secretory component (SC) and SC bound to IgA (S-IgA) or IgM (S-IgM). These assays do not require preliminary fractionation of the biological fluids to be tested. The specificity of the assays is achieved with monoclonal antibodies specific for free SC (855 SC) and for SC bound to IgA or IgM (8545 SA). The amount of the three SC molecules in various biological fluids is reported. We demonstrate the presence of low levels of free SC in most of these fluids, including normal serum. Moreover our results suggest that S-IgM in serum may result from a non-covalent association between serum IgM and free SC.

Early detection of liver metastasis in patients with colorectal carcinoma by increased levels of circulating IgA- and IgM-associated secretory component

One hundred patients operated for colorectal carcinoma were followed clinically and with serial blood samples from 5 to 8 years. Levels of secretory component (SC) associated with IgA and IgM in serum were measured and related to Dukes' stage, histological differentiation, tumour expression of SC, and circulating carcinoembryonic antigen (CEA). On the whole, elevated levels of SC in serum were found in 15 of the 20 patients who already had (n = 15), or later developed (n = 5), liver metastasis. Four of the latter 5 patients showed raised SC levels with a 5.5 months median lead time from the first positive serum sample to clinically manifest liver disease. These data are interesting in view of the promising results reported for liver resection in patients with colorectal carcinoma.

Circulating secretory component in breast neoplasms

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

Circulating secretory immunoglobulins of the A and M isotypes in chronic liver disease

Serum levels of secretory IgA (SIgA) and secretory IgM (SIgM) were quantified by an enzyme-linked immunosorbent assay in 97 patients with various chronic liver diseases and 17 patients with uncomplicated ulcerative colitis. The values obtained were compared with 89 matched controls and related to other serum variables. All types of liver disease had elevated median levels of serum SIg. Patients with primary biliary cirrhosis (PBC) had the highest SIg levels, particularly SIgM, but increased total serum IgM was slightly more specific for PBC. Thus, the SIg levels did not add more discriminative information than several other variables. Elevated levels of circulating SIgA correlated mainly with variables that indicate reduced liver function. The difference observed between patients with PBC and primary sclerosing cholangitis (PSC) in the alkaline phosphatase (ALP)-to-SIg ratio is discussed.

Elevated levels of secretory immunoglobulins A and M in serum of patients with large bowel carcinoma indicate liver metastasis

Preoperative serum levels of secretory IgA (SIgA) and secretory IgM (SIgM) were quantified by an enzyme-linked immunosorbent assay in 100 patients with large bowel carcinoma. The values obtained were related to tumor characteristics such as Dukes' stage, differentiation, DNA ploidy pattern, expression of secretory component (SC), volume, and plasma level of carcinoembryonic antigen (CEA). Statistical comparison was made with matched controls. Only patients with Stage D tumors showed significantly increased serum levels of SIgA and SIgM (P less than 0.004). The combined diagnostic sensitivity of SIg and CEA in Stage D was 0.94. In patients with liver involvement, serum SIgA and SIgM were elevated in 67% and 53%, respectively. However, circulating SIg was neither correlated with tumor SC expression nor with any other studied variable. Thus, the raised serum SIg levels were apparently not caused by release of SC from the tumors but, instead, by hampered liver function due to hepatic metastasis.